RU2498957C1 - COMPOSITE CERAMIC MATERIAL IN SiC-Al2O3 SYSTEM FOR HIGH-TEMPERATURE USE IN OXIDATIVE MEDIA - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to ceramic material science, particularly production of a composite material for high-temperature use, based on refractory oxygen-free and oxide compounds. The composite ceramic material for high-temperature use in oxidative media contains aluminium oxide, magnesium oxide and silicon carbide, with the following ratio of components, wt %: Al₂O₃ - 20-50; MgO - 5-10; SiC - the balance. Aluminium oxide and magnesium oxide can have particle size of 120-400 nm and silicon carbide can have particle size of 0.1-5 mcm.

EFFECT: high oxidative and thermal stability.

6 cl, 5 ex, 1 tbl

Description

The invention relates to ceramic materials science, in particular to the production of a composite material for high-temperature applications based on refractory oxygen-free and oxide compounds, characterized by high strength, thermal and oxidative stability, resistance to thermal shock at a temperature gradient of up to 2000 K under conditions of high-speed oxidative flow.

Known composite ceramic material developed jointly by Helsa-Automotive Gmbh & Co and Friedrich-Alexander-Universitet Erlangen-Nurnberg, described in international application WO 2007/003428 A1 of January 11, 2007, including a process for producing porous ceramic material, in which Al ₂ O ₃ protects SiC from oxidation. Composite ceramic material has oxidative stability at temperatures up to 1650 ° C. However, it is known that porous ceramic materials are not used under conditions of exposure to high-speed oxidative flows due to insufficient strength and low erosion resistance.

Known composite ceramic material for high temperature applications, described in Japanese patent JP 3963407 (B2) class C04B 35/66 from 08.22.2007, the authors Soeda Tomomi, Hibino Mitsunobu, Chihara Kenji ("Tokyo Yogyo Co Ltd"), including 5-90 wt.% SiC, 5-90 wt.% Al ₂ O ₃ , 0-20 wt.% carbon. In this case, Al ₂ O _{3 is} also used to increase the oxidative stability of SiC. However, the introduction of free carbon reduces the oxidative stability of the SiC-Al ₂ O _{3 system} , since carbon is characterized by low-temperature oxidizability when heated in oxidizing environments.

The closest in composition and adopted for the prototype is a composite ceramic material containing SiC, Al ₂ O ₃ and MgO with a ratio of components in wt.%: Al ₂ O ₃ - 50-98.9; SiС - 1-40; MgO - 0.1-10 (patent RU No. 2397196 C2, class C04B 35/10, 08/20/2010 "Method for producing composite ceramic material (options)"). This composite ceramic material is used as a luminescent material and is not suitable for high-temperature applications under the conditions of exposure to high-speed oxidizing fluxes for PCT products.

A known group of inventions on methods for producing a composite ceramic material based on mixing powder components containing aluminum oxide, magnesium oxide, silicon carbide, granulating them, subsequent pressing, drying and sintering (see, for example, patent RU No. 2397196 C2, class C04B 35/10, 08/20/2010 "Method for producing composite ceramic material (options)"). The disadvantage is the creation of a nanostructured composite ceramic material, unsuitable for use in aggressive environments with increased oxidative and thermal stability.

The problem to which the invention is directed, is to obtain a high-density composite ceramic material with increased oxidative and thermal stability.

The technical result consists in the possibility of using composite ceramic material in an oxidizing medium at a temperature of 2000 K at an oxidizing flow velocity of 350 m / s.

This is achieved by the fact that a high-density composite ceramic material for use in heat-loaded units of RCT products contains aluminum oxide, magnesium oxide and silicon carbide, moreover, aluminum oxide and magnesium oxide with a particle size of 120-400 nm, with an aluminum oxide content of 20-50 (wt.%) . The method of its preparation is based on mixing powder components containing aluminum oxide, magnesium oxide, silicon carbide, granulating them, subsequent pressing, drying and sintering, while the obtained powder composite mixture is formed by compression at a pressure of 250-300 MPa, then sintering at a temperature of 1700 -1800 ° C and a pressure of 1-1.2 MPa. Stirring is carried out in a planetary mill, granulated with the addition of polyvinyl alcohol (PVA), dried at a temperature of 150-200 ° C and sintering is carried out at 1700-1800 ° C in argon and kept at a final temperature for 2 hours.

Increased resistance to oxidation of the proposed high-density composite material is achieved by introducing into the composition of the oxide components nanodispersed aluminum oxide and nanodispersed magnesium oxide, which during sintering form aluminum-magnesian spinel, the synthesis of which is accompanied by an increase in volume. In addition, the sintering of the material is carried out at a temperature of 1700-1800 ° C, when the diffusion processes during solid phase sintering are most activated. This provides a high-density durable material with high temperature and oxidation resistance.

It is known that Al ₂ O ₃ -MgO is one of the most durable mixtures of oxides. In the Al ₂ O ₃ —MgO system, only one chemical compound is formed — the alumino-magnesian spinel, containing 28.3% MgO and 71.7% Al ₂ O ₃ (wt.%). This compound is stable, its melting point is 2135 ° C. Spinel with MgO forms a eutectic composition of 45% MgO and 55% Al ₂ O ₃ with a melting point of 2030 ° C, and with α-Al ₂ O _{3 an} almost complete series of solid solutions giving an eutectic with alumina at 1925 ° C.

