Differential thermal analysis of montmorillonite

The paper provides an overview of publications on the DTA of montmorillonites (in the temperature range 20–1100°C), starting with the first experiments of Le Chatelier (1887) and ranging up to the present. Consideration is given to the dehydration, dehydroxylation, amorphization and rehydration of montmorillonite (42 references).     

The thermal decomposition of some primary explosives as studied by differential scanning calorimetry

Most currently used stab- and percussion-sensitive mixes consist of lead azide, lead styphnate or lead dinitroresorcinate in admixture with 2–5% tetrazene, which functions as an energetic sensitizer. A major problem with the use of such compositions is the poor thermal stability of tetrazene, depletion of which leads to loss of activity. The thermal decomposition of some 24 compounds, all identified as potential replacements for tetrazene in stab and percussion mixes, has been studied by non-isothermal differential scanning calorimetry, and the physicochemical parameters which characterise these explosive reactions have been determined and compared with data from temperature of ignition measurements.     

Differential thermal analysis of low-rank coals

Differential thermal analysis (DTA) of low-rank coals of high lignite to subbituminous rank from coal mines of Pakistan is reported. The studies carried out in dynamic oxygen atmosphere indicate that the exothermic reactions occur between 300 and 650°C and that the samples undergo stepwise oxidation of the organic matter rather than a continuous process as indicated by the pattern of shoulders from 250 to 350°C accompanying the main peak around 450°C. The effect of heating rate, particle size and volatile content was also studied in relation to oxidation. The results show that the increase in heating rate from 10 to 80 deg min⁻¹ results in a marked shift in all the events in the DTA curve towards higher temperatures. As for the effect of particle size, the DTA records of 100–75, 150–100, 250–150 μm and greater than 250 μm fractions show that the magnitude and position of shoulder peaks are more sensitive to changes in particle sizes compared to the main peak. The curves recorded to study the effect of changing volatile content of samples between 30–40% indicate a complex pattern of shoulders accompanying the main peak. In general, the number of shoulder peaks increases with increasing volatile content of samples but their positions do not follow any trend. The DTA curves recorded in nitrogen contain ill-de-fined oxothermic effects over the 300–750°C temperature range. These curves consist of an endothermic peak around 150°C, two exothermic shoulders in the temperature region 300–400°C and a large broad exothermic whip between 500 and 700°C. The heating rates have similar effects as in oxygen while the particle size do not influence the results. It has been concluded that the organic matter in the coals studied here is extremely heterogeneous with different burning characteristics; as a result it is very difficult to quantify energy changes associated with poorly resolved exothermic events along the DTA curve. The effects also dominate in N₂ atmosphere thus making identification of mineral matter difficult. The overall pattern of DTA events in oxygen can be correlated with the heating rate, particle size and volatile content of samples.     

Differential thermal analysis of titanium enamels

Over 30 white and coloured titanium enamels of different origin were tested with a derivatograph. Thermoceram crucibles were used, which enabled the tests to be interrupted when a change was indicated by the DTA curve. The crucible was removed from the derivatograph, and the sample pulverized and studied by X-ray diffraction method. A major difference compared to previous observations was the fact that the exothermic peak indicating the anatase-rutile transformation was also found on the DTA curves of certain anatase-type enamels. With these enamels the temperature relating to the start of the transformation peak was regarded as the critical temperature, as at a temperature below this the enamel was stable, but above it unstable.

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Zusammenfassung Mehr als 30 weiße und gefärbte Titanenemails verschiedener Herkunft wurden mit dem Derivatographen untersucht. Die Prüfung erfolgte in Korund-Tiegeln, die eine Unterbrechung der Untersuchungen bei Änderungen in der DTA-Kurve ermöglichten, um die pulverisierte Probe einer röntgenographischen Analyse zu unterwerfen. Es gelang, die durch die Anatase-Rutil Umwandlung hervorgerufene Spitze in der DTA-Kurve verschiedener Emails vom Anatase-Typ zu beobachten. Bei diesen Emails ist der Anfang der Umwandlungsspitze als die kritische Temperatur zu betrachten, unter welcher das Email stabil und über welcher es unstabil ist.

