RU2573146C1 - COMPOSITION OF CARBON BLANK FOR OBTAINING SiC/C/Si CERAMICS AND METHOD FOR OBTAINING SiC/C/Si PRODUCTS - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: composition of carbon blank for SiC/C/Si - ceramics includes milled artificial graphite with density from 1.7 to 1.85 g/cm³ particle size less than 50 mcm, 63-50 mcm and 100-63 mcm and organic binding agent (the remaining part). Claimed are compositions, which contain 80 wt % of artificial graphite with particle size less than 50 mcm or obtained by addition into said composition of powders with particle size 63-50 mcm and 100-63 mcm of graphite of the same density with different ratios of powders of different fractions. Method of obtaining siliconcarbide products consists in production of carbon blank by mixing composition components, its moulding and/or pressing, burning in inert medium, thermal-processing and soaking with silicon melt. Pressing is realised at pressure 100-350 kg/cm², and before soaking with silicon melt carbon blank is shaped, close to shape of final product, by mechanical processing.

EFFECT: obtaining products with increased stability from siliconcarbide ceramic with different content of residual carbon.

2 cl, 5 dwg, 1 tbl, 3 ex

Description

The invention relates to the field of production of ceramic materials based on silicon carbide (SiC) and can be used to obtain products of high resistance for use as structural in various industries - oil and oil refining, chemical, metallurgical, food, military-industrial complex, housing and communal services, etc.

A known composition for producing ceramics based on silicon carbide, the composition of which prior to impregnation with molten silicon includes a carbon-containing component and a filler, which can be used as the so-called "primary" silicon carbide, as well as a temporary binder or plasticizer [Silicon carbide materials. Gnesin G.G. M., "Metallurgy", 1977., 216 S.].

The closest technical solution is the composition of the carbon preform for the production of siliconized antifriction materials (US 4435538, C08K 3/34, published 06.03.1984), including carbon powder, a binder - phenol-formaldehyde resin and glass metal in the following ratio of components, mass. %:

carbon 65-85 binder 12-30 sitall 3-5

There is a disadvantage associated with the complexity of processing the initial matrix blank, due to the presence of the abrasive phase of the glass in it. In addition, the materials obtained using this composition have little possibility of varying the content of silicon carbide fraction, residual silicon and carbon. This limits the area of use of the obtained silicon carbide based composites and makes them applicable mainly in antifriction products.

The problem to which the invention is directed, is to obtain SiC / C / Si ceramics with a low content of residual silicon and a given content of residual carbon, superior in characteristics to the known siliconized graphites and reaction-bonded silicon carbide ceramics, as well as in the manufacture of products of complex shapes from SiC / C / Si ceramics.

The technical result achieved by the implementation of the claimed invention is to obtain SiC / C / Si ceramics with a density of up to 3.1 g / cm ³ , reducing the content of residual silicon and porosity of the material at the outlet, controlling the content of residual carbon.

The technical result is achieved due to the fact that the composition of the carbon preform for the preparation of SiC / C / Si ceramics includes carbon and an organic binder, crushed artificial graphite with a density of 1.7 to 1.85 g / cm ³ with particle sizes is used as carbon less than 50 microns, 63-50 microns and 100-63 microns, the rest is an organic binder in the following ratio of components, mass. %:

graphite powder with particle sizes less than 50 microns 80 binder rest or graphite powder with a particle size of 63-50 microns 25 graphite powder with particle sizes less than 50 microns 55 binder rest or graphite powder with a particle size of 100-63 microns 30-40 graphite powder with a particle size of 63-50 microns 30-20 graphite powder with particle sizes less than 50 microns twenty binder rest

During pressing, the organic binder joins the graphite particles, after annealing in an inert medium, passing into the coke residue of 35-40%, while the open porosity with a pore size of at least 20 μm is retained in the volume of the carbon preform, which is sufficient for the complete delivery of the silicon melt into the volume of carbon-containing blanks. For the preparation of carbon filler powders, graphite with a density of 1.7 to 1.85 g / cm ^{3 is used} , since powders prepared from less dense graphite completely dissolve in the silicon melt, and powders from denser graphite do not have the desired reactivity.

Varying the phase composition of the powders of the carbon billet, as well as the pressing pressure allows you to get graphite billets with a density of from 0.9 g / cm ³ to 1.46 g / cm ³ . After impregnation with molten silicon, in this way, SiC / C / Si ceramics with a density of 2.32 g / cm ³ for the most dense carbon preform up to 3.1 g / cm ³ for the least dense with different residual carbon contents are obtained. The presence in the volume of the material of residual carbon in the inventive ceramic is required for some applications, for example in tribotechnology.

