US3192065A - Method of forming molybdenum silicide coating on molybdenum - Google Patents

Method of forming molybdenum silicide coating on molybdenum Download PDF

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US3192065A
US3192065A US199267A US19926762A US3192065A US 3192065 A US3192065 A US 3192065A US 199267 A US199267 A US 199267A US 19926762 A US19926762 A US 19926762A US 3192065 A US3192065 A US 3192065A
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molybdenum
coating
bath
hours
carbon
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US199267A
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John P Page
Roger D Moeller
George V Sneesby
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North American Aviation Corp
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North American Aviation Corp
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    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/18—Solid state diffusion of only metal elements or silicon into metallic material surfaces using liquids, e.g. salt baths, liquid suspensions
    • C23C10/20—Solid state diffusion of only metal elements or silicon into metallic material surfaces using liquids, e.g. salt baths, liquid suspensions only one element being diffused
    • C23C10/22—Metal melt containing the element to be diffused

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  • Our invention relates to a method of providing an oxidation-resistant coating on molybdenum, and more particularly to an improved method of providing a molybcnum silicide coating on molybdenum.
  • Refractory metals that is metals with melting points above that of chromium (34-05 R), are of increasing importance.
  • the advanced new technologies require metals capable of withstanding extremely high temperatures, and frequently material-s problems are key limitations to more rapid advancement in the air-craft and space fields,
  • the refractory metals are the subject of intensive research and development because of their high temperature strength characteristics.
  • the refractory metals of principal interest are tungsten, tantalum, molybdenum,
  • Molybdenum is unique in its relative availability and low material cost, plus its combination of low density, high melting point, and high temperature strength.
  • the refractory metals however, have very poor oxidation re sistance because, unlike many other metals, they do not form their own thin, surface-protective oxide coating.
  • Considerable effort is bein expended in the evelopment of oxidation-resistant coatings for refractory metals. See for example the article, Oxidation-Resistant Coating for Refractory Metals, by C. A. Krier in BattelleTechnical Review, June 1961, vol. 10, No. 6, pp. 11-15. This reference indicates that silicide coatings have been placed on molybdenum bases by such methods as pack cementation.
  • molybdenum refers both to the metal and alloys thereof, for example Mo-Ti and Mc v Ti-Z-r.
  • an improved method of forming a molybdenum silicide coating on molybdenum which comprises providing a molten alkali metal bath, dissolving therein silicon and at least one additive selected from the class consisting of carbon and tin, and placing the molybdenum in the bath, thereby obtaining a coating of molybdenum silicide on the molybdenum.
  • molybdenum silicide coatings obtained in this mannor are found to greatly improve the oxidation resistance of molybdenum.
  • the hardness, ductility. resistance to thermal shock, surface appearance, erosion and abrasion resistance, and resistance to mechanical impact are among the other properties which are improved.
  • the term molybdenum silicide is used to identify the coating since the precise stoichiometry is not known. It is probable that MoSi is the predominant phase, and such other phases as 'MO3Si5 maybe present.
  • molybdenum silicide itself is'subject to oxidative attack, it is probable that the mechanism of protecting the molybdenum base involves the formation of SiO by reaction of oxygen and MoSi The Si0 is glassy and relatively impermeable to oxygen.
  • the additives improve appearance and performance as compared with a molybdenum silicide coating applied from an alkali metal bath. containing only silicon.
  • the role of the additives are not fully understood; however,
  • the oxidation characteristics may be improved by formation of intermediate molybdenum silicide phases; mechanical properties may be improved by raising the ductility of the coating and making the coefficient of thermal expansion more nearly that of the base metal; and the kinetics of the coating process may be altered by retarding the back reaction consisting of dissolution of the coating in the bath, thereby resulting in a more even coating on the molybdenum.
  • the reaction rate with the additives is slower than without the additives, and there is less molybdenum dissolution in the bath.
  • a coating having an average, highly irregular thickness of 6 mils of molybdenum silicide is obtained after about /2 hour and the original wire diameter is reduced to about 12 mils of molybdenum.
  • the additives about 2-6 hours is required under the same conditions to produce a molybdenum silicide coating of a uniform 3 mils, but the original molybdenum wire diameter is reduced to only 23 mils.
  • Carbon is used herein to embrace both carbon and inorganic compounds thereof, including such carbides as boron carbide; carbon in noncompounded form is the preferred additive.
