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  • Author or Editor: H. Suga x
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Abstract  

Several DTA experiments followed by calorimetric works are reviewed here to emphasise the importance of complementary role of both techniques. The thermal analysis is advantageous in the sense that it gives quickly the overall view of thermal behaviour of a material under various conditions. Calorimetric work provides accurate heat capacity data which enable to derive thermodynamic functions including the enthalpy and entropy. The latter quantity is especially important in judging whether the material obeys the third law of thermodynamics. However, calorimetric work leads occasionally to an erroneous conclusion if the work is not preceded by thermal analysis performed under various conditions. Sometimes, quality of information obtained by DTA exceeds that obtained by laborious calorimetry.

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Abstract  

A survey of materials science through our experiences shows that our knowledge of amorphous solids is quite poor compared with that of crystalline solids. Most pure substances can be obtained, in principle, as crystalline as well as non-crystalline states by physical and chemical methods. Destruction of the three-dimensional periodicity in crystalline substances will produce novel properties which cannot be anticipated from knowledge of crystal sciences. One direction of materials science in the coming century will surely be a new realm of amorphous condensed matter science.

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Summary {\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}} \viewkind4\uc1\pard\f0\fs20 Principle and technical development of low temperature calorimetry are described. Typical experimental results obtained by our group at Osaka University over the four decades are given. These include phase transitions in equilibrium crystals and glass transitions in non-equilibrium frozen-in disordered solids including crystals. It can be concluded that the glass transitions observed exclusively in liquids so far are just one example of transitions that must be of wide occurrence in solids arising from freezing of relevant degrees of freedom. Interplay between the phase and glass transitions in crystals is discussed in relation to useful dopant that may accelerate some molecular motions that had failed to maintain equilibrium at low temperatures. \par }

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Abstract  

Heat capacities of aqueous solutions of cetyltrimethylammonium (CTA) salicylate, of CTA m-hydroxybenzoate and of CTA p-hydroxybenzoate were measured using a scanning microcalorimeter. Only the salicylate solution exhibited heat-capacity anomaly around 330 K, depending on the heating rate. The transition enthalpy was 3.5±0.2 kJ mol–1, which was similar to that observed in solution of 1:1 intermolecular compound between CTA bromide (CTAB) and o-iodophenol (OIPh). The enthalpy of formation H f of the 1:1 intermolecular compound from CTAB and OIPh was determined by measuring the enthalpies of solution of the relevant crystals into ethanol. Positive value f H=3.0±0.3 kJ mol–1 was explained from a large difference between the heat capacities of the 1:1 compound and 1:1 mixture of the component crystals.

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Heat capacities of the thiourea clathrate compound of 1,1,2,2-tetrachloroethane, {(NH2)2CS}3(CHCl2)2, were measured at temperatures between 13 and 330 K. Two phase transitions were found. The enthalpy and entropy changes of the transition are 5940 J·mol−1 and 28.1 JK−1· mol−1 for the one occurring at 224 K and 2756 J·mol−1 and 11.3 JK−1·mol−1 for the other at 248 K. It is concluded from the transition entropy values that the guest molecules are orientionally disordered nearly to the same extent as in the neat liquid.

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Glass transition phenomena of four binary systems composed of simple hydrocarbons were studied by means of the differential thermal analysis (DTA). For all the systems, a definite glass transition was observed and a monotonous relation between the glass transition temperature (T g) and composition (x) was obtained. The composition dependence ofT g was analyzed in terms of the entropy theory based on the regular solution model. The theoretical prediction could not reproduce our results other than (1-butene)x(1-pentene)1−x system. This disagreement is considered to be due to deviations of the present systems from the regular solution, and the accompanying excess configurational entropy Sc E was estimated as a function of composition. Extraordinarily large values of Sc E? were obtained for (propene)x(propane)1−x and (propene)inx(1-pentene)1−x systems.

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Abstract  

Amorphous solid of tri-O-methyl-β-cyclodextrin was produced by grinding its crystalline sample with a rod-milling machine at room temeprature. Structural and thermal characterizations of the sample during amorphizing process were done by X-ray powder diffraction and differential scanning calorimeter. The glass transition for a fully amorphized sample was found to occur at essentially the same temperature as that for a liquid-quenched glass. The heat capacities of the non-crystalline solids realized by grinding and liquid quenching and of the crystalline solid were measured by a low temperature adiabatic calorimeter. Excess enthalpies of the ground amorphous solid and liquid quenched glass over that of the hypothetical equilibrium liquid were determined calorimetrically. Similar and dissimilar thermal behavior of both non-crystalline solids were compared.

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Heat capacities of structure I and II trimethylene oxide (TMO) clathrate hydrates doped with small amount of potassium hydroxide (x=1.8×10−4 to water) were measured by an adiabatic calorimeter in the temperature range 11–300 K. In the str. I hydrate (TMO·7.67H2O), a glass transition and a higher order phase transition were observed at 60 K and 107.9 K, respectively. The glass transition was considered to be due to the freezing of the reorientation of the host water molecules, which occurred around 85 K in the pure sample and was lowered owing to the acceleration effect of KOH. The relaxation time of the water reorientation and its distribution were estimated and compared with those of other clathrate hydrates. The phase transition was due to the orientational ordering of the guest TMO molecules accommodated in the cages formed by water molecules. The transition was of the higher order and the transition entropy was 1.88 J·K−1(TMO-mol)−1, which indicated that at least 75% of orientational disorder was remaining in the low temperature phase. In the str. II hydrates (TMO·17H2O), only one first-order phase transition appeared at 34.5 K. This transition was considered to be related to the orientational ordering of the water molecules as in the case of the KOH-doped acetone and tetrahydrofuran (THF) hydrates. The transition entropy was 2.36 JK−1(H2O-mol)−1, which is similar to those observed in the acetone and THF hydrates. The relations of the transition temperature and entropy to the guest properties (size and dipole moment) were discussed.

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