Advanced Materials Research Vol. 624

Abstract: It has many advantages with liquid phase reduction method to prepare the nano-silver, such as experimental conditions are simple, low cost, energy-saving, etc.. At the same time, the nano silver powder prepared by this method has high surface activity, catalytic property and wide usage. In this paper, nano-silver powder was prepared by changing the amount of protective agents with chemical liquid phase reduction method. This paper focuses on the impact of the amount of protective agent on the nano-silver. In addition, we also analyzed the reaction temperature, PH value of solution, viscosity and electrical conductivity on the preparation of nano-silver. Finally, test results from the TEM shows that the nano-silver was prepared with smaller size, uniform size and good dispersion.

Abstract: Gel casting foam is a novel method which was developed in latter 1990s for the fabrication of porous materials with regular round pores and a relatively high flexural strength. It also has the advantages of simplicity in degreasing processing and short production cycle. However, the gelating system used in this method commonly contains acrylatnide, which is toxic and sensitive to oxygen, due to which, foaming and polymerization of the substance have to be performed in an oxygen-free environment. In this work, we use agar as the gelating agent in replace of acrylatnide to prepare alumina macroporous ceramics. The effects of foaming speed, foaming time, gelating time and valeric acid on the pore diameter of the sample were investigated. Results show that the average pore diameter increasing with the foaming speed, but decreasing with the increasing foaming time. Moreover, the addition of valeric acid reduces the bubble size during foaming and increase the stability of the foams. By controlling the foaming and gelating conditions, we achieve alumina macroporous ceramics with regular round pores of over 100μm by this method.

Abstract: CeO₂ nanobundles were obtained by the microwave homogeneous precipitation method using cerium nitrate and urea as raw materials. Ag nanoparticles were obtained by the microwave solvolthermal method using silver nitrate, PVP and ethanol as raw materials. Nanostructured Ag/CeO₂ was prepared by the impregnation method. The products were characterized by X-ray diffraction, SEM, TEM, UV-vis spectrum, BET. The photocatalytic properties of CeO₂ and Ag/CeO₂ nanomaterials were evaluated by degradation of methyl orange. The results show that the photocatalytic degradation of modified cerium oxide modified by nano silver on methyl orange is significantly improved. For the Ag (0.1 wt%)/CeO₂ material, the degradation rate on methyl orange is up to 83.2% under visible light irradiation for 1h. The catalytic activity of nanostructured Ag (0.1 wt%)/CeO₂ in dye decolorization is substantially higher than the standard reference TiO₂ P25.

Abstract: Alumina matrix composites containing 20 wt % of Ni was sintered by spark plasma sintering (SPS) process. The influence of sintering temperature (1400-1550 °C) on densification and grain size of the composites were investigated (heating rate: 200 °C /min, sintering time: 5 min). Wear behavior of samples obtained by SPS were evaluated in a dry condition with reciprocate ball-on-disk testing machine. The results show that the relative density and alumina grain sizes increase with the increasing sintering temperature, and the fine-grained structure (alumina size controlled in 1–2 µm) are obtained at a temperature lower than 1400 °C; the alumina grain sizes increase to 5 µm at a temperature higher than 1500 °C. The fine-grained structure samples exhibits higher wear resistance.

Abstract: The aim of this invitro study was to evaluate the fracture resistance of endodontically treated canines restored with one-piece milled zirconia post and core in the varying ferrule modes. Fifty recently extracted human maxillary canines were endodontically treated and randomly divided into 5 groups of 10 specimens each. According to the defect degree of ferrule, intact ferrule was classified as group A and served as control, 2 mm ferrule height without buccal ferrule was classified as group B, 2 mm ferrule height without mesial and buccal ferrule was classified as group C, 2 mm ferrule height without mesial, buccal and lingual ferrule was classified as group D, no ferrule preparation was classified as group E. All of the teeth were restored with one-piece milled zirconia post and core, and zirconia crowns. The teeth were prepared to standardized specifications. The restored teeth were loaded to fracture at a 135° angle to their long axis, at a cross-head speed 0.5 mm/min, and the load (N) at failure was recorded. Statistical analysis was performed by SNK pairwise multiple comparisons (α=0.05). The mean fracture resistance of five groups as follows: 1019.30±139.01N for group A, 861.20±105.67N for group B, 833.70±100.56N for group C, 733.20±96.91N for group D, 698.00±99.90N for group E. The fracture resistance of restored teeth between group B and group C, group D and group E had no statistically significant difference(P>0.05). The fracture resistance of the rest pairwise group comparisons had statistically significant difference(P<0.05). Increasing the absence degree of ferrule, it was found that the fracture resistance decrease. The buccal and lingual ferrule were more important than mesial ferrule for enhanced fracture resistance. This in vitro study supports evidence that reserving the buccal and lingual ferrule is a key point to increase the fracture resistance of canines restored with one-piece milled zirconia post and core.