  • the carbon additions serveto increase the thickness of the coating and the oxidation performance of the coated metal; ductility is not significantly improved.
  • the tin addition increases the thickness slightly, but uniformly, and improves the ductility and oxidation performance.
  • the carbon and tin additions result in a very attractive metal coating, having markedly improved oxidation performance.
  • the alkali metal bath contain saturation concentrations or" silicon and the additives at the process operating temperature in order to improve the reaction rate. This will constitute, for example, in a sodium bath maintained at a temperature of about 1500 F and containing 50-100 grams of sodium,- silicon weighing approximately 10% of the weight of the sodium and added in the form of crushed crystals. Approximately 2 wt. percent of boron carbide or carbon may be added; the tin additions are satisfactorily approximately 10 wt. percent.
  • the temperature of the alkali metal bath may satisfactorily vary over a considerablev range, for example 1000-2000 F., while it is found that a temperature of about 1400-1600 F., particularly for sodium, is optimum.
  • Thebath is maintained under an inert gas atmosphere, for example argon or another noble gas.
  • the time required for the coating process to be completed varies with such parameters as the temperature of the bath and the coating thickness desired.
  • the additives slow down the molybdenum silicide formation rate as compared with molybdenum silicide coating from a similar hath not containing carbon or tin additives.
  • the plating time will vary between about /2-6 hours, depending on the coating thickness desired; a time of about 3-5 hours is generally satisfactory.
  • Example I The coating process was performed in a stainless steel capsule (type 304), 1.15-inch O.D., 0.05-inch wall thickness, -,-inch-thick end caps, and 6.5 inches in length.
  • the end caps were welded on, one in'the shop and the other in an argon atmosphere glove box after the capsule was filled.
  • the capsule was filled with 75 grams of sodium to about A of its capacity, and a molybdenum wire 0.062 inch in diameter was placed in the capsule. About 7.5 grams of silicon, 1.5 grams of carbon, and 5.0 grams of tin were also placed in the capsule and the capsule then sealed. Two such samples were heated at 1450 .F. for 5 hours and a third sample at 1400 F. for 3 hours.
  • Example 11 The procedure of Example I was followed except that 1.5 grams of carbon was the only additive to the bath in addition to the silicon. The capsule was heated at 1400 F. for 3 hours. The coated wire was removed and subjected to resistance heating at 1570 C. Time to failure was 38 hours-..
  • Example I The procedure of Example I was followed except that 5.0 grams tin was the only additive to the silicon.
  • the capsule was heated at 1450 F. for 5 hours.
  • the coated wire was removed and subjected to resistance, heating.
  • the time to failure was 524 hours.
  • Example IV The same as Example I except that 1.5 grams of boron carbide was the only additive in addition to the silicon.
  • the capsule was heated at 1450 F. for /2 hour, and the sample removed. Two coated samples were subjected to resistance heating, and their lives to failure were 9 and 16 hours, at 1350 C.
  • Example V The same as Example I except that 5.0 grams of tin and 1.0 gram of boron carbide were added to the bath. The capsule was heated at 1450 F. for 5 hours. The coated sample. was removed, and subjected to resistance heating at 1570 C. until failure occurred after 54 hours.
  • Example VI The same as Example 1 except that the alkali metal bath was 22% Nil-78% K, and the Mo wire was 0.025 inch in diameten The time to failure of the test sample under resistance heatingin air at 3000 F. was 22 hours.
  • a method of forming a molybdenum silicide coating of improved uniformity and adherence on molybdenum which comprises providing a molten alkali metal bath under an inert gas atmosphere, dissolving effective amounts of silicon and at least one additive selected from the class consisting of tin and carbon in said bath, placing said molybdenum in said bath, and maintaining said molybdenum in said bath until said coating of molybdenum silicide is obtained.
  • a method of forming a molybdenum silicide coating on molybdenum which comprises providing a molten alkali metal bath maintained at a temperature of approximately 1400-1600" F. under an inert gas atmosphere, dissolving therein approximately saturation concentrations of silicon, carbon, and tin, placing said molybdenum in said bath, and maintaining said molbydenum in said bath for a period of approximately 3-5 hours, thereby forming a coating of molybdenum silicide on said molybdenum.
  • alkali metal is selected from the class consisting of NaK and sodium.
  • a method of forming a molybdenum silicide coating on molybdenum which comprises providing a molten sodium bath maintained at a temperature of approximately 1400l600 F. under'an inert gas atmosphere, dissolving in said bath approximately 10 wt. percent silicon, 5 wt. percent tin, and 1 wt. percent carbon, placing said molybdenum in said bath, maintaining said molybdenum in said bath for a period of approximately 3-5 hours, thereby forming a molybdenum silicide coating on said molybdenum.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Silicon Compounds (AREA)

