Na-Gd phosphate glasses

Summary The present paper deals with preparation, thermal properties and radioluminescence of Ce-doped Na-Gd phosphate glasses. Thanks to their high radioluminescence intensity, three times greater than that of BGO, these glasses are promising materials for the detection of neutrons, - and X-rays. The glasses with a Gd concentration up to 89 mol% were prepared by a rapid quenching technique in air. Their thermal properties were determined using DSC and temperatures of glass transition were measured in addition using TMA. Temperatures of glass transition, crystallization and melting depend on Gd concentration and they follow the liquidus line in a phase diagram of binary system in which two eutectics and a congruently melting compound exist. High glass-forming ability of this glass system was found evidenced. The glasses containing at least 30 mol% Gd were moisture resistant.     

DTA curves and non-isothermal reaction rates

Differential thermal analysis (DTA) is an effective means for studying chemical reactions, but its application to reaction kinetics is handicapped by the involvement of temperature feedback from the reaction heat and by the solvent dependence of the thermal conductivity.General, empirical relationships are derived from digital computer application which allow to transform half width and shape index of a DTA curve of any first-order process in a uniformly temperated sample to the values of the corresponding rate curve at linearly increased temperature.The expressions are complemented by some new relationships for an n-order reaction and are useful for the kinetic study of complex processes.     

Crystallization Kinetics of Lithium Diborate Glass by DTA

The crystallization process of Li₂B₄O₇ in the glass of stoichiometric composition, characterized by the crystal growth of pre-existing nuclei, was analyzed kinetically by means of DTA. Because the number of pre-existing nuclei for the subsequent growth varies depending on the cooling rate of the glass-forming melt and heating rate of the as-prepared glass, a modified Kissinger plot was applied for evaluating the apparent activation energy to the crystal growth in the glass samples with three different thermal histories, i.e., the pre-annealed, slowly quenched and quickly quenched glasses. The process was characterized by the three dimensional growth of pre-existing nuclei with the apparent activation energy of ca 340 kJ mol⁻¹. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crystallization kinetic of fluoro- zirconate glasses by non-isothermal analysis

Fluoride glasses have been extensively studied due to their high transparency in the infrared wavelength. The crystallization kinetics of these systems has been studied using DTA and DSC techniques. Most of the experimental data is frequently investigated in terms of the Johnson-Mehl-Avrami (JMA) model in order to obtain kinetic parameters. In this work, DSC technique has been used to study the crystallization of fluorozirconate glass under non-isothermal conditions. It was found that JMA model was not fit to be applied directly to these systems, therefore, the method proposed by Málek has been applied and the Šesták-Berggren (SB) model seems to be adequate to describe the crystallization process. This revised version was published online in July 2006 with corrections to the Cover Date.     

DTA using single particles

A DTA sample holder for single particles was constructed using three thermocouples to hold the sample and reference material, respectively. The arrangement can be used to multiparticle samples too by setting a spherical-section sample holder on the three thermocouple junctions.The author is grateful to the National Science Foundation for its support of this work.     

Crystallization of iron phosphate glasses

Differential thermal analysis (DTA), thermogravimetric analysis (TG), X-ray diffraction and Mössbauer spectroscopy were employed in the investigation of crystalline products of FeO_x-P₂O₅ glasses generated by various heat treatments. In glasses with a high value of =Fe²⁺/(Fe²⁺ + Fe³⁺), absorption of oxygen occurs in a broad temperature range identified by TG. Depending on the value of , two exotherms appear in the DTA curves, the low-temperature one corresponding to crystallization of the Fe₃(PO₄)₂ type regions, and the high-temperature one being related to various phases with dominating FePO₄. Each exotherm has its own transformation region, identical in absolute value. The Mössbauer spectra of glasses which underwent thermal treatment at higher temperatures exhibit some indication of phases of the types Fe₃(PO₄)₂ · xH₂O and FePO₄ · xH₂O.

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Zusammenfassung Differentialthermoanalyse (DTA), thermogravimetrische Analyse (TG), Röntgendiffraktion und Mössbauerspektroskopie wurden bei der Untersuchung (von kristalliner Produkte) durch verschiedene thermische Behandlungen hergestellten FeO_x-P₂O₅ Gläsern eingesetzt. In den Glasarten mit einem hohen Wert von =Fe²⁺/(Fe²⁺ + Fe³⁺) erfolgt die Sauerstoffabsorption in einem durch TG [nachgewiesenen breiten Temperaturbereich. In Abhängigkeit von dem -Wert erscheinen zwei Exothermen in den DTA-Kurven, von denen der bei niedriger Temperatur die Kristallisation des Fe₃(PO₄)₂ entspricht, und jener bei höheren Temperaturen in verschiedenen Phasen dem FePO₄. Jede Exotherme hat ihr eigenes Umwandlungsgebiet, das in absolutem Wert identisch ist. Die Mössbauer-Spektren der Gläser welche einer Wärmebehandlung bei höheren Temperaturen unterzogen worden sind, weisen einige Indikationsphasen der Typen Fe₃(PO₄)₂ · xH₂O und FePO₄ · xH₂O auf.

