RU2605257C1 - Polymer composition for producing silicon carbide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical industry for producing heat-resistant highly porous articles from silicon carbide, which are used as filters, heat insulation, absorbents. Polymer composition for producing silicon carbide of stoichiometric composition in form of finished porous articles contains powdered phenol binder based on novolac phenol-formaldehyde resin and urotropin, lubricant in form of zinc stearine or zinc stearate, and a silicon dioxide support, in form of ground quartz fibre from industrial wastes of their production, in following ratio of components, wt%: ground quartz fibre - 45.2-48.7; phenol binder - 46.1-52.0; lubricant - 2.0-5.5.

EFFECT: invention widens raw material sources for producing silicon carbide, improves chemical purity of finished product, as well as rational use of industrial wastes for production of quartz fibre.

1 cl, 1 tbl, 5 ex

Description

The invention is intended for the chemical industry. Heat-resistant highly porous silicon carbide products are used as filters, thermal insulation, absorbents, etc.

Currently, silicon carbide is obtained by heat treatment of mixtures of powders of silica and carbon-containing substances in various furnaces.

It is known from the prior art that silicon carbide is obtained from natural rock - shungite containing silica and carbon [patent RU 2163563 C1, publ. 02/27/2001; patent RU 2169701 C2, publ. 06/27/2001] or from polymer compositions containing shungite [patent RU 2472703 C2, publ. 01/20/2013].

The disadvantage of these technical solutions for producing silicon carbide is the high content of impurities in the resulting silicon carbide.

The closest analogue of the claimed invention, according to the applicant, is a polymer composition for producing stoichiometric silicon carbide in the form of finished porous products, containing a powdery phenolic binder in an amount of 47-48 wt.%, A lubricant in an amount of 3-5 wt.% And a silicon dioxide carrier , which use biosilica in the amount of 48-50 wt.% [patent RU 2542275 C1, publ. 02/20/2015]. Preformed product blanks from the specified polymer composition are heated to 800 ° C in an oxidation protective environment at a rate of 400-600 ° C / h at atmospheric pressure, kept at 800 ° C for 1 hour and cooled with the oven. The synthesis of silicon carbide is carried out in products that have undergone heat treatment at 800 ° C by heating to 1300-1500 ° C at a speed of 400-700 ° C / h at a pressure in the vacuum furnace of 0.02-0.06 kPa.

A disadvantage of the known polymer composition for producing silicon carbide is the presence of impurities in the resulting silicon carbide.

The technical result of the claimed invention consists in expanding the sources of raw materials for producing silicon carbide, increasing the chemical purity of the finished product, as well as in the rational use of industrial waste from the production of quartz fiber.

The specified technical result is achieved by the fact that the polymer composition for producing stoichiometric silicon carbide in the form of porous products contains a powdered phenolic binder, lubricant and silicon dioxide carrier, which is crushed silica fibers from industrial waste from their production, in the following ratio, wt.%:

Ground Quartz Fibers 45.2-48.7 Phenolic binder 46.1-52.0 Grease 2.0-5.5

The polymer composition and the blanks from it are prepared by known techniques adopted in the production of phenolic plastics and products from them [Katsnelson M.Yu., Balaev G.A. Plastics: Properties and Applications: Reference. - 3rd ed. reslave. - L .: Chemistry, 1978. - 384 p.].

In the proposed composition, a commercial phenolic powder binder is used based on novolac phenol-formaldehyde resin and urotropin, which, firstly, allows to obtain workpieces from a composition with crushed silica fiber (SiO ₂ ) and a lubricant in a highly economical manner adopted in the technology of plastics, and, secondly, being a carbon carrier, it allows to obtain stoichiometric silicon carbide.

Quartz fiber has a rare combination of properties: high tensile and compressive strength, incombustibility, heat resistance, low hygroscopicity, resistance to chemical and biological effects. Materials are made from it with high electrical, heat, sound insulation properties and mechanical strength. On the basis of fibrous materials, various types of products are manufactured that successfully replace traditional materials, and also have only their inherent fields of application.

