WO2008013478A1

WO2008013478A1 - Composite sialon-based ceramic material and a method for the production thereof

Info

Publication number: WO2008013478A1
Application number: PCT/RU2007/000385
Authority: WO
Inventors: Nikolay Victorovich Stepanov; Svetlana Evgenyevna Stelmak; Petr Anatolievich Aleksandrov; Evegeniy Viktorovich Burlakov; Mikhail Andreevich Pavlov; Evgeniy Stepanovich Lukin
Original assignee: Nikolay Victorovich Stepanov; Svetlana Evgenyevna Stelmak; Petr Anatolievich Aleksandrov; Evegeniy Viktorovich Burlakov; Mikhail Andreevich Pavlov; Evgeniy Stepanovich Lukin
Priority date: 2006-07-28
Filing date: 2007-07-13
Publication date: 2008-01-31
Also published as: RU2006127397A; RU2329997C2

Abstract

The group of inventions relates to refractory materials, in particular to a composite sialon-based ceramic material and to the method for the production thereof. The invention can be used for producing construction materials, machine parts, metal-cutting tools, metal-shaping tools, plain bearings etc. The inventive composite sialon-based ceramic material also comprises calcium, sodium, magnesium and a plasticiser, wherein aluminium is embodied in the form of a powder, at the following component ratio expressed in mass %: 91.7-81.4 silicon dioxide (SiO2), 3.0-5.0 aluminium powder (Al), 0.1-0.5 magnesium (Mg), 0.01-0.1 calcium (Ca), 0.001-0.01 sodium (Na), 5.0-10.0 nitrogen (N2) and 0.1-3.0 plasticiser (polycarbosilane). The inventive method for producing articles made of sialon consists in pre-grinding silicon dioxide, in preparing a mixture by mixing aluminium powder, magnesium, sodium, nitrogen, plasticiser and ground silicon dioxide, in hydrostatically forming a semi-finished product and subsequently in exposing said semi-finished product to multi-stage heat treatment.

Description

Composite ceramic material based on sialon and a method for producing products from it.

The field of technology.

The proposed group of inventions relates to refractory materials, in particular, to a composite ceramic material based on sialon, and a method for producing products from it.

The present invention can be used for the manufacture of building materials, mechanical engineering parts, metal cutting tools, metal forming tools and for plain bearings, etc.

The prior art.

Known composite ceramic material containing silicon nitride, aluminum nitride, silicon oxide, aluminum oxide, boron nitride, carbon, boride, silicide, carbide, nitride, transition metal oxide Sh-Ul group of the periodic system, silicon carbide and / or silicon boride, boron carbide and at least one metal oxide with a particle size of 0.1 to 10.0 μm from the group comprising lithium, beryllium, magnesium, calcium, strontium, barium. (see RF application N293045157 according to class C04B35 / 58, 1993). The known material has high thermal resistance, as well as erosion and corrosion resistance to metal melts.

However, it has a number of significant drawbacks, namely, the high content of components, most of which are expensive.

The closest in technical essence to the proposed solution is a composite ceramic material based on sialon, containing silicon dioxide, aluminum, nitrogen and a plasticizer (weed of conference reports on “Application high-strength ceramics in engineering products))

. 1967, article S. Tfmebauashi, Natiopal Ipdustrial Researsh Ipstitute ° F Kuushu, Shuku-machi, Tosu City, Saga Ip Rref.Darap.Somrositiops the Si ₆ - _{_{_Z}} AI _Z O _Z N _8-Z system », 1967). In addition, the composition of the material includes oxides of titanium, iron, potassium, while using almost pure aluminum 99.7%.

Closest to the technical nature of the present invention is a method for producing products from a composite material based on sialon, including preparing a mixture of components, grinding it, forming a semi-finished product and obtaining a finished product in a nitrogen atmosphere (conference proceedings on the use of high-strength ceramics in mechanical engineering products)) article S. Tfmebauashi, Natiopal Ipdustrial Researsh Ipstitute ° F Kuushu, Shuku-mashi, Situ Tosu, Saga Rref, Jarap, Ip Somrositiops the Si _6- zAl _z 0 ₂ N8 _-z system », 1967)

The disadvantages of the group of known technical solutions, namely, composite material and the method of obtaining products from it are:

A large amount of aluminum in the material complicates the control of the aluminothermy process, which leads to an increase in the porosity of the material;

- the inclusion in the material composition of components with different affinities for oxygen and different deoxidation temperatures complicates the manufacturing process of the product, the structure of the sialon in which is heterophasic, and this leads to a sharp decrease in the mechanical properties of the sialon.

-use only pure silica SiOg (sand) without clay impurities, because the product is obtained by hot pressing at high temperatures 1750-2200 ⁰ C ₅ and this leads to high energy costs.

- a long time of the process of obtaining the product in a nitrogen atmosphere at very high pressures up to 500A. The problems solved by the proposed group of inventions are the creation of composite ceramic material based on sialon and a method for producing products from it, which can reduce the time to obtain products with improved physical and mechanical characteristics , i.e. reduce the porosity of the product and thereby increase its thermal insulation properties.

