Decomposition of SiCl4 and deposition of Si in inductively coupled plasmas of H2+SiCl4

The mechanism of homogeneous reactions in plasmas of H₂+5%SiCl₄ was studied by mass spectrometry and was compared to the mechanism observed in plasmas of Ar+H₂+SiCl₄. Contrary to the behavior with Ar, the results indicate that without argon the SiCl₄ molecule undergoes only fragmentation and the deposition proceeds through SiCl₂. No polymerization was observed. The deposition rates of c-Si were lower and the amounts of chlorine incorporated in the films were higher in the plasma of SiCl₄+H₂ than in the argon-containing plasma.     

Metal-containing initiator systems. V. Radical and cationic polymerizations with initiator systems of reduced nickel and chlorosilanes

The polymerizations of methyl methacrylate, styrene, and isobutyl vinyl ether with the binary systems of reduced nickel and chlorosilanes [(CH₃)_nSiCl_4?n, n = 0–3] have been investigated. It was found that these systems could act as both radical and cationic initiators, depending on the nature of vinyl monomers used. The kinetic investigations indicated that methyl methacrylate polymerized via a radical mechanism, and the initiating activity of chlorosilanes decreased in the following order: SiCl₄ > CH₃SiCl₃ > (CH₃)₂SiCl₂ > (CH₃)₃SiCl ? 0. Cationic initiations were observed in the polymerizations of styrene and isobutyl vinyl ether. In the latter case, the activity of chlorosilanes was in the following order: (CH₃)₃SiCl > (CH₃)₂SiCl₂ > CH₃SiCl₃ ? SiCl₄. From the results obtained, a possible mechanism of selective initiation with these systems is proposed and discussed.     

The Combustion of SiCl4 in Hot O2/H2 Flames

A simple kinetic model describing the molecular gas phase reactions during the formation of fumed silica (AEROSIL®) was developed. The focus was on the formation of molecular SiO₂, starting from SiCl₄, hydrogen and oxygen. Wherever available, kinetic and thermodynamic parameters were taken from the literature. All other parameters are based on quantum chemical calculations. From these data, an adiabatic model for the combustion reaction has been developed. It was found that a significant amount of molecular SiO₂ forms after about 0.1 and 0.6 ms at starting temperatures between 1000 and 2000 K. The initial reaction of the SiCl₄ combustion in a hydrogen/oxygen flame was found to be different from the combustion in air: The high reactivity of SiCl₄ towards water is favored over the SiCl₄ dissociation, which is the initial and rate‐determining step during the combustion of SiCl₄ in air.     

Fabrication of silane-modified magnetic nano sorbent for enhanced ultrasonic wave driven removal of methylene blue from aqueous media: Isotherms,kinetics, and thermodynamic mechanistic studies

In this study, we report a simple and economic one-pot synthesis of magnetite (Fe₃O₄) nanostructure and its modification with tetraethyl orthosilicate by coprecipitation method. The synthesized (Fe₃O₄@SiO₂) nano sorbent was applied for enhanced adsorptive removal of methylene blue by ultrasonic wave driven batch experiments. After successful synthesis, the nanostructure was characterized for their physical structure by FT-IR, VSM, TEM, and XRD. For the maximum adsorptive performance of nano sorbent, various parameters were optimized, such as dose, pH, time, concentration, and temperature. The adsorption mechanism was best fitted by Langmuir isotherm with a maximum capacity of 148.69 mg/g, while kinetics best fitted by pseudo-second-order kinetic. The synthesized nano sorbent was successfully applied for enhanced adsorptive removal of toxic methylene blue from aqueous media. The proposed method is promising and effective in terms of simplicity, cost operation, green energy consumption, reproducible, excellent reusability, and magnetically separability with fast kinetic.     

