Electrochemical behavior of gold and its associated minerals in alkaline thiourea solutions

Electrochemical measurements were conducted to study the electrochemical behavior of gold (Au) and its commonly associated minerals in alkaline thiourea solutions. The results indicated that without addition of any stabilizer, selective dissolution of Au from stibnite and pyrite was only possible at relatively low thiourea concentrations. As Na₂SiO₃ was added, pyrite started to become active and an oxidation peak appeared; the oxidation peaks of arsenopyrite and chalcocite appeared earlier than that of Au. The chalcocite peak shifted in the positive direction and the peak current increased. Stibnite did not show an oxidation peak and its current was nearly zero. Adding Na₂SiO₃ favored the selective dissolution of Au when its minerals were associated with chalcocite and stibnite. At pH 12, the Au anode dissolution peak current increased with stabilizer concentration. At 0.38 and 0.42 V and for Na₂SiO₃ concentration below 0.09 M, the current density continuously increased with Na₂SiO₃ concentration. The Na₂SiO₃ concentration had to be adequate to stabilize thiourea. When the potential was higher than 0.42 V, the surface of the Au electrode started to passivate. With an additional increase in potential, the presence of Na₂SiO₃ could not stop the inevitable decomposition of thiourea.     

Effects of Zn content on the microstructure and the mechanical and corrosion properties of as-cast low-alloyed Mg–Zn–Ca alloys

The effects of Zn content on the microstructure and the mechanical and corrosion properties of as-cast low-alloyed Mg–xZn–0.2Ca alloys (x=0.6wt%, 2.0wt%, 2.5wt%, hereafter denoted as 0.6Zn, 2.0Zn, and 2.5Zn alloys, respectively) are investigated. The results show that the Zn content not only influences grain refinement but also induces different phase precipitation behaviors. The as-cast microstructure of the 0.6Zn alloy is composed of α-Mg, Mg₂Ca, and Ca₂Mg₆Zn₃ phases, whereas 2.0Zn and 2.5Zn alloys only contain α-Mg and Ca₂Mg₆Zn₃ phases, as revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Moreover, with increasing Zn content, both the ultimate tensile strength (UTS) and the elongation to fracture first increase and then decrease. Among the three investigated alloys, the largest UTS (178 MPa) and the highest elongation to fracture (6.5%) are obtained for the 2.0Zn alloy. In addition, the corrosion rate increases with increasing Zn content. This paper provides an updated investigation of the alloy composition–microstructure–property relationships of different Zn-containing Mg–Zn–Ca alloys.     

Software Module Clustering Algorithm Using Probability Selection

Software module clustering problem is an important and challenging problem in software reverse engineering whose main goal is to obtain a good modular structure of the software system. The large complex software system can be divided into some subsystems that are easy to understand and maintain through the software module clustering. Aiming at solving the problem of slow convergence speed, the poor clustering result, and the complex algorithm, a software module clustering algorithm using probability selection is proposed. Firstly, we convert the software system into complex network diagram, and then we use the operation of merger, adjustment and optimization to get the software module clustering scheme. To evaluate the effectiveness of the algorithm, a set of experiments was performed on 5 real-world module clustering problems. The comparison of the experimental results proves the simplicity of the algorithm as well as the low time complexity and fast convergence speed. This algorithm provides a simple and effective engineering method for software module clustering problem.     

Microstructure and electrolysis behavior of self-healing Cu-Ni-Fe composite inert anodes for aluminum electrowinning

The microstructure evolution and electrolysis behavior of (Cu₅₂Ni₃₀Fe₁₈)-xNiFe₂O₄ (x=40wt%, 50wt%, 60wt%, and 70wt%) composite inert anodes for aluminum electrowinning were studied. NiFe₂O₄ was synthesized by solid-state reaction at 950℃. The dense anode blocks were prepared by ball-milling followed by sintering under a N₂ atmosphere. The phase evolution of the anodes after sintering was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results indicate that a substitution reaction between Fe in the alloy phase and Ni in the oxide phase occurs during the sintering process. The samples were also examined as inert anodes for aluminum electrowinning in the low-temperature KF-NaF-AlF₃ molten electrolyte for 24 h. The cell voltage during electrolysis and the corrosion scale on the anodes were analyzed. The results confirm that the scale has a self-repairing function because of the synergistic reaction between the alloy phase with Fe added and the oxide phase. The estimated wear rate of the (Cu₅₂Ni₃₀Fe₁₈)-50NiFe₂O₄ composite anode is 2.02 cm·a-1.     

