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Showing papers in "Journal of Thermal Analysis and Calorimetry in 1993"


Journal ArticleDOI
TL;DR: ModModulated DSCTM (MDSC) as mentioned in this paper is a new extension to conventional DSC which provides information about the reversing and nonreversing characteristics of thermal events, as well as the ability to directly measure heat capacity.
Abstract: Modulated DSCTM (MDSC) is a new, patent-pending extension to conventional DSC which provides information about the reversing and nonreversing characteristics of thermal events, as well as the ability to directly measure heat capacity. This additional information aids interpretation and allows unique insights into the structure and behaviour of materials., A number of examples of its use are described.

492 citations


Journal ArticleDOI
TL;DR: In this paper, the theoretical basis for modulated DSC is described, and the additional information in can give over conventional DSC illustrated for some polymers, such as polysilicon.
Abstract: The theoretical basis for Modulated DSC is described and the additional information in can give over conventional DSC illustrated for some polymers.

388 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined the reason for using the latter tempers rather than the former ones in cooking pots and found that the monocrystalline calcite tempers prevent formation of defects in the cooking pots during firing or during use.
Abstract: Limestone and monocrystalline calcite tempers (grains) are abundant in ancient pottery. In pottery from the Canaan area the former is common in Iron Age storage and table-ware vessels and the latter is present in cooking pots. Limestone is much more widespread than monocrystalline calcite and the potters used it often as tempers when manufacturing pottery vessels, but usually not for cooking pots. While defects appear frequently around limestone tempers, they do not appear around monocrystalline calcite ones. This study examines the reason for using the latter tempers rather than the former ones. Raw materials of carbonate tempers in a clay matrix were fired and the decarbonation process was followed by quantitative IR thermospectrometry. The results indicate that the monocrystalline calcite tempers prevent formation of defects in the cooking pots during firing or during use. The reasons for this are higher thermostability at elevated temperatures, lower intensity of decarbonation, and retention...

82 citations


Journal ArticleDOI
TL;DR: In this article, the phase transition behavior of water molecules in hydrogels was classified into three categories according to phase transition behaviour; non-freezing, freezing bound and free water.
Abstract: Water molecules in hydrogels were classified into three categories according to phase transition behavior; non-freezing, freezing bound and free water. Melting, crystallization, and glass transition of water in hydrogels reflected the state of the water interacting with polysaccharides. Freezing bound water formed metastable ice by slow cooling and formed amorphous ice by quenching. From the isothermal crystallization measurement, nucleation rate and crystal growth rate were obtained. The crystal growth rate of freezing bound water was about ten times slower than that of free water. The DSC characterization of water in hydrogels was summarized.

82 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the kinetic spherulite growth parameters obtained by non-isothermal optical microscopy are, within the experimental errors involved, the same as those obtained by isothermal OOM or isothermal DSC.
Abstract: Differential scanning calorimetry (dual furnace, null-balance, DSC) and optical microscopy (OM) have been used to study the isothermal crystallization kinetics of poly(oxymethylene)-POM The non-isothermal crystallization of the same material has also been studied by optical microscopy A very controversial problem is whether the isothermal kinetic parameters may be applied to describe the non-isothermal crystallization The results show that the kinetic spherulite growth parameters obtained by non-isothermal optical microscopy are, within the experimental errors involved, the same as those obtained by isothermal optical microscopy or isothermal DSC The importance of this finding is highlighted

62 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of sample mass on the kinetics of isothermal dehydration of crushed crystals of Li2SO4·H2O were investigated using conventional TG and a combination of Avrami-Erofeyev and contracting geometry models.
Abstract: Effects of sample mass on the kinetics of isothermal dehydration of crushed crystals of Li2SO4·H2O were investigated using conventional TG. The process was characterized by a combination of Avrami-Erofeyev and contracting geometry models. Distribution of the fractional reaction, α, in particles within the sample assembly as well as the change in the rate of gross diffusion of the evolved water vapour appear responsible for the sample-mass-dependent kinetic parameters obtained for the system.

