Thermal stability of fluorochloroindate glasses

New fluorindate glass compositions have been investigated in order to improve optical transmission as well as thermal properties. Chloride inclusion extends transmission of a fluoride matrix to longer wavelength in infrared region. In the present work thermal parameters of an IZnBS composition, based on InF₃, ZnF₂, BaF₂ and SrF₂, with various amounts of alkaline chlorides were investigated by differential scanning calorimetry. The chloride presence decreased all characteristic temperatures and increased both thermal stability and glass forming ability up to 10% of MCl content, where M=Li, Na, K and Rb. The presence of NaCl promoted glass phase separation. For samples containing same concentration of NaCl, this effect is accentuated for increasing the contents of SrF₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal analysis and crystallization kinetics of polyurethane

Journal of Thermal Analysis and Calorimetry - Non-isothermal crystallization kinetics of polyurethane was investigated by differential scanning calorimetry at different cooling rates. Various...     

Thermal crystallization studies on Ga−Te glasses

Semiconducting Ga_xTe_100?x (17≤x≤25) glasses have been prepared by melt quenching method and thermal crystallization studies carried out using differential scanning calorimetry. On heating, virgin Ga_xTe_100?x glasses exhibit one glass transition and two crystallization reactions. The first crystallization reaction corresponds to the precipitation of hexagonal Te and the second one to the crystallization of the matrix into zinc blende Ga₂Te₃ phase. If Ga_xTe_100?x glasses are quenched to ambient temperature fromT _crl and reheated, they exhibit the phenomenon of double glass transition.     

Thermal properties and stability of lithium titanophosphate glasses

DTA was used to study thermal properties and thermal stability of (50-x)Li₂O-xTiO₂-50P₂O₅ (x=0–10 mol%) and 45Li₂Ot-yTiO₂-(55-y)P₂O₅ (y=5–20 mol%) glasses. The addition of TiO₂ to lithium phosphate glasses results in a non-linear increase of glass transition temperature. All prepared glasses crystallize under heating within the temperature range of 400–540°C. The lowest tendency towards crystallization have the glasses with x=7.5 and y=10 mol% TiO₂. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were LiPO₃, Li₄ P₂O₇, TiP₂O₇ and NASICON-type LiTi₂(PO₄)₃. DTA results also indicated that the maximum of nucleation rate for 45Li₂O-5TiO₂-50P₂O₅ glass is close to the glass transition temperature.     

Crystallization kinetics of Ag-doped Se–Bi–Te chalcogenide glasses

Effect of Ag doping on the crystallization kinetics of amorphous Se_80.5Bi_1.5Te_18?yAg_y (for y = 0, 1.0, 1.5, and 2.0 at.%) glassy alloys has been studied by differential scanning calorimetry (DSC). The DSC curves recorded at four different heating rates are analyzed to determine the transition temperature, activation energy, thermal stability, glass forming ability, and dimensionality of growth during phase transformation. Present study shows that the thermal stability and the glass-forming ability increase with an increase in the Ag content which is in agreement with the earlier studies. Our results show that Se_80.5Bi_1.5Te₁₆Ag₂ composition is thermally more stable and has a little tendency to crystallize in comparison to other compositions under study. The increase in thermal stability with increasing Ag concentration is attributed to an increase in the cohesive energy.     

Isothermal crystallization kinetics of the chalcogenide glass Bi10Se70In20

Results of DSC under isothermal conditions on the chalcogenide glass Bi₁₀Se₇₀In₂₀ are reported and discussed. The Johnson-Mehl-Avrami equation was used to evaluate the crystallization activation energy (E _a) and the crystallization mechanism was studied. The results indicate that the crystallization mechanism involves one dimensional and surface processes for Bi₁₀Se₇₀In₂₀. The average calculated value ofE _a for Bi₁₀Se₇₀In₂₀ is 34.38±1.46 kcal/mol.

