The thermal decomposition of NaHCO3 powders and single crystals

The thermal decomposition of four commercial powders and of differently stored single crystals of sodium hydrogen carbonate is studied by power compensation DSC and by optical and FT-IR microscopy. Independently of manufacturer, specified purity and price, the thermal curves of all the commercial powders show a more or less pronounced low temperature peak preceding the one due to the main decomposition. Such small peak is not observed when samples of laboratory recrystallized material are used. However the thermal behaviour of the latter preparation differs remarkably depending on storage conditions: the material kept in closed glass containers decomposes at temperatures higher than those of the material stored in a dessiccator in the presence of concentrated H₂SO₄. The observation by optical microscopy of the behaviour of the surfaces of single crystals coming from different storage conditions when the temperature is raised in a Kofler heater helps the interpretation of the data collected. The mechanism of the decomposition is discussed and the relevant kinetic parameters reported.     

四氢键二聚体和分子组装

介绍了最近几年新的四氢键有机二聚体研究的进展及其在分子自组装和分子聚 集体化学研究中的应用。     

XPS,AFM, ATR and TPD evidence for terraced,dihydrogen terminated, 1×1 (100) silicon

Heating (100) silicon at high temperature (say, higher than 850 °C) in H₂, cooling to 670–700 °C in the same ambient, and quenching to room temperature in N₂ results in environmentally robust, terraced 1 × 1 (100) SiH₂. Evidence for this conclusion is based on angle‐resolved x‐ray photoelectron spectroscopy, atomic force microscopy, infrared absorption spectroscopy in the attenuated total reflection mode, thermal programmed desorption, and reflection high‐energy electron diffraction. Copyright © 2005 John Wiley & Sons, Ltd.     

Fe-Ni-B-O纳米合金的合成及其催化制氢性能的研究

Preparation and catalytic performance of Fe-Ni-B-O nano-alloy having crystal-palpus structure has been studied. Black powder was synthesized by reducing mixture solution of Fe²⁺, Ni²⁺ with KBH₄ as reducing agent and polyethylene glycol as dispersant. Fe-Ni-B-O nano-alloy of crystal-palpus structure was obtained after hydrogen reduction of black powder. TEM shows that crystal-palpus length is 200～400 nm, diameter is 2～4 nm. The analytic results indicate that the total content of Fe and Ni is 86.6%, B is 5.08%. The alloy exhibits excellent catalytic performance. Hydrogen generation rate can approach 100% especially when pH is 8.     

硫酸氢铵分解动力学及其分解机理的研究

为了筛选适合的化学贮能系统,Wentworth等人曾提出了十项筛选标准。照此标准衡量,硫酸氢铵的分解-合成反应是一个十分理想的贮能系统: NH_4HSO_4(l)?NH_3(g)+H_2(g)+SO_3(g)Prengle也曾就此反应应用于太阳能电站贮能系统的可行性作过理论上的探讨.但是,有关该反应的基础研究进行的还很不够,特别有关分解动力学和分解机理的研究文献尚未见报导。本文用等温热重法和程序升温热重法对硫酸氢铵的热分解动力学进行了研究,并确定了分解机理,为贮能系统的实际应用提供了基础数据。     

三氧化二铝溶胶-凝胶固定过氧化氢生物传感器

三氧化二铝溶胶凝胶将辣根过氧化物酶和硫堇同时固定在玻碳电极上,紫外-可见光谱结果表明酶在固定过程中生物活性保持得较好.传感器在pH 7.0外加电压为-0.22 V条件下,对过氧化氢浓度为1.76×10-3～5.5×10-2 mol/L的范围内呈线性响应,检出限为1.1×10-4 mol/L.传感器的选择性和稳定性较好,使用3个星期后,仍能保持其初始活性的80%.     

Chemihiminescence by the interaction of XeO3 and the products of photolysis of uranyl solutions in sulfuric acid

Using the chemiluminescence oxidation of U(IV) and H₂O₂ with xenon trioxide as a model, it has been found that during the photolysis of solutions of UO₂SO₄ in sulfuric acid in the absence of any organic compounds, the accumulation of U(SO₄)₂ and H₂O₂ takes place as a result of the reaction of the primary products of the photoreduction of uranyl ion,i.e., UO₂ ⁺ and the OH radical.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 751–754, April, 1994.The work was financially supported by the Russian Foundation for Basic Research, Project 93-03-12291.     

Hydrogen Oxidation on a Platinum Microelectrode: Effect of Carbon Monoxide Impurities

The kinetics of the hydrogen oxidation and the CO adsorption on a Pt (ultra)microelectrode is studied in a 0.5 M H₂SO₄ solution saturated with a mixture of gaseous H₂ and CO at partial CO pressures p _CO = 10–500 ppm. The balance between rates of diffusion and adsorption of CO at different adsorption times is studied. Studied is the effect of CO impurities in H₂ on steady-state polarization curves for the hydrogen ionization and nonsteady-state curves of the oxidation current decay with time at 0.02–0.05 V. Conditions under which in a certain time interval and at a certain CO concentration the slope of an I vs. t curve is proportional to p _CO are determined. The obtained dependence may be used when designing a technique for monitoring CO impurities in technical hydrogen.     

Polychronous kinetics with nonstationary rate constants. Effect of a medium

Characteristic features of the kinetics of solid-state cage reactions with distributed parameters of the relaxing matrix were considered. Depending on the ratio of the constants of the reaction rate and relaxation of environment, the kinetics of chemical conversions can be either exponential or nonexponential. Plausible reasons for the unsteady-state character of the kinetics of the processes of two types,viz., the reactions of alkyl radicals in amorphous alcohol matrices and conversions in biological systems, were discussed. The main reason for the unsteady-state character of the reactions of the first type is a dispersion of the equilibrium distances between the reagents. Kinetics of the reactions of the second type, such as rebinding of the ligands in the heme-containing proteins (e.g., in myoglobin), is determined by the distances in the pairs of reagents and the relaxation transitions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 469–476, March, 1997.