Advanced Materials Research Vols. 105-106

Abstract: It is difficult to calculate with finite element method or actually measure the temperature distribution of the ceramic sintering at irregular sintering curve. Trained by the temperature distribution data of ceramic sintering analyzed with ANSYS under linear sintering curves including different slopes, the neural network can be used to simulate that under irregular sintering curve at certain precision, so the temperature evolution of the ceramic hot geometry centroidal point (HGCP) can be fast obtained by the result simulated with the trained neural network. This research sets up series-parallel BP neural network model with MATLAB. The ceramic sintering date analyzed with ANSYS under linear sintering curves with ten different slopes is used as training sample of the neural network which is tested by the sample under non-linear sintering curve. The result indicates that the BP neural network is feasible for simulating temperature distribution of the ceramic sintering.

Abstract: A series of phosphor of (MxMg1-x)2SiO4: Dy3+, Eu3+ (M=Ca, Sr, Ba) were synthesized by high temperature solid-state reaction method and studied. The structure and emission spectrum excited by near violet light were investigated. The excitation spectra of single-doped (MxMg1-x)2SiO4: Dy3+ show strong absorption near 322nm, 347nm, 362nm and 391nm due to 6H15/2→4I9/2, 6H15/2→6P5/2, 6H15/2→4F7/2, 6H15/2→4G11/2 transition of Dy3+. The emission light is at about 469nm, 474nm, 483nm and 494nm under 391nm UV excitation. In order to obtain white light emission, (MxMg1-x)2SiO4: Dy3+, Eu3+ (M=Ca, Sr, Ba) were prepared to enhance the red light emission.

Abstract: In the paper, the flaky alumina was synthesized using Na2SO4-K2SO4 as flux by the molten salt method. The mole ratio of molten salt to alumina, temperature of synthesis and the amount of Cr3+ were investigated. The size of flake alumina was analyzed by laser sizer, the phases of the reaction products and the microstructures at different Cr3+ doping content was ascertained by XRD and the surface of flake alumina was observed by SEM. The alumina with two-dimensional planar structure, a large aspect ratio and adapting to preparation of pearlescent pigment was synthesized under the mole ratio of molten salt to alumina between 4 to 5 , the synthesis temperature about 1200°C, the heat preservation time in 4h and the mole amount of Cr2O3 about 2%.

Abstract: The rheological behavior of alumina suspension stabilized with Tri-ammonia citrate (TAC) was studied. It was thought that there would form some particle clusters due to the collisions between particles caused by their relative motion in the suspension, and such particle clusters are classified as thermodynamic clusters and hydrodynamic clusters by their origin. Shear thinning is the result of decomposition of the thermodynamic clusters, while shear thickening is the result of formation of the hydrodynamic clusters. From the view of cluster-forming potential barrier, it was deemed that the viscosities of alumina suspensions at low and high shear rates are respectively determined by zeta potential and Stern potential on the particle surface, and shear thickening behavior can be suppressed with some excessive TAC.

Abstract: The novel visible-light-driven Bi2WO6 photocatalyst with orthorhombic structures was synthesized via a reverse microemulsion method. The as-prepared Bi2WO6 samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The photocatalytic activity of the Bi2WO6 powders was determined by degradation of methyl orange molecules in water under visible light irradiation (λ>400nm). The results revealed that the particle and crystallite sizes of the Bi2WO6 powders significantly depended on the synthesis temperature of the reverse microemulsion solutions. The photocatalytic tests indicated that the synthesis temperature also can significantly affect the visible light driven photocatalytic activities.

Abstract: A hydrothermal route for preparing large size xonotlite fibers without special instruments and synthesis conditions was development. Effect of pH values in system on the crystal phase and morphology of synthesized xonotlite fibers was studied by using XRD and SEM. The results indicated that the different pH systems have little effect on the crystallinity of synthesized xonotlite, but have great impact on the morphology of xonotlite fibers. The higher pH value is, the lager scale xonotlite fibers appear when the pH values are among 12.0, 12.5, 13.0 and 13.5. The formation of xonotlite fibers was promoted and xonotlite fibers with 10-30 μm in length and 100-200 nm in diameter were prepared at 220 °C for 15 h in the system of pH 13.5. The evaluation of thermal property revealed that synthesized fibers were excellent in thermal stability at high temperature, and could be potential candidate as reinforcement reagents in composite areas.

Abstract: The elongated grain evolution of alumina ceramics doping with Al2O3-CaO-SiO2(CAS), Nb2O5, and 3Y-TZP was studied under pressureless sintering. From in-situ growth elongated grain cooperating with second phase to toughen the alumina ceramics, microstructure and sintering properties were firstly studied systematically. The effect of additives on the alumina ceramics with columnar grain were analyzed by means of TEM, SEM, XRD, etc. Basing on the analyzed sintering process by the principle of dynamics, the elongated grain growth mechanism was further studied.

Abstract: In this paper, phase transition of forsterite in carbothermal reduction processing was studied. Phase composition and microstructure of the products were characterized by XRD, SEM and XRF. The influences of calcination temperature (1400, 1500, and 1600 °C), carbon content (lacking 50% and 10%, theoretical content, exceeding 10%, 50% and 100%) and holding time (1 h, 2 h and 4 h) on phase composition of carbothermal reduction products were discussed. The results showed that forsterite can be reduced to β-SiC, Fe and MgAl2O4 when it was reacted with carbon exceeded 50wt% of theoretical content at 1600°C for 4 h, while it was stable when treated below 1500°C.

Abstract: Traditionally, silica aerogels with low thermal conductivity are prepared by supercritical drying, however, the process is expensive and hazardous due to it run in autoclaves. In order to overcome these disadvantages, a cheaper and safer process, drying at ambient pressure has been developed for decades, but tedious repetitive gel washing and solvent exchange steps are involved. Therefore, in the present study, a novel vacuum freeze-drying was utilized to prepare the super thermal insulating SiO2 cryogels. The wet gels were synthesized via acid-base catalysis using tetraethoxysilane (TEOS) as a silica precursor and ethanol as a solvent. After vacuum freeze drying, nanoporous SiO2 cryogels with low density in the range of 0.08-0.15 g/cm3 were obtained.

Abstract: Gp/SiC composite was prepared with electrode graphite particle and SiC powders as the raw materials, using coating process and hot-pressing sintering technology. The microstructure and phase constitution was measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron energy spectrum (EDS). It was found that the graphite cores are embedded in the SiC matrix as the islands. The apparent porosity increased, density decreased, with graphite particle content increasing, the bending strength decreased, however, fracture toughness increased with the graphite particle content increasing. Increasing hot-pressing sintering temperature imparted Gp/SiC composite characteristic behaviors of better mechanical strength. The apparent porosity, bulk density, bending strength, fracture toughness were 4.0%, 2.58 g•cm-3, 50 MPa, 6.3 MPa•m1/2, respectively, with the size 200 μm graphite core at 2050 °C, while the volume rate of SiC and graphite was 6:4.