The implementation of the invention is illustrated by drawings and an example of a specific implementation:

FIG. 1. The microstructure of the carbon preform with a density of: a) 1.24 g / cm ³ , b) 0.93 g / cm ³ .

FIG. 2. Change in the phase composition of SiC / C / Si materials after impregnation with molten silicon, depending on the density of the carbon blanks:

a) ρ _angle = 1.46 g / cm ³ : SiC-C-Si (25-70-5), ρ _sic = 2.32 g / cm ³ ; b) ρ _angle = 1.28 g / cm ³ : SiC-C-Si (40-50-10), ρ _sic = 2.45 g / cm ³ .

FIG. 3. Change in the phase composition of SiC / C / Si materials after impregnation with molten silicon, depending on the density of the carbon blanks:

a) ρ _angle = 1.16 g / cm ³ : SiC-C-Si (70-25-5), ρ _sic = 2.75 g / cm ³ ; b) ρ _angle = 0.91 g / cm ³ : SiC-C-Si (92-0-8), ρ _sic = 3.10 g / cm ³ .

Example 1

Carbon powders are obtained by crushing and grinding graphite wastes of the EG-84M grade with a density of 1.73 g / cm ³ (used in the manufacture of brushes for electric machines) on a hammer mill and ball mill, sieving on fractions used for preparing the charge: 100- 63 microns, 63-50 microns and less than 50 microns; pulverbakelite of the SFPN-011L brand according to TU 2257-111-05015227-2006 is used as a binder. Mixing carbon powders with a binder is performed for 30 minutes on a drunk barrel mixer.

The blanks are pressed in a hydraulic press at a pressure of 100 kg / cm ² - 350 kg / cm ² .

Then annealing (carbonization) of the workpieces is carried out in a protective atmosphere at a temperature of 900 ° C for 8 hours. For different ratios of graphite powders of various fractions, the amount of binder and pressing pressure, graphite blanks with a density ranging from 0.9 to 1.46 g / cm ³ are obtained. In FIG. 1 (a, b) shows the microstructure of carbon blanks with a density of 1.24 g / cm ³ and 0.93 g / cm ³ .

The preforms are impregnated with a molten silicon in a high-temperature vacuum furnace at a temperature of 1850 ° C for 20 minutes. This is followed by cooling and unloading.

After impregnation with molten silicon of carbon preforms with a density of 0.9 to 1.46 g / cm ³ , SiC / C / Si ceramics with a density of 2.32 g / cm ³ for the most dense carbon preform up to 3.1 g / cm ³ for carbon blanks with a density of 0.9 g / cm ³ .

Table 1 presents the parameters of SiC / C / Si ceramics.

From table 1 it follows that changing the phase composition of the carbon billet powders within the specified limits and pressing pressure allows you to control the content of residual carbon in the ceramic material, to obtain SiC / C / Si ceramics with a density of up to 3.10 g / cm ³ , to minimize the content of residual silicon.

The strength indices of siliconized products for compression and bending increase with increasing density and content of the silicon carbide phase.

In FIG. 2, 3 shows the microstructure of SiC / C / Si materials, according to table 1.

A known method for producing SiC / C / Si ceramics is the impregnation with molten silicon of artificial graphite blanks with the addition of primary silicon carbide. [Silicon carbide materials. Gnesin G.G. M., "Metallurgy", 1977. 216 p.]

The closest technical solution is the method of manufacturing siliconized antifriction products described in the patent (US 4435538, C08K 3/34, publ. 06.03.1984). The method consists in injection molding (170 ° C, 100 kgf / cm ² ) of a carbon preform, the composition of which consists of carbon powder with particle sizes of 10-500 μm, a glass powder (a given proportion of Al ₂ O ₃ - 10, CaO - 12, MgO - 9, Na ₂ O - 5, the rest is SiO ₂ ) and a phenolic binder. Further, the preforms are subjected to calcining annealing at a temperature of 1000 ° C in vacuum with the formation of a fine structure of the glass metal phase uniformly distributed over the volume in the form of small crystals. After annealing, the resulting calcined base (carbon-containing preform) can be machined to give it a shape close to the shape of the finished product. Finally, to obtain the product, the workpiece is subjected to silicon melt silicon at a temperature of 1950 ° C.

This method has drawbacks in that the calcined carbon preform contains a fine crystalline glass phase necessary to give the preform mechanical strength before machining. The presence of the abrasive phase of the ceramic in the workpieces leads to increased wear of the tools in the case of the use of machining the workpieces before impregnation with molten silicon.

