Molecular orbital study for Na, Mg, and Al adsorption on the Si (111) surface

We investigated the interactions between the Si(111) surface and the Na, Mg, and Al atoms using cluster model calculations. Calculations were performed at levels of complete-active-space self-consistent-field (CASSCF) and multi-reference singly and doubly excited configuration interaction (MRSDCI) calculations using the model core potential method. Our calculations revealed that the most favorable sites of Na, Mg, and Al adsorption on Si(111) are on top (T₁), bridge (B₂), and 3-fold filled (T₄) sites, respectively. The nature of chemical bonds between these metal atoms and the dangling bonds of the surface Si atoms are found to be essentially covalent.     

Determination of the interface band alignment of Mg2Si/4H-SiC heterojuction for potential photodetector application

The Mg₂Si/4H-SiC heterojunction was prepared by radio frequency (RF) magnetron sputtering technique. The binding energies of Mg 2p, Si 2p, and C 1s core levels and the maxima of valence band were measured by X-ray photoelectron spectroscopy (XPS). Using the optical bandgap of Mg₂Si (0.78 eV) and 4H-SiC (3.25 eV), the band offsets of valence band (VBO) and conduction band (CBO) at Mg₂Si/4H-SiC interface were identified as 1.47 and 1.00 eV, respectively. The band alignment was evaluated to be type-I band alignment. The Mg₂Si/4H-SiC heterojunction could be a promising candidate for the infrared (IR) photodetector.     

Influence of the modified Becke-Johnson exchange potential on thermoelectric properties: application to Mg2Si

The electronic and transport properties of Mg(2)Si are calculated using the density-functional and semi-classical Boltzmann transport theories. A detailed comparison of the efficiency of the Perdew, Burke, and Ernzerhof (PBE) and the modified Becke-Johnson (m-BJ) exchange potentials on the prediction of these properties is presented. We show that the m-BJ potential is able to predict the Mg(2)Si thermoelectric properties with better agreement with the experimental data than the PBE potential. These findings are correlated with a small modification of the valence orbitals of the materials and the opening of the gap.     

Mg-SiO_2体系制备Mg_2Si/AZ91D复合材料的研究

采用原位合成技术制备了Mg2Si/AZ91D复合材料,并通过光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)等对添加碱土、稀土元素的影响进行了研究。结果表明:AZ91D镁合金中加入SiO2(其中Si占合金质量的3%)后,出现多边形状或树枝晶状的初生Mg2Si相,以及汉字状的共晶Mg2Si相,树枝晶状Mg2Si的平均尺寸约25~50μm,汉字状Mg2Si的平均尺寸约12~15μm;Mg2Si对镁合金中的β-Mg17Al12相有细化作用。添加Ca,Sr,Y对Mg2Si形貌、尺寸有明显的改善,当添加0.9%Ca,0.1%Sr,0.5%RE(80%Y)变质处理后,Mg2Si形貌全部变为多边形状,平均尺寸约0.8~5μm。     

(Ni,Mg)3Si2O5(OH)4 solid-solution nanotubes supported by sub-0.06 wt % palladium as a robust high-efficiency catalyst for Suzuki-Miyaura cross-coupling reactions

(Ni(1-x),Mg(x))(3)Si(2)O(5)(OH)(4) solid-solution nanotubes (NTs) with tunable compositions were hydrothermally synthesized by altering the molar ratio of Mg(2+) to Ni(2+). The as-synthesized NTs were loaded with sub-0.06 wt % palladium (Pd; ～0.045 wt %) for Suzuki-Miyaura (SM) coupling reactions between iodobenzene or 4-iodotoluene and phenylboronic acid. The (Ni,Mg)(3)Si(2)O(5)(OH)(4) (Mg(2+):Ni(2+) = 1.0:1.0) NTs supported by 0.045 wt % Pd promoted the iodobenzene-participated coupling reaction with a high yield of >99%, an excellent recycling catalytic performance during 10 cycles of catalysis with yields of ～99%, and also an extremely low Pd releasing level of ～0.02 ppm. High-activity Pd and PdO clusters, multitudes of dislocations, and defects and terraces contained within the NTs should contribute to the (Ni,Mg)(3)Si(2)O(5)(OH)(4) (Mg(2+):Ni(2+) = 1.0:1.0) NTs supported by 0.045 wt % Pd as a robust, reusable, and high-efficiency catalyst for SM coupling reactions with an extremely low Pd releasing level. The present hydrothermally stable (Ni,Mg)(3)Si(2)O(5)(OH)(4) (Mg(2+):Ni(2+) = 1.0:1.0) solid-solution silicate NTs provided an ideal alternative tubular-structured support for noble- or transition-metal catalysts with low Pd loading, good recycling, and extremely low ppb levels of Pd release, which could also be extended to some other SM coupling reactions.     

