| Description |
106 leaves in various foliations : illustrations ; 29 cm |
| Summary |
"Thermal expansion, thermal hysteresis, and the monoclinic tetragonal phase transformation of ZrO₂ have been studied with high temperature x-ray diffractometry. The initial transformation temperature in pure ZrO₂, on heating, is about 1150°C. The transformation occurs over a 100°C temperature range and thermal hysteresis occurs on heating and cooling. The mechanism of the transformation is related to preferred vibrational modes of atoms on the A[subscript O] -C[subscript O] plane of the monoclinic structure. Because the monoclinic B[subscript O] axis is parallel with the tetragonal [110] axis, structural relationships can be seen to be a controlling factor in the transformation. Initiation of the transformation is probably related to the vibrational energy of the atoms, and formation energy of tetragonal domains; hysteresis behavior is the result of development of strain energy between semi-coherent monoclinic and tetragonal domains. The effects of addition of CaO on the monoclinic --> <-- tetragonal transformation of ZrO₂ and some phase relationships in the system ZrO₂-CaO were studied by high temperature diffractometry, and heating and quenching techniques. Addition of 1 mole % CaO lowered the initial transformation from 1150° to 1100°C on heating and from 1050° to 1000°C on cooling. Further addition of CaO affects the hysteresis characteristics but not initiation of the mono- clinic-tetragonal transformation. Increasing CaO content causes widening of the hysteresis loop. This phenomenon is explained by formation of a cubic solid solution, semi-coherent with the tetragonal phase. The thermal history of the samples also affects the width of the hysteresis loops, possibly related to difference in defect concentration. Phase equilibria of the system Zro₂-CaO was studied in some detail. A cubic solid solution and the compound CaZrO₃ are stable binary phases in this system. The stability field of the cubic solid solution is wider at higher temperatures. The phase boundary of the cubic field at 20 mole % CaO is almost vertical and exists to low temperatures"--Abstract, leaves ii-iii |
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