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, , FeO_x-P₂O₅, . , =Fe²⁺/(Fe²⁺+Fe³⁺) . , - : Fe₃(PO₄)₂, – FePO₄. , . , , Fe₃(PO₄)₂ · ₂ FePO₄ · ₂.

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The authors thank Mrs. Simonyiová for assistance in the experimental part of these investigations, and Dr. Horváth and Dr. Vondrovic for performing the X-ray and TG analyses.     

The Piloyan method in DTA studies of glass devitrification

A kinetic analysis of the applicability of the Piloyan method to the process of glass devitrification for evaluation of the exponentn in the Johnson-Mehl-Avrami equation is carried out.Criado's conclusions concerning the value of the slope of the Piloyan plot are criticized.     

A DTA study of phenols

A comprehensive DTA study is reported of 17 halophenols and of the corresponding p-nitrobenzoylchloride 3,5-dinitrobenzoylchloride and p-phenylazobenzoylchloride derivatives, prepared “in-situ”by heating intimate mixtures of phenol and acid chloride in the DTA system. The thermal analysis data, in particular, the derivative formation temperatures, are interpreted in terms of the inductive, mesomeric and steric effects associated with the ring substituents of the phenol and acid chloride and the extent of inter- and intramolecular hydrogen-bonding existing in these systems. The DTA data collectively provide a reference base for the identification and characterization of halophenols via thermal analysis.     

A DTA study of phenols

A comprehensive DTA study is reported of ten polyhydroxy-phenols and eight naphthols and of the correspondingp-phenylazo benzoylchloride,p-nitrobenzoylchloride and 3,5-dinitrobenzoylchloride derivatives, prepared in situ by heating intimate mixtures of phenol and acid chloride in a conventional DTA system. The thermal analysis data and, in particular, the derivative formation temperatures, are interpreted in terms of the inductive, mesomeric and steric effects associated with the phenol and acid chloride and the extent of inter- and intramolecular hydrogen-bonding existing in these systems. The DTA data collectively, provide a comprehensive data base for the identification and characterisation of these phenols via DTA.

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Zusammenfassung Dies ist eine umfassende DTA-Untersuchung von zehn Polyhydroxyphenolen und acht Naphtholen sowie der entsprechendenp-Phenylazobenzoylchlorid-,p-Nitrobenzoylchlorid- und 3,5-Dinitrobenzoylchlorid-Derivate, die durch Erhitzen inniger Gemische des jeweiligen Phenoles und Säurechlorides in situ in einem herkömmlichen DTA-Gerät hergestellt wurden. Die bei der Thermoanalyse erhaltenen Angaben, insbesondere die Bildungstemperatur der Derivate wurde bezüglich des induktiven, mesomeren und sterischen Effektes bei Phenol und Säurechlorid sowie der Stärke der in diesem System existierenden inter- und intramolekularen Wasserstoffbrückenbindungen interpretiert. Die Gesamtheit der DTA-Daten bietet eine umfassende Datensammlung für Identifizierung und Charakterisierung dieser Phenole mittels DTA.

     

A DTA study of phenols

A comprehensive DTA study is reported of eight methyl-phenols, 4-methoxy-phenol and four methyl-halo-phenols and of the correspondingp-nitrobenzoylchloride, 3,5-dinitrobenzoylchloride andp-phenylazobenzoylchloride derivatives, prepared in situ by heating intimate mixtures of phenol and acid chloride in a DTA system. The thermal analysis data, in particular, the derivative formation temperatures, are interpreted in terms of the inductive, mesomeric and steric effects associated with the ring substituents of the phenol and acid chloride and the extent of inter- and intramolecular hydrogen-bonding existing in these systems. The DTA data collectively, provide a comprehensive data base for the identification and characterisation of these phenols via DTA.

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Zusammenfassung An durch Erhitzen inniger Mischungen aus Phenol und Säurechloriden in einem DTA-System hergestellten acht Methylphenolen, an 4-Methoxyphenol, an vier Methylhalophenolen und an den entsprechendenp-Nitrobenzoylchlorid-, 3,5-Dinitrobenzoylchlorid- undp-Phenylazobenzoylchloridderivaten wurden ausführliche DTA-Untersuchungen durchgeführt. Thermoanalytische Ergebnisse, insbesondere die Bildungstemperatur der Derivate wurden als Ausdruck des induktiven, mesomeren und sterischen Effektes bezüglich der Substituenten am Phenolring und des Säurechlorides sowie des Ausmaßes der in diesem System existierenden inter- und intramolekularen Wasserstoffbrückenbindungen gewertet. Die Gesamtheit der DTA-Daten ist gleichzeitig eine ausführliche Datenreferenz zur Identifizierung und Charakterisierung dieser Phenole mittels DTA.

     

Crystallization and glass properties of pentitols

Thermodynamic and dynamic data of the four pentitols, xylitol, adonitol, l-arabitol and d-arabitol, measured by temperature modulated DSC (TMDSC) in the crystalline and amorphous states are presented. The properties of the supercooled liquids clearly show two distinct kinds of thermal behaviors with regard to their aptitude to crystallize. The capacity of the TMDSC technique to characterize both the molecular mobility and the thermal behavior is used to analyze the stability of the supercooled liquid state of the compounds. The comparison between the pentitols shows that the crystallization processes are mainly dominated by the interfacial energy rather than by a competition between the thermodynamic driving force and the molecular mobility. This revised version was published online in July 2006 with corrections to the Cover Date.     

