US20090038712A1 - Protection of aluminum during a loss-of-coolant accident - Google Patents
Protection of aluminum during a loss-of-coolant accident Download PDFInfo
- Publication number
- US20090038712A1 US20090038712A1 US12/214,895 US21489508A US2009038712A1 US 20090038712 A1 US20090038712 A1 US 20090038712A1 US 21489508 A US21489508 A US 21489508A US 2009038712 A1 US2009038712 A1 US 2009038712A1
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- US
- United States
- Prior art keywords
- aluminum
- aqueous solution
- corrosion
- silicon
- cooling water
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- Abandoned
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 title claims abstract description 118
- 229910052782 aluminium Inorganic materials 0.000 title claims abstract description 118
- 239000002826 coolant Substances 0.000 title claims abstract description 12
- 230000007797 corrosion Effects 0.000 claims abstract description 113
- 238000005260 corrosion Methods 0.000 claims abstract description 113
- 239000000243 solution Substances 0.000 claims abstract description 67
- 238000000034 method Methods 0.000 claims abstract description 58
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 57
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 51
- 239000010703 silicon Substances 0.000 claims abstract description 51
- 229910000838 Al alloy Inorganic materials 0.000 claims abstract description 49
- 239000007864 aqueous solution Substances 0.000 claims abstract description 34
- 239000000498 cooling water Substances 0.000 claims abstract description 33
- 239000000463 material Substances 0.000 claims abstract description 23
- 239000000956 alloy Substances 0.000 claims abstract description 20
- 150000001875 compounds Chemical class 0.000 claims abstract description 13
- -1 silicate compound Chemical class 0.000 claims abstract description 13
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 6
- 239000001301 oxygen Substances 0.000 claims abstract description 6
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 35
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 claims description 18
- 229910000323 aluminium silicate Inorganic materials 0.000 claims description 7
- 239000003638 chemical reducing agent Substances 0.000 claims description 7
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- 238000000576 coating method Methods 0.000 claims description 7
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 claims description 6
- 229910052909 inorganic silicate Inorganic materials 0.000 claims description 5
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- 229910052791 calcium Inorganic materials 0.000 description 23
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- 238000002161 passivation Methods 0.000 description 16
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- OYACROKNLOSFPA-UHFFFAOYSA-N calcium;dioxido(oxo)silane Chemical compound [Ca+2].[O-][Si]([O-])=O OYACROKNLOSFPA-UHFFFAOYSA-N 0.000 description 7
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
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- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 5
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- 238000004458 analytical method Methods 0.000 description 4
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- UQGFMSUEHSUPRD-UHFFFAOYSA-N disodium;3,7-dioxido-2,4,6,8,9-pentaoxa-1,3,5,7-tetraborabicyclo[3.3.1]nonane Chemical compound [Na+].[Na+].O1B([O-])OB2OB([O-])OB1O2 UQGFMSUEHSUPRD-UHFFFAOYSA-N 0.000 description 4
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- 229910052911 sodium silicate Inorganic materials 0.000 description 3
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 description 3
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 2
- 239000004801 Chlorinated PVC Substances 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 229910004835 Na2B4O7 Inorganic materials 0.000 description 2
- 239000004115 Sodium Silicate Substances 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
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- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910001335 Galvanized steel Inorganic materials 0.000 description 1
- 241000272168 Laridae Species 0.000 description 1
- 229910003243 Na2SiO3·9H2O Inorganic materials 0.000 description 1
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- FUFJGUQYACFECW-UHFFFAOYSA-L calcium hydrogenphosphate Chemical compound [Ca+2].OP([O-])([O-])=O FUFJGUQYACFECW-UHFFFAOYSA-L 0.000 description 1
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- PNDPGZBMCMUPRI-UHFFFAOYSA-N iodine Chemical compound II PNDPGZBMCMUPRI-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F14/00—Inhibiting incrustation in apparatus for heating liquids for physical or chemical purposes
- C23F14/02—Inhibiting incrustation in apparatus for heating liquids for physical or chemical purposes by chemical means
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
- C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids
- C23F11/18—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids using inorganic inhibitors
- C23F11/182—Sulfur, boron or silicon containing compounds
Definitions
- the present invention relates to a method of chemically treating aluminum and its alloys in a manner that reduces corrosion thereof, especially under, but not limited to, containment water conditions found in a nuclear power plant loss-of-coolant accident situation and to the treated aluminum and aluminum alloy materials.
- the Nuclear Regulatory Commission (NRC) has regulatory authority over the safety of nuclear power plants in the United States.
- a scenario under investigation for many years is the hypothetical loss-of-coolant accident (LOCA), in which a pipe break in the primary cooling loop releases hot pressurized water and steam into the containment building.
- LOCA loss-of-coolant accident
- the collateral damage following a LOCA can be exacerbated by corrosion of metals that are submerged in the pool of cooling water that forms in the containment building.
- the cooling water in a pressurized water reactor (PWR) is demineralized water containing a low concentration of lithium hydroxide (LiOH) ( ⁇ 0.7 mg/L) and up to 16,000 mg/L of boric acid (H 3 BO 3 ). This solution is highly corrosive.
- LiOH lithium hydroxide
- H 3 BO 3 boric acid
- additional chemicals may be present in the containment pool water depending on the kind of pipe insulation used in the containment building (fiberglass or molded rigid calcium silicate) and the chemicals (sodium hydroxide, trisodium phosphate, or sodium tetraborate) used in the emergency core cooling system (ECCS) to raise pH and minimize volatilization of radioactive iodine.
- the corrosion/dissolution of concrete and metals and the suspension of dust and debris from containment surfaces can also contribute to the complexity of the chemical properties of the containment pool water.
- the containment pool water following a LOCA has a unique and complex chemistry that contributes to the corrosion of any metals submerged in the pool.
- Test results indicate that differences in test conditions caused substantial differences in the rate of aluminum corrosion. In two tests, the rate of corrosion was orders of magnitude lower than would be predicted based on the solution chemistry.
- Aluminum is a reactive metal. In air, it reacts to form a thin, transparent oxide film over the entire exposed aluminum surface [reference 8]. This film controls the rate of corrosion and protects the substrate aluminum metal. In water, however, the air-formed film breaks down [reference 9]. The degree of corrosion depends on the relative rates of film repair/growth and film breakdown [reference 9]. It has been proposed that the dominant mechanism of pure aluminum corrosion is mainly determined by the anodic reaction in alkaline solution [references 10,11]. The mechanism involves consecutive oxide film formation and dissolution and simultaneous water reduction. The reported reaction is:
- the corrosion rate depends on solution pH, temperature, fluid velocity, surface-to-volume ratio, duration of submersion, and presence of anions (e.g., Cl ⁇ , NO 3 ⁇ , SO 4 2 ⁇ , and H 3 SiO 4 ⁇ ) [references 9,11,12,13,14].
- the corrosion rate increases as temperature increases [reference 13], as surface-to-volume ratio increases, and as fluid velocity increases up to 4 cm/s [references 12,15].
- Aluminum corrosion also increases rapidly as pH increases above 6 [references 11,13,16,17].
- silicate passivation of aluminum has been noted in the literature under high pH and high silicate conditions, it is important to note that there is no existing literature on the ability of silicate to passivate the surface of aluminum or aluminum alloys in solution conditions similar to those present following a LOCA, when high concentrations of borate are present.
- the present invention provides a method for chemically treating aluminum and its alloys using an aqueous treatment in a manner that reduces aqueous corrosion thereof.
- the present invention is especially useful under representative LOCA containment pool cooling water conditions when high contents of borate are present, although the invention is not so limited since the chemical treatment method can be used to reduce corrosion in other service applications or as a pretreatment of aluminum and aluminum alloys materials before exposure to a corrosive environment.
- a chemical treatment method involves providing a corrosion-reducing agent comprising silicon in the reactor cooling water following a loss-of-coolant accident or in other aqueous solutions in a manner effective to reduce corrosion of aluminum or aluminum alloys exposed to the cooling water/aqueous solution.
- the corrosion-reducing agent preferably comprises a dissolvable compound of silicon and oxygen, such as a silicate compound for purposes of illustration and not limitation.
- Practice of the method can reduce severe corrosion of aluminum and aluminum alloy components loss-of-coolant accident when the aluminum or aluminum alloy surfaces are in contact with the chemicals used for the emergency reactor core cooling system at PWR nuclear power plants.
- Practice of the invention after a loss-of-coolant accident can reduce aluminum or aluminum alloy corrosion during emergency cooling of the nuclear reactor and thereby reduce transportable chemical products that can exacerbate blockage of the recirculation sump screen.
- a chemical pretreatment method involves contacting an aluminum or aluminum alloy material with an aqueous solution having silicon therein in a manner to form a protective silicon-bearing layer or coating thereon before exposure of the material to a corrosive environment.
- a treated aluminum or aluminum alloy material having a protective silicon-bearing layer or coating thereon.
- the protective coating can comprise aluminum and silicon, such as aluminosilicate for purposes of illustration and not limitation.
