RU2379257C1 - Method for making alumina ceramic products - Google Patents

Abstract

FIELD: construction engineering.

SUBSTANCE: method for making alumina ceramic products involves mixing fine aluminium oxide with a modifying additive of nanocrystalline aluminium oxide powder with particle size 4-6 nm prepared by gasoline. It is followed with thermoplastic moulding and baking.

EFFECT: higher durability and microhardness of products.

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Description

The invention relates to a technology for producing ceramic products based on aluminum oxide with high mechanical characteristics.

Ceramics based on aluminum oxide or corundum ceramics are solid, wear-resistant, chemically inert and mechanically strong materials that can work for a long time under conditions of mechanical and thermal stresses, abrasive loads, and exposure to aggressive environments. High physical and technical characteristics and operational qualities of corundum ceramics can be realized in a material with a fine uniform structure, well-formed grain boundaries and a density close to theoretical. An effective modern method for solving this problem is the use of ultrafine powders in the production of ceramics, which can significantly increase the mechanical strength, wear resistance, surface quality of products, and expand the scope of ceramics.

A known method of producing ceramics from aluminum oxide without the introduction of sintering additives by hot isostatic pressing (US patent No. 5352643, C04B 35/10; publ. 04.10.94). Ceramic material has a grain size of less than 3 microns, a high uniformity of structure. The compressive strength of this ceramic was 5566 MPa, bending 908 MPa.

The method has great technical complexity and is not applicable for mass production.

A known method of sintering ceramic nanopowders at high pressure and low temperature (US patent No. 6395214, H05B 6/00; publ. 08.05.02). Ceramics obtained by this method have a density close to theoretical, high hardness, strength, wear resistance. The disadvantages of this method are the complexity of the process, the need for complex expensive equipment and the difficulty of manufacturing products of complex shape.

A known method of manufacturing aluminosilicate and corundum products using an ultrafine component added to the material in the form of a suspension, in an amount of 20-48% by weight. (RF patent No. 2153482, C04B 35/18; publ. 06/18/98). After molding and firing at 1500 ° C, the compressive strength of ceramics is 200-300 MPa. The ceramic obtained by this method does not have sufficiently high mechanical characteristics.

Closest to the proposed technical solution (prototype) is a method of producing ceramics from a mass based on alumina with the addition of plasma-chemically obtained aluminum oxide (RF patent No. 2150442, C04B 35/10; publ. 10.06.2000). Alumina-based ceramic mass contains 3.0-30.0 wt.% As a modifying additive. plasma-chemically obtained alumina. By pressing followed by sintering at 1500 ° C, ceramic was obtained with a bending strength of up to 640 MPa and a microhardness of 16–20 GPa.

The purpose of the claimed technical solution is to increase the strength and microhardness of corundum ceramics.

This goal is achieved by the fact that in the mixture of finely dispersed aluminum oxide add 5-30% wt. nanocrystalline alumina with a particle size of 4-6 nm, which is pre-treated with gasoline-solvent. Nanosized particles are sintering active; as a result, at a relatively low firing temperature, a fine homogeneous ceramic structure is formed, providing its increased mechanical strength and microhardness. To achieve the hardening effect of ceramics, the amount of nanocrystalline powder in the mixture should be such that it fills the voids between the larger grains of alumina as much as possible. In order to prepare a thermoplastic slip from a charge with a high content of nanosized particles, it is necessary to significantly increase the amount of temporary technological binder. This will inevitably lead to a decrease in the density of the semi-finished product and will not allow to realize the benefits of introducing nanocrystalline additives. The proposed technical solution consists in the fact that the nanocrystalline alumina powder is pre-treated with gasoline before mixing it with the main fraction. For processing used gasoline solvent for the rubber industry. Processing nanocrystalline powder with gasoline-solvent allowed to maintain its nanoscale structure, reduce the amount of thermoplastic binder introduced to 14-20% wt. and get a slip with good casting properties.

To achieve a technical result, powders were selected as the main component for the preparation of ceramics:

- alumina obtained by calcining alumina G-00 at 1550 ° C, followed by grinding in a ball mill to a specific surface of 4300 cm ² / g;

- aluminum oxide obtained by calcining alumina G-00 at 1450 ° C with the addition of H ₃ BO ₃ , CaCO ₃ , SiO ₂ followed by grinding in a ball mill to a specific surface of 3500 cm ² / g. According to the phase composition, the main component is α-corundum with a particle size of 1-3 microns.

As a nanocrystalline additive, alumina powder with a crystallite size of 4-6 nm was selected; by phase composition it is 100% γ-Al ₂ O ₃ . The nanocrystalline powder was pre-treated with gasoline by mixing in a high-speed mixer, followed by removal of excess liquid by natural drying.

Nanocrystalline powder was mixed with the main component until a uniform distribution of the additive was achieved over the volume of the main component. A thermoplastic slip with a temporary binder content of 14–20% wt. Was prepared from the obtained mixture. For the molding of products, a high-performance method of plasticized casting was chosen, which allows one to obtain products of complex configuration. Ceramics were sintered in a gas furnace at a temperature of 1550 ° C.

The resulting ceramics has a homogeneous fine-grained structure with a particle size of 1-5 μm, its microhardness is up to 24 GPa, and the tensile strength under static bending is up to 800 MPa.

Examples of the method

Example 1. Alumina obtained by calcining alumina at 1550 ° C, followed by grinding in a ball mill to a specific surface of 4300 cm ² / g, was mixed with 10% wt. nanocrystalline alumina powder with an average size of 5 nm, pre-treated with gasoline. A thermoplastic slip with a content of 20% wt. Was prepared from the obtained mixture. temporal ligament. Formed by thermoplastic molding, the samples were fired at a temperature of 1550 ° C. The ceramics had a microhardness of 22 GPa, and a tensile strength with static bending of 650 MPa.

Example 2. Alumina obtained by calcining alumina G-00 at 1450 ° C with the addition of H ₃ BO ₃ , CaCO ₃ , SiO ₂ , followed by grinding in a ball mill to a specific surface of 3500 cm ² / g, was mixed with 30% wt. nanocrystalline alumina powder with a particle size of 4-6 nm, pre-treated with gasoline. A thermoplastic slip with a content of 14% wt was prepared from the obtained mixture. temporal ligament. Formed by thermoplastic molding, the samples were fired at a temperature of 1550 ° C. Ceramics had a microhardness of 24 GPa, tensile strength with static bending of 800 MPa.

As can be seen from the presented examples, the proposed method solves the problem of obtaining corundum ceramics, characterized by high mechanical characteristics.

Claims (1)

A method of manufacturing products from corundum ceramics, comprising mixing finely dispersed alumina with a modifying additive of alumina powder, forming a billet and firing, characterized in that nanocrystalline alumina powder with a particle size of 4-6 nm, pre-treated with gasoline, is used as a modifying additive molding is carried out by thermoplastic molding.