The use of high pressure DTA,heat flow and adiabatic calorimetry to study exothermic reactions

Cellulose, a commonly found carbohydrate, exhibits exothermic decomposition, when heated above 180C. These reactions have been detected and quantified by a range of thermal analysis and calorimetric techniques giving complementary information. The presented results are of interest for process safety.

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Zusammenfassung Cellulose, ein weit verbreitetes Kohlenhydrat, zeigt beim ErwÄrmen auf Temperaturen oberhalb 180C exotherme Zersetzung. Die damit verbundenen Reaktionen wurden mittels einer Reihe komplementÄrer thermoanalytischer und kalorimertrischer Methoden erfasst und quantifiziert. Die vorgestellten Resultate sind für die AbschÄtzung von Prozessrisiken bedeutungsvoll.

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The authors gratefully acknowledge many discussions with C. Foetisch (Linor, Orbe, CH), Prof. R. C. Reid (Lexington, Massachusetts, USA) and I. Horman (Nestlé Research Centre, Vers-chez-les-Blanc, CH).     

Application of thin-film DTA to amorphous selenium layers

A system of evaporated thin-film Ag-Bi thermocouples was used as a differential temperature sensor for DTA measurements. The crystallization of thin amorphous selenium layers was observed by means of this method. The presented method may be useful in studying the thermal transformations of thin films that have different compositions and various applications.

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Zusammenfassung Das System von aufgedampften Ag-Bi Dünnschicht-Thermoelementen wurde als Differentialtemperatursensor zu DTA-Messungen eingesetzt. Die Kristallisation dünner amorpher Selenschichten wurde durch diese Methode verfolgt. Die beschriebene Methode kann bei der Untersuchung thermischer Umwandlungen der dünnen Schichten verschiedener Zusammensetzungen Anwendung finden.

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Résumé Des thermocouples en films minces évaporés Ag-Bi ont été utilisés pour la détection de la différence de température en ATD. On a observé, par cette méthode, la cristallisation des couches minces de sélénium amorphe. La méthode présentée peut être utile dans l'étude des transformations thermiques des pellicules minces de compositions différentes et d'applications diverses.

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Ag-Bi , . . .

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The work was financially supported by the Ministry of Science, Higher Education and Technology, according to Contract No. MR-I-21.     

DTA of some reduceable metal ion exchanged montmorillonites

Stable montmorillonites with exchange of Cu, Ni, Ce, Ag, Pd and Pt are possible to be prepared. Ni²⁺ only migrates into the octahedral space and thus stabilising the structure.     

Application of heat conduction calorimetry to high explosives

This paper describes some thermal analysis experiments conducted on high explosive samples. These employ differential scanning calorimetry to monitor thermal effects at elevated temperatures (around 200 °C) and heat conduction calorimetry to record thermal effects at much lower temperatures (below 100 °C).The work shows that, due to the generally high thermal stability of many high explosive compositions, heat generation rates are very low, if detectable at all, at normal storage temperatures, even when using a very sensitive instrument. The sensitivity and reproducibility of this technique has been investigated in detail by Wilker et al. [S. Wilker, U. Ticmanis, G. Pantel, Detailed investigation of sensitivity and reproducibility of heat flow calorimetry, in: Proceedings of the 11th Symposium on Chemical Problems Connected with the Stability of Explosives, Sweden, 1998] and shown to be capable of recording heat generation rates of less than a microwatt. This allows continuous measurement of decomposition processes in nitrate ester based propellants at temperatures as low as 40 °C. However, the measurement of very low levels of heat generation is difficult, time consuming and therefore expensive. If the assumption is made that the life limiting process is invariably the slow decomposition of the energetic component, this will frequently lead to very long service lifetime predictions.A number of possible complications are identified. Firstly, due to its low detection threshold, a heat conduction calorimeter may detect other reactions which will not lead to failure, but which may still dominate the heat flow signal. Secondly, the true failure process may generate little energy and be overlooked. In view of these considerations, at present it seems unwise to rely on heat conduction microcalorimetry as the only tool for the assessment of the life of high explosive energetic systems.Based on examples of life terminating processes in high explosives during storage and use, it is clear that decomposition of the energetic material is not invariably the cause of system failure. It is also by no means the only reaction that may take place in, and be observed by, a heat conduction calorimeter.     

