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31.
Moriya K. Yamada T. Sakai K. Yano S. Baluja S. Matsuo T. Pritz I. Vysochanskii Y. M. 《Journal of Thermal Analysis and Calorimetry》2002,70(2):321-328
Heat capacities of the Pb2xSn2(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 Pb2xSn2(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. 相似文献
32.
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。 相似文献
33.
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. 相似文献
34.
35.
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 总被引:17,自引:1,他引:17
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%。 相似文献
36.
Gérald Perron Jean-François Côté Daniel Lambert Johanne Pageau Jacques E. Desnoyers 《Journal of solution chemistry》1994,23(2):121-133
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, 76th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65th birthday. 相似文献
37.
Andrzej Czopnik Nataly Shitsevalova Alexander Krivchikov Vasyl Pluzhnikov Yuriy Paderno 《Journal of solid state chemistry》2004,177(2):507-514
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. 相似文献
38.
J.?MajumdarEmail author F.?Cser M.?C.?Jollands R.?A.?Shanks 《Journal of Thermal Analysis and Calorimetry》2004,78(3):849-863
Differential scanning calorimetry has been used to study the heat flow during melting and crystallisation of a range of polypropylene post-consumer waste (PP PCW) grades and blends. The heat flow curves and the heat capacity curves indicated that the PP PCW grades and blends contained contaminants even after manual sorting and a cleaning process. The enthalpies of the PP PCW grades were lower than that for the virgin grades, as a result of degradation. Small amounts of polymeric contaminants (up to 10%) did not affect the enthalpies of PP PCW although other contaminants may have had some effect. The enthalpies of the PCW blends could in general be predicted by a linear additive rule, which is of importance for recycling a variety of PP PCW products.The authors would like to thank Dr. M. Killen (Basell Australia Pty. Ltd.), Mr. P. Slaven (Citiwide MRF), Dasma Valley Waste Prop. Ltd. and Mr. I. Janetzki (Huhtamaki Australia Ltd.) for supplying materials for this project. Financial support for the project was provided by Basell Australia and Ecorecycle Victoria, Australia. 相似文献
39.
40.
Y. Marcus 《Journal of solution chemistry》1994,23(7):831-848
The water-structural contributions to the entropies and heat capacities of hydration of over 120 ions and the viscosity B-coefficients of nearly 80 aqueous ions are tabulated and correlated. B-coefficients for many more ions are predicted from this relationship and from their dependence on ionic size and charge. The structural entropies determine a unique scale of water structure making and breaking by the ions. 相似文献