DTA study on lead chloride

The hydrolysis of lead chloride by residual water is responsible for the appearance of a second peak in the DTA curve, due to melting of the eutectic PbCl₂-PbO in repeated measurement runs on the same sample. This effect has previously been misinterpreted as a solid-solid transition in pure PbCl₂.     

Derivation of the Kissinger equation for non-isothermal glass transition peaks

A brief derivation of the Kissinger’s equation for analysis of experimental data of non-isothermal glass transition peaks based on the free volume model is given. This equation was applied successfully to Cu_0.3(SSe₂₀)_0.7 chalcogenide glass for different heating rates. For granted this model, the obtained glass transition activation energy, E _g must be constant throughout the whole glass transition temperature range. This required that T _g to be determined for three characteristic temperature points for each DSC curve.     

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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, ( , , ) ( , ).

     

Comprehensive study on compositional modification of Tb3+ doped zinc phosphate glass

Series of glass composition (60-x) P₂O₅ -40 ZnO –(x) Tb₂O₃ where x = 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol % are prepared by conventional melt quenching technique. X-Ray Diffraction (XRD), FTIR, UV-Vis-NIR and the photoluminescence (PL) spectroscopy are used to characterize the physical, structural and optical behavior of the glass sample. The XRD pattern confirms the amorphous nature and DTA verified the thermal stability of all the glass samples. Glass with 1.5 mol % of Tb₂O₃ possesses the highest thermal stability. Glass density is found to increase proportionally with increasing amount of Tb³⁺ while the molar volume behaves reversely. Six main IR absorption bands centered at about 540, 748, 891, 1085 and 1294 cm^{− 1} are evidenced. The UV-Vis NIR absorption spectra reveals the absorption center band at about 540, 376, 488 and 1920 nm corresponding to the absorption from ⁷F₆ ground state to various excited state of Tb³⁺ ion. The optical band gaps for direct and indirect transition are in the range 4.53–5.07 eV and 4.30 eV-4.56 eV respectively. The Urbach energy decreases with the increasing concentration of Tb₂O₃. The PL emission spectra reveals several prominent peaks at 413, 435, 457, 488, 540, 585 and 620 nm due to electronic transition from ⁵D₃→⁷F₅, ⁵D₃→⁷F₄, ⁵D₃→⁷F₃, ⁵D₄→⁷F₆, ⁵D₄→⁷F₅, ⁵D₄→⁷F₃ and ⁵D₄→⁷F₅ respectively.     

Crystallization kinetics of isotactic polypropylene nucleated with octamethylenedicarboxylic dibenzoylhydrazide under isothermal and non-isothermal conditions

Octamethylenedicarboxylic dibenzoylhydrazide (TMC-300) was used as a nucleating agent for isotactic polypropylene (iPP) for the first time. The Avrami method and the Caze method were used to analyze the isothermal and non-isothermal crystallization kinetics of iPP incorporated with TMC-300, respectively. During isothermal crystallization, the half crystallization time at 130 °C reduces from 130 s of virgin iPP to 44 s after addition of TMC-300, which reflects that TMC-300 increased the crystallization rate of iPP obviously. The crystallization activation energy decreases from 382.5 kJ mol^?1 of virgin iPP to 275.3 kJ mol^?1 of iPP/TMC-300. During non-isothermal crystallization, the crystallization peak temperature of iPP nucleated with TMC-300 was increased by 5.1 °C when compared to that of virgin iPP at the cooling rate of 20 °C min^?1, and both the reduction of half crystallization time and the increase in peak crystallization temperature also justified that the addition of TMC-300 accelerated the crystallization of iPP.

     

A study of different aspects of DTA calibration

In this work, an attempt is made to establish the relation of proportionality between the heat of transition inside the sample and the corresponding area on the DTA peak vs. temperature curve. The influence of the particle size in this relation of proportionality is demonstrated. Finally, a theoretical model of DTA is discussed.     

DTA study of thermal combustion of textile fibres

A modification of the Speil theory is used to compute the heat of combustion of textile fibres, via a standard curveH/S (S: thermal peak area of standards) against temperature (T).     

Crystallization of a melt spun Fe-Ni based metallic glass

The crystallization kinetics of a melt spun Fe-Ni based alloy has been investigated, with both isothermal and continuous heating experiments, by means of differential scanning calorimetry. The alloy presents two separated crystallization processes. In order to perform the kinetic analysis of a melt spun metallic glass and to decide which kinetic model agrees better with the experimental crystallization data as the crystallized fraction x. We compare the experimental dependence of ln(k0f(x)) vs. (1-x) and that predicted, assuming different model equations for f(x). Both crystallization processes follow the JMAE equation and the master curve is the same for isothermal and non-isothermal data. This revised version was published online in July 2006 with corrections to the Cover Date.