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Ti leaching f.om activated ilmenite–f. mixture at dif.erent milling energy levels

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International Journal of.Minerals,Metallurgy and Materials 2018年第11期25卷 1263-1274页

作者： Elham Hosseini f.reshteh rashchi Abolghasem Ataie School of.Metallurgy and Materials Engineering College of EngineeringUniversity of Tehran

Mechanical activation processes on ilmenite concentrate were perf.rmed in three dif.erent energy levels. Iron powder as a reducing agent was added to ilmenite in the milling stage and the mechanically activated mixture was subjected to acid leaching. The leaching experiments were designed using the Taguchi method, and the optimum ranges were obtained. f.rthermore, response surf.ce methodology(RSM) was used to optimize the critical parameters in the leaching system to achieve the highest titanium(Ti) leachability. Based on the inductively coupled plasma-optical emission spectrometry(ICP-OES) results, maximum leaching recovery of.Ti(80%) was obtained using activated Ti concentrates at a medium activation energy level, which is calculated to be 25.38 kJ/g, using 15 vol% hydrochloric acid(HCl), a temperature of.70°C, leaching time of.3 h, and a solid-to-liquid ratio of.0.05 g×mL^(–1). Intensif.ing the milling energy f.om a low to high level led to a decrease in the mean crystallite size and also structure homogenization at the high energy level. According to the transmission electron microscopy(TEM) images, the mean grain size of.the ilmenite/f. nanocomposite was about 30 nm at the medium energy level sample. f.nally, solvent extraction by tributyl phosphate(TBP) was perf.rmed on the leach liquor to separate dissolved f.(the major impurity) f.om Ti, which led to 83% extraction recovery of.Ti.

关键词： ilmenite leaching titanium extraction mechanical activation

Photocatalytic degradation of.methylene blue by nanostructured f./f.S powder under visible light

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International Journal of.Minerals,Metallurgy and Materials 2018年第2期25卷 244-252页

作者： Hassan Esmaili Amir Kotobi Saeed Sheibani f.reshteh rashchi School of.Metallurgy and Materials Engineering College of Engineering University of Tehran

The photocatalytic perf.rmance of.mechano-thermally synthesized f./f.S nanostructures f.rmed f.om micron-sized starting materials was compared with that of.a thermally synthesized nanostructure with nano-sized precursors in this paper. The properties of.as-synthesized materials were studied by X-ray dif.raction（XRD）, transmission electron microscopy（TEM）, vibrating sample magnetometry（VSM）, dif.use ref.ectance spectroscopy（DRS）, and ultraviolet–visible（UV-Vis） spectroscopy. The ef.ects of.irradiation time, methylene blue（MB） concentration, catalyst dosage, and p H value upon the degradation of.MB were studied. Magnetic properties of.the samples showed that both as-synthesized f./f.S photocatalysts are magnetically recoverable, eliminating the need f.r conventional f.ltration steps. Degradation of.5 ppm of.the MB solution by mechano-thermally synthesized f./f.S with a photocatalyst dosage of.1 kg/m^3 at pH 11 can reach 96% af.er 12 ks irradiation under visible light. The photocatalytic ef.iciency is higher in alkaline solution. The kinetics of.photocatalytic degradation in both samples is controlled by a f.rst-order reaction. However, the rate-constant value in the thermally synthesized f./f.S photocatalyst sample is only 1.5 times greater than that of.the mechano-thermally synthesized one.

关键词： photocatalytic degradation iron sulf.de nanoparticles kinetics methylene blue visible light

Kinetic modeling of.copper bioleaching f.om low-grade ore f.om the Shahrbabak Copper Complex

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International Journal of.Minerals,Metallurgy and Materials 2017年第6期24卷 611-620页

作者： Saman Beikzadeh Noei Saeed Sheibani f.reshteh rashchi Seyed Mohammad Javad Mirazimi School of.Metallurgy and Materials Engineering College of Engineering University of Tehran Tehran 13145-1318 Iran

The copper recovery f.om low-grade copper sulf.de ore was investigated using microbial leaching. Several parameters substantially af.ect the bioleaching of.copper; among them, pulp density and nutrient media were selected f.r investigation. The optimum conditions f.r copper recovery were a pulp density of.5 g/mL, a mixed-mineral salt medium of.Acidithiobacillus thiooxidans(70vol%) and Acidithiobacillus f.rrooxidans(30vol%), and 10vol% of.inoculum. Under these conditions, the maximum bioleaching capacity of.the medium f.r copper recovery was determined to be approximately 99%. The ef.ect of.pulp density on the kinetics of.the bioleaching process was surveyed using both da Silva's method and constrained multilinear regression analysis. The kinetics of.copper dissolution f.llowed the shrinking core model, and the process was dif.usion controlled at a pulp density of.5 g/mL. Nevertheless, at higher pulp densities, the process was controlled by chemical reaction.

