RU2394761C1 - Tungsten carbide wc synthesis method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in metallurgical industry, in making tools and catalysis. Tungsten carbide WC is obtained via mechanochemical activation of mixtures of tungsten metal with carbon material and subsequent calcination in an inert gas medium. The carbon material used is graphite or anthracite or activated carbon or soot or carbon xerogel or carbon nanofibre or carbon fibre made from polyacrylonitrile or any of their mixtures. The carbon material and tungsten are taken in amount which ensures a ratio which is 10-50% more than required for formation of tungsten carbide WC. The calcination temperature lies between 650 and 800°C.

EFFECT: obtaining pure tungsten carbide with high dispersion, lower power consumption and shorter synthesis time.

3 cl, 1 dwg, 5 ex

Description

The invention relates to the field of inorganic synthesis, namely to the production of tungsten carbides, and may find application in the metallurgical industry, tool manufacturing, catalysis.

WC tungsten carbide is widely used for alloying steels and making coatings for cutting tools. It is also known about the use of carbides as catalysts for the reactions of dehydrogenation of cyclohexane to benzene [G. Gaziev // DAN USSR, 1961, t.140, v.4, p.863], hydrogenation of carbon monoxide [Patterson P.M., Das T.K., Davis B.H. // Appl. Catal: General, 2003, v.251, p.449-455]. Recently, a lot of research has been devoted to the use of tungsten carbides as catalysts for electrocatalytic processes, for example, the oxidation of hydrogen in fuel cells [Nara Y., Minami N., Itagaki H. // Appl. Catal .: General, 2007, v. 323, p. 86-93; McIntyre DR, Burshtein GT, Vossen A. // J. Power Source, 2002, v.107, p.67-73] or nitromethane reduction [Zheng H., Ma Ch., Wang W., Huang J. // Electrochem . Comm., 2006, v. 8, p. 977-981]. The advantages of tungsten carbides in these processes over platinum catalysts are their low cost, chemical inertness and high resistance to poisoning by carbon monoxide, which, as a rule, is present in hydrogen in amounts up to several hundred ppm.

Tungsten carbide (WC), used for alloying steels, is produced by three methods [Kosolapova T.Ya. Carbides. M., 1968].

- The interaction of tungsten with carbon in a hydrogen medium at temperatures of 1430-1630 ° C.

- The interaction of tungsten trioxide, tungsten acid or ammonium paratungstate with hydrogen and methane at temperatures of 900-1000 ° C.

- The decomposition of tungsten carbonyl W (CO) ₆ at a temperature of 1030 ° C.

Even more stringent conditions are required to obtain tungsten carbide W ₂ C: the interaction of tungsten with carbon in a hydrogen medium at temperatures of 3000-3200 ° C [Kosolapova T.Ya. Carbides. M., 1968].

In all cases, coarse tungsten carbide is formed, which is unsuitable for use in the manufacture of tools and as catalysts. In [Patterson P.M., Das T.K., Davis B.H. // Appl. Catal .: General, 2003, v.251, p.449-455; Nar Y., Minami N., Itagaki H. // Appl. Catal: General, 2007, v.323, p.86-93] describes methods for producing tungsten carbides by carbonization of nitride and tungsten sulfide in a medium of carbon-containing gases (hydrocarbons, CO) and hydrogen. With such methods, as a rule, a mixture of several tungsten carbides is obtained.

Closest to the proposed invention is a method for producing composites containing tungsten carbide by mechanochemical activation (MXA) of a mixture of tungsten powder with carbon and copper [Baikalova Yu.V., Lomovsky O.I. // Journal of Alloys and Compounds, 2000, v. 297, p. 87-91] or cobalt [RF 2120840, B22F 9/054, 27.101998]. The content of tungsten carbides in the resulting composites is not more than 5 wt.%.

As a prototype, a method of preparing a mixture for tungsten carbide-based carbides, including machining the powders of the components of the mixture, was machined, tungsten, carbon and cobalt powders were subjected to mechanical treatment in a mechanochemical reactor at an acceleration of 40-60 g for 10-30 min [RF 2120840, B22F 9/054, 27.101998]. The content of tungsten carbides in the resulting composite is not more than 5 wt.%.

The disadvantages of the known methods of preparation are: high energy consumption, the need for high temperatures, a long synthesis time, low productivity in the case of using MHA.

