HIGH TEMPERATURE REACTIONS AND PHASE EQUILIBRIA IN THE STRONTIUM OXIDE-ZIRCONIUM OXIDE SYSTEM.

摘要

An investigation of the strontium oxide-zirconium oxide system by x-ray diffraction,differential thermal analysis,thermogravimetric,and metallographic analysis has lead to the construction of the equilibrium phase diagram. The diagram is characterized by two compounds. The compound SrZrO3,strontium zirconate,was found to be stable from 85K to above 2000C and its reported melting point is above 2600C. There is a very limited solid solution range on the zirconia rich side (<1%) and on the strontia rich side (<3%). The Sr3Zr2O7compound was found to be stable from room temperature to 2280C where it decomposed in a peritectic reaction forming SrZrO3plus liquid. Pure zirconia was found to accept less than 0.5% SrO in solid solution up to 2050C,above which 5% SrO was taken into cubic solid solution. Strontium zirconate, SrZrO3,was found to be in equilibrium with (1) monoclinic zirconia from room temperature to 1110C, (2) tetragonal zirconia from 1110to 2080C,and (3) cubic zirconia from 2080C to the eutectic at 2290C. The eutectic composition was found to be near 27.5-mole % SrO. Compositions containing more than 50% SrO were found to be extremely sensitive to moisture in the atmosphere and special precautions were taken to prevent hydration. No evidence was found to support the presence of the two compounds Sr4Zr3O10and Sr2ZrO4previously reported. A second eutectic in the system was found at 75% SrO and 2180C. (Author)