SU413753A1 - Method for producing tungsten carbides - Google Patents

Description

The invention relates to a technique for producing tungsten carbides, widely used as components of hard alloys, protective high temperature, erosion-resistant and emission coatings.

Currently, the existence of two tungsten carbides WC (6.12% C) and WsC (3.15%) is known.

One of the methods for producing these tungsten carbides is to reduce tungsten halides with hydrogen in the presence of hydrocarbons at 900-1200 ° C.

The disadvantages of this method of producing tungsten carbides are high energy intensity and complexity of the design of the equipment, due to the high. deposition terations, as well as the duration of the process and the possibility of contamination of the final product with impurities. Furthermore, this method does not allow the production of tungsten carbides with a different carbon content, for example, WeC.

The purpose of the invention is to develop such a method for producing tungsten carbides, which will allow to obtain high-purity tungsten carbides at relatively low temperatures in the form of compact d-axis with a density close to the theoretical and various stoichiometric and phase compositions.

This is achieved by reducing tungsten hexafluoride with hydrogen in the presence of propane cracking products at 400-900 ° C. Selection of tungsten hexafluoride, which does not form stable lower fluorides of tungsten, hydrogen and propane, under certain conditions, allows to obtain a new tungsten carbide with carbon content 0.8-1.2 wt% and the stoichiometric formula WsC.

It should be noted that, depending on the process conditions, tungsten carbides of different stoichiometric composition can be obtained:

1. At propane: hydrogen ratios of 0.15-0.5 and tungsten hexafluoride to hydrogen 0.04-0.09, with preliminary thermal catalytic cracking, WgC is formed, which has not been obtained previously by any other means.

The specified carbide has a density of 18.6-18, 7 g / ai and a microhardness of 3500 KZJMM, which makes it possible to use it as a coating with a higher wear resistance than the CERV and WC WC carbides.

2. At a ratio of propane to hydrogen of 1.0-1.5 and hexafluoride to hydrogen of 0.1-0.25, in preliminary thermocatalytic cracking of propane, WjC carbide crystallizes,

having a tight 17.5, microhardness of the order of 3100 kg / mm and containing from 3.0 to 3.2 weight. % carbon.

3. When the ratio is applied to hydrogen of 1.8-2.4 and hexafluoride to hydrogen of 0.2-0.4 with the preliminary thermocatalytic cracking of propane, higher WC tungsten carbide is formed, having a density of 15.6- 15.7 g / cm and microhardness 1700 kg / mm.

Thus, in the temperature range of 400-900 ° C, with different ratios of components on substrates that do not interact with the components of the reaction mixture, it is possible to obtain tungsten carbides WgC, WsC and we.

The proposed method for producing tungsten carbides was tested in a laboratory setup, in which both tungsten carbides and coatings are obtained.

Example 1. Getting tungsten carbide WgC.

A mixture of reactive gases is fed to the copper tube, which serves as the reaction zone and is heated by a resistance furnace. The propane is propanely cracked and passed through a heated stainless steel tube that serves as a cracking catalyst. At initial process parameters: deposition temperature of 600 ° C, ratio of tungsten hexafluoride to hydrogen WFe:: H2 0.045 and ratio of propane to hydrogen CzH8: H2 0.4, total pressure 1 atm, sc (gas flow rate 12 cm / sec the length of the reaction zone (30 cm) receive a precipitate of tungsten carbide WsC.

Example 2. Getting tungsten carbide WsC.

The coating of tungsten carbide WaC nano.ст on the surface of a flat thoriated tungsten emitter. The 50 mm long and 3 mm wide zmitters are mounted inside the copper tube along a generatrix. The deposition process is carried out with the following initial parameters: a precipitation temperature of 620 ° C, a cracking temperature of 600 ° C, a ratio of tungsten hexafluoride to hydrogen PWFO: Ph2: 0.12, a ratio RsNH Ph, 1.4 and a gas flow rate of 7 cm / sec. 20 min

On the surface of the emitters, a layer of tungsten carbide W2C with a thickness of 200 μm is obtained, which adheres well to the substrate.

Example 3. Getting tungsten carbide WC.

Production of tungsten carbide WC is carried out as in Example 1, with the difference that the process is carried out with the following initial parameters: deposition temperature

650 ° C, the propane cracking temperature is 600 C, the ratio of the partial pressures of tungsten hexafluoride to hydrogen is P WF: PH., 0.3, the RsNH: PH ratio is 2.1, and the gas flow rate is 5 cm / sec. Over the entire length of the reaction zone (30 cm) a precipitate of tungsten carbide WC is obtained.

The identity of the precipitates obtained to tungsten carbides WsC, WsC and WC is established by X-ray phase and chemical analysis.

Claims (4)

1. A method for producing tungsten carbides 5 by reducing tungsten hexafluoride with hydrogen in the presence of hydrocarbons, characterized in that, in order to obtain carbides of different stoichiometric composition, the process is carried out at 400-900 ° C, and the initial hydrocarbon, for example propane, is subjected to thermal catalytic cracking. 2. A method according to claim 1, characterized in that, in order to obtain WsC carbide, the process is carried out at a ratio of hexafluoride to hydrogen from 0.04 to 0.09 and the ratio of propane to hydrogen from 0.15 to 0.5. 3. A method according to claim 1, characterized in that, in order to obtain tungsten carbide W2C, the process is carried out with a ratio of tungsten hexafluoride to hydrogen of 0.1 to 0.25 and a ratio of propane to hydrogen of 1 to 1.5. 4. A method according to claim 1, characterized in that, in order to obtain tungsten carbide WC, the process is carried out with a ratio of tungsten hexafluoride to hydrogen of 0.2-0.4 and propane to hydrogen of 1.8-2.4.