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Zusammenfassung Die Ergebnisse von isothermen DSC-Untersuchungen an dem Chalkogenglas Bi₁₀Se₇₀In₂₀ wurden beschrieben und diskutiert. Die AktivierungsenergieE _a der Kristallisierung wurde mit Hilfe der Johnson-Mehl-Avrami-Gleichung ermittelt und der Kristallisierungsmechanismus untersucht. Die Ergebnisse zeigen, da\ der Kristallisierungsmechanismus von Bi₁₀Se₇₀In₂₀ eindimensionale und OberflÄchenvorgÄnge beinhaltet. Der errechnete mittlere Wert vonE _a betrÄgt für Bi₁₀Se₇₀In₂₀ 34.38±1.46 kcal/mol.

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The authors are grateful to Dr. N. Afify for many helpful discussions. This work was partly supported by a Grant-in-Aid for Scientific Research from the Deutsche Gesellschaft für Technische Zussammenarbeit (G.T.Z.) and D.A.A.D., Germany     

Thermal stability and spectroscopic properties of Er3+-doped antimony-borosilicate glasses

This paper reports on the optical spectroscopic properties and thermal stability of Er(3+)-doped antimony-borosilicate glasses for developing 1.5mum optical amplifiers. Upon excitation at 980nm laser diode, an intense 1.5mum infrared fluorescence has been observed with the maximum full width at half maximum (FWHM) of 90nm for Er(3+)-doped antimony-borosilicate glasses. The emission cross-section and the lifetime of the (4)I(13/2) level of Er(3+) ions are 6.3x10(-21)cm(2) and 0.30ms, respectively. It is noted that the product of the emission cross-section and FWHM of the glass studied is as great as 567x10(-21)cm(2)nm, which is comparable or higher than that of bismuthate and tellurite glasses.     

Non-isothermal crystallization kinetics of V2O5-MoO3-Bi2O3 glasses

Characteristic temperatures, such as T _g (glass transition), T _x (crystallization temperature) and T _l (liquidus temperature) of glasses from the V₂O₅-MoO₃-Bi₂O₃ system were determined by means of differential thermal analysis (DTA). The higher content of MoO₃ improved the thermal stability of the glasses as well as the glass forming ability. The non-isothermal crystallization was investigated and following energies of the crystal growth were obtained: glass #1 (80V₂O₅·20Bi₂O₃) E _G=280 kJ mol^-1, glass #2 (40V₂O₅·30MoO₃·30Bi₂O₃) E _G=422 kJ mol^-1 and glass #3 (80MoO₃·10V₂O₅·10Bi₂O₃) E _G=305 kJ mol^-1. The crystallization mechanism of glass #1 (n=3) is bulk, of glass #3 (n=1) is surface. Bulk and surface crystallization was supposed in glass #2. The presence of high content of a vanadium oxide acts as a nucleation agent and facilitates bulk crystallization. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calorimetric relaxation in pharmaceutical molecular glasses and its utility in understanding their stability against crystallization

Glassy states of three pharmaceuticals, acetaminophen, griseofulvin, and nifedipine, and an acetaminophen-aspirin (1:1 mol) alloy were made by slow cooling of the melt and studied by calorimetry. Measurements were performed by cooling and heating at significantly slow rates of 20 K/h, which were comparable to the rate used in adiabatic calorimetry. The results were modeled in terms of a nonexponential, nonlinear structural relaxation. The calorimetric relaxation of all four pharmaceutical samples were less nonexponential than those of polymeric or inorganic glasses, and this finding was attributed to additional contributions to energy change that would arise from temperature and time dependent variation in the hydrogen bond population, the extent of isomerization, and/or the ionic equilibria that exist in these materials. Four calculated and relevant parameters for the pharmaceutical samples were, ln A = -183, beta = 0.75, x = 0.4, and Delta h* = 457 kJ/mol for acetaminophen, ln A = -170, beta = 0.75, x = 0.45, and Delta h* = 516 kJ/mol for griseofulvin, ln A = -189, beta = 0.69, x = 0.39, and Delta h* = 503 kJ/mol for nifedipine, and ln A = -160, beta = 0.70, x = 0.50, and Delta h* = 363 kJ/mol for the acetaminophen-aspirin alloy. The significance of these parameters and, in particular, their values are discussed in the context of the stability of the pharmaceuticals against crystallization and compared against the significance of the localized motions of the JG relaxation in the same context. Acetaminophen was found to be significantly more prone to crystallization on heating than the other two pharmaceuticals as well as the acetaminophen-aspirin alloy.     

