Xiumin Chen

Prediction of Covalent Interactions Between Si and B, Fe, Al or Ca in Metallurgical Grade Silicon Using abinitio Molecular Dynamic Simulations

Boron removal from metallurgical grade silicon (MG-Si) by metallurgical process plays an important role in the production of solar grade silicon (SoG-Si). However, the effects of other impurities in MG-Si on boron removal are not yet well known. The covalent interactions between Si and B, Fe, Al or Ca in the corresponding binary and ternary structures at 1873 K are studied in present work by ab initio molecular dynamic simulations based on the Si supercell and the Si-B structure, respectively. The bond lengths of Si-B, Si-Fe, Si-Al and Si-Ca and the partial density of states (PDOS) of electric charge distribution in the binary structures indicate that the impurities Fe and Ca in MG-Si have an important effect on boron removal. The bond strength order is Si-Fe >Si-Ca >Si-B >Si-Al in the binary Si-B, Si-Fe, Si-Al and Si-Ca structures and the order of effect for impurities Fe, Al or Ca in MG-Si on boron removal is Fe >Ca >Al in the ternary Si-B-Fe, Si-B-Al and Si-B-Ca structures. The results indicate that the metallic impurities should be firstly removed prior to the boron removal for the metallurgical process.

Influence of vacuum upon preparation and luminescence of Si4+ and Ti4+ codoped Gd2O2S:Eu phosphor

As a novel red long afterglow phosphor, Si(4+) and Ti(4+) ion codoped Gd2O2S:Eu phosphor with spherical morphology, sub-micrometer size and narrow particle size distribution was synthesized by solid-state reaction in vacuum. The vacuum synthesis mechanism was determined by thermal analysis. The crystal structure, luminescence properties and mechanisms were investigated respectively by XRD, SEM and fluorescence spectrophotometer. The results show that well-crystallized Gd2O2S:Eu,Si,Ti phosphors are of hexagonal structure which is in agreement with the standard powder peak positions of Gd2O2S hexagonal phase. It displays pure red emission because of the strongest peaks at 627nm and 617nm which are attributed to energy transfer ((5)D0-(7)F2). There is a little blue shift of charge transfer excitation band in the excitation spectra between the bulk and sub-micrometer-sized samples, which may stem from size dependent shift and different lattice distortion in the position of the Eu(3+)-ligand electron transfer absorption/excitation band. To further study the influence of the impurities in Gd2O2S:Eu crystals on crystal growth, the simulated crystal face and its XRD patterns were illustrated. The preferred orientation of crystal growth changed from crystal face (101) to (100) thus to result in different luminescence mechanisms.

Study on Effect of Al-O-C Compound in Alumina Carbothermal Reduction

In this paper, The structures and properties changes for single unit cell of alumina, Al-O-C compounds and aluminium carbide were simulated by first principles method. According to theoretical calculation results, alumina carbothermal reductions with coal and charcoal separately used as reductant were carried out under vacuum. The major equations in carbonthermal reduction reduced to three general equations by reaction temperature; the sequence for each substance which formed in reductions was Al4O4C→Al2OC→Al4C3

Preparation of activated ceria and its desulfurization performance

Activated ceria (CeO2/γ-Al2O3) prepared by impregnation was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and hydrogen temperature-programmed reduction (TPR). The desulfurization of the activated ceria was investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TG). The results showed that ceria could be highly dispersed or crystallized on the surface of γ-alumina. The reduction temperatures of 0.1CeO2/γ-Al2O3, 0.45CeO2/γ-Al2O3, and CeO2 ranged from 250°C to 470°C, 330°C to 550°C, and 350°C to 550°C, respectively. The reduction peak temperature of 0.45CeO2/γ-Al2O3 was higher than that of 0.1CeO2/γ-Al2O3, which was consistent with the reduction temperature of CeO2. O2 participated in the reaction between ceria and sulfur dioxide. The desulfurization product was cerium(III) sulfate. The intensity of the hydroxyl band decreased with the formation of sulfate species.

Theoretical Study on the Interactions of Impurity Boron on Si(110) Surface with H+, OH– AND O2

This paper proposed the optimization work for the Si(110) structure before and after Boron-doped based on the first principle of the density functional theory (DFT). Construction optimization, bond length and population and density of states (DOS) calculation were applied on Si(110) surface where the impurity element boron interacted with H+, OH− or O2. The results showed that the structure of Si(110) surface after Boron-doped was significantly affected, and the interaction between H+, OH− or O2 with boron on Si(110) surface also affect the structure of Boron-doped on Si(110) surface significantly; H+, OH− or O2 interacted with boron had no obvious effect on the length and strength of Si-Si bond, and the strength of the Si-B bond was significantly weakened in turn. The results provided a theoretical basis of exploring the reaction mechanism of boron removal by hydrometallurgy from metallurgical grade silicon (MG-Si).

