Physical Properties of Amorphous Carbon

Like that of diamond and graphite, the specific heat of amorphous carbon is variable and increases with temperature. In accordance, however, with its lower density the specific heat of amorphous carbon is greater.at corresponding temperature than that of graphite or diamond. The following results were obtained by Wigand:

	Density.	Specific Heat.	Temperature
Diamond.	3.518	0.1128	10.7
Graphite.	2.25	0.1604	10.8
Gas-carbon	1.885	0.2040	24.68

Earlier investigations on the specific heat of amorphous carbon were made by Regnault (from 1840), Bettendorff and Wiillner3 (1868), and Weber (1875). Dewar obtained the value 0.3145 for gas-carbon for the temperature interval 20°-1040°, and Kunz has measured the specific heat of wood-charcoal at various temperatures and calculated the following interpolation formula, which applies to all temperatures between 400° and 1300°.

S = 0.2143 + 0.1436×10^-3t – 0.1975×10^-8t².

The conductivity for heat of gas-carbon, which is fifteen times as "great as that of coal, is 0.0103; i.e. the amount of heat that passes in one second from one surfaceTto the other of a uniform plate of 1 sq. cm. area and 1 cm. thick, there being 1° C. temperature difference between the two surfaces, would heat 0.0103 gram of water 1° C.

The electric conductivity of gas-carbon resembles that of graphite; its value at 0° C. is 0.0145×10⁴. Von Streintz has investigated the electric conductivity of compressed lampblack, and found that it increases with rising temperature between -77° C. and 12° C., like that of an electrolyte; but Dewar and Fleming have shown that the conductivity of electric-light filaments below the temperature of liquid air ( -182°) is similar to that of metals, i.e. it decreases with rising temperature. The conductivities of electric-light filaments are, according to Dewar and Fleming:

at -182° C. λ = 0.0235×10⁴
at -100° C. λ = 0.0241×10⁴
at 18.9° C. λ = 0.0252×10⁴

It has been found by Moore that the thermoelectric properties of amorphous carbon vary with temperature, and depend on the raw material used and its treatment. Consequently it is inferred that amorphous carbon is not a single, definite substance.