二元有机液体混合物热容与过剩热容的测定

溶液的热容及过剩热容是热力学的重要函数，对其测定与研究具有理论与实际意义．首先，热容是化工传热计算中的基础数据，过剩热容则可检验溶液中分子间的相互作用，并可利用其计算混合物的热容．本文报告了用法国Setaram公司生产的MS-80型Calvet微量热仪对环己酮-芳烃（苯、甲     

Heat capacity and glass transition of ethylene oxide clathrate hydrate

The heat capacity of structure I ethylene oxide clathrate hydrate EO-6.86 H₂O was measured in the temperature range 6–300 K with an adiabatic calorimeter. The temperature and enthalpy of congruent melting were determined to be (284.11 ± 0.02) K and 48.26 kJ mol^–1, respectively. A glass transition related to the proton configurational mode in the hydrogen-bonded host was observed around 90 K. This glass transition was similar to the one observed previously for the structure II tetrahydrofuran hydrate but showed a wider distribution of relaxation times. The anomalous heat capacity and activation enthalpy associated with the glass transition were almost the same as those for THF-hydrate.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.Author for correspondence.     

Kinetic studies on the formation of N-nitroso compounds

Acetic acid/acetate ion buffer acts catalytically upon the nitrosation of amines under conditions in which the only nitrosating agents are N₂O₃ and NOBr, but inhibits nitrosation by H₂NO ₂ ⁺ . The kinetic characteristics of these phenomena have been analysed quantitatively and compared with similar effects caused by the solventsTHF, DMSO and dioxane. The experimental results show that this behaviour is an effect of the medium.

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Kinetische Untersuchungen zur Bildung von N-Nitroso-Verbindungen, 8. Mitt.: Nachweis eines Medium-Effekts von Essigsäure/Acetat-Puffer auf die Geschwindigkeitskonstante der Nitrosierung

Zusammenfassung Essigsäure/Acetat-Puffer wirkt bei der Nitrosierung von Aminen katalytisch, unter Bedingungen, wo die alleinigen nitrosierenden Agentien N₂O₃ und NOBr sind; andererseits wird die Nitrosierung durch H₂NO ₂ ⁺ unterbunden. Die kinetischen Charakteristika dieses Phänomens wurden quantitativ analysiert und mit ähnlichen Effekten der LösungsmittelTHF, DMSO und Dioxan verglichen. Die experimentellen Ergebnisse zeigen, daß dieses Verhalten auf einen Mediumeffekt zurückzuführen ist.

     

Thermodynamics of 2D polymerized tetragonal phase of fullerene C60 in the range from T→0 to 650 K at standard pressure

By dynamic calorimetry the temperature dependence of heat capacity for two-dimensional (2D) polymerized tetragonal phase of C₆₀ has been determined over the 300-650 K range at standard pressure mainly with an uncertainty ±1.5%. In the range 490-550 K, an irreversible endothermic transition of the phase, caused by the depolymerization of the polymer, has been found and characterized. Based on the experimental data obtained and literature information, the thermodynamic functions of 2D polymerized tetragonal phase of C₆₀, namely, the heat capacity C°_p(T), enthalpy H°(T)−H°(0), entropy S°(T), and Gibbs function G°(T)−H°(0), have been calculated over the range from T→0 to 490 K. From 150 to 330 K in an adiabatic vacuum calorimeter and between 330 and 650 K in a dynamic calorimeter the thermodynamic properties of the depolymerization products have been examined and compared with the corresponding data for the monomeric phase C₆₀.     

Density measurements of potassium phosphate buffer from 4 to 45 degrees C

Potassium phosphate buffer is often used in methods such as equilibrium dialysis, high performance liquid chromatography (HPLC), and affinity capillary electrophoresis (ACE) for characterizing the binding of drugs and hormones with proteins or other ligands within the body. In these experiments, the buffer density is often approximated to be that of water and the concentrations of all reagents are assumed to be constant with temperature. However, some difference in density between phosphate buffer and water would be expected, and variations in this density could lead to significant changes in the concentrations of dissolved solutes with temperature. This, in turn, could affect the binding observed for a solute-ligand system in such a buffer. In this study, the densities of potassium phosphate buffers with concentrations up to 0.10 M were measured at or near physiological pH for temperatures ranging from 4-45 °C. The general change in density versus temperature followed a quadratic equation, while the changes in density with concentration and pH followed a linear response. The results were used to formulate a general equation that could be used to calculate the density of potassium phosphate buffer at any pH, temperature, and concentration within the tested range. This equation and more specialized relationships developed in the temperature, concentration, and pH studies were found to give much greater accuracy in describing the density of these buffers versus a previous relationship developed for solutions containing only potassium dihydrogen phosphate.     

