Application fo pressure DTA (DSC) to thermal hazard evaluation

Any hazard evaluation program should necessarily include assessment of the thermal hazards of a material. To this end, differential thermal methods (DTA and DSC) are commonly employed. The utility of these methods in thermal hazard evaluation can be significantly extended if pressurized atmospheres are also employed. The characterization of volatile chemicals as much as 100°C beyond their atmospheric boiling temperature may be achieved with pressures under 1654 kPa (225 p.s.i.g.). The effective oxygen reactivity is enhanced with a pressurized air atmosphere. Also the confined conditions in a pressurized DTA (DSC) atmosphere produce results which can be used in many instances for the semi-quantative assessment of the pressure—temperature change to be expected in more time-consuming “heating under confinements tests”.     

Observation of surface characteristics by DSC and DTA

The three types of hydroxyl groups on surfaces of goethite crystals have previously been shown to be distinguishable by inflections on the leading edge of the dehydroxylation endotherm on DSC curves. The same inflections can be observed on DTA curves and it is now established that the main prerequisite for their observation is rapid removal of water vapour from particle surfaces, although small particle size (i.e. large surface area) and uncontaminated surfaces are also important.

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Zusammenfassung Bei den drei Typen von Hydroxylgruppen an den Oberfläche von Goethitkristallen wurde zuvor festgestellt, daß sie durch den Wendepunkt an der Leitkante der Dehydroxylierungs-Endothermen an den DSC-Kurven zu unterscheiden sind. Dieselben Wendepunkte können auch an DTA-Kurven beobachtet werden und es steht nun fest, daß die Hauptvoraussetzung ihrer Beobachtung in der schnellen Entfernung des Wasserdampfes von der Teilchenoberfläche besteht, obwohl die kleine Teilchengrösse (d. h. eine grosse spezifische Oberfläche) und unkontaminierte Oberflächen auch von Bedeutung sind.

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The authors wish to express their sincere thanks to Mr E. L. Charsley of Stanton Redcroft Consulting Service for very kindly carrying out a determination on the STA-780 apparatus.     

DTA and DSC studies on polymers containing fire retardants

This publication surveys the results obtained by means of thermal analysis particularly with DTA and DSC methods in the field of synthetic and natural polymers treated with various flame retardant additives. The 167 references citated cover the most important territories of the up to date problems.     

DTA/DSC study of nanocrystallization in oxyfluoride glasses

Crystallization of glasses of the Na₂O-Al₂O₃-SiO₂-LaF₃ system was studied by DTA/DSC, XRD and TEM methods. It has been found that the nanocrystallization of LaF₃ in the NAS-based glass strongly depends on ratio of Na₂O/(SiO₂+Al₂O₃) and amount of doped LaF₃. Analysis of the local atomic interactions in the structure of oxyfluoride glasses has been used to explain the course of the crystallization. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermogravimetric investigation on combustion characteristics of oil shale and high sulphur coal mixture

Co-combustion experiments of mixture of Huadian oil shale and Heshan coal with high sulphur content have been conducted using a thermogravimetric analyzer. The effects of five different Ca/S mol ratios on the combustion characteristics of mixture fuel are analyzed using TG and DTG curves. The results show that the initial temperature of combustion of mixture fuel is decreased with an increase in the oil shale content of mixture fuel. The combustion characteristic of mixture fuel is superior to that of Heshan coal. Adding about 20 mass% Huadian oil shale into Heshan coal is feasible for desulfurization of mixture fuel during combustion.     

Baseline interpolation in DTA and DSC quantitative analysis of slow processes

A simple method is described for use with the differential scanning calorimeter for baseline interpolation in continual processes over a wide temperature interval. For the process of water desorption from the synthetic zeolite LiA with the coveragegq=1.5, the measured heat of desorption wasQ=11.2±0.5 kcal/mole.The authors wish to thank V. Vueli and D. Karauli for their help and interest in solving the problem of the baseline interpolation.     

