RU2683107C1 - Method of obtaining mixtures of high-differed heterogeneous powders based on boron carbide - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to ceramic technology and powder metallurgy and is intended for production of highly dispersed heterogeneous powder compositions, which can be used for production of ceramic armor elements, materials operating under abrasive wear conditions, products used in mechanical engineering, in energy and chemical technologies, in aerospace engineering. Required powders are obtained by reducing a mixture of oxides of boron, silicon and/or d-metal with highly dispersed carbon (soot) in vacuum or in protective gaseous medium at temperatures between 1500 and 1800 °C. As starting materials, powders of boric acid, boric anhydride, can be used, silicon oxide, transition d-metal oxide of a secondary subgroup of groups IV–VI of the Periodic system of elements. To ensure uniform distribution of components and high dispersion of mixtures, the starting oxygen-containing substances are pre-homogenized by their co-melting in air with the subsequent formation of precursors in the glass-crystalline state, containing oxide components necessary for the synthesis, uniformly distributed at the atomic-ionic level directly in the structure of the glass-ceramic precursor.EFFECT: said homogenization prevents the formation of agglomerates of particles of one of the components by shielding particles of synthesized components from each other, which increases the diffusion path of atoms of the same name and complicates the process of secondary recrystallization, which results in highly dispersed synthesis products.1 cl, 6 dwg, 2 ex

Description

The invention relates to ceramic technology and powder metallurgy, in particular to the synthesis of heterophase mixtures of oxygen-free refractory compounds containing boron carbide, and can be used for the production of ceramic armor elements, materials operating under abrasive wear, products used in mechanical engineering, in energy and chemical technologies in aerospace engineering.

A known method of producing boron carbide by the method of carbothermic reduction of boric anhydride (Kosolapova T.Ya. Carbides. M: Metallurgy, 1968, p. 190):

2B ₂ O ₃ + 7С → В ₄ С + 6СО

F. Boron carbide - a comprehensive review, Journal of the European Ceramic Society, 1990, 6, 205-225.) получают стехиометрический карбид бора со средним размером частиц 0,5-5 мкм. Основной недостаток указанного способа заключается в наличии примеси свободного углерода (графита) в составе порошка в случае использования стехиометрического соотношения исходных реагентов вследствие потери части бора в виде оксида бора в процессе синтеза.When conducting synthesis in a low-productivity graphite tube furnace at temperatures of 1700-1800 ° C in a protective environment (

F. Boron carbide - a comprehensive review, Journal of the European Ceramic Society, 1990, 6, 205-225.) Obtain stoichiometric boron carbide with an average particle size of 0.5-5 microns. The main disadvantage of this method is the presence of an admixture of free carbon (graphite) in the composition of the powder in the case of using a stoichiometric ratio of the starting reagents due to the loss of part of boron in the form of boron oxide in the synthesis process.

The invention (patent RU 2550848, СВВ 31/36, published on 05/20/2015) relates to a method for the synthesis of boron carbide, which is realized by high-speed heating of a mixture from a mixture of amorphous boron and highly dispersed carbon material, in particular nanofibrous carbon. The mixture is loaded into a crucible made of glassy carbon, which is placed in a quartz reactor, the latter, in turn, is inserted into the inductor of the induction furnace. The synthesis is carried out in argon at a temperature of 1700-1800 ° C with exposure for 15-20 minutes. The invention allows to prevent the possibility of the appearance of free carbon impurities in the production of boron carbide composition in the range of its homogeneity region. Losses in the synthesis practically does not occur. The disadvantages of the proposed technical solution is its economic unprofitability and the requirement for special equipment.

A known method of producing a powder of a refractory substance, including refractory metals, their alloys, carbides, borides, nitrides, carbonitrides, etc. (patent RU 2446915, B22F 9/10, publ. 04/10/2012). The initial charge in the form of solid granular material is heated to a temperature of 0.4-0.8 of the melting temperature of the charge and fed into a rotating water-cooled crucible located in the chamber, where it is melted by exciting the plasma arc between the crucible, which is the anode, and the cathode of the plasma-arc source heating up. The obtained melt, characterized by a homogeneous composition, is sprayed in a gaseous medium (argon, helium, nitrogen or a mixture thereof) and finely dispersed drops of the melt crystallize upon cooling. As a result, the spherical powder obtained by spraying is homogeneous in composition and structure. The disadvantage of this solution is the difficulty in implementing the proposed process due to the need for special installations. In addition, this method is aimed at obtaining powders of electrically conductive objects, to which boron carbide does not apply.

