Phase Evolution During Formation of SrAl2O4 from SrCO3 and α-Al2O3/AlOOH

Through the execution of experimental investigation, thermogravimetry, X-ray diffractometry, Fourier transform-infrared spectrometry, transmission electron microscopy, and energy-dispersive spectrometry, a variant reaction mechanism model was proposed for the solid-state reaction between SrCO₃ and Al₂O₃/AlOOH for formation of SrAl₂O₄ material. The solid-state reaction is observed to be dependent on the calcination temperature. At temperatures lower than the transformation temperature of SrCO₃ from orthorhombic to hexagonal (920°C), the reaction is attributed to the interfacial reaction between SrCO₃ and alumina. Conversely, at temperatures higher than that, the solid-state reaction is dominated by the diffusion of Al³⁺ ions into the SrCO₃ lattice. In this mechanism, two metastable species, hexagonal SrCO₃ and hexagonal SrAl₂O₄, were observed. The activation energies of SrCO₃ decomposition in the solid-state reaction also support these results. The interfacial reaction at low temperatures is characterized by a high activation energy of ∼130 kJ/mol; whereas, in the reaction at higher temperatures, the activation energy of SrCO₃ decomposition decreases to 34 kJ/mol.     

Nonisothermal Reaction Kinetics of SrNb2O6 and BaNb2O6 for the Formation of SrxBa1−xNb2O6

The solid-state reaction of SrNb₂O₆ and BaNb₂O₆ to form Sr _x Ba_{1− x} Nb₂O₆(SBN) at different temperatures and heating rates was investigated. The reaction kinetics were analyzed by X-ray diffractometry for quenched samples, and the internal-standard method was applied to quantify the extent of the reaction. A nonisothermal kinetic empirical model was proposed to evaluate the activation energy and rate constant of SBN with different Sr:Ba ratios. It was found that the kinetic form would change above and below a transition at a reaction fraction of ∼60%, which might be due to the change of the frequency factor. It was also verified that the model that was presented was more favorable to describe the nonisothermal reaction kinetics of SBN.     

Kinetic Study of Cu+−Cu2+ Equilibrium in Sodium Na2O−Al2O3−B2O3 Glass

The Cu⁺−Cu²⁺ equilibrium in sodium aluminoborate glass with an air atmosphere was studied at 950°, 1050°, and 1150°C. Equations suggested to represent the equilibrium reaction between oxidized and reduced species and oxygen were critically examined. An equation to represent the Cu⁺−Cu²⁺ equilibrium reaction was suggested. The reaction was observed to follow first-order kinetics. Enthalpy of the reaction was—12.5 kcal/mol.     

Alumina–Aluminide Alloys (3A) Technology: II, Modeling of TixAly–Al2O3 Composites Formation

The reaction sintering of Ti _x Al _y –Al₂O₃ composites from TiO₂/Al starting powder mixtures has been characterized by thermogravimetry and differential thermal analysis (TG/DTA), in situ temperature measurements, and predictions via a continuum model. In order to model the TiO₂/Al reaction system, it was necessary to first determine the postmill reactant concentrations and the dominant reaction. The postmill reactant concentrations were obtained from TG/DTA measurements in air, while X-ray diffraction (XRD) was used to gain insight into the reaction mechanisms. A continuum model of the process was fitted to in situ temperature measurements by adjusting two parameters. The model was then used to investigate the effects of various processing conditions on the reaction behavior.     

Reaction of TiO2-Al-C in the Combustion Synthesis of TiC-Al2O3 Composite

Reaction mechanisms and the thermal structure in the reaction zone during the combustion of TiO₂, Al, and C to form TiC-Al₂O₃ composite were studied. The reaction between each component was studied and the combustion wave structure and real-time temperature profile were analyzed. Titanium aluminide species, present in the aluminothermic reduction of TiO₂, did not occur in the presence of C, because of the high thermodynamic stability of TiC. The activation energies of the exothermic reaction in the 3TiO₂-4Al-3C system were determined by DSC analysis. This suggests that the combustion reaction is mainly controlled by carbon diffusion through solid TiC. The combustion wave was observed to propagate in an unstable mode. The temperature profiles in the reaction zone were of the sawtooth type and the products were of layered structure.     