Topological relationships and building blocks in Zintl phases of the composition Ba(n+1)(Mg,Li)2nSi2(n+1)

The structures of two novel Zintl phases, Ba6Mg5.2Li2.8Si12 and BaMg0.1Li0.9Si2, are presented. Both compounds contain chains in cis-trans conformation. The silicon partial structure of Ba6Mg5.2Li2.8Si12 (C2/m; a = 1212.0(1), b = 459.78(4), c = 1129.10(9) pm; beta = 91.77(2) degrees; Z = 1) is built of unbranched, planar Si6 chains while BaMg0.1Li0.9Si2 (Pnma; a = 725.92(5), b = 461.36(3), c = 1169.08(8) pm; Z = 4) consists of infinite Si(n) chains. The compounds show all electronic and structural characteristics that are typical for the special subset of Zintl phases with highly charged planar anions. The structures of the new compounds, as well as that of Ba2Mg3Si4, can be derived from the common parent type BaMg2Si2. It is shown that a comprehensive picture of a chemical twinning based on BaMg2Si2 can be derived.     

Copper adsorption and Si, Al, Ca, Mg, and Na release from clinoptilolite

Copper adsorption onto clinoptilolite (natural zeolite), Al/Si dissolution, and Mg, Ca, and Na release from the substrate were the subjects of the investigation described here. Experimental variables were Cu and electrolyte concentrations and solution pH. Copper adsorption was found to increase with increased pH and with decreased electrolyte concentration. Large amounts of K were also adsorbed from electrolyte. Since solution pH was assumed as a variable, the effects of [H(+)] differentiation on Cu adsorption and on Al/Si dissolution were also examined. Al dissolution was affected mainly by electrolyte concentration, whereas Si dissolution was affected mainly by adsorbed Cu amount. It was assumed that the release of Mg, Ca, and Na occurs through ion-exchange reactions with solution K(+), because their release is affected more by electrolyte concentration than by adsorbed Cu. From the study of FTIR spectra for various samples used in the present investigation, we observed that the removal of framework Si/Al shifts the band which was attributed to O-T-O stretching vibration toward higher frequency. Significant changes were observed for the bands assigned to Si-OH-Al bridges and to monomeric and polymeric hydrogen bonds at the region between 3650 and 3200 cm(-1). It is proposed that the Cu species caused the destruction of H-bonded structures, whereas K adsorbed species were located at exchangeable sites after an ion-exchange process between K and Ca, Mg, and Na from the zeolite's surface. An expansion of the zeolite framework was detected from XRD patterns under acid conditions.     

Li2Mg2Si4O10F2、H2Mn8O16•1.4H2O和Li1.3Ti1.7Al0.3(PO4)3在高浓度LiCl水溶液中的离子交换行为

研究了用功能材料Li2Mg2Si4O10F2 (LHT)、H2Mn8O16•1.4H2O (CRYMO)和Li1.3Ti1.7Al0.3(PO4)3 (LTAP)分别去除高浓度氯化锂水溶液中的杂质Fe3＋、K＋和Na＋.实验结果表明，这几种功能材料分别对溶液中的杂质Fe3＋、K＋和Na＋有很高的选择性，除杂效果明显.分析和研究了这几种功能材料在高浓度氯化锂水溶液中分别与Fe3＋、K＋和Na＋的交换行为.结果表明，在高浓度氯化锂溶液中这几种功能材料与杂质交换的动力学行为可近似用JMAK方程描述.     

Determination of Zn, B, Fe, Mg, Ca, Na and Si in anisette samples by inductively coupled plasma atomic emission spectrometry

A comparative study of several digestion methods of anisette samples has been carried out. Two dry ashing (DA) treatments as well as four wet ashing (WA) procedures using different mixtures of acids were applied for the sample mineralisation before analysis. Once the anisette samples were mineralised, the contents of Zn, B, Fe, Mg, Ca, Na and Si were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Each method has been studied statistically and also attending to their feasibility. After performing the optimisation of the different treatments tested, it was concluded that one wet ashing method employing a HNO₃:H₂O₂ (10:1) mixture was the most suitable. This method was applied to the analysis of anisette samples. Na, Ca, Mg and Si were present in concentrations up to 215 mg l⁻¹ for Na, 11.6 for Mg, 6.2 for Ca and 5.1 for Si. Fe and B concentrations were not higher than 0.12 mg l⁻¹ and lower for Zn.     

