Thermodynamic modeling of thorium migration behavior in Th-doped GTA tungsten electrode

A tungsten-based electrode is a crucial material for generating gas tungsten arc (GTA) heat sources, but erosion always take place to damage the tip state and further deteriorates electrode performance. The dopant evolution within tungsten is key to determining arc properties and electrode's lifespan. In this study, an integrated evaporation-diffusion simulation model is developed to investigate doped thorium (Th) atom transformation behavior in Th-doped tungsten electrode. Results show that after arcing, the tungsten electrode tip surface is divided into three zones: Th-depleted zone, Th-enriched zone, and unaltered zone. At 200A arcing for 300s, Th evaporation primarily occurs within 0.5 mm of electrode tip where evaporation flux quickly drops from 1.5 × 10−4 mol/(m2·s) to 0 and slower Th diffusion compared to evaporation leads to Th-depleted zone's formation. With increased arcing current from 200A to 500A, evaporation flux rises from 1.50 × 10−4 mol/(m2·s) to 0.24 mol/(m2·s), expanding the Th-depleted zone length from 0.19 mm to 0.61 mm. At 200A, Th-depleted zone grows slowly with an electrode consumption rate of 2 × 10−4 mm/s; at 500A, Th-depleted zone grows quickly with a consumption rate of 3.7 × 10−4 mm/s. This study provides critical insights into the thermodynamic behavior of Th-doped tungsten electrode in arc heat source, offering guidance for optimizing electrode performance.