Zr2MoP2O12/ZrO2 composites were successfully synthesized by the solid state method in attempt to fabricate the near-zero thermal expansion ceramics. The phase composition, micromorphology and thermal expansion behavior of the Zr2MoP2O12/ZrO2 composites with different mass ratios were investigated using X-ray diffraction, scanning electron microscopy and thermal mechanical analysis. Results indicate that Zr2MoP2O12/ZrO2 composites can be prepared by pre-sintering at 500°C for 3 h and then sintering at 1050°C for 6 h. The resulting Zr2MoP2O12/ZrO2 composites consisted of orthorhombic Zr2MoP2O12 and monoclinic ZrO2. With increasing content of Zr2MoP2O12, the Zr2MoP2O12/ZrO2 ceramics became more compact and the coefficient of thermal expansion decreased gradually. Zr2MoP2O12/ZrO2 composites show an adjustable coefficient of thermal expansion (CTE) from 5.57 × 10−6 K−1 to −5.73 × 10−6 K−1 by changing the mass ratio of Zr2MoP2O12 and ZrO2. The Zr2MoP2O12/ZrO2 composite with a mass ratio of 2:1 showed near zero thermal expansion, and the average linear thermal expansion coefficient is measured to be 0.0065 × 10−6 K−1 in the temperature range from 25 to 700°C.
ZrO2 doped with 7.5% (volume percent) nanoalumina ceramics were prepared by microwave sintering processes. The effects of nanoalumina additions and various sintering temperature on densification, phase composition, microstructure and mechanical properties of Al2O3-ZrO2 ceramics were investigated. The results show that the m-ZrO2 phase transformed into t-ZrO2 during the process of microwave sintering. Relative densities between 95% and 99% were attained in the different conditions. In any cases the grain size was maintained at a submicron scale at a processing microwave sintering. The presence of Al2O3 grains had an effect of hindering grain growth of ZrO2 grains. When the microwave sintering temperature was 1500°C, 7.5Al2O3-ZrO2 composite ceramics presented excellent mechanical properties: HV=12.0 GPa, σf=715.7 Mpa, KIC=11.9 MPa·m1/2. Compared with that of pure ZrO2 ceramic, the bending strength and the fracture toughness were improved 45% and 23% at least, respectively. The fracture mode was associated with sintering temperature: when the sintering temperature was 1350°C~1450°C, the intergranular fracture and transgranular fracture coexisted; when the sintering temperature was 1500°C, intergranular fracture was the main fracture mode.
Al2O3(x)/ZrO2composite ceramics were successfully prepared by microwave sintering. The influence of variety content of nanoAl2O3on mechanical properties and microstructure of ZrO2dental materials were studied, and analysied the mutual relations of chemical composition, mechanical properties and microstructure to investigate the reason of strengthening and toughening. Results indicated that The relative density of the Al2O3(x)/ZrO2composite ceramics reached more than 96.8%.The HV hardness ,bending strength and fracture toughness presented excellent mechanical properties as 12.5GPa, 753.8MPa and 11.8MPa·m1/2with the content of nanoAl2O3was 7.5%. Compared with that of pure ZrO2ceramics, the bending strength and the fracture toughness were improved 19% and 96%, respectively. The main crystal phases in this composite ceramics were t-ZrO2and α-Al2O3.The nanoAl2O3have a obvious effect on the strength and toughness of ZrO2based ceramics. The reason of strengthening and toughening mainly the additions reduced the ZrO2grains growth and promoted grains size uniformity, and changed the fracture mode from transgranular fracture to intergranular fracture characteristics.
Nb2O5-7.5La2O3-Al2O3 composite ceramics were prepared by microwave sintering. The influence of Nb2O5 and La2O3 proportion on the microstructure and mechanical properties of Al2O3 ceramics was investigated. The results show that when the Nb2O5 content was lower than La2O3, the columnar LaAl11O18 grains were generated by the reaction of La2O3 with Al2O3. When the Nb2O5 content was higher than La2O3, the surplus Nb2O5 induced the formation of columnar Al2O3 grains. The growth of columnar Al2O3 grains were promoted synergistically by LaNbO4 formed in-situ and Nb2O5. The 5Nb2O5-7.5La2O3-Al2O3 composite ceramic exhibited excellent comprehensive properties: ρr=99.3% (relative density), HV=11.2GPa (microhardness), KIC= 6.4MPa·m1/2 (fracture toughness), σ=304.3MPa (bending strength).
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