Application of the calorimetry to studies of colloidal phenomena

The importance of calorimetric methods in studies of colloidal phenomena is illustrated by the analysis of the experimental enthalpies of dilution and adsorption for aqueous solutions of three zwitterionic surfactants: 1–12 betaine, 3–12 betaine, and 3–12 sulfobetaine. The batch microcalorimeter ‘Montcal 3’, used to obtain these data, is described. The molar enthalpies of micellization and the differential molar enthalpies of adsorption onto silica gel are shown to be functions of the headgroup hydrophilicity, fixed by the type of negatively charged center and the number of methylene groups separating the charged sites.     

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”.     

Application of calorimetry and thermodynamics to critical problems in materials science

Calorimetry and thermodynamic studies have long been playing a very important role in the research fields of fundamental science and technology. Some topics and examples of thermodynamics studies are given, and the details are explained on the basis of the present author’s experience, focusing attention to application of adiabatic calorimetry and thermodynamics to solve critical problems in materials science: (1) condensed gas calorimetry and third law entropy, (2) phase transition and polymorphism in simple molecular crystals, (3) incommensurate phase transitions, (4) particle size effects on the phase transitions in ferroelectric/ferroelastic crystals, (5) relaxor ferroelectrics and multi-ferroics, and some other topics in materials science and technology.     

Application of differential scanning calorimetry to freeze-dried milk and milk fractions

Journal of Thermal Analysis and Calorimetry - Four ionic cobalt hexacyanidoferrate(II) complexes with formulae [Co(NH3)6]4[Fe(CN)6]3·12H2O (1) [Co(NH3)6]2Cl2[Fe(CN)6]·4H2O (2),...     

Alkali metal additions to unsaturated systems

Treatment of tetrakis(dimethoxyboryl)methane, C[B(OMe)₂]₄, with lithium methoxide or butyllithium followed by triphenyltin chloride yields (triphenylstannyl)tris(dimethoxyboryl)methane, Ph₃SnC[B(OMe)₂]₃, which on further treatment with butyllithium disproportionates to form bis(triphenylstannyl)bis(dimethoxyboryl)methane, (Ph₃Sn)₂C[B(OMe)₂]₂. The analogous monolead compound proved too base-sensitive to isolate, and only bis(triphenylplumbyl)bis(dimethoxyboryl)methane, (Ph₃Pb)₂C[B(OMe)₂]₂, was obtained from C[B(OMe)₂]₄, BuLi, and Ph₃PbCl. A brief study of protodeboronation and other reactions of these compounds has been carried out.     

Application of the Zdanovskii rule to liquid metal systems with strong interaction of components

Applicability of the Zdanovskii rule to liquid metal systems with strong deviations from ideal behavior is discussed for the example of the lead-thallium-sodium system.     

Application of DTA and TG to studies of the CaCO3-CaF2 phase diagram

A new method (based on DTA and TG) for the determination of the eutectic composition is proposed for systems in which one of the components is unstable in the vicinity of the eutectic melting temperature. The eutectic composition established by means of this method for the CaCO₃-CaF₂ system is in very good agreement with the results obtained in a classical way.

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Zusammenfassung Eine neue Methode zur Bestimmung der eutektischen Zusammensetzung von Systemen, deren eine Komponente in der Nähe der eutektischen Temperatur instabil ist, beruht auf der simultanen TG-Messung. Mit der vorgeschlagenen Methode wird die eutektische Zusammensetzung des Systems CaF₂-CaCO₃ in sehr guter Übereinstimmung mit den Ergebnissen klassischer Untersuchungen gefunden.

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, . , CaCO₃-CaF₂, , .

     

Evaluating cement hydration by non-conventional DTA; An Application to Waste Solidification

This paper presents a method to study cement hydration at ambient temperatures by using a micro processed non-conventional differential thermal analysis (DTA) system, which was used to evaluate the solidification/stabilization process of tannery wastes produced in the leather industry. The DTA curves of pastes composed by slag cement, Wyoming bentonite and waste are obtained in real time and used to analyze the heat effects of the reactions during the first 24 h of hydration. By applying a deconvolution method to separate the overlapped DTA peaks, the energy released in the several hydration stages may be estimated and consequently, the effects of each component on the solidification process. The highest separated DTA peak occurs during the several early stages of cement hydration and is due mainly to tricalcium silicate hydration. Very good correlation shows that the greater is the waste content in the paste composition, the higher is its effect on the rates of reactions occurring during the induction (dormant) period of cement hydration. The presence of bentonite used as a solidification additive in the stabilization process has a similar but less dramatic effect on the dormant period. This revised version was published online in July 2006 with corrections to the Cover Date.     

