DE1239907B - Process for the production of a silicide coating by electrolytic means - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

EUCHES

PATENT OFFICE

EDITORIAL

Int. Cl .:

C23b

dZi-7)

German class: 48 a - 5/60

Number: 1 239 907

File number: G 34320 VI b / 48 a

Filing date: February 22, 1962

Open date: May 3, 1967

The invention relates to a method for producing a silicide coating by contact deposition with possibly additional external EMF on metal bodies with a melting point of at least 600 ° C and of at least 50 mol percent of at least one metal with the order number 23 to 29, 41 to 47, 73 to 79, by depositing silicon from a molten pool of silicon compound.

A normal practice in forming a silicide coating on metal is to allow silicon halide vapors to be exposed to the metal at a temperature sufficient to decompose the halide and deposit a silicon coating on the metal. The metal must then be heated to an even higher temperature so that the silicon diffuses into the metal and alloys with the metal. In the absence of a reducing gas, a shift reaction occurs in which part of the metal replaces the silicon in the silicon halide. In the presence of hydrogen, the silicon halide is reduced to silicon and hydrogen halide. Temperatures of the order of 1200 to 1400 ^° C. are required to achieve sufficient deposition rates. The rate of deposition must be carefully controlled because rapid deposition will form a lower layer of silicide and an outer layer of molten silicon on top. In order to obtain well-adhering coatings, it is normally necessary to first deposit a very thin coating and then to anneal it in a hydrogen atmosphere so that the coating diffuses into the metal. To achieve the desired coating thickness, further coatings are then applied in the same way. This method is not suitable for the production of precision parts that have to be machined to very precise tolerances before a silicide coating is applied. Due to the high temperatures and phase changes to which the parts are exposed when a coating is applied during heating and cooling, the parts are deformed, especially if multiple treatments are required to achieve the desired coating thickness, whereby the tolerance limits are exceeded. The rate of deposition of silicon depends very strongly on the rate of the silicon halide sweeping over the metal surface and on the temperature of the metal object to be coated. Because these conditions are very difficult to control, especially in large or irregularly shaped processes for making a silicide coating
electrolytically

Applicant:

General Electric Company,

Schenectady, N.Y. (V. St. A.)

Representative:

Dipl.-Ing. M. Licht and Dr. R. Schmidt,

Patent Attorneys, Munich 2, Theresienstr. 33

Named as inventor:
Newell Choice Cook,
Schenectady, NY (V. St. A.)

Objects, the coatings applied over the entire surface are usually not uniform.

It is known to apply iron and Stahlsilizide by electrolysis in a molten Natriumsilikatbad which is situated at a temperature of 1100 ⁰ C and contains as the flux is sodium fluoride. A graphite anode and iron or steel wire as the cathode are used. High current densities are required at a voltage of 3 volts. The metal silicide forms a loose, crystalline powder that can be easily removed from the surface and is therefore completely unsuitable as a corrosion-resistant coating for iron and steel objects.

It has now been found, unexpectedly, that a uniform, well-adhering, tough, corrosion-resistant silicide coating achieved when in the method of the type mentioned a from 0.5 to 50 mole percent of at least one alkali metal fluoride and at least one alkali metal fluoride, Melt bath held at about 600 to 800 ° C is used and has a silicon anode at a current density of up to 5 amps per square decimeter in the substantial absence of Oxygen is worked.

Is an electrical outside of the molten bath between the metal body and the silicon anode Connection established, then silicon goes into solution in the molten bath, and silicon ions are attached the metal body surface, whereby the SiIi-

709 578/276

3 4

cium diffuses directly into the metal and the with the metal to form a silicon coating, fluorides and fluorosilicates of the alkali metals lithium, reacted. It has been found that the Lö- sodium, potassium, rubidium and cesium are used and the rate of deposition of silicon. As to prevent damage self-regulated, so that no more silicon is ever deposited or deformed with a silicide layer when diffusing into the metal and seeing objects as low as possible can alloy with the metal. If a lower temperature is desired, you can use the If the rate of deposition is desired, melt pools of one or more fluorides can be used this can easily be achieved in a manner known per se and one or more fluorosilicates exist which, for example, can be used by switching on a corresponding mixes that have a lower corresponding resistance in the circuit, through the melting point as the individual components of the bath the surface exposed to the bath, etc.