In practice, MgO additive is widely used in the manufacture of durable corundum products. The additive does not lead to a decrease in sintering temperature, but significantly reduces the recrystallization of α-Al ₂ O ₃ . And also the introduction of an additive of finely dispersed magnesium oxide stimulates the defect formation reaction inside nanostructured aluminum oxide and promotes the formation of alumina-magnesian spinel at grain boundaries, which, in turn, dissolving in corundum, causes the formation of vacancies in aluminum. Despite the fact that the presence of vacancies in aluminum contributes to the sintering of corundum grains, a noticeable effect on the kinetics of shrinkage does not occur due to the fact that the spinel layer present on the surface of alumina grains slows down the transport of matter across the boundary, which, in turn, slows down the recrystallization process or grain growth. Corundum crystals acquire a more isometric shape.

Physico-mechanical characteristics were studied on samples with a size of 6 × 6 × 50 (mm) and plates with a size of 63 × 60 × 8 (mm). The compositions of the components and properties of the proposed composite ceramic material, including beyond, are presented in the table.

Example 1

Ceramic powders in the ratio of 15% nanosized magnesium oxide, 35% nanosized aluminum oxide, 50% (wt.) Silicon carbide are ground in acetone on a planetary mill to a fineness of 0.1-5 microns. A molding mass is prepared containing 5% (wt.) Technological binder of polyvinyl alcohol and 95% (wt.) Composite ceramic powder.

Composite charge is compacted by pressing at a pressure of 250-300 MPa. Drying is carried out in air at a temperature of 150-200 ° C. Sintering is carried out at a temperature of 1400-1800 ° C in argon atmosphere at a pressure of 1-1.2 MPa with exposure at a final temperature for 2 hours (Properties in the table).

Example 2

By co-grinding in a planetary mill to a fineness of 0.1-5 microns in anhydrous ethanol, a composite powder mixture is prepared consisting of 40% (wt.) Nanosized aluminum oxide, 50% silicon carbide and 10% nanosized magnesium oxide. Drying is carried out in air at a temperature of 70-80 ° C. A molding mass is prepared containing 5% (wt.) Technological binder of polyvinyl alcohol and 95% (wt.) Composite ceramic powder. Composite charge is compacted by pressing at a pressure of 250-300 MPa. Drying is carried out in air at a temperature of 150-200 ° C. Sintering is carried out at a temperature of 1400-1800 ° C in argon atmosphere at a pressure of 1-1.2 MPa with exposure at a final temperature for 2 hours (Properties in the table).

Example 3

Ceramic powders in the ratio of 7% nanosized magnesium oxide, 33% nanosized aluminum oxide, 60% (wt.) Silicon carbide are ground in acetone on a planetary mill to a fineness of 0.1-5 microns. The crushed mixture is granulated with the addition of 5% (wt.) Polyvinyl alcohol. Composite charge is compacted by pressing at a pressure of 250-300 MPa. Drying is carried out in air at a temperature of 150-200 ° C. Sintering is carried out at a temperature of 1400-1800 ° C in argon atmosphere at a pressure of 1-1.2 MPa with exposure at a final temperature for 2 hours (Properties in the table).

Example 4

A composite powder consisting of 50% (wt.) Nanosized aluminum oxide, 5% nanosized magnesium oxide, 35% silicon carbide is ground in a planetary mill in anhydrous alcohol to a fineness of 0.1-5 microns. Drying is carried out in air at a temperature of 70-80 ° C. The crushed mixture is granulated with the addition of 5% (wt.) Polyvinyl alcohol. Composite charge is compacted by pressing at a pressure of 250-300 MPa. Drying is carried out in air at a temperature of 150-200 ° C. Sintering is carried out at a temperature of 1400-1800 ° C in argon atmosphere at a pressure of 1-1.2 MPa with exposure at a final temperature for 2 hours (Properties in the table).

The proposed high-density composite ceramic material has the following characteristics: density 99% of theoretical, bending strength 500 ± 50 MPa, compressive strength 1400 ± 100 MPa, Vickers hardness 25-27 GPa, K1 _s - 8.5-11.0 MPa · m ^1/2, oxidation resistance ≤0,015 mg / cm ² · s, the operating temperature of 2000 K. The material was tested for resistance teploerozionnuyu at 2000 K under oxidative flow rate of 350 m / s and showed the absence of erosive ash.

Products from the proposed material can be used for the manufacture of heat-stressed parts operating at temperatures up to 2000 K in conditions that require high strength, hardness and oxidation resistance, as well as in conditions of thermal shock, for example, thermocouple covers for continuous monitoring of the temperature of metal melts in the metal industry for the manufacture of cutting tools in the oil and gas industry (valve devices and o-rings of pumps), mouthpieces for I welding, nozzle nozzles for sandblasting machines and sprayers of chemical solutions.

Claims (6)

1. Composite ceramic material for high temperature applications in oxidizing environments, containing aluminum oxide, magnesium oxide and silicon carbide, characterized in that it contains aluminum oxide and magnesium oxide with a particle size of 120-400 nm, and silicon carbide with a particle size of 0.1-5 μm in the following the ratio of components, wt.%: Al ₂ O ₃ - 20-50; MgO - 5-10; SiC - the rest. 2. The method of obtaining a composite ceramic material according to claim 1, based on mixing powder components containing aluminum oxide, magnesium oxide, silicon carbide, subsequent granulation, pressing, drying and sintering, characterized in that the mixture is molded by compression at a pressure of 250-300 MPa sintering is carried out at a temperature of 1700-1800 ° C and a pressure of 1-1.2 MPa. 3. The method according to claim 2, characterized in that the mixing is carried out in a planetary mill. 4. The method according to claim 2, characterized in that it is granulated with the addition of polyvinyl alcohol. 5. The method according to claim 2, characterized in that it is dried at a temperature of 150-200 ° C. 6. The method according to claim 2, characterized in that the sintering is carried out in argon medium with exposure at a final temperature for 2 hours.