Simultane Bestimmung von N, Mg, Si, P und K in Pflanzenmaterial durch 14 MeV-Neutronenaktivierungsanalyse

Zusammenfassung Eine Methode zur simultanen Bestimmung von N, Mg, Si, P und K in Pflanzenmaterial wurde ausgearbeitet. Die Analysenproben wurden mit 14 MeV-Neutronen bestrahlt, die Gammaspektren mit einem NaJ(Tl)-Szintillationskristall gemessen und in einem Vielkanalanalysator gespeichert. Die Spektren wurden mit einem 16 K-Rechner quantitativ ausgewertet. Die Methode wurde mit einem NBS-Referenzmaterial überprüft, wobei sich eine gute Übereinstimmung zwischen den zertifizierten und den von uns ermittelten Elementkonzentrationen ergab.

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Simultaneous determination of N, Mg, Si, P and K in plant material by 14 MeV-neutron activation analysis

A method for the simultaneous determination of N, Mg, Si, P and K in plant material was worked out. The samples were irradiated with 14 MeV neutrons, -spectra were measured by means of a NaI(Tl) scintillation crystal and stored in a multi-channel analyzer. Quantitative evaluation was performed with a 16 K computer. Ten different plant material samples were analyzed and the method was checked with an NBS-reference material. The obtained concentration values were in good agreement with the certified data.

     

Pseudo-Jahn-Teller origin of geometry and pseudorotations in second row tetra-atomic clusters X4 (X=Na, Mg, Al, Si, P, S)

Experimentally determined or ab initio calculated molecular geometries carry no information about their origin. Employing the Jahn-Teller (JT) vibronic coupling effects as the only source of instability and consequent distortions of high-symmetry molecular configurations, we have worked out a procedure that allows us to trace the origin of particular geometries and determine the detailed electronic mechanism of their formation. This procedure is illustrated by considering a series of X(4) clusters with X=Na, Mg, Al, Si, P, and S. It shows explicitly why Na(4), Si(4), and Al(4) have a rhombic geometry in the ground state, while Mg(4) and P(4) are tetrahedral, whereas S(4) is a trapezium. Even when the minimum-energy geometries are the same (as in the case of rhombic Na(4), Si(4), and Al(4)), the electronic mechanism of their formation is quite different. In particular, in Na(4) and Si(4) the rhombic minima are produced by a strong pseudo JT coupling between two excited states in the square-planar configuration (different in the two cases) that stabilizes one of them and makes it the ground state by rhombic distortions. The rhombic configuration of Al(4) is due to the pseudo JT effect in its ground-state square-planar configuration, and the trapezium in S(4) is formed by two pseudo JT couplings essentially involving excited states. In several cases this analysis shows also the tunneling paths between equivalent configurations.     

电感耦合等离子体原子发射光谱法同时测定石灰石中铁、铝、钙、镁、硅

采用碱熔法,以移液枪分取试样,用电感耦合等离子体原子发射光谱法同时分析石灰石中铁、铝、钙、镁、硅5种化学成分。在分析过程中对氩气加湿,避免盐析效应的影响,铁、铝、钙、镁、硅的分析谱线分别为259.940,396.152,315.887,279.553,251.611 nm。5种成分在各自的线性范围内均具有良好的线性,线性相关系数在0.990 74~0.999 99之间,方法检出限为0.000 6%~0.005 1%,回收率为95.6%~105.4%,测定结果的相对标准偏差小于1%(n=6)。该方法检出限低、重现性好,适合于石灰石样品中铁、铝、钙、镁、硅的快速检测。     

Preparation and Characterization of Al8.31Si1.91Mg3.78O20/Al4.8Si1.2O9.6/Mg2.0Al4.02Si4.98O18 Multiphase Material

A two-step sintering method was used to prepare Al8.31Si1.91Mg3.78O20 (corundum solid solution)/Al4.8Si1.2O9.6 (mullite solid solution)/Mg2.0Al4.02Si4.98O18 (cordierite solid solution) multiphase material, for the purposes of making these three crystal structures have point defects which could help the particles diffuse and transfer at high temperature, accelerate the sintering efficiently and enhance the material strength as well as the bulk density. The impacts of different formulas on the structure and properties of the multiphase material were investigated. With XRD and SEM analyses, for each sample, the crystal structure and microstructure were characterized, the crystalline phase content and cell parameters were determined with Rietveld Quantification software, and the properties were tested. The comparative optimal formula determined was calcinated chamotte of 80wt% and calcinated sludge of 20wt%; and its corresponding bending strength and retention rate of bending strength after a thermal shock were 29.74 MPa and 80.15%, respectively.     