To achieve a higher speed, the process is at a temperature of not

to carry an additional DC voltage below approximately 600 ° C into the circuit, even if

source must be switched on. 15 the melt pool has a much lower melting temperature

The invention will now be explained in more detail. At ratur has to ensure an adequate separation

to achieve with the method according to the invention with a speed and diffuse in

Silicide coating coatable metals is the silicon in the metal for the purpose of forming the SiIi-

in order to guarantee the metals with the ordinal numbers 23 to one. At lower temperatures

Finally 29, 41 up to and including 47 and 73 up to and including 20 there is the possibility that the silicon is only on

finally 79. For these atomic number ranges, the metal surface is deposited and not in the

hear the metals diffusing into Lange's handbook tall.

of Chemistry ", 9th Edition, Handbook Publishers, The Alkali Metal Fluorosilicate Located in Gleich-Inc, Sandusky, Ohio, 1956, on pages 56 and 57 weighted with silicon tetrafluoride and the alkaline periodic table of elements shown in the 25 metal fluoride. Rising temperatures promote groups IB, VB, VIB, VIIB and VIII listed decomposition of the alkali metal fluorosilicate. At Tempes are. Group IB includes copper, silver temperatures of over 800 ° C, the vapor pressure of and gold, group VB vanadium, niobium and tan silicon tetrafluoride so high that silicon tetrafluoride tal, group VIB chromium, molybdenum and Wolf from the molten salt bath evaporates. This can be prevented by ram, the group VIIB manganese, technetium and 3 ° use of overpressure. For rhenium and group VIII iron, cobalt, nickel, to avoid these difficulties, one works with ruthenium, rhodium, palladium, osmium, iridium comfortably at temperatures below 800 ° C.
and platinum. Because of the equilibrium reaction, it is also possible for alloys of these metals to use the desired alkali metal fluorosilicate directly or for alloys in a molten salt bath by dissolving silicon earths in which these metals are the main component, tetrafluoride in molten alkali metal fluoride to ie with over 50 mole percent, but usually with form. The molten bath should normally be little more than 75 mole percent, and preferably above at least 0.5 mole percent, alkali metal fluorosilicate-90 mole percent present and with other metals. The amount of alkali metal fluorosilicate is alloyed as a secondary component, ie with a molten bath of less than 4 ° it can be up to 50 mol percent. Ge-50 mole percent, but usually less than normal, a concentration of 25 mole percent and preferably less than 10 mole- 1 to 5 mole percent is used. Below 0.5 mole percent, with the proviso that the amounts do not decrease the quality and the melting point of formation of the resulting alloy noticeably at the rate of suicide. Amounts below 600 ° C. The silicide coating arises from more than 5 mol percent, although there is no disadvantageous effect even with alloys of the metals listed above, but they are uneconomical, as the secondary constituents consisting of another metal or other higher concentration contain the formation of the silicide superordinate metals. This secondary constituent can be formed by any pressure of the silicon tetrafluoride and therefore the spoiled metals of the periodic table.

be, d. H. of metals of groups IA, II A, IIB, The starting salts should be as free from water

IIIA, IIIB, IVA, IVB, VA and VIA. These metals are or should be ser and all impurities

have the ordinal numbers 3, 4, 11 up to and including by simply heating them up during melting

13, 19 up to and including 22, 30 up to and including 32, dries and can be cleaned. The influence

37 up to and including 40, 48 up to and including 51, 55 55 of the impurities is not yet known exactly.

up to and including 72, 80 up to and including 84 and 87 oxides influence the silicide formation reaction

up to and including 98. In the description and in the favorable. Oxygen also has a detrimental effect on the

