RU2400521C2 - Procedure for production of self-sintered mesophase powder for structural materials - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to procedure for production of self-sintered mesophase carbon powder for structural materials consisting of carbonisation of peck to formation of mesophase matrix, in crumbling, and in extracting in organic solvent with successive filtration and drying. Prior to carbonisation peck is mixed with a modified additive of few-layer carbon nano-structures added at amount of 0.3-1.0 wt %; also peck is carbonised in interval of temperatures 430-470°C at rate of temperature rise 0.5-1.5 degree per minute.

EFFECT: production of material with high physic-mechanical and operational characteristics.

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Description

The invention relates to a technology for producing raw materials for the production of dense graphite isotropic structural materials and products based on them for electroerosion processing, nozzles for continuous casting of steel and alloys.

The raw material for the production of graphitized structural materials with high density and strength is self-sintering mesophase carbon powder.

A known method of producing mesophase carbon powder company Kawasaki (KMFS) used in the production of carbon blocks [1]. The powder is obtained by extraction with an organic solvent of pyrolyzed coal tar pitch with the release of mesophase spheres, which are formed during heating and separation, followed by filtration.

The production process consists of 4 stages:

1. Heat treatment of pitch, which is the starting material.

2. Extraction with an organic solvent followed by filtration.

3. Firing.

4. Classification (grinding, sieving).

Along with coal tar pitch, to obtain a mesophase powder according to the above scheme, oil pitch can be used, which heat treat at a temperature of 440-450 ° C [2].

Mesophase powders are obtained from low carbonized semi-coke. The closest conditions for obtaining a low-sulfurized coke are the temperature-time conditions for the formation of a mesophase matrix in the process of producing coke with a pseudo-isotropic structure from coal tar pitch [3].

The process of processing coal tar pitch involves starting heating the high-temperature pitch to a liquid state and subsequent carbonization of the pitch melt by raising the temperature to 550 ° C. The temperature of the molten pitch is raised at a speed of no more than 20 ° C / h from the temperature of the fluid state 300 ° C to the temperature of the onset of carbonization and the formation of mesophase particles in the isotropic carbonizable mass of the pitch 400 ° C.

Upon reaching this temperature, conditions are maintained that stimulate the growth of the number and size of mesophase particles by slowly increasing the temperature at a rate of not more than 8 ° C / h to a temperature of 480 ° C, at which the formation of the mesophase matrix is completed. By raising the temperature to 550 ° C, which is conducted at a speed of 50 ° C / h, the formed mesophase matrix is fixed by transferring it to the solid state of semicoke.

It is known that in order to increase the physicomechanical properties of materials from self-sintering carbon powders, they are modified by introducing additives. Closest to the proposed technical solution is the use of natural graphite additives of different grain sizes to mesophase carbon powder [4].

The basis of the invention is the task of obtaining a new type of carbon raw material for the production of isotropic composite material with increased values of density, strength and other physico-chemical characteristics.

The solution of this problem is to obtain a self-sintering mesophase carbon powder from carbonized coal raw materials, modified with low-layer nanocarbon, by selective extraction in an organic solvent.

Upon receipt of the carbonized product, the nature of the coal tar pitch itself is of great importance. The composition of the feedstock and the method for producing pitch determine their influence on the quality of the product and the processes of mesophase transformations in the carbonization process.

High-temperature coal tar pitch contains a significant amount of fine dispersed particles in the initial state, which at a temperature above 410 ° C, corresponding to the beginning of the formation of the mesophase, with the appearance of mesophase spheres, are located on their surface. In volumes containing a larger number of dispersed particles, the mesophase spheres are substantially smaller. We can assume that these particles inhibit the growth of spheres, preventing the supply of matter from the pitch phase [5].

In the medium-temperature pitch, the number of dispersed particles is 5-6 times less, therefore, the process of formation and growth of mesophases in the heat treatment process takes place without interference.

At a higher rate of temperature rise, the resulting mesophase spheres are highly isotropic and practically incapable of deformation. With delayed heating, the mesophase particles reach a relatively large size. Due to deformation and subsequent decomposition, they acquire the ability to form a texture and to a high degree of three-dimensional ordering during graphitization.

As the feedstock for carbonization, medium-temperature coal tar pitch was mainly used. Modifying additive of low-layer nanocarbon in the amount of 0.3-1.0 wt.% Was introduced into the initial pitch by mechanical mixing.

Nanocarbon is one of the new forms of carbon. Distinguish single-layer, low-layer and multilayer nanotubes, i.e. nanotubes, the walls of which are formed from one or more layers. Carbon nanostructures have high strength, high electrical and thermal conductivity, low coefficient of thermal expansion, which makes them a promising material as modifying additives in carbon compositions.

Low-carbon (3-4 layers) carbon nanotubes obtained by methane pyrolysis on a specially synthesized catalyst containing molybdenum and cobalt were introduced into the composition of the carbonization feedstock. The specific surface area of the used nanotubes is 600 m ² / g.

The quantitative interval of the introduced additive is due to the fact that when the additive is introduced less than 0.3 wt.%, There are no changes in the properties of the material in terms of strength and physico-mechanical characteristics.

The additive content of more than 1.0 wt.% Leads to deformation and desalination of the samples after firing at 1000 ° C, which indicates an excess of the added additive.

The carbonization process was carried out in the temperature range 430-470 ° C. The choice of the temperature range corresponds to the conditions for the formation of the mesophase matrix before its transition to the solid state of semicoke (480 ° С). The rate of rise of the process temperature of 0.5-1.5 degrees per minute ensures the formation of mesophase spheres of optimal size. The ranges of carbonization temperature and the rate of its rise were selected experimentally and provide the best results for obtaining a mesophase matrix.

