Thermal conductivity of the urea-hexadecane inclusion compound

The thermal conductivity and the heat capacity per unit volumec _p have been measured for the urea-hexadecane inclusion compound using the transient hot-wire method. Measurements were made under isobaric conditions at a pressure of 0.1 GPa and in the temperature range of 100–300 K. There was evidence for a phase transition at a temperature of about 160 K, in reasonable agreement with previous work. For the high-temperature phase was independent of temperature within ±1%. The low-temperature phase showed a weak temperature dependence, with (d In/d InT) _p = –0.13. It was inferred that interaction between acoustic phonons and low-frequency vibrational excitations of the guest molecules made a major contribution to the thermal resistivity. For the quantityc _p a weak maximum was observed in the region of the phase transition temperature.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Wärmekapazitätsmessungen Nach Scanning-Methoden Bis Zu Hohen Temperaturen

Scanning calorimetric methods permit determination of heat capacities at high temperatures up to 1600°C. For disk systems with power compensation application limits are in order of 700°C, and for cylindrical systems with electrical calibration up to 1000°C. For the high temperature range above 1000°C DSC plates and a cylindrical calorimetric systems based on the CALVET principle ('MULTI HTC’) are known. For cylindrical calorimetric systems the precision of the Cp data is between 2 and 5% even at high temperatures without any requirements on the kind and shape of samples. These results are better than data provided by DSC plate systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ferroelectric phase transitions in Pb2xSn2(1-x)P2Se6 system

Heat capacities of the Pb_2xSn_2(1-x)P₂Se₆ crystals (x=0, 0.098, 0.251, 0.402 and 1.0) were measured using an adiabatic calorimeter at temperatures between 10 and 350 K. In the crystal of x=0, two heat capacity anomalies corresponding to the ferroelectric commensurate - intermediate incommensurate(C-IC) phase transition temperature T _i, and the incommensurate - paraelectric (IC-N) phase transition temperature T _c, were observed at 193.24±0.10 and 220.07±0.15 K, respectively. The phase transition temperatures decreased with an increase in Pb²⁺ concentration. The anomaly at Ti disappeared at x=0.251 in the mixed systems of the Pb_2xSn_2(1-x)P₂Se₆. In the crystal of Pb₂P₂Se₆ (x=1.0), no phase transition was observed. The normal heat capacities for the mixed crystals were determined by least squares fitting of the Debye and Einstein functions to the experimental data. The anomalous heat capacities gave the phase transition entropies of 8.5 and 1.5 J mol^-1 K^-1 for x=0. The large transition entropies are consistent with an order-disorder mechanism in the ferroelectric-paraelectric phase transitions in x=0. This revised version was published online in August 2006 with corrections to the Cover Date.     

对MDTA中测样品热容量的准恒温法的评述

对用调制差热分析（ＭＤＴＡ）准恒温法测样品热容量的情形进行了讨论。通过结合最基本的热传导定律和ＭＤＴＡ模型，指出了目前国际上测量样品热容量的准恒温法只能得到在所测温度范围内的物质热容量平均值，调制温度的幅度越大或调制频率越高，所得到的热容量数据越平滑。在所测温度范围内样品热容量基本不变时，用ＭＤＴＡ准恒温法较好；但当样品热容量在所测温度范围内有明显变化时，用传统差热分析法（ＤＴＡ）更好一些。     

The ionization of perchloric and hydrofluoric acids in aqueous solution

Cyclical bifurcated hydrogen bonded structures are proposed for aqueous solutions of hydrofluoric acid and for the bifluoride ion which are consistent with the spectral data. The structure proposed for HF is also applicable to solutions in organic solvents. Raman spectra of tetramethylguanidinium perchlorate suggest that the corresponding Raman spectra of perchloric acid solutions may not be interpreted in terms of a completely dissociated acid. Other evidence including activity coefficient, heat capacity and partial molal volume data suggest that there is some association in relatively dilute perchloric acid solutions between the perchlorate ion and the hydrated proton. This association decreases in concentrated aqueous solutions.     

