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WO1998031197A1 - Revetements ameliores destines a des elements chauffants electriques a gaine metallique - Google Patents

Revetements ameliores destines a des elements chauffants electriques a gaine metallique Download PDF

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Publication number
WO1998031197A1
WO1998031197A1 PCT/US1998/000438 US9800438W WO9831197A1 WO 1998031197 A1 WO1998031197 A1 WO 1998031197A1 US 9800438 W US9800438 W US 9800438W WO 9831197 A1 WO9831197 A1 WO 9831197A1
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WO
WIPO (PCT)
Prior art keywords
coating
tantalum
heating element
refractory metal
sheath
Prior art date
Application number
PCT/US1998/000438
Other languages
English (en)
Inventor
Thanh D. Huynh
Original Assignee
Emerson Electric Co.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Emerson Electric Co. filed Critical Emerson Electric Co.
Priority to AU62392/98A priority Critical patent/AU6239298A/en
Publication of WO1998031197A1 publication Critical patent/WO1998031197A1/fr

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/40—Heating elements having the shape of rods or tubes
    • H05B3/42—Heating elements having the shape of rods or tubes non-flexible
    • H05B3/48—Heating elements having the shape of rods or tubes non-flexible heating conductor embedded in insulating material
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/62—Heating elements specially adapted for furnaces
    • H05B3/64—Heating elements specially adapted for furnaces using ribbon, rod, or wire heater

