Amorphous carbon may be formed in a variety of ways, but its preparation in a state of purity is difficult. It is liberated in the following reactions:
- Decomposition of carbonaceous matter at high temperature (sugar, vegetable and animal charcoal, coke).
- Deposition from dissociated hydrocarbon vapours (lampblack, soot, gas-carbon).
- Explosive decomposition of endothermic compounds, e.g. acetylene.
- Deposition in electrolysis:
- at anode in electrolysis of silver acetylide;
- at kathode in electrolysis of concentrated sulphuric acid with carbon electrodes;
- at kathode in electrolysis of fused BaCO3 + BaCl2 at 600° C.
- Reduction of CO and CO2 by metals: e.g. CO2 by magnesium, calcium and the alkali metals, and CO by iron at high temperature.
- Decomposition of CO:
- by heat at 1690° C. into CO2 and free carbon;
- by radium emanation into O2, CO2, and carbon.
Sugar-charcoal and lampblack yield the purest forms of amorphous carbon, because they need contain no mineral impurity. |