Claims, the expression "silicide" is used for loading reaction, so that the process according to the previous

drawing of any invention made of silicon and metal in an oxygen-free atmosphere

standing solid solution or alloy used, 60 sphere, for example in a neutral gas atmosphere

regardless of whether the silicon must be carried out with a sphere or in a vacuum. Sulphates have a very disadvantageous effect, as they make it impossible to achieve a proper silicide layer in a certain stoichiometric ratio, which is represented by a chemical formula or makes it extremely difficult. Others can be too. For example, molybdenum forms with 65 compounds, the formation of poor silicon a compound that by the formula can result in silicide layers. The best result MoSi ₂ can be shown. However, gold forms nits if one uses chemical

with silicon only a solid solution. mixed pure salts are used and the process im

Performs vacuum. It has been found that chemical electrode reactions have the effect that the chemically pure salts, even commercially available, deposition rate is too high, that water does not have to be subjected to further purification, that there are contacts or corrosion-attacked conditions, so that the process can be carried out satisfactorily, etc. can. This further purification can easily be carried out under such circumstances by satisfactorily carrying out the process according to the invention, however, processes should first be carried out with rejects and these conditions should be eliminated if possible, preferably made of the same material as the more effective one Working method is guaranteed. The goods to be treated later consists and on this, for example, the anode consists of a solid silicide coating, possibly using a silicon rod, then the voltage is sometimes applied with an additional voltage, as a result of which these values exceed, because the impurities deposited in the molten bath due to the low conductivity of silicon the resistance in the current and removed, which is the formation of a high-circle high. This can, for example, prevent usable silicide coating. It is avoided that the silicon is used in connection with the implementation of the process under vacuum is green with a highly conductive core.
When using the voltages mentioned above, for example water, certain current density limits should not be over-evaporated from the weld pool. It is also desirable to step if it is desired to have good efficiency and the metal surface prior to insertion into the proper coatings. Since the diffusion melt bath is cleaned well, for example by the treatment speed of the pickling into the cathode material, possibly combined with a scrubbing of silicon migrating from the material. Temperature and the thickness of the

It has also been found that for the first coating depends, the upper one also fluctuates aiming a uniform silicide coating on the large limit of the current density. In general, jeßen has Surfaces a perforated, conductive 25 but it turned out that at 700 ° C the following current container it is desirable, which should not be exceeded with the densities: approximately Process conditions behave neutrally, for example 0.2 amps per square decimeter for metals wise a perforated graphite basket, which the slow diffusion, for example tantalum and WoIf silicon in the form of small pieces. This ram at about 1 amp per square decimeter at Arrangement is better than a single silicon body, metals with moderate diffusion, e.g. coda Silicon is not a good conductor of electricity, and webait and niobium, and about 5 amps per square meter of the voltage drop in the silicon body is mainly decimeter in metals with fast diffusion, by the way where the silicon body goes into solution, for example iron and molybdenum. Will the temperain the weld pool is immersed. This means that the door is increased to 800 ° C, then also in ent this point closest to the area of the 35 speaking, the current density to a value treated object more silicon than to be increased, which is about two to three times as much an area farther from this point is as large as the value used at 700 ° C. at The object is deposited even if both surfaces are produced using even higher current densities Part of the solid silicon body contains the same elemental silicon in the form of non-adherent have stood. Will be a conductive, silicon-filled 40 layers or in the form of granular crystalline containers used, then silicon can uniformly precipitate, which give a rough coating that Go into solution over the entire surface, and it emerges during further electrolysis or when cooling down If there is a uniform room temperature on small objects, it tends to splinter. Such never-silicide coating, if the silicon electrode is at least as strong as electrolytic Ge-6 mm, preferably 25 to 50 mm, from the object 45 extraction of silicon from silicon compounds is. Should be extraordinarily large counter-wishes.

If an external EMF is used, for example, a silicide layer

for example a plate in which one side is connected to a battery or another DC voltage

the silicon electrode is shielded, then these should be used in series in the outer

If you can turn on two or more silicon circuits that the negative

electrodes that are used around the object for educa- tional terminal with the metal to be coated and the

development of a uniform coating in a corresponding positive terminal connected to the silicon electrode

Way are arranged. that will. This adds up the tension of the

The method according to the invention can properly cell to the externally supplied voltage.

without the use of an additional EMF in the electronic 55 To control the process, in

Irish circuit to be carried out. It can be the outer circle measuring instruments, for example

However, a small voltage from the outside impressed on voltmeters and ammeters, resistors, timers

if the deposition rate of, etc. are turned on.