Definitions

  • the present invention relates to improved coatings for electrical, metal sheathed heating elements and, more particularly, coatings for such heating elements comprised of a refractory metal, refractory metal oxide, ceramic, inter-metallic, or mixtures thereof.
  • Heating elements are widely employed in order to raise the temperature of such media as liquids and gases.
  • the element When utilizing a heating element to raise the temperature of a medium, the element is typically immersed in the liquid or gas which is desired to be heated. The immersed element is then heated via a power source such that the generated heat is radiated to the liquid or gas and the temperature of the liquid or gas rises.
  • the liquid or gas to be heated is itself corrosive to the heating element, contains corrosive substances, or contains substances which become corrosive upon heating. Corrosion of the heating element often results which necessitates excess repair and replacement costs to the unit which contains the heating element.
  • heating elements are often encapsulated with a thick, i.e. from about 0.32 to about 0.65 centimeters, layer of a substance such as a synthetic fluorine containing resin.
  • synthetic resins for example, TeflonTM
  • TeflonTM are well-known coating agents for many items, including cookware, because of their "non-stick" properties.
  • the resin coating protects the heating element somewhat from corrosion but, unfortunately, has many deficiencies.
  • TeflonTM TeflonTM
  • the coating decreases the efficiency of the heating element by reducing the transfer of heat from the element to the media to be heated.
  • a related problem is that due to its non-stick properties, TeflonTM does not adhere well to the heating element surface. Therefore, the heating element must be encapsulated by the TeflonTM. This requires sleeving a thick pre-formed, open-ended TeflonTM tube around the element. Often during such sleeving the heating element may be damaged. Additionally, the open-end of the TeflonTM sleeving allows for the possibility that corrosive materials may come into contact with part of the heating element because condensation is trapped between the TeflonTM sleeve and the surface of the heater.
  • TeflonTM protective sleeves Yet another deficiency of TeflonTM protective sleeves is that above about 260°C in air, the TeflonTM coating will often degrade. Such degradation may be difficult to detect before significant corrosion of the heating element occurs. However, even if the degradation is detected, the sleeve is not easily repaired and often must be replaced in its entirety via the sleeving process described above.
  • Another manner of protecting heating elements from corrosion is to use a sheath made entirely of ceramic rather than coating a metal sheath with TeflonTM. Such ceramic sheathed elements are disclosed in US Patent No. 5,084,606. Unfortunately, when the sheath is made of solid ceramic, the heating element is fragile due to the brittleness of the ceramic. Such elements are also expensive due to the amount of ceramic.
  • ceramic is not very conductive and thus heat is not readily transferred by the element. It would be desirable to discover a coating for an outer metallic shell of a heating element which is significantly thinner than the TeflonTM coating currently employed. If such a coating could be discovered then the heating elements would be efficient, as well as, less expensive and fragile than a ceramic sheathed heating element. It would further be desirable if such a coating would adhere to the heating element such that it could be applied via a simple process which would not harm the heating element and such that the coating did not leave an opening for corrosive materials to attack the heating element. It would yet further be desirable if such a coating would offer protection to the heating element at high temperatures and in corrosive environments and could be repaired easily if such repair becomes necessary.
  • a refractory metal, refractory metal oxide, ceramic, inter-metallic. or a mixture thereof may be utilized to coat heating elements.
  • Such coatings offer excellent corrosion protection in many different environments including acidic environments.
  • the coatings are very energy efficient in that heat is readily conducted through the coating.
  • the numerous processes which may be utilized to apply the refractory metal, refractory metal oxide, ceramic, inter-metallic, or mixture thereof to the heating element offer significant advantages.
  • One advantage is that the processes do not damage the heating element.
  • the coatings do not require sleeving the heating element with an open-ended tubular structure such as TeflonTM, but rather, coat the entire heating element. In this manner, if the coating becomes damaged, it may be repaired at the point of damage and replacement of the entire coating is not necessary. Also, by not having an open end, the heating element is better protected from corrosion.
  • Figure 1 illustrates a typical heating element which is coated with a corrosion resistant coating in accordance with the instant invention.
  • FIG. 2 illustrates the coatings of the instant invention. Detailed Description of the Invention
  • heating element refers to any electrical resistance heating element used to raise the temperature of a liquid such as water or a gas such as air.
  • electrical resistance heating elements are of many different shapes and sizes depending upon the intended application. Among such shapes include disks, tubes, filaments, and cartridges. The sizes may vary from a small heating element suitable for a personal hair dryer to a large heating element suitable for a commercial water heater.
  • useful elements to be coated in this invention typically produce watt density of at least 5, preferably at least 50, more preferably at least 200 watts per square inch.
