SU64547A1 - The method of obtaining pieces of boron carbide, given form - Google Patents

Description

During the process of melting boron carbide in crucibles of boron nitride in a nitrogen atmosphere, boron nitride is destroyed. This circumstance is used to increase the boron content in boron carbide, which is subject to melting. In this way, especially in a hydrogen atmosphere, it is possible to increase the boron content to 85% and higher. However, this circumstance is unfavorable for obtaining products of a given shape, due to the destruction of the form of boron nitride and the formation of shells in pieces of boron carbide due to the evolution of gases during the decomposition of boron nitride. This occurs in the event of excessive overheating of the melt of boron carbide during the process of obtaining boron carbide with a dense structure. To avoid this phenomenon, according to the invention, it is proposed to melt boron carbide in pressed forms of boron nitride in a nitrogen atmosphere under elevated pressure, which raises the decomposition temperature of boron nitride. The mixture of boron carbide should be prepared strictly defined composition. This operation is recommended by using boron carbide that does not contain boron nitride or boric anhydride with a composition close to the formula (B-78.3%; C- 21%).

If necessary, use products with higher viscosity, but with less wear resistance, it is necessary to use a mixture with a boron content above 78.3%. On the contrary, in the absence of negative effects when using larger products, but with the required increased wear resistance, boron carbide of composition 78.3% B should be used. You can use boron carbide and a few percent lower Kdro composition, but not lower than 73-74% B. To correct the composition of the initial boron carbide charge, if there is a large amount of carbon in it, the mixture, when crushed, is in the appropriate proportion (with a small amount with an excess of carbon saturation due to hydrocarbons) is mixed with boron nitride and calcined in a hydrogen atmosphere at a temperature of 2100 ° for two hours or less, depending on the loading volume and content of boron nitride in it, after which, for convenience, It is sintered by raising the temperature to 2370 ° C and transferred to the refrigerator. In the described process, as well as in the subsequent ones, it is necessary to thoroughly clean the gas, which is the atmosphere of the furnace, from traces of moisture, carbon dioxide and oxygen. Melting should be carried out in a sealed furnace with rubber gaskets (the flanges near the gaskets are cooled with water). The pressure can be produced in the furnace using a nitrogen cylinder and a reducing valve.

A favorable factor affecting the absence of destruction of the outer parts of the boron nitride mold at the point of contact with the coal pipe (in the case of melting not in a high-frequency furnace, but in Tamman furnaces) is an insulating gasket made from tantalum, from its carbide, or nitride.

Conducted experiments on heating a boron nitride boat placed on an insulating gasket made of tantalum tin laid on a heated coal pipe to a temperature of 2700 ° in the atmosphere

nitrogen, showed no interaction tantalum tin with boron nitride in a nitrogen atmosphere. The prepared forms of boron nitride (for melting boron carbide) must be porous; Molds can be made by pressing boron nitride with additives, which are subsequently removed with a slow pre-calcination of these forms.

Subject invention

Claims (2)

1. A method for producing boron carbide pieces of a given shape by melting in crucibles of a suitable form in a nitrogen atmosphere, characterized in that, in order to eliminate the destruction of a mold made of boron nitride and the formation of sinks in boron carbide pieces, the melting in a nitrogen atmosphere is carried out pressure. 2. A method according to claim 1, characterized in that a gasket made of tantalum, tantalum carbide or its nitride is placed between the form of boron nitride and the coal tube of the furnace.