粉状阳离子聚丙烯酰胺的研制

用聚丙烯酰胺胶体,在≥20％浓度的硫酸盐溶液中,进行Mannich反应,经真空干燥后,制取水溶性阳离子型高分子。初步探讨了盐浓度、温度、时间、配比对产物的阳离子度、溶解性的影响。     

SYNTHESIS OF CHEMICAL REACTION PATHS: ECONOMIC AND SPECIFICATION CONSTRAINTS

The synthesis of alternative reaction paths leading to a desired chemical has received increasing attention in the recent past. A procedure to develop new reaction schemes in a systematic manner was reviewed by the authors ( [ 1 -3] ). The algorithm presented in these earlier papers implied the generation of an infinite number of reaction paths. The thermodynamic feasibility is a preliminary screening which reduces the number of chemical production schemes. Further screening is necessary, taking into account considerations which are related to economics, processing, safety and so on. Some constraints related with role specification, gross added value and demand/supply requirements are analysed in this paper. Examples illustrate the application of the screening procedure, showing that the addition of a few constraints results in a dramatic decrease of alternative reaction paths.     

Film morphology and reaction rate for the CVD of tungsten by the WF6—SiH4 reaction

Journal of Electronic Materials - Low pressure chemical vapor deposition (LPCVD) of tungsten (W) by SiH4 reduction of WF6 on Si(100) surfaces was studied in a single-wafer, cold-wall reactor over a...     

Kinetics of oxygen absorption in aqueous sodium dithionite solutions

The absorption and reaction of oxygen in aqueous alkaline solutions of sodium dithionite has been experimentally investigated in a novel gas-liquid contactor. The novel gas-lift bubble column contactor was used to study the kinetics over wide ranges of reactant concentrations, temperature, and pH. The oxygen-sodium dithionite reaction was found to be first-order with respect to dithionite in the range of dithionite concentration < 0.1 M, and second-order in the range of dithionite concentration > 0.1 M. The reaction with respect to oxygen was found to be zero-order for all dithionite concentrations. These results and experimental investigations of the effect of solution alkalinity and temperature on the reaction rate are consistent with previous findings obtained in different gas-liquid contactors. The results thus confirm the feasibility of using the gas-lift bubble column for the kinetics of gas-liquid reactions.     

Drying with Chemical Reaction in Cocoa Beans

Desirable flavor qualities of cocoa are dependent on how the cocoa beans are fermented, dried, and roasted. During fermentation and drying, polyphenols such as leucocyanidin and apecatechin are oxidized by polyphenols oxidase to form o-quinone, which later react nonenzymatically with a hydroquinone in a condensation reaction to form browning products and moisture. The objective of this article is to model the cocoa beans drying together with the browning reaction. A Luikov drying model for the moisture and a simple Fick's law diffusion model combined with first-order reactions for both the enzymatic oxidation and nonenzymatic condensation reactions were constructed. Both models were used to identify moisture diffusivity coefficient and total polyphenols diffusivity in cocoa beans from experimental drying and polyphenols degradation data and published kinetic data of the reactions. The theoretical drying model fitted the experimental cocoa bean drying curves with low mean square of residuals. The polyphenols diffusion and reaction model also fitted the experimental polyphenols degradation curves with minimum mean residual squares. The rate of polyphenols degradation in the cocoa beans increases at higher temperature and higher relative humidity. This is because the increasing reaction rate of polyphenols oxidation reaction as well as higher moisture diffusion at higher relative humidity and temperature. The effective moisture diffusivity in cocoa beans is estimated to be between 8.194 × 10^-9 and 8.542 × 10^-9 m²·s^-1, which is of the same order of magnitude as published data. The effective total polyphenols diffusivity is estimated to be between 8.333 × 10^-12 to 1.000 × 10^-11 m²·s^-1 with minimum mean residual squares. It is three orders of magnitude less than the estimated moisture diffusivity because of the larger polyphenols molecules. The estimated polyphenols diffusivity is very close to those published in the literature for sorption and ultrafiltration processes.     