43 citations


Journal ArticleDOI
TL;DR: In this article, a series of PDPS/PDMS copolymers were synthesized through living anionic polymerization withn-butyllithium as an initiator.
Abstract: A series of PDPS/PDMS copolymers were synthesized through living anionic polymerization withn-butyllithium as an initiator. The changes of thermal property as a function of PDPS content were compared with respect to different types of monomer sequence using differential scanning calorimetry and thermogravimtery. The results indicated that the related variations of the thermal propertiesvs. the PDPS content and the monomer sequence provided independent operative control for preparing materials with desired thermal properties. The thermal stability of these copolymers was dramatically improved with introducing PDPS segment. However, the degree of these improvement pedended greatly on the monomer sequence in the copolymers.

41 citations


Journal ArticleDOI
TL;DR: In this article, the simultaneous SAXS/WAXD technique is used to provide an unambiguous method for following structural changes taking place during the programmed heating of a range of multiphase polymeric materials.
Abstract: The simultaneous SAXS/WAXD technique is shown to provide an unambiguous method for following structural changes taking place during the programmed heating of a range of multiphase polymeric materials. Results are given for polyethylene, block copolyurethanes and block copolyesters containing liquid crystalline hard segments.

39 citations


Journal ArticleDOI
TL;DR: In this article, the maximum glass transition Tg∞ of a thermosetting resin is measured by differential scanning calorimetry in the second scan (Tg2scan), after a previous scan by heating up the sample to a temperature where the exothermic curing reaction has been completed.
Abstract: The measurement of the maximum glass transitionTg∞ of a thermosetting resin is usually performed by differential scanning calorimetry in the second scan (Tg2scan), after a previous scan by heating up the sample to a temperature where the exothermic curing reaction has been completed However, this method can eventually produce thermal degradation, decreasing the crosslinking density and theTg of the sample Values ofTg2scan between 95† and 102†C were found in an epoxy resin based on DGEBA cured with phthalic anhydride Thermal degradation effects can be avoided if the measurement is performed by isothermal curing and further determination ofTg ATg∞ value of 109†C is achieved, which is the maximum value ofTg according to the topological limit of conversion

36 citations


Journal ArticleDOI
TL;DR: In this article, thermal methods (TG and DSC), X-ray powder diffraction, and by FT-IR, UV-VIS and NMR spectroscopy were used for the analysis of norfloxacin.
Abstract: Norfloxacin was studied by thermal methods (TG and DSC), X-ray powder diffraction, and by FT-IR, UV-VIS and NMR spectroscopy. The drug substance can be prepared in two different crystalline forms and in amorphous state, depending on the experimental conditions of preparation. DSC examinations were carried out at various heating rates and by cycling the samples in the temperature range 50°–250°C. The unstable crystalline form undergoes two irreversible solid-solid phase transitions at 176.5° and 197.6°C. The polymorph melts in the temperature range 218.5°–220.0°C.

33 citations


Journal ArticleDOI
TL;DR: In this paper, the selectivity and activity for propane transformation into propene are very different depending on the nature of the precursor and of the active phases obtained after thermal activation, and the more selective high-temperature β phase of NiMoO4 has been obtained at a lower temperature (500°C) than previously reported (700°C).
Abstract: NiMoO4 obtained by calcination of precursors has been shown to be a very effective catalyst for oxidative dehydrogenation of propane into propene. Preparation conditions and thermal decomposition of two precursors have been studied by TG-DTA, HTXRD, FFT-IR, and thermo-desorption coupled to mass spectroscopy in order to determine their composition and to define the best treatment to favour the oxidative dehydrogenation process. The selectivity and activity for propane transformation into propene are very different depending on the nature of the precursor and of the active phases obtained after thermal activation. The more selective high-temperature β phase of NiMoO4 has been obtained at a lower temperature (500°C) than previously reported (700°C).