Description

United States Patent 3,12,065 METHOD 0? FQERMING MGLYEDENUM SILHCIDE CGATKNG 0N MGLYBDENUM John P. Page, Thousand Oaks, Roger D. Mueller, Simi,
and George V. Sneeshy, Paeohna, Calif, assignors to North American Aviation, Inc.
No Drawing. Filed June 1, 1962, Ser. No. 199,267
8 Claims. (Cl. 117-414) Our invention relates to a method of providing an oxidation-resistant coating on molybdenum, and more particularly to an improved method of providing a molybcnum silicide coating on molybdenum.
Refractory metals, that is metals with melting points above that of chromium (34-05 R), are of increasing importance. The advanced new technologies require metals capable of withstanding extremely high temperatures, and frequently material-s problems are key limitations to more rapid advancement in the air-craft and space fields, The refractory metals are the subject of intensive research and development because of their high temperature strength characteristics. The refractory metals of principal interest are tungsten, tantalum, molybdenum,
' and columbium.
Molybdenum is unique in its relative availability and low material cost, plus its combination of low density, high melting point, and high temperature strength. The refractory metals, however, have very poor oxidation re sistance because, unlike many other metals, they do not form their own thin, surface-protective oxide coating. Considerable effort is bein expended in the evelopment of oxidation-resistant coatings for refractory metals. See for example the article, Oxidation-Resistant Coating for Refractory Metals, by C. A. Krier in BattelleTechnical Review, June 1961, vol. 10, No. 6, pp. 11-15. This reference indicates that silicide coatings have been placed on molybdenum bases by such methods as pack cementation. Uniformity of coating and adherence of the coating to the substrates have been problems in the prior art. A generally satisfactory method of applying protective diffusion coatings, including silicide, on metal bases is disclosed in the copending application of the common assignee, S.N. 85,457, filed January 30, 1961, in the name of Roger D. Moeller for Diffusion Coating Method for etals and Alloys. In this method a protective coating is applied by placing the base metal in a molten alkali metal bath having the coating material dissolved therein; the dissolved material diffuses through the bath on to the base metal. The resulting articles have shown improved mechanical and chemical properties due to the formation of diffusion coatings, generally involving intermctallic compound formation on the surface of the base metal. Molybdenum silicide coatings prepared in such a manner, while improved over the prior art, showed, however, irregular thicknesses and varied performance lifetimes. As u-scd herein, molybdenum refers both to the metal and alloys thereof, for example Mo-Ti and Mc v Ti-Z-r.
lf id fid Patented June 2%, recs "ice In accordance with our present invention, we have developed an improved method of forming a molybdenum silicide coating on molybdenum, which comprises providing a molten alkali metal bath, dissolving therein silicon and at least one additive selected from the class consisting of carbon and tin, and placing the molybdenum in the bath, thereby obtaining a coating of molybdenum silicide on the molybdenum.
The molybdenum silicide coatings obtained in this mannor are found to greatly improve the oxidation resistance of molybdenum. The hardness, ductility. resistance to thermal shock, surface appearance, erosion and abrasion resistance, and resistance to mechanical impact are among the other properties which are improved. The term molybdenum silicide is used to identify the coating since the precise stoichiometry is not known. It is probable that MoSi is the predominant phase, and such other phases as 'MO3Si5 maybe present. Since molybdenum silicide itself is'subject to oxidative attack, it is probable that the mechanism of protecting the molybdenum base involves the formation of SiO by reaction of oxygen and MoSi The Si0 is glassy and relatively impermeable to oxygen.
The additives improve appearance and performance as compared with a molybdenum silicide coating applied from an alkali metal bath. containing only silicon. The role of the additives are not fully understood; however,
