Melting point of yttria

Fourteen samples of 99.999 percent Y2O3 were melted near the focus of a 250-W CO2 laser. The average value of the observed melting point along the solid-liquid interface was 2462 +- 190C. Several of these same samples were then melted in ultrahigh-purity oxygen, nitrogen, helium, or argon and in water vapor. No change in the observed temperature was detected, with the exception of a 200C increase in temperature from air to helium gas. Post test examination of the sample characteristics, clarity, sphericity, and density is presented, along with composition. It is suggested that yttria is superior to alumina as a secondary melting-point standard