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed cristalline behavior with X-rays diffraction and showed that coral aragonite and pure aragonitic aragonites have two different temperatures for aragonit-calcite phase transition: 300° and 470°C.
Abstract: Coral is a natural biomaterial used nowadays frequently in medical applications. Our recent studies show that a coral implanted in bone tissue is gradually transformed to become a neoformed bone. In some special cases, high temperature has to be used as sterilization mean instead of gamma or electron irradiations. Here, we perform this method and we analyse cristalline behaviourvs. temperature with X-rays diffractions. We show that coral aragonite and mineral pure aragonite have two different temperatures for aragonite-calcite phase transition: 300° and 470°C.

Journal ArticleDOI
TL;DR: New zinc acetate based complex compounds (of general formula Zn(CH3COO)2·1−2L·nH2O) containing one or two molecules of urea, thiourea, coffeine and phenazone were prepared.
Abstract: New zinc acetate based complex compounds (of general formula Zn(CH3COO)2·1−2L·nH2O) containing one or two molecules of urea, thiourea, coffeine and phenazone were prepared namely: Zn(CH3COO)2·2.5H2O, Zn(CH3COO)2·2u·0.5H2O, Zn(CH3COO)2·tu·0.5H2O, Zn(CH3COO)2·2tu, Zn(CH3COO)2·cof·2.5H2O, Zn(CH3COO)2·2cof·3.5H2O, Zn(CH3COO)2·2phen·1.5H2O.

Journal Article
TL;DR: In this paper, the thermal behavior of mixed metal oxalates, FeCu(ox) 2.3H 2 O, Coox-2H 2O, Niox.
Abstract: The mixed metal oxalates, FeCu(ox) 2 .3H 2 O, CoCu(ox) 2 .3H 2 O, and NiCu(ox) 2 .3.5H 2 O, [ox= C 2 O 4 ] have been prcpared by coprecipitation from solution. The thermal behaviour of these compounds in nitrogen and in oxygen has been examined using thermogravimetry (TG), thermomagnetometry (TM), differential scanning calorimetry (DSC) and evolved gas analysis (EGA). The thermal behaviour of the mixed oxalates, MCu(ox) 2 .xH 2 O, differed from that of the individual metal oxalates, Cuox, Coox-2H 2 O, Niox.2H 2 O and Feox.2H 2 O

Journal ArticleDOI
TL;DR: In this paper, the authors review current applications for thermal methods within the pharmaceutical industry as well as present some early work on potential applications for two new thermal methods: Hi-Resolution Thermogravimetric Analysis and Modulated Differential Scanning Calorimetry.
Abstract: The aim of this paper is to review current applications for thermal methods within the pharmaceutical industry as well as to present some early work on potential applications for two new thermal methods: Hi-Resolution Thermogravimetric Analysis and Modulated Differential Scanning Calorimetry.

Journal ArticleDOI
TL;DR: The 124 superconductor YBa2Cu4O8 was prepared from the oxalate precursor Y2(C2O4)3 at one atmosphere oxygen pressure as mentioned in this paper, and it is strongly dependent on the gas atmosphere: in O2 and in air there is no significant weight change as long as the temperature does not exceed 800°C.
Abstract: The 124 superconductor YBa2Cu4O8 was prepared from the oxalate precursor Y2(C2O4)3. ·4BaC2O4·8CuC2O4·xH2O at one atmosphere oxygen pressure. In O2 the precursor decomposes in one step at 300°C and more gradually (300°–600°C) in Ar. The stability of the superconductor is strongly dependent on the gas atmosphere: in O2 and in air there is no significant weight change as long as the temperature does not exceed 800°C, whereas in a 1% O2-99%N2 mixture decomposition starts at about 670°C with the formation of CuO and YBa2Cu3Ox withx<7. The reduction of YBa2Cu4O8 in a 5% H2-95% Ar mixture takes place in at least four major steps with formation of products such as Y2O3, BaO, Cu2O, Cu, BaY2O4 and Ba4Y2O7.

