Advanced Materials Research Vols. 750-752

Abstract: Mullite-aluminum titanate-cordierite multiphase ceramics were prepared by high alumina clinker, Aluminum Titanate and Cordierite. The sintering property and thermal shock resistance of composite materials were tested. The experimental results show that the sinter property and themal shock resistance of Mullite-aluminum titanate-cordierite multiphase ceramics are relatively preferably, which the materials composition are 30 wt.% high alumina clinker, 60 wt.% cordierite and 10 wt.% aluminum titanate. The component samples show porosity of 33.17%, volume density 1.9 % and normal temperature flexural strength 20.66 MPa. Thermal residual flexural strength of the samples is still as high as 10.29 Mpa by 5 times thermal residual tests, and there are only little flexural strength lower after three times earthquake test.

Abstract: Glutin-urea system was used to prepare ultrafine zirconia suspension for gelcasting. Premixed solution was prepared at deionized water/glutin/urea ratio of 90/10/5 (by weight). Adjusting pH value to11, zirconia powders and A-type dispersant (polyacrylic salt) were added. After ball-milled about 12 hours, 45vol% zirconia slurry was acquired and the viscosity of which was less than 1 PaS.

Abstract: The behavior of dielectric and microwave properties against sintering temperature was been carried out on CaO-B₂O₃-SiO₂ glass-ceramics with Na₂O addition by XRD and SEM. The results show that 0.5 wt.% Na₂O addition is advantageous to improve the dielectric and microwave properties due to increasing the major crystalline CaSiO₃. With further increasing Na₂O content, α-SiO₂ is the predominant crystalline phase instead of CaSiO₃. The CBS glass-ceramics with 0.5 wt.% Na₂O sintered at 875°C has a bulk density of 2.51g·cm^-3, and which possesses good dielectric properties: ε_r =6.2, tanδ=1.9×10^-3(10 MHz) and low dielectric constant below 2×10^-3 over a wide frequency range. The proposed dielectrics can find applications in microwave devices, which require low dielectric loss and low dielectric constant.

Abstract: The relationship between microstructures and sintering, heat treatment processes have been investigated in 8mol% MgO-0.5mol% Y₂O₃-PSZ ceramics. The result show that the T phase exhibits two different morphologies during sintering below 1800°C and isothermal holding or aging anew at 1500°C. Their shape, size, distribution and stability all have obvious difference, so they have different effects on the phase transformation toughening.

Abstract: In order to investigate the evidence for the formation of Sr²⁺-Zr⁴⁺ defect complexes in high-k Sr and Zr co-doped BaTiO₃ ceramics, BaTiO₃, (Ba_0.85Sr_0.15)TiO₃, Ba (Ti_0.8Zr_0.2)O₃, and (Ba_0.85Sr_0.15)(Ti_0.8Zr_0.2)O₃ (BS15TZ20) ceramics were prepared using a mixed oxide method. The Y5V-type BS15TZ20 shows a high-k diffuse phase transition behavior (ε ́_m = 8000) and its Curie peak occurs near room temperature. The evolution in crystal structure and in dielectric property for the four samples gives four evidences for the formation of Sr²⁺-Zr⁴⁺ defect complexes in BS15TZ20. The splitting of the 720 cm^-1 Raman band does not relate to Sr²⁺-Zr⁴⁺ defect complexes, but to a multiphonon (A₁ (TO₂) + A₁ (TO₃)).

Abstract: As a research object, the samples with various Ba/Ti ratios (Ba/Ti=0.95~1.05) were synthesized by solid phase reaction method. Effect of sintering temperatures and Ba/Ti ratio on dielectric properties and crystal structure of BaTiO₃ ceramic were investigated. Crystal structure and crystal phase composition were investigated by scanning electron microscopy and X-ray diffraction. The dielectric properties were studied by Agilent 4294A at 1 kHz. The results show that the BaTiO₃ ceramic has high permittivity and dielectric loss at 1340°C. The permittivity of BaTiO₃ ceramic with Ba/Ti=0.95 change small as the sintering temperatures vary at 1320°C. With the increasing of Ba/Ti ratio, the Curie temperature first increases and then decreases as the sample sintering at 1320°C. When Ba/Ti=1, the Curie temperature increase with the sintering temperature increasing.

Abstract: The Al₂O₃ ceramics with high thermal conductivity prepared the spark plasma sintering (SPS) technology. The structure, image and magnetic properties of the SPS Al₂O₃ ceramics was characterized by X-ray, field emission scanning electron microscope (FE-SEM) and the vibrating sample magnetometer (VSM) at room temperature. The results shown that the average grain size of the Al₂O₃ ceramics is about 5~15μm, the thermal conductivity of Al₂O₃ ceramics up to 24.928 W/(m·K), and the remanent magnetization as higher as 0.00546emu/g and the saturation magnetization as higher as 0.0321 emu/g, respectively. The room-temperature ferromagnetism, which is different from the traditional, possibly originates from the oxygen vacancies.

Abstract: Fused quartz powder (d₅₀=19μm) was used as raw material, nano-Yb₂O₃, nano-Nd₂O₃ and nano-Dy₂O₃ were dividedly used as additive with dosages of 3% each. Fused quartz ceramic materials were sintered in reduction atmosphere at 1300°C, 1350°C and 1400°C for 1h. The influence of rare earth nanooxides on sintering and crystallization of the fused quartz ceramic were researched by measurements of apparent porosity, bending strength and thermal expansion ratios, and analyses of XRD and SEM. The results showed that samples added nano-Yb₂O₃ and nano-Nd₂O₃ have lower apparent porosity, higher bending strength and lower thermal expansion rate. It can be deduced that additives nano-Yb₂O₃ and nano-Nd₂O₃ have obvious effect on facilitating sintering and inhibiting crystallization of fused quartz materials at experimental temperatures.

Abstract: Al (OH)₃, Suzhou kaolin, AlF₃ and V₂O₅ were premixed and pelleted to form the precursor for fabricating the mullite whisker, and then the precursor was added into the calcined bauxite and Suzhou kaolin mixture according to a certain mass percent. The mullite-corundum refractory materials with well-dispersed needle-like mullite formed in-situ were prepared. Through studying the effect of different sintering temperatures on the performances of the as-fabricated mullite-corundum refractory materials, it was concluded that the appropriate sintering temperature was 1450 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), water absorption, bending strength, coefficient of thermal expansion and the first thermal stress fracture factor were used to characterize and evaluate the materials. The results show that the sintering character and thermal expansion coefficient of the refractory materials increase with the rising sintering temperature. The bending strength of the refractory materials sintered at 1500 °C presented the maximum value and the first thermal stress fracture factor appeared the highest value at 1450 °C.

Abstract: Mullite-corundum multiphase ceramic materials were prepared at 1400°C for 2h with bauxite chamotte and clay clinker as raw material (size<74 μm), molded at pressure of 50 MPa. Effect of raw materials composition on sintering and themal shock resistance of composite were researched by measurements of apparent porosity, bending strength，thermal shock resistance and thermal expansion rates, and analysed by XRD and SEM. The results showed that the best weigh percentage of raw materials with better sintering and themal shock resistance are bauxite chamotte 50 wt%, clay clinker 50wt% for mullite-corundum multiphase ceramic materials. The test results for high temperature gas cleaning dust removal technology development and the application of the composite ceramic material has important application value.