Silicon should be increased. The diffusion serves to explain the invention in more detail

sion speed of the examples below in the subject under 60. Within the scope of the invention,

Formation of silicide invading silicon does not, of course, meet the stated reaction conditions

exceeded. The impressed EMF should be 0.5 volts and respondents in many ways.

do not exceed and are normally changed between 0.1,

and 0.3 volts. Higher voltages are on example 1

due to the fact that somewhere in the circuit there is a 65

high resistance is present that in the bath or a stainless steel vessel (depth 280 mm, on the surface of the electrodes impurities inside diameter 120 mm) with a nickel lining that interfere with the desired manure (depth 266 mm, inner diameter 114 mm)

was charged with 2610 g (45 mol) of chemically pure anhydrous KF, 1170 g (45 mol) of chemically pure LiF and 420 g (10 mol) of chemically pure NaF. The vessel was covered with a glass hood which had two openings for the electrodes, one opening for a thermocouple and a connection for a vacuum source. A silicon rod (12 x 12 x 200 mm) attached by nickel wire to a nickel rod with a diameter of 6.5 mm was secured in one of the electrode openings by means of a rubber tube gasket. Similarly, a molybdenum tape (20 x 100 x 0.25 mm) was also attached in the second electrode opening.

The jar was placed in an electric furnace consisting of an alumina tube with a chrome-nickel heating coil. The vessel was then evacuated and brought to a temperature of 630 ^° C. at which the salt mixture formed a water-clear melt. From a bottle, 1 mole of silicon tetrafluoride gas was added to the molten gas and dissolved therein very quickly, with a vapor pressure of 0.1-0.2 mm above the melt at 630 ° C. All reactions given below were carried out at pressures of 0.1 to 1.0 mm. On the other hand, successful reactions have also been carried out under atmospheric pressure in a neutral atmosphere, but vacuum is preferred because a vacuum process gives excellent, flawless results. The silicon anode and the molybdenum cathode were immersed in the melt. A moderate EMF was switched on in the external circuit connecting the anode to the cathode and the electrolysis was carried out. An ammeter and a voltmeter were connected to the external circuit in a known manner. The following results were achieved:

Time temperature Current density Minutes ⁰ C A / dm ² 0 630 0.50 19th 630 0.63 20th 630 0.50 83 630 0.48 115 630 0.45 183 630 0.50

introduced, the vessel evacuated, the salt melted again and another electrolysis using the system and the procedure according to Example 1 carried out.

Time temperature Current density Minutes ⁰ C A / dm ² IO 0 640 0.45 . 3 640 0.73 9 640 0.50 33 640 0.50 15th 145 640 0.50 223 640 0.48

The increase in weight of the molybdenum strip was 188 mg or 98% of the theoretically possible weight increase of 192 mg. The coating was smooth and uniform and no blank could be found under microscopic inspection. A metallographic examination showed a coating thickness of 0.020 to 0.023 mm, while an X-ray examination showed that, in addition to Mo ₃ Si and Mo ₃ Si _2, mainly

borrowed MoSi _{2 was} present.

Example 3

Another experiment was carried out with the same melt and in the same way, however, a current density five times as high was used. The following results were obtained:

40 Time temperature Current density Minutes ⁰ C A / dm ² 0 640 3.25 45 5 640 2.50 15th 640 2.50 31 640 2.50 50 52 640 2.50 58 640 2.25 to 2.50

The electrodes were pulled out of the salt bath and the melt before opening the jar cooled in vacuo. The increase in weight of the molybdenum ribbon was 116 mg, or 80% of that theoretically possible weight gain. The coating had some stains that were not suicidal had taken place. These spots are typical of a first-time experiment in which the melt still contains impurities that are eliminated in the process.

Example 2

A molybdenum strip with the same dimensions as in Example 1 was inserted into the cathode opening Towards the end of the electrolysis, small silicon crystals were observed on the surface of the cathode and then floated away. The electrode had a smooth and uniform coating, however, the weight gain was only 159 mg or 60% of the theoretical value. This low Yield is typical for a current density that is too high at the temperature used.

Example 4

Using the same test conditions as in Example 3, another test was carried out carried out, however, the temperature was up

7ϋΟ ^υ C increased. The following results were obtained:

Time
Minutes temperature
⁰ C Current density
A / dm ² 0
6th
51 700
700
700 2.50
2.50
2.63

Niobium is one of the metals in which silicide formation is moderately easy.