Journal ArticleDOI
TL;DR: In this article, three high-purity, thermally stable liquid crystals were used to perform a temperature calibration of an electrcial compensation DSC on cooling, and the dependence of the real temperature on the indicated temperature has been established for all the combinations of the heating and cooling rates of practical interest.
Abstract: Temperature calibration of DSCs is usually carried out on heating. In order to accurately control the temperature during cooling experiments, the calibration has to be carried out on cooling. Therefore, three high-purity, thermally stable liquid crystals were used to perform a temperature calibration of an electrcial compensation DSC on cooling. All three liquid crystals have several liquid crystalline phases, and they all were purified to a 99.9% lovel. Temoperatures of the isotropic to nematic or cholesteric and the mesophase to mesophase transitions were used. It was verified that these liquid crystals have sufficient thermal stability for carrying out the calibration on cooling. The dependence of the real temperature on the indicated temperature has been established for all the combinations of the heating and cooling rates of practical interest. It is also shown that the vant's Hoff equation can only be applied to the crystal to a liquid crystal transition, but not to the liquid crystal to liquid crystal or liquid crystal to isotropic transitions.

Journal Article
TL;DR: In this article, the authors studied the DTA effects produced between 950 o and 1500 o C after dry-grinding of kaolinite and pyrophyllite and found that the exotherm at ≃1000 o C is shifted to lower temperature as the grinding time increases.
Abstract: The aim of this work was to study the DTA effects produced between 950 o and 1500 o C after the dry-grinding of kaolinite and pyrophyllite. When ground kaolinite is heated, the exotherm at ≃1000 o C is shifted to lower temperature as the grinding time increases; the effects at ≃1250 o and ≃1460 o C disappear, and two new closer exothermic effects are detected at around 1200 o C after grinding in a hard porcelain mill. When ground pyrophyllite is heated, the former effect also disappears, a new effect is detected at ≃1200 o C, and a new intense exothermic effect appears at 982 o C, associated with mullite formation at lower temperature

Journal ArticleDOI
TL;DR: In this article, the acidity and basicity of alumina-boria catalysts supported on porous or non-porous alumina have been studied by adsorption microcalorimetry of probe molecules (ammonia, pyridine and sulphur dioxide).
Abstract: Acidity and basicity of alumina-boria catalysts supported on porous or non-porous alumina have been studied by adsorption microcalorimetry of probe molecules (ammonia, pyridine and sulphur dioxide) Despite decreasing in initial heats, the total acidity as determined by ammonia adsorption increased in number and strength as a function of percentage of boron oxide Ammonia, as a strong base, was shown to cover all types sites from strong to weak acid sites Pyridine, as a weaker probe, was shown to dose only the stronger sites of the samples which stay nearly constant after B203 coverage approaching the monolayer The basic sites of the amphoteric alumina support are neutralized by 10 wt% of boron oxide on non-porous aJumina and 20 wt% of B203 on porous alumina The catalytic activity for partial oxidation of ethane increased with acidity and reached a maximum constant value above 20 wt% of boron oxide

Journal ArticleDOI
TL;DR: Simultaneous DTA-TG has been carried out on a set of natural vermiculite samples as discussed by the authors, which can be divided in two groups: (a) pure vermiculties and (b) those with peak temperatures at 95°-115°C.
Abstract: Simultaneous DTA-TG has been carried out on a set of natural vermiculite samples. Based on their dehydration behaviour the samples can be divided in two groups: (a) those with DTA endothermic peak temperatures at 140°–150°C and 240°–270°C (pure vermiculties) and (b) those with peak temperatures at 95°–115°C (vermiculite with mica or mica-vermiculite interstratifications). The low temperature at which the endothermic effect in group (b) appears is discussed on the basis of dilution due to the inert layers of mica, differences in chemical composition, and lowering of interlamellar water bond energy.