  • a typical heating element which may be utilized in the instant invention is illustrated in Figure 1.
  • the heating elements of this invention are useful in immersion heaters which are subject to corrosive environments. Such heaters are often used in heating chemicals and thus subject to the corrosive environments thereof.
  • Such immersion heaters typically are comprised of an electrically conductive resistive heating element and a metallic sheath covering the element, the sheath being insulated from the element by conventional insulation.
  • the coatings of the instant invention are useful to cover the sheath and protect the element from corrosion even when the current flow through the element produces a watt- density of at least 5, preferably at least 50, more preferably at least 200 watts per square inch.
  • refractory metals refers to those metals capable of withstanding temperatures to which a heating element may be subjected. Typically, such metals may withstand temperatures up to 100, preferably up to 500, more preferably up to 1000 °C.
  • refractory metals those found most suitable for this invention include tantalum, niobium, hafnium, and rhenium. The most preferable refractory metal is tantalum.
  • refractory metal oxide refers to a compound which contains oxygen and a refractory metal in any ratio sufficient for use as a coating in the instant invention.
  • useful oxides of this invention include tantalum oxide, niobium oxide, hafnium oxide, and rhenium oxide such as, for example, Ta 2 0 5 , Nb 2 0 5 , Hf 2 0 5 , and Re 2 0 5 .
  • ceramics generally refers to metallic or non-metallic compounds which are capable of withstanding temperatures to which a heating element may be subjected. Typically, such materials may withstand temperatures up to 100, preferably up to 500, more preferably up to 1500 °C.
  • Ceramics are described generally in, for example, Electric Process Heating by Maurice Orfeuil, Batelle Press, (1987) pp. 60-61, which is incorporated herein by reference.
  • the term ceramics includes “carbides”, “nitrides” and “oxides”.
  • the term “carbides” refers to a compound, metallic or non- metallic, associated with carbon such as silicon carbide (SiC), tantalum carbide (TaC), hafnium carbide (HfC), aluminum nitride (A1N), niobium carbide (NbC), rhenium carbide (ReC), and zirconium carbide (ZrC), as well as, diamond.
  • nitrides refers to a compound, metallic or non-metallic, associated with nitrogen such as boron nitride (BN), tantalum nitride (TaN or Ta N), silicon nitride (Si 3 N 4 ), and hafnium nitride (HfN).
  • oxides refers to a compound, metallic or non-metallic, associated with oxygen such as silicon dioxide (Si0 2 ), tantalum pentoxide (Ta 2 0 5 ) or lithium oxide.
  • inter-metallics is a two or more component system which has a semiconducting metal.
  • a typical inter-metallic compound for use in the present invention includes nickel suicide (Ni 3 Si).
  • the term "coating” means a film or thin layer applied to an outer metallic shell, i.e., sheath, of a heating element.
  • the sheath often encompasses components of an element which are in need of protection from corrosion. Such components may include thermocouples, resistance wires, and connectors.
  • the thickness of such films or layers varies depending upon the particular coating material and the surface smoothness of the heating element.
  • the coatings of the instant invention are at least 1000, preferably at least 10,000, more preferably at least 50,000 Angstroms thick.
  • the coatings are not so thick that ductility is lost or the coating becomes fragile.
  • the coating are less than 100, preferably less than 10, more preferably less than 1 microns thick.
  • the coatings of the instant invention are substantially pinhole and stress free.
  • the coating adheres strongly to the surface of a metallic sheath of the heating element at temperatures ranging from - 20° to over 1000° C. After multiple thermal cycling, the coatings also conserves its strong adherence.
  • the undercoat may include any of the materials used for coatings herein.
  • a particularly preferred undercoating material is tungsten.
  • the thickness of the undercoat is typically less than 5, preferably less than 1, and more preferably less than 0.1 micrometers.
  • the instant invention provides a tenacious, stress, and pinhole-free coating suitable for protecting heating elements
  • the invention is particularly applicable to heating elements which are in need of such protection.
  • Typical heating elements in need of such protection include those heating elements used in immersion and gas heaters subjected to a corrosive environment.
  • the coatings of the instant invention offer protection because the coatings are substantially impermeable to many corrosive environments which the heating element may be subjected.
  • a corrosive environment to which an immersion heater may be subjected often includes those environments where concentrated acids exist.
  • the corrosive environment has a pH of from about less than 1 to about 6 and may comprise sulfuric acid, nitric acid, chromic acid, phosphoric acid, or other acids harmful to unprotected heating elements, as well as, mixtures of the aforementioned acids.
  • a heating element may be subjected to a corrosive gaseous environment, such as one comprising cyanide, chlorine, sulfur, or mixtures thereof.
  • a corrosive environment may include high temperatures, for example, temperatures from about 100 to about 1000°C, pressures from about 0 to about 1 atmospheres, as well as, acidic pH's, for example, from about 0.01 to about 6, or basic pH's, for example, from about 9 to about 14.
  • acidic pH's for example, from about 0.01 to about 6, or basic pH's, for example, from about 9 to about 14.
  • Proper surface preparation fosters adhesion between the element and coating.