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Résumé On a examiné plus de 30 émaux au titane, de différentes origines, blancs et colorés, à l'aide du Derivatograph. L'emploi de creusets en thermoceram a permis d'interrompre l'essai au moment où l'on observe un changement sur les courbes d'ATD, de sortir le creuset, de pulvériser l'échantillon et d'en faire l'examen aux rayons X. Une différence importante par rapport aux observations précédentes consiste en ce que le pic exothermique indiquant la transformation anatase-rutile apparaît sur les enregistrements d'ATD de certains émaux de type anatase. Pour ceux-ci, la température correspondant au début du pic de transformation a été considérée comme température critique puisqu'au-dessous de celle-ci l'émail est stable, tandis qu'au-delà il ne l'est plus.

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Differential thermal analysis of potassium perchlorate

A study has been made of the differential thermal analysis of (i) potassium perchlorate in powdered form, (ii) potassium perchlorate in pelletized form, (iii) potassium perchlorate recrystallized from liquid NH₃, and (iv) potassium perchlorate preheated for 24 hours at 375°. Pretreatment of potassium perchlorate leads to a desensitization of both endothermic and exothermic processes. Additionally, the pretreatment tends to convert the symmetric exotherm into an asymmetric exotherm due to merging of the two exotherms. An analysis of the factors causing asymmetry in the exotherm has thrown fresh light on the mechanism of thermal decomposition of potassium perchlorate.

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Zusammenfassung Eine differentialthermoanalytische Untersuchung wurde an, (i) Kaliumperchlorat in Pulverform, (ii) Kaliumperchlorat in pelletisierter Form, (iii) Kaliumperchlorat, umkristallisiert aus flüssigem Ammoniak und (iv) Kaliumperchlorat, 24 Stunden bei 375° vorgeheizt, durchgeführt. Die Vorbehandlung von Kaliumperchlorat führt zu einer Verdichtung sowohl der endothermen als auch der exotherman Vorgänge. Ausserdem führt die Vorbehandlung zur Umwandlung der symmetrischen Exotherme in eine asymmetrische Exotherme durch Vereinigung der zwei Exothermen. Die Analyse der die Asymetrie der Exothermen verursachenden Faktoren zeigte den Mechanismus der thermischen Zersetzung des Kaliumperchlorats unter neuen Gesichtspunkten.

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Résumé On a effectué l'étude par analyse thermique différentielle du perchlorate de potassium: (i) en poudre, (ii) sous forme comprimée, (iii) recristallisé dans NH₃ liquide, (iv) préchauffé à 375° pendant 24 heures. Le traitement préalable du perchlorate de potassium entraîne la désensibilisation des processus endothermiques et exothermiques. De plus, le traitement préalable tend à convertir l'exotherme symétrique en un exotherme asymétrique, du fait de la fusion des deux exothermes. Une analyse des facteurs causant l'asymétrie de l'exotherme a donné une vue nouvelle du mécanisme de la décomposition thermique du perchlorate de potassium.

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This work has been supported by a grant from the Indian Space Research Organization (I.S.R.O). It also includes financial support to one of the authors (D. S.). This support is gratefully acknowledged.     

Differential thermal analysis of commercial fertilizers

Commercial fertilizers were analyzed via DTA. Characteristic endotherm patterns were noted for virtually all samples. The endotherms were identified, and characterized by comparison with known compounds. This relatively simple and fast method yields qualitative and semiquantitative data amenable to identification or quality control.     

Differential thermal analysis of porous silicon

Porous silicon materials, macro- and mesoporous silicon, obtained by electrochemical anodic etching of n- and p-Si were studied by differential thermal analysis at a steady temperature rise and under isothermal conditions in nitrogen atmosphere and in air. The method was used to estimate the presence and amount of phases of surface volatile compounds. The possibility was studied to perform a comparative estimate of the specific surface area of different types of porous silicon from data on the surface oxidation kinetics determined by the dynamic differential thermal analysis in air.     