The problem to which the claimed invention is also directed is to obtain products of a given complex shape from SiC / C / Si ceramics using processing modes applied to low and medium density graphites.

The technical result achieved by the implementation of the claimed invention is to facilitate the mechanical processing of carbon preforms prior to impregnation with molten silicon, to avoid deformation of carbon preforms subjected to impregnation with molten silicon, to obtain complex parts from SiC / C / Si ceramics with a density of up to 3.1 g / cm ³ .

The technical results indicated by the applicant are achieved due to the fact that the abrasive fractions that wear tooling and equipment, reduce the mechanical strength of the carbon-containing workpiece and do not allow the mechanical processing of the carbon-containing workpiece by traditional methods used for low-carbon, are excluded from the composition for the workpiece subjected to interaction with the silicon melt - and medium-dense graphites (carbide tools - drilling, turning and milling, machining on CNC machines Y).

Technical results are also achieved due to the fact that the method of obtaining products from silicon carbide ceramics includes the manufacture of a carbon blank by mixing the composition according to this invention, molding and / or pressing at a pressure of 100 kg / cm ² - 350 kg / cm ² , annealing in an inert medium, machining the carbon billet with a carbide tool and melt impregnation of silicon in a vacuum furnace.

When pressing carbon blanks by varying the pressure within the indicated limits, the amount of residual carbon in the SiC / C / Si ceramic can be controlled. For the highest pressing pressure, the amount of residual carbon is maximum up to 70% (Fig. 2a), and the lowest indicated pressing pressure allows to obtain high-density SiC / C / Si ceramics in the absence of residual carbon, FIG. 3b (table 1). Case studies and photographs of SiC / C / Si products illustrate these cases.

FIG. 4. The body of the temperature meter in a hot gas stream: carbon billet before impregnation with molten silicon (a) and after impregnation with molten silicon (b).

FIG. 5 High-temperature equipment for an experimental setup of complex shape with cavities in the volume after silicon impregnation of the carbon blank of the part.

Example 2

To manufacture the body of the temperature meter in a hot gas stream from a cylindrical carbon billet, the manufacturing process of which is described in Example 1 using a pressing pressure of 100 kg / cm ² , the workpiece is cut by processing on a CNC machine with a given program (Fig. 4a). After the workpiece is impregnated with molten silicon (Example 1), the finished part is obtained from high-density SiC / C / Si ceramics (Fig. 4b). After impregnation with molten silicon, dimensional changes of parts amount to tenths of a percent, i.e. their geometric shape is practically unchanged.

Example 3

For the manufacture of stop valves operating in an aggressive environment at high temperature from a cylindrical carbon blank, the manufacturing process of which is described in Example 1 using a pressing pressure of 350 kg / cm ² , blanks of parts that have a complex shape are cut by machining on a CNC machine with a given program, the use of turning and milling. The finished part is obtained by impregnating the workpiece with molten silicon (Fig. 5) and subsequent finishing machining. The structure of the material of the part contains a high amount of residual carbon, which provides dry lubrication of the rubbing parts and a sufficient amount of silicon carbide phase to ensure mechanical characteristics and high resistance to aggressive working environment.

All obtained carbon blanks according to the proposed invention have sufficient strength for their machining on drilling, turning, milling, CNC machines with conventional carbide tools, using processing modes applied to low and medium density graphites.

If you want to obtain a part with a polished / polished surface or to ensure the size with high accuracy (up to hundredths of a millimeter), then when machining a carbon billet, an allowance of 0.5 to 1 mm per size for finishing machining is provided.

Claims (2)

1. The composition of the carbon preform for producing SiC / C / Si ceramics, which includes carbon and an organic binder, characterized in that the quality of the carbon is crushed artificial graphite with a density of from 1.7 to 1.85 g / cm ³ with particle sizes less than 50 microns, 63-50 microns and 100-63 microns, the rest is an organic binder in the following ratio of components, mass. %:
graphite powder with particle sizes less than 50 microns 80 binder rest or graphite powder with a particle size of 63-50 microns 25 graphite powder with particle sizes less than 50 microns 55 binder rest or graphite powder with a particle size of 100-63 microns 30-40 graphite powder with a particle size of 63-50 microns 30-20 graphite powder with particle sizes less than 50 microns twenty binder rest 2. A method of obtaining SiC / C / Si products, including the manufacture of a carbon blank from the composition according to claim 1 of this invention by mixing, molding and / or pressing at a pressure of 100 kg / cm ² - 350 kg / cm ² , annealing in an inert medium, machining with carbide tools and impregnation with a molten silicon in a vacuum furnace.

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