The effect of graphite filler in sample preparation for automated mineralogy – a preliminary study

Abstract

Mineral particulate sample material is often prepared as polished sections for SEM based automated quantitative mineralogical analysis. A common practice is to mix ultra-pure graphite with sample material to avoid segregation and touching particles, and aid random orientation, as suggested by Jackson et al. (1984). However, the actual effect of adding graphite on these parameters is not well documented. This paper presents a preliminary study on the effect of adding graphite on segregation and touching particles. A mineral particle concentrate, with equal volumes of quartz and pyrite, was made in two size fractions (53 74 µm and 104-147 µm). Each fraction was mixed with graphite in sample:graphite weight ratios 1:1 and 1:2. In addition, 1:3 was made for the finer fraction. Two types of graphite were used: fine grained (<20 µm) ultra-pure graphite, and coarse grained ultra-pure graphite in the same size range as the sample material. Reference samples without graphite were made for both fractions.The results suggest that using graphite as filler does not necessarily prevent segregation. However, it introduces a positive effect on preventing touching particles; fine graphite is the most efficient. The epoxy resin:sample ratio needs to be better controlled to confirm the results.