. it is postulated that any of the following mechanisms may be involved: the oxidation characteristics may be improved by formation of intermediate molybdenum silicide phases; mechanical properties may be improved by raising the ductility of the coating and making the coefficient of thermal expansion more nearly that of the base metal; and the kinetics of the coating process may be altered by retarding the back reaction consisting of dissolution of the coating in the bath, thereby resulting in a more even coating on the molybdenum.
Various examination methods, such as metallographic, X-ray diffraction, and spectographic, have not clearly shown the presence of carbides or tin compounds in the molybdenum silicide coatings. It would appear possible, therefore, that the additives perform principally by controlling the bath conditions to produce a more uniform,
reproducible coating of high quality. The reaction rate with the additives is slower than without the additives, and there is less molybdenum dissolution in the bath. For example, in the coating of a ZS-mil molybdenum wire in sodium at a temperature of l4901500 F. under an inert gas atmosphere, a coating having an average, highly irregular thickness of 6 mils of molybdenum silicide is obtained after about /2 hour and the original wire diameter is reduced to about 12 mils of molybdenum. With the additives, about 2-6 hours is required under the same conditions to produce a molybdenum silicide coating of a uniform 3 mils, but the original molybdenum wire diameter is reduced to only 23 mils.
We find that the separate additions of carbon and tin individually serve to improve the quality of the coating, and that the combination of tin and carbon is particularly effective and is preferred. Carbon is used herein to embrace both carbon and inorganic compounds thereof, including such carbides as boron carbide; carbon in noncompounded form is the preferred additive. The carbon additions serveto increase the thickness of the coating and the oxidation performance of the coated metal; ductility is not significantly improved. The tin addition increases the thickness slightly, but uniformly, and improves the ductility and oxidation performance. The carbon and tin additions result in a very attractive metal coating, having markedly improved oxidation performance.
Our process may be suitably performed in any alkali metal bath. Sodium is the preferred alkali metal medium,
and alloys thereof such as NaK are also very suitable. The process is operable with even small silicon and additive concentrations, although the coating rate may beretarded. It is generally preferred that the alkali metal bath contain saturation concentrations or" silicon and the additives at the process operating temperature in order to improve the reaction rate. This will constitute, for example, in a sodium bath maintained at a temperature of about 1500 F and containing 50-100 grams of sodium,- silicon weighing approximately 10% of the weight of the sodium and added in the form of crushed crystals. Approximately 2 wt. percent of boron carbide or carbon may be added; the tin additions are satisfactorily approximately 10 wt. percent.
The temperature of the alkali metal bath may satisfactorily vary over a considerablev range, for example 1000-2000 F., while it is found that a temperature of about 1400-1600 F., particularly for sodium, is optimum. Thebath is maintained under an inert gas atmosphere, for example argon or another noble gas. The time required for the coating process to be completed varies with such parameters as the temperature of the bath and the coating thickness desired. The additives slow down the molybdenum silicide formation rate as compared with molybdenum silicide coating from a similar hath not containing carbon or tin additives. The plating time will vary between about /2-6 hours, depending on the coating thickness desired; a time of about 3-5 hours is generally satisfactory.
The following examples are offered to illustrate our process in greater detail.
Example I The coating process was performed in a stainless steel capsule (type 304), 1.15-inch O.D., 0.05-inch wall thickness, -,-inch-thick end caps, and 6.5 inches in length. The end caps were welded on, one in'the shop and the other in an argon atmosphere glove box after the capsule was filled. The capsule was filled with 75 grams of sodium to about A of its capacity, and a molybdenum wire 0.062 inch in diameter was placed in the capsule. About 7.5 grams of silicon, 1.5 grams of carbon, and 5.0 grams of tin were also placed in the capsule and the capsule then sealed. Two such samples were heated at 1450 .F. for 5 hours and a third sample at 1400 F. for 3 hours.
