Study On Microstructure And Thermal Physical Properties Of Ln_xZr_1-xO_2-x/2(Ln=Nd, Sm) Nano Ceramic Powders And Bulk Materials

ZrOCl₂·8H₂O and rare earth oxides of Ln₂O₃ (Ln=Nd, Sm) powders are used as starting materials to synthesize Ln_xZr_1-xO_2-x/2(Ln=Nd, Sm) (x=0.1, 0.2, 0.3, 0.4) with a chemical coprecipitation followed by calcination method. The Ln_xZr_1-xO_2-x/2 powders were first heat treated at 800℃for 5 hours, and were then sintered into Nd_xZr_1-xO_2-x/2 and Sm_xZr_1-xO_2-x/2 bulk materials by pressureless sintering process. The microstructure, thermal capacity, thermal expansion coefficient, thermal diffusivity and thermal conductivity of different bulk materials have been investigated by DSC, X-ray diffraction (XRD), scanning electron microscopy (SEM) and various thermal analysis techniques.The Nd_xZr_1-xO_2-x/2 and Sm_xZr_1-xO_2-x/2 powders are synthesized with the chemical coprecipitation followed by calcination method. Ln0.1Zr0.9O1.95(Ln=Nd, Sm) powders consist of m and t phases,however, the Ln_xZr_1-xO_2-x/2(Ln=Nd, Sm) (x=0.2, 0.3, 0.4) are composed of t and c phases. The Ln_xZr_1-xO_2-x/2 powders exhibit a particle size of below 100nm. With the pressureless sintering process at a temperature of 1600℃for 15 hours, The Ln_xZr_1-xO_2-x/2 ceramics consist mainly of m and t phase, while Ln_xZr_1-xO_2-x/2 (x=0.2, 0.3, 0.4) ceramic are composed of t and c phase. However Ln0.4Zr0.6O1.8 ceramics are composed of pyrochlore phase. The LnxZr1-xO2-x/2 bulk materials with a grain size range of 4⁵μm are fabricated.From the results on the thermal capacity of sintered Sm_xZr_1-xO_2-x/2(x=0.1, 0.2, 0.3, 0.4), the phase transformation from monoclinic to tetragonal phase was identified for Sm0.1Zr0.9O1.95 ceramics at 768.8℃, however, no phase transformation is found in other Sm_xZr_1-xO_2-x/2 (x=0.2, 0.3, 0.4) ceramics. With the increase of the Sm2O3 addition, the thermal capacity of Sm_xZr_1-xO_2-x/2 (x=0.2, 0.3, 0.4) decreases. While, the phase transformation from monoclinic to tetragonal phase was identified for Nd0.1Zr0.9O1.95 ceramics at 911.3℃, and no phase transformation is found in other Nd_xZr_1-xO_2-x/2 (x=0.2, 0.3, 0.4) ceramics. With the increase of the Nd2O3 addition, the thermal capacity of Nd_xZr_1-xO_2-x/2 (x=0.2, 0.3, 0.4) also decreases.The results on thermal conductivity indicate that, the thermal conductivity of Sm0.1Zr0.9O1.95 is smallest. The thermal conductivity of Sm_xZr_1-xO_2-x/2(x=0.2, 0.3, 0.4), which is located in the range of 1.51 to 2.39W·m-1·K-1, decreases with the increase of the Sm2O3 addition. For the Nd_xZr_1-xO_2-x/2(x=0.2, 0.3, 0.4) ceramics, the thermal conductivity is in the range of 1.54 to 2.45W·m-1·K-1.The results on thermal expansion coefficients indicate that, the identical phase transformation process takes place for Sm0.1Zr0.9O1.95 ceramics at 768.8℃. The thermal expansion coefficients of Sm_xZr_1-xO_2-x/2(x=0.2, 0.3, 0.4) increase with the increase of the Sm2O3 addition. The same situation is found for the Nd_xZr_1-xO_2-x/2 at x= 0.2, 0.3, 0.4.