- the present invention is advantageous to reduce aluminum corrosion in an LOCA in that the release of aluminum ions and subsequent precipitation of aluminum hydroxide can be reduced, potentially reducing or eliminating the chemical product contributions to clogging in the ECCS and to reduce aluminum corrosion in other aqueous environments.
- the present invention also is advantageous as a pretreatment to protect industrial aluminum components and structures before exposure in a variety of adverse chemical environments.
- FIG. 1 shows a plot of aluminum concentrations in solution over the duration of pilot Tests 1 and 5 (the aluminum concentration in pilot Tests 2, 3, and 4 were below the detection limit.).
- FIG. 2 a shows an SEM (scanning electron microscope) image of new aluminum alloy coupon
- FIGS. 2 b and 2c show SEM images of corroded aluminum alloy coupons from pilot Tests 1 and 4, respectively.
- FIG. 3 shows a plot of aluminum concentrations in solution during bench tests.
- FIGS. 5 a and 5 b show the XPS spectra (vertical axis CPS and horizontal axis binding energy (eV)) on the aluminum alloy coupons ( FIG. 5 a ) virgin aluminum coupon, and FIG. 5( b ) soaked in Na 2 SiO 3 solution.
- the present invention provides a method for chemically treating aluminum and its alloys using an aqueous treatment in a manner that reduces aqueous corrosion thereof.
- the present invention can be practiced to reduce corrosion of aluminum metal and aluminum alloys where aluminum is 50 weight % or more of the alloy.
- Illustrative aluminum alloys include, but are not limited to, the 1000 through 8000 series aluminum and aluminum alloy materials (International Alloy Designation System).
- the aluminum or aluminum alloys can be made or available in various wrought, cast, or other forms such as including, but not limited to, machined components, forged components, cast components, hot and/or cold rolled plate or sheet components, consolidated powder components, films or layers, and other forms.
- the present invention is especially useful to reduce corrosion of aluminum and aluminum alloys under representative LOCA containment pool water conditions when high contents of borate are present.
- practice of the invention is not so limited since the chemical treatment method can be used to reduce corrosion in other service applications or as a pretreatment of aluminum and aluminum alloys materials before exposure to a corrosive environment.
- the method of the invention is useful as a chemical pretreatment method involving contacting an aluminum or aluminum alloy material with an aqueous solution having a corrosion-reducing agent comprising silicon therein in a manner to form a protective silicon-bearing coating thereon before exposure of the material to a corrosive environment.
- Practice of the chemical treatment method of the invention involves providing a corrosion-reducing agent comprising silicon in the reactor cooling water (e.g. the containment pool water) following a loss-of-coolant accident, or in another aqueous solution environment, in a manner effective to reduce corrosion of aluminum or aluminum alloys exposed to the containment pool water or other aqueous solution environment.
- the corrosion-reducing agent preferably includes a water-dissolvable compound of silicon and oxygen and includes, but is not limited to, a compound such as silicic acid, sodium silicate, disodium metasilicate, calcium silicate, or other silicate-containing compounds.
- the corrosion-reducing agent can be provided in the reactor cooling water (e.g.
- containment pool water during an LOCA scenario by one or more of several techniques including, but not limited to: (a) injecting dissolved silicate solution into emergency cooling water sprays, (b) injecting dissolved silicate solution into cooling water pools, and (c) exposing caches of dry silicate-containing compounds to spilled cooling water.
- the chemical treatment method can be practiced to reduce corrosion of aluminum and its alloys in containment pool water following a loss-of-coolant accident, or in another aqueous solution environment, where the pH is in the range of about 7 to about 11 and borate is initially present in an amount of about 2,000 to about 2,800 mg/L (measured as boron, but present as total borate, including boric acid, conjugate bases of boric acid, and any polyborate species formed during the dissolution of boric acid or borax) of the containment pool water or aqueous solution at a temperature in the range of ambient temperature to 150 degrees C.
- Containment pool cooling water may be in the temperature range of 50 to 150 degrees C. after an LOCA for example.
- practice of the method can reduce severe corrosion of aluminum and aluminum alloy components loss-of-coolant accident when the aluminum or aluminum alloy surfaces are in contact with the chemicals used for the emergency reactor core cooling system at PWR nuclear power plants.
- the chemical treatment method can be effective within 48 hours of immersion time for standard aluminum alloys described above with existing air-induced oxidation present on the aluminum or alloy surface and nominal concentration of 90 mg/L Si in the reactor cooling water (e.g. containment pool cooling water) or aqueous treatment solution.
- the content of silicon in the reactor cooling water or aqueous solution can be relatively low in an effective amount to reduce corrosion in the range of greater than zero to not exceeding about 1,000 mg/L as Si, preferably greater than zero to not exceeding 500 mg/L as Si of the cooling water or aqueous solution, and even more preferably from about 20 mg/L to about 100 mg/L as Si of the cooling water or aqueous solution.
- a content of silicon in the reactor cooling water or aqueous solution in an amount of about 45 to about 100 mg/L of the cooling water or aqueous solution was especially useful to reduce corrosion.
- the protective coating can comprise aluminum and silicon, such as aluminosilicate for purposes of illustration and not limitation, which protects or passivates the surface to reduce corrosion in containment pool water following a loss-of-coolant accident and in another aqueous solution environments of the types described above.
- pilot tests Two types of experiments are described below: pilot tests and bench tests.
- the pilot tests were conducted in a large (946 L) tank and identified the ability of silicate to passivate aluminum under realistic LOCA conditions, when other metals, concrete, insulation, and other dust and debris were present in the aqueous system.
- the bench tests were conducted in 1 L containers and were controlled experiments that demonstrated that silicate is the specific species that passivates aluminum surfaces under the conditions present in the pilot tests.
- the experimental setup is described in more detail in the following paragraphs.
- Tests 1 through 4 addressed a 2 ⁇ 2 matrix that varied the pipe insulation material and the chemical used to establish the initial pH. Some operating nuclear power plants primarily use fiberglass pipe insulation, while others use a combination of fiberglass and calcium silicate. During a LOCA, some plants have systems that inject aqueous NaOH into the containment spray water to raise the pH, while others have baskets of dry trisodium phosphate (TSP or Na 3 PO 4 ⁇ 12H 2 O), which dissolves and raises the pH. Therefore, Tests 1 through 4 evaluated the effect of each pH chemical with each insulation combination.
- TSP dry trisodium phosphate
- Test 5 represented the chemistry of an ice-condenser plant, where pH in the containment pool is established by the addition of sodium tetraborate (Na 2 B 4 O 7 ⁇ 10H 2 O). Other chemical concentrations are lower in ice-condenser plants because of dilution of the pool water by a melting ice column.
- the chemical doses and pH ranges shown in Table 2 are representative of actual values expected in operating nuclear power plants of each type.
- the primary components of the pilot test system were a test tank, a recirculation pump, and instrumentation.
- the test tank was made of 304 L stainless steel (SS) and was equipped with heating elements and water spray nozzles to simulate the post-LOCA scenario.
- the volume of the test solution was 946 L (250 gal).
- the tank contained aluminum alloy, carbon steel, galvanized steel, zinc-primer-topcoated steel, and copper coupons, a formed concrete slab, pulverized concrete, pipe insulation materials, and “latent debris” (dust and debris that was representative of materials found on the surfaces of a containment building).
- Added chemicals included H 3 BO 3 , LiOH, hydrochloric acid (HCl), and the appropriate pH-adjustment chemicals.
- Tests 1 and 4 represent plants with NaOH spray injection
- Tests 2 and 3 represent plants using dry TSP
- Test 5 represents ice-condenser plants that release sodium tetraborate from a melting ice column.
- All corrosion coupons, chemicals, and other materials added to the tank were scaled in proportion to actual conditions in operating nuclear power plants using an area:volume ratio, a volume:volume ratio, or a concentration as appropriate.
- the demineralized water used for the solution was produced by a reverse osmosis system and had a conductivity less than 15 ⁇ S/cm.
- the solution temperature was maintained at 60 ⁇ 3° C. throughout the tests.
- the solution was circulated at 94.6 ⁇ 5 L/min during the entire test to achieve representative fluid velocities over the submerged corrosion coupons.
- Monitoring of the tests included collection of grab samples and continuous on-line monitoring of recirculation flow rate, test solution temperature, and pH. Solution samples were collected daily, fiberglass insulation samples were collected periodically during the tests, and metallic coupons were examined after the tests. All sampling procedures and water quality analyses were conducted in accordance with appropriate standard methods and approved project instructions [reference 2 which is incorporated herein by reference].
- Aluminum alloy 3003 was used in this study. Each aluminum alloy coupon was 30.5-cm (12-in) square and 0.16-cm ( 1/16-in) thick, with an average weight of about 392 g. In each test, three aluminum alloy coupons were submerged in the solution. A chlorinated polyvinyl chloride (CPVC) coupon rack provided sufficient separation between the test coupons to prevent galvanic interactions.
- CPVC chlorinated polyvinyl chloride
- the bench tests described here focused on identifying conditions that could affect aluminum corrosion under representative LOCA solution conditions.
- Three 1-L solutions were used for the test. All three contained 16,000 mg/L H 3 BO 3 .
