1.1 Heating Method for Oxidation
By calcining Silicon Carbide Powder, we could have free C and graphite oxidized by oxygen in the air and turn into CO2 or CO.
Here are 2 experiments:
Experiment 1 : Calcining temperature :900℃
Calcining period: 3 hours
Result: Carbon could be eliminated totally
Experiment 2: Calcining temperature : 450～560℃
Calcining period : 4 hours
Oxidation media: air
Result: ratio of elimination : 98. 6%～99. 2%
Conclusion: With certain temperatures and calcining-periods, the ratio could be 98%.
Because of the high BET of Silicon Carbide Powder, when grits are put through too much heat, there will be a thin oxidation film covering grits and prohibiting the elimination of carbon.
1.2Chemical Method for Oxidation
To eliminate free C in Silicon Carbide Powder, we would use acids or add inorganic oxidants into the acids.
Kinds of acid: 1. Nitric acid,
2. Sulfuric acid,
3. Perchloric acid
4. Mixed acid of those three acids
Inorganic oxidants ：KMnO4 and K2Cr2O7
This chemical method could eliminate free C by oxidizing and turning them into gas. However, these strong oxidability acids would have serious corrosion on workers and machines. This method can’t be wildly applied in large-scale industrial silicon carbide manufacture.