Differential thermal analysis of hydrazinium derivatives

A thermobalance with two symmetrical pans was constructed in order to avoid thermogravimetry errors under pressure. The balance functions at 1000°C under 50 atm of hydrogen. The influence of parameters such as pressure, temperature and gas flow rate on the baseline deviation was studied. An example is given of the application of this balance to the hydrogenation of lignite char.     

Differential thermal analysis of drawn PET-films

Summary PET films were uniaxially drawn in a water bath at temperatures below and near glass transition temperature. Draw velocity and draw ratio were varied. DTA curves were recorded and analysed. For discussion of DTA density and birefringence were measured. DTA data are shown to supply information about morphology, which cannot be given by knowing density and birefringence. On the contrary drawing procedure modifies the resulting morphology in a complex way.

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Zusammenfassung PET-Filme wurden in einem Wasserbad bei Temperaturen unterhalb und nahe der Glasübergangstemperatur uniaxial verstreckt. Verstreckgeschwindigkeit und -grad wurden variiert. DTA-Kurven dieser Proben wurden aufgenommen und analysiert. Zur Diskussion der DTA-Daten wurden Dichte und Doppelbrechung ermittelt. Die DTA-Daten liefern Informationen über die Morphologie der Proben, die aus Dichte- und Doppelbrechungswerten nicht erhalten werden können. Es zeigt sich vielmehr, daß die Durchführung des Verstreckungsprozesses in komplexer Weise die Morphologie der verstreckten Proben bestimmt.

With 15 figures     

Differential thermal analysis with capillary tubes

Zusammenfassung Ein Verfahren zur Durchführung von Differential-Thermoanalysen in verschlossenen Kapillarröhrchen wurde beschrieben, womit Aktivierungsenergien und andere kinetische Daten für thermisch induzierte Reaktionen ermittelt werden künnen. Proben von 2 bis 4 mg werden verwendet. Die Ergebnisse entsprechen denen, die mit dem kürzlich beschriebenen Makrosystem ermittelt wurden.     

Pulsed fast/thermal neutron analysis: a technique for explosives detection

Explosives, narcotics and other contraband material contain various chemical elements, such as hydrogen, carbon, nitrogen and oxygen, etc. in quantities and ratios that differentiate them from each other and from other innocuous substances. Neutrons and gamma-rays have the ability to penetrate through various materials to large depths. They are able to interrogate, in a non-intrusive manner, volumes ranging from suitcases to Sea-Land containers. Pulsed fast/thermal neutron analysis (PFTNA) is a neutron-based technique which utilizes the (n,n'gamma), (n,pgamma), and (n,gamma) reactions to identify and quantify a large number of elements. The elements emit characteristic gamma-rays that are the 'fingerprints' of each isotope. This technique is being employed in a variety of applications: bulk coal analysis, contraband detection and detection of explosives.     

The thermal behavior of powder emulsion explosives

The determination of the most probable mechanism function and the calculation of kinetic parameters of thermal decomposition of powder emulsion explosives have been achieved by different kinetic equations and different kinetic methods from data non-isothermal SC-DSC curves, DSC curves, and thermal explosion delay curve. The courses which the reaction would follow under adiabatic conditions are predicted.

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Zusammenfassung Mittels verschiedener kinetischer Gleichungen und verschiedener kinetischer Methoden wurde anhand der Angaben aus nichtisothermen SC-DSC-Kurven, DSC-Kurven und thermischer Explosionsverzugskurven die wahrscheinlichste Mechanismusfunktion der thermischen Zersetzung von Pulveremulsions-Sprengstoffen ermittelt und die diesbezüglichen kinetischen Parameter berechnet. Der Reaktionsweg unter adiabatischen Bedingungen wird vorausgesagt.

