Arsenic loss during metallurgical processing of arsenical bronze

Abstract

The chemical composition of ancient copper-based metal changes over time due to repetitive recycling and mixing of old metal. Prehistoric copper usually contains impurities from the copper ores themselves, and some have been used as evidence of anthropomorphically induced chemical change. Research into these changes has historically relied upon the assumption of element loss linearity, which is highly misleading and in fact varies with a multitude of factors. To illustrate the complexity of such losses for prehistoric alloys, we have selected arsenical bronze (Cu-As alloys) for study. The mass loss of several Cu-As-alloys under reducing atmosphere was measured by DTA/TGA. From our comparison of the experimental results to thermodynamic calculations and literature data, it was unclear whether weight losses were solely caused by the elemental loss of arsenic. However, a prolonged time temperature-cycling run demonstrated that mainly arsenic volatilizes; hence, the non-linear mass loss from the alloy can be directly attributed to arsenic.