Example 7

A tungsten strip (15 × 130 × 0.25 mm) was made under similar conditions as niobium with a Provided the following results:

The coating was perfectly smooth and uniform and the tape increased in weight the theoretically possible weight increase of 227 mg silicon. The results of Examples 2, 3 and FIG. 4 show the influence of temperature on the yield as a function of the current density.

Example 5

In another experiment, an iron tape (20-150-0.25 mm) was used as the cathode and underneath Use of the experimental set-up and general procedure described in Example 1 provided with a silicide layer.

Time temperature Current density Minutes ⁰ C A / dm ² 0 800 0.33 5 800 0.55 17th 800 0.55 35 800 0.55 60 800 0.55

Time temperature Current density Minutes ⁰ C A / dm ² 0 700 0.82 5 700 0.82 17th 700 0.76 35 700 0.76

The weight gain of the iron was 64.5 mg or approximately 93% of the theoretically possible value. The silicide coating was smooth and uniform. The metallographic examination showed the coating to be 0.0125 mm thick, and X-ray examination showed that the coating _{contained Fe 3} Si. The coating resulted in an increase in dimension of 0.0065 mm per side.

The weight gain of the tungsten strip was 14.5 mg or 28% of the theoretical value. The tungsten strip was covered with a metallic, silver-gray coating which was approximately 0.025 to 0.050 mm thick, adhered very well and could not be removed by bending. During the X-ray examination, WSi _{2 was found} among other unidentifiable structures. Tungsten is an example of the metals that can be coated with a silicide layer only slowly or with difficulty.

Example 6

Two niobium wires (160 x 0.50 mm) were made using the equipment described in Example 1 and general procedure silicided with the following results achieved became:

45

Example 8

In a vessel with a monel lining, a salt mixture similar to that in Examples 1 to 7 was added prepares the 1 mole percent potassium fluorosilicate instead of the salt mixture under vacuum introduced silicon tetrafluoride gas was added. Under similar conditions to the previous ones Examples 1 to 7 were a molybdenum tape (20 × 120 × 0.75 mm) with a silicide layer Mistake. However, no additional EMF was applied to the electrodes, and the weld pool was turned off operated as an electrical cell in which the cathode is connected to the anode via an ammeter became. A potential of 0.161 volts was present on the open circuit of the cell.

Time temperature Current density Minutes ⁰ C A / dm ² 0 710 1.0 13th 714 0.4 42 719 0.4 232 700 0.4

Time temperature Current density 50 Minutes ⁰ C A / dm ² 0 703 0.22 2 703 0.22 129 705 0.17 55 205 705 0.14

The weight increase of the two niobium wires was 10.6 mg silicon with a theoretically possible value of 20.8 mg. The coatings were slightly gray in color, were hard, smooth and adhered very well. The thickness of the wire increased by 0.0125 mm and the coating had a thickness of 0.0125 mm. The X-ray examination revealed that only NbSi _{2 was} present in the coating. The increase in weight of the molybdenum strip was 76 mg of silicon with a theoretical value of 75 to 80 mg. The coating was 0.010-0.012 mm thick, uniform, adhered well, and curable to a radius of at least 25 mm before the coating cracked.

Example 9

An iron strip (18 · 125 · 0.25 mm) was made without the use of an additional EMF for the two

709 578/276

Game 8 provided conditions with a silicide layer.

Time temperature Current density Minutes ⁰ C A / dm ² 0 705 0.66 8th 700 0.56 23 700 0.46 24 * 700 0 42 * 700 0 54 * 703 0 55 703 0.66 70 705 0.53 115 702 0.45

The molybdenum strip was suspended from a nickel rod with tantalum wire (diameter 0.5 mm). The whole Molybdenum strips and part of the tantalum wire were completely immersed in the salt bath.

Time temperature Current density Minutes ⁰ C A / dm ² 0 695 0.8 ¹⁰ 5 700 0.8 7th 700 0.5 100 700 0.5 200 700 0.5

15th

* The formation of the silicide layer was interrupted by opening the circuit for 30 minutes to determine the rate at which the voltage of the open circuit increased.

The weight gain of the iron strip was 75 mg with a theoretical value of 84 mg. The coating (thickness about 0.030 mg) was smooth and uniform and could flex significantly without cracking. Coatings up to 0.18-0.20 mm thick were applied to iron with a silicon content of 1 to 3% without any evidence of splitting. X-ray examinations of the thin layers only _{revealed diffraction patterns of Fe 3} Si, while the thicker layers also contained Fe ₅ Si ₃ and FeSi.