The coated wires were removed and subjected to selfresistance heating by passing an electric current there-- Example 11 The procedure of Example I was followed except that 1.5 grams of carbon was the only additive to the bath in addition to the silicon. The capsule was heated at 1400 F. for 3 hours. The coated wire was removed and subjected to resistance heating at 1570 C. Time to failure was 38 hours-..
Example. 111
The procedure of Example I was followed except that 5.0 grams tin was the only additive to the silicon. The capsule was heated at 1450 F. for 5 hours. The coated wire was removed and subjected to resistance, heating. The time to failure was 524 hours.
Example IV The same as Example I except that 1.5 grams of boron carbide was the only additive in addition to the silicon.
. The capsule was heated at 1450 F. for /2 hour, and the sample removed. Two coated samples were subjected to resistance heating, and their lives to failure were 9 and 16 hours, at 1350 C.
Example V The same as Example I except that 5.0 grams of tin and 1.0 gram of boron carbide were added to the bath. The capsule was heated at 1450 F. for 5 hours. The coated sample. was removed, and subjected to resistance heating at 1570 C. until failure occurred after 54 hours.
Example VI The same as Example 1 except that the alkali metal bath was 22% Nil-78% K, and the Mo wire was 0.025 inch in diameten The time to failure of the test sample under resistance heatingin air at 3000 F. was 22 hours.
Similar Wires coated in /2 hour at 1450 F. in a bath comprised of sodium and silicon only yielded lifetimes of 1 hour at 1300 C., 0.2 hour at 1350 C., and 0.7 and 9.0 hours at 1570 C.
The above examples are illustrative rather than restrictive of our invention, which should be understood to be limited only as is indicated in the appended claims.
We claim:
- 1. A method of forming a molybdenum silicide coating of improved uniformity and adherence on molybdenum which comprises providing a molten alkali metal bath under an inert gas atmosphere, dissolving effective amounts of silicon and at least one additive selected from the class consisting of tin and carbon in said bath, placing said molybdenum in said bath, and maintaining said molybdenum in said bath until said coating of molybdenum silicide is obtained.
2. The method of claim 1 wherein said bath is maintained at a temperature of approximately 1000-2000 F.
3. The method of claim 1 wherein said molybdenum is maintained in said bath for a period of approximately /z6 hours.
4. The method of claim 1 wherein said molybdenum is maintained in said bath at a temperature of approximately 1400-1600 F. for a period of approximately 35 hours.
5. A method of forming a molybdenum silicide coating on molybdenum, which comprises providing a molten alkali metal bath maintained at a temperature of approximately 1400-1600" F. under an inert gas atmosphere, dissolving therein approximately saturation concentrations of silicon, carbon, and tin, placing said molybdenum in said bath, and maintaining said molbydenum in said bath for a period of approximately 3-5 hours, thereby forming a coating of molybdenum silicide on said molybdenum.
6 The method of claim 5 wherein said alkali metal is selected from the class consisting of NaK and sodium.
7. The method of claim 5 where approximately 10 wt. percent silicon, 5 wt. percent tin, and 1 wt. percent carbon are added to said alkali metal bath.
8. A method of forming a molybdenum silicide coating on molybdenum, which comprises providing a molten sodium bath maintained at a temperature of approximately 1400l600 F. under'an inert gas atmosphere, dissolving in said bath approximately 10 wt. percent silicon, 5 wt. percent tin, and 1 wt. percent carbon, placing said molybdenum in said bath, maintaining said molybdenum in said bath for a period of approximately 3-5 hours, thereby forming a molybdenum silicide coating on said molybdenum.
References Cited by the Examiner UNITED STATES PATENTS 2,848,352 8/58 Noland et al 117-114 3,085,028 4/63 Logan l17ll4 3,086,886 4/63 Kiefferet-al. 117-114 RICHARD D. NEVIUS, Primary Examiner.

