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Abstract  

The volume and enthalpy relaxation rate of inorganic glasses and organic polymeric materials subjected to temperature jump T has been analyzed. It is shown that the relaxation behavior in isothermal conditions can be compared on the basis of the fictive relaxation rate defined as R f=(dT f/dlogt)i. No significant difference between volume and enthalpy relaxation rate has been found for all materials examined. A simple equation relating the R f and parameters of Tool-Naraynaswamy-Moynihan (TNM) phenomenological model has been derived. This equation predicts increasing R f with the magnitude of temperature jump. It seems that correct determination of TNM parameters might be problematic for slowly relaxing polymers as the effect of these parameters becomes comparable with experimental uncertainty.

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Journal of Thermal Analysis and Calorimetry
Authors: Giovanna Bruni, C. Milanese, G. Bellazzi, V. Berbenni, P. Cofrancesco, A. Marini, and M. Villa

Abstract  

The processes of production of drugs and dosage forms in the solid state often cause unwanted transformation of portions of the substances into amorphous state, with significant changes of properties such as stability and bio-availability. When this amorphous fraction is of the order of a few percent, it usually goes unnoticed, but it should be accurately determined within a quality control system. In this work, we consider a model drug, perphenazine, where partial amorphisation may be induced by standard mechanical treatments. We show that Differential Scanning Calorimetry (DSC) leads to consistent estimations of the amorphous fractions induced by the treatment. Furthermore, DSC also yields the expected amounts of amorphous perphenazine when analysing known mixtures of perfectly crystalline samples (untreated) and partially amorphous samples (treated). We show that even amorphous fractions of the order of 1% are accurately estimated by our method.

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difference, Δ S and enthalpy difference, Δ H . Gibbs free energy difference, Δ G between undercooled melt and corresponding crystalline solid acts as the driving force of crystallization. In an amorphous alloy system, lower value of Δ G indicates less

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Journal of Thermal Analysis and Calorimetry
Authors: Dhruthiman R. Mantheni, M. P. K. Maheswaram, Hany F. Sobhi, Naullage Indika Perera, Alan T. Riga, M. Ellen Matthews, and K. Alexander

crystalline solid drug, e.g., sulphapyridine and acetanilide had a conductivity of about 10 −2 pS/cm and when the drug melted the liquid amorphous drug had a conductivity of 10 6 pS/cm as well as organic salts had conductivity of 10 8 pS/cm [ 1 ]. Our lab

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Summary Thermally induced structural transformation of fibrous hydrogen-bonded molecular assemblage formed from an amphoteric pyridinecarboxylic acid of 6-[2-propyl- 4-(4-pyridylazo)phenoxy]hexanoic acid (C5PR) was studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermogravimetry (TG). The organized fibrous morphology formed in an aqueous solution was stable at temperatures below 150°C. The ordered crystalline solid phase (K1) of the original fibrous material altered to a disordered crystalline solid phase (K2) at 150°C and subsequently to an isotropic phase (I) at 172°C. In the isotropic state, the C5PR molecule was slowly decomposed by decarboxylation. Once the molecular assemblage was subjected to the mesophase by heating, another ordered crystalline solid phase (K3) appeared reversibly at 17°C. The heat budget analyses by DSC indicated that a conformational entropy change such as the side-chain propyl group and the main-chain pentamethylene unit in the hydrogen-bonded molecular assemblage took place between the two ordered crystalline solid phases K1 and K3.

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Abstract  

Based on solvent extraction and fractional precipitation methods, the retention in iodate and periodate targets were measured. Influence of temperature of irradiation in crystalline and solution phase have been observed. Higher retentions were observed in crystalline solids than in corresponding solution phase irradiation at room temperature. The role of physicochemical properties of the salts and the solvent is discussed.

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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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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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Abstract  

Y(III) and lanthanide(III) mesaconates were prepared as crystalline solids with general formula Ln2(C5H4O4)3nH2O, where n=7 for La−Pr, n=4 for Y,Nd−Ho, n=8 for Er−Lu. IR spectra of the prepared mesaconates suggest that carboxylate groups are bidentate bridging anf chelating. During heating the hydrated complexes are dehydrated in one (Y, Nd−Lu) or two steps (La−Pr) and then decompose directly to oxides (Y, Ce, Pr, Sm, Gd−Lu) or with intermediate formation Ln2O2CO3 (La, Nd, Eu).

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Abstract  

The complexes of yttrium(III) and lanthanides(III) with 1,2,4,5-benzenetetracarboxylic acid were prepared as crystalline solids of the general formula Ln4(C10H2O8)3⋅14H2O. They are insoluble in water. On heating in air or inert gas atmosphere all compounds lose water molecules; next anhydrous compounds decompose to oxides. The yttrium complex and heavy lanthanide (from Ho to Lu) ones crystallize in monoclinic crystal system. The dehydration does not change the crystal structure of the compounds.

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