The quality of the obtained product for subsequent extraction was evaluated by the content of volatile substances and the content of ash residue. The volatile content characterizes the degree of carbonization of the product and its sintering ability. The ash impurities present in the feedstock undergo practically no changes in the selected temperature range and are present in the composite material, where their content is regulated.

In the carbonized material obtained in the selected temperature-time regimes, the content of volatile substances is 20-30 wt.%, The ash content is not more than 0.3 wt.%.

The carbonated product was subjected to selective extraction in organic solvents at their boiling point for 1 hour. Toluene, benzene and isooctane were used as extractants.

The mesophase powder obtained by extraction of carbonized pitch in an organic solvent, at its boiling point for 1 hour, contains the optimal amount of volatile substances, providing the possibility of obtaining molded samples and their sintering during further processing.

A strict time limit is determined based on research on the selective extraction process.

The solid residue filtered after extraction was dried at a temperature of 110-120 ° C to constant weight. The dried solid residue is a self-sintering mesophase carbon powder. The temperature range of drying is selected empirically. It is such a drying temperature that allows one to obtain self-sintering mesophase carbon powder of the required quality.

The main characteristic of mesophase carbon powders is the ability to sinter. Powders obtained from products with a lower degree of carbonization have a slightly larger liquid-moving layer and give better sintering properties than powders from a highly carbonized residue.

The criterion for assessing the quality of the mesophase carbon powder, characterizing its sintering ability, is the content of volatile substances and the ash content in it. The content of volatile substances is 8-11 wt.%, The ash residue is not more than 0.3 wt.%.

Concrete example

In the medium-temperature coal tar pitch with a softening temperature of 67 ° C according to GOST 10200-83, by mechanical mixing, a modified additive of low-layer nanocarbon was introduced in an amount of 0.3-1.0 wt.%, Then carbonized in the temperature range 430-470 ° C with a process speed of 0 , 5-1.5 degrees per minute in the SNOL electric furnace.

The resulting product, a mesophase matrix, was crushed in a vibration eraser to a fraction of less than 100 μm, then selective extraction was performed on a laboratory apparatus AP Miniplan (Germany) in an organic solvent, which was used toluene according to GOST 5789-78 at its boiling point for 1 hour. Filtration was carried out through a glass funnel on a white strip filter.

The resulting solid residue was dried in a laboratory oven at 110-120 ° C to constant weight.

Model samples with a diameter of 20 mm were formed from the powder thus obtained at a specific pressure of 60-70 MPa, which were heat treated to a temperature of 1000 ° C with a temperature rise rate of 2 degrees per minute in the SNOL laboratory furnace. The calcined samples were graphitized at a temperature of 2500 ° С according to standard conditions in a Tamman furnace.

The modes of production of a carbonized product with a modifying additive to isolate a mesophase carbon self-sintering powder, its qualitative characteristics, production conditions and characteristics of the obtained mesophase powder, as well as the properties of model samples based on it are presented in Table. No. 1, 2, 3.

Table 1.
Modes of obtaining carbonized product with a modifying additive for the allocation of self-sintering mesophase carbon powder and its quality characteristics №№
examples Carbonization modes The output of volatile in-TV,% Ash content,% T-ra, ° C Lifting speed, ° С / min one 420 1,0 47.0 0.23 2 430 1,0 30,0 0.23 3 450 1,0 26.1 0.23 four 470 1,0 22.2 0.23 5 480 1,0 19.2 0.23 6
(prototype) 550 0.8 - 0.4

Table 2.
Production conditions and characteristics of self-sintering mesophase carbon powder No. of examples Extraction modes T-ra drying, ° C The content of volatile in-TV,% Ash content,% T, ° С τ min one 110 60 120 13.0 0.24 2 110 60 115 10.0 0.24 3 110 60 115 9.6 0.24 four 110 60 110 8.0 0.24 5 110 60 110 7.5 0.24 6 (prototype) - - - - -

Table 3.
Table of model samples from self-sintering mesophase powder with a modifying additive No. of examples The number of modif. additives, wt.% Bulk density, dk, g / cm ² Strength at compression, MPa one - 1.80 110 2 0.3 1.90 140 3 0.5 1.92 180 four 1,0 1.89 130 5 1,5 - - 6 (prototype) - 1.81 -

Examples 1, 5 are performed according to modes beyond the scope of the claims.

Examples 2-4 explain the solution proposed by the authors.

Example 6 is made according to the technology specified in the prototype.

From the above examples it follows that the proposed method for producing a self-sintering mesophase carbon powder with the introduction of an additive of low-layer nanotubes provides a higher density and strength of the material based on it when the additive is contained in optimal intervals.

Industrial production of this class of materials is necessary in various branches of technology.

Information sources

1. N. Fukuda, M. Honma // Kawasaki steel tehnical report No. 16, gane 1987, P.114-116.

2. M. Martinezz-Eskandell // Carbon, Vol. 40. 2002. P. 2843-2853.

3. A method of processing coal tar pitch for structural materials. Patent 7 C10C 3/10 No. 2230770. 2004.

4. A. Mirhabibi, B. Rand // Carbon, Vol. 41. 2003, P.1593-1603.

5. Smirnov B.N., Fialkov A.S. Chemistry of Solid Fuels, No. 6, 1969, pp. 60-66.

Claims (1)

A method for producing a self-sintering mesophase carbon powder for structural materials, including carbonization of pitch to form a mesophase matrix, grinding, extraction in an organic solvent, followed by filtration and drying, characterized in that the pitch is mixed with a modifying additive of low-layer carbon nanostructures, added in an amount of 0, before carbonization 3-1.0 wt.%, While the carbonization of the pitch is carried out in the temperature range 430-470 ° C with a rate of temperature rise of 0.5-1.5 degrees per minute.