What happens when molybdenum trioxide sublimates during roasting?

When molybdenum trioxide (${\text{MoO}}_3$) sublimates, it vaporizes directly from the solid state into a gas.1

In the context of roasting molybdenite concentrate, this process is generally avoided because the temperature in the furnace should not exceed 650 °C (1,200 °F), which is the point at which sublimation occurs.1

However, sublimation is intentionally utilized in a separate refining stage to produce chemically pure ${\text{MoO}}_3$. During this process, technical-grade oxide is heated in electric retorts to temperatures between 1,200 and 1,250 °C (2,200 and 2,300 °F). The resulting sublimed vapors are swept from the furnace tubes by air and collected in filter bags to separate pure ${\text{MoO}}_3$ from volatile impurities.2