A special type of carbon black produced by pyrolysis of gaseous hydrocarbons in a preheated chamber in the absence of air. Thermal black consists of relatively large individual spheres (100-500 nm diameter) and aggregates of a small number of pseudospherical particles. The preferred alignment of the layer planes is parallel to the surface of the spheres.
Source:
PAC, 1995, 67, 473. 'Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995)' on page 505 (https://doi.org/10.1351/pac199567030473)