  • Surface preparation also eliminates foreign objects and debris which could cause cracks or holes in the coating and allow corrosion of the heating element.
  • Typical surface preparation may include a number of different steps or combination of steps.
  • Typical surface preparation steps comprise, for example, one or more of the following: electropolishing, mechanical polishing, chrome plating, deburring, electroless nickel plating, acid or chemical etching, plasma etching, utrasonical cleaning, or vapor degreasing.
  • a particularly preferred surface preparation procedure involves mechanically polishing the surface of the metal sheath of the heating element onto which the coating will be deposited.
  • the polishing may include removing from about 0.1 to about 30 micrometers or more of the surface of the metal sheath.
  • the above polishing be accomplished by use of an automated polishing process.
  • the polishing is highly precise and efficient, for example, often on the order of seconds for a typical polished tube of dimensions from about 35 to about 200 centimeters in length and from about 4 to about 6 centimeters in outside diameter.
  • Electropolishing is another preferred method of preparing the surface of the heating element. This method is of particular importance when minimizing the roughness profile of the metal surface.
  • a mirror-like surface of the metal sheath may be achieved with an immersion time of from about 5 to about 15 minutes or longer.
  • the process used to coat the heating element with the refractory metal, refractory metal oxide, ceramic, inter-metallic, or mixture thereof is not particularly critical so long as the coating is impermeable to corrosive fluids and adheres strongly to the surface of the metal sheath. It is preferable for most applications that the coating be of uniform thickness and adhere via physical means or chemical means to the heating element. Often the coating process utilized is based upon the size and shape of the heating element to be coated.
  • coating methods as electrolysis, electroplating, electrodeposition, conventional chemical vapor deposition such as the deposition of tantalum via a liquid or solid precursor, gas and solid diffusion such as pack cementation and chemical vapor deposition, physical vapor deposition such as RF and DC sputtering including both reactive and non-reactive processes (non-reactive processes generally consists of using inert or non-reactive gases such as Argon or Helium), plasma enhanced, or ion beam- assisted vapor deposition, as well as, vacuum or mechanical coating means including brushing, spraying such as thermal or plasma spraying, calendering, dip coating, roller coating, or any combination thereof may be utilized.
  • conventional chemical vapor deposition such as the deposition of tantalum via a liquid or solid precursor, gas and solid diffusion such as pack cementation and chemical vapor deposition
  • physical vapor deposition such as RF and DC sputtering including both reactive and non-reactive processes (non-reactive processes generally consists of using inert or non-reactive gases such as Ar
  • a particularly preferred coating process is that of pack cementation.
  • This process consists of placing the heating element to be coated into a semi-permeable enclosure, for example, a box.
  • the enclosure contains, or is subsequently filled, with the refractory metal, refractory metal oxide, ceramic, inter-metallic, or mixture thereof which is to become the coating.
  • the enclosure also contains, or is subsequently filled with, a halide which is volatile at the temperature of heat treatment.
  • the pack cementation process of coating includes thermal decomposition of the metallic halide followed by a thermal deposition and diffusion of the refractory metal or oxide onto the surface of, and into the surface of, the outer metal sheath of the heating element.
  • Typical deposition stages may be represented as follows:
  • Another particularly preferable coating process is that of physical vapor deposition. As described above, it is preferable to surface treat the heating element and then clean it by a means such ultrasonic cleaning or vapor degreasing before coating by a means such as physical vapor deposition.
  • the surface of the heating element After cleaning, it is preferable to plasma etch the surface of the heating element in argon under ultra-high vacuum and then sputter coat the surface with reactive or non-reactive gases in conjunction with the desired coating material.
  • the operation of the aforementioned process at ultra high vacuum avoids the introduction of most impurities onto the heating element's surface.
  • low to high voltage biasing can be applied to promote a strong adhesion of the coating to the surface of the metal sheath of the heating element.
  • the coating will also usually become highly dense when this biasing method is employed.
  • Pulsing technique can also be utilized for coating of semi-conductive material such as silicon carbide. The above process often allows the heating element to be processed at low temperatures, preferably less than 400 degrees Celsius.
  • the chemical vapor deposition technique is based upon a chemical reaction, such as thermal decomposition (pyrolysis), between a gaseous phase and a heated surface of the element to be coated.
  • the surface of the heating element is first directly or indirectly heated via induction heating.
  • a gaseous phase comprised of a non-chlorinated organo-metallic, metal carbonyls or metal hydrides compound comprising a refractory metal. It is necessary to select a non-chlorinated precursor, such as tetramethylsilane. which can generate the desired coating at reaction temperatures below 750° C due to the large mismatch in thermal expansion between the coatings and the materials of the heating element.
  • deposition temperatures below 750° Celsius eliminate formation of microcracks in the coatings during the cooling process.
