Siliconized Graphite Vs. SiC

Carbon graphite material has self-lubrication, high mechanical strength, low coefficient of friction, high temperature resistance, good anti-wear, widely used in machinery, chemical industry, petroleum, instrumentation, pumps and other fields. Conventional graphite materials are less than ideal in terms of wear resistance and corrosion resistance, while silicified graphite, as a novel engineering material, has the properties of both carbon graphite and silicon carbide, and is used in a wide range of applications.

What is graphite silicide?

Siliconized graphite is a composite material composed of a silicon carbide layer coated on the surface of graphite material. Silicon carbide layer thickness of 1 ~ 1.5mm, silicon carbide layer and graphite matrix combined closely. The hardness of graphite silicide is actually the hardness of SiC, which is second only to diamond, boron nitride, boron carbide, and higher than the hardness of tungsten carbide and aluminum trioxide.

Graphite silicide not only has the self-lubrication of carbon graphite materials, good electrical and thermal conductivity, thermal shock resistance and sealing, but also has the advantages of high strength, oxidation resistance, chemical corrosion resistance of silicon carbide, and is particularly suitable for heavy loads, high temperatures, and other demanding occasions, so the graphite silicide materials are more and more widely used in the field of sealing, friction, chemical industry, metallurgy, and aerospace and nuclear industry.

Preparation of graphite silicide

There are three main production methods of graphite silicide chemical vapor deposition (CVD), chemical vapor reaction (CVR) and liquid silicon permeation reaction method.

1. Chemical vapor deposition (CVD)) method

The gas containing silicon and carbon through the high temperature graphite substrate thermal decomposition, generating SiC deposited on the surface of the graphite substrate. Raw materials for trichloromethylsilane (CH3SiC3), silicon tetrachloride, hydrogen, silicon vapor and so on. The deposition temperature range is wide, from 1175℃ to 1775℃. SiC layer generated by this method is very dense, uniform thickness, the general thickness of about 0.1 ~ 0.3 mm, but the combination of SiC and graphite substrate for the pure mechanical bonding, the bonding force is weak, in the rapid change in temperature SiC layer is prone to cracking, peeling.

2. Chemical vapor phase reaction (CVR) method

Raw materials for coke powder and excess quartz sand or amorphous silica powder, when heated to 2000 ℃ when the chemical reaction occurs, the generation of SiO vapor, SiO vapor and carbon substrate reaction to generate SiC. SiC layer and carbon substrate two have no obvious interface, the bond is very strong, in the case of sudden changes in temperature and high load will not come off, but the CVR method is the SiO gas penetration of carbon substrate to carry out the reaction, so still retain the porous nature of the carbon substrate. However, CVR method is the reaction of SiO gas infiltration into the carbon matrix, therefore, it still retains the porous nature of the carbon matrix, when used as a sealing material, it is necessary to use resin impregnation or CVD method to fill the pores.

3. Liquid Silicon Permeation

This method also belongs to a kind of CVR. Under vacuum conditions, heated to 1700-1900 ℃, the carbon substrate directly immersed in molten silicon liquid, liquid silicon gradually penetrate into the carbon substrate, the reaction occurred to generate SiC. 99.9999% of the raw material for the pure silicon. SiC layer thickness of up to 3.5 mm. After the reaction, the carbon substrate contains about 17% of the free silicon to fill the base of the pore, so that the substrate has become dense and impermeable. However, the presence of free silicon reduces the corrosion resistance and high-temperature oxidation resistance of silicified graphite.

Difference between siliconized graphite and SiC

1.Siliconized graphite (siliconized graphite) is a composite material composed of a silicon carbide layer coated on the surface of graphite material. Siliconized graphite hardness is SiC hardness, it is second only to diamond, boron nitride, boron carbide, than tungsten carbide, aluminum oxide and other high hardness. Graphite silicide can be used as phosphoric acid, phosphorus amine and hydrofluoric acid pump bearings. In addition, the semiconductor industry, as silicon epitaxial growth of the heat sheet substrate and fixture and the manufacture of artificial joints, artificial heart valves, artificial tooth roots.

2.Silicon carbide (SiC) is made of quartz sand, petroleum coke (or coal coke), wood chips (the production of green silicon carbide need to add salt) and other raw materials through the high temperature smelting resistance furnace. Silicon carbide also exists in nature as the rare mineral, moissanite. Silicon carbide is also known as carbon silica. In contemporary C, N, B and other non-oxide high-tech refractory raw materials, silicon carbide for the most widely used, the most economical one, can be called gold steel sand or refractory sand. At present, China's industrial production of silicon carbide is divided into black silicon carbide and green silicon carbide two kinds, are hexagonal crystals, specific gravity of 3, 20 ~ 3, 25, microhardness of 2840 ~ 3320kg/mm2

What is Graphite Silicide and what industries is it used in?

Siliconized graphite is a composite material consisting of a silicon carbide layer coated on the surface of graphite material. The hardness of graphite silicide is the hardness of SiC, which is second only to diamond, boron nitride, boron carbide, and higher than tungsten carbide and aluminum trioxide. Graphite silicide can be used as phosphoric acid, phosphoric acid and hydrofluoric acid pump bearings. In addition, the semiconductor industry, as silicon epitaxial growth of the heat sheet substrate and fixture and the manufacture of artificial joints, artificial heart valves, artificial tooth roots. Silicon carbide is made from quartz sand, petroleum coke (or coal coke), wood chips (salt is added to produce green silicon carbide) and other raw materials by high-temperature smelting in a resistance furnace. Silicon carbide also exists in nature as a rare mineral, moissanite. Silicon carbide is also known as carbon silica. In contemporary C, N, B and other non-oxide high-tech refractory raw materials, silicon carbide for the most widely used, the most economical one, can be called gold steel sand or refractory sand. At present, China's industrial production of silicon carbide is divided into two kinds of black silicon carbide and green silicon carbide, are hexagonal crystals, specific gravity of 3, 20 ~ 3, 25, microhardness of 2840 ~ 3320kg/mm2.

Graphite silicide as a kind of silicon carbide reinforced graphite composite material, not only has the high hardness, high wear resistance and high temperature oxidation resistance of silicon carbide, but also has the good self-lubricating properties of graphite, thermal conductivity and low coefficient of thermal expansion, which can be applied to mechanical seals and other high-precision parts.

The sealing end face of the mechanical seal is composed of the rotating dynamic ring installed on the shaft and the static ring fixed on the seat, which requires the material to have good wear resistance, low coefficient of friction, corrosion resistance, high thermal conductivity, and strong seismic performance, and the silicide graphite can precisely meet these requirements. It is measured, when the PV value (sealing pressure and speed of the product) up to 147MPa-m/s, carbide steel ring that produces thermal stress cracks, and graphite silicide self-paired sealing ring and its Pv value up to 687MPa-m/s without damage. In addition can also be used for shielding pumps and high-powered diesel engine water seals and other seals. Graphite silicide can be used as phosphoric acid, phosphoric acid and hydrofluoric acid pump bearings. In addition, the semiconductor industry, as silicon epitaxial growth of the heating plate substrate and fixture and the manufacture of artificial joints, artificial heart valves, artificial tooth roots, etc.

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