Journal ArticleDOI
TL;DR: The non-isothermal devitrification of lithium germanate glasses, examined by DTA and XRD, is reported and discussed in this article, where the glass compositions are expressed by the general formula:xLi2O(1−x)GeO2 withx=0.050, 0.125,0.200 and 0.250.
Abstract: The non-isothermal devitrification of lithium germanate glasses, examined by DTA and XRD, is reported and discussed. The glass compositions are expressed by the general formula:xLi2O(1−x)GeO2 withx=0.050, 0.125, 0.167, 0.200 and 0.250. All the glasses studied, unlike GeO2 glass, exhibit internal crystal nucleation without the addition of any nucleating agent. The devitrification processes occur in one or more steps. Phases which crystallized at each step are identified and crystallization mechanisms proposed. These crystallization mechanisms are related to structures of the crystallizing phases. Activation energy values as well as those for glass transition temperatures, do not vary linearly with increase in Li2O content but pass through a maximum atx=0.200.

Journal ArticleDOI
TL;DR: In this article, a new method called electrothermal explosion (ETE) is described, in which uniform heating of samples at extremely high rates (up to 105 deg. sec−1) is achieved.
Abstract: A new thermoanalytikal method, called electrothermal explosion (ETE) is described in which uniform heating of samples at extremely high rates (up to 105 deg. sec−1) is achieved. Heating is by direct passing of an electric current through the sample in the initial stages and by chemical heat release after the ignition conditions have been attained. ETE is the only direct method that allows the macrokinetics of heterogeneous reactions occurring in condensed systems to be studied at high temperature and at short conversion times, which are prohibitive for traditional thermoanalytical devices (up to 3500 K and 10−2 sec respectively).

Journal ArticleDOI
TL;DR: In this article, the activation energies of Zn, Cd and Hg of isatin isonicotinoyl hydrazone were calculated and the magnitude of ΔE was found to be affected by the nature of the metal and the pH of preparation.
Abstract: The complexes of Zn, Cd and Hg of isatin isonicotinoyl hydrazone were prepared at two differentpHs. Their thermal studies (TG, DTG and DTA) have been made and the DC electrical conductivity of compressed powder samples as a function of temperature was investigated. The activation energies (ΔE) were calculated for the ligand and the complexes which showed that the ligand has a lower value of ΔE than the complexes. The magnitude of ΔE was found to be affected by the nature of the metal and thepH of preparation.

Journal ArticleDOI
TL;DR: In this article, the thermal diffusivity of high density polyethylene (PE) has been measured by a new a. c. Joule-heating method, which is based on the phase shift of temperature waves across film sample.
Abstract: Thermal diffusivity of high density polyethylene (PE) has been measured by a new a. c. Joule-heating method. The diffusivity was determined at various temperatures between room temperature and above melting point in heating and cooling processes. This method is based on the phase shift of temperature waves across film sample, so that it offers several advantages, e.g., easy measuring in polymer melts.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the site energies of the three different populations are randomly distributed and the resulting weight loss steps from each population can be described by the integral of a simple normal distribution with temperature.
Abstract: Thermogravimetric analysis of silica gel has shown that the loss in weight between 30° and 910°C can be quantitatively explained on the basis of water being lost from three distinct and different populations of sites on the silica gel surface. The results indicate that the site energies of the three different populations are randomly distributed and, consequently, the resulting weight loss steps from each population can be described by the integral of a simple normal distribution with temperature. The calculated weight loss obtained by assuming three different site-groups having randomly distributed adsorption energies is, within experimental error, coincident with the experimental data. It is also shown that the water evolved from the second population of sites originates from strongly bound water and may also contain water generated by the condensation of (geminal) silanol groups contained in the overlapping and neighbouring population.

Journal ArticleDOI
TL;DR: In this paper, the effect of sample mass, heating rate and partial pressure of carbon dioxide on the decomposition of some common carbonates has been investigated and it was shown that these variables gave a marked effect, similar in magnitude for both DTG and DTA.
Abstract: The effect of sample mass, heating rate and partial pressure of carbon dioxide on TG, DTG and DTA curves for the decomposition of some common carbonates has been investigated. These variables gave a marked effect, similar in magnitude for both DTG and DTA. The effect of sample mass, or depth of undiluted sample, is shown to be due to an increase in the partial pressure of carbon dioxide within the reacting powder. This effect is most pronounced in nitrogen but is much reduced in carbon dioxide. Inert diluents have little effect on the curves since they do not increase the partial pressure of CO2. The first stage of the decomposition of dolomite (CaMg(CO3)2) varies with increasing partial pressure of carbon dioxide in an anomalous manner and hence the effects of these procedural variables (except heating rate) are not similar to those observed for magnesite (MgCO3) and calcite (CaCO3). The second stage is, however, strongly dependent on these variables and behaves in a manner that would be predicted for a sample of calcite diluted with magnesite.