  • Typical deposition pressures are usually between 0.0132 atmosphere (10 torr) and 0.131 atmosphere (100 torr).
  • Yet another preferred method of applying the coating to the surface of the metal sheath of the heating element is by gas diffusion via chemical vapor deposition. In this process, a halide of the solute metal is passed in vapor form over the metallic surface of the heating element to be coated, the surface being heated such that it is at a temperature at which diffusion can take place. Such temperatures are generally from about 400 to about 1000 degrees Celsius or more, depending on the precursor for the coating.
  • the carrier gas for the halide vapor can be a reducing gas such as hydrogen, cracked ammonia, or the like or inert gases such as helium or argon.
  • a reducing gas such as hydrogen, cracked ammonia, or the like or inert gases such as helium or argon.
  • the metal halide BX 2 in gaseous form is reduced to metal B which then diffuses into the solvent metal A.
  • the three major chemical reactions for this gas phase diffusion process can be summarized as follows: Interchange reaction: A + BX 2 (gas) — > AX 2 + B Reduction reaction: BX 2 + H 2 — > 2HX + B
  • the interchange reaction implies the removal of one atom of A at the surface for each atom of B deposited.
  • the deposition of tantalum can also be processed via gas or liquid precursor such as tantalum pentachloride or other derivatives of tantalum, provided that the thermodynamics for thermal decomposition of tantalum precursor can occur at temperatures less than 1000 degrees Celsius or preferably less than 500 degrees Celsius.
  • the pressure used for this process can range from about full vacuum to about 0.98 atmospheres.
  • the heating elements of this invention are particularly useful in corrosive environments. The heating elements of the invention will typically not show any pits, crevices, holes, or cracks indicating degradation of the coating even when subjected to pH's of less than about 1.0 (such as concentrated chromic plating solution and nitric acid) at boiling temperatures for more than 60, preferably more than 100 hours.
  • the coatings of this invention may be modified by addition of such substances such as metals, non-metals, alloys, as well as, inorganic and organic compounds so long as such substance does not destroy the functionality of the protective coating.
  • Such modifications may often be desirable in order to alter one or more of the properties, for example electrical, thermo-mechanical, or chemical properties, of the coating for a particular application.
  • the coating may be doped with boron or titanium to promote such ductility.
  • materials such as inter-metallic substances, for example, nickel suicide, which have a coefficient of thermal expansion which is relatively equivalent to the thermal expansion coefficient of a base material of the heater. In this manner, efficient heating is accomplished.
  • the coatings of this invention may have more than one layer. This may be desirable if the heating element is to be subjected to a particularly corrosive environment for an extended length of time or if the heating element is unusually fragile.
  • the use of layered coatings may reinforce the failure of the outer layers in case of a severe electrochemical attack. Often if multiple layers are to be utilized, the number of layers will range from one (1) to one hundered (100) or more, preferably one (1) to ten (10), depending on the specific application.
  • the thickness of each layer may generally vary from about 100 to 5000 Angstroms and it may be desirable to use a material such as tungsten between the layers to enhance the adhesion of the layers to each other. Each layer may be of different or identical materials and optimum performance may be achieved via routine experimentation.
  • the coated heating elements of this invention may be easily inspected for defects such as microcracks, cracks, holes, or other failures in the coating. Such inspection may be accomplished in numerous ways.
  • leakage current is tested by immersing the coated area of the heating element in deionized water and acidic solution in conjunction with a metallic electrode probe. A current, for example 12 volts, is applied to the uncoated area of the heater and metallic electrode probe. If the probe detects a voltage change, then a defect exists within the coating. Typically, the magnitude of the voltage change increases as the size of the defect.
  • a second method useful for coatings which are conducting, semi-conducting, or insulating is that of potentiodynamic polarization.
  • a coated heating element may be repaired in a similar manner to which it was coated.
  • the repair steps include surface preparation, cleaning, and then reapplying the coatings onto the clean surface of the heating element as described above.
  • FIG. 1 A schematic of a resistance heating device of the instant invention is described in Figure 1.
  • the internal elements of the heating device comprise of a resistance wire (1), refractory or ceramic insulation (2), a Chromalox patented connector (3) used to control the overheating of the resistance wire (1) and a terminal block (4).
  • the internal elements are protected by an outer metallic shell or sheath (5).
  • the base (6) of the metallic sheath comprises a heavy-gauge disk which is securely welded.
  • a corrosion-resistant coating of the instant invention (7) surrounds the sheath.
  • Figure 2 shows as an embodiment of this invention, the high performance corrosion resistant coating (7) of refractory metals, refractory metal oxides, ceramics, inter-metallics. or mixture thereof which is applied onto and into the outer surface of the metallic sheath of the heating device is illustrated in 2a of Figure 2.
