DE654270C - Process for the electrolytic production of coatings from tungsten alloys - Google Patents

Description

GERMAN EMPIRE

ISSUED ON DECEMBER 20, 1937

REICH PATENT OFFICE

PATENT LETTERING

ΛΙ 654270 CLASS 48 a GROUP 6 so

Harry Howard Armstrong and Arthur Burley Menefee in Beverly Hills, Calif., V. St. A.

Patented in the German Empire on May 29, 1935

The invention relates to a method for the electrolytic production of Coatings made of tungsten alloys and is characterized by the fact that an electrolyte is used, in which the tungsten is contained as acid fluoride and either in Presence of a salt of the alloy metal dissolved in the electrolyte or with a Anode, which contains the alloy metal and tungsten, is worked.

According to the method of the invention, it is possible to produce tungsten alloys from aqueous solutions with a tungsten content fluctuating within very wide limits, both knock down binary as well as ternary and polynary alloys. In these alloys tungsten need not be the predominant element.

The coating produced according to the invention is characterized by high adhesive strength on the base metal, high chemical resistance to the corrosive effects of acids and the like, as well as largely improved physical properties, e.g. ductility, erosion and abrasion resistance, low coefficient of friction, easy machinability, etc. These and others inherent in the new material

to because of the high solution resistance that

residential properties in conjunction with the well-known favorable thermal and The electrical properties of alloys containing tungsten reveal the wide range of uses that the material can be used for.

It has already been proposed to electrolytically deposit tungsten. The known However, processes work using an alkaline bath, which Contains tungsten as a complex radical. However, the known methods are not sufficient effective, and the precipitates produced do not have sufficient adhesive strength on the substrate. The difficulty lies in the fact that tungsten has a pronounced tendency to oxidize and, as a result, easily oxidic deposits develop. As a result, the metal layer produced is impure and does not adhere.

Because of the great difficulty in producing such oxides as a result of the strong hydrolysis in To reduce aqueous solutions, attempts have been made to reduce a non-aqueous Electrolytes, i.e. the dissolution of a tungsten salt in organic solvents, use. These procedures are however

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required high temperature and because of disruptive phenomena resulting from the use of organic solvents, not advantageous. ■ ·; - .. All the difficulties mentioned f but eliminated by the new procedure. The process has the advantage that the permissible ptf area is very large. The tungsten content of the precipitates can fluctuate considerably. For example, it is easily possible to produce tungsten-nickel coatings with a tungsten content of ½ to 70%. The metal precipitates are tight and the bath used has a high conductivity, comparatively low currents are required, and the current density can be varied within wide limits without incurring difficulties, the temperature of the electrolyte can be kept low, and yet the anodic decomposition is high The possibility of largely changing the composition of the precipitates makes the products accessible for post-treatment, for example cold and hot treatment, saturation with carbon and the like, which means that products can be produced which are advantageously used in various technological fields. To the author In order to explain this in more detail, some examples of its implementation will be given below.

4 parts by weight of NaHF ₂ or KHF ₂ or the equivalent amount of hydrofluoric acid are dissolved in 100 parts of water, and about 5 parts by weight of sodium chloride and 1 part by weight of concentrated hydrochloric acid are added to the solution. The solution is then ^{heated to 40 to 75 °} C., possibly even higher, and ^{electrolyzed for two hours or even longer at I 1} Z ₂ to 6 volts or higher voltage, the anode being made from tungsten carbide, from the carbide of a tungsten alloy, such as Tungsten-nickel carbide, or consists of tungsten, while any highly conductive material, such as copper, brass, etc., can serve as the cathode. As soon as the electrolysis starts, the electrolyte takes on a deep brown color, which is due to the fact that the anode is decomposed and tungsten goes into solution. For various reasons it is assumed that this is the oxidation stage that is present _{in tungsten dioxide WO 2.} "

Provided the anode is not made of the carbide of tungsten alloy, such as tungsten-nickel, tungsten, cobalt, etc., but of pure tungsten carbide, about _^2/10 by weight or more of the Métail in the form of a salt is added, the metal base with the W ^T ungsten in Coating is to be alloyed. Such salts are, for example, Ni Cl ₂ or 2 Ni C Cy 3 Ni (OH) ₂ · 4 H ₂ O or Ni (OH) ₃ etc. When the salt is dissolved, the p _A value is usually below 4. Er $ d divided by the addition of NaOH, KOH, NH ₃ zif other alkaline substances so that it comes to lie between 4.5 and 6.8. The temperature of the solution is kept between 35 and 85 ° C or higher, then the cathode to be coated is immersed in the solution and electrolyzed at about 14 amps on a cathode area of 0.093 m².

