Advanced Materials Research Vols. 311-313

Abstract: Zinc acetate and ammonium bicarbonate are used as raw material, zinc oxide prepared by direct precipitation of new technology. This paper discusses the effection of the formation in zinc oxide from the reactant concentration of zinc acetate, HCO^3-/Zn₂+ molarity ratio, reaction temperature, reaction time and condition in thermal decomposition of basic zinc carbonate. Using transmission electron microscopy (TEM), thermogravimetric / differential thermal analysis (TG / DTA) and other methods, preparation of nano-ZnO are characterized. Good conditions for the better system of nano- ZnO are 0.75mol /L in the concentration of zinc acetate solution, 2.5:1 in bicarbonate of ammonia and zinc acetate molar ratio, 45 °C of reaction temperature, 1.0h of reaction time, and 350 °C in thermal decomposition temperature, 3.0h of pyrolysis time. Zinc oxide obtained average particle size is 20 ~ 80nm, for the hexagonal crystal form.

Abstract: A finite element model is developed in this paper for simulating cyclic deformation in ultra-fined polycrystalline metals. The grain material is characterized by conventional theory of mechanism-based strain gradient plasticity (CMSG). A cohesive interface model was used to simulate the initiation and propagation of intergranular cracks. The simulation results show that inhomogeneous plastic deformation induces high strain gradient effects and severely plastic hardening in the grain interior, and the intergranular crack has a significant influence on the overall mechanical properties of ultra-fined polycrystalline metals subjected to cyclic loading.

Abstract: Compare investigate physicochemical properties of fine powder and two ultrafine powders of Dragon’s Blood, and then to determinate particle size distribution for ultrafine powders of Dragon’s Blood. Specific surface area and porosity, surface morphology and moisture absorption of Dragon’s Blood powders were investigated. The content and the in vitro dissolution of dracorhodin in Dragon’s Blood powders were determined by HPLC. The results showed that the content of dracorhodin had no significant difference among three Dragon’s Blood powders. With the decreasing of particle size the degree of moisture decreased. The dissolution of dracorhodin in the order of: ultrafine powder I > ultrafine powder II > fine powder. An appropriate degree of superfine grinding can improve moisture absorption of Dragon’s Blood powders and dissolution of dracorhodin. Particle size distribution of Dragon’s Blood ultrafine powder should be controlled about 40 μm.

Abstract: An effective technology of hydrothermal synthesizing flower-sphere MoS₂ by reaction of Na₂MoO₄ and CS(NH₂)₂ with NH₂OH•HCl as reductant was researched. The effect of the molar ratio of Mo to S, reaction temperature, reaction time, aging time on the yield, purity and morphology of the product was explored by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the optimal synthesis conditions are as follows: the molar ratio of Mo to S of 1:7, the temperature of 220°C, the reaction time of 24h and the aging time of 16h. Under these conditions, the inerratic and pure flower-sphere MoS₂ was obtained. Its average particle size is about 2μm and the petal is self-assembly growth. The yield of the product can reach 88%.

Abstract: Polyacrylonitrile(PAN) microspheres were synthesized by soapless emulsion polymerization of acrylonitrile(AN) in water. The effects of monomer and initiator concentration on the conversion of AN and the diameter of microspheres were investigated. The results showed that when the concentration of monomer increases, the conversion of AN decreases while the diameter of PAN microspheres increases. When the concentration of initiator increases, the conversion of AN and the diameter of PAN microspheres both increase. For this method of PAN microspheres synthesis, the highest conversion of AN is about 60% and the diameter can be controlled in need ranging from approximately 140 to 500nm.

Abstract: One-dimensional magnetite particles were prepared by a seed-mediated growth method under magnetic field. The amount of seed, seed size, PolyvinylPyrrolidone concentration (PVP) and reaction time have a significant effect on the morphology of the samples. The addition of a small amount of 100nm seeds leads to obtain rod-like particles, while chain-like particles are formed when the seed size is increased to 700 nm. The aspect ratio of the rod is controlled by varying the volume ratio of seed to iron salt. Increasing the reaction time is favorable to the formation of chain-like particles.

Abstract: In this paper, the effect of heat treatment and strain rate on the tensile property of extruding magnesium alloys 1Mn1Zn4Y is studied by using tensile tests. It can be concluded that because the grain size of the sample with solid solution (T4) is coarser than that of the sample without heat treatment，the elongation and the strength of the specimen treated with solid solution are lower. However, owing to many fine and dispersed particles of the second phase precipitated from the solid solution, the strength of sample treated with solid solution + aging (T6) is the highest.

Abstract: The flow behavior and associated structural changes of an AZ61 Mg alloy were analyzed by using hot compression tests in the temperature and strain rate ranges of 250–400 °C and 0.001 to 1 s^–1, respectively. The stress–strain curves exhibited the trend typical of materials in which deformation is recovery-controlled in the high Z regime (Z is the Zener–Hollomon parameter), while at low strain rates and high T, the flow curves exhibited a softening typical of recrystallization phenomena. Microstructure analysis has been performed to correlate the microstructure changes to the flow behaviors.

Abstract: In this work, the effects of rare element yttrium (Y) on the microstructure and mechanical properties of the as-cast Zn-25Al-5Mg-2.5Si alloy at room and elevated temperature (100°C and 180°C) have been investigated. The alloys were prepared by conventional melting and casting routs with different Y contents (0 wt.%,0.1 wt.%,0.4 wt.%,0.8 wt.%,1.2 wt.% and1.5 wt.%). The results showed that the addition of Y element led to the formation of Al3Y phase and Y₂Zn₁₇ phase in the microstructure and the mechanical properties of the alloys rose at first and then dropped with the Y content increasing. When Y content was 0.4 wt.%, the optimization of microstructure and properties especially the tensile strength at high temperature was obtained. The tensile strength of the alloy at 180°C could be increased by 26.4%.

Abstract: In order to achieve the numerical calculating rheological forming process of materials, a series of tension experiments under the different temperatures and different strain rates were done on the standard samples of sheet TC1 titanium alloy. The experimental results were analyzed theoretically and the rheological stress constitutive models of TC1 titanium alloy are built combining the strong points of the Perzyna model and Johnson-Cook model. Comparing the calculation results conducted from the model with the experimental results, it proves that the model can reflect the temperature effect and strain rate effect of TC1 titanium alloy.