  • the coating can be single (2b of Figure 2) or layered (2c of Figure 2). According to this invention, the coating diffuses into the surface or grain boundaries of the metallic sheath or tube to promote a strong adhesion.
  • the coating is 100 percent (%) dense.
  • Each layer of the multi-layer coatings (2c of Figure 2) can be of identical or different materials selected from refractory metals, refractory metal oxides, ceramics, inter-metallics, or a mixture thereof.
  • RF Bias sputtering was used to apply 100% dense amorphous silicon carbide to the surface of four steel tubes.
  • an undercoating layer of tungsten of 100 Angstroms thick was deposited prior to the silicon carbide coating to enhance adhesion.
  • Silicon carbide was then deposited on each of the four steel tubes.
  • the first steel tube was coated with a single layer of silicon carbide which was 3 micrometers in thickness.
  • the second steel tube was coated with 10 layers of silicon carbide, each layer being 1000 Angstroms.
  • the third steel tube was coated with 20 layers of silicon carbide, each layer being 1000 Angstroms.
  • the fourth steel tube was coated with 30 layers of silicon carbide, each layer being 1000 Angstroms. Upon visual inspection, each steel tube was found to be free of microcracks and pinholes.
  • the silicon carbide coated steel tubes were tested by immersing them in chromic plating solution at boiling temperature for 48 hours.
  • the chromic plating solution had a pH near 0.0 at boiling temperature.
  • the average weight loss was 0.1 percent (%).
  • DC Bias magnetron sputtering was used to apply 100% dense tantalum to the surface of steel disks, tubes, and shells of cartridge and tubular type heaters.
  • a typical heating element having a tantalum coating is shown in Figure 2.
  • the sputtering atmosphere was argon.
  • the temperature of the surface of the substrate was 250°C.
  • the DC bias voltage was 500 volts to 4 kilovolts.
  • the argon pressure was 1.31 x 10 " atmospheres.
  • the sputtering time ranged from 60 to 90 minutes.
  • the resulting tantalum coatings were about 3 micrometers in thickness.
  • the tantalum coated steel disks, tubes, and shells of cartridge and tubular type heaters were examined for defects under a microscope at a magnification of 500 times and 5000 times. No defects- were observed and the tantalum coating adhered strongly to the surface of the metallic sheath..
  • the tantalum coated steel disks, tubes, and shells of cartridge and tubular type heaters were tested by immersing them in chromic plating solution at 67° C for 100 hours.
  • the chromic plating solution had a pH of 1.0 at 67° C.
  • the average weight loss was 0.005 percent (%).
  • the tantalum coated steel disks, tubes, and shells of cartridge and tubular type heaters were tested by immersing them in chromic plating solution at boiling temperature for 100 hours.
  • the chromic plating solution had a pH near 0.0 at boiling temperature.
  • the average weight loss was 0.09 percent (%).
  • Ion beam-assisted deposition in particular, electron beam evaporation is useful to apply 100% dense tantalum to the surface of steel disks, tubes, and shells of cartridge and tubular type heaters.
  • the metal substrate was biased to enhance the adhesion of the coating.
  • the bias voltage was 500 volts to 2 kilovolts.
  • Low temperature processing of less than 250 degrees Celsius is useful for the heat sensitive surfaces of the outer sheaths. Tantalum chips, pellets, or a mixture thereof are evaporated under high vacuum by an electron beam.
  • An ion beam of argon via an ion gun bombards the tantalum vapors onto and into the surface to be coated. Tantalum films which are 100 percent (%) dense, about 3 micrometers thick, defect-free, and have strong adhesion to the outer metal sheath are obtained using this deposition method of coating.
  • a gas diffusion method was used to apply 100 percent (%) dense tantalum to the surface of steel disks, tubes, and shells of cartridge and tubular type heaters.
  • the surface was first heated to temperatures ranging from 300 to 500 degrees Celsius. Tantalum chips or pellets were then heated to their sublimation temperature. Tantalum vapor was then transported to the deposition chamber with a carrier gas such as Argon. Hydrogen was also introduced directly into the deposition chamber during the gas diffusion process. A typical in-depth diffusion of 0.5 to 1 micrometers of tantalum into the surface of the shell heater was achieved within 30 minutes to two hours. Tantalum was also introduced into the deposition chamber by using tantalum pentachloride (gas) as a precursor associated with tantalum. Hydrogen was used to decompose tantalum pentachloride into tantalum at temperatures of less than 900 degrees Celsius.
  • Typical deposition parameters useful for high density Tantalum coating onto and into carbon steel sheath via gas diffusion - chemical vapor deposition are as follows: Etching gas: Hydrochloric (HC1)
  • Etching temperature 400 degrees Celsius
  • Flushing gas and pressure Argon @ 0.026 atmosphere (20 torr) Flushing time: 15 minutes
  • Tantalum deposition parameters Total Pressure: 0.013 atmosphere (10 torr)
  • Tantalum chips to sublimation temperature Deposition temperature 500 degrees Celsius
  • Example Three were examined for defects under a microscope at a magnification of 500 times and 5000 times. No defects were observed.
  • the tantalum coated steel disks, tubes, and shells of cartridge and tubular type heaters were tested by immersing them in chromic plating solution at 67° C for 100 hours.
  • the chromic plating solution had a pH of 1.0 at 67° C.
  • the average weight loss was 0.1 percent (%).
  • the tantalum coated steel disks, tubes, and shells of cartridge and tubular type heaters were tested by immersing them in chromic plating solution at boiling temperature for 100 hours.
  • the chromic plating solution had a pH near 0.0 at boiling temperature.
  • the average weight loss was 0.5 percent (%).