Example 10

A piece of molybdenum-tungsten wire (length 110 mm, diameter 7.5 mm, 50 percent by weight Tungsten and 50 weight percent molybdenum) was made using those described in Example 8 Plant and mode of operation and under similar conditions as in Examples 4 and 5 in the tertiary salt mixture provided with a silicide layer.

45

50

The increase in weight of the wire was 10.7 mg with a theoretical value of 12.5 mg. The fat of the wire increased by approximately 0.020 mm. The coating was smooth, uniform, very adherent, and had a thickness of about 0.018 to 0.020 mm.

Example 11

A molybdenum strip (130 x 50 x 1.5 mm) was made using those described in Example 8 Process steps provided with a silicide layer. However, a perforated one was used as the anode Carbon basket (length 127mm, outer diameter 23mm, inner diameter 16mm) used the with silicon grains (with a grain size corresponding to the mesh size of test sieves with approximately 1.6 to 3.1 meshes per centimeter) was filled. A moderate external emf was applied. Of the

Time temperature Current density Minutes ⁰ C A / dm ² 0 700 0.19 38 700 0.19 55 700 0.19 58 700 0.19

The increase in weight of the molybdenum strip corresponded to the theoretically possible increase of 636 mg. The thickness of the strip increased by 0.025 mm. The coating was smooth, uniform, and approximately 0.025 mm thick. The tantalum wire, partially immersed in the molten salt bath, had no silicide layer at all, although it would have been provided with one in the absence of molybdenum. As a result, in the presence of two metals, the silicide layer is formed on the metal which is more easily alloyed with silicon.

Example 12

A mixture consisting of 50 mole percent cesium fluoride and 50 mole percent potassium fluoride (100 g) was placed in a carbon lining which was located inside an evacuated quartz tube (diameter 50 mm) which was provided with two electrode openings and with an opening for the insertion of a thermocouple. The salt mixture formed a water-clear melt at 640 ° C. and easily absorbed 1000 cm ³ (normal conditions) of silicon tetrafluoride with a residual pressure of less than 0.1 mm. A silicon anode and a cathode made of palladium wire (length 40 mm, diameter 3.5 mm) were immersed in the salt bath and electrolysis was carried out in vacuo using a moderate external emf.

Time
Minutes temperature
⁰ C Current density
A / dm ² 0
20th
32 640
640
640 2.0
4.0
4.0

The weight increase of the palladium wire was 20 mg with a theoretically possible increase of 28 mg. The diameter of the palladium wire increased by 0.075 mm. The palladium wire was uniform covered with a hard, gray, brittle silicide coating with a thickness of 0.075 mm.

The following table lists the results obtained when applying a silicide layer other metals and alloys were found. The procedure described in Example 1 was carried out accordingly Procedure followed, but instead of 1 mole percent gaseous silicon tetrafluoride was used 1 mole percent potassium fluorosilicate used. All of the coatings were smooth and even and adhered well, except for gold, in which part of the gold silicide formed melted

Eutectic mixture formed, which prevents 31 atomic percent lower current density or thereby Contains silicon and has a melting point of 370 ° C that you can use when applying the silicide layer Has. This melting can be done by using a no external emf applies.

