As one of the commonly used abrasive materials, silicon carbide(Carborundum) has many advantages in thermodynamics, chemicals, and physics. It is suitable for lapping，abrasives，paints and refractories. The properties of silicon carbide are demonstrated in the following aspects:
The properties of silicon carbide in chemicals:
Silicon carbide has strong oxidation resistance.
When heated to 1000 °C in the air, silicon carbide only oxidizes on the surface, forming a silicon dioxide film. The film can protect the silicon carbide material from oxidation.
When heated to 1300 °C, cristobalite began to precipitate in the silicon dioxide film layer. The change of crystal form caused the film layer to crack, and the oxidation rate increased slightly.
When heated to 1500-1600 °C, the silicon dioxide film layer will thicken, and the ability to protect against oxidation will increase. So silicon carbide could be very stable at high temperatures. When heated to above 1627 °C, the oxidation resistance of silicon carbide will decline rapidly.
Silicon carbide has strong chemical stability.
The chemical stability of silicon carbide is also due to its ability to resist oxidation.
The effects of various corrosive substances on silicon carbide are as follows:
| Reactive compound substance | Temperature ( °C) | Reaction & Erosion of silicon carbide |
| MgO | 740 | No reaction |
| 1000 | Reaction begin | |
| 1555 | Decomposition reaction of silicon carbide occurs obviously | |
| CaO | 1000 | Reaction begin |
| 1690-1740 | Produce calcium carbide and calcium silicate | |
| Al2O3 | 1700 | No reaction |
| TiO2 | 1720 | Reaction in the presence of carbon |
| Cr2O3 | 1600 | The reaction occurs and chromium silicate is formed |
| Fe2O3 & FeO | 1300 | Reaction begin |
| 1500 | Obvious reaction | |
| 1500-1600 | Fe2O3 reacts with SiC to form iron silicate in the presence of carbon | |
| CuO | 800 | Reaction begin |
| 1500 | Reaction to produce copper silicate | |
| Na2O3 | In an oxidizing atmosphere, silicon carbide is completely oxidized | |
| KOH | Calcium carbide decomposes and melts | |
| Alkaline Carbonate | Attacks and decomposes silicon carbide | |
| Na2CO3 | 900 | Attacks and decomposes silicon carbide |
| K2CO3 | 1100(for 15 min) | Silicon carbide is completely dissolved |
| CaS | 525 | No reaction |
| FeS | 1200(for 15 min) | Silicon carbide is corroded |
| Sodium silicate | 1300 | In a strong oxidizing atmosphere, silicon carbide decomposes |
| Calcium silicate | 1700(for 15 min) | No reaction |
| 2FeO. SiO2 | 1400(for 15 min) | Reaction |
The properties of silicon carbide in physics :
The hardness of silicon carbide
The hardness of silicon carbide is between fused alumina and diamond. The Mohs hardness of Black silicon carbide is 9.2-9.3, Mohs hardness of green silicon carbide is 9.4-9.5. Vickers hardness of carborundum is 3100-3400kg/mm2. The hardness of silicon carbide will decrease with the increase in temperature. At a high temperature of 1200 °C, the hardness of silicon carbide can reach twice that of fused alumina.
The toughness of silicon carbide
The toughness of silicon carbide abrasive refers to the difficulty of breaking under the action of external force. Taking F46 grit as an example, the toughness of carborundum tested by the static pressure method is about 68-78%.
Compared with fused alumina, the mechanical strength of silicon carbide is higher. F120 for example, the compressive strength of silicon carbide is 186KN/cm2, and the compressive strength of corundum abrasive is 100KN/cm2.
The color of silicon carbide
Silicon carbide is divided into black silicon carbide and green silicon carbide. Its color is caused by the content and type of impurities in the crystal. Black silicon carbide is light blue-black, the purity of first-grade black SiC is 98%. Green silicon carbide is green, and the purity of first-grade green SiC is 99%.
Thermal conductivity and linear expansion coefficient of silicon carbide
The thermal expansion coefficient of silicon carbide at different temperatures (x10-6/ °C):
| 100-500 °C | 100-900 °C | 15-1000 °C | 25-1700 °C | 20-1000 °C | 20-1525 °C | 20-1000 °C | 20-1470 °C |
| 4.1 | 4.47 | 4.35 | 4.3 | 5.2 | 4.9 | 4.3 | 4.5 |
It can be seen that at a temperature of 25-1400 °C, the average thermal expansion coefficient of silicon carbide is 4.4×10-6/°C, while the thermal expansion coefficient of fused alumina is 7-8×10-6/°C.
The electrical conductivity of silicon carbide
Due to the introduction of impurities, silicon carbide has semiconductor properties. The conductivity of silicon carbide increases rapidly with the increase of the electric field intensity, and it has a nonlinear characteristic. In addition, the conductivity of silicon carbide also changes with temperature.