RU2261848C2 - Method for preparing beta-sialone powder - Google Patents

Abstract

FIELD: chemical technology.

SUBSTANCE: method for preparing β-sialone powder by carbothermal reduction of kaolin involves thermal treatment of charge in nitrogen atmosphere at 1710-1780°C for 5-25 min. Charge comprises a carbon component with particles size 20-500 nm. An average size of particles of prepared β-sialone powder can be regulated by using the disperse carbon component of charge with the required size of particles. Invention provides the development of rapid and simple in realization method for preparing β-sialone powder providing preparing β-sialone with the required size of particles.

EFFECT: improved preparing method.

2 cl, 3 ex

Description

The invention relates to the production of sialon materials and compositions used in various fields of science and technology.

The known method [1] for producing highly porous sialonic material using clay and carbon components as the initial mixture in the following ratio of components in the mixture, wt.%: Clay component - 76-82, carbon component - 18-24. In this case, kaolin is taken as a clay component, and graphite as a carbon component. The method includes forming a briquette by pressing the mixture at a pressure of 25-100 MPa and then annealing it in a nitrogen atmosphere at 1400-1450 ° C for 3-4 hours.

The disadvantage of this method is the large (more than 3 hours) time of high-temperature firing.

The closest in technical essence and the achieved result to the proposed technical solution is a method [2] for producing β-sialon (Si _6-z Al _z N _8-z O _z , z = 2.7-4.0) from mineral raw materials, in particular from a mullite-forming rock (kaolin), by means of its carbothermic reduction at a temperature of 1300-1500 ° C for 0.5-6 hours in a nitrogen atmosphere. The method involves preliminary heat treatment of the initial mullite-forming rock in the presence of alkali to remove amorphous silicon oxide and obtain a mixture that is active with carbothermic nitriding with a specific surface of the aluminosilicate component of more than 50 m ² / g.

The disadvantages of this method are (1) the complexity and duration of the process due to the presence of complex operations of preliminary preparation of mullite-forming rocks, as well as (2) a large dispersion in particle sizes of the obtained β-sialon powder.

The present invention solves the problem of creating a faster and easier to implement method for producing β-sialon powder, which allows, in addition, to obtain β-sialon powder with a given particle size.

The problem is solved in that when obtaining β-sialon powder by carbothermal reduction of kaolin in a nitrogen atmosphere, a charge containing a carbon component with a particle size of 20-500 nm is used, and its heat treatment is carried out at a temperature of 1710-1780 ° C for 5-25 minutes .

In this case, a charge can be used with a given particle size of the carbon component, determined on the basis of the ratio

D _c = D _SIALON / 1.93,

where D _c is the average particle size of the carbon component introduced into the charge,

D _SIALON is the average particle size of the resulting β-sialon powder.

The technical result of the invention is the conversion of a solid aluminosilicate component of the charge into a gaseous state and, accordingly, accelerating its reaction with a solid carbon component and gaseous nitrogen.

The technical result is achieved by choosing the temperature and time regime of carbothermal reduction of kaolin in a nitrogen atmosphere. At a temperature of 1710-1780 ° C, the thermal decomposition product of kaolin (aluminosilicate component) is reduced to gaseous oxides Al ₂ O and SiO, after which it quickly (within several minutes) interacts with the particles of the carbon component together with nitrogen so that the particle of the carbon component transforms into a particle of β-sialon. The transfer of aluminosilicate components into the gas phase makes it possible to increase the rate of the β-sialon formation reaction. The participation of the carbon component as a substrate in the formation of β-sialon in the interaction with gaseous nitrogen, Al ₂ O and SiO allows you to control the particle size of the resulting β-sialon by using a dispersed carbon component with a given particle size.

The proposed method is as follows. The starting component for the preparation of β-sialon is kaolin (Al ₂ O ₃ · 2SiO ₂ · 2H ₂ O) and a carbon component, which can be used as furnace soot. The mixture is prepared in one of the known ways. For example, kaolin (70-80 wt.%) And furnace black (20-30 wt.%) Are mixed in the presence of water at a moisture content of 60-70% in a paddle mixer for 15-40 minutes. The resulting suspension is dried at a temperature of 110-120 ° C. The dried mixture (charge) in a graphite crucible is placed in a flow furnace with a graphite heater. A flow of nitrogen is organized through the working volume of the furnace at a flow rate of 1-5 l / min. The furnace is heated to a temperature of 1710-1780 ° C at a speed of 50-100 ° / min and maintained at this temperature for 5-25 minutes. Cooling is carried out together with the oven to room temperature. The product is removed from the graphite crucible, frayed thoroughly and product certification is carried out using x-ray phase, electron microscopy and chemical analyzes.

The proposed method for producing particles of β-sialon with a certain size is illustrated by the following examples.

