SU3568A1 - The method of coating bodies with tungsten by electrolysis of molten salts - Google Patents

Description

The proposed method of coating a body consisting of an electrically conductive material with tungsten consists in melting tungstate (a salt of tungstic acid) or a mixture of molten tungstates undergoing electrolysis at a current density at which tungsten is separated on the body, connected instead of the cathode, in the form hot layer Tungstates are compounds of the composition nXgOmWOs, where n and w are integer numbers, and X is metal. According to the author, it turned out that with the proposed method, electrolysis proceeds with a very favorable result if the current density is less than 100 milliamperes per square meter. see the surface of the cathode. It is generally recommended to come from tungstate or from a mixture of tungstates with low melting points. According to the invention, predominantly electrolyzed molten alkali tungstate or a mixture of molten alkali tungstates undergoes electrolysis; particularly good results are obtained by electrolyzing lithium tungstate (LioWOJ.

The temperature at which the electrolysis is carried out is higher than 900 ° C, since at a temperature of lower 900 ° C a tungsten mist can be obtained which does not precipitate as a solid on the cathode but remains in the colloidal solution in the bath. In general, it is recommended that the temperature at which the electrolysis is carried out is not too close to the melting point of the tungstate or the tungstate mixture, since, in the case of a small difference between these temperatures, the molten mass

acquires too much viscosity, which prevents good electrolysis progress.

These conditions are met by, for example, lithium tungstate (Li2WO4), which melts at approximately 950 °. It is also advantageous to apply a euteclic mixture of lithium tungstates (Li2WO4) and potassium (KgWOj, the melting point of which is approximately 500 °, or a known mixture of sodium tungstates (Na.WOj) and potassium (KgWOJ, floating at about 650, although good results can be obtained when using other nX2OmWOg tungstates.

In electrolysis, it is generally necessary to take measures so that in the bath does not begin to form too large an excess of WOg. It turned out that an excess of WOg can cause the separation of tungsten bronzes containing less oxygen than tungstates and the corresponding general formula pXaO-j-nWOs - mO. These tungsten bronzes are sometimes formed even with an excess of WOg of only. The cathode on which tungsten is deposited may be a single-chip tungsten body. In this case, as it turned out, the body continues to grow further, as a single-chip body. To do this, during electrolysis, single-crystal wire, single-crystal tungsten rods, etc., items include, in the form of a cathode against the anode, which completely or almost completely surrounds the cathode. Such an anode can have, for example, a cylinder shape, or it can consist of rods arranged parallel to each other in the shape of a multi-sided prism.

The proposed method is illustrated in the drawing.

In a porcelain crucible 1 containing lithium tungstate (LijWOj there are two electrodes 2 and 3, of which one anode consists of tungsten and the other cathode, for example, represents a body made of copper. These electrodes are connected to each other through a potentiometer, 4 is a DC source, and 5 is a regulating resistance. It turned out that this results in proper separation of tungsten on the cathode and that this tungsten adheres strongly to the cathode as a bonding layer if the voltage between the electrodes is 0 , 08 volts, and density Current 75 milliamperes per sq. cm.

If the body, which is desirable to cover with tungsten, consists of a substance to which tungsten sticks to less well, then it is recommended to cover the object first with a layer to which tungsten sticks well. For example, if you want to coat an iron object with tungsten, it is first coated with copper and only after that is coated with tungsten. To coat tungsten with objects made of non-conductive material, you can first supply them with one or more layers of material that conducts electricity, and then cover them with tungsten, for example, cover with graphite first, then copper, and finally tungsten.

When a cylindrical anode is used, a single-crystal tungsten wire, included as a cathode, has a diameter of 300 microns and is immersed 3 cm in molten lithium tungstate, grows within two hours into single-crystal tungsten rods with a diameter of 2 mm if the voltage between the electrodes is 0.08 volts and current density -100 milliampere.

The subject of the patent.

1. A method of coating bodies with tungsten by electrolysis of molten salts, characterized in that molten alkaline tungstate or a mixture of molten alkali tungstates is electrolyzed at a temperature above 900 ° C and at a low current density of about 100 milliamps per square meter. see electrode surface or lower, in order to deposit tungsten in the form of a dense layer.

2. In the method described in paragraph 1 in the case of coating nonconducting bodies with tungsten sediment, precoating them with one or more layers of electrically conductive material.

3. In the method described in paragraph 1, using a single-chip tungsten body as a cathode.

4. In the method described in paragraph 3, the use of such an anode form that it completely or almost completely embraces the cathode.