Thermal stability and folding kinetics analysis of disordered protein,securin

Lacking a stable tertiary structure, intrinsically disordered proteins (IDPs) possess particular functions in cell regulation, signaling, and controlling pathways. The study of their unique structural features, thermal stabilities, and folding kinetics is intriguing. In this study, an identified IDP, securin, was used as a model protein. By using a quasi-static five-step (on-path) folding process, the function of securin was restored and analyzed by isothermal titration calorimetry. Fluorescence spectroscopy and particle size analysis indicated that securin possessed a compact hydrophobic core and particle size. The glass transition of securin was characterized using differential scanning microcalorimetry. Furthermore, the folding/unfolding rates (k_obs) of securin were undetectable, implying that the folding/unfolding rate is very fast and that the conformation of securin is sensitive to solvent environmental change. Therefore, securin may fold properly under specific physiological conditions. In summary, the thermal glass transition behavior and undetectable k_obs of folding/unfolding reactions may be two of the indices of IDP.     

A remark on the applicability of DTA and the reliability of non-isothermal determination for the crystallization kinetics of glasses

The most decisive phenomena arising either from specific DTA measurements (heat inertia, temperature deviation, self-heating) or from non-isothermal kinetic treatment (overlapping models, characteristics determinations) are discussed.

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Zusammenfassung Die entscheidensten Phänomene werden diskutiert, die entweder bei spezifischen DTA-Messungen (Wärmeträgheit, Temperaturabweichungen, Selbsterhitzung) oder bei der nichtisothermen kinetischen Behandlung (überlappende Modelle, Charakteristikbestimmungen) auftreten.

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Crystallization kinetics of metallic glasses

In this study, the temperature-heating rate diagram of the main crystallization process of two metallic glasses, Fe₇₄Ni_3.5Mo₃B₁₆Si_3.5 and Fe₄₁Ni₃₈Mo₃B_18, was obtained from one experimental differential scanning calorimetry (DSC) scan and the knowledge of their activation energy as determined by an isoconversional method. A good concordance was observed between the diagram curves obtained by calculation (isoconversional approach) and the experimental data, which verifies the reliability of the method and the validity of the kinetic approach in these alloys.     

Avrami exponent of crystallization in tellurite glasses

Nucleation process and crystal growth for three samples of the (20-x)Li₂O–80TeO₂–xWO₃ glass system were studied using X-ray diffraction and differential scanning calorimetry techniques. X-ray diffraction data confirmed the amorphous characteristic of the as-quenched samples and indicated the growth of crystalline phases formed due to the thermal treatment for annealed samples. These results reveal the presence of three distinct γ-TeO₂, α-TeO₂ and α-Li₂Te₂O₅ crystalline phases in the TL sample, and two distinct α-TeO₂ and γ-TeO₂ crystalline phases in the TLW5 and TLW10 samples. The activation energy and the Avrami exponent were determined from DSC measurements. The activation energy values X-ray diffraction data of the TLW10 glass sample suggest that γ-TeO₂ phase occur before the α-TeO₂. The results obtained for the Avrami exponent point to that the nucleation process is volumetric and that the crystal growth is two or three-dimensional.     

Photoluminescent coordination polymer bulk glasses and laser-induced crystallization

We synthesized luminescent coordination polymer glasses composed of d¹⁰ metal cyanides and triphenylphosphine through melt-quenching and mechanical milling protocols. Synchrotron X-ray total scattering measurements and solid-state NMR revealed their one-dimensional chain structures and high structural dynamics. Thermodynamic and photoluminescence properties were tunable by the combination of heterometallic ions (Ag⁺, Au⁺, and Cu⁺) in the structures. The glasses are moldable and thermally stable, and over centimeter-sized glass monoliths were fabricated by the hot-press technique. They showed high transparency over 80% from the visible to near-infrared region and strong green emission at room temperature. Furthermore, the glass-to-crystal transformation was demonstrated by laser irradiation through the photothermal effect of the glasses.

