ASTM C561

Ash in a Graphite Sample

Applicability: ASTM C561 applies to manufactured carbon and graphite materials including graphite electrodes, extruded carbon rods, isostatic graphite blocks, and fine-grained graphite components used in metallurgical, chemical, and electronic applications. It covers samples from both primary manufactured graphite and secondary recycled graphite materials, with ash contents typically ranging from 0.005% to several percent by mass. Very high-purity nuclear-grade graphite requiring detection limits below the method sensitivity may need supplementary analytical techniques.

Purpose: ASTM C561 determines the ash content of graphite samples by combusting a weighed, powdered sample in a platinum or silica crucible in a muffle furnace at 925°C to constant mass, with the non-combustible residue expressed as a percentage of the original dry sample weight. Ash content is a critical purity indicator for graphite used in high-purity applications such as semiconductor furnace components, nuclear moderator blocks, and electrochemical electrodes, where metallic impurities must be minimized to prevent process contamination or structural degradation of the component in service.