- the first container was a blank for comparison to the pilot tests, the second contained 88.7 mg/L silicon (added as Na 2 SiO 3 ⁇ 9H 2 O), and the last contained 50 mg/L calcium (added as CaCl 2 ).
- the selected concentration of silicon or calcium was based on their measured concentrations near the end of pilot Test 4.
- the test was conducted in capped, 1-L, Nalgene® bottles. All solutions were preheated to 60° C. and pH was adjusted to 9.5 using NaOH before small aluminum coupons were placed into the containers. The solution was semi-open to the atmosphere, since air contact occurred during sampling procedures. The temperature of the solutions was maintained at 60° C. in a constant temperature oven for 30 days.
- the aluminum concentration in solution was used as an indicator of the rate of aluminum corrosion.
- the aluminum concentration in solution, total mass of aluminum in solution, and predicted aluminum solubility in each test are shown in Table 3. The results show relatively significant corrosion in Tests 1 and 5, but nearly no corrosion in Tests 2, 3, and 4.
- Tests 2, 3, and 4 the aluminum concentration was near or below the detection limit (i.e., 0.5 mg/L) during the entire 30-day test.
- Aluminum concentrations in daily samples from the remaining two tests are shown in FIG. 1 . From these results, it is clear that the rate of aluminum corrosion varied greatly from test to test.
- the aluminum concentration increased from zero to about 360 mg/L after 18 days. After that, the concentration oscillated around 360 mg/L through day 30.
- Test 5 the concentration increased from zero to about 50 mg/L in 14 days and stayed in the range of 50 mg/L for the remainder of the test.
- solution concentrations as an indication of corrosion requires that the solution concentration not be controlled by external factors such as solubility.
- the solubility of aluminum under these conditions is controlled by aluminum hydroxide. While crystalline forms such as gibbsite have lower solubility, it has been shown that solution concentrations are initially controlled by the precipitation of amorphous aluminum hydroxide, the kinetically-favored precipitation product.
- the solubility of amorphous aluminum hydroxide in aqueous solution increases dramatically with higher pH above 6.3.
- the solubility of aluminum in each test i.e., the applied chemical concentrations, measured pH range, and 60° C. was calculated using Visual Minteq 2.30 [see reference 22]. As shown in Table 3, modeling results indicate that the measured concentrations of aluminum were below the predicted saturation limits in all tests.
- Weight loss measurements from the corrosion coupons were a second indicator of aluminum corrosion during the pilot tests. As shown in Table 3, there is overall good agreement between weight lost from the coupons and the mass of aluminum measured in solution. In Tests 1 and 5, the mass of aluminum measured in solution was slightly more than the mass lost from the coupons, indicating that some corrosion products adhered to the coupons and interfered slightly with the weight loss calculations. However, generally the weight loss measurements serve as a good confirmation of the solution concentration measurements.
- SEM provides a visual picture of corrosion on a microscopic level.
- SEM images of an unused aluminum coupon and coupons after 30 days of submersion in Tests 1 and 4 are shown in FIGS. 2 a , 2 b , and 2 c .
- the SEM images give additional insight into the extent of corrosion reflected by the aluminum concentration in the solution and the weight loss of the coupons.
- the coupon from Test 1 had a very rugged surface that appeared to be the formation of extensive corrosion products. However, the Test 4 coupon had little or no corrosion, and the coupon surface appeared relatively smooth.
- Tests 3 and 4 Exceptions to the expected corrosion rates occurred in Tests 3 and 4, which had measured corrosion rates less than 0.001 g/m 2 ⁇ h.
- the pH range for Test 3 is shown as 7.3 to 8.1 in Table 2, the pH was nearly 8.0 for most of the test (except the first 2 days).
- the observed corrosion rate in Test 3 is at least 1 to 2 orders of magnitude lower than expected.
- the key constituent present in Tests 3 and 4 that was not present in the other tests was the calcium silicate insulation (see Table 2).
- XRF spectrometry revealed that the primary elements present in the calcium silicate insulation were, as expected, calcium and silicon.
- the concentrations at the end of each test are shown in Table 4.
- the silicon concentration in the Test 3 and 4 solutions reached about 45 mg/L and 82 mg/L, respectively. These concentrations were substantially higher than in Test 1 or 5.
- the silicon concentration in Test 2 was initially low, but close to Test 3 at the end of the test.
- Table 4 shows that Tests 3 and 4 also had the highest calcium concentrations, with values of about 110 mg/L and 50 mg/L, respectively. In contrast, lower calcium concentrations were observed in Tests 1, 2, and 5.
- Table 4 indicates that the silicon and calcium concentrations were both highest in Tests 3 and 4. Based on these observations, silicon, calcium, or both might be involved in the formation of an insoluble coating or passivation layer on the surface of the submerged aluminum alloy coupons. Water quality modeling using Visual Minteq 2.3 was used to predict the most likely forms of Si and Ca in solution. Silicon was predicted to have been present almost entirely as H 4 SiO 4 in Test 3 but predominantly as H 3 SiO 4 ⁇ with less than 25% H 4 SiO 4 in Test 4 (the pKa 1 of H 4 SiO 4 is around 9.9 at 30° C. [reference 25]).
- the H 3 SiO 4 ⁇ species may be more important than H 4 SiO 4 with regard to forming a passivation layer on the aluminum surface, which would explain why the passivation was more notable in Test 4 than in Test 3.
- Water quality modeling predicted that the calcium was present primarily as Ca 2+ and CaH 2 BO 3 + in Test 4 and as Ca 2+ , CaH 2 BO 3 + , and CaHPO 4(aq) in Test 3.
- Bench tests were conducted to clarify whether silicon or calcium was responsible for passivation of the aluminum surface noted in pilot Tests 3 and 4. The bench tests focused on conditions similar to Test 4, which exhibited the greatest degree of passivation. Bench-scale corrosion tests were prepared with the same stock solution chemistry as Test 4 (Table 2, but without insulation or debris) with the addition of either 88.7 mg/L of Si (added as sodium silicate) or 50 mg/L of Ca (added as calcium chloride); a reference test was also conducted using only the stock solution chemistry without either additive. The measured aluminum concentrations over the duration of the tests are shown in FIG. 4 .
- FIG. 3 shows that the presence of silicon in solution caused a strong passivation effect.
- the aluminum concentration was less than 1 mg/L and near the detection limit (i.e., 0.5 mg/L) throughout the test.
- the corresponding corrosion rate was less than 0.002 g/m 2 ⁇ h in 14 days, a 300 ⁇ reduction in the corrosion rate (2.5 orders of magnitude) compared to the coupon in the solution that contained no Si or Ca.
- silicate anions reacted with aluminum at the coupon surface. Consequently, an insoluble aluminosilicate coating was formed, which impeded further aluminum dissolution and corrosion.
- the introduction of 50 mg/L calcium caused a 2 ⁇ reduction in aluminum corrosion; i.e., the aluminum concentration increased to only 92 mg/L after 30 days.
- the corrosion rate was 0.34 g/m 2 ⁇ h in 14 days, about half of the corrosion rate of the coupon in the solution that contained no Si or Ca.
- One possible mechanism explaining the reduced corrosion is that calcium may react with carbonate to form a protective calcium carbonate layer at the aluminum alloy coupon surface. Carbonate is present in solution from carbon dioxide in the air. Compared to the effect of silicate, however, the effect of calcium is relatively minor.
- FIG. 4 a , 4 b , and 4 c show SEM images of the aluminum alloy coupons after the bench tests. Consistent with the aluminum concentration results, the roughest and most corroded coupon surface was observed from the solution that contained no Si or Ca. In contrast, the coupon from the solution containing 88.7 mg/L silicon was mostly smooth and uniform. The roughness of the coupon from the 50 mg/L Ca solution was nearly the same as the coupon immersed in the solution without Si or Ca.
- the subsurface of the virgin aluminum coupon to a depth of 10 nm was composed of Al 2 O 3 (64 weight percent), Al(OH) 3 (27 weight percent), and Al (9 weight percent).
- the subsurface of the silicate-passivated coupon contained mainly Al 2 OSiO 4 (98 weight percent) with a small amount of Al 2 O 3 (2 percent). This result indicates that silicon reacted with aluminum at the coupon surface.
- the thickness of the passivation layer was at least 10 nm, based on the depth of examination by XPS. In contrast to the virgin aluminum coupon, no aluminum metal was detected in the top 10 nm of the silicate-passivated coupon surface.
- the principal mechanism of surface passivation of aluminum or its alloys appears to occur whereby the ionic species H 3 SiO 4 ⁇ reacts with exposed aluminum to form a layer of insoluble Al 2 OSiO 4 which inhibits oxidation reactions from removing aluminum from the solid surface.
- the treatment methods described above can be applied during a nuclear power plant LOCA scenario, or other industrial facility accident, that exposes aluminum to corrosive aqueous environments, particularly those with elevated temperature and pH.
- the bench-scale tests demonstrated that a relatively low dose of silicate (i.e., less than less than 90 mg/L) could passivate the aluminum surface and dramatically reduce the rate of corrosion.
