Study on Granular Caranular Carbon for Use of Telephone Transmitter

Abstract

For the purpose to establish the requirements for coal used as raw material of granular carbon for telephone transmitter, studies are carried out on the physical and chemical properties of the coal and on the electrical properties of the granular carbon prepared from the coal. Anthrecite coal from Honge is crushed into small blocks. They are classified into five groups according to their appearances. Each of these groups is found to be distinctly different with each other in microscopic surface texture, chemical composition, form, purity, density and homogeneity. The difference observed in electrical properties of the granular carbons prepared from the fine powders of these classified groups of coal by roasting at 950°C in an atmosphere of town gas can be explained qualitatively from the difference in the physical and chemical properties of the raw materials. From the results it is concluded that the anthracite suitable for manufacturing granular carbon for use of telephone transmitter should (1) be lustrous and smooth in fractured surface (2) not be flaky and have no sharp edge, (3) be dense and homogeneous, (4) be abundant in fixed carbon and (5) be scarce in ashes especially in iron compounds.