Carbon Electrode: Oil-Coke Pressed with Tar and Baked at 1200° (Thorpe, 1912)

Amorphous carbon electrodes as made for aluminium reduction: oil-coke is selected, ground and calcined, pressed hard with tar as a binder, and baked at about 1200° in a kiln like a pottery kiln, packed in carbon so the surface does not burn. A good electrode conducts electricity well but heat poorly, is hard, resists surface oxidation, has low porosity and is even throughout. Thorpe gives 25 to 60 amperes per square inch as the permissible current density, though much less is used in practice. Not given: the tar proportion, the pressure and the sizes. Source: T. E. Thorpe, Dictionary of Applied Chemistry vol. I (1912), p. 107. Picture: the book's text.