Application of TGA/DTA/MS to the Historic Preservation of Stone

The combined technique TGA/DTA/MS, thermogravimetric analysis/differential thermal analysis/mass spectrometry, has been used, in conjunction with other analytical techniques, FTIR, SEM, XRD, and optical microscopy, to analyze a specific patching material that had become seriously discolored on its surface after being used to repair a historic stone pillar at Bethesda Terrace in Central Park, New York in the 1980s. The stone patch was found to contain a polyacrylate binder which was associated with the discoloration.This revised version was published online in November 2005 with corrections to the Cover Date.     

Ignition temperatures of carbon samples containing metal oxide catalysts by a DTA method

The variation of the ignition temperature of a carbon black impregnated with various amounts of manganese oxide and uranium oxide has been measured by a DTA method. The technique allows a rapid assessment to be made of sample reactivity and only small amounts (approximately 5 mg) are required. Correlation of sample reactivity by ignition temperature measurement and isothermal weight-loss data is shown.     

Application of heat flow calorimetry to the study of oilwell cements

The majority of previous studies of the hydration of cements using heat flow calorimetry have been carried out isothermally. However, with oilwell cements the slurry is mixed on the surface at ambient temperature and then gradually increases in temperature as it is pumped down the well. A Setaram C-80 calorimeter has been used to simulate the temperature ramp in API oilwell cement test schedules. This approach has enabled cementing reactions to be studied for the first time under conditions approaching those encountered in the field, and has shown that the results obtained from isothermal experiments may be misleading.The permission of the British Petroleum Company PLC to publish this paper is gratefully acknowledged.     

Application of adsorption calorimetry to the study of heterogeneous catalysis reactions

This survey sets out to show that adsorption calorimeters, and particularly conduction-type calorimeters, can be used to measure catalytic activities and determine (i) rate laws, (ii) probable reaction mechanisms, (iii) the secondary processes which cause catalyst activation or deactivation, and (iv) the site distribution at the catalyst surface. The merits and limitations of the various applications of adsorption calorimetry to the study of heterogeneously catalyzed reactions are critically discussed. Most examples are taken from the author's previous publications.     

Solubility diagrams in solvent-antisolvent systems by titration calorimetry

Isothermal titration calorimetry (ITC) has been used to develop a method to construct the solid-liquid equilibrium line in ternary systems containing the solute to precipitate and an aqueous mixed solvent. The method consists in measuring the heat of dissolution of a solid component (the solute) during successive additions of the liquid solvent. The cumulated heat, resulting from the successive heat peaks obtained for the different injections of known volumes of solvent, plotted vs. the ratio of the numbers of moles n _solvent/n _solute is represented by two nearly straight lines. The intercept of the two lines gives the solubility limit and the corresponding enthalpy of dissolution of the solute in the solvent. Solubility diagrams have been established at 303.15 K in binary mixed solvents ethanol-water over the whole concentration range for seven compounds of pharmaceutical interest, namely: urea, phenylurea, l-valine, dl-valine, l-valine ethyl ester hydrochloride, tris(hydroxymethyl)amino methane.     

Determination of adhesion in bitumenmineral systems by heat-of-immersion calorimetry

The strength of chemical bonds formed between eight rock-forming minerals and six bitumen samples were examined by heat-of-immersion calorimetry. The materials were characterised by their physical and chemical properties. The amount of energy released by the bitumen-mineral interaction was much larger than expected for an immersion reaction, exceeding usual values by a factor of up to 10². An oxidation mechanism, catalysed at the mineral surface, is proposed to account for this observation, and trends in the heat-of-immersion data are correlated with chemical properties of the bitumen and mineral samples.     

Determination of adhesion in bitumen-mineral systems by heat-of-immersion calorimetry

Chemical factors influencing bitumen-mineral adhesion have been examined by heat-of-immersion calorimetry. Two chosen minerals (quartz and calcite) and bitumen derived from Venezuelan and Middle East crude oils were characterised and the energy released by the bitumen-mineral interaction measured. Heat-of-immersion data are correlated with the concentration of heteroatomic species present in the bitumen and the structure of the mineral surfaces. Bitumen-quartz bonding is promoted by the presence of basic species in the bitumen and bitumen-calcite adhesion is favoured by the presence of acidic groups. A mechanism is proposed to account for the observed bond energies.