Mechanism of silicon film deposition in the RF plasma reduction of silicon tetrachloride

Plasma-chemical reduction of SiCl₄ in mixtures with H₂ and Ar has been studied by optical emission spectroscopy (OES) and laser interferometry techniques. It has been found that the Ar:H₂ ratio strongly affects the plasma composition as well as the deposition (r _D) and etch (r _E) rates of Si: H, Cl films and that the electron impact dissociation is the most important channel for the production of SiCl_x species, which are the precursors of the film growth. Chemisorption of SiCl_x and the reactive surface reaction SiCl_x+H–SiCl_(x–1)0+HCl are important steps in the deposition process. The suggested deposition model givesr _D [SiCl_x][H], in agreement with the experimental data. Etching of Si: H, Cl films occurs at high Ar: H₂ ratio when Cl atoms in the gas phase become appreciable and increases with increasing Cl concentration. The etch rate is controlled by the Cl atom chemisorption step.     

草酸沉淀法合成自组装纳米Co_3O_4及性质

<正>一维纳米材料具有高比表面积,表现出很多奇特的物理和化学性能,因此一维纳米材料的合成和性质引起了人们的广泛关注。目前,合成一维纳米氧化物的方法很多,如模板法合成一维纳米铁氧体、水热法合成γ-MnOOH纳米棒、静电纺丝法合     

基于静电喷射法活性多孔磁性炭球的制备及其对亚甲基蓝的吸附

在利用静电喷射一步法获得壳聚糖(CS)磁性微球(Fe₃O4/CS)的基础上,对Fe₃O4/CS进行高温炭化和碱活化处理获得活性磁性多孔炭球(A-Fe₃O4/C),并对A-Fe₃O4/C吸附水中亚甲基蓝(MB)分子的性能进行了研究。在利用扫描电子显微镜、红外吸收光谱仪、比表面分析仪对制备微球的形貌和结构进行分析的基础上,深入研究溶液pH、吸附时间、温度以及活化剂种类等因素对A-Fe₃O4/C吸附性能的影响。研究结果表明,A-Fe₃O4/C对MB的吸附量随着pH值的增加而增大,且经KOH活化后的A-Fe₃O4/C对MB表现出较优的吸附性能。A-Fe₃O4/C对MB的吸附过程符合伪二级动力学方程和Langmuir等温线模型,理论最大吸附容量可达300.6 mg·g^-1。此外,A-Fe₃O4/C表现出良好的重复利用性能,6次循环后对MB的去除率没有明显下降。     

基于静电喷射法活性多孔磁性炭球的制备及其对亚甲基蓝的吸附

在利用静电喷射一步法获得壳聚糖(CS)磁性微球(Fe₃O₄/CS)的基础上,对Fe₃O₄/CS进行高温炭化和碱活化处理获得活性磁性多孔炭球(A-Fe₃O₄/C),并对A-Fe₃O₄/C吸附水中亚甲基蓝(MB)分子的性能进行了研究。在利用扫描电子显微镜、红外吸收光谱仪、比表面分析仪对制备微球的形貌和结构进行分析的基础上,深入研究溶液pH、吸附时间、温度以及活化剂种类等因素对A-Fe₃O₄/C吸附性能的影响。研究结果表明,A-Fe₃O₄/C对MB的吸附量随着pH值的增加而增大,且经KOH活化后的A-Fe₃O₄/C对MB表现出较优的吸附性能。A-Fe₃O₄/C对MB的吸附过程符合伪二级动力学方程和Langmuir等温线模型,理论最大吸附容量可达300.6 mg·g^-1。此外,A-Fe₃O₄/C表现出良好的重复利用性能,6次循环后对MB的去除率没有明显下降。     

