Papers by Keyword: Impurity

Abstract: The effects of ammonium adding temperature and coefficient on precipitation rate and product quality for a certain kind of vanadium-bearing solution are studied in this paper. On this basis, a further investigation is carried out to probe into the effects of Na, Si, and Al on the precipitation rate and product quality. It can be found in the experiments that the precipitation rate can reach to 99.328% or above with the optimal parameters listed as follows: ammonium adding temperature at 35~65°C, ammonium adding coefficient at 2, and Na, Si and Al content under 25 g/L, 1.5 g/L, and 0.1 g/L respectively. As a result, Na, Si, and Al content in ammonium polyvanadate(APV) is 0.058%, 0.053%, and 0.01% respectively.

Abstract: The basic features of salt rock in China are as follows: thickness single layer, more layered distribution and impurities and others. The unstable mechanical parameters are caused by the different types and content of minerals in natural salt rock. Elastic modulus and Poisson ratio of natural samples from certain northern area in China which are compressed under different confining pressure is then analysed with the impurity content to get the relationship between them. Comparing the experimental values with the predicted calculated by Mori-Tanaka method, a linear estimation formula is proposed for the prediction of mechanical parameters suitable for practical engineering applications in this area.

Abstract: The element phosphorus plays key role in plants metabolism. It is widely used as fertilizer. This element is usually found in insoluble forms (Ca₁₀(PO₄)₆F₂). The solubilization in phosphoric acid (H₃PO₄) is a process widely used in fertilizer industry. The impurities in the phosphate exert significant influence on recovery and productivity phosphoric process, besides affecting the quality of products. The objective of this work is to analyze the influence of some of these main impurities (iron, aluminum and magnesium) in the production process of phosphoric acid. A referential methodology (induced crystallization) of phosphoric acid production was developed. Samples of igneous phosphate concentrate contaminated with iron, aluminum and magnesium were prepared for the experiments. The reaction control parameters were similar to an industrial operation of phosphoric acid dihydrate process. Reductions in conversions, increases in viscosity and density of phosphoric acid were observed with increasing presence of these impurities. In the filtration step was found increase in resistivity of the cake with the increase of the impurities content. The iron mineral element promoted an increase in induction time of crystals nucleation.

Abstract: The powder metallurgy (PM) approach is widely used for cost-effective production of titanium alloys and articles. In the PM approach the large specific surface of starting powders heightens the risk of excessive impurity presence and, hence, degradation of final alloy properties. The present study analyzes the opportunity to produce sintered commercially pure titanium (CP-Ti) with acceptable impurity content from powder materials. Starting titanium and titanium hydride powders were comparatively examined. The impurity elements (oxygen, chlorine, carbon) and their conditions on the powder particle surface, as well as the surface processes and gases emitted from powders upon heating, have been analyzed by means of surface science techniques. The role of hydrogen emitted from titanium hydride in material purification has been discussed. The opportunity to produce titanium materials with final admissible content of interstitials (O, C, Cl, and H) using starting titanium hydride powder has been demonstrated.

Abstract: An annealing study, in the 100-1400 C temperature range ,was carried out on Cl-implanted n- or p-type 4H-SiC epilayers. The electrical characterization of the epilayers shows the rise of several deep levels and the role of Cl, on both carrier concentration and defects' microscopic structure, is discussed in the light of theoretical results obtained by density functional calculations performed on a 64-atom cubic SiC supercell.

Abstract: A new method for removal of impurities in pure molten aluminum has been presented in this paper. The basic principle of this method is that the molten fluxes are forced to inject into the molten aluminum under counter-gravity, creating strong vortex to mix fully with the molten aluminum. In this way, the impurities in the aluminum will transfer into the flux because of the absorption of the flux to the inclusions. As the result, the molten aluminum is purified. The experiments were carried out for pure aluminum combined with the flux (40wt.% NaCl，30wt.% KCl，10wt.% NaF and 20wt.%Na3AlF6). The results show that after 3 purifying cycles (6 minutes), the inclusion contents decreased from 2. 1% to 0.35%, a removal rate of 83.3%; and hydrogen concentration decreased from 0.37ml/100gAl to 0.12ml/100gA, with hydrogen removal rate being 68%.

Abstract: Using the first principles method, which is based on the density function theory (DFT), the structures and electronic properties of S atoms are adsorbed on the Fe (100) surface for X(X is Cr, Ni, Mo, C, Mn ,Si,P and S) impurities in Fe, and their molecular orbital and absorption energies were calculated with the generalized gradient approximation. The results show that S adsorbed on H site for Cr, Ni, Mn, C and Mo impurities in Fe is stable but for Si, S and P is B site. The adsorption energy for Ni in impurity Fe is almost nearby for the purity Fe and the effect for Ni in S absorption on Fe (100) surface is very small. In order to prevent S absorption on Fe surface，we can reduce the percentage of Ni.

Abstract: The main characteristic of cathodic copper is the concentration of impurities because it depends on mechanical characteristics, i.e. ductility, of the derived copper wires. The standard mechanical tests that evaluate their ductility, are quick elongation and spiral elongation tests. The results of these essais shown that there is not a clear correlation among the impurities content in cathodes and wire ductility. Also, the two mechanical tests actually used are not able to discriminate differences on the copper ductility associated to variations in impurities concentration, at ppm level. In this work, a design of new specimen for traction test, with a reduced gage length of 10 mm that clearly discriminate differences on copper ductility associated to variations in impurities concentration is exposed. In addition, from traction tests to copper wires and observation of their fracture surfaces by means of SEM and EDS it is concluded that the principal impurity affecting the ductility of the copper wires is the oxygen, mainly incorporated during the melting of the cathodes and casting of the rods. Also, the traditional annealing to the samples previous to the tensile tests must to be avoid since produces a dispersion on the matrix of the Cu₂O oxides and so the deleterious effect of the oxygen on the copper ductility cannot be detected.

Abstract: Multi-crystalline silicon ingot was prepared by directional solidification method using metallurgical grade silicon as raw materials. The influence of impurities and crystalline defects in mc-Si on the minority carrier lifetime and resistivity was investigated. The results indicate that both grain boundary and impurities play important roles in the deterioration of the minority carrier lifetime.

Abstract: The effect of C substitution on the glass forming ability (GFA) and soft magnetic properties of Fe-based bulk metallic glasses (BMG) Fe_79.4-xC_xSi_3.5B_5.1P_8.9Mo₃Mn_0.1 (x = 4.2, 5.2, and 7.0) alloys have been investigated. It is revealed that fully glassy alloy rods with diameters up to 4 mm can be prepared by conventional copper mold casting method even using the low-cost industrial Fe-P master alloy. Properly substituting of Fe by C gives rise to an enhancement of GFA. Moreover, all the samples exhibit good soft magnetic properties with high saturation magnetization up to 1.16 T and low coercivity of 204 A/m.