Crystallization and glass-transition phenomena were studied for amorphous chlorobenzene (CB)/toluene (TL) binary systems as
the function of composition. Samples were prepared by vapor-deposition onto cold substrates, and their structural changes
due to temperature elevation were monitored with Raman scattering and light transmission. It was found that the crystallization
temperature (Tc) of CB-rich amorphous samples increases as the TL concentration is increased. This is similar to the linear dependence of
glass-transition temperatures (Tg) of many organic compounds on the concentration of additive. Also found was that Tc of TL-rich supercooled-liquids decrease as the CB concentration is increased. Issues related to the two kinds of Tc are discussed briefly.
Authors:C. Bacharan, C. Dessaux, A. Bernès, and C. Lacabanne
Thermally Stimulated Current (TSC) spectrometry has been applied to the characterization of polymeric materials. The study
of a series of amorphous polymers having different physical structures has shown that the compensation parameters are independent
of physical aging; contrarily, the activation enthalpy distribution reflects the evolution of the heterogeneity of the amorphous
In copolymers, TSC allows us to identify segregated amorphous phases. In semi-crystalline polymers, with semi-rigid chains,
we have shown the existence of an amorphous crystalline interphase characterized by a plateau in the temperature distribution
of activation enthalpy.
Hydrogen sorption properties and some corresponding changes in the crystallization of amorphous TM33Zr67 (TM=Fe, Co, Ni) alloys have been investigated. Relatively large amount of hydrogen was found to dissolve into the amorphous alloys
during electrochemical hydrogen charging. The microstructural evolution during annealing of H-charged Ni33Zr67 was studied as well. The weaker bonded hydrogen desorbs in a large temperature range (440–625 K) before the crystallization
of the amorphous alloys to start. A hydride phase (ZrH2) was found to form during annealing the H-charged amorphous Ni33Zr67 alloy. During heating at constant heating rate the hydride decomposes at about 715 K and formation of Zr2Ni immediately takes place. The final microstructure of the Zr2Ni, crystallized from the H-charged matrix, is noticeably finer compared to the material crystallized from the H-free amorphous
alloy, most probably due to the higher temperature of Zr2Ni formation in the H-charged amorphous alloy than in the H-free sample.
Authors:Sheri L. Shamblin, Eva Y. Huang, and G. Zografi
The purpose of this study was to measure the effect of co-lyophilized polymers on the crystallization of amorphous sucrose, and to test for a possible relationship between the ability of an additive to raise theTg of a sucrose-additive mixture, relative to theTg of pure sucrose, and its ability to inhibit crystallization. Differential scanning calorimetry was used to measure the glass transition temperature,Tg, the non-isothermal crystallization temperature,Tc, and the induction time for crystallization,Q, of sucrose in the presence of co-lyophilized Ficoll or poly(vinylpyrrolidone) (PVP). The effect of these polymers on the crystallization of sucrose was significant as demonstrated by a marked increase inTc, and in the induction time (Q) in the presence of relatively small amounts (1–10%) of additive. Surprisingly, small amounts of polymeric additive had no effect on theTg of sucrose, although at higher concentrations, theTg increased proportionally. Thus, it appears that the inhibition of sucrose crystallization by the additition of small amounts of a higher-Tg component cannot be attributed solely to changes in molecular mobility associated with an increase inTg.
Precise calorimetry was performed for (AgI)x(AgPO3)1–x and (AgI)x(Ag2PO3.5)1–x glasses with very high AgI compositions (x0.75). The glasses showed -glass transitions due to the freezing-in of the rearrangement of conductive Ag+ ions. Magnitude of the associated heat-capacity jump increased with increasing the AgI composition in the respective glass systems, and was larger in the former system than in the latter when compared at the same AgI composition. All the results were well explained by the amorphous AgI aggregate model for the AgI-based fast ion conducting glasses, indicating the appropriateness of the model for the structure of the glasses with high AgI compositions. The formation of the hypothetical bulk amorphous AgI was also indicated in the glasses at the highest limit of AgI composition.
Authors:Y. Yoshihashi, H. Iijima, E. Yonemochi, and K. Terada
stability of amorphous drug in solid dispersion was estimated using differential
scanning calorimetry (DSC). Tolbutamide (TB) and flurbiprofen (FBP) were selected
as insoluble drugs in water. Polyvinylpyrrolidone (PVP) was selected as a
polymer for solid dispersion. Solid dispersions of various ratios of TB or
FBP and PVP-K25 were prepared by solvent evaporation method and the induction
period of crystallization from amorphous drug in solid dispersion was measured
by DSC. Compared with FBP, the induction period of crystallization from TB
was delayed by an addition of PVP. The improvement of the physical stability
by the addition of PVP-K25 was estimated from the activation energy of diffusion
of drug molecules and the interfacial free energy between drug crystal and
supercooled liquid of drug in solid dispersion. From thses results, the hindrance
of the diffusivity of the drug molecule might be mainly affected the delay
of the induction period of crystallization of TB and FBP.
The glass transition of amorphous polymers is a kinetic transition, thus it has considerable time dependence. One of the consequences of this time dependence is the appearance of the so-called hysteresis peak
Authors:Valentina Martena, Roberta Censi, Ela Hoti, Ledjan Malaj, and Piera Di Martino
Amorphous drugs may prove important for pharmaceutical formulations because their greater apparent solubility and faster dissolution rates may lead to higher bioavailability [ 1 ]. Since, the majority of drugs in
Authors:Musa Gogebakan, Ibrahim Karteri, Baris Avar, and Celal Kursun
Although magnesium and its alloys are the lightest materials, they suffer from low strength, low ductility, and poor corrosion resistance. Therefore, amorphous Mg-based alloys have been developed to improve tensile
Authors:K. Chrissafis, K. Efthimiadis, E. Polychroniadis, and S. Chadjivasiliou
In this work we study the influence of Mo admixtures on the crystallization process of amorphous Fe78-xMoxSi9B13 (x=1, 2, 3 and 4) alloys by measurements of differential scanning calorimetry and on the soft ferromagnetic properties of the
alloys by magnetic measurements. The addition of Mo by replacing Fe, results in magnetic hardening of materials. In DSC curves
two peaks appear which are distinct when the concentration of Mo is 1 at.% and partly overlap when the Mo content is 2 at.%.
Further increase in the Mo content leads to the appearance of just one peak. The activation energy was calculated both with
Kissinger's and isoconversional Flynn, Wall and Ozawa methods.