Comparison of the Reaction Systems ZrO2-Si3N4 and TiO2-Si3N4

Reaction mechanisms occurring in the systems ZrO2-Si₃N₄ and TiO2-Si₃N₄ have been compared. The thermodynamics of several overall reaction mechanisms have been analyzed, including the effects of the gas phase composition to determine the most energetically favorable course of each reaction .     

固体碱K_2CO_3/Al-Ni及K_2CO_3/Al-Ni-O催化制备生物柴油

分别采用合成的铝镍类水滑石和其焙烧后复合氧化物为载体,负载K_2CO_3制得负载型固体碱催化剂,并用于催化食用菜籽油制生物柴油的反应。考察甲醇与菜籽油物质的量比、反应时间和反应温度对催化性能的影响,结果表明,在甲醇与菜籽油物质的量比10∶1、反应温度60℃、反应时间6 h和催化剂用量为油质量的5%条件下,生物柴油产率最高,为82.4%,且催化剂可重复使用,具有稳定的催化作用。     

Mechanistic study on the SCR of NO by C3H6 over Pt/V/MCM-41

Pt/V/MCM-41 has a high activity for the selective catalytic reduction (SCR) of NO with C₃H₆ over a wide temperature range. Its broad activity–temperature window is due to three different reactions occurring in each different temperature range. One of these reactions is the reaction occurring on usual Pt-based catalysts. The experimental result of Pt dispersion effect suggested that this reaction follows the redox mechanism. The second reaction is that of molecularly adsorbed NO on Pt with surface carbonaceous species on Pt/V/MCM-41. Experiments for the reaction of NO with carbonaceous materials present on Pt/V/MCM-41 used in the SCR of NO confirmed that carbonaceous species can take part in the reaction. The third reaction is that occurring on support V/MCM-41.     

Preparation of Bi4Ti3O12 Powders in the Presence of Molten Salt Containing LiCl

The reaction between Bi₂O₃ and TiO₂ in molten LiCl-KCl was examined with special emphasis on the reaction mechanism and the size of Bi₄Ti₃O₁₂ particles. The oxides reacted with LiCl to form an intermediate compound, which changed into Bi₄Ti₃O₁₂ on extended heating. Potassium chloride retarded the reaction between the oxides and LiCl and promoted the change from the intermediate compound to Bi₄Ti₃O₁₂. Bi₄Ti₃O₁₂ particles prepared in the flux were platelike, irrespective of the preparation conditions, but their size depended on reaction temperature and time, the ratio of LiCl to KCl, and the amount of flux.     

Effect of Li2CO3 on Reaction Between CaO and CO2

Reaction between CaO powders and CO₂( g ) is often limited by slow diffusion of CO₂ through the CaCO₃ product. Additions of Li₂CO₃ are shown to increase the reaction rate. At temperatures around 940 K, near to the Li₂CO₃-CaCO₃ eutectic temperature, 935 K, complete reaction of the CaO with CO₂ can be achieved when the heating rate and Li₂CO₃ content are optimized. At lower temperatures Li₂CO₃ causes lesser but measurable increases in reaction rates. SEM and surface area observations suggest different reaction paths when Li₂CO₃ is present, when Li₂CO₃ and eutectic are present, and when eutectic alone is present.     

Surface Modification of Al2O3/TiC Cutting Ceramics

Cutting ceramics with a graded TiC-rich surface have been obtained by an in situ reaction. Al₂O₃/TiC ceramics, prepared by reaction sintering, have been subjected to various thermal posttreatments at atmospheric pressure. The temperature, dwelling time, and reaction atmosphere have been varied. It has been observed that a TiC-rich surface develops in CO-containing atmospheres. The microstructure of the bulk remains unaffected. Thermal treatment under a CO atmosphere at 1600 ° C for 1 h resulted in a dense TiC layer on the ceramic. A schematic model is proposed for this layer formation process.     

Character of Hydration of 3CaO.Al2O3

The C₃A compacts were hydrated and the reaction was studied by DTA, X-ray diffraction, mercury porosimetry, and volume change analysis. The hexagonal hydroaluminates C₂AH₈ and C₄AH₁₉ formed at 2°, 12°, and 23°C by a direct mechanism between C₃A and H₂O. The hydration reaction at 52° and 80°C was stopped by formation of C₃AH₆ around the C₃A grains. The rate of conversion of the hexagonal hydrates to cubic C₃AH₆ increased with temperature. Volume change analysis confirmed that C₃AH₆ grows epitaxially on the surface of the C₃A grain. The reaction at this surface and the passage of water through the layer of hexagonal hydroaluminates control the overall reaction rate. The conversion of the hexagonal hydrates to C₃AH₆ accelerates the reaction by removing the layer of products from around the C₃A grain by a solution mechanism. At 52° and 80°C, C₃AH₆ may form without the intermediate formation of the hexagonal hydrate.     

