Zirconia formation by reaction of zirconium sulfate in molten alkali-metal nitrates or nitrites

Abstract

Thermogravimetry up to 500 °C reveals several multi-stage reactions between Zr(SO₄)₂ and molten alkali-metal nitrates which form poorly crystallised mixtures of tetragonal and monoclinic zirconia. The use of NaNO₃ gives incomplete transformations. The addition of NaCl as well as the use of LiNO₃-KN0₃, leads the reaction to completion; the increase of basicity by the addition of Na₂CO₃ also has the same effect, if it is assumed that Na₂ZrO₃ is formed together with ZrO₂. Pure and finely divided tetragonal zirconia is produced by a single-stage reaction at a temperature lower than 300 °C, when the basicity of the medium is increased by replacing LiN03–KNO₃ by NaNO₂–KNO₃.