Apparent Temperatures Measured at Melting Points of Some Metal Oxides in a Solar Furnace

Abstract

Six metal oxides (A120r, TiO,, NbzO5, Ta205, La203, and Dy20a) were melted in a solar furnace and the apparent temperatures at their melting points were measured by means of a conventional optical pyrometer. The apparent temperatures of three of them (A120s, Ti02, and NbzOa) were 2025O, 1840°, and 1496°C. respectively, in close agreement with the melting points as determined by other investigators using other methods. The apparent temperatures of the other three varied widely and bore no relation to their melting points. The method therefore does not have general utility for the measurement of unknown melting points.

Low-Pressure Oxidation of Niobium at 1200°–1700°C

“…This change is concluded to be associated with the transition from solid to liquid Nb205. The melting point of Nb205 is about 1490~ (7,8).…”

“…It also rules out a defect structure involving oxygen vacancies. However, a possible explanation could be that the defects in NbO 2 involve interstitial oxygen according to the relationship 1/2 O2(g) ~-Oi z-4ze + [8] and that diffusion of oxygen takes place through an interstitially mechanism. A pressure dependence of plmo 2 could in principle be obtained either if the electron holes, e +, are associated with the interstitial oxygen ion or if intrinsic ionization of electrons from Ke the conduction to the valence band (nil ~ e + 4-e-) yields an electron hole concentration which is very much larger than that produced from Eq.…”

“…A pressure dependence of plmo 2 could in principle be obtained either if the electron holes, e +, are associated with the interstitial oxygen ion or if intrinsic ionization of electrons from Ke the conduction to the valence band (nil ~ e + 4-e-) yields an electron hole concentration which is very much larger than that produced from Eq. [8], i.e., if {e + } = Ke w2 >> O~ z-.…”

“…According to Eq. [8] NbO2 is proposed to contain excess oxygen relative to the stoichiometric oxide. NbO2 has possibly a small homogeneity range (17), but otherwise little is known about its defect structure.…”

“…The above considerations (Eq. [8]) are therefore at this stage purely speculative and are put forth solely to explain the oxygen pressure dependence of the parabolic oxidation.…”