The objective of the invention is to develop a method for producing nanoscale tungsten carbides with low energy consumption and short synthesis time.

The task of producing WC tungsten carbide is solved by mechanochemical activation of mixtures of tungsten metal with carbon and subsequent calcination in an inert gas atmosphere. Graphite, or anthracite, or activated carbon, or soot, or carbon xerogels, or nanofibrous carbon, or polyacrylonitrile carbon fibers, or any mixture thereof, is used as a carbon source. The mechanically activated mixture is subjected to heat treatment in an inert gas atmosphere at a temperature of 650-800 ° C. Helium, or nitrogen, or argon, or carbon dioxide, or any mixture thereof, is used as an inert gas. The carbon material and tungsten are taken in an amount that provides a ratio that is 10-50% higher than that required for the formation of WC tungsten carbide.

To remove impurities of metallic iron formed during abrasive wear of the drums of mills and grinding media, the resulting materials are treated with solutions of nitric or hydrochloric acid.

EFFECT: obtained pure WC tungsten carbide with crystallite sizes of 13-25 nm and a specific surface of 80 m ² / g. High dispersion allows to increase the efficiency of using the material as a catalyst and to produce abrasive tools that can improve the class of processing.

The invention is illustrated by the following examples and the drawing.

Example 1

47 g of W and 3.5 g of C (soot grade P-245) are loaded into the drum of a planetary mill. The mixture is subjected to mechanochemical activation in an ACE planetary mill at a rotational speed of drums of 17s ^-1 for 10 minutes. The activated mixture is heated at a temperature of 750 ° C in an inert gas (argon) for 2 hours. According to x-ray phase analysis, the obtained sample contains WC tungsten carbide (see drawing).

Example 2

47 g of W and 3.4 g of C (nanofiber carbon) are loaded into the drum of a planetary mill. The mixture is subjected to mechanochemical activation in an ACE planetary mill at a drum rotation speed of 17 s ^-1 for 10 minutes. The activated mixture is heated at a temperature of 800 ° C in an inert gas (argon) for 2 hours. According to x-ray phase analysis, the obtained sample contains tungsten carbide WC. The diffractogram of the sample is similar to that shown in the drawing.

Example 3

4.7 g W and 0.45 g C (anthracite) are charged into the drum of a planetary mill. The mixture is subjected to mechanochemical activation in an EI-2 * 150 planetary mill at a drum rotation speed of 11 s ^-1 for 60 minutes. The activated mixture is heated at a temperature of 750 ° C in an inert gas (nitrogen) for 2 hours. According to x-ray phase analysis, the obtained sample contains WC tungsten carbide. The diffractogram of the sample is similar to that shown in the drawing.

Example 4

4.7 g W and 0.34 g C (carbon fiber PAN) are loaded into the drum of a planetary mill. The mixture is subjected to mechanochemical activation in an EI-2 * 150 planetary mill at a drum rotation speed of 11 s ^-1 for 360 minutes. The activated mixture is heated at a temperature of 650 ° C in an inert gas (nitrogen) for 2 hours. According to x-ray phase analysis, the obtained sample contains WC tungsten carbide. The diffractogram of the sample is similar to that shown in the drawing.

Example 5

Samples according to examples 1-4 are treated with diluted nitric acid to remove impurities of metallic iron. The resulting products contain 100% WC tungsten carbide.

As can be seen from the above examples and diffraction patterns, the inventive method allows to obtain tungsten carbide composition WC or its mixture with other components that can be used for alloying steels, the manufacture of abrasive tools, catalysts and fuel cells.

Claims (3)

1. A method of producing tungsten carbide WC, comprising mechanochemical activation of mixtures of tungsten metal with a carbon material and subsequent calcination of the activated mixture in an inert gas medium, characterized in that graphite or anthracite, or activated carbon, or soot, or carbon are used as the carbon material xerogels, or nanofibrous carbon, or carbon fibers from polyacrylonitrile, or any mixtures thereof, carbon material and tungsten are taken in an amount providing a ratio exceeding necessary for the formation of tungsten carbide WC by 10-50%, the calcination temperature is selected from the interval 650-800 ° C. 2. The method according to claim 1, characterized in that helium, or nitrogen, or argon, or any mixture thereof, is used as an inert gas. 3. The method according to claim 1, characterized in that to remove impurities of metallic iron, the resulting materials are treated with solutions of nitric or hydrochloric acid.

Images