The technical result in the present invention is achieved by creating a composite ceramic material based on sialon containing silicon dioxide, aluminum, nitrogen, in which according to the invention, calcium, sodium and magnesium and a plasticizer are additionally introduced, and aluminum is used in the form of aluminum powder, with the following components, in mass%: silicon dioxide (SiCh) 91.7-81.4 aluminum powder (Al) 3-5 magnesium (Mg) 0.1-0.5 calcium (Ca) 0.01-0.1 sodium (Na) 0.001-0.01 nitrogen (Ng) 5-10 plasticizer 0.1-3 The invention is also characterized in that Polycarbosilane is used as a plasticizer.

This allows introducing into the composition of the composite ceramic material additional ionized nitrogen necessary to increase the physicomechanical properties of the material. The proposed composite ceramic material is cheap compared to the prototype, because cheap raw materials used:

- use any sand with clay and any fraction; - use aluminum production waste in the form of powder with any content of impurities;

- the use of polycardosilane even with small doses ensures the introduction of ionized nitrogen into the material due to which it is possible to carry out a method for producing the product at low pressure (1- l, 5 atm)

The technical result in the present invention is achieved by creating a method of manufacturing a product from Sialon, including preparing a mixture of components, grinding, forming a semi-finished product and obtaining the finished product in a nitrogen atmosphere, in which, according to the invention, silicon dioxide is pre-crushed, the mixture is prepared by mixing aluminum powder, magnesium calcium, sodium, nitrogen, plasticizer and crushed silicon dioxide, then hydrostatic formation of the semi-finished product is carried out Ia with subsequent multi-stage heat treatment.

The invention is also characterized in that multistage heat treatment is carried out at the first stage by a slow temperature increase for 90-100 min to a temperature of 180-200 ⁰ C, then heated to 600 -750 ⁰ C with a shutter speed of 10-15 minutes, and further heating to 1400-1450 ⁰ C with exposure for 15-30 minutes.

The proposed method allows to reduce the time of manufacturing products, due to the additional saturation of the mixture components of ionizable azone released from polycarbosilane and the introduction of azone.

The proposed composite ceramic material and method of manufacturing a product from Sialon are environmentally friendly, because There are no emissions of harmful substances into the atmosphere and an increase in oxygen in the air due to the use of nitrogen.

A method of manufacturing a product from sialon is as follows:

Pre-crushed silicon dioxide, for example in a jet mill.

Depending on the specified technological properties of the proposed material, the content of the components included in the composition of the material is selected in the following limits, wt%: silicon dioxide (SiCh) 91, 7-81, 4 aluminum powder (Al) 3-5 magnesium (Mg) OD-0.5 calcium (Ca) 0.01 - 0.1 sodium (Na) 0.001-0.01 nitrogen (N ₂ ) 5 -10 However, it should be noted that the physical and mechanical properties of the proposed composite material are most affected by the content of sand, aluminum powder and plasticizer, (polycarbosilane), therefore, Table l shows the results of their various contents in s and their influence on the properties of the material. The mixture is prepared by mixing aluminum powder, magnesium (Mg), calcium (Ca), sodium (Na), nitrogen (Ng), a plasticizer and crushed silicon dioxide.

Dispersing the aluminum powder in a solution of a ceramic-forming polymer (polycarbosilane) in benzene or another solvent is designed for uniform distribution of aluminum in the volume of sand.

Then, the semi-finished product is hydrostatically formed by hydrostatic pressing, the modes of which are known and the applicant does not claim to be new.

Subsequent multi-stage heat treatment is carried out to obtain the finished product.

Multistage heat treatment is carried out at the first stage by slowly increasing the temperature for 90-100 minutes to a temperature of 180-200 ⁰ C at a rate of 2 ° C / min, then heating to 600 -750 ⁰ C with a shutter speed of 10-15 minutes, and then heating to 1400-1450 ⁰ C with holding for 15-30 minutes.

The tests showed that only with such heat treatment modes can you get the desired technical result. Deviations from the proposed modes and the side of increasing or decreasing the intervals leads to an increase in processing time, deterioration of physical and mechanical properties, etc. Heating to 180-200 ⁰ C at a rate of 2 ° C / min is caused by the fact that the dissociation of carbosalan into silicon carbite, hydrocarbons and atomic nitrogen proceeds slowly, while silicon carbide and atomic nitrogen are absorbed by the porous semi-finished product.

In the process of obtaining sialon from sand, aluminum and carbosilane, silicon is restored from its dioxide due to aluminothermy with the release of heat of reaction and subsequent nitriding of silicon, also with the release of heat.

So that exotherm during deoxidation of sand and nitriding of silicon does not lead to melting of aluminum and silicon, which is inevitable leads to porosity in the product, aluminum and sand are coated with a solution of polycarbolan, which passivates exothermy, because it has a high heat capacity, and the mixture is heated to a temperature of 650-700 ⁰ C, it is necessary to reduce the power supply of the heater so that there is no overheating due to esothermic reactions of alumotherapy and silicon nitriding.

