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Abstract: Polycrystalline BaTi2O5 (BT2) was prepared by pressureless sintering in air using BaCO3 and TiO2 as starting materials. XRD results of the calcined powder showed BaCO3 and TiO2 reacted completely after being calcined above 950°C, showing a mixture of BaTiO3 (BT), BT2, BaTi4O9 and Ba4Ti13O30. A small amount of ZrO2 (less than 0.1wt%) was effective to prepare BT2 in a single phase and the second phase of BT and B6T17 increased with ZrO2 content. BT2 sintered body in a single phase was obtained at 1175–1300°C when ZrO2 content was 0.08wt%. The maximum permittivity of BT2 sintered body was 340 at the Curie temperature (T c) of 463°C and the frequency of 100kHz. [Copyright &y& Elsevier]

Abstract: Porous La0.8Sr0.2MnO3 cathode materials were prepared by the gelcasting technology. Carbon was employed to produce pores. It is shown that the open porosity decreases with increasing temperature. The proper sintering temperature is 1100°C and the median pore size of the sample obtained at this temperature is about 460nm. The microstructure indicates that the grain grows as the sintering temperature increases, which leads to the decrease of the number of open pores. Generally, the pores are located at multi-grain boundaries. Some closed pores appear in the sample prepared at 1100°C and more. Both the conductivity and the interface bonding between La0.8Sr0.2MnO3 and YSZ get better as the temperature increases. When the sintering temperature is more than 1250°C, La and Mn ions begin to diffuse into YSZ, and therefore interface reactions happen. According to ln(σT)∼1/T curves, E a was calculated to be 10.18kJ/mol. [Copyright &y& Elsevier]

Ni-coated Al2O3 powders were prepared by the heterogeneous precipitation method. After hot-pressing at 1300–1450 °C and 20 MPa, the density of homogeneous Al2O3/Ni composites ranges from ∼98% (NA4) to ∼94% (NA8.5) of the theoretical density. Examination by transmission electron microscope (TEM) and scanning electron microscopy (SEM) shows micrometer-size Ni grains to be located at the triple junctions, and with increasing Ni content, the fracture mode of Al2O3/Ni composites to change from intergranular mode to transgranular mode due to the thermal stresses. The strength and toughness of composites was much higher than that of the dense monolithic Al2O3. The strengthening and toughening mechanisms of the composites with respect to the microstructure are analyzed. [Copyright &y& Elsevier]

Al2O3/Ni nanocomposites were prepared by a chemical method and hot-pressing technique using Al(NO)3·9H2O and NiO as the starting materials. At 1450 °C the composites can achieve >98% theoretical density after hot-pressing. Microstructural results revealed that Ni grains were uniformly dispersed in the Al2O3 matrix, some fine Ni grains of ∼100 nm were entrapped within Al2O3 grains, some Ni grains of 100–300 nm were dispersed at the grain boundary, forming intra/inter-type nanocomposite. The three-point bending strength and the fracture toughness of the dense Al2O3 composite increased by 26 and 79%, respectively, with the addition Ni content. The strengthening and toughening mechanisms of the composite with respect to the microstructure are analyzed. [Copyright &y& Elsevier]

Al2O3–4vol.%Ni composites were prepared by hydrogen reduction and hot pressing of powder mixtures of NiO and Al2O3 obtained by two processes, namely, the ball-milled mixing process (process A) and the coating process (process B). The microstructural features and sintering behavior of the powder mixtures, and mechanical properties of composites were investigated. The samples obtained by hot pressing powder mixtures synthesized through process A and B at 1450 and 1400 °C reached >98% theoretical densities. The microstructural homogeneity of the samples was in agreement with characteristics of two different powder mixtures. Compared with that by process A, the samples fabricated by process B exhibited an increase in toughness and a decrease in strength. The toughening was mainly attributed to crack deflection and crack branching. The difference of strength was discussed through the observed microstructure and fracture model of the composites. The standard deviations (S.D.) of the strength and toughness indicated the samples prepared by process B had better reliability and stability. [Copyright &y& Elsevier]

A heterogeneous precipitation method was employed to prepare Ni-coated-Al2O3 powders using Al2O3, Ni(NO3)2·6H2O and NH4HCO3 as the starting materials. The coated powders were characterized by TEM, AES, ζ-pH. Results showed that a continuous amorphous NiCO3·2Ni(OH)2·2H2O film uniformly coated the Al2O3 particles surface. After calcining at 400 °C for 2 h in air and reducing at 700 °C for 4 h in hydrogen atmosphere, NiCO3·2Ni(OH)2·2H2O was converted to Ni with size of about 20 nm, meanwhile, the continuous amorphous film become discontinuous. [Copyright &y& Elsevier]

