DTA studies

The decomposition of MgC03 (magnesite) is an interface process [734] between 813—873 K and E = 150 kJ mole-1. In the presence of C02, E was increased to 234 kJ mole-1 but was reduced slightly on the addition of ZnO or NiO. Admixture with CaO reduced the value of E to 54 kJ mole-1. This is a surprising result since the value of E for decomposition [734,753] of the mixed carbonate (Ca, Mg)C03, dolomite, is 220 kJ mole-1, larger than the value for each constituent. The influence of PCOz and of alkali metals on MgC03 decomposition has been the subject of a DTA study [404]. 

It is apparent from DTA studies [1021] of the decompositions of Group IA formates in inert or oxidizing atmospheres that reaction is either preceded by or accompanied by melting. Anion breakdown leading to carbonate production may involve formation of the oxalate, through dimerization [1022] of the postulated intermediate, C02, especially during reaction of the Na and K salts in an inert atmosphere and under isothermal conditions. Oxalate production is negligible in reactions of the Li and Cs formates. Reference to oxalate formation is included here since this possibility has seldom been considered [1014] in discussions of the mechanisms of decompositions of solid formates. 

From DTA studies [1105] of the decompositions of Ni, Co and Cu tartrates, the temperatures of onset of reaction and values of E were... 

In a DTA study [1193] of decomposition reactions in Ag2C03 + CaC03 mixtures, the presence of a response peak, absent on heating the silver salt alone, resulted in the identification of the double salt Ag2C03 2 CaC03, stable at <420 K. One important general consideration which arises from this observation is that the formation of a new phase, by direct interaction between the components of a powder mixture, could easily be overlooked and, in the absence of such information, serious errors could be introduced into attempts to formulate a reaction mechanism from observed kinetic characteristics. Due allowance for this possibility must be included in the interpretation of experimental data. 

Ueda and coworkers reported, in 1975, the preparation of polyamides 11 from unsaturated bisazlactones 10 and a variety of diamines (Scheme 3) (JL1). In a DTA study of one of these polyamides (11, R = CHj.Tr = (CHo)g), an endotherm was noted near 200dC. It was suggested, without supporting evidence, that this endotherm might be due to a cyclodehydration reaction leading to polyimidazolinone 12. 

According to an O.S. amendment sheet, the procedure as described [1] is dangerous because the reaction mixture (dicyanodiamide and ammonium nitrate) is similar in composition to commercial blasting explosives. This probably also applies to similar earlier preparations [2]. An earlier procedure which involved heating ammonium thiocyanate, lead nitrate and ammonia demolished a 50 bar autoclave [3], TGA and DTA studies show that air is not involved in the thermal decomposition [4], Explosive properties of the nitrate are detailed [5], An improved process involves catalytic conversion at 90-200°C of a molten mixture of urea and ammonium nitrate to give 92% conversion (on urea) of guanidinium nitrate, recovered by crystallisation. Hazards of alternative processes are listed [6],... 

The title cobalt chelate exploded at 175°C during DTA studies, 30° lower than the Co chelate of dicupferron . 

A solution, prepared by mixing saturated solutions of cadmium sulfate and sodium azide in a 10 ml glass tube, exploded violently several horns after preparation [1], The dry solid is extremely hazardous, exploding on heating or light friction. A violent explosion occurred with cadmium rods in contact with aqueous hydrogen azide [2], A DTA study showed a lesser thermal stability than lead azide [3], It is strongly endothermic (AH°f (s) +451 kJ/mol, 2.32 kJ/g). 

Simultaneous TG/DTA studies of zinc hydroxystannate (Figure 6), indicate that dehydration of this compound occurs during the temperature range 190°-285°C, with a loss of 19.1% of its initial weight, this corresponding to the loss of 3 moles of water ... 

DTA study of calcium oxalate CaC204. H20 showing the effect of changing the atmosphere from (a) nitrogen to (b) air. 

In a DTA study of 14 anthraquinone dyes, most had high flash points (225-335°C) and ignition points (320-375°C). Purpurin dianilide [107528-40-5] was exceptional with the much lower values of 110 and 155°C, respectively. 

Derie, R. Ghodsi, M. Calvo-Roche, C. (1976) DTA study of the dehydration of synthetic goethite a-FeOOH. J. Thermal Analysis 9 435-440... 

It was experimentally shown in ref.[3] that the conformation could be confirmed by the pleochromic profile in the IR spectra of the phenyl group. Also, the TG-DTA studies showed that the dyes were confined to keeping such conformations between the interlayers over the melting temperature of the dye (e.g. 300°C). 

DSC traces of polyethyleneimine complexed with Nal also give evidence [58] for strong interaction of the salt with the polymer by a decrease in crystallinity of the polymer and at a molar (NaI/CH2CH2NH) ratio of 0.15, crystallization is completely prevented. At higher concentrations, a new end-otherm manifests at 150 °C due to the specific crystalline complex between Nal and PEO. DTA studies of PEO-Nal and PEO-NaSCN complexes further reveal that melting temperature of the lamellar phase (crystalline) is independent of the nature of the anion [56]. 

