Abstract: Corundum structure alumina (α-Al2O3) powders were prepared via a non-hydrolytic sol-gel (NHSG) method using aluminum as raw material, ethanol as solvent, and iodine as catalyst. X-ray diffraction (XRD), differential thermal analysis (DTA), thermo gravimetric analysis (TG) were used to characterize the crystal phase of the products, while scanning electron microscopy (SEM) and transmission electron microscope (TEM) were employed to analyze the morphology. The results indicated that γ-Al2O3 was completely changed to α-Al2O3 at 1100 o C with a bit of aggregation. When 3 wt.% polyethylene glycol 600 (PEG 600) was introduced on the NHSG process, the dispersion was improved and the particle size decreased to100 nm.
Abstract: Hexagonal boron nitride ceramic（h-BN）has been prepared by pressureless sintering method. The effect of sintering aids, moulding pressure and sintering temperature on the mechanical properties and microstructures of h-BN were investigated. The results show that the densification of as-prepared h-BN ceramic can be contributed to the addition of sintering-aids and the formation of card-house structure. Because of the high densification and card-house microstructure, the obtained h-BN demonstrates higher bending strength and lower porosity when the moulding pressure is 200MPa, sintering temperature is 1850°C and the contents of sintering aids is 10wt%.
Abstract: Encapsulated carbon black pigment was prepared by layer-by-layer self-assembly method. The RX8002 carbon black particles were well coated by a SiO2 layer, which makes it has good connection with ZrSiO4 layer. Meanwhile, dense ZrSiO4 layer was coated on the C@SiO2 particles surface to prevent the corrosive effects of glaze. The structure and morphology of samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The chromatic value of the pigments was measured by the CIE color system. The results show that the carbon black particles can be well coated by SiO2 and ZrSiO4 layer. When the TEOS/H2O ratio is 0.002 and the ZrSiO4/C ratio is 0.71, the chromatic value of the encapsulated carbon black pigment is 42.55, and the pigment has a good stability in glaze.
Abstract: A kind of high alumina content ceramic stand wear and tear has been designed. The interface chemical reaction between single crystal alumina (in order to eliminate the influence of grain boundaries) and Nd2O3 powder has been observed. Microstructure and wear rate of the ceramic were investigated by SEM and by a purposely designed experimental device for the measurement of wear rate. Perimental results showed that a rare earth aluminate formed on the interface and the wear rate of a sample has reduced by 34%. The newly formed compound and single crystal alumina formed a compact structure which could make the grain boundaries strengthened and also lead to a beneficial effect on the elimination of pore and the density of the ceramic, at the same time improve abrasive resistance.
Abstract: Many literatures reported rare earth ions would segregate at grain boundaries toinhibit grain growth and improve the ceramic performance. However, the mutualinfluence between segregation and alumina grains was rarely seen in thereports. In this article, interface reaction between single crystal alumina (inorder to eliminate the influence of grain boundaries) and praseodymium oxidewas designed to further understand the influence mechanism. The resultssuggested that a composite oxide was formed at the junctions. Besides, largestresses produced between the composite oxide and alumina because of the thermalexpansion coefficient difference. This stresses would weaken grain boundariesbonding strength and reduce wear resistance.
Abstract: The present study proposed a convenient method to characterize the stability of aluminum foams by utilizing the resulting foam height. The factors influencing foam height in gas injection process was investigated including the blowing gas (N2 and air), particle content (5vol.%-15vol.%), gas flow rate (0.03m3/h-0.3m3/h) and orifice size (0.3mm and 0.5mm). Factors that contribute to the foam stability including oxygen in the blowing gas and larger particle content in the melt was proved to be positively related to the foam height. Moreover, it was found that larger gas flow rate and smaller orifice size lead to larger foam height. The cell wall microstructure and thickness was also analyzed to better understand the foaming behavior. The present study offers favorable proof that the foam height in the gas injection process can be a good index for the foam stability.
Abstract: Over 80% of solar grade silicon is produced by using Siemens process. The chemical and physical phenomenon involved in the Siemens CVD reactors is very complex. For the purpose of finding the effect of gas phase reactions on the deposition rate of silicon in Siemens CVD reactors, four different gas phase reaction routes were applied in computational simulations using a commercial software Ansys Fluent. The simulation results show that the gas phase reaction mechanisms have great impact on the predicted Si growth rates. Specifically, the silicon growth rates decrease with an increase in HCl concentration on the rods’ surfaces with a fixed surface temperature. The formation of SiCl4, however, shows insignificant impacts on the growth rate of Si, and the surface concentration of SiCl4 is not directly associated with that of HCl.
Abstract: A synthetic jet (SJ) is a fluid jet flow generated from fluid oscillations during a periodical fluid exchange between an actuator cavity and surrounding fluid. A water synthetic jet was generated from submerged piezoelectric-driven SJ actuator. The actuator slot width was 0.36 mm. The experiments were performed using laser induced fluorescence (LIF) flow visualization and particle image velocimetry (PIV) techniques, both in a phase locked setup. The LIF visualization was used to demonstrate three-dimensional nature of the SJ formation process and to estimate SJ velocity. The PIV experiment quantified SJ velocity cycles in chosen plans. The driven frequency was adjusted near the resonance at approximately 46 Hz. It was evaluated theoretically and confirmed experimentally by means of LIF visualization. The time-mean orifice velocity and the Reynolds number were estimated as U0 = 0.07–0.10 m/s and Re = 100–150, respectively.
Abstract: In this research, methyl acrylate has been synthesized from industrial raw material methyl acetate through highly efficient and eco-friendly method, One-step aldol condensation, using acid-base bifunctional catalyst Cs, P and K as catalysts. Carbon deposits and other issues led to the catalysts deactivation in the process of fixed bed, which led to the production interruption. While, the process of circulating fluidized bed can overcome this defect and the catalyst can maintain good catalytic activity in the whole process. Cs (8%), P (5%), K (2%)/γ-Al2O3/ catalyst showed better performance due to its high surface area and more weak basicity and acidity. In addition, theoretical calculations and cold model experiments were also conducted in this work to determine the catalyst particle size，operation gas velocity and gas distributor plate.