Over centimeter-sized luminescent coordination polymer glasses were fabricated. They showed high transparency (over 80%) and strong green emission at room temperature. The glass-to-crystal transformation by laser irradiation was demonstrated.     

Computer simulation of crystallization kinetics and morphology in fiber-reinforced thermoplastic composites. III. Thermal nucleation

A computer simulation has been used to predict crystallization kinetics and crystalline morphology in composite materials based on thermally nucleated crystallizable matrices. As demonstrated for athermally nucleated composites, the presence of reinforcing fibers increases the complexity of the system. Fibers are shown to have a dual effect on the spherulitic crystallization process. The influence that fibers have depends on the interplay between the enhancing effects that fibers have on nucleation and the depressing effects that fibers have on spherulitic growth. Fibers that do not provide additional nuclei to the system depress the rate of crystallization relative to an unreinforced polymer, while fibers that add nuclei to the system increase the rate of crystallization. The transcrystalline morphologies that develop in thermally nucleated fiber-reinforced polymers are controlled primarily by the relative numbers of bulk and fiber nuclei. The extent of transcrystalline regions can be suppressed either by increasing the rate of bulk nucleation, or by decreasing the rate of fiber nucleation. Finally, the qualitative appearance of the morphology in the transcrystalline region was found to be indicative of the mode of fiber nucleation. © 1995 John Wiley & Sons, Inc.     

Luminescence and nonradiative relaxation of Pb2+, Sn2+, Sb3+, and Bi3+ in oxide glasses

Absorption and fluorescence spectra of Sn²⁺ and Sb³⁺ in borax, phosphate, and germanate glasses were measured in the temperature range 87–295°K. Fluorescence decay times of these ions in borax glass at 87°K was a single exponent with τ ≈ 6–11 μsec. At 293°K, two decay times were resolved in the range of 50–2000 nsec. The nonexponential behavior is interpreted by the repopulation of the ³P₁ level from the ³P₀ level. The temperature dependence of fluorescence and the low values of quantum efficiencies of fluorescence are explained by means of the configurational coordinate diagram model.     

Adjusting non-isothermal crystallization kinetics through similar solute element Ga microalloying for Al in novel La-Al-C metallic glasses

Journal of Thermal Analysis and Calorimetry - In this text, the influence of similar solute element Ga microalloying for Al on the non-isothermal crystallization kinetics between novel light...     

Thermal stability and nonisothermal crystallization of short fiber-reinforced poly(ether ether ketone) composites

The thermal stability of a short carbon-fiber-reinforced PEEK composite was assessed by thermogravimetry and by a Rheometrics dynamic analyzer. The results indicated that holding for 10 min at 380°C was a suitable melting condition to avoid the thermooxidative degradation under air. After proving that the heating rate of 50°C/min can be used to evaluate the crystallinity, a heating stage was used to prepare nonisothermally crystallized specimens using cooling rates from 1 to 100°C/min after melting at 400°C for 3 or 15 min. The degree of crystallinity and the melting behavior of these specimens were investigated by DSC at a heating rate of 50°C/min. The presence of three or four regions indicated that the upper melting temperature, T_m, changed with the crystallization temperature. The first region with the highest T_m, which corresponded to the cooling rate of 1°C/min, can be associated with the crystallization in regime II. There was a second region where T_m decreased as the amount of crystals formed in regime II decreased with increasing cooling rate from 5 to 20°C/min. The third region, a plateau region, corresponded to regime III condition in which the crystals were imperfect. In the fourth region, the cooling was so fast that crystallization was incomplete during the cooling for the melting condition of 400°C for 15 min. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2225–2235, 1998