- XPS examination confirmed that a passivation layer composed of Al 2 OSiO 4 can be formed with a thickness of more than 10 nm. Pilot-scale tests confirmed that this effect would be true even in realistic LOCA conditions, where other metals, concrete, insulation, and other dust and debris are adding complexity to the solution chemistry.
- the present invention is advantageous to reduce aluminum corrosion in an LOCA in that the release of aluminum ions and subsequent precipitation of aluminum hydroxide can be reduced, potentially reducing or eliminating the chemical product contributions to clogging in the ECCS and to reduce aluminum corrosion in other aqueous environments.
- the present invention also is advantageous as a pretreatment to protect industrial aluminum components and structures before exposure in a variety of adverse chemical environments.
- the treatment method described above may be used in many industrial applications (particularly those that require immersion in or exposure to water of mechanical structures and components) that include, but are not limited to, (a) surface and subsurface marine environments, (b) water quality treatment, (c) chemical processing, (d) mining and drilling, (e) aviation construction, (f) automotive construction, and (g) liquid process piping and pumping.
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Abstract
Description
- This application claims benefits and priority of provisional application Ser. No. 60/937,423 filed Jun. 26, 2007, the disclosure of which is incorporated herein by reference.
- This invention was made with government support under Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of Energy. The Government has certain rights in this invention.
- 1. Field of the Invention
- The present invention relates to a method of chemically treating aluminum and its alloys in a manner that reduces corrosion thereof, especially under, but not limited to, containment water conditions found in a nuclear power plant loss-of-coolant accident situation and to the treated aluminum and aluminum alloy materials.
- 2. Description of the Related Art
- The Nuclear Regulatory Commission (NRC) has regulatory authority over the safety of nuclear power plants in the United States. A scenario under investigation for many years is the hypothetical loss-of-coolant accident (LOCA), in which a pipe break in the primary cooling loop releases hot pressurized water and steam into the containment building. The collateral damage following a LOCA can be exacerbated by corrosion of metals that are submerged in the pool of cooling water that forms in the containment building. The cooling water in a pressurized water reactor (PWR) is demineralized water containing a low concentration of lithium hydroxide (LiOH) (≦0.7 mg/L) and up to 16,000 mg/L of boric acid (H3BO3). This solution is highly corrosive. Following a LOCA, additional chemicals may be present in the containment pool water depending on the kind of pipe insulation used in the containment building (fiberglass or molded rigid calcium silicate) and the chemicals (sodium hydroxide, trisodium phosphate, or sodium tetraborate) used in the emergency core cooling system (ECCS) to raise pH and minimize volatilization of radioactive iodine. In addition, the corrosion/dissolution of concrete and metals and the suspension of dust and debris from containment surfaces can also contribute to the complexity of the chemical properties of the containment pool water. As a result, the containment pool water following a LOCA has a unique and complex chemistry that contributes to the corrosion of any metals submerged in the pool.
- The University of New Mexico and Los Alamos National Laboratory, under a contract with the NRC, conducted an extensive experimental investigation of the corrosion potential of aluminum alloy under conditions representative of the containment pool following a LOCA. The general results of that study are reported elsewhere [see
references - Test results also indicate that differences in test conditions caused substantial differences in the rate of aluminum corrosion. In two tests, the rate of corrosion was orders of magnitude lower than would be predicted based on the solution chemistry.
- Aluminum is a reactive metal. In air, it reacts to form a thin, transparent oxide film over the entire exposed aluminum surface [reference 8]. This film controls the rate of corrosion and protects the substrate aluminum metal. In water, however, the air-formed film breaks down [reference 9]. The degree of corrosion depends on the relative rates of film repair/growth and film breakdown [reference 9]. It has been proposed that the dominant mechanism of pure aluminum corrosion is mainly determined by the anodic reaction in alkaline solution [
references 10,11]. The mechanism involves consecutive oxide film formation and dissolution and simultaneous water reduction. The reported reaction is: -
2Al+6H2O+2OH−→3H2+2Al(OH)4 − (1) - The corrosion rate depends on solution pH, temperature, fluid velocity, surface-to-volume ratio, duration of submersion, and presence of anions (e.g., Cl−, NO3 −, SO4 2−, and H3SiO4 −) [
references 9,11,12,13,14]. The corrosion rate increases as temperature increases [reference 13], as surface-to-volume ratio increases, and as fluid velocity increases up to 4 cm/s [references 12,15]. Aluminum corrosion also increases rapidly as pH increases above 6 [references 11,13,16,17]. After 20 days of immersion at 60° C., it is reported that the corrosion rate at pH=10 (0.048 g/m2·h) was more than five times higher than the corrosion rate at pH=8 (0.009 g/m2·h) [reference 13]. - Solution conditions following a LOCA have the potential to dramatically increase the corrosion rate of aluminum. The effect of boric acid and its conjugate base, borate, has been evaluated in experiments by several groups of researchers at pH values ranging from 9.2 to 10 and temperatures ranging from 50 to 130° C., as shown in Table 1 [references 18,19,20].
-
TABLE 1 Measured corrosion rates of aluminum in water containing borate. Temper- Corrosion Borate ature rate conc. Purge (° C.) (g m−2h−1) (M) pH Method1 gas Reference 50 0.15 0.1 9.2-9.3 1 air [20] 55 0.59 0.28 9.3-9.4 4 air [19] 60 0.459 0.236 10 2 air [18] 0.986 0.259 10 2 N2 [18] 1.01 0.236 10 2 N2 [18] 1.22 0.236 10 3 N2 [18] 70 0.6 0.1 9.2-9.3 1 air [20] 90 1.45 0.1 9.2-9.3 1 air [20] 1.89 0.259 10 2 N2 [18] 3.5 0.236 10 3 N2 [18] 100 8.9 0.28 9.3-9.4 4 air [19] 110 1.23 0.1 9.2-9.3 1 air [20] 2.2 0.259 10 2 N2 [18] 7.04 0.236 10 3 N2 [18] 130 3.06 0.1 9.2-9.3 1 air [20] 1Methods: 1 = electrical resistance, 2 = polarization resistance, 3 = current impedance, 4 = weight loss. - A strong dependence on temperature is evident, with increasing temperature resulting in faster aluminum corrosion rates. At 60° C., Jain, et al. [reference 18] reported aluminum corrosion rates ranging from 0.459 to 1.22 g/m2·h, which are 1 to 2 orders of magnitude higher than rates measured at similar temperature and pH without borate. Experimental measurements by Griess and Bacarella [reference 19] and Piippo, et al. [reference 20] generally support these values. Griess and Bacarella [reference 19] conducted experiments on the corrosion of various metals, including six alloys of aluminum, in solutions containing 0.28 M H3BO3 and 0.15 M sodium hydroxide (NaOH) at 55° C. and 100° C. For aluminum alloy 3003, which is the alloy used in the current experiments, the reported corrosion rates were 0.59 g/m2·h at 55° C. and 8.9 g/m2·h at 100° C. In short, although there is variability in the measured corrosion rates from different researchers and with different methods, it is clear that the corrosion rate of aluminum in solution conditions following a PWR LOCA is 1 to 2 orders of magnitude higher than at similar pH and temperature when there is no borate in solution.
- Under high pH conditions, the presence of silicate has been observed to minimize corrosion [reference 14]. Labbe and Pagetti [reference 14] indicated that silicate caused an effective inhibition of aluminum corrosion under conditions used for cleaning operations in the dairy industry (60° C. and 0.1 N NaOH, corresponding to pH=13), when the silica concentration was 3,600 mg/L as SiO2. Lee and Babić [ reference21] found that silicon dissolved into 2.3 M KOH solutions (corresponding to pH>14) could passivate aluminum, but only when the concentration was greater than 126,000 mg/L as SiO2. So, while silicate passivation of aluminum has been noted in the literature under high pH and high silicate conditions, it is important to note that there is no existing literature on the ability of silicate to passivate the surface of aluminum or aluminum alloys in solution conditions similar to those present following a LOCA, when high concentrations of borate are present.
- The present invention provides a method for chemically treating aluminum and its alloys using an aqueous treatment in a manner that reduces aqueous corrosion thereof. The present invention is especially useful under representative LOCA containment pool cooling water conditions when high contents of borate are present, although the invention is not so limited since the chemical treatment method can be used to reduce corrosion in other service applications or as a pretreatment of aluminum and aluminum alloys materials before exposure to a corrosive environment.
- In an illustrative embodiment of the invention, a chemical treatment method involves providing a corrosion-reducing agent comprising silicon in the reactor cooling water following a loss-of-coolant accident or in other aqueous solutions in a manner effective to reduce corrosion of aluminum or aluminum alloys exposed to the cooling water/aqueous solution. The corrosion-reducing agent preferably comprises a dissolvable compound of silicon and oxygen, such as a silicate compound for purposes of illustration and not limitation. Practice of the method can reduce severe corrosion of aluminum and aluminum alloy components loss-of-coolant accident when the aluminum or aluminum alloy surfaces are in contact with the chemicals used for the emergency reactor core cooling system at PWR nuclear power plants. Practice of the invention after a loss-of-coolant accident can reduce aluminum or aluminum alloy corrosion during emergency cooling of the nuclear reactor and thereby reduce transportable chemical products that can exacerbate blockage of the recirculation sump screen.