The use of ionized azone, even at atmospheric pressure, provides a high nitriding rate, and, as a result of non-porous sintering in a short time of 30-45 minutes. Thus, the properties of sialon depend on the amount of aluminum and carbosilane, but both components increase the cost of the product.

If we take the cost of burnt brick as a standard, then the product from sialon should not contain more than 5% of aluminum and carbosilane.

Physico-mechanical tests of the obtained samples of sialon show the optimality of the selected concentration

In addition, starting from an aluminum concentration of 3%, whiskers of sialon grow on the internal surfaces of the product, significantly reducing its thermal conductivity.

The use of aluminum powder and carbosialon with atomic nitrogen leads to the formation of sialon on the inner and outer surfaces of the semi-finished product during heating of thin-fiber crystals, which on the inner surface sharply reduces the thermal conductivity of the product, because excludes convection, and from the external surface it can be collected as a by-product for use in electrical engineering, in the manufacture of filters, etc.

The use of atmospheric pressure of nitrogen due to its ionization and dramatically reduces the cost of thermal equipment, increases productivity, because it does not require the injection of nitrogen, its cooling before depressurization, accelerates the loading of the kiln.

Table.l

Industrial applicability. The proposed composite ceramic material based on sialon and a method for producing products from it were obtained and tested.

We used nitrogen from the air, washed river sand SiO ₂ , aluminum powder, plasticizer.

In this case, samples were obtained with a density of 99.6 ÷ 99.8% of theoretical with a shrinkage of about 1%.

The obtained physicochemical properties at a temperature of 20 ⁰ C are shown in table 2

Here σ and σ _mfd _czhat - flexural strength and compression at a temperature

20 ⁰ C,

E is the modulus of elasticity, To TR - coefficient of thermal expansion, Q - thermal conductivity, Δ T - thermal cycling

Termotsiklirov ^'Contents were conducted 1000 times with the change of temperature from -100 ⁰ C to 100 ⁰ C by lowering articles into the liquid. It was found that there are no visible changes in the material.

When carrying out the sintering process under a pressure of 1 kbar, the bending strength increases 3 times to 900 MPa. In terms of structure, the proposed composite ceramic material based on sialon is a nanocrystalline material with a noticeable proportion of sialon glass. The high binding energy in the molecular components of the material (Si ₃ N ₄ , AlN, Al ₂ O ₃ , Si ₂ N ₂ O, SiC) determines its high strength and heat resistance. The proposed material does not melt even at 3200 ⁰ C, but begins to sublimate with the absorption of a large amount of heat. The practical absence of water absorption (<0, l%) and chemical resistance make it possible to use the proposed material as a building material with high resistance to atmospheric and seismic effects.

For construction purposes, experimental building blocks of 300 x 300 x 250 mm in size with an average specific gravity of 0.5-0.8 g / cm ³ and a block weight of 10-16 kg were made.

Due to the air gaps in the block filled with whiskers, the total thermal conductivity per block is reduced by 4.5 times. Blocks are interconnected using sealant and structural elements of the blocks obtained in their manufacture. Sealants need very little due to the high accuracy of the manufacture of blocks.

The proposed composite ceramic material is approximately 10 times more durable than brick and concrete, has 3-5 times lower coefficient of thermal expansion, has

10 times more frost resistance and 10-15 times less moisture absorption than conventional building materials. The properties of the proposed material make it possible to make of it not only the walls of the house, but also the foundation, roof covering and other elements. Due to its high compressive strength and low specific gravity, the use of sialon for underwater structures, rescue chambers, etc. is promising.

The use of sialon in metallurgy and the chemical industry is very promising for the lining of high-temperature units where high chemical resistance is required.

Claims

Claim.

1. Composite ceramic material based on sialon, containing silicon dioxide, aluminum, nitrogen, characterized in that it additionally contains a plasticizer, calcium, sodium and magnesium, polycarbosilane is used as a plasticizer, and aluminum is used in the form of aluminum powder, with the following content components, in mass%: silicon dioxide (SiCh) 91.7-81.4 aluminum powder (Al) 3-5 magnesium (Mg) 0.1-0.5 calcium (Ca) 0.01-1.1 sodium ( Na) 0.001-0.01 nitrogen (Na) 5-10 plasticizer 0.1-3

2. The composite ceramic material according to claim 1, characterized in that polycarbosilane is used as a plasticizer

3. A method of manufacturing products from Sialon, including preparing a mixture of components, grinding, forming a semi-finished product and obtaining the finished product in a nitrogen atmosphere, characterized in that the silicon dioxide is pre-crushed, the mixture is prepared by mixing aluminum powder, plasticizer and crushed silicon dioxide, then produce hydrostatic formation of a semi-finished product with its subsequent multi-stage heat treatment.

4. The method according to p. 3, characterized in that the multi-stage heat treatment is carried out at the first stage by slowly increasing temperature for 90-100 minutes to a temperature of 180-200 ⁰ C, then heating to 600 -750 ⁰ C with a shutter speed of 10-15 min., and further heating to 1400-1450 ⁰ C. with exposure for 15-30 minutes.