Rh/SiO2催化剂上双环戊二烯氢甲酰化

采用浸渍法制备了SiO₂低负载量的铑催化剂Rh/SiO₂。研究以三苯基膦为配体的Rh/SiO₂催化剂对双环戊二烯氢甲酰化合成三环癸烷不饱和单醛的催化性能及其影响因素。结果表明,Rh/SiO₂催化剂对双环戊二烯氢甲酰化具有良好的催化作用,双环戊二烯合成三环癸烷不饱和单醛选择性超过99%。双环戊二烯氢甲酰化过程与催化剂用量、三苯基膦浓度、反应压力和反应温度有关。反应过程中存在一定诱导期,随着压力增加,诱导期逐渐缩短;增加催化剂用量和三苯基膦浓度有利于提高双环戊二烯转化率和三环癸烷不饱和单醛收率;升高温度虽然有利于双环戊二烯转化,却降低了三环癸烷不饱和单醛选择性。当催化剂与双环戊二烯质量比为1∶25、三苯基膦浓度10.0 g·L^－1、负载铑质量分数1‰、反应温度110 ℃、反应压力3.0 MPa和反应时间240 min时,双环戊二烯转化率超过99%,三环癸烷不饱和单醛选择性超过99%。     

Aluminum Titanate Formation by Solid-State Reaction of Fine Al2O3 and TiO2 Powders

The formation of Al₂TiO₅ has been studied in equimolar Al₂O₃-TiO₂ powder mixtures of ∼1μm particle sizes and moderate purity (∼99.8 wt%) at temperatures around 1300°C, where the free energy of formation is very small. Micro-structural development and reaction kinetics indicate that different mechanisms operate depending on the advancement of the reaction. The rapid initial reaction stage is interpreted as the nucleation-growth of Al₂TiO₅ cells in a virtually non-reacting matrix. The final reaction stage corresponds to the slow diffusion-controlled elimination of Al₂O₃ and TiO₂ dispersoids trapped during the growth of the initial Al₂TiO₅ cells.     

Synthesis of γ-Ga2O3–Al2O3 Solid Solutions by the Glycothermal Method

The reaction of mixtures of aluminum isopropoxide and gallium acetylacetonate in 1,4-butanediol or 1,5-pentanediol at high temperatures (glycothermal reaction) directly gave the γ-Ga₂O₃–Al₂O₃ solid solutions, which had high catalytic activities for selective reduction of NO using methane as the reducing agent. However, the reaction with a higher Al/(Ga+Al) charged ratio yielded the glycol derivative of boehmite as a by-product and the catalytic activity of the solid solution decreased. Therefore, synthesis of the solid solution using various glycols was examined and it was found that solid solutions with high Al contents without contamination of the glycol derivative of boehmite were obtained by using 1,6-hexanediol as a reaction medium. The solid solution exhibited a higher NO conversion than that synthesized in other glycols.     

Development of a transient kinetic model for the CO oxidation by O2 over a Pt/Rh/CeO2/γ-Al2O3 three-way catalyst

A transient kinetic model was developed for the CO oxidation by O₂ over a Pt/Rh/CeO₂/γ-Al₂O₃ three-way catalyst. The experiments which were modelled consisted of periodically switching between a feed stream containing 0.5 mol% CO in helium and a feed stream containing 0.5 mol% O₂ in helium, with a frequency from 0.1 to 0.25 Hz, in the temperature range 393–433 K. These temperatures are representative for cold start conditions. The transient experiments yield information about the reaction mechanism. A transient kinetic model based on elementary reaction steps was developed which describes the experimental data in the above mentioned range of experimental conditions adequately. The kinetic model consists of two monofunctional and one bifunctional contribution. The first monofunctional reaction path comprises competitive adsorption of CO and O₂ on the noble metal surface followed by a surface reaction. The second monofunctional reaction path consists of CO adsorption on an oxygen atom adsorbed on the noble metal surface, followed by a reaction to CO₂. The bifunctional reaction path involves a reaction between CO adsorbed on the noble metal surface and oxygen from ceria at the noble metal/ceria interface. Also, reversible adsorption of carbon dioxide on the support is taken into account. The kinetic parameters, i.e. preexponential factors and activation energies for the different elementary reaction steps, and the oxygen storage capacity were estimated using multi-response non-linear regression analysis of the oxygen, carbon monoxide and carbon dioxide outlet concentrations.     