Oxidation stability of polymeric materials dynamic DSC/DTA method

The dynamic DSC/DTA method was observed to give better selectivity and reproducibility than the isothermal method when estimating relative oxidation stability of plastics materials. The dynamic DSC/DTA method is in this survey exposed to a round robin test. Results of various instruments and test stations are compared, and their compatibility is unexpectedly good. Subsequently the dynamic DSC/DTA method was chosen as the quality control method and will be published as Finnish standard SFS 3449.

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Zusammenfassung Bei der Bestimmung der relativen Oxydationsbeständigkeit plastischer Materialien wurden mit der dynamischen DSC/DTA-Methode eine bessere Selektivität und Reproduzierbarkeit als mit der isothermen Variante beobachtet. Die dynamische Methode wurde in verschiedenen Laboratorien getestet. Die mit verschiedenartigen Geräten in verschiedenen Laboratorien erhaltenen Testergebnisse stimmen überraschend gut überein. Die dynamische DSC/DTA-Methode wurde deshalb als Qualitätskontrollmethode gewählt und wird als finnische Norm SFS 3449 herausgegeben.

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, / , . . , . , . / SFS 3449.

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Thanks are due to the Finnish Plastics Industries Federation and its member companies for the helpful interest in the course of this survey.     

Determination of reaction kinetic parameters from variable temperature DSC or DTA

An equation is derived for evaluating the kinetic parameters of a transformation from variable temperature DSC or DTA, taking account of the variation in the reaction rate constant with time and temperature. Kinetic parameters for the crystallization of a ZrF₄-BaF₂-LaF₃ glass are calculated using this equation.

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Zusammenfassung Es wird eine Gleichung zur Bestimmung der kinetischen Parameter einer Umwandlung aus DSC- und DTA-Messungen bei variabler Temperatur abgeleitet, die den Veränderungen der Reaktionsgeschwindigkeit mit der Zeit und der Temperatur Rechnung trägt. Kinetische Parameter der Kristallisation von ZrF₄-BaF₂-LaF₃-Glas werden unter Benutzung dieser Gleichung berechnet.

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, , . , ZrF₄-BaF₂-LaF₃.

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This work was carried out under a grant from the National Aeronautics and Space Administration, Materials Processing in Space Program.     

Compatibility studies of trioxsalen with excipients by DSC,DTA, and FTIR

Psoralens are widely used for the treatment of psoriasis. Trioxsalen is a drug prescribed low-dose, belonging to the group of substituted psoralen. The aim of this study was to evaluate the compatibility of trioxsalen with pharmaceutical excipients used in the solid forms by analytical techniques. Binary mixtures between the trioxsalen and pharmaceutical excipients (namely, magnesium stearate, α-lactose, microcrystalline cellulose 102, pregelatinized starch, mannitol, sodium lauryl sulfate, sodium starch glycolate, and croscarmellose sodium) were examined. The trioxsalen–sodium lauryl sulfate mixture displayed some physical interaction based on the DTA and DSC results, but the FTIR study ruled out any chemical change.     

The applicability of DTA and DSC techniques to the study of the kinetics of phase transition reactions

Differential thermal analysis and differential scanning calorimetry techniques have been used to study the kinetics of phase transitions. The aragonite/calcite transformation was chosen as test reaction.Marked discrepancies were observed between the DTA kinetic results and those obtained from isothermal kinetic measurements. This disagreement is associated with the difficulty of determining accurately the reaction rate of the process from a DTA curve.In contrast, in DSC measurements, where the reaction rate is given by the height of the peak from the base-line, it is possible to get a satisfactory fit of the data, and the kinetic results obtained with this technique are in good agreement with the isothermal ones.

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Zusammenfassung Die Differentialthermoanalyse und DSC wurden zur Untersuchung der Kinetik von Phasenübergängen eingesetzt. Die Umwandlung Aragonit/Calcit wurde als Testreaktion gewählt.Bedeutende Diskrepanzen wurden zwischen den kinetischen Ergebnissen der DTA und den durch isotherme kinetische Messungen erhaltenen Ergebnissen beobachtet. Diese Abweichungen sind damit verbunden, daß es schwierig ist, die Reaktionsgeschwindigkeit des Vorgangs aus einer DTA-Kurve genau zu ermitteln.Bei DSC-Messungen,wo die Reaktionsgeschwindigkeit durch die Höhe des Peaks von der Grundlinie gegeben ist, kann eine befriedigende Anpassung der Daten erhalten werden, und die durch diese Technik erhaltenen kinetischen Ergebnisse sind in guter Übereinstimmung mit den isothermen Ergebnissen.

