On the oxidation mechanism of pure tungsten in the temperature range 600–800 °C

The oxidation behavior of International Thermonuclear Experimental Reactor (ITER)-reference tungsten grade has been evaluated in dry air in the temperature range 600–800 °C. At 600 °C, the scale remained protective while the integrity of W18O49 layer was kept. Rapid increase in mass gain resulted from massive cracking at local areas in the W18O49 layer. Then, a coarse non-protective columnar WO2.92 scale was developed which favoured rapid inward oxygen transport into the alloy. At 700 and 800 °C, growth stresses in the scale were released through local cracking. At this stage, WO2.92 became progressively transformed into WO3 when the oxygen partial pressure increased across the scale thickness.

► Oxidation mechanism of pure tungsten is reviewed between 600 and 800 °C. ► Low kinetics are related to initial W18O49 formation. ► Linear kinetics are due to cracking in W18O49 scale. ► Cracking favors formation of WO2.92. ► Model proposed for cavity development in the scale and WO3 formation on the surface.