Alkaline digestion behavior and alumina extraction from sodium aluminosilicate generated in pyrometallurgical process

In pyrometallurgical process, Al-and Si-bearing minerals in iron and aluminum ores are easily transformed into sodium aluminosilicates in the presence of Na₂O constituents, which alters the leaching behaviors of Al₂O₃ and SiO₂. It was confirmed that sodium aluminosilicates with different phase compositions synthesized at various roasting conditions were effectively digested in the alkaline digestion process. Under the optimum conditions at temperature of 100-120℃, liquid-to-solid ratio (L/S) of 10:2 mL/g, caustic ratio of 4, and Na₂O concentration of 240 g/L, the actual and relative digestion ratio of Al₂O₃ from the synthesized sodium aluminosilicates reached maximums of about 65% and 95%, respectively, while SiO₂ was barely leached out. To validate the superior digestion property of sodium aluminosilicate generated via an actual process, the Bayer digestion of an Al₂O₃-rich material derived from reductive roasting of bauxite and comprising Na_1.75Al_1.75Si_0.25O₄ was conducted; the relative digestion ratio of Al₂O₃ attained 90% at 200℃.     

Dynamic characteristics of the planetary gear train excited by time-varying meshing stiffness in the wind turbine

Wind power has attracted increasing attention as a renewable and clean energy. Gear fault frequently occurs under extreme environment and complex loads. The time-varying meshing stiffness is one of the main excitations. This study proposes a 5 degree-of-freedom torsional vibration model for the planetary gear system. The influence of some parameters (e.g., contact ratio and phase difference) is discussed under different conditions of a single teeth pair and double pairs of teeth. The impact load caused by the teeth face fault, ramped load induced by the complex wind conditions, and the harmonic excitation are investigated. The analysis of the time-varying meshing stiffness and the dynamic meshing force shows that the dynamic design under different loads can be made to avoid resonance, can provide the basis for the gear fault location of a wind turbine, and distinguish the fault characteristics from the vibration signals.     

Image forgery detection using segmentation and swarm intelligent algorithm

Small or smooth cloned regions are difficult to be detected in image copy-move forgery (CMF) detection. Aiming at this problem, an effective method based on image segmentation and swarm intelligent (SI) algorithm is proposed. This method segments image into small nonoverlapping blocks. A calculation of smooth degree is given for each block. Test image is segmented into independent layers according to the smooth degree. SI algorithm is applied in finding the optimal detection parameters for each layer. These parameters are used to detect each layer by scale invariant features transform (SIFT)-based scheme, which can locate a mass of keypoints. The experimental results prove the good performance of the proposed method, which is effective to identify the CMF image with small or smooth cloned region.     

Reaction mechanism for in-situ β-SiAlON formation in Fe3Si-Si3N4-Al2O3 composites

In this work, Fe₃Si-Si₃N₄-Al₂O₃ composites were prepared at 1300℃ in an N₂ atmosphere using fused corundum and tabular alumina particles, Al₂O₃ fine powder, and ferrosilicon nitride (Fe₃Si-Si₃N₄) as raw materials and thermosetting phenolic resin as a binder. The effect of ferrosilicon nitride with different concentrations (0wt%, 5wt%, 10wt%, 15wt%, 20wt%, and 25wt%) on the properties of Fe₃Si-Si₃N₄-Al₂O₃ composites was investigated. The results show that the apparent porosity varies between 10.3% and 17.3%, the bulk density varies from 2.94 g/cm3 and 3.30 g/cm3, and the cold crushing strength ranges from 67 MPa to 93 MPa. Under the experimental conditions, ferrosilicon nitride, whose content decreases substantially, is unstable; part of the ferrosilicon nitride is converted into Fe₂C, whereas the remainder is retained, eventually forming the ferrosilicon alloy. Thermodynamic assessment of the Si₅AlON₇ indicated that the ferrosilicon alloy accelerated the reactions between Si₃N₄ and α-Al₂O₃ fine powder and that Si in the ferrosilicon alloy was nitrided directly, forming β-SiAlON simultaneously. In addition, fused corundum did not react directly with Si₃N₄ because of its low reactivity.     

Spheroidization of silica powders by radio frequency inductively coupled plasma with Ar-H2 and Ar-N2 as the sheath gases at atmospheric pressu

Amorphous spherical silica powders were prepared by inductively coupled thermal plasma treatment at a radio frequency of 36.2 MHz. The effects of the added content of hydrogen and nitrogen into argon (serving as the sheath gas), as well as the carrier gas flow rate, on the spheroidization rate of silica powders, were investigated. The prepared silica powders before and after plasma treatment were examined by scanning electron microscopy, X-ray diffraction, and laser granulometric analysis. Results indicated that the average size of the silica particles increased, and the transformation of crystals into the amorphous state occurred after plasma treatment. Discharge image processing was employed to analyze the effect of the plasma temperature field on the spheroidization rate. The spheroidization rate of the silica powder increased with the increase of the hydrogen content in the sheath gas. On the other hand, the spheroidization rate of the silica power first increased and then decreased with the increase of the nitrogen content in the sheath gas. Moreover, the amorphous content increased with the increase of the spheroidization rate of the silica powder.     

差异展示法鉴定GA3诱导的水稻差异表达的mRNA

赤霉素是植物生长发育过程中一类重要的调节激素，在水稻不育系上喷施合适浓度的ＧＡ３（赤霉素的一种）可以克服其包颈现象。运用反转录和聚合酶链式反应建立了一套旨在分离差异表达ｃＤＮＡ的差异展示方法。