Reaction of carboxylic acids with tetrachlorosilane

Tetrachlorosilane reacted with carboxylic acids RCOOH (R = Me, Bu, t-Bu) to give the corresponding acid chlorides RCOCl in 75–95% yield. The reactions of SiCl₄ with trichloroacetic and 2-fluorobenzoic acids (R = Cl₃C, 2-FC₆H₄) occurred more difficultly, presumably for steric reasons, and the yields of the corresponding acid chlorides were 11 and 22%, respectively. Tetrachlorosilane failed to react with stearic acid under analogous conditions. Products of the reactions of SiCl₄ with chloroacetic and benzoic acids RCOOH (R = ClCH₂, Ph) were tetraacyloxysilanes Si(OCOR)₄, and tetrakis(chloroacetoxy)silane was formed in almost quantitative yield. The reaction of SiCl₄ with glutaric acid led to the formation of a rubber-like polymeric material with the composition C₅H₆Cl₂O₄Si. The effect of pKa values of carboxylic acids on the direction and mechanism of the examined reaction is discussed.     

Catalytic Effect of Some Chromites on the Thermal Decomposition of KClO4. Mechanistic and non-isothermal kinetic studies

The catalytic effect of two different groups of chromites on the non-isothermal decomposition of KClO₄was studied. TG and DSC curves of the thermal behaviour obtained for KClO₄-alkaline earth chromites (Series 1) mixtures indicate the formation of K₂Cr₂O₇, through a solid-solid interaction, before accelerating the decomposition stage of KClO₄. Such an accelerating effect becomes more pronounced in the case of admixing KClO₄ with some transition metal chromites (Series 2). The results were discussed taking into consideration the electronic configuration of cations and the electrical properties of the chromite catalysts. The presence of coordinatively active cations, able to form surface complex with the oxygen of the perchlorate anion, was proved to be necessary for obtaining an active catalyst. The kinetic parameters and models describing the catalyzed thermal decomposition process of KClO₄ were evaluated by using a computer program that allows the analysis using five different methods. It was found that the adopted kinetic model for pure KClO₄ and that mixed with catalysts from Series 1 is one-dimensional movement of phase boundary. On the other hand, random nucleation mechanism was achieved in the presence of catalysts from Series 2. Finally, a tentative reaction mechanism consistent with the obtained results was suggested. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation,characterization and thermal decomposition of phenylenediammonium sulfate salts Part. XVI

Polyaniline/α-Al₂O₃ (PANI/α-Al₂O₃) composites were synthesized by in situ polymerization through ammonium persulfate ((NH₄)₂S₂O₈, APS) oxidized aniline using HCl as dopant. XRD and FTIR were used to characterize the PANI/α-Al₂O₃ composites. The thermal stabilities and glass transition temperature (T _g) of PANI/α-Al₂O₃ composites were tested using thermogravimetric (TG) method and modulated differential scanning calorimetry (MDSC) technique. The results of TG showed that the thermal stability of PANI/α-Al₂O₃ composite increased and then decreased with the increase in α-Al₂O₃ content. The derivative thermogravimetry (DTG) curves showed one step degradation of PANI when the α-Al₂O₃ content was lower than 52.5 mass%, and exhibited two steps degradation when the α-Al₂O₃ content was higher than 63.6 mass%. The MDSC curves showed that the T _g of PANI/α-Al₂O₃ composites increased and then decreased with the augment of α-Al₂O₃ for the interaction between PANI chains and the surface of α-Al₂O₃.     

Synthesis and thermal decomposition of bismuth peroxotitanate to Bi2Ti2O7

Bi-peroxotitanate was synthesized by a peroxo method and after thermal decomposition Bi₂Ti₂O₇ was obtained. DTA, TG and DSC curves of Bi₂[Ti₂(O₂)₄(OH)₆]5H₂O were recorded and used to determine isothermal conditions suitable for obtaining the intermediate samples corresponding to the phases observed during the thermal decomposition. The samples were identified by quantitative analysis, IR spectroscopy and X-ray analysis. The experimental results were used to propose a mechanism of thermal decomposition of the investigated compound to a nanosized Bi₂Ti₂O₇. The optimum conditions were also determined for obtaining Bi₂Ti₂O₇, which is applicable for piezosensors.     