From time to time small amounts of the salt of the "metal, which is with the Tungsten to be alloyed should be added as the solution to this salt gradually increases impoverished. If a tungsten-nickel-carbide anode is used, so it is seldom necessary to also add nickel salt, since the decomposition of the anode is sufficient to remove the to supply the necessary amount of metal ions for the coating.

It is particularly noteworthy that in the bath according to the invention very high Can achieve concentrations. For example, tests have shown that in the above solution 5 ο o / o and still can dissolve more salt and always get satisfactory coatings if you use the Voltage and current density changes only slightly.

For coatings which are strong acids against corrosion resistant, the best results were obtained at a _pH value 5 to 6 Thick metal coatings can be obtained with p // values below 5 and above. If the alloy metal, e.g. As nickel or cobalt, is easily precipitated, it is advisable to use up a sufficient amount of sugars or organic acids at a _pH value of 6.6.

The current density should be 6 to 35 amps on 0.093 square meters when thick metal deposits are generated immersed cathode area. Coatings with good resistance to Acid corrosion is obtained at about 14 amps.

The voltage to generate thick metal deposits is kept below 6 volts. The best results come when using a voltage of 1 to 3 volts is used.

Good results for coating with tungsten alloys are obtained when the immersed areas of the anode and cathode are the same. If the cathode dips deeper, the electrolyte is prematurely depleted of tungsten. In this case it is advisable to increase the acidity of the solution or to add _{tungsten dioxide WO 2.}

The bath can also be produced from the outset by dissolving tungsten dioxide WO ₂ , and one can work with insoluble anodes, such as platinum or carbon anodes. To revive impoverished solutions, it is advisable to acidify either with acidic fluorides or with hydrofluoric acid to a p _{/ r} value of 4 and then to electrolyze with carbide electrodes or tungsten dioxide,

ίο which is dissolved in an acidic fluoride or in hydrofluoric acid, to be added. Double salts are also suitable as additives, for example 2NaF-W0 »F« or KF-W0.F.-2 H.0 or NH ₄ F-WO.F ₂ · H ₂ O etc.

It has been observed that the proportions of the alloying metal which is simultaneously deposited with the tungsten, depending on the desired properties of the coating, is the most favorable ratio. For example, it has been established through experiments that mari requires higher current densities with the tungsten-nickel alloy, the more nickel is present in the electrolyte. The coatings produced are, however, more and more dense and acid-resistant as the nickel content increases. However, if the amount of nickel content is increased beyond a certain level, the acid resistance of the coating decreases again. In general, the most beneficial effect is achieved when the nickel content is around 65%. A strong, very acid-resistant coating is obtained by the method of the invention when the deposited metal contains about 35% tungsten and 65% nickel. Attempts have been made to find a theoretical interpretation for the phenomena observed. Without the indication being intended to imply a definition, it should be mentioned that there is presumably a complex in the bath according to the invention which contains tungsten and fluorine, for example WO ₂ F ₂ . During electrolysis, this complex would ^{break down into (W 7} O ₂ ) - and (F ₂ ) - whereupon the tungsten from the radical (WO ₂ ) - is deposited by reduction. If a tungsten-nickel precipitate is produced, the equivalent of a double salt, for example tungsten-nickel dioxide fluoride NiF ₂ -WO ₂ F ₂ -IOH ₂ O, should therefore be present in the bath.

If you want to precipitate tungsten, it is best to dissolve tungstic anhydride in an acidic fluoride. Acid ammonium fluoride is particularly suitable for this. the physical properties of the precipitate can also be improved, though instead of tungstic anhydride, wolframates, metatungstates, paratungstates, tungstic acid are used etc. used.