A comparison of the thermal decomposition mechanism of wurtzite AlN and zinc blende AlN

The sublimation route is one of the primary and most significant methods for the synthesis of an aluminum nitride (AlN) single crystal. Its long synthesis time and high reaction temperature, however, limit the production of its commercial product. In this work, we applied HSC Chemistry 6 software, ab initio molecular dynamics, and X-ray diffraction to investigate the thermal decomposition of AlN. We calculated the decomposition temperatures of AlN under vacuum and simulated the decomposition mechanism of AlN by the ab initio molecular dynamics method. According to the thermodynamic calculations, the decomposition temperature of AlN decreased following a decrease in the system pressure. The ab initio molecular dynamics results indicated that wurtzite-type AlN (w-AlN) was decomposed by the layer-by-layer mechanism and followed a decomposition reaction equation of AlN → Al(g) + 0.29N2(g) + 0.42N(g), which originated from the inequality sp3 hybridization. The zinc-type AlN (z-AlN) decomposed from the surface to interior of the structure because of the equality of the sp3 hybridization, and the z-AlN decomposition reaction equation followed AlN → Al(g) + 0.5N2(g). The AlN decomposition experiments further verified that Al(g) was the product of the wurtzite-type AlN thermal decomposition. This work can provide valuable information for the preparation of the AlN single crystal.

The Density Functional Theory Investigation on the Structural, Relative Stable and Electronic Properties of Bimetallic PbnSbn (n = 2–12) Clusters

Recently, bimetallic clusters have attracted a great deal of attention from research community because clusters yield intriguing properties ranging from the molecular and the bulk materials, which have extensive applications in nanomaterials. Clusters with tailored properties are governed by cluster size, geometrical structures, and elemental composition. Motivated by that we systematically investigated the structural, relative stable, and electronic properties of PbnSbn (n = 2–12) clusters by means of density functional theory. In this paper, the ground state structures, average binding energies, fragmentation energies, HOMO–LUMO gaps, and density of states were theoretically calculated. The results demonstrate that the large clusters adopt distorted ellipsoid structures with no symmetry. The average binding energies tend to be stable when cluster size n ≥ 4. Pb5Sb5 and Pb9Sb9 clusters are more chemically stable compared with the neighboring PbnSbn clusters, which may serve as the cluster assembled materials. The density of states of PbnSbn (n = 2–12) clusters moving toward more negative energy levels with the growing cluster size n, which also becoming more nonlocalized as the clusters size n increasing.

Theoretical insights into the structural, relative stable, electronic, and gas sensing properties of PbnAun (n = 2–12) clusters: a DFT study

Recently, Au-based clusters have been provoking great interest due to their potential applications in nanotechnology. Herein, the structural, relative stable, electronic, and gas sensing properties of PbnAun (n = 2–12) clusters were systematically investigated using density functional theory together with scalar relativistic pseudopotential. The ground state structures, average binding energies, dissociation energies, second order energy differences, HOMO–LUMO gaps, and average Mulliken charges of PbnAun (n = 2–12) clusters were calculated. The results revealing that the PbnAun (n = 4, 6, and 8) clusters are more relatively stable than their neighboring clusters. Furthermore, charges are always transferred from the Pb atoms to Au atoms based on Mulliken charge analysis. Furthermore, through the investigations of CO or NO molecule adsorption onto PbnAun (n = 4, 6, and 8) clusters, it is found that CO or NO molecule can chemisorb on those clusters with high sensitivity, and the charges are transferred from PbnAun (n = 4, 6, and 8) clusters to the gas molecules. According to the analysis of the electric conductivity, PbnAun (n = 4, 6, and 8) clusters can be served as potential gas sensors in CO and NO molecules detection.

Quantitative Analysis of The Trace Elements in Purity Indium Material by Glow Discharge Mass Spectrometer

In this study, the analysis method of trace element in pure indium using glow discharge mass spectrometry (GD-MS) has been established by correcting the analysis result, which was obtained from non-standard quantitative method of GD-MS. The effect of instrument operating parameters, the resolution and isotopes and the pre-sputtering time on the determination results were investigated respectively. The optimized operating parameters of the instrument were obtained as follows: the discharge current was 37.5mA and discharge airflow was 475ml/min. Mass spectral interferences have been eliminated using selected resolution and isotope. The pre-sputtering time was 30 min. 4 trace elements in two pure samples were determined for 6 times. The RSD were less than 20%. The content of trace elements in indium samples was determined by GD-MS and Chemical Analysis Method of Indium which is tested by inductively coupled plasma atomic emission spectrometry, respectively. The results were consistent with each other.

Thermodynamic Analysis and Dynamic Simulation on Carbothermic Chlorination Reaction of Al 2 O under Vacuum

In this research, thermodynamic analysis and CASTEP package of the Material Studio program which is based on density functional theory (DFT) formalism were used to study the carbothermic-chlorination (AlCl3) reaction of Al2O under vacuum. Thermodynamic calculations indicated that AlCl(g) can be generated by carbothermic-chlorination process at 1760K and 60Pa. The interaction of Al2O and AlCl3 with C showed that the chemical adsorption of Al2O and AlCl3 did take place on C(001) crystal plane, at the same time, new chemical bond have been formed between Al atom dissociated from Al2O and Cl atom dissociated from AlCl3 molecule. The result, after 1ps dynamics simulation, indicated that adsorbed AlCl and CO molecules have been generated in Al2O-AlCl3-C system, and they would escape from C surface after a longer period of dynamics simulation time. It means that the reaction of Al2O and AlCl3 with C can be carried out under given constraint condition.