     

Differential thermal analysis of pressure crystallized polyethylene

Summary The results presented here demonstrate that although medium-density polyethylene in addition to linear polyethylene can crystallize in extended-chain as well as folded-chain crystals, the branches have a significant effect on the ease of forming extended-chain crystals. Besides the two types of crystals having different melting points, as measured by DTA, an endothermic peak assumed to be due to the onset of rotational motion and located just below the respective melting peaks is associated with each type of crystal. Melting itself does not result in a complete disappearance of order; if the sample is held just above the melting point for a short period of time sufficient seed nuclei remain to produce crystallization at a higher temperature than commensurate with the cooling rate employed. This crystallization at atmospheric pressure takes place through chain folding even though the nuclei are remnants of extended-chain crystals. In addition to fractionation and segregation by molecular weight during crystallization under pressure, for which some further evidence is presented, the results obtained here suggest that fractionation by branching content may also occur.

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Zusammenfassung Die wiedergegebenen Daten zeigen für Poly?thylen mittlerer Dichte, das wie lineares Poly?thylen sowohl mit gestreckten Ketten wie mit gefalteten Ketten kristallisieren kann, da? die Verzweigungen einen wesentlichen Einflu? auf die Leichtigkeit der Ausbildung von gestreckten Ketten haben. Au?erdem besitzen beide Typen von Kristallen verschiedene Schmelzpunkte, gemessen mittels DTA. Ein endothermer Pik würde dem Einsetzen von Rotationen zuzuordnen sein und tritt kurz unterhalb des bezüglichen Schmelzpiks der entsprechenden Kristallart auf. Das Schmelzen besteht nicht in einem vollst?ndigen Verschwinden der Ordnung. Wenn eine Probe kurz über dem Schmelzpunkt für nicht zu lange Zeit gehalten wird, verbleiben genügend Keime, um Kristallisation bei h?herer Temperatur zu erzeugen als der angewendeten Abkühlungsgeschwindigkeit entspricht. Diese Kristallisation bei 1 Athmosph?re l?uft ab unter Faltung auch dann, wenn die Keime aus dem Aufschmelzen gestreckter Kristalle stammen. Zus?tzlich zur Fraktionierung und Segregation nach dem Molekulargewicht w?hrend der Kristallisation unter Druck, für welche einige Hinweise pr?sentiert werden, ergeben die Kristalle weitere Hinweise, da? die Fraktionierung durch den Gehalt an Verzweigung eintritt.

     

新型高能炸药热分解研究进展

炸药的热分解对其安定性和库存可靠性等研究是很重要的。本文总结了国内外有关TNAZ(1,3,3-三硝基氮杂环丁烷)、NTO(3-硝基-1,2,4-三唑-5-酮)、LLM-105(1-氧-2,6-二氨基-3,5-二硝基吡嗪)、FOX-7(1,1-二氨基-2,2-二硝基乙烯)等几种新型高能炸药的热分解研究。分别从理论上、实验上阐述了它们的热分解研究现状,指出了以前研究中存在的问题,预测了钝感高能炸药热分解的发展前景。参考文献32篇。     

Differential thermal analysis - evolved gas analysis of synthetic goethite

Samples of synthetic goethite have been studied by combined DTA-EGA. The total CO₂ content of the samples ranged between 1.0 and 2.7 %wt. The origin of the evolved CO₂ is discussed and it is proposed that the samples contain CO₂ as surface complexes and incorporated in the crystal structure.     

Differential thermal analysis of some fibers containing chlorine

The differential thermal analysis curves of four fibers containing chlorine (Saran, Cordelan, Teklan and Kanekalon), and their blends, are influenced by experimental conditions, although not to the same extent as those of poly(vinyl chloride) resin in powder form. The curves were determined using two different (Du Pont) cells, and are discussed in terms of sample holder geometry and material composition. The importance of procedural variables in “fingerprint” applications of thermal analysis for routine fiber identification is re-emphasised.