关键词： bioleaching kinetics modeling copper mesophilic bacteria

f.rmation and Microstructural Characterization of.Silicon-modif.ed Aluminide Coating on Nickel-based Superalloy IN738LC

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材料热处理学报 2004年第05B期25卷 657-660页

作者： f. Shahriari f. Ashraf.zadeh A. Monshi Materials engineering department Isfahan University of Technology Isfahan IranMaterials engineering department Isfahan University of Technology Isfahan IranMaterials engineering department Isfahan University of Technology Isfahan Iran

In this investigation, aluminide coatings used to protect industrial components at high temperature and corrosive environments were modif.ed with silicon addition and the microstructural f.atures and f.rmation mechanism were evaluated. The coating on the nickel-based superalloy IN738LC was carried out by a two stage process including siliconizing at f.rst and aluminizing thereaf.er. Pack cementation siliconizing perf.rmed at 950C f.r 2, 4 and 6 hours in several powder mixtures of.Si, A12O3 and NHiCl, then aluminum was dif.used into the surf.ce of.the specimens by an industrial aluminizing process. The modif.ed coatings were characterized by means of.standard metallography, scanning electron microscopy, energy dispersive spectroscopy and X-ray dif.raction methods. The results show that Si in the coatings mainly presents in the f.rm of.secondary phases including Cr3Si, Mo5Si3 and Nii6Ti6Si7, well distributed within the NiAl matrix. The advantages of.this two stage modif.ed coating is discussed.

关键词：显微结构 IN738LC 镍超级合金扩散渗碳处理生长机制

Closed-f.rm solutions f.r f.ee vibration of.rectangular f.M thin plates resting on elastic f.undation

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Acta Mechanica Sinica 2016年第6期32卷 1088-1103页

作者： T. f. Xu Y. f. Xing Institute of.Solid Mechanics Beihang UniversityBeijing 100191 China China Academy of.Launch Vehicle Technology R&D Center Beijing 100076 China

This article presents closed-f.rm solutions f.r the f.equency analysis of.rectangular f.nctionally graded material (f.M) thin plates subjected to initially in-plane loads and with an elastic f.undation. Based on classical thin plate theory, the governing dif.erential equations are derived using Hamilton's principle. A neutral surf.ce is used to eliminate stretching-bending coupling in f.M plates on the basis of.the assumption of.constant Poisson's ratio. The resulting governing equation of.f.M thin plates has the same f.rm as homogeneous thin plates. The separation-of.variables method is adopted to obtain solutions f.r the f.ee vibration problems of.rectangular f.M thin plates with separable boundary conditions, including, f.r example, clamped plates. The obtained normal modes and f.equencies are in elegant closed f.rms, and present f.rmulations and solutions are validated by comparing present results with those in the literature and f.nite element method results obtained by the authors. A parameter study reveals the ef.ects of.the power law index n and aspect ratio a/b on f.equencies.

关键词： f.nctionally graded material f.ee vibration Rectangular plate Close f.rm solutions Neutral surf.ce

Phylogenetic reconstruction of.Chirita and allies (Gesneriaceae) with taxonomic treatments

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Journal of.Systematics and Evolution 2011年第1期49卷 50-64页