Pretreatment of Samples. For standardization all samples used in IR and DTA studies were pretreated in air at 450°C, followed by a special activation procedure (described below). Samples for ESR studies were heated for 10 hours in air at different temperatures (see Results) and for 10 hours under vacuum (10 4 torr) at the same temperatures. 

DTA studies were done with a DTA apparatus (Netzsch-Geratebau, GmbH, Selb) in an argon atmosphere with heating at 10°/min. ESR signals were taken in the X-band with an ER 9 spectrometer (VEB Carl Zeiss Jena) and in the Q-band with a 35-GHz ESR-XQ spectrometer (Akademie der Wissenschaften der DDR, Berlin). 

In a DTA study of 14 anthraquinone dyes, most had high flash points (225—335°C) and ignition points (320—375°C). Purpurin dianilide [107528-40-5] was exceptional with the much lower values of 110 and 155°C, respectively [1]. A similar study of indigo type dyes and vat solubilised modifications is reported. The basic dyes decompose over 350°C, destabilised to around 200°C for solubilised dyes. The relation between functional groups, structure and flammability is discussed [2]. Sulfonyl azides have been employed for attachment of reactive dyes, it is claimed they are safer used in supercritical carbon dioxide than in water [3]. 

Ahmed, N., Varadachari, C., and Ghosh, K. (2002). Soil clay-humus complexes. II. Bridging cations and DTA studies. Aust. J. Soil Res. 40, 705-713. 

Potential as a Tool for Thermal Analysis ofNOM. DTA studies of NOM are relatively scarce, due primarily to DTA s inability to provide quantitative... 

The TG-DSC technique has recently been reviewed [56]. Redfern [57] has reviewed single sample simultaneous thermal analysis, i.e., TG-DSC and TG-DTA studies of polymers. 

A TG-DTA study of the thermochemical processes occurring at vulcanisation temperatures with N-oxydiethylene-2-benzthiazyl sulphenamide and N-cyclohexyl-2-benzthiazyl sulphenamide and their mixtures with sulphur showed the formation of high molecular weight polysulphides [73]. The influence of metallic oxides (Fe203, Sn02) on hot air ageing of one-pack room temperature vulcanised fluorosilicone rubber has been studied by means of TG-DTA [74, 75]. TG-DTA and TG were both applied to study the thermal characteristics of room temperature vulcanised silicone rubber [76]. 

Fe with the template ion. DTA studies indicate that Fe-faujasites have lower thermal stability than their Al—analogs.The (OH) vibration frequency shifts from 3540 and 3630 to 3570 and 3643 cm respectively on isomorphous substitution of Al by Fe. Relative changes in the intensity of the ESR peak at g = 4.3 at low temperatures also support the conclusion that iron can be inserted in the fauja-site lattice positions. 

McDonald ( ) reports an uncertainty of 50 cal mol, we feel a value of 100 cal mol reflects better the scatter of the various studies. Kubaschewski ( ) quoted values for A gH of 2.030 0.080 and 1.830 0.090 kcal mol" from the unpublished work of Reinartz and a thesis of Wittig, respectively. The calorimetric studies of Ginsberg and Wrigge (9) and the DTA study of Chiotti et al. (1 ) led to values of 90.6 2 cal/g (2.202t0.049 kcal mol" ) and 1.970 0.016 kcal mol", respectively. An enthalpy study of Stull and McDonald (IJ ) led to a heat of melting of 2.14 kcal mol" however, this value was thought to be in error due to a container reaction. These reported values all support the adopted value. The enthalpy study of Awbery and Griffiths (3) led to a much lower value of 1.130 kcal mol". ... 

The original work extends the discussion to more complex reactions and the determination of activation energies and heats of reaction. However, the equations were developed for homogeneous reactions in solution and required twelve assumptions some of which are very difficult to satisfy when applied to dta studies of solid state reactions. These assumptions 2u e (/) the heat transfer coefficients and heat capacities of reactants and products are equal and constant, and (ii) that the temperature is uniform throughout the sample and reference material. Freeman and Carroll and Wendlandt have suggested simplifications in Borchardt and Daniels procedure. 

The reaction did not occur until after the metal melted, i.e., all reactants were preheated to the melting temperature of the metal. This is consistent with the differential thermal analysis (DTA) studies in the Zr-B4C system. 

Borchardt and Daniels [70,71] developed a method for DTA studies of homogeneous liquid-phase reactions, that involves the calculation of the rate coefficient, k, from the expression [72] ... 

A comparative DTA study [86] of some 25 oxalates in Nj and in Oj has been pubhshed. The onset temperatures of dehydration and decomposition reactions are given and the influence of atmosphere upon the temperatures and products of decomposition is discussed. Variations in the surface areas of the solid products fi om decomposition of a number of oxalates have been reported by Dollimore and Nicholson [87]. 

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