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DSC determination of coal specific energy

The specific energy of several types of Australian coal was determined directly by DSC, using a standard coal as calibrant. By subdivision of the combustion profile into separate peaks representing combustion of volatile matter and residual char, the specific energies of these components were also determined.     

Thermal characterization of HCN polymers by TG-MS, TG, DTA and DSC methods

This paper presents a thermogravimetry (TG) study of hydrogen cyanide polymers, synthesized from the reaction of equimolar aqueous solutions of sodium cyanide and ammonium chloride. Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) were also used to evaluate the thermal behaviour of these black polymers, which play an important role in prebiotic chemistry. A coupled TG-mass spectrometer (MS) system allowed us to analyze the principal volatile thermal decomposition and fragmentation products of the isolated HCN polymers under dynamic conditions and an inert atmosphere. After dehydration, a multi-step decomposition occurred in this particular polymeric system, due to the release of ammonia, hydrogen cyanide (depolymerization reaction), isocyanic acid (or cyanic acid) and formamide; these two latter species allow us identify bond connectivities. Finally, data collected from TG experiments in an oxidative atmosphere showed significant differences at higher temperatures, above 400 °C. According to these results, the different techniques of thermal analysis here applied have demonstrated to be an adequate methodology for the study and characterization of this complex macromolecular system, whose structure remains controversial even today.     

Pyrolysis study of hydrophobic tholins By TG-MS, TG, DTA and DSC methods

This study presents the thermogravimetry (TG) of hydrophobic tholins, obtained from different simulation experiments of prebiotic synthesis carried out in a CH₄/N₂/H₂ atmosphere with spark discharge activation of aqueous aerosols and liquid water. Differential thermal analysis and differential scanning calorimetry were also used to evaluate the thermal behaviour of these complex organic compounds that could play an important role in prebiotic chemistry. A coupled thermogravimetry-mass spectrometry system allowed us to analyse the principal volatile thermal decomposition and fragmentation products of the hydrophobic tholins under dynamic conditions and an inert atmosphere. During their thermal degradation, which occurs in two stages, a wide variety of hydrocarbon products including methane, vinyl monomers (such as ethylene and propylene), acetylene, oligomers, and some other unknown compounds are found. Besides, a thermally stable structure is present (graphitic structure) in these particular organic substances. Finally, data collected from TG experiments in an oxidative atmosphere showed significant differences at temperatures above 240 °C. According to these results, the different techniques of thermal analysis here applied have proved to be an adequate methodology for the study and characterization of these complex systems, structures of which remain controversial even in these days.     

Thermophysical properties of oil shale minerals

The thermal diffusivity values of eight minerals that are commonly associated with oil shales of the Green River formation have been measured by the laser flash technique. Data are presented in the temperature range 25–500°C for quartz, dolomite, calcite, plagioclase, analcite, pyrite, potassium feldspar and low albite. A comparison of the thermal conductivities of some of these minerals, calculated from experimentally measured thermal diffusivity and density, with the experimental values reported in the literature reveals good agreement. Trends in the variation of thermal diffusivity with temperature and anisotropic effects in thermophysical parameters are discussed from the point of view of grain boundary effects in these polycrystalline mineral aggregates.     

The effect of the simultaneous variation of sample mass and heating rate in DTA and DSC

Quantitative correlations between kinetic parameters (energy of activation, E), procedural factors (sample mass, m, and heating rate, φ) and the dependent variables (the temperature of inception of reaction, T_i, and temperature T_α at which a constant fraction α has decomposed) have been derived for differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The relations have the same form as those derived from earlier TG studies. The dependent variables T_i and T_α are related to m, φ and E by the equations

where C₃ and C₂ are constants, and

where C₄ and C₅ are constants for a given α. The variation of C₅ with α is given by C₅ = a + b α where a and b are constants. The equations are applicable to TG, DTA and DSC.