Papers by Keyword: Reaction Mechanism

Abstract: Using H₂ and Al (CH₃)₃(TMA) as precursor, we investigated the atomic layer deposition mechanism of the metal Al on Si (100) surface by density functional theory. The reaction process comprises two half-reaction depositions: TMA "half-reaction" includes I and II on the H blunt reaction surface; H₂ "half-reaction" includes the subsequent reaction Ⅲ and Ⅳ. In the TMA half reaction process, trimethyl aluminum first molecularly adsorbed in the active site of H*-Si₉H₁₂-H* to form a stable complex in the form of chemical adsorption state. Potential curves show that at 298 K, adsorption energy is -2.26kJ/mol, with respect to the chemical adsorption state, the activation barrier energy is 124.72kJ/mol, and finally the whole exothermic reaction energy is 41.4kJ/mol. After H₂ half reaction, the bond length between Al-Si can be considered equal; two Al-C bonds become relatively stable molecular structure. The adsorption energy is -0.10kJ/mol at 298 K, and the activation barrier energy 189.15kJ/mol. The results show that two half-reaction process mechanism is similar, TMA endothermic reaction needs more energy to be carried out under heating conditions ; endothermic and exothermic reaction energy is basic balance, the activation energy is large, so the reaction is the best using ionized gas to be carried out.

Abstract: The reaction mechanism of electrochemical extraction of Fe_xTi alloys direct from natural ilmenite in molten CaCl₂ has been investigated. The electrochemical deoxidation experiment process was carried out at 1000 °C and 3.8 V, and a solid oxide oxygen-ion-conducting membrane (SOM) filled with carbon-saturated liquid metal was served as the inert anode of the electrolytic cell. The macro-/micro-structure variations of the samples during electrolysis were investigated. The reaction routes from natural ilmenite to Fe_xTi alloys are proposed and discussed. It is found that element Fe is reduced firstly from ilmenite and thus serves as electronic conductor to accelerate subsequent deoxidation, Fe_xTi alloys can be produced directly from natural ilmenite by electrolysis in molten salt. It is suggested that Fe_xTi phase can be formed directly from Fe_xTiO_y compounds and/or from deoxidation-generated Ti and Fe through various reaction routes.

Abstract: In situ aluminum matrix composites were fabricated through exothermic dispersive (XD) reaction from a powder mixture of Al and Cr₂O₃. The reaction mechanism was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and differential scanning calorimetry (DSC) analysis. When the temperature increases to around 1050K, Al can react with Cr₂O₃ to form the reinforcments Al₂O₃ particles and CrAl₄ blocks. With the increase of heating rate, DSC analysis shows that the reaction peak shifts to a higher temperature and the corresponding ignition temperature also increases. Based on DSC curves with different heating rates, the activation energy can be calculated and its value is 191.8 kJ/mol.

Abstract: Nanocrystalline ZnO powders have been synthesized by a novel and simple microwave-assisted combustion synthesis method using urea, glycine, carbohydrazine and citric acid as fuels and zinc nitrate as oxidant. The starting materials were directly mixed and a slurry precursor with high homogeneity was formed due to the hygroscopicity of the reactants. The precursor could be ignited at room temperature, resulting in dry, loose and voluminous ZnO powders. An interpretation based on an adiabatic flame temperature, amount of gases produced during reaction for various fuel-to-oxidizer molar ratios (ψ), has been proposed for the nature of combustion and its correlation with the characteristics of as-synthesized product. The variation of adiabatic flame temperature (T_ad) with the ψ value was calculated theoretically according to the thermodynamic concept. The reaction process of the precursor was investigated by XRD techniques.

Abstract: The reaction of oxygen atom with difluoric methyl radical has been studied using DFT method at 6-311++g** level. All the geometries, vibration frequencies and energies of different stationary points are calculated by B3LYP/6-311++G** and the results agree with the experimental values. The relationship and the changes among them can confirm the mechanism of the reaction and the process of electron transfer. Through the analysis, the major reaction channel and the minor reaction channel are confirmed.