- In another illustrative embodiment of the invention, a chemical pretreatment method involves contacting an aluminum or aluminum alloy material with an aqueous solution having silicon therein in a manner to form a protective silicon-bearing layer or coating thereon before exposure of the material to a corrosive environment.
- In still another embodiment of the invention, a treated aluminum or aluminum alloy material is provided having a protective silicon-bearing layer or coating thereon. The protective coating can comprise aluminum and silicon, such as aluminosilicate for purposes of illustration and not limitation.
- The present invention is advantageous to reduce aluminum corrosion in an LOCA in that the release of aluminum ions and subsequent precipitation of aluminum hydroxide can be reduced, potentially reducing or eliminating the chemical product contributions to clogging in the ECCS and to reduce aluminum corrosion in other aqueous environments. The present invention also is advantageous as a pretreatment to protect industrial aluminum components and structures before exposure in a variety of adverse chemical environments.
- These and other advantages of the present invention will become readily apparent from the following drawings taken with the detailed description.
-
FIG. 1 shows a plot of aluminum concentrations in solution over the duration of pilot Tests 1 and 5 (the aluminum concentration in pilot Tests 2, 3, and 4 were below the detection limit.). -
FIG. 2 a shows an SEM (scanning electron microscope) image of new aluminum alloy coupon andFIGS. 2 b and 2c show SEM images of corroded aluminum alloy coupons frompilot Tests -
FIG. 3 shows a plot of aluminum concentrations in solution during bench tests. -
FIGS. 4 a, 4 b, and 4 c show SEM images of aluminum alloy coupons after being soaked in the bench experimental solutions at 60° C. for 30 days. All solutions contained 0.259 M H3BO3 and were initially adjusted to pH=9.5 using NaOH. The solution ofFIG. 4 a did not include silicon or Ca in solution. The solutions used for the tests ofFIGS. 4 b and 4 c included the indicated amount of silicon (88.7 mg/L) and calcium (50 mg/L), respectively. -
FIGS. 5 a and 5 b show the XPS spectra (vertical axis CPS and horizontal axis binding energy (eV)) on the aluminum alloy coupons (FIG. 5 a) virgin aluminum coupon, andFIG. 5( b) soaked in Na2SiO3 solution. - The present invention provides a method for chemically treating aluminum and its alloys using an aqueous treatment in a manner that reduces aqueous corrosion thereof. The present invention can be practiced to reduce corrosion of aluminum metal and aluminum alloys where aluminum is 50 weight % or more of the alloy. Illustrative aluminum alloys include, but are not limited to, the 1000 through 8000 series aluminum and aluminum alloy materials (International Alloy Designation System). The aluminum or aluminum alloys can be made or available in various wrought, cast, or other forms such as including, but not limited to, machined components, forged components, cast components, hot and/or cold rolled plate or sheet components, consolidated powder components, films or layers, and other forms.
- The present invention is especially useful to reduce corrosion of aluminum and aluminum alloys under representative LOCA containment pool water conditions when high contents of borate are present. However, practice of the invention is not so limited since the chemical treatment method can be used to reduce corrosion in other service applications or as a pretreatment of aluminum and aluminum alloys materials before exposure to a corrosive environment. For example, the method of the invention is useful as a chemical pretreatment method involving contacting an aluminum or aluminum alloy material with an aqueous solution having a corrosion-reducing agent comprising silicon therein in a manner to form a protective silicon-bearing coating thereon before exposure of the material to a corrosive environment.
- Practice of the chemical treatment method of the invention involves providing a corrosion-reducing agent comprising silicon in the reactor cooling water (e.g. the containment pool water) following a loss-of-coolant accident, or in another aqueous solution environment, in a manner effective to reduce corrosion of aluminum or aluminum alloys exposed to the containment pool water or other aqueous solution environment. The corrosion-reducing agent preferably includes a water-dissolvable compound of silicon and oxygen and includes, but is not limited to, a compound such as silicic acid, sodium silicate, disodium metasilicate, calcium silicate, or other silicate-containing compounds. The corrosion-reducing agent can be provided in the reactor cooling water (e.g. containment pool water) during an LOCA scenario by one or more of several techniques including, but not limited to: (a) injecting dissolved silicate solution into emergency cooling water sprays, (b) injecting dissolved silicate solution into cooling water pools, and (c) exposing caches of dry silicate-containing compounds to spilled cooling water.
- The chemical treatment method can be practiced to reduce corrosion of aluminum and its alloys in containment pool water following a loss-of-coolant accident, or in another aqueous solution environment, where the pH is in the range of about 7 to about 11 and borate is initially present in an amount of about 2,000 to about 2,800 mg/L (measured as boron, but present as total borate, including boric acid, conjugate bases of boric acid, and any polyborate species formed during the dissolution of boric acid or borax) of the containment pool water or aqueous solution at a temperature in the range of ambient temperature to 150 degrees C. Containment pool cooling water may be in the temperature range of 50 to 150 degrees C. after an LOCA for example. For example, practice of the method can reduce severe corrosion of aluminum and aluminum alloy components loss-of-coolant accident when the aluminum or aluminum alloy surfaces are in contact with the chemicals used for the emergency reactor core cooling system at PWR nuclear power plants. The chemical treatment method can be effective within 48 hours of immersion time for standard aluminum alloys described above with existing air-induced oxidation present on the aluminum or alloy surface and nominal concentration of 90 mg/L Si in the reactor cooling water (e.g. containment pool cooling water) or aqueous treatment solution. In practice of the invention, the content of silicon in the reactor cooling water or aqueous solution can be relatively low in an effective amount to reduce corrosion in the range of greater than zero to not exceeding about 1,000 mg/L as Si, preferably greater than zero to not exceeding 500 mg/L as Si of the cooling water or aqueous solution, and even more preferably from about 20 mg/L to about 100 mg/L as Si of the cooling water or aqueous solution. A content of silicon in the reactor cooling water or aqueous solution in an amount of about 45 to about 100 mg/L of the cooling water or aqueous solution was especially useful to reduce corrosion.
- Practice of the present invention produces a treated aluminum or aluminum alloy material that includes a protective silicon-bearing coating on a surface thereof. The protective coating can comprise aluminum and silicon, such as aluminosilicate for purposes of illustration and not limitation, which protects or passivates the surface to reduce corrosion in containment pool water following a loss-of-coolant accident and in another aqueous solution environments of the types described above.
- The following EXAMPLE is offered to further illustrate but not limit the present invention.
- Two types of experiments are described below: pilot tests and bench tests. The pilot tests were conducted in a large (946 L) tank and identified the ability of silicate to passivate aluminum under realistic LOCA conditions, when other metals, concrete, insulation, and other dust and debris were present in the aqueous system. The bench tests were conducted in 1 L containers and were controlled experiments that demonstrated that silicate is the specific species that passivates aluminum surfaces under the conditions present in the pilot tests. The experimental setup is described in more detail in the following paragraphs.
- The pilot tests simulated the expected containment pool chemistry during the recirculation phase of a LOCA. Five tests, each run for 30 days, explored a range of chemical conditions, as detailed in Table 2.
Tests 1 through 4 addressed a 2×2 matrix that varied the pipe insulation material and the chemical used to establish the initial pH. Some operating nuclear power plants primarily use fiberglass pipe insulation, while others use a combination of fiberglass and calcium silicate. During a LOCA, some plants have systems that inject aqueous NaOH into the containment spray water to raise the pH, while others have baskets of dry trisodium phosphate (TSP or Na3PO4·12H2O), which dissolves and raises the pH. Therefore, Tests 1 through 4 evaluated the effect of each pH chemical with each insulation combination.Test 5 represented the chemistry of an ice-condenser plant, where pH in the containment pool is established by the addition of sodium tetraborate (Na2B4O7·10H2O). Other chemical concentrations are lower in ice-condenser plants because of dilution of the pool water by a melting ice column. The chemical doses and pH ranges shown in Table 2 are representative of actual values expected in operating nuclear power plants of each type. - The primary components of the pilot test system were a test tank, a recirculation pump, and instrumentation. The test tank was made of 304 L stainless steel (SS) and was equipped with heating elements and water spray nozzles to simulate the post-LOCA scenario. The volume of the test solution was 946 L (250 gal). The tank contained aluminum alloy, carbon steel, galvanized steel, zinc-primer-topcoated steel, and copper coupons, a formed concrete slab, pulverized concrete, pipe insulation materials, and “latent debris” (dust and debris that was representative of materials found on the surfaces of a containment building). Added chemicals included H3BO3, LiOH, hydrochloric acid (HCl), and the appropriate pH-adjustment chemicals.