A novel methanol-tolerant Ir-Se chalcogenide electrocatalyst for oyxgen reduction

A novel methanol-tolerant oxygen-reduction catalyst, Iridium-selenium (Ir-Se) chalcogenide, was synthesized by chemical precipitation in an organic solvent. Auger electron spectroscopy (AES) analysis confirmed that the synthesized Ir-Se chalcogenide had a chemical formula of Ir₄Se. This chalcogenide showed strong catalytic activity towards the oxygen reduction reaction (ORR) and a high methanol tolerance. It was found that most of the oxygen could be directly reduced to water through a four-electron pathway with less than 10% hydrogen peroxide (H₂O₂) being produced during the ORR. The improvement in catalytic activity of the Ir-Se chalcogenide in comparison with that of pure Ir might be attributed to the effect of a bimetallic interaction.     

EC与~（99m）Tc－GH之间的配体交换反应动力学研究

实验表明，ＥＣ浓度与配体交换反应速度常数无关，体系的ｐＨ值对速度常数和９９ｍＴｃ－ＥＣ的标记率影响较大。测定并计算了不同ｐＨ值的交换反应速度常数。结果表明，为保证用配体交换法制备９９ｍｃ－ＥＣ时９９ｍｃ－ＥＣ的标记率大于９０％，体系的ｐＨ值必须≥８。     

Comparison of interfaces in Ti composites reinforced with uncoated and TiB2/C-coated SiC fibres

Interfaces play an important role in determining the mechanical properties of composite materials. The interfaces established between a titanium-alloy matrix (Ti-6Al-4V) and uncoated and TiB₂/C-coated SiC fibres are analysed by scanning electron microscopy, transmission electron microscopy and X-ray techniques. Emphasis is placed upon the interfacial morphology and microstructure, identification of reaction products, and the stability of the coating layer. Complex multi-reaction layers are observed frequently in the interfacial zones. Previous, often contradictory, reports about the interlayers are reviewed. Experimental observation demonstrates that the type and distribution of interlayers vary in a given system, due to prolonged treatment of the samples at temperature. The formation and distribution of the interlayers are discussed further, with respect to these and previous findings. Methods of reducing interfacial reactivity are discussed.     

高能球磨AL─Cu合金固态合成反应研究

采用扫描电镜、能谱分析、Ｘ射线衍射和示差扫描量热分析研究了具有较大负混合焓的Ａｌ＿ｘＣｕ＿（１－ｘ）对称扩散系合金的高能球磨固态合成反应。高能球磨时组元晶粒细化达纳米级，造成纳米晶界亚互溶，为室温固态合成反应创造了条件，球磨强度对反应进程影响显著，在ｘ＝０．３～０．７范围内仅形成一种金属间化合物。     

The Synthesis of Covalent Triazine-Based Frameworks via Friedel–Crafts Reactions of Cyanuric Chloride with Thienyl and Carbazolyl Derivatives for Fluorescence Sensing to Picric Acid,Iodine and Capturing Iodine

A multifunctional thiophene-based covalent triazine framework (TTPATTh) with triphenylamine as core is synthesized by Friedel–Crafts reaction of cyanuric chloride with thienyl derivative for the first time. The yield of TTPATTh (99.59%) is far higher than that of the carbazole-based CTF (TTPATCz, 47.03%). TTPATTh and TTPATCz possess high BET surface areas with 1235 and 2501 m² g^–1 as well as high pore volumes with 1.60 and 2.23 cm³ g^–1, respectively. TTPATTh and TTPATCz have high thermal stability with high thermal decomposition temperatures of 514 and 598 °C in nitrogen atmosphere. With the introduction of triazine rings, the fluorescence sensing sensitivities of TTPATTh and TTPATCz to picric acid and iodine are improved significantly. Especially for TTPATTh, the K_sv values reach 5.95 × 10⁵ and 1.61 × 10⁴ L mol^–1, and LODs reach 1.02 × 10^–12 and 1.86 × 10^–12 mol L^–1. To the best of the knowledge, this is the most sensitive value among thiophene-based porous organic polymers to PA and I₂. Furthermore, TTPATTh and TTPATCz can also adsorb iodine in vapor phase, cyclohexane solution and aqueous solution, and release iodine by heating or in ethanol solution. The efficiency of controlling the release of iodine is higher than that in ethanol.