Abstract: When poly (lactic acid-co-melamine) [P(LA-co-MA)] is synthesized via direct melt polycondensation (DMP), with the more MA in the feed content, the copolymer with a three-MA-core structure linked by the ether bond is formed. Increasing the molar feed ratio n(LA)/n(MA), the structure of the copolymers is gradually changed from multi-core structure into SPLA structure only containing one MA core, and a peak value of M_w exists as expected. The aromatic cores with different functional groups have an important influence on the M_w peak value, and the internal factors are the conjugate effect and the nucleophilicity caused by the different functional groups themselves.

Abstract: H₂O₂ aerosol was used to oxidize dichlorvos vapor. 80.7% of dichlorvos, with the initial concentration of 90.9 mg/m³, was decontaminated when the H₂O₂ concentration kept in the range of 110~130 mg/m³ within 60 min. According to the oxidation products, analyzed by GC-MS, the decontamination reaction mechanism was discussed. Radical chain reaction is the main decontamination mechanism. H₂O₂ is dissociated to HOO^-, which can induce the formation of ·OH. The double bond in dichlorvos molecule is attacked by ·OH to form molecule radical, which is further oxidized to 1,1-dichloro ethoxy dimethyl phosphate, 1,1,1-trichloro-2-hydroxyl-ethyl dimethyl phosphate, dimethyl phosphite, dimethyl phosphate, trimethyl phosphate, methyl phosphate, dichloro acetaldehyde, oxalic acid, CH₂Cl₂, CHCl₃, parts of which are mineralized to phosphoric acid, CO₂, H₂O and chloridion.

Abstract: The Dielectric Barrier Discharge plasma (DBD) plasma was used to treat Diisopropyl fluorophosphate (DFP, a stimulant of sarin) in the air. The influence factors of degradation efficiency, including power, carrier gas flow velocity and initial concentration of DFP were investigated. As a result, the degradation efficiency increased with the power increasing. The degradation efficiency increased fastly when the power less than 105W, but slowly when the power more than 105W. The degradation efficiency decreased obviously with the carrier gas flow velocity increasing, because the time of DFP stayed in plasma reactor decreased and the concentration of DFP increased. The degradation efficiency rose firstly and then fell with the initial DFP increasing, when the initial concentration was less than 80 mg/m³, but decreased with the the initial concentration increasing, when the initial concentration was more than 80 mg/m³. The main products were acetone, isopropanol, phosphoric acid, pyrophosphoric acid, carbon dioxide and water, analyzed by GC-MS. Reaction mechanism was discussed according to degradation products.

Abstract: The cordierite was synthesized at relatively low temperature by pressureless sintering method, using calcined bauxite, talcum , quartz and feldspar as raw materials in this paper. The water absorption (Wa), porosity (Pa), bulk density (D_b) and bending strength of samples have been tested, and the synthetic process and mechanism have been investigated by XRD, SEM, and so on. The results showed that the cordierite could be synthesized at 1280°C and the range of synthetic temperature is 1160~1300°C, when the sample was sintered at 1280°C for 2h, its bulk density and bending strength were 2.20g/cm³ and 72.13MPa, respectively. XRD analysis showed that the main phase of sample was cordierite, the cordierite content was about 88wt%, and the minor phases were MgAl₂O₄ spinel and corundum. SEM results showed that the samples were dense and the pore sizes were 5 μm~100μm, the grains were growth and development well, the grains size were 0.5μm~6μm. High reaction activity corundum and mullite were provided by calcined bauxite, then coupled with the role of feldspar, thus reduced the synthetic temperature of cordierite.

Abstract: Several reaction pathways on the potential energy surface (PES) for the radical-radical reaction of CH₃O₂ + CN have been investigated theoretically at the CCSD (T)//B3LYP/6-311++G (3df, 3pd) level. The calculations show that the CH₃OOCN and CH₃OONC are the most stable intermediates. The direct dissociation of CH₃OOCN (im2) leading to CH₃O + NCO is predominant on the energy surface, and the CH₂O + HNCO are expected to be secondary products.