-
TABLE 2 Chemical conditions in the pilot scale tests [reference 2]. Constituent added, mg/ L Test 1 Test 2Test 3Test 4Test 5 H3BO3 16,000 16,000 16,000 16,000 6,850 NaOH 7,677 — — 9,600 — Na3PO4•12H2O — 4,000 4,000 — — Na2B4O7•10H2O — — — — 10,580 HCl 100 100 100 100 43 LiOH 0.7 0.7 0.7 0.7 0.3 Fiberglass insulation 5,270 5,270 1,050 1,050 5,270 Calcium silicate insulation — — 20,800 20,800 — Pulverized concrete/ debris 90 90 90 90 90 Measured pH 9.3-9.5 7.1-7.4 7.3-8.1 9.5-9.9 8.2-8.5 Note: Tests Test 5 represents ice-condenser plants that release sodium tetraborate from a melting ice column. - All corrosion coupons, chemicals, and other materials added to the tank were scaled in proportion to actual conditions in operating nuclear power plants using an area:volume ratio, a volume:volume ratio, or a concentration as appropriate. The demineralized water used for the solution was produced by a reverse osmosis system and had a conductivity less than 15 μS/cm. The solution temperature was maintained at 60±3° C. throughout the tests. The solution was circulated at 94.6±5 L/min during the entire test to achieve representative fluid velocities over the submerged corrosion coupons. Monitoring of the tests included collection of grab samples and continuous on-line monitoring of recirculation flow rate, test solution temperature, and pH. Solution samples were collected daily, fiberglass insulation samples were collected periodically during the tests, and metallic coupons were examined after the tests. All sampling procedures and water quality analyses were conducted in accordance with appropriate standard methods and approved project instructions [
reference 2 which is incorporated herein by reference]. - Aluminum alloy 3003 was used in this study. Each aluminum alloy coupon was 30.5-cm (12-in) square and 0.16-cm ( 1/16-in) thick, with an average weight of about 392 g. In each test, three aluminum alloy coupons were submerged in the solution. A chlorinated polyvinyl chloride (CPVC) coupon rack provided sufficient separation between the test coupons to prevent galvanic interactions.
- As is evident from the description above, the pilot tests were conducted in a very complex chemical system that was designed to include many possible interactions between materials that might occur in a containment building during a real LOCA. While this design has clear advantages for identifying unintended interactions, the disadvantage is that it is not always possible to determine which constituents or interactions might be contributing to a particular observed effect. Thus, bench-scale tests were conducted to provide a more controlled environment that could be used to formulate a mechanistic understanding of results observed in the pilot tests.
- The bench tests described here focused on identifying conditions that could affect aluminum corrosion under representative LOCA solution conditions. Three 1-L solutions were used for the test. All three contained 16,000 mg/L H3BO3. The first container was a blank for comparison to the pilot tests, the second contained 88.7 mg/L silicon (added as Na2SiO3·9H2O), and the last contained 50 mg/L calcium (added as CaCl2). The selected concentration of silicon or calcium was based on their measured concentrations near the end of
pilot Test 4. The test was conducted in capped, 1-L, Nalgene® bottles. All solutions were preheated to 60° C. and pH was adjusted to 9.5 using NaOH before small aluminum coupons were placed into the containers. The solution was semi-open to the atmosphere, since air contact occurred during sampling procedures. The temperature of the solutions was maintained at 60° C. in a constant temperature oven for 30 days. - The 3003 aluminum alloy used in the bench tests was the same as that used in the pilot tests. Each aluminum alloy coupon was 24×13×1.8 mm and weighed about 1.59 g. In contrast to the pilot tests, the solution of the bench tests was mostly stagnant. Prior to the test, the aluminum coupons were ultrasonically cleaned in 95-percent ethanol, rinsed with ultra-pure water (R=18.2 MΩ·cm), and dried in air. The deionized water used in the tests was obtained from a research-grade laboratory water purification system.
- Throughout the pilot test series, daily solution samples were obtained for measurements of pH and elemental concentrations. An inductively-coupled plasma / optical emission spectrometer (ICP-OES) (Optima 5300 DV, Perkin Elmer) was used to analyze Al, Ca, and Si concentrations in the solution. The weight loss method provided a second measure of corrosion rates. Prior to weight measurements, the coupons were dried in air but no techniques were employed to remove corrosion products adhered to the surface. Since the presence of corrosion products on the coupon surface could interfere with corrosion rate calculations, weight loss measurements and solution concentrations were used together to evaluate the rate of corrosion in these tests.
- Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) (Model JXA-8200, JEOL) analyses were conducted on the metal coupons. The samples were coated with Au/Pd to enhance the conductivity of the surface. X-ray photoelectron spectrometry (XPS) was also used to examine the surface of the aluminum alloy samples before and after corrosion. In the XPS measurements, a Kratos Axis Ultra spectrometer provided the chemical composition of the coupon subsurface down to a depth of 10 nm.
- The aluminum concentration in solution was used as an indicator of the rate of aluminum corrosion. The aluminum concentration in solution, total mass of aluminum in solution, and predicted aluminum solubility in each test are shown in Table 3. The results show relatively significant corrosion in
Tests Tests - In
Tests FIG. 1 . From these results, it is clear that the rate of aluminum corrosion varied greatly from test to test. InTest 1, the aluminum concentration increased from zero to about 360 mg/L after 18 days. After that, the concentration oscillated around 360 mg/L throughday 30. InTest 5, the concentration increased from zero to about 50 mg/L in 14 days and stayed in the range of 50 mg/L for the remainder of the test. -
TABLE 3 Weight loss and corrosion rates in the pilot tests. Al conc. Al mass Solubility of Al Mass lost3 Corrosion rate based on measured measured predicted by water from the Al conc. in solution in solution chemistry modeling2 coupons measurements4 Test (mg/L) (g) (mg/L) (g) (g/m2 · h) 1 360 340 980-1,600 296 1.40 in 18 days 2 BDL1 BDL 6-12 2.7 0.007 3 BDL BDL 9-60 <0.1 <0.001 4 BDL BDL 1,600-3,920 <0.1 <0.001 5 50 47.3 74-150 33.6 0.25 in 14 days 1BDL = below detection limit, i.e., 0.5 mg/L. 2Visual Minteq v. 2.30. 3Measured at the end of the 30-day test. 4The corrosion rate in Test 2 is based on the weight loss after the 30-day test; the minimum corrosion rates forTests - The use of solution concentrations as an indication of corrosion requires that the solution concentration not be controlled by external factors such as solubility. The solubility of aluminum under these conditions is controlled by aluminum hydroxide. While crystalline forms such as gibbsite have lower solubility, it has been shown that solution concentrations are initially controlled by the precipitation of amorphous aluminum hydroxide, the kinetically-favored precipitation product. The solubility of amorphous aluminum hydroxide in aqueous solution increases dramatically with higher pH above 6.3. The solubility of aluminum in each test (i.e., the applied chemical concentrations, measured pH range, and 60° C.) was calculated using Visual Minteq 2.30 [see reference 22]. As shown in Table 3, modeling results indicate that the measured concentrations of aluminum were below the predicted saturation limits in all tests.
- Solubility has another vital role in these tests. Modeling indicates that aluminum solubility decreases as temperature decreases. No corrosion-induced precipitates were observed in the test solutions at 60° C. However, in
Test 1, a substantial amount of white material precipitated as the solution cooled to room temperature. Precipitation was evident upon cooling as early as the first day of the 30-day test. XRD results indicate that the precipitate was mostly amorphous. In other research, the formation of a similar precipitate clogged simulated components of the ECCS [references 23,24], so these results indicate that aluminum corrosion may have a potentially severe impact on the proper operation of the ECCS. The ability of precipitates to form following corrosion was a key focus of this research. No corrosion-induced precipitates formed either at test temperature or upon cooling inTests Test 4, but this phenomenon was attributed to the reaction between TSP and calcium silicate to form calcium phosphates). A small amount of precipitate formed when theTest 5 solution cooled, starting with theDay 2 sample and proceeding until the end of the test, but the amounts were substantially less than those observed inTest 1. Analyses of the precipitates indicated that the precipitates were mainly amorphous aluminum hydroxide with a significant amount of adsorbed boron. - Weight loss measurements from the corrosion coupons were a second indicator of aluminum corrosion during the pilot tests. As shown in Table 3, there is overall good agreement between weight lost from the coupons and the mass of aluminum measured in solution. In Tests 1 and 5, the mass of aluminum measured in solution was slightly more than the mass lost from the coupons, indicating that some corrosion products adhered to the coupons and interfered slightly with the weight loss calculations. However, generally the weight loss measurements serve as a good confirmation of the solution concentration measurements.