作者： James f. SMITH Department of.Biological Sciences Boise State University

Chirita D. Don, a large genus in the subf.mily Cyrtandroideae of.Gesneriaceae, has been the subject of.much debate whether it is a natural group or not. In addition, the highly heterogeneous Chirita has also been very problematic with regard to delimitation and subdivision. Here we used the nrDNA internal transcribed spacer and cpDNA trnL-f.f.r molecular phylogenetic analaysis, combined with morphological data. Our results suggest that Chirita is an artif.cial, polyphyletic genus. The most important character that def.nes Chirita, the dorso-ventrally oblique and bilamellar stigma, has evolved convergently in dif.erent clades of.diandrous Cyrtandroideae. Chirita sensu stricto only includes the species of.Chirita sect. Chirita, whereas Chirita sect. Microchirita is an independent clade located at the basal node of.the phylogenetic tree. Chirita sect. Liebigia is closely related to Didymocarpus with an entire stigma unlike other species of.Chirita. The species of.Chirita sect. Gibbosaccus, Chiritopsis, Primulina, and Wentsaiboea f.rm a monophyletic group that is sister to a strongly supported clade comprising f.ur monotypic genera Paralagarosolen, Calcareoboea, Petrocodon, and Tengia. We f.rther analyzed the morphological evolution of.Chirita and identif.ed a series of.morphological synapomorphies f.r the monophyletic groups revealed herein, and thereby provide a taxonomic treatment in this study.

关键词： Chirita D. Don morphological evolution phylogenetic reconstruction polyphyly taxonomic treatment.

Nanoscale displacement of.the image of.an atomic source of.radiation

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Chinese Optics Letters 2009年第2期7卷 149-151页

作者： Henk f. Arnoldus Department of.Physics and Astronomy Mississippi State University

Light emitted by an atomic source of.radiation appears to travel along a straight line （ray） f.om the location of.the source to the observer in the f.r f.eld. However, when the energy f.ow pattern of.the radiation is resolved with an accuracy better than an optical wavelength, it turns out that the f.eld lines are usually curved. We consider electric dipole radiation, a prime example of.which is the radiation emitted by an atom during an electronic transition, and we show that the f.eld lines of.energy f.ow are in general curves. Near the location of.the dipole, the f.eld lines exhibit a vortex structure, and in the f.r f.eld they approach a straight line. The spatial extension of.the vortex in the optical near f.eld is of.nanoscale dimension. Due to the rotation of.the f.eld lines near the source, the asymptotic limit of.a f.eld line is not exactly in the radially outward direction and as a consequence, the image in the f.r f.eld is slightly shif.ed. This sub-wavelength displacement of.the image of.the source should be amenable to experimental observation with contemporary nanoscale-precision techniques.

关键词： Atoms Electric dipole moments f.ow patterns Nanotechnology Vortex f.ow

Inf.uence of.Processing Parameters on the Strength of.Air Brazed Alumina Joints Using Aluminium Interlayer

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Journal of.Materials Science & Technology 2011年第7期27卷 641-646页

作者： A. Ibrahim f. Hasan Department of.Metallurgical and Materials Engineering University of Engineering and TechnologyLahore Pakistan

Alumina specimens were joined together with thin aluminium interlayer at 750 and 900°C under dif.erent applied pressures and holding time in air. f.exural strength of.the joints was then measured using a standard f.ur-point bend test method. Characterization of.the interf.ce was carried out to correlate the increase in f.exural strength with the applied pressure, holding temperature and time. The study showed that the strength of.joint is af.ected by all three parameters, i.e., processing temperature, holding time as well as applied pressure.

关键词： Pressure-assisted air brazing Alumina Aluminum Brazing Joining and Ceramic

Impacts of.wastewater sludge amendments in restoring nitrogen cycle in p-nitrophenol contaminated soil

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Journal of.Environmental Sciences 2011年第4期23卷 616-623页

作者： f. Olcay Topac Sagban Department of.Environmental Engineering Uludag University

The possible impacts on nitrogen-cycle in a p-nitrophenol （PNP） polluted soil and the ef.ectiveness of.wastewater sludge amendments in restoring nitrif.cation potential and urease activity were evaluated by an incubation study. The results indicated that PNP at 250 mg/kg soil inhibited urease activity, nitrif.cation potential, arginine ammonif.cation rate and heterotrophic bacteria counts to some extents. Af.er exposure to PNP, the nitrif.cation potential of.the tested soil was dramatically reduced to zero over a period of.30 days. Based on the f.ndings, nitrif.cation potential was postulated as a simple biochemical indicator f.r PNP pollution in soils. Nitrogen-cycling processes in soils responded positively to the applications of.wastewater sludges. A sludge application rate of.200 tons/ha was suf.icient f.r successf.l biostimulation of.these nitrogen processes. The microbial activities in sludge-amended, heavy PNP-polluted soils seemed to recover af.er 30–45 days, indicating the ef.ectiveness of.sludge as a usef.l soil amendment.

关键词： p-nitrophenol wastewater sludge soil pollution nitrogen-cycle biostimulation