To produce such a bath, tungstic anhydride is dissolved with ammonium bifluoride in water at 42 to 100 ° C. This solution is filtered and boric acid H ₂ BO ₃ , sodium fluoride and tartaric acid are added and the temperature is again raised to 48 to 60 ° C. A salt of the metal which is to be alloyed with the tungsten is now added, for example basic nickel carbonate 2 Ni CO ₃ • 3 Ni (OH) ₂ • 4 H ₂ O. The resulting solution is electrolyzed with a current density of 6 to 100 Amp. On a cathode area of 0.093 m². Favorable results are achieved if the p _fl value of the solution is set between 1 and 10.

Another convenient way to prepare the bath is to dissolve tungstic anhydride, ammonium bifluoride, sodium fluoride and a soluble salt of the alloy metal at the same time in water, heat the solution to a temperature of 60 to 100 ° C. for 30 minutes and then filter it. The pH value is adjusted to 5.5 and the electrolysis is carried out at 60 ° C. with an amperage of 30 amps using a W ₂ C tungsten carbide anode.

Another favorable bath composition is achieved when molten ammonium bifluoride with Wolframsäureanhvdrid dissolves at about 72 ⁰ C in water, filtered and the resulting solution was added sodium fluoride, sodium chloride, and the salt of the alloying metal. The solution is electrolyzed at about 72 ° C with a current density of 35 Amp. On 0.093 square meters, whereby the anode can consist of platinum or tungsten carbide.

In terms of numbers, the regulations for the production of baths are set out below specified exemplary embodiments.

example 1

200 g of WO ₃ and 240 g of NH ₄ HF ₂ are dissolved in 4.54 l of water; the solution is heated to 72 to 100 ° C. and filtered. The filtrate is 120 g boric acid, oogNatriumfluorid and 60 g of tartaric acid, erhitztauf 48 to 60 ⁰ C and adds 10 g of basic nickel carbonate. The pH value of the solution is adjusted to 5.3 to 6.3 and the current density is 6 to 100 amps for a cathode area of 0.093 m². One works with a tungsten or a nickel anode or with a combined tungsten carbide and nickel anode or with an anode made of platinum.

Example 2

The following dry salts are added to 4.54 l of water at 60 to 100 ° C.: 120 g WO ₃ , 60 g NiCO ₈ - Ni (OH) ₃ -4H ₂ O, 240 g NH ₄ HF ₂ , 240 g NaF, 240 g NaCl. The temperature is maintained for about 30 minutes and then filtered. The p ^ value

is set as in Example ι, the electrolysis temperature is 60 ⁰ C, the anode consists of tungsten carbide or nickel or of both substances, and you work with a current density of around 30 amps.

Example 3

170 g of NH ₄ HF ₂ and 80 g of WO ₃ are melted at a temperature just above the melting point of the ammonium bifluoride. The cake obtained is dissolved in 4,541 in water at a temperature of 70 ⁰ C. 160 g of sodium fluoride, 80 g of sodium chloride and, if necessary, 20 g of 2 NiCO ₃ · 3 Ni (OH) ₂ · 4 H ₂ O or a similar salt of the alloy metal are added to the solution. The p # value is similar to that of Examples 1 and 2. The electrolysis temperature is J2 ° C. The anode used is platinum, tungsten carbide or nickel at a current density of about 35 amps. It has been found that the current density can be up to 500 Amp. And still get good results. The bath temperature can fluctuate ^{between 26 and 82 ° C.} This great elasticity of the process causes its high technical value, since the working conditions are largely variable. For example, the concentration of the bath can be increased by dissolving up to 170 g of WO ₃ to 4.541 bath solution. In spite of the high tungsten content, the solutions are clear and free from undissolved components, for example from the oxides that are always present in the known tungsten baths. By dissolving tungsten compounds, one can achieve significantly higher tungsten concentrations than is possible through anodic decomposition. The anodic decomposition yields a maximum of about 60 g of tungsten to 4.54 1. On the other hand, from 40 g of tungstic anhydride and 40 g of ammonium bifluoride to 200 ecm 90% and more of the reacting substances are still completely in solution. Depleted solutions can easily be revived _{by adding WO 3 and bifluoride.} The solubility of the tungsten salts is not affected by the presence of alkali halides, citric acid, tartaric acid, boric acid, sugar or soluble nickel salts. Such solutions can contain 15 parts tungsten to one part nickel, and the ratio can be varied to within one part tungsten to one part nickel. In order to prevent the precipitation of nickel, organic compounds such as tatrates, citrates, acetates, dextrose, etc. can also be added. The presence of borates is useful as a buffer because, as salts of a weak acid, they cause a significant change in the hydrogen ion concentration. prevent tration. Beryllium and lithium hydroxide, lithium carbonate, etc. are also suitable as buffers.