The chemical composition of SiO ₂ (wt.%) Is 99.9%.

Density - 2.21 g / cm ³ .

Softening point - 1670 ° C.

Quartz fiber industrial waste can contain up to 12% of products removed by calcination. The quartz fiber waste crushed into crumbs, for example, in the form of scraps of nonwoven materials, is dosed together with the other components according to the recipe into a vibrating or ball mill, where the fibers are milled and mixed at the same time — the mixture is obtained (examples 1 and 2). It is possible pre-grinding the fiber and subsequent mixing to obtain a mixture (examples 3-5).

Products from the proposed polymer composition withstand high heating rates up to 400-600 ° C / h without cracking in the first heat treatment stage, which is carried out for carbonization of the phenolic binder, and up to 100 ° C / min when heated to 1300-1500 ° C for carbide synthesis . Preliminary heat treatment of quartz fibers is not necessary, as when products are heated to 800 ° C, organic products are completely removed (examples 1, 3-5: the content of organic impurities was 9.85%). To remove free carbon, the products are heated and incubated in air at 700 ° C for 4 hours (examples 1-3, 5).

As a lubricant, substances commonly used in the production of phenolic plastics and products from them can be used [Katsnelson M.Yu., Balaev G.A. Plastics: Properties and Applications: Reference. - 3rd ed. reslave. - L .: Chemistry, 1978. - 384 p.]. Preferably, stearin or zinc stearate is used as a lubricant in amounts that provide the necessary technological properties of the compositions in the manufacture of blanks.

The present invention is illustrated by the following examples.

Example 1

Preform products from the polymer composition obtained in accordance with the recipe shown in Table 1 are heated in an oxidation protective environment, for example, in a coke bed in a chamber or muffle furnace, to 800 ° C at a rate of 600 ° C / h and maintained at this temperature 1 hour, cool with the oven. Heat-treated products are loaded into a vacuum oven and heated to 1400 ° C at a speed of 100 ° C / min at a furnace pressure of 0.02 kPa, kept at a temperature of 1400 ° C for 4 hours and cooled at the indicated pressure. The finished product is characterized by high chemical purity, the absence of difficult to remove inorganic impurities, high porosity and sufficient strength.

Examples 2-5 are performed as described above with the difference that is indicated in table 1 according to the composition of the mixture and the conditions for the preparation of the filler (described above).

X-ray phase analysis of the structure made of the proposed composition of the refractory material in the form of porous products showed that silicon carbide with a cubic structure (a = 4.3573 Å) corresponding to the β-modification was obtained.

The total porosity of the products is 76-88%, open porosity is 74-86%. With such a high porosity and chemical purity of silicon carbide products have a higher mechanical strength compared to the prototype.

Congruent shrinkage of products from the proposed composition upon heating, which results in the processes of carbonization of the phenolic binder and the subsequent formation of silicon carbide, allows the molding of products of complex configuration and to exclude mechanical processing.

Thus, stoichiometric silicon carbide is obtained from the proposed polymer composition in the form of finished highly porous products of a given configuration that do not require additional processing, while in the finished product there are no difficult to remove inorganic impurities. The use of SiO ₂ , obtained by grinding quartz fiber, allows us to solve the problem of rational use of industrial waste and to guarantee the production of a high-purity chemical product - silicon carbide and products from it with high strength.

Claims (1)

A polymer composition for producing stoichiometric silicon carbide in the form of finished porous products, containing a powdered phenolic binder based on novolac phenol-formaldehyde resin and urotropine, a lubricant that uses zinc stearin or zinc stearate, and a silicon dioxide carrier, characterized in that it is a dioxide carrier silicon use crushed quartz fibers from industrial waste of their production, while the components are present in the composition in the following ratio, wt.%:
Ground Quartz Fibers 45.2-48.7 Phenolic binder 46.1-52.0 Grease 2.0-5.5