example metal Vanadium temperature
⁰ C Current density
A / dm ² the end
prey coating 13th 700 1 30th Thickness 0.075 mm, dark gray, flexible sam, VSi ₂ and probably chrome V ₅ Si ₃ present 14th 700 1 100 Thickness 0.025 mm, light gray, moderate cobalt flexible 15th 750 0.5 50 Thickness 0.0125mm, blue-gray, very copper flexible, very hard 16 600 0.8 100 Thickness 0.050mm, shiny, fine, Rhodium crystalline surface, brittle 17th 700 3 25th Thickness 0.0025mm, dark gray, very palladium brittle 18th 700 1 100 Thickness 0.050 mm, matt black, silver brittle 19th 700 1 5 Thickness less than 0.0025 mm, Tantalum matt black, brittle 20th 800 0.4 10 Thickness 0.0025 mm, light gray, flexible rhenium sam 21 700 0.6 12th Thickness 0.0038 mm, gloss black, iridium flexible, very hard, ReSi ₂ 22nd 700 2 100 Thickness 0.0125 mm, dark gray, platinum flexible 23 700 1 100 Thickness 0.025 mm, matt black, flexible sam, PtSi, Pt ₂ Si and Pt ₈ Si ₂ gold act 24 700 1 100 Part of the silicide coating melted and formed at the end of the strip a droplet of gold-silicon Eutectic. Weight gain 9.5 mg. Surface of gold InconelX (70VoNi, 15 ° / oCr, 7 Vo harder than untreated gold 25th Fe, 2.5Vo Ti, 1 · / β Ta + Nb, 710 1 90 Thickness 0.025 mm, light gray, moderate 0.7VoMn, 0.7VoAl, 0.5VoSi, flexible 0.37VoC) HastelloyX (45Vo Ni, 22Vo Cr, 26th 23VoFe, 9VoMo) 700 1 54 Thickness 0.025 mm, light gray, moderate Silicon - iron 3.5% Si) flexible 27 Molybdenum - Titanium (0.5 Vo Ti) 700 0.75 100 Thickness 0.20 mm, matt gray, brittle 28 Chromium - iron (17 Vo Cr) 700 1 100 Thickness 0.15 mm, shiny, flexible 29 710 0.5 90 Thickness 0.05 mm, light gray, moderate S 816 (38VoCo, 20VoNi, 20Vo flexible 30th Cr, 6Vo Fe, 5VoW, 4Vo Mo, 700 0.5 90 Thickness 0.025 mm, gray, flexible 4 Vo Ta + Nb, 2 Vo Mn, 1 Vo Si)

Example 31

A hairpin loop was formed from a molybdenum wire (406 x 0.5 mm), and the molybdenum wire was similar to those described in Example 1 with the exception of 25 mm at both ends Process provided with a silicide layer. When using a melt bath temperature of 660 ° C the current density was 2 amps per square centimeter

60 meters and the treatment time 172 minutes. The silicide coating had a thickness of 0.033 to 0.038 mm. This silicide-coated hairpin loop was attached to water-cooled electrodes attached and by passing an electrical

65 tric current through the wire in the air to one Heated to a temperature of 1000 ° C. A was connected to an AC voltage source with 110 volts Regulating transformer used to power the

To keep surface temperature constant. After 1003 hours there was no evidence of electrical resistance change or failure. Under similar conditions, a molybdenum wire would have been destroyed without a Silizidüberzug at 1000 ⁰ C already within one minute. The temperature was raised to 1200 ° C and held for 24 hours. The temperature was then increased to 1300 ° C., and after it had been kept at this temperature for 11 hours, the wire burned out due to a faulty point.

The above examples serve to illustrate preferred embodiments of the invention. However, many modifications are possible within the scope of the present invention. For example, the silicide coating can be applied to a metal which is itself a coating applied to another metal, for example a chrome coating applied to iron.

Since the toughness, the adhesiveness and the corrosion resistance of the applied according to the invention Silicide coatings on all areas of the treated areas have a uniform value the metallic objects provided with a silicide layer according to the present invention can be used for a variety of purposes. For example, they can be used to manufacture chemical reaction vessels, for the production of heating elements that can be used in the air without them attacked by oxidation at high temperatures, for the manufacture of turbine blades from Gas and steam turbines that cope with the corrosive and leaching effects of the gaseous propellant are used to manufacture gears, bearings and other items where a hard, abrasion-resistant surface is required. There are of course many other uses are also conceivable.

Claims (2)

Patent claims: 1. Process for the production of a silicide coating by contact deposition with optionally additional external EMF on metal bodies with a melting point of at least 600 ° C and of at least 50 mole percent of at least one metal with atomic number 23 to 29, 41 to 47, 73 to 79, by depositing silicon from a molten pool of a silicon compound, characterized in that one of 0.5 to 50 mole percent of at least one alkali metal fluosilicate and at least one Alkali metal fluoride existing, maintained at about 600 to 800 ° C molten bath used and with a silicon anode at a current density of up to 5 amps per square decimeter below extensive absence of oxygen is used. 2. The method according to claim 1, characterized in that the melt pool for elimination is kept under vacuum by oxygen. 709 578/276 4.67 © Bundesdruckerei Berlin