- SEM provides a visual picture of corrosion on a microscopic level. SEM images of an unused aluminum coupon and coupons after 30 days of submersion in
Tests FIGS. 2 a, 2 b, and 2 c. The SEM images give additional insight into the extent of corrosion reflected by the aluminum concentration in the solution and the weight loss of the coupons. The coupon fromTest 1 had a very rugged surface that appeared to be the formation of extensive corrosion products. However, theTest 4 coupon had little or no corrosion, and the coupon surface appeared relatively smooth. - Together, the aqueous aluminum concentrations, coupon weight measurements, and SEM images present a consistent picture of aluminum corrosion. Corrosion rates based on these results are shown in Table 3. In most cases, the measured corrosion rates are consistent with expectations based on existing literature. The measured value of 1.40 g/m2 h for
Test 1 is close to the values identified in Table 1 for corrosion of aluminum at high pH in the presence of borate. The low corrosion rate inTest 2, likewise, is consistent with the low corrosion rate expected at neutral pH. The corrosion rate of 0.25 g/m2 h forTest 5 was lower thanTest 1, which is expected based on the lower pH value. - Exceptions to the expected corrosion rates occurred in
Tests Test 3 is shown as 7.3 to 8.1 in Table 2, the pH was nearly 8.0 for most of the test (except the first 2 days). A corrosion rate of 0.009 g/m2·h has been reported at pH=8.0 and 60 ° C. without borate [reference 13], and borate has been shown to increase the corrosion rate by at least an order of magnitude. Thus, the observed corrosion rate inTest 3 is at least 1 to 2 orders of magnitude lower than expected. Similarly, corrosion rates of 0.459 to 1.22 g/m2·h at pH=10, 60° C., with borate present are reported in Table 1; thus, the corrosion rate inTest 4 is 2 to 3 orders of magnitude lower than expected based on the literature for similar test conditions. Visual inspection of the coupons as shown inFIG. 3 also supports these results. The entire surface of the coupons fromTests Test 4 coupons appeared nearly identical to an unused coupon. Significant portions of theTest 3 coupons appear uncorroded but some patches of corrosion were present, indicating that the coupons inTest 3 were more affected by corrosion than inTest 4. However, consistent with the corrosion rate in Table 3, theTest 3 coupons were clearly less corroded than theTest 2 coupons, even though the higher pH of the solution should have permitted more aggressive surface degradation. - The key constituent present in
Tests Test Test Test 2 was initially low, but close toTest 3 at the end of the test. Table 4 shows that Tests 3 and 4 also had the highest calcium concentrations, with values of about 110 mg/L and 50 mg/L, respectively. In contrast, lower calcium concentrations were observed inTests -
TABLE 4 Concentrations of calcium and silicon at the end of each test. Test Silicon (mg/L) Calcium (mg/L) 1 7 18 2 45 10 3 45 110 4 82 50 5 4 32 - Table 4 indicates that the silicon and calcium concentrations were both highest in
Tests Test 3 but predominantly as H3SiO4 − with less than 25% H4SiO4 in Test 4 (the pKa1 of H4SiO4 is around 9.9 at 30° C. [reference 25]). The H3SiO4 − species may be more important than H4SiO4 with regard to forming a passivation layer on the aluminum surface, which would explain why the passivation was more notable inTest 4 than inTest 3. Water quality modeling predicted that the calcium was present primarily as Ca2+ and CaH2BO3 + inTest 4 and as Ca2+, CaH2BO3 +, and CaHPO4(aq) inTest 3. - Bench tests were conducted to clarify whether silicon or calcium was responsible for passivation of the aluminum surface noted in
pilot Tests Test 4, which exhibited the greatest degree of passivation. Bench-scale corrosion tests were prepared with the same stock solution chemistry as Test 4 (Table 2, but without insulation or debris) with the addition of either 88.7 mg/L of Si (added as sodium silicate) or 50 mg/L of Ca (added as calcium chloride); a reference test was also conducted using only the stock solution chemistry without either additive. The measured aluminum concentrations over the duration of the tests are shown inFIG. 4 . Without silicon or calcium present, the aluminum concentration followed the same general trend asTest 1 in the pilot tests, although the concentration leveled off at about 182 mg/L in the bench tests compared to 360 mg/L in the pilot tests. The calculated corrosion rate in 14 days was 0.60 g/m2·h in this test. A difference in maximum aluminum concentration between the bench and pilot tests may have occurred because the complex solution chemistry in the pilot tests was more corrosive than the carefully controlled conditions in the bench tests. Another possible cause for the difference is that the coupons in the pilot tests were exposed to continuous fluid movement while the solution of the bench tests was mostly stagnant. It was noted earlier that corrosion rates could increase as fluid movement increases [reference 12]. When the fluid is stagnant, a concentration boundary layer can form next to the coupon surface, and the localized high concentration of aluminum ions and corrosion products near the surface can decrease the concentration gradient, impede mass transfer, slow dissolution of the film layer, and thereby slow the corrosion process. -
FIG. 3 shows that the presence of silicon in solution caused a strong passivation effect. When 88.7 mg/L silicon was present, the aluminum concentration was less than 1 mg/L and near the detection limit (i.e., 0.5 mg/L) throughout the test. As a result, the corresponding corrosion rate was less than 0.002 g/m2·h in 14 days, a 300× reduction in the corrosion rate (2.5 orders of magnitude) compared to the coupon in the solution that contained no Si or Ca. One plausible mechanism to explain this effect is that silicate anions reacted with aluminum at the coupon surface. Consequently, an insoluble aluminosilicate coating was formed, which impeded further aluminum dissolution and corrosion. - The introduction of 50 mg/L calcium caused a 2× reduction in aluminum corrosion; i.e., the aluminum concentration increased to only 92 mg/L after 30 days. The corrosion rate was 0.34 g/m2·h in 14 days, about half of the corrosion rate of the coupon in the solution that contained no Si or Ca. One possible mechanism explaining the reduced corrosion is that calcium may react with carbonate to form a protective calcium carbonate layer at the aluminum alloy coupon surface. Carbonate is present in solution from carbon dioxide in the air. Compared to the effect of silicate, however, the effect of calcium is relatively minor.
-
FIG. 4 a, 4 b, and 4 c show SEM images of the aluminum alloy coupons after the bench tests. Consistent with the aluminum concentration results, the roughest and most corroded coupon surface was observed from the solution that contained no Si or Ca. In contrast, the coupon from the solution containing 88.7 mg/L silicon was mostly smooth and uniform. The roughness of the coupon from the 50 mg/L Ca solution was nearly the same as the coupon immersed in the solution without Si or Ca. - Based on the bench experimental results, it appears that an insoluble aluminosilicate compound was predominantly responsible for passivating the aluminum coupons in
pilot Tests - Direct evidence that a passivation layer formed on the aluminum alloy coupon surface was obtained by analyzing the surface of a pre-cleaned virgin aluminum alloy coupon and a silicate-passivated aluminum alloy using XPS, as shown in
FIG. 6 . Before XPS examination, the silicate-passivated aluminum coupon was removed from the bench test solution, rinsed gently with pure water several times, and stored in a nitrogen-filled desiccator for drying. - As illustrated in
FIGS. 5 a and 5 b, the subsurface of the virgin aluminum coupon to a depth of 10 nm was composed of Al2O3 (64 weight percent), Al(OH)3 (27 weight percent), and Al (9 weight percent). However, the subsurface of the silicate-passivated coupon contained mainly Al2OSiO4 (98 weight percent) with a small amount of Al2O3 (2 percent). This result indicates that silicon reacted with aluminum at the coupon surface. The thickness of the passivation layer was at least 10 nm, based on the depth of examination by XPS. In contrast to the virgin aluminum coupon, no aluminum metal was detected in the top 10 nm of the silicate-passivated coupon surface. It appears that the passivation layer formed on the original coupon surface and subsequently covered the aluminum metal. Further tests indicated that, although the aluminosilicate passivation layer was soluble in acidic solution (e.g., pH 2.2), it was stable under alkaline conditions (e.g., pH 9.5). Because the containment pool of the ECCS after a LOCA requires high pH to sequester radioactive iodine, an aluminosilicate passivation layer like those found inTests - Although not wishing or intending to be bound by any theory, the principal mechanism of surface passivation of aluminum or its alloys appears to occur whereby the ionic species H3SiO4 − reacts with exposed aluminum to form a layer of insoluble Al2OSiO4 which inhibits oxidation reactions from removing aluminum from the solid surface. The treatment methods described above can be applied during a nuclear power plant LOCA scenario, or other industrial facility accident, that exposes aluminum to corrosive aqueous environments, particularly those with elevated temperature and pH.
- The bench-scale tests demonstrated that a relatively low dose of silicate (i.e., less than less than 90 mg/L) could passivate the aluminum surface and dramatically reduce the rate of corrosion. XPS examination confirmed that a passivation layer composed of Al2OSiO4 can be formed with a thickness of more than 10 nm. Pilot-scale tests confirmed that this effect would be true even in realistic LOCA conditions, where other metals, concrete, insulation, and other dust and debris are adding complexity to the solution chemistry.
- These results indicate that addition of a compound containing silicon, such as a silicate, into the reactor ECCS recirculation water may be an effective way to prevent aluminum corrosion and thereby prevent the precipitation of related chemical products that have the potential to degrade the performance of the ECCS. The bench-scale testing further illustrated that an Al2OSiO4 passivation layer, once formed, is stable with respect to drying and reimmersion in alkaline conditions. This opens a viable opportunity for pretreating industrial aluminum components and structures to enhance their corrosion resistance to a variety of operational and accidentally induced chemical environments.
- The present invention is advantageous to reduce aluminum corrosion in an LOCA in that the release of aluminum ions and subsequent precipitation of aluminum hydroxide can be reduced, potentially reducing or eliminating the chemical product contributions to clogging in the ECCS and to reduce aluminum corrosion in other aqueous environments. The present invention also is advantageous as a pretreatment to protect industrial aluminum components and structures before exposure in a variety of adverse chemical environments. The treatment method described above may be used in many industrial applications (particularly those that require immersion in or exposure to water of mechanical structures and components) that include, but are not limited to, (a) surface and subsurface marine environments, (b) water quality treatment, (c) chemical processing, (d) mining and drilling, (e) aviation construction, (f) automotive construction, and (g) liquid process piping and pumping.