Abstract: The preparation of ultrafine-grained alumina ceramics by the fast sintering technique Self-propagating High-temperature Synthesis plus Quick Pressing (SHS-QP) method was reported. The reaction heat generated by combustion reaction was applied to act as a high temperature source. An alumina compact was loaded inside the combustion reactants, which form a “SHS-furnace”, and great mechanical pressure was applied when the temperature reached the maximum. Dense ultrafine-grained alumina ceramic was prepared using a lower heating rate (900 °C /min), and the effects of sintering time, and pressure on the densification and grain size were discussed. Within a short sintering time of 3 min, full-density alumina ceramics with ultrafine-grained structure are obtained under a pressure of 120 MPa.

Abstract: The present work observed and analyzed the microstructures of various starting powders including SiC, AlN-R (Y / La) ₂O₃ as additives for LPSing (Liquid Phase Sintering), B/C additives for SSSing (Solid State Sintering), as well as the spray granulated powders as comparison, by using scanning electron microscopy SEM. The microstructure of molded green bodies was also posted. Present paper opens out the characters of the various perfect and defect of microstructures of these samples. Their effect on the processing and properties of SiC ceramics was analyzed and discussed.

Abstract: β-Sialon/Ti(C,N) composites were prepared using low and middle grade bauxite and ilmenite as raw material,while coke as reducing agent in high purity nitrogen atmosphere through carbothermal reducrion-nitridation(CRN).The main phases of low and middle grade bauxite are kaolinire(Al2O3•2SiO2•2H2O) and (Al2O3•H2O)2 and ilmenite mainly contain ilmenite(FeTiO3) and rutile(TiO2).The reaction products of bauxite are the β-Sialon(Z=3,Si3Al3O3N5) while those of ilmenite are TiC and Fe.The results showed that the main phases are β-Sialon,Ti(C,N),Al2O3 and Fe when the reaction temperature is at 1400°C holding for 4 hours(10wt% ilmenite and 90wt% bauxite as raw material).However,β-Sialon decomposes into 21R at 1450°C and into 15R and AlN at 1500°C.So 1400°C is selected as the proper temperature to synthesize β-Sialon/Ti(C,N) composites.At 1400°C,the β-Sialon crystals with the largest quantity grow well and show long column in shape.With the increase of the reacrion temperature β-Sialon begin to decompose,the β-Sialon crystals change to short columnar,with the number decreasing quickly.

Abstract: The electronic structure, chemical bonding and elastic properties of Ti3AC2 (A=Al, Si, Sn) were investigated by generalized gradient approximation (GGA) based on density functional theory (DFT). The calculated lattice parameters and equilibrium volumes are in good agreement with the available experimental data. The density of state (DOS) and partial density of states (PDOS) show that the DOS at the Fermi level (EF) is located at the bottom of a valley and originate mainly from the Ti-3d electrons. Population analyses suggest that there are strong covalent bonding in Ti1-C and Ti2-C atoms in Ti3AC2 (A=Al, Si, Sn). Single-crystal elasticity constants were calculated and the polycrystalline elastic modules were estimated according to Voigt, Reuss and Hill’s approximations (VRH). The Young’s modulus Y, Poisson’s ratio ν and BH/GH are also predicted. Results conclude that the hexagonal phase Ti3AC2 (A=Al, Si, Sn) are mechanical stable and behaves in a brittle manner. Polycrystalline elastic anisotropy coefficients AB and AG are also derived from polycrystalline bulk modulus B and shear modulus G.

Abstract: The electronic structure and elastic properties of Si doping Ti3Al1-xSixC2 (x=0-1) were studied by generalized gradient approximation (GGA) based on density functional theory (DFT) and virtual crystal approximation (VCA). The calculated lattice parameters and equilibrium volumes are in good agreement with the available experimental data. The density of state (DOS) shows that the DOS at the Fermi level (EF) is located at the bottom of a valley. Single-crystal elastic constants were calculated and the polycrystalline elastic modules were estimated according to Voigt, Reuss and Hill’s approximations (VRH). The results show that the bulk modules increase monotonously and the Poisson ratio v as well as BH and BG increase first and then decrease with the increasing of the doping Si. The Passion ratio v and BH/GH indicate that Ti3Al1-xSixC2 (x=0-1) are brittle compounds. Polycrystalline elastic anisotropy coefficients AB and AG were also derived and are very small.