RU2370435C2 - Carbon-containing composition for making silicicated components - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of structural components based on carbon or graphite, particularly silicicated graphite. The composition contains carbon in form of powdered graphite with particle size of not more than 200 mcm in amount of 10-80 wt %, silicon carbide in amount of 10-60 wt % and binder - the rest. Carbon and silicon carbide are in inverse proportion and their total content in the composition is in the range 60-95 wt %. Density of the obtained material is 2.92-3.08 g/cm³, and ultimate compression strength is 4550-4970 kgf/cm².

EFFECT: increased corrosion resistance.

2 cl, 2 tbl

Description

The invention relates to the production of structural products based on carbon or graphite, in particular siliconized graphite, intended for use in thrust and thrust bearings, plain bearings, mechanical seals of pumps pumping various liquids, including with abrasive particles, in the manufacture of cladding panels in chemical and metallurgical industries, in the production of glass and mineral fibers, etc.

A known composition for producing siliconized refractory products, including graphite (3-35 wt.%), Silicon (3.0-12.5 wt.%), Silicon carbide (1.5-40 wt.%), Coke (20- 30 wt.%), The rest of the phenolic binder (USSR copyright certificate No. 1072398).

Siliconized graphite obtained using this composition has a rather large fraction of the carbon component due to the poor silicability of coke, and therefore a significant proportion of free (unreacted) silicon, which is exacerbated by the early introduction of free silicon into the initial composition. A significant amount of free silicon in the final material (up to 25-30 wt.%) When using, for example, the material as facing plates can lead to its evaporation from the material due to the high vapor pressure of silicon, i.e. to the appearance of porosity and a decrease in strength. A similar picture occurs when in contact with aggressive melts, such as liquid glass or basalt.

The closest technical solution is a carbon-containing composition for siliconizing, taken as a prototype (application UK No. 1437178, 1976), including carbon, silicon carbide and a binder.

A disadvantage of the known technical solution is that the products obtained on the basis of this composition have low strength and also residual porosity, which reduces the physical and mechanical characteristics of products from this composition.

The problem solved by the present invention is to increase the density, strength and erosion resistance of products based on the proposed composition.

The problem is solved in that the composition has the following composition, wt.%:

Carbon 10-80 Silicon carbide 10-60 Binder rest

The total proportion of carbon and silicon carbide in the composition is in the range of 60-95 wt.%, And the amount of carbon and silicon carbide in the composition are inversely proportional. As carbon, crushed graphite with a particle size of not more than 200 microns is used.

Silicon carbide introduced into a graphite charge has a dual function: it fills small pores that are not accessible to liquid silicon during liquid-phase impregnation; secondly, silicon carbide particles are crystallization centers of secondary silicon carbide formed during high-temperature impregnation of a carbon-containing base.

Thus, the mixture, consisting of graphite chips and silicon carbide powder, helps to obtain after impregnation with liquid silicon dense, durable products, which are a continuous structure consisting mainly of silicon carbide. Moreover, the density of the final products over the entire volume of the product is above 2.7 g / cm ³ .

The products are manufactured according to the following technology: artificial graphite (waste, marriage by cracks and chips) is first crushed into pieces from 5-10 to 30 mm in size, then crushed in a hammer mill, ball mill to a particle size of not more than 200 microns and mixed with powder silicon carbide dosed into a working mixing machine, to which a binder is then added - phenol-formaldehyde resin or pitch. Mixing the mixture is carried out for 1-2 hours.

Products are pressed in a mold heated to 60-90 ° C, at a pressure of 50-120 kgf / cm ² . Preliminary heat treatment is carried out in an electric furnace with a working temperature of up to 300 ° C, without relieving pressure from the mold, for 15-30 minutes, after which the mold is cooled and the workpiece or part is pressed out. Firing is carried out at 950-1100 ° C in a coke bed for 24 hours.

The samples are impregnated with liquid silicon in a high-temperature vacuum furnace in a vacuum of no worse than 10 mm Hg. at a temperature of 1950 ° C for 15 minutes, followed by cooling and unloading the furnace.

Table 1 presents the tested compositions. As a binder in the examples of table 1, a phenolic powder binder (TFP) was used. Similar results occur when using pitch, so they are not given in the table.

Some physico-mechanical properties of the obtained compositions after silicification in comparison with the prototype are shown in table 2.

Corrosion resistance of siliconized products was evaluated in NaOH at 80 ° C for 1000 hours according to GOST 13819-68.

From table 2 it follows that the introduction of primary silicon carbide according to examples 1-9 in all cases leads to an increase in density compared with the prototype, strength and corrosion resistance, which is associated with a decrease in the material of free silicon, which is washed out in an alkali medium, and an increase in the proportion silicon carbide.

Siliconized products based on a carbon-containing composition, in addition to the above, can be used as nozzles for spraying air with abrasive particles, burners in thermal gas furnaces, broaches in the manufacture of wire, etc.

Table 1 Fractional composition of the charge The composition of the mixture according to examples No., wt.% one 2 3 four 5 6 7 8 9 Graphite fifteen 25 45 fifty 55 60 70 65 fifty Silicon carbide 80 70 45 thirty 35 25 fifteen twenty 25 Binding SFP 5 5 10 twenty 10 fifteen fifteen fifteen 25

table 2 The composition of the charge (example No.) The density of the material after impregnation, g / cm ³ The limit of compressive strength, oszh, kgf / cm ² Weight loss over 1000 hours in 40% NaOH at 80 ° C,% one 3.08 4970 0.16 2 3.04 4950 0.17 3 3.00 4850 0.19 four 2.95 4620 0.20 5 2.98 4750 0.20 6 2.94 4600 0.21 7 2.92 4580 0.21 8 2.96 4650 0.19 9 2.92 4550 0.22 Prototype 2.65 3590 0.41

Claims (2)

1. A carbon-containing composition for producing siliconized products, including carbon, silicon carbide and a binder, characterized in that crushed graphite with a particle size of not more than 200 μm is used as carbon in the following ratio, wt.%:
carbon - 10-80
silicon carbide - 10-60
the binder is the rest
while the total proportion of carbon and silicon carbide in the composition is in the range of 60-95 wt.%. 2. The carbon-containing composition according to claim 1, characterized in that the amounts of carbon and silicon carbide in the composition are inversely proportional.