Claims (1)

1. A METHOD OF FORMING A MOLYBDENUM SILICIDE COATING OF IMPROVED UNIFORMITY AND ADHERENCE ON MOLYBDENUM WHICH COMPRISES PROVIDING A MOLTEN ALKALI METAL BATH UNDER AN INERT GAS ATMOSPHERE, DISSOLVING EFFECTIVE AMOUNTS OF SILICON AND AT LEAST ONE ADDITIVE SELECTED FROM THE CLASS CONSISTING OF TIN AND CARBON IN SAID BATH, PLACING SAID MOLYBDENUM IN SAID BATH, AND MAINTAINING SAID MOLYBEDENUM IN SAID BATH UNTIL SAID COATING OF MOLYBDENUM SILICIDE IS OBTAINED.
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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3383235A (en) * 1965-03-29 1968-05-14 Little Inc A Silicide-coated composites and method of making them
US3397078A (en) * 1964-06-24 1968-08-13 North American Rockwell Silicon-containing diffusion coating for ferrous metals
US3523832A (en) * 1965-06-11 1970-08-11 Siemens Ag Thermogenerator with germanium-silicon semiconductors
US3931447A (en) * 1973-05-04 1976-01-06 The United States Of America As Represented By The United States National Aeronautics And Space Administration Fused silicide coatings containing discrete particles for protecting niobium alloys
US5135782A (en) * 1989-06-12 1992-08-04 Rostoker, Inc. Method of siliciding titanium and titanium alloys
CN103320735A (en) * 2013-06-07 2013-09-25 钢铁研究总院 Continuous silicon plating process of molybdenum and alloy thereof

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2848352A (en) * 1956-12-07 1958-08-19 Robert A Noland Fuel elements and method of making
US3085028A (en) * 1958-02-10 1963-04-09 Wean Engineering Co Inc Method and means for depositing silicon
US3086886A (en) * 1958-06-04 1963-04-23 Schwarzkopf Dev Co Process of providing oxidizable refractory-metal bodies with a corrosion-resistant surface coating

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2848352A (en) * 1956-12-07 1958-08-19 Robert A Noland Fuel elements and method of making
US3085028A (en) * 1958-02-10 1963-04-09 Wean Engineering Co Inc Method and means for depositing silicon
US3086886A (en) * 1958-06-04 1963-04-23 Schwarzkopf Dev Co Process of providing oxidizable refractory-metal bodies with a corrosion-resistant surface coating

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3397078A (en) * 1964-06-24 1968-08-13 North American Rockwell Silicon-containing diffusion coating for ferrous metals
US3383235A (en) * 1965-03-29 1968-05-14 Little Inc A Silicide-coated composites and method of making them
US3523832A (en) * 1965-06-11 1970-08-11 Siemens Ag Thermogenerator with germanium-silicon semiconductors
US3931447A (en) * 1973-05-04 1976-01-06 The United States Of America As Represented By The United States National Aeronautics And Space Administration Fused silicide coatings containing discrete particles for protecting niobium alloys
US5135782A (en) * 1989-06-12 1992-08-04 Rostoker, Inc. Method of siliciding titanium and titanium alloys
CN103320735A (en) * 2013-06-07 2013-09-25 钢铁研究总院 Continuous silicon plating process of molybdenum and alloy thereof
CN103320735B (en) * 2013-06-07 2015-01-21 钢铁研究总院 Continuous silicon plating process of molybdenum and alloy thereof

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