- Although the present invention has been described above with respect to certain embodiments thereof for purposes of illustration, the invention is not so limited since changes, modifications, and the like can be made thereto within the scope of the invention is set forth in the appended claims.
-
- [1] D. Chen, K.J. Howe, J. Dallman, B.C. Letellier, M. Klasky, J. Leavitt, B. Jain, Experimental analysis of the aqueous chemical environment following a loss-of-coolant accident, Nucl. Eng. Des. Vol. 237, No. 20-21, p 2126-2136. November, 2007.
- [2] J. Dallman, B. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe, L. Archuleta, F. Sciacca, Integrated Chemical Effects Test Project: Consolidated Data Report; NUREG/CR-6914, Vol. 1, U.S. Nuclear Regulatory Commission, Washington D.C., 2006.
- [3] J. Dallman, J. Garcia, M. Klasky, B. Letellier, K. Howe, Integrated Chemical Effects Test Project:
Test 1 Data Report; NUREG/CR-6914, Vol. 2, U.S. Nuclear Regulatory Commission, Washington D.C., 2005. - [4] J. Dallman, B. Letellier, J. Garcia, M. Klasky, W. Roesch, J. Madrid, K. Howe, D. Chen, Integrated Chemical Effects Tests:
Test 2 Data Report; NUREG/CR-6914, Vol. 3, U.S. Nuclear Regulatory Commission, Washington D.C., 2005. - [5] J. Dallman, B. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe, L. Archuleta, F. Sciacca, Integrated Chemical Effects Tests:
Test 3 Data Report; NUREG/CR-6914, Vol. 4, U.S. Nuclear Regulatory Commission, Washington D.C., 2005. - [6] J. Dallman, B. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe, L. Archuleta, F. Sciacca, Integrated Chemical Effects Tests:
Test 4 Data Report; NUREG/CR-6914, Vol. 5, U.S. Nuclear Regulatory Commission, Washington D.C., 2005. - [7] J. Dallman, B. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe, L. Archuleta, F. Sciacca, Integrated Chemical Effects Tests:
Test 5 Data Report; NUREG/CR-6914, Vol. 6, U.S. Nuclear Regulatory Commission, Washington D.C., 2005. - [8] K. R. Trethewey, J. Chamberlain, Corrosion for Students of Science and Engineering, Longman Scientific & Technical, Hong Kong, 1988, pp. 281.
- [9] K. F. Lorking, J. E. O. Mayne, The corrosion of aluminum, J. Appl. Chem. 11 (1961) 170-180.
- [10] E. Deltombe, M. Pourbaix, The electrochemical behavior of aluminum, Corrosion 14 (1959) 496t-500t.
- [11] S. I. Pyun, S. M. Moon, Corrosion mechanism of pure aluminum in aqueous alkaline solution, J. Solid State Electrochem 4 (2000) 267-272.
- [12] H. P. Godard, W. B. Jepson, M. R. Bothwell, R. L. Kane, The Corrosion of Light Metals, John Wiley and Sons, New York, 1967, pp. 15-17.
- [13] M. R. Tabrizi, S. B. Lyon, G. E. Thompson, J. M. Ferguson, The long-term corrosion of aluminum in alkaline media, Corros. Sci. 32 (1991) 733-742.
- [14] J. P. Labbe, J. Pagetti, Study of an inhibiting aluminosilicate interface by infrared reflection spectroscopy, Thin Solid Films 82(1) (1981) 113-119.
- [15] T. E. Wright, H. P. Godard, Laboratory studies on the pitting of aluminum in aggressive waters, Corrosion 10 (1 954) 195-198.
- [16] J. R. Davis, Corrosion of Aluminum and Aluminum Alloy, ASM International, Materials Park, Ohio, 1999, pp. 27.
- [17] W. Stumm, J. J. Morgan, Aquatic Chemistry: Chemical Equilibria and Rates in Natural Waters, third ed., John Wiley & Sons, New York, 1995, pp. 273.
- [18] V. Jain, et al., Corrosion Rate Measurements and Chemical Speciation of Corrosion Products Using Thermodynamics Modeling of Debris Components to Support GSI-191; NUREG/CR-6873, the U.S. Nuclear Regulatory Commission, Washington D.C., 2005.
- [19] J. C. Griess et al., Design Considerations of Reactor Containment Spray Systems-Part III. The Corrosion of Materials in Spray Solutions, Oak Ridge National Laboratory, Oak Ridge, Tennessee, December 1969.
- [20] J. Pippo et al., Corrosion Behavior of Zinc and Aluminum in Simulated Nuclear Accident Environments; STUK-YTO-TR 123, Finish Centre for Radiation and Nuclear Safety, Helsinki, Finland, February 1997.
- [21] S. B. Lee, D. J. Babić, Observation and characterization of aluminum passivation in silicon-doped KOH solutions, Electrochem. Soc. 147(12) (2000) 4512-4518.
- [22] Software from the Department of Land and Water Resources Engineering, Royal Institute of Technology, Sweden
(http://www.1wr.kth.se/English/OurSoftware/vminteq/). - [23] R. C. Johns, B. C. Letellier, K. J. Howe, A. K. Ghosh, T. Y. Chang, Small-scale Experiments: Effects of Chemical Reactions on Debris-Bed Head Loss; NUREG/CR-6868, the U.S. Nuclear Regulatory Commission, Washington D.C., 2005.
- [24] J. H. Park, K. Kasza, B. Fisher, J. Oras, K. Natesan, W. J. Shack, Chemical Effects Head-Loss Research in Support of Generic Safety Issue 191; NUREG/CR-6913, U.S. Nuclear Regulatory Commission, Washington D.C., 2006.
- [25] M. Klasky, J. Zhang, M. Ding, B. Letellier, D. Chen, K. Howe, Aluminum Chemistry in a Prototypical Post-Loss-of-Coolant-Accident, Pressurized-Water-Reactor Containment Environment; NUREG/CR-6915, U.S. Nuclear Regulatory Commission, Washington D.C., 2006.
- [26] H. Lee, F. Xu, C. S. Jeffcoate, H. S. Isaacs, Cyclic polarization behavior of aluminum oxide films in near neutral solutions, Electrochem. Solid State Lett. 4(10) (2001) B31-B34.
- [27] A. Y. Shatalov, Effect de pH sur le Comportement Electrochemique des Metaux et Leur Resistance la Corrosion, Doklady Akad. Nauk. U.S.S.R. 86 (1952) 775-777.
- [28] D. R. Lide, et al. (Eds.) CRC Handbook of Chemistry and Physics, 84th ed., CRC Press, New York, 2003.
- [29] K. R. Trethewey, J. Chamberlain, Corrosion for Students of Science and Engineering, Longman, Hong Kong, 1988, pp. 234.
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US8609254B2 (en) | 2010-05-19 | 2013-12-17 | Sanford Process Corporation | Microcrystalline anodic coatings and related methods therefor |
US10214827B2 (en) | 2010-05-19 | 2019-02-26 | Sanford Process Corporation | Microcrystalline anodic coatings and related methods therefor |
WO2025090957A1 (en) * | 2023-10-26 | 2025-05-01 | Ecolab Usa Inc. | Non-phosphate corrosion inhibition compositions and methods for mitigating corrosion in cooling water applications |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3971674A (en) * | 1975-03-03 | 1976-07-27 | Aluminum Company Of America | Selective black coating for aluminum |
US4564465A (en) * | 1983-04-20 | 1986-01-14 | Air Refiner, Inc. | Corrosion inhibition additive for fluid conditioning |
US20010054454A1 (en) * | 1998-04-08 | 2001-12-27 | Modi Paresh R. | System and method for inhibiting corrosion of metal containers and components |
-
2008
- 2008-06-23 US US12/214,895 patent/US20090038712A1/en not_active Abandoned
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3971674A (en) * | 1975-03-03 | 1976-07-27 | Aluminum Company Of America | Selective black coating for aluminum |
US4564465A (en) * | 1983-04-20 | 1986-01-14 | Air Refiner, Inc. | Corrosion inhibition additive for fluid conditioning |
US20010054454A1 (en) * | 1998-04-08 | 2001-12-27 | Modi Paresh R. | System and method for inhibiting corrosion of metal containers and components |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8609254B2 (en) | 2010-05-19 | 2013-12-17 | Sanford Process Corporation | Microcrystalline anodic coatings and related methods therefor |
US9260792B2 (en) | 2010-05-19 | 2016-02-16 | Sanford Process Corporation | Microcrystalline anodic coatings and related methods therefor |
US10214827B2 (en) | 2010-05-19 | 2019-02-26 | Sanford Process Corporation | Microcrystalline anodic coatings and related methods therefor |
WO2025090957A1 (en) * | 2023-10-26 | 2025-05-01 | Ecolab Usa Inc. | Non-phosphate corrosion inhibition compositions and methods for mitigating corrosion in cooling water applications |
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