2-羟丙基三甲基氯化铵壳聚糖的制备及其性能研究

以脱乙酰度为95.37%的壳聚糖(CTS)为原料,异丙醇为溶剂,2,3-环氧丙基三甲基氯化铵为改性剂,于80℃反应12 h合成了水溶性季铵盐2-羟丙基三甲基氯化铵壳聚糖(HACC)。HACC的吸水保水性是CTS的2倍～3倍,加入化妆品中培养2周后菌落总数少于100 CFU.g-1。     

PbO~2纳米粉体的固相合成及其对MnO~2电极材料的改性作用

利用固相氧化反应制备了PbO~2纳米粉体样品，借助XRD，TEM以及循环伏安测试对其性质进行了表征。同时，对反应条件的选择进行了讨论。将所得样品用于改性MnO~2电极，恒流放电测试结果表明，样品掺杂量在1.25%～5.00%间对MnO~2有良好的改性效果，可使改性MnO~2的放电容量得到极大提高。循环伏安测试结果表明，铅的掺入改变了MnO~2的放电机理。在循环扫描过程中，掺杂物与MnO~2均不再以单纯氧化物的形式存在，而是形成了一系列Pb(X)(X=0,Ⅱ)Mn(Y)(Y=Ⅳ，Ⅲ，Ⅱ)复合物的共氧化与共还原，抑制了电化学惰性物质Mn~3O~4的生成和积累，从而有望改善MnO~2的可充性能。纳米PbO~2与常粒径PbO~2与常粒径PbO~2(标记为S)对MnO~2的改性机理类似。但前者对MnO~2的改性效果明显优于后者，当恒流放电至-1.0V时，其放电容量较S样改性MnO~2的放电容量平均高出约30%。     

Volume and heat capacity of model non-aqueous self-assembly systems

Blends of immiscible polymers are often stabilized by block copolymers which can form non-aqueous micelles and microemulsions in the liquid polymers. The phase diagrans, apparent volumes and apparent heat capacities of model non-aqueous binary and ternary systems were studied in order to investigate the conditions under which such self-assembly systems could form. 1,2-Hexanediol, which can cosolubilize hexane and ethyleneglycol, forms inverse micelles in hexane and weak microaggregates in ethyleneglycol. Genapol X-060, a commercial alcoholic surfactant containing on the average an aliphatic chain of 13 carbons and 6 oxyethylenes (C₁₃E₆), forms microaggregates in poly(ethyleneglycol) 400. These self-assembly systems are strengthen in the presence of a third component which has an affinity for the inner phase.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

Thermal properties of rare earth dodecaborides

We have measured heat capacity and thermal expansion of rare earth dodecaborides REB₁₂ (RE=Y, Tb-Tm, Lu). YB₁₂ and LuB₁₂ are diamagnetics whereas the other dodecaborides are ordered antiferromagnetically. The amplitude of the heat capacity discontinuity at the Néel temperature and the shape of the heat capacity variation in the critical region for all these antiferromagnetics are characteristics for amplitude-modulated magnetic structures. In the ordered state TbB₁₂ reveals two first-order phase transitions, most likely due to magnetic structure changes. The heat capacity of ErB₁₂ just below the Néel point shows an anomaly of unclear origin. From the Schottky contribution to the heat capacity we have determined crystal field parameters. They are completely different than that is estimated from Point Charge Model.     

Thermodynamic quantities for the acid dissociation of alkylammonium ions in water over a wide temperature range

Enthalpies of protonation in aqueous solution have been determined from calorimetric measurements between 0 and 100°C for methylpentylamine, butyldimethylamine, and quinuclidine; between 0 and 125°C for di-iso-propylamine; and between 0 and 75°C for 1-azacycloheptane. Values ofpK_a at 25°C have been determined from pH measurements using a glass electrode for di-iso-propyl-, methylpentyl-, and butyldimethylamine. The calorimetric results are used together with values ofpK_a at 25°C to derive expressions which allow the calculation of accuratepK_a values over a large temperature range. The heat capacity and entropy changes for the protonation of aqueous alkylamines found in the present and in previous studies are discussed in terms of differences in hydrophobic solvation of the alkyl groups in the neutral amines and the ions.