Theoretical Study on the Structure and Stability of Si5X （X = Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl） Clusters

1 INTRODUCTION In the later 60s of last century, silicon substituted for germanium to present as mainstream in semicon- ductor. The semi-conductive devices made by silicon have many advantages, for example, refractory pro- perty, high radioresistance, simple and stable process- ing technic, high machinability and low cost. So it was widely used to manufacture large power appara- tuses, for instance, digit and linear integrated circuit, large scale integrated circuit (LSI), etc. Thus, th…     

ICP-AES法测定铝中铁、硅、铜、镓、镁、锌、锰和钛

用 50g L氢氧化钠溶液溶解铝样品 ,硝酸 (1 1 )酸化 ,以ICP AES测定其中铁、硅、铜、镓、镁、锌、锰和钛等 8种杂质元素。     

Polyhedral members of the Mg2nP2m family derived from dimeric magnesium trialkylsilylphosphandiide

The magnesiation of tri(tert-butyl)silylphosphane in THF yields tetrameric (tetrahydrofuran-O)magnesium tri(tert-butyl)silylphosphandiide 1. The central moiety is a slightly distorted Mg4P4 cube with tetracoordinate magnesium and phosphorus atoms. The reaction of dibutylmagnesium with H2PSitBu3 in toluene gives tetramagnesium tetrakis[mu-tri(tert-butyl)silylphosphanide] bis[mu 4-tri(tert-butyl)silylphosphandiide] 2. The central fragment is a Mg4P2 octahedron with the phosphorus atoms in a trans position. The Mg...Mg edges are bridged by the phosphanide substituents. Crystallographic data of 1: C68H148Mg4O5P4Si4, monoclinic, P2(1)/c, a = 13.454(1) A, b = 26.123(1) A, c = 24.539(2) A, beta = 96.53(1) degrees, Z = 4; crystallographic data of 2: C72H166Mg4P6Si6, monoclinic, P2(1)/n, a = 13.951(1) A, b = 14.269(1) A, c = 24.209(2) A, beta = 102.415(1) degrees, Z = 2.     

In situ observation of the formation of Si clathrate Ba8Si46 at high pressures and high temperatures

X-ray diffraction measurements at high pressures and high temperatures revealed that Si clathrate Ba 8Si 46 is formed by a solid-phase reaction of an 8:30 molar mixture of SrSi 2-phase BaSi 2 and Si after BaSi 2 undergoes the BaSi 2-to-EuGe 2 and the EuGe 2-to-SrSi 2 transitions. The volume reduction during the formation of Ba 8Si 46 is the largest, 7.6%, among the observed transitions. On the other hand, an 8:30 molar mixture of SrSi 2-phase SrSi 2 and Si does not result in the formation of Sr 8Si 46 at high pressures and high temperatures; only SrSi 2 transforms from the SrSi 2 phase into the alpha-ThSi 2 phase, and Si remains in the diamond phase.     

Struktur und Eigenschaften von Ba2Mg3Si4, einer Zintl-Phase mit planaren Si6-Einheiten

Structure and Properties of Ba₂Mg₃Si₄, a Zintl Phase with Planar Si₆ Units Within the scope of the investigations on the phase system Ba/Mg/Si a new ternary Zintl phase of the composition Ba₂Mg₃Si₄ was found and structurally characterized. The silicon substructure is built up of Si₂ pairs and a new type of Zintl anion, a planar Si₆ chain. Temperature dependent measurements of the electric conductivity and the magnetic susceptibility show a metallic behavior. Accompanying quantumchemical investigations on the base of the LMTO-ASA method confirm these results and allow an insight in the present bond situation.     

Mg3Ir3Si8, ein neues Magnesium‐Iridium‐Silicid mit Tetraedern und gekappten Tetraedern aus Silicium‐Atomen

Mg₃Ir₃Si₈, a New Magnesium Iridium Silicide with Si₄ Tetrahedra and Si₁₂ Truncated Tetrahedra The ternary silicide Mg₃Ir₃Si₈ (cubic, a = 1221.4(1) pm, space group , 8 formula units per unit cell) was prepared by reaction of the elemental components in a sealed molybdenum container (1000 °C, 1 d, cooled with 100 °/h). The crystal structure was determined from single crystal data. Short distances in the three‐dimensional iridium silicon network indicate strong Ir‐Si‐bonding (d(Ir‐Si) = 240.5(2) and 245.6(1) pm). In addition, homonuclear bonding seems to be important, resulting in the formation of Si₄‐tetrahedra (d(Si‐Si) = 257(1) pm), and Mg centered Si₁₂‐polyhedra with the shape of truncated tetrahedra (d(Si‐Si) = 241(1) and 261.0(9) pm). Furthermore, Mg₄‐tetrahedra with Mg‐Mg‐distances of 355(2) pm are formed. The structure may be derived from the structure of the isotypic compounds Mg₅Pd₁₀Si₁₆ and Mg₅Pt₁₀Si₁₆ by adding a Mg siteset and subtracting a platinum metal siteset. It can be described by an expanded cubic “close” packing of MgIr₆‐octahedra in which Si₄‐tetrahedra reside in the octahedral holes while Mg₄‐tetrahedra and MgSi₁₂‐units occupy one half of the tetrahedral holes each.