The closest technical solution to the claimed adopted as a prototype is the joint production of powders in the B ₄ C-SiC system by carbothermal reduction of B ₂ O ₃ and SiO ₂ oxides with soot (Rocha R.M., Mello F. C. L. Sintering of B ₄ C-SiC powder obtained in situ by carbothermal reduction, Materials Science Forum, 2008, 591-593, 493-497). As a source of boric anhydride, the ground product of boric acid dehydration at a temperature of 300 ° C was used. In order to compensate for the loss of boron in the form of boron oxide / suboxide, an excess of ₂ O ₃ in the amount of 25 wt% was introduced into the charge. in excess of stoichiometric value. The synthesis was carried out in argon at a temperature of 1700 ° C for 30 minutes. The phase composition of the obtained powders is represented by phases B ₄ C, β-SiC, in some cases B ₂ O ₃ , C. Besides the presence of impurity phases in the powders, the disadvantage of this method is “Coarse” dispersion of the obtained product (without additional grinding): the particle size of boron carbide reaches 5 microns, silicon carbide - 20 microns; this suggests that the uniform distribution of unlike particles (particles of different phases) in the powder volume is not ensured.

The essence of the claimed invention consists in the joint production of highly dispersed heterophasic powder compositions comprising boron carbide and one or more of the following compounds: silicon carbide, boron transition d-metals of a subgroup of groups IV-VI of the Periodic Table of the Elements.

The problem to which the invention is directed, is to provide a high degree of homogenization of the components in the volume of the mixture. The problem is solved due to the fact that the initial oxygen-containing sources of boron, silicon and / or d-metal are pre-homogenized by co-melting them in air and then reduced with highly dispersed carbon (soot) in vacuum or in a protective gas environment at temperatures of 1500-1800 ° FROM.

The technical result is to achieve uniform distribution of the components of the synthesized mixtures and their high dispersion. The technical result of the invention is achieved by creating precursors in the glass crystalline state, containing oxide components necessary for the synthesis, uniformly distributed at the atomic-ion level directly in the structure of the glass crystalline precursor. The specified homogenization prevents the formation of agglomerates of particles of one of the components due to the shielding of the particles of the synthesized components from each other. Screening of the particles of the components from each other increases the diffusion path of the atoms of the same name and complicates the process of secondary recrystallization, which leads to the production of highly dispersed synthesis products.

The claimed technical solution is new, has an inventive step and is industrially applicable.

FIG. 1 - Electron micrograph of particles of a glass crystalline precursor in the B ₂ O ₃ -SiO _{2 system} .

FIG. 2 - X-ray diffraction pattern of the synthesized powder in the system B ₄ C-SiC

FIG. 3-electron micrograph of synthesized powder particles in a B ₄ C-SiC system.

FIG. 4 - Electron micrograph of particles of a glass crystalline precursor in the B ₂ O ₃ -SiO ₂ -TiO _{2 system} .

FIG. 5 - X-ray diffraction pattern of the synthesized powder in the system B ₄ C-SiC-TiB ₂ .

FIG. 6 - Electron micrograph of particles of the synthesized powder in the B ₄ C-SiC-TiB _{2 system} .

The method is as follows. Powders of boric acid (or boric anhydride), silicon oxide and / or transitional d-metal oxide of a side subgroup of groups IV-VI of the Periodic Table of Elements are mixed in a predetermined ratio and loaded into a crucible to melt the mixture in air at temperatures in the range of 500-1800 ° C, after which the liquid melt is poured onto a stainless steel plate. The average particle size of the obtained glass crystalline precursors is in the range of 50-200 nm depending on the composition. At this stage, a high degree of homogenization of the oxide components in the volume is ensured. Further, the glass-crystalline material is crushed and ground to a particle size of less than 1 μm, then mixed with highly dispersed carbon (soot) in the ratio required for the synthesis of oxygen-free compounds. The resulting mixture is placed in a carbon crucible. The synthesis is carried out in vacuum or in a protective gas environment with a heating rate of 350-400 deg / h with exposure at temperatures of 1500-1800 ° C. The finished product is a mixture of powders of boron carbide, silicon carbide and / or boride transition d-metal side subgroup IV-VI groups of the Periodic system of elements with a high degree of homogenization of the components in volume. The morphology of the particles of the synthesized mixtures is represented by submicron or micron polyhedral particles of boron carbide surrounded by highly dispersed particles of all components of the mixture.

