Graphite Powder Density
Graphite powder is soft and flexible, with a Mohs hardness of 1 (talc), but is strong and non-brittle. Graphite powder has good thermal and electrical conductivity, is a refractory and is chemically inert. It is used in crucibles, foundry facings, lubricants, marking materials ("lead" pencils), electrodes, brake linings, powder metallurgy, fertilizers, glass manufacture, and conductive coatings. Graphite is produced by the metamorphosis of amorphous carbon materials under high temperature and pressure, typically in metamorphic environments such as schists or pegmatites. It also occurs in igneous environments such as peridotites or sillimanite dykes.
Typical sources of raw natural and synthetic flake graphite include coal, petroleum coke and bauxite ore. The graphite is purified by a series of chemical processes, washed, separated and crushed to obtain the graphite powder. It is further processed by vibration milling and air flow separation to achieve various grades of material.
A simple method for characterizing a graphite powder is to measure the apparent density of the graphite under compression. This is measured by holding a thick cylindrical sample of the material between two conducting pistons. The volume of the powder is then calculated from the weight of the pistons and the pressure exerted. The apparent density of the graphite is a good approximation to the tamped density of the sample.
The process according to the invention significantly increases the Scott density and/or tamped density of graphite powders of any particle size distribution by optimizing the grinding effect. It also leads to markedly lower absorption properties of the graphite in liquid media, which leads to a significant increase in the solids content of the graphite dispersions produced with the powders treated in this manner.