Kinetics and mechanism of the oxidative dehydrogenation of ethane over Li/Dy/Mg/O/(Cl) mixed oxide catalysts

The microkinetic reaction network of the oxidative dehydrogenation of ethane to ethene over Li/Dy/Mg/O and Li/Dy/Mg/O/Cl catalysts was investigated. With Li/Dy/Mg/O catalysts, the reaction kinetics is compatible with a heterogeneous-homogeneous radical based reaction mechanism. The formation of ethyl radicals on the surface is concluded to be the rate-determining step. In contrast, the reaction kinetics for Li/Dy/Mg/O/Cl is in line with a purely surface catalyzed reaction mechanism. However, also in this case, alkane activation is rate determining.     

The reactivity of epoxy/polycarbonate/BF3-MEA system

The cationic reaction of an epoxy/BF₃-MEA system occurs between the oxirane group and the oxonium group. The addition of polycarbonate to the system does not cause a transesterification reaction between the carbonate group and the oxonium group, thus the molecular weight of the PC is unchanged during the reaction. PC crystallization is observed in the cured system because the epoxy monomer accelerates the PC crystallization. The epoxy/BF₃-MEA and epoxy/PC/BF₃-MEA systems all follow the first order reaction. The PC modified systems show lower activation energy, a lower pre-exponential factor and a higher reaction rate constant.     

对苯二甲酸丁二醇酯二聚体水/醇/氨解机理的理论研究

采用密度泛函理论M06-2X/6-311G（d）方法,对对苯二甲酸丁二醇酯二聚体的水/醇/氨解反应机理进行了量子化学理论研究。提出了各种可能的水/醇/氨解反应路径,对各反应的中间体、过渡态及产物进行了几何结构优化和频率计算以获得热力学与动力学参数值,分析了对苯二甲酸丁二醇酯二聚体主链酯键中的酰氧键位置水/醇/氨降解的反应机理。计算结果表明：水/醇/氨解条件下能够降低对苯二甲酸丁二醇酯二聚体主链酯键中的酰氧键裂解的反应活化能,使反应更易于进行,水/醇/氨解中主要基元反应步的反应能垒分别约为170.0、155.0和165.0 kJ/mol。对苯二甲酸丁二醇酯二聚体水解产物主要为对苯二甲酸和1,4-丁二醇,醇解产物主要为对苯二甲酸二甲酯和1,4-丁二醇,氨解产物主要为芳香腈和1,4-丁二醇等,其中1,4-丁二醇会进一步降解形成四氢呋喃。在对苯二甲酸丁二醇酯二聚体水/醇/氨解反应过程中,甲醇介质中的裂解反应优于氨气气氛中的反应、氨气气氛中的反应优于水分子环境中的反应,且反应温度的升高可以增加其自发性。     

Low-Temperature Synthesis of ZrC Powder by Cyclic Reaction of Mg in ZrO2–Mg–CH4

We investigated the conditions for low-temperature synthesis of ZrC fine powder from ZrO₂–Mg–CH₄. The synthesis utilizes a thermite-type reaction, with Mg as the reducing agent, and a reaction between Mg and CH₄ gas as a carbon source. The Mg/ZrO₂ molar ratio as well as the heating rate were varied. Because C can be continuously fed into the reaction group by the cyclic reaction of Mg through the formation and decomposition of Mg₂C₃ (2Mg + 3CH₄→ Mg₂C₃+ 6H₂→ 2Mg + 3C), a molar ratio of 2.2 for Mg/ZrO₂ was sufficient for the synthesis of single-phase ZrC. ZrC powders were synthesized under the following conditions: Mg/ZrO₂ molar ratio = 2.2, heating rate = 20°C/min, and temperature maintained at 750°C for 30 min. The amount of reaction heat produced in the reduction reaction of ZrO₂ by Mg depended on the Mg/ZrO₂ molar ratio, specifically, the amount of ZrO₂ contained. Moreover, the cyclic reaction of Mg-Mg₂C₃–Mg was influenced by the amount of reaction heat described above and by the heating rate. The ZrC fine powder showed little aggregation and high dispersibility.