重铬酸钾晶体低温热容及热力学性质的研究

用精密自动绝热量热计测定了重铬酸钾晶体在100～390 K温区内的摩尔热容.实验结果表明在研究温度区间内重铬酸钾无相变和其它热反常现象发生,但其热容在不同的温度范围表现出不同的变化趋势.在100 K≤ T ≤ 275 K和350 K≤ T ≤390 K区间内,其热容随温度的升高明显增大,在275 K≤ T ≤350 K区间,其热容约为定值.将重铬酸钾摩尔热容实验值Cp,m(J•K－1•mol－1)拟合成温度T的多项式方程,在100 K≤ T ≤275 K,为Cp,m=0.0050T2－1.0320T＋125.22； 275 K≤ T ≤ 350 K,为Cp,m=209.37； 350 K≤ T ≤390 K,为Cp,m= 0.0266T2－18.823T＋3542.3.根据热力学函数关系式,从热容值计算出了298.15 K～ 400 K温区范围内每隔5 K的热力学函数值.     

Standards for pH measurements and first ionization constants ofo-phthalic acid. Methylcellosolve-water solvent mixtures from −10 to 45°C

From reversible emf measurements of the cell Pt/H₂/KHPh+KCl/AgCl/Ag/Pt, reference value pH-metric standards, pH _RVS , for 0.05 mol-kg^–1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 20, 50, and 80 wt % methylcellosolve (2-methoxyethanol, CH₃O-CH₂CH₂OH)-water solvent mixtures from –10 to +45°C, have been determined in compliance with the criteria endorsed by IUPAC. The corresponding values of the first ionization constant ofo-phthalic acid (H₂Ph, benzene-1,2-dicarboxylic acid), which is a key quantity for the acquisition of pH _RVS standards, have been determined from emf measurements of the reversible cell Pt/H₂/H₂Ph+KHPh+KCl/AgCl/Ag/Pt.     

Effect of rapid solidification on heat capacities of Al-Sr alloys

Heat capacities of both the ingot-like and melt-spun Al-Sr alloys have been measured through the temperature range 373 to 1060 K using differential scanning calorimetry. The experimental results show that rapid solidification has a slight effect on the temperature dependence of the heat capacities of the Al-Sr alloys. The heat capacities of the melt-spun Al-Sr alloys increase more slowly than those of the ingot-like alloys with increasing temperature from 373 to 900 K. Furthermore, the effect of rapid solidification on the heat capacities becomes more obvious with increasing Sr concentration in the Al-Sr alloys. The data of the heat capacities between 373 and 900 K have been fitted with the least square method and a linear dependence on temperature was assumed for that temperature range. This revised version was published online in July 2006 with corrections to the Cover Date.     

纳米铁的低温热容和热力学性质研究

用扫描电子显微镜(SEM)测定了纳米铁试样的粒径, SEM结果表明Fe试样平均粒径d为25 nm. 在84～350 K温区, 用精密低温绝热量热计测定了该纳米铁试样的等压摩尔热容, 拟合出其等压摩尔热容与热力学温度的函数关系式: Cp=36.831+14.772x−5.4968x2−0.7099x3−1.3188x4, 其中x=(T−234)/156. 根据热容与热力学函数关系, 计算了以298.15 K为基准的纳米Fe(d=25 nm)热力学函数, 并与文献报导的粗晶Fe及粒径87 nm Fe的热容进行了比较, 从能量角度分析了不同粒径Fe热容曲线差别产生的原因.     

Production of fuel alcohol from wheat by VHG technology

Very high gravity (VHG) wheat mashes containing more than 300 g of dissolved solids per liter were prepared and fermented with active dry yeast at 20, 25, 30, and 35°C with and without yeast extract as nutrient supplement. At 20°C, mashes with 38% (w/v) dissolved solids end-fermented without any nutrient supplementation and maximum ethanol yields of 23.8% (v/v) were obtained. With increasing temperatures, the sugar consumption decreased. Addition of yeast extract stimulated the rate of fermentation at all temperatures, but did not increase the total amount of sugar consumed. The stimulatory effect of yeast extract on cell multiplication decreased with increasing sugar concentration, and virtually no difference in cell number was observed between yeast extract-supplemented and unsupplemented mashes at sugar concentrations above 33% (w/v). The fermentative capacity of the yeast (expressed as maximum specific rate of sugar consumption) remained the same at all sugar concentrations in unsupplemented mashes, but decreased in yeast extract-supplemented mashes at sugar concentrations below 33% (w/v). When the sugar concentration was above 33% sugar (w/v), the fermentative capacity in yeast extract-supplemented mashes was greater than that observed in unsupplemented samples.