β−cyclodextrins-based inclusion complexes of CoFe2O4 magnetic nanoparticles as catalyst for the luminol chemiluminescence system and their applications in hydrogen peroxide detection

β−cyclodextrins (β−CD)-based inclusion complexes of CoFe₂O₄ magnetic nanoparticles (MNPs) were prepared and used as catalysts for chemiluminescence (CL) system using the luminol-hydrogen peroxide CL reaction as a model. The as-prepared inclusion complexes were characterized by XRD (X-ray diffraction), TGA (thermal gravimetric analysis) and FT-IR. The oxidation reaction between luminol and hydrogen peroxide in basic media initiated CL. The effect of β−CD-based inclusion complexes of CoFe₂O₄ magnetic nanoparticles and naked CoFe₂O₄ magnetic nanoparticles on the luminol-hydrogen peroxide CL system was investigated. It was found that inclusion complexes between β−CD and CoFe₂O₄ magnetic nanoparticles could greatly enhance the CL of the luminol-hydrogen peroxide system. Investigation on the kinetic curves and the chemiluminescence spectra of the luminol-hydrogen peroxide system demonstrates that addition of CoFe₂O₄ MNPs or inclusion complexes between β−CD and CoFe₂O₄ MNPs does not produce a new luminophor of the chemiluminescent reaction. The luminophor for the CL system was still the excited-state 3-aminophthalate anions (3-APA*). The enhanced CL signals were thus ascribed to the possible catalysis from CoFe₂O₄ MNPs or inclusion complexes between β−CD and CoFe₂O₄ nanoparticles. The feasibility of employing the proposed system for hydrogen peroxide sensing was also investigated. Experimental results showed that the CL emission intensity was linear with hydrogen peroxide concentration in the range of 1.0 × 10⁻⁷ to 4.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 2.0 × 10⁻⁸ mol L⁻¹ under optimized conditions. The proposed method has been used to determine hydrogen peroxide in water samples successfully.     

Oxidation Behaviour of A Boron Carbide Based Material in Dry and Wet Oxygen

The oxidation behaviour of a B₄C based material was investigated in a dry atmosphere O₂(20 vol.%)-CO₂(5 vol.%)-He and also in the presence of moisture H₂O (2.3 vol%) as boron oxide is very sensitive to water vapour. The mass changes of samples consisting of a chemical vapour deposit of B₄C on silicon nitride substrates were continuously monitored in the range 500–1000°C during isothermal experiments of 20 h. The stability of boron oxide formed by oxidation of B₄C was also studied in dry and wet atmospheres to explain the kinetic curves. In both atmospheres, oxidation is diffusion controlled at 700 and 800°C and enhanced by water vapour. At 900°C and higher temperatures, boron oxide volatilisation and consumption by reaction with water vapour modifies the properties of the oxide film and the material is no more protected. At 600°C, B₄C oxidation is weak but the process remains diffusion controlled in dry conditions as boron oxide volatilisation is negligible. However, in the presence of water vapour, B₂O₃ consumption rate is significant and mass losses corresponding to this consumption and to the combustion of the excess carbon are observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of core–shell structure Fe3O4@Ta2O5 microspheres for selective enrichment of phosphopeptides for mass spectrometry analysis

Protein phosphorylation is one of the most important post-translational modifications. Due to the dynamic nature and low stoichiometry of the protein phosphorylation, enrichment of phosphopeptides from proteolytic mixtures is often necessary prior to their characterization by mass spectrometry. Many metal oxides such as titanium dioxide and zirconium dioxide have been successfully applied to isolation and enrichment of phosphopeptides. Recently, niobium pentoxide was proved to have the ability for selective enrichment of phosphopeptides. Considering the proximity of tantalum to niobium, we supposed that Ta₂O₅ can be used as affinity probes for phosphopeptide enrichment. In the work, we synthesized Fe₃O₄@Ta₂O₅ magnetic microspheres with core–shell structure for selective enrichment of phosphopeptides. To demonstrate its ability for selective enrichment of phosphopeptides, we applied Fe₃O₄@Ta₂O₅ magnetic microspheres to isolation and enrichment of the phosphopeptides from tryptic digestion of standard proteins and real samples, and then the enriched peptides were analyzed by matrix-assisted laser desorption mass spectrometry analysis (MALDI-MS) or liquid chromatography coupled to electrospray ionization mass spectrometry (LC–ESI-MS). Experiment results demonstrate that Ta₂O₅ coated-magnetic microspheres show the excellent potential for selective enrichment of phosphopeptides.     

