Advanced Materials Research Vols. 881-883

Abstract: In present, refining of metallurgical grade silicon is one of the promising routes to low-cost solar grade silicon for solar cells. Alloying with Ca has shown a great potential as efficient refining method of MG-Si in combination with acid leaching. Compared with Ca metal, Ca-Si alloy is cheaper and more secure. Great removal of impurity depends on microstructure of MG-Si after alloyed with Ca-Si alloy. In the work, the change of impurity phase which was performed by the change of the microstructure of MG-Si before and after alloyed with Ca-Si alloy has been analyzed. It was determined that CaSi₂ phase contained significant phosphorus content after alloying with Ca-Si alloy, It also investigated the optimal acid leaching condition after leaching, which confirmed that metallurgical grade silicon with Ca-Si alloy addition followed by acid leaching could be a potential route to remove phosphorus from MG-Si.

Abstract: The phase composition and particle size of the boron mud is investigated by X-ray diffractometry (XRD), scanning electron microscope (SEM) and laser particle size analyzer. The mainly phase composition of the boron mud are magnesite (MgCO₃) and forsterite (Mg₂SiO₄). The mainly phase composition of the calcined boron mud are forsterite (Mg₂SiO₄) and a small amount magnesia (MgO). the sizes of the boron mud are about 2~6μm and a few of them are bigger and less than 10μm and the particle size of less than 10μm is about 60%.

Abstract: The composition, microstructure and formation mechanism of the bottom dross in hot-dipping Zn-0.1%Ni alloy bath have been investigated through XRF, XRD and SEM. It is found that the bottom dross is an aggregation consisting of FeZn₁₃ (ζ), FeZn₁₅ and a small amount of Ni₃Zn₂₂. The formation mechanism of bottom dross can be described that loose ζ phase formed on the steel substrate and then flakes off from substrate; ferroalloy is formed and precipitated from the melt with diffusion of Fe into molten zinc if the dissolved Fe surpass its solubility in the molten zinc. It also indicated that there exists a trace of Ni in the bottom dross in hot-dipping Zn-0.1%Ni alloy bath.

Abstract: The disproportionation of AlCl was investigated by thermodynamics analysis. The results demonstrated that Gibbs free energy change of the disproportionation of AlCl decreases with decreasing temperature and increasing the AlCl pressure. The onset temperature of the disproportionation is 1521K in the standard atmosphere, and those are 878K and 1096K, respectively, at the AlCl partial pressure of 5Pa and 200Pa as the AlCl₃ partial pressure is 200Pa. The AlCl equilibrium partial pressure is about 10^-4Pa at 500K, demonstrating that the disproportionation of AlCl is complete below this temperature. The temperature in the condenser used in the experiments was below 1200K and the top near to the water-cooled cover of the furnace should be below 500K, therefore the disproportionation of AlCl occurred and was completed in the condenser.

Abstract: In this work, fine-lamellar structured TiB2 ceramic wettable cathode coatings were deposited on carbon cathodes of aluminium oxide reduction cells by atmosphere plasma spraying (APS). Cathode carbon blocks consisting of coatings 800 μm thick of plasma sprayed TiB₂ finepowder on carbon substrate were fabricated. In order to investigate the results of coating, the microstructure and phase composition of the wettable cathode coating were characterized by scanning electron microscopy (SEM). It is found that TiB₂ fine-powders were partly oxidized during the plasma spraying process. The coating was mostly formed by a matrix of fully molten particles where the presence of semi-molten feedstock agglomerates. The APS method is believed to be a good choice to deposit TiB₂ wettable cathode coating with high performance and reliability.

Abstract: In this study, a confocal scanning laser microscopy was used to in situ observe the collision and aggregation behavior of inclusions in molten state and the pushing/engulfing behavior in the solidifying interface of tire cord steel. The results show that the inclusion particles will be captured into the grains in the solidification front for the inclusions with a diameter are larger than 53.4μm at a cooling rate of 1 K/s. Moreover, the attraction force of inclusion particles in molten state is in the order of 10^-16N~10^-14 N in tire cord steel.

Abstract: The effects of solid solution temperature on the structures and properties of TC16 titanium alloy bars that made solid solution treatment in 780°C, 800°C, 850°C, 900°C, respectively, the processing time for 30min, then cooled in the air were studied. The results show that during solid solution treatment under 800°C, the alloy structures are the primary ɑ phase and the metastable β phase, while solid solution temperature rise to 800°C, the alloy structures begin to appear ɑ" martensite phase. With the increase of solid solution temperature, the alloy grain grow up somewhat, material tensile strength increases gradually, yield strength firstly decreases and then increases, elongation at break firstly increases and then decreases, percentage reduction of area at break decreases gradually. Solid solution state of TC16 titanium alloy bars are not suitable for cold heading forming, strengthening the titanium alloy must be subsequent artificial aging treatment.

Abstract: The effect of semi-solid processing on microstructures and mechanical properties of rheo-sulrries A356 sand cast produced by Gas Induce Semi-Solid (GISS) process was investigated. Step plate sand molds were used in this study. The results found that the initial solid fraction of rheo-slurries did not influence on the non dendritic α-Al phase size of the as-cast alloy, while no initial solid fraction of low temperature conventional casting specimens obtained dendritic α-Al phase microstructure. In addition, both α-Al phase size and dendrite arm spacing increased with increasing the casting modulus. Tensile strengths and elongations of rheo-slurry casting specimens are higher than that of conventional casting specimens. This study indicates that low initial solid fraction slurry is suitable for gravity sand casting due to higher feeding time of this alloy and obtain the highest quality index value of 400 (tensile strength of 281 MPa and elongation of 6.1%).

Abstract: Tensile properties of rheo-cast 7075-T6 Al alloy produced by Gas Induced Semi-Solid (GISS) technique was investigated as a function of temperatures from 25°C to 250 °C in order to assess the potent of high temperature applications. It was found that the ultimate tensile strength and yield strength of the alloy decreased steadily with increasing temperature. There was loss in strength of about 33% at 200°C and 46% at 250 °C comparing to the strength at room temperature. At T = 250 °C, the ultimate tensile strength and yield strength of the rheo-cast 7075-T6 Al alloy were higher than those of the wrought 7075-T651 Al alloy. Keyword: 7075 Al alloy; Gas Induced Semi Solid (GISS) technique; Elevated temperature tensile.

Abstract: In this thesis the object of study is a low grade sandstone copper with complex composition. Through the process mineralogy research on a sandstone copper ore,the result showed that the primary sulfide copper minerals are tetrahedrite and chalcopyrite; secondary sulfide copper minerals are bornite, chalcocite and azurite; the main oxide copper mineral is malachite; the main gangue mineral is quartz. The grade of copper is 0.77% and the oxidation rate is 45.45% in the run of mine, it is an oxide copper ore with not thoroughly oxidation. There is a part of disseminated particle size of copper minerals is relatively fine. Mainly sulfide copper minerals are paragenesis with dolomite and pyrite; oxide copper minerals are often blended with limonite. So the key of obtaining the good flotation index is selecting reasonably grinding fineness and making the part of fine-grained disseminated copper full liberation.