Journal ArticleDOI
TL;DR: The ICTAC Committee on Standardisation has formed a Task Group to investigate the suitability of the certified reference materials for DTA, covering the temperature range 450°-1100°C, for accurate temperature calibration purposes.
Abstract: The ICTAC Committee on Standardisation has formed a Task Group to investigate the suitability of the ICTAC Certified Reference Materials for DTA, covering the temperature range 450°–1100°C, for accurate temperature calibration purposes and to evaluate their potential as enthalpy calibrants for DTA and DSC equipment. This paper reports the results of preliminary round-robin studies on barium carbonate and strontium carbonate, using a dual-point calibration method based on the melting points of aluminium and gold. In addition the fusion of ICTAC potassium sulphate has been investigated as a possible calibration transition.

Journal ArticleDOI
TL;DR: Nickel oxide films were prepared by chemical deposition on glass substrates using nickel sulphate and potassium persulphate in ammonia solution Coatings dried in air and at 85°C were characterized by thermal analysis (TG and DTG), FT-IR spectroscopy and X-ray diffraction as discussed by the authors.
Abstract: Nickel oxide films were prepared by chemical deposition on glass substrates using nickel sulphate and potassium persulphate in ammonia solution Coatings dried in air and at 85°C were characterized by thermal analysis (TG and DTG), FT-IR spectroscopy and X-ray diffraction The films could be formulated as hydrated forms of 4Ni(OH)2·NiOOH and Ni3O2(OH)4 respectively The coatings lost water and oxygen on heating to give NiO

Journal ArticleDOI
TL;DR: In this article, transition metal montmorillonites were saturated with benzidine (BEN) and heated gradually to 200°C, in a vacuum cell supported by KBr windows, and IR spectra were recorded before and after the thermal treatment and at various temperatures during this treatment.
Abstract: Transition metal montmorillonites were saturated with benzidine (BEN) and heated gradually to 200°C, in a vacuum cell supported by KBr windows. IR spectra were recorded before and after the thermal treatment and at various temperatures during this treatment. X-ray diffractions were recorded before and after the thermal treatment. Hg clay shows properties similar to those of Mg and Ca clays. In the interlayer BEN is bound to Hg through a water molecule bridge, either by proton accepting (typeA) or by proton donation (typeB). Some BEN is also protonated (typeD). Initially typeA predominates, but after the thermal treatment, when the film is rehydrated, the amounts of typesB andD increase. With Mn-, Co-, Ni-, Zn- and Cd-montmorillonite a direct coordination of the benzidine by the dehydrated metallic cation is obtained (typeC), in addition to small amounts of typesA,B andD. During the thermal treatment water is evolved and associationsA andB are completely transformed toC. At elevated temperatures the following associations were identified in trace amounts, ammonium-amine, BEN bound to non-structured water, hydrophobic adsorbed BEN and BEN bound to the oxygen plane (typesE, F, H andJ, respectively). During the thermal treatment of Co and Cd clays some of the benzidine was oxidized, probably to semiquinone and quinoidal cation.

Journal ArticleDOI
TL;DR: In this article, DSC was used together with other methods of pharmaceutical analysis (spectrophotometry, thin-layer chromatography) to estimate the quality and standardization of two drugs.
Abstract: DSC was used together with other methods of pharmaceutical analysis (spectrophotometry, thin-layer chromatography) to estimate the quality and standardization of two drugs—lipoic acid (polymerization upon melting, purity) and progesterone (melting temperature, polymorphism).