Example 1. Take 16 g (80 wt.%) Of Prosyanovsky kaolin and 4 g (20 wt.%) Of carbon in the form of soot PM-75 (average carbon particle size - 40 nm). The components are thoroughly mixed in the presence of water (humidity 65%), dried to constant weight and placed in a graphite crucible in a flow furnace with a graphite heater. The nitrogen flow through the working volume of the furnace is 1 l / min. The furnace is heated at a rate of 50 ° C / min. up to 1710 ° C. The crucible with the mixture is kept at this temperature for 5 minutes in a stream of nitrogen. The crucible is cooled to room temperature with the oven. According to chemical and x-ray phase analyzes, the resulting product is a β-sialon of the general formula Si ₃ Al ₃ O ₃ N ₅ , and the impurities are SiC, AlN. The yield is 87%. According to scanning electron microscopy, the average particle size of the obtained powder is 110 nm.

Example 2. Take 35 g (70 wt.%) Kyshtym kaolin and 15 g (30 wt.%) Carbon in the form of soot PM-100 (average carbon particle size - 30 nm). The components are thoroughly mixed in the presence of water (humidity 70%), dried to constant weight and placed in a graphite crucible in a flow furnace with a graphite heater. The consumption of nitrogen through the working volume of the furnace is 5 l / min. The furnace is heated at a rate of 70 ° C / min to 1780 ° C. The crucible with the mixture is kept at this temperature for 25 minutes in a stream of nitrogen. The crucible is cooled to room temperature with the oven. According to chemical and x-ray phase analysis, the resulting product is a β-sialon of the general formula Si ₃ Al ₃ О ₃ N ₅ , impurities - SiC, AlN. The yield is 86%. According to scanning electron microscopy, the average particle size of the obtained powder is 76 nm.

Example 3. Take 30 g (75 wt.%) Glukhovetsky kaolin and 11.25 g (25 wt.%) Carbon in the form of soot PM-150 (average carbon particle size - 20 nm). The components are thoroughly mixed in the presence of water (humidity 60%), dried to constant weight and placed in a graphite crucible in a flow furnace with a graphite heater. The nitrogen flow through the working volume of the furnace is 3 l / min. The heating of the furnace is carried out at a speed of 100 ° C / min to 1750 ° C. The crucible with the mixture is kept at this temperature for 15 minutes in a stream of nitrogen. The crucible is cooled to room temperature with the oven. According to chemical and x-ray phase analysis, the resulting product is a β-sialon of the general formula Si ₃ Al ₃ О ₃ N ₅ , impurities - SiC, AlN. The yield is 85%. According to scanning electron microscopy, the average particle size of the obtained powder is 65 nm.

The choice of parameters for the implementation of the proposed method is due to the following.

When the carbon content in the initial charge is less than 20 wt.%, The resulting material contains corundum as an impurity. When the carbon content in the initial charge is more than 30 wt.%, The resulting material contains more than 18 wt.% SiC.

When the mixing time of kaolin and carbon is reduced to less than 15 minutes, the spatial conjugation of the particles of kaolin and the carbon component in the mixture necessary to achieve a technical result does not occur.

When the flow rate of nitrogen passed through the working zone of the furnace is less than 1 l / min, its quantity is insufficient for the carbothermic nitriding reaction to occur.

When the furnace is heated to a heat treatment temperature at a rate of less than 50 ° / min, the reaction mixture is at a temperature <1500 ° C for a long time, at which kaolin mullitization occurs, which impedes the achievement of a technical result and leads to a decrease in the content of β-sialon in the synthesis product.

Insufficient time (less than 5 min) for heat treatment of the reaction mixture at the synthesis temperature leads to incomplete chemical reactions and, as a result, to carbon contamination of the product. Heat treatment for more than 25 min leads to sintering (increase in particle size) of the reaction product and, therefore, prevents the regulation of the particle size of the resulting β-sialon.

A decrease in the carbon particle size of less than 20 nm leads to the fact that the synthesis results in β-sialon powder with a particle size less than the upper boundary of the region of critical sizes of β-sialon (D ⁺ _SIALON = 40-60 nm), which causes its high sintering activity and, therefore, prevents the regulation of the particle size of the resulting β-sialon. An increase in carbon particle size of more than 500 nm reduces the rate of formation of β-sialon.

Thus, the proposed method for producing β-sialon allows not only to reduce the synthesis time of β-sialon, but also to control the particle size of the β-sialon powder in a simple technological way, eliminating a number of additional operations.

Sources of information used:

1. Pat. RU 2191759, Antsiferov V.N., Gilev V.G. A method of obtaining a porous material, IPC C 04 V 35/599, 1999.10.26.

2. Pat. EP 0289440, Moya Corral Jose S., De Aza Pendas Salvador, Morales Poyato Francisco, Valle Fuentes Francisco J., Osendi Miranda Isabel, Martinez Caceres Rafael, Corral Martinez Ma Paz, A method for the production of beta'-sialon based ceramic powders , IPC C 01 B 21/082, C 04 B 35/58, 1988.11.02.

Claims (2)

1. The method of producing β-sialon powder by carbothermal reduction of kaolin in a nitrogen atmosphere, characterized in that the mixture contains a carbon component with a particle size of 20-500 nm, and its heat treatment is carried out at a temperature of 1710-1780 ° C for 5-25 minutes 2. The method according to claim 1, characterized in that the charge is used with a given particle size of the carbon component, determined based on the ratio D _C = D _SIALON / 1.93, where D _C is the average particle size of the carbon component introduced into the charge; D _SIALON is the average particle size of the resulting β-sialon powder.