Why Diamond has higher melting point than Silicon Carbide?

1 Answer
Sep 23, 2016

Answer:

Neither diamond nor silicon carbide melts at standard pressures.

Explanation:

However, they both sublimate at high temperatures.

Structures

Both diamond and silicon carbide have a tetrahedral covalent network structure.

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Diamond

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Silicon carbide

Physical Properties

Diamond does not melt at ordinary pressures. It converts to graphite and sublimates at about 3680 °C.

Silicon carbide sublimates at about 2700 °C.

Explanation

The difference appears to be caused by the differences in bond lengths and bond strengths.

Silicon carbide has a #"C-Si"# bond length of 186 p.m. and a bond strength of 318 kJ/mol.

Diamond has a much shorter #"C-C"# bond length (154 pm) and stronger bonds (348 kJ/mol).

Thus, it takes more energy to vaporize diamond, and diamond has the higher sublimation temperature.