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  • Other Surface Treatments For Metallic Materials (AREA)

Abstract

L'invention concerne des éléments chauffants munis de nouveaux revêtements qui sont constitués d'un métal réfractaire, d'un oxyde de métal réfractaire, d'un matériau céramique ou intermétallique ou d'un mélange de ceux-ci. Lesdits revêtements offrent à l'élément chauffant une excellente protection contre la corrosion et, de ce fait, conviennent particulièrement bien aux éléments chauffants employés dans des environnements hautement corrosifs; en outre, ils sont faciles à appliquer et se prêtent à la réparation, en cas de besoin.
PCT/US1998/000438 1997-01-07 1998-01-07 Revetements ameliores destines a des elements chauffants electriques a gaine metallique WO1998031197A1 (fr)

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AU62392/98A AU6239298A (en) 1997-01-07 1998-01-07 Improved coatings for electrical, metal sheathed heating elements

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US3577397P 1997-01-07 1997-01-07
US60/035,773 1997-01-07
US88406797A 1997-06-27 1997-06-27
US08/884,067 1997-06-27

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DE20121115U1 (de) * 2001-12-21 2003-04-24 Fritz Eichenauer GmbH & Co. KG, 76870 Kandel Elektrische Heizeinrichtung zum Beheizen einer korrosiven Flüssigkeit in einem Kfz
US8602248B2 (en) 2011-03-02 2013-12-10 Bose Corporation Cooking utensil
US8796598B2 (en) 2007-09-07 2014-08-05 Bose Corporation Induction cookware
US9630206B2 (en) 2005-05-12 2017-04-25 Innovatech, Llc Electrosurgical electrode and method of manufacturing same
IT201800004346A1 (it) * 2018-04-10 2019-10-10 Nuovi sistemi di protezione/rivestimento di materiali utilizzabili in varie applicazioni caratterizzate da ambienti chimicamente o fisicamente aggressivi attraverso la deposizione di strati nano- e micro-metrici sulla superficie esterna
DE102021117913A1 (de) 2021-07-12 2023-01-12 Lenz Elektronik Gmbh Verdampfer zur Erzeugung von Dampf für Modellfahrzeuge
EP4231777A1 (fr) * 2022-02-21 2023-08-23 Fratini, Roberto Résistance pour machine à laver

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FR2392162A1 (fr) * 1977-05-25 1978-12-22 Elpag Ag Chur Corps de chauffe tubulaire pour appareils menagers
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DE20121115U1 (de) * 2001-12-21 2003-04-24 Fritz Eichenauer GmbH & Co. KG, 76870 Kandel Elektrische Heizeinrichtung zum Beheizen einer korrosiven Flüssigkeit in einem Kfz
US9630206B2 (en) 2005-05-12 2017-04-25 Innovatech, Llc Electrosurgical electrode and method of manufacturing same
US10463420B2 (en) 2005-05-12 2019-11-05 Innovatech Llc Electrosurgical electrode and method of manufacturing same
US11246645B2 (en) 2005-05-12 2022-02-15 Innovatech, Llc Electrosurgical electrode and method of manufacturing same
US8796598B2 (en) 2007-09-07 2014-08-05 Bose Corporation Induction cookware
US8602248B2 (en) 2011-03-02 2013-12-10 Bose Corporation Cooking utensil
IT201800004346A1 (it) * 2018-04-10 2019-10-10 Nuovi sistemi di protezione/rivestimento di materiali utilizzabili in varie applicazioni caratterizzate da ambienti chimicamente o fisicamente aggressivi attraverso la deposizione di strati nano- e micro-metrici sulla superficie esterna
DE102021117913A1 (de) 2021-07-12 2023-01-12 Lenz Elektronik Gmbh Verdampfer zur Erzeugung von Dampf für Modellfahrzeuge
DE102021117913B4 (de) 2021-07-12 2023-07-06 Lenz Elektronik Gmbh Verdampfer zur Erzeugung von Dampf für Modellfahrzeuge
EP4231777A1 (fr) * 2022-02-21 2023-08-23 Fratini, Roberto Résistance pour machine à laver

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