The presence of NaF and NaCl not only increases the conductivity, but because of the higher concentration of halogen ion also the anodic decomposition of tungsten, nickel or Carbides! electrodes. Experiments have shown that the solution has a shows increased metal content when common salt or sodium fluoride are added. as well Hydrofluoric acid promotes anodic decomposition.

In addition to nickel and cobalt, other alloy metals, the double fluorides, can also be used form, for example sodium, copper, chromium, etc., can be used.

In the course of the tests it was found that the acid resistance of the precipitates tungsten alloys can be improved in some cases, for example when it comes to the production of a coating on iron, if the iron is previously coated with copper, brass or cadmium. Tungsten or tungsten alloys may have a special protective effect in contact with such intermediate metals, similar to that known from platinum. It was found that 1½ weak test coatings of tungsten-nickel over brass or copper-coated brass or copper withstood 100 hours in concentrated hydrochloric acid or sulfuric acid. The same coatings withstood cold concentrated nitric acid for 11 hours before being permanently destroyed. The coatings obtained according to the invention are very suitable for treatment with carbon. It is known that tungsten is converted into carbide when heated to 815 ^° C. and sometimes even at a lower temperature in the presence of carbon or a carbon-releasing substance. If you need hard, heat-resistant surfaces, for example for valves, valve seats, cylinder walls of internal combustion engines, pump cylinders, gun barrels, etc., you can very easily and easily harden the precipitates obtained by the method described with carbon. This transition of the tungsten in the alloys seems to take place automatically when the precipitates are exposed to a carbon-containing atmosphere in the heat, for example in valves, cylinder walls, gun barrels, etc., because the coatings become harder and harder over time.

The type of salts that make up the bath also allows it to be a dry mixture to produce, which one simply dissolves in water before the start of the electrolysis, whereby

if necessary, the hydrogen ion concentration is also regulated. This will make the application the procedure is particularly facilitated.

The finished precipitates can be subjected to any type of hot or cold treatment will. For example, it has been found that the adhesive strength between thin base metal and the coating even further can be improved by polishing, hammering or other processing of the surfaces.

Claims (11)

Patent claims: 1. Process for electrolyte ti see manufacture of coatings made of tungsten alloys, characterized in that an electrolyte is used in which the Tungsten is contained as an acid fluoride and either in the presence of one in the electrolyte dissolved salt of the alloy metal or with an anode, which contains the alloy metal and tungsten, worked will. 2. A method for producing an electrolyte according to claim i, characterized in that . draws that a tungsten compound with an ammonium or alkali bifluoride solution is preferably treated at an elevated temperature. Process for the production of an electrolyte according to Claim 1, characterized in that that the bath is obtained by dissolving the product, which when melting a tungsten compound with an alkali fluoride is formed. A method for producing an electrolyte according to claims 1 to 3, characterized in characterized in that the bath contains a solution of alkali halides and (or) boric acid is added. 5. The method according to claim 1 to 4, characterized in that the electrolysis is carried out at a p _w value of 4.5 to 6.8. 6. The method according to claim 1, characterized in that one in a free Hydrofluoric acid containing bath works with a tungsten anode. 7. The method according to claim 6, characterized in that one with anodes works that contain both tungsten and the alloy metal. 8. The method according to claim 1, characterized in that there is an electrode made of tungsten carbide and used at temperatures of 35 to 80 ° C with a Current density of 6 to 40 Amp. Per 0.093 square meter of immersed cathode area works. 9. The method according to claim 1 to 8, characterized in that the to Plating metal first with a layer of it in the tension series related metal and then provided with the precipitation of the tungsten alloy. 10. The method according to claim 1 to 9, characterized in that the After electrolysis, the coating is heated in the presence of carbon. 11. Process for the preparation of pure Tungsten, characterized in that one according to claims 1 to 9 Tungsten alloy is produced and then the alloy metal is dissolved out. BERLIX. DRIED IN THE