Isolation of lappaconitine from Aconitum septentrionale roots by adsorption

Extracts of Aconitum septentrionale Koelle roots obtained using chloroform, isopropanol, and ethanol were purified using chloroform and basic γ-Al₂O₃. Ballast materials were selectively adsorbed by γ-Al₂O₃, increasing the mass fraction of lappaconitine in the extract. The ethanol extract was purified most. The degree of lappaconitine extraction by chloroform was unaffected by the presence of γ-Al₂O₃. However, the mass fraction in the extract and lappaconitine extraction from Aconitum septentrionale were increased more than twice. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 274–276, May–June, 2006.     

Kinetics of the Selective Reduction of NO with CH4 Over an In-Fe2O3/HZSM-5 Catalyst

A kinetic model presented for the selective reduction of NO with CH₄ over an In-Fe₂O₃/HZSM-5 catalyst by considering the process as a combination of two simultaneous reactions: NO+O₂+CH₄ (reaction 1) and O₂+CH₄ (reaction 2). Linear regression calculation was employed to find the kinetic parameters. It was found that although the activation energies of the two reactions were almost identical, the reaction rate constants were dramatically different, namely, k₁k₂, indicating that the NO+O₂+CH₄ reaction was more preferable to take place on the In-Fe₂O₃/HZSM-5 catalyst as compared with the O₂+CH₄ reaction.     

Effect of FeO x on the electrocatalytic properties of NiCo2O4 for O2 evolution from alkaline solutions

Mixtures of NiCo₂O₄ and FeO _x were obtained by thermal decomposition of the nitrates of Ni, Co, and Fe in appropriate proportions. Two series of electrodes were prepared: (1) at constant composition (20 mol% FeO _x ) and various calcination temperatures in the range 200 to 480 °C and (2) at constant calcination temperature (300 °C) and various compositions in the whole composition range 0 to 100 mol% FeO _x . The oxide layers were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and cyclic voltammetry. Experimental data showed that the layers consist of a mixture of phases in which Fe oxide is present as Fe₂O₃. The electrocatalytic properties were assessed by means of quasi-stationary potentiostatic current-potential curves for the O₂ evolution reaction from alkaline solution. Results have shown that the mechanism of O₂ evolution depends on composition moderately. The electrocatalytic activity appears to depend on composition only slightly. Dedicated to Professor Oleg Petrii on the occasion of his 70th birthday on August 24th, 2007.     

An evaluation on thermokinetic parameters for hydrogen peroxide at various concentrations by DSC

Information about the kinetics and thermal decomposition of hydrogen peroxide (H₂O₂) has been required for safety reasons, due to its broad applications in many chemical industries. To determine the inherent hazards during H₂O₂ manufacturing, transportation, disposal, usage, and so on, this study deliberately selected various H₂O₂ concentrations and analyzed them by differential scanning calorimetry (DSC). In addition, thermokinetic parameters were not only established for each of these reactions, but also aimed at comprehensive, kinetic models with various tests conducted at different heating rates. To build up a comprehensive kinetic model, various tests were conducted by heating rates of 1, 2, 4, 10°C min^–1, respectively. According to dynamic DSC tests, the experimental curves show that H₂O₂ decomposition has one exothermic peak and may start to decompose under 47–81°C. The total heat of decomposition is about 192–1079 J g^–1. Not only can these results prevent accidents caused by H₂O₂ during storage and transportation, but also assess its inherent hazards and thereby design procedures for emergency response while runaway reactions occurring.