A heterogeneous precipitation method is described for obtaining nanocomposite powders consisting of Ni nanoparticles homogeneously dispersed within γ-Al2O3. The amorphous Al(OH)3 was nucleated on the surfaces of NiO nanoparticles and crystallized to γ-Al2O3 at 900 °C. The porosity of γ-Al2O3 allowed the growth of NiO nanoparticles during calcinations. After the calcined nanocomposite powders were selectively reduced at 700 °C in a hydrogen atmosphere, NiO nanoparticles were converted to Ni with the size of 25–35 nm. TEM observation and AES analysis showed Ni nanoparticles were uniformly dispersed in the γ-Al2O3 matrix. [Copyright &y& Elsevier]

Abstract: Polycrystalline BaTi2O5 (BT2) was prepared by solid state sintering in air using BaCO3 and TiO2 as starting materials. A rod-like BT2 sintered bodies in a single phase were obtained above 1025 °C by adding 5 wt.% B2O3. The densification of BT2 sintered bodies decreased with increasing sintering temperature. The maximum permittivity of BT2 sintered body was 640 at the Curie temperature (T c) of 461 °C and the frequency of 100 kHz. The addition of B2O3 was effective to obtain BT2 in a single phase at low temperatures with elongated microstructure and to improve the permittivity, indicating the formation of preferred orientation at low temperature was related with liquid-phase sintering mechanism. [Copyright &y& Elsevier]

• Energy beams emitted from a surface micro-element are divided into M (M ≥ 1) point. • The sampling of surface reflection is eliminated. • The sampling of surface emission and gas scattering are only arranged one time. • More efficient and time-saving. An improved Monte Carlo method (IMCM) is developed in this paper to solve the total radiant exchange areas (TEAs), which can greatly improve calculation accuracy and save CPU time. This approach, features two main improvements on the basis of the Monte Carlo method (MCM). First, the location of the surface emission points and the number of emission energy beams are subdivided, thereby improving the calculation accuracy. Specifically, it is assumed that the energy beams emitted by one micro-element are emitted from M points on average. Second, the energy beams emitted by the surface and gas micro-elements are only arranged once, and the sampling of surface reflection is eliminated, thereby improving the calculation efficiency. Specifically, the ratio of the energy beams emitted by one micro-element directly to other micro-elements can be calculated. The reflection and scattering energy of one micro-element to other micro-elements are obtained by iterative accumulation. This approach can greatly save CPU time compared with sampling the reflected and scattered energy beams. The application of IMCM to a two-dimensional (2D) square cavity is considered in this study. The effects of surface emissivity and boundary temperature on radiative heat transfer are analyzed. IMCM was used to solve the TEAs, and the calculated results of IMCM, MCM and the pathlength method (PLMCM) were compared based on the results of the reduced integration scheme (RIS). The all results show that the IMCM is more accurate than the MCM and PLMCM and is more efficient than the MCM and PLMCM for calculating the TEAs. As shown in the figure, the flow chart for solving the TEAs, the left side is the basic steps of IMCM, and the right side is the basic step of MCM. The basic steps of IMCM mainly include: calculating the share and proportion of the emitted energy beams of each micro-element to other micro-elements, calculating the energy of each micro-element reflected and scattered to the specified micro-element and store it, determining whether the accuracy is met. The basic steps of MCM mainly include: determining whether the energy beam is in the enclosure, if yes, reaching to gas micro-elements, determining whether the energy beam is scatter, if yes, resampling determine the scattering direction and distance; if the energy beams reaching to surface micro-elements, determining whether the energy beam is reflect, if yes, resampling determine the reflecting direction and distance. By comparing MCM with IMCM to solve the TEAs, it can be found that IMCM reduces the number of steps for needed to resample the distance and angle of the reflected and scattered energy beams, thereby reducing the CPU time. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The La0.8Sr0.2MnO3 green body was prepared by a gelcasting forming process. TGA analysis indicates the organic matter is removed at ∼400°C. In contrast to the dry-pressing process, the green body obtained by the gelcasting process exhibits uniform microstructure, small pore size, narrow distribution, high density and strength. [Copyright &y& Elsevier]

Inverse estimation of temperature-dependent refractive index and absorption coefficient of semitransparent media is studied in this work. The forward transient coupled radiation-conduction heat transfer in semitransparent media is simulated by the finite volume method. The time-varying radiative response signals at the boundary (not the laser irradiation boundary) is adopted as measurement information in the inverse model. An improved teaching-learning-based optimization (ITLBO) algorithm is developed to retrieve the temperature-dependent refractive index and absorption coefficient simultaneously. Effects of model parameters (i.e. the laser heating time and measurement errors) and thermophysical parameters (i.e. the thermal conductivity and heat capacity) on the estimated results are analyzed thoroughly. All the retrieval results show that the inverse model and inverse algorithm is accurate and effective for predicting the temperature-dependent radiative properties of semitransparent media. • Temperature-dependent refractive index and absorption coefficient are estimated simultaneously. • The improved teaching-learning-based optimization is developed to solve the inverse problems. • Effects of model and physical parameters on retrieval results are analyzed. [ABSTRACT FROM AUTHOR]