Examples of the invention.

, с=12,12

, пр. гр. R-3m) и карбида кремния SiC (гексагональный, а=3,08

, с=15,12

, пр. гр. P63mc). По данным РЭМ (фиг. 3) морфология частиц синтезированного порошка представлена многогранниками карбида бора, достигающими размера 5 мкм, окруженными ультрадисперсными частицами всех компонентов (В₄С, SiC) со средним размером 300-500 нм.Example 1. Powders of boric acid and silicon dioxide in the ratio of H ₃ BO ₃ : SiO ₂ = 14.41: 1 (wt.) Are mixed and loaded into a crucible for melting at a temperature of 1000 ° C in air, after which the liquid melt is poured onto stainless steel plate. The average particle size of the obtained glass crystalline precursor is less than 100 nm (Fig. 1). At this stage, a high degree of homogenization of the oxide components in the volume is ensured. Further, the glass-crystalline material is crushed and ground to a particle size of less than 1 μm, then mixed with highly dispersed carbon (soot) in the ratio required for the synthesis of oxygen-free compounds. The resulting mixture is placed in a carbon crucible. The synthesis is carried out in vacuum with a heating rate of 400 deg / h with an exposure of 1 hour at a temperature of 1700 ° C. According to x-ray phase analysis (Fig. 2), the synthesis product is a powder mixture of phases of boron carbide B ₄ C (rhombohedral, a = 5.61

, c = 12.12

, sp. gr. R-3m) and silicon carbide SiC (hexagonal, а = 3.08

, s = 15.12

, sp. gr. P63mc). According to SEM (Fig. 3), the morphology of the particles of the synthesized powder is represented by boron carbide polyhedra reaching a size of 5 μm, surrounded by ultrafine particles of all components (B ₄ C, SiC) with an average size of 300-500 nm.

, с=12,09

, пр. гр. R-3m), карбида кремния SiC (гексагональный, а=3,08

, с=15,12

, пр. гр. P63mc) и диборида титана TiB2 (гексагональный, а=3,03

, с=3,23

, пр. гр. Р6/mmm). По данным РЭМ (фиг. 6) морфология частиц синтезированного порошка представлена многогранниками карбида бора размером 0,3-1,0 мкм, окруженными наночастицами всех компонентов (В₄С, SiC, TiB₂) со средним размером ~ 50 нм.Example 2. Powders of boric acid, silicon dioxide and titanium dioxide in the ratio of H ₃ BO ₃ : SiO ₂ : TiO ₂ = 28.19: 1.67: 1 (wt.) Are mixed and loaded into a crucible for melting at a temperature of 1400 ° C in air, after which the liquid melt is poured onto a stainless steel plate. The average particle size of the obtained glass crystalline precursor is less than 200 nm (Fig. 4). At this stage, a high degree of homogenization of the oxide components in the volume is ensured. Further, the glass-crystalline material is crushed and ground to a fineness of less than 1 μm, then mixed with soot in the ratio required for the synthesis of oxygen-free compounds. The resulting mixture is placed in a carbon crucible. The synthesis is carried out in vacuum with a heating rate of 400 deg / h with an exposure of 1 hour at a temperature of 1600 ° C. According to x-ray phase analysis (Fig. 5), the synthesis product is a powder mixture of phases of boron carbide B ₄ C (rhombohedral, a = 5.60

, s = 12.09

, sp. gr. R-3m), silicon carbide SiC (hexagonal, а = 3.08

, s = 15.12

, sp. gr. P63mc) and titanium diboride TiB2 (hexagonal, а = 3.03

, s = 3.23

, sp. gr. P6 / mmm). According to SEM data (Fig. 6), the morphology of the particles of the synthesized powder is represented by boron carbide polyhedra with a size of 0.3-1.0 μm, surrounded by nanoparticles of all components (B ₄ C, SiC, TiB ₂ ) with an average size of ~ 50 nm.

Claims (1)

 A method of obtaining highly dispersed heterophasic powder compositions comprising boron carbide and one or more of the following compounds: silicon carbide, borides of transition d-metals of a subgroup of groups IV-VI of the Periodic Table of the Elements, characterized in that the initial oxygen-containing sources of boron, silicon and / or d-metals are pre-homogenized by co-melting them in air and then reduced with highly dispersed carbon (soot) in a vacuum or in a protective gas environment at temperatures 1500-1800 ° C.

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