The thermal decomposition of NaHCO3 powders and single crystals

The thermal decomposition of four commercial powders and of differently stored single crystals of sodium hydrogen carbonate is studied by power compensation DSC and by optical and FT-IR microscopy. Independently of manufacturer, specified purity and price, the thermal curves of all the commercial powders show a more or less pronounced low temperature peak preceding the one due to the main decomposition. Such small peak is not observed when samples of laboratory recrystallized material are used. However the thermal behaviour of the latter preparation differs remarkably depending on storage conditions: the material kept in closed glass containers decomposes at temperatures higher than those of the material stored in a dessiccator in the presence of concentrated H₂SO₄. The observation by optical microscopy of the behaviour of the surfaces of single crystals coming from different storage conditions when the temperature is raised in a Kofler heater helps the interpretation of the data collected. The mechanism of the decomposition is discussed and the relevant kinetic parameters reported.     

Thermal analysis of the multiple melting behavior of poly(butylene succinate‐co‐adipate)

The melting behavior of poly(butylene succinate‐co‐adipate) (PBSA) isothermally crystallized from the melt was investigated by differential scanning calorimetry. Triple, double, or single melting endotherms were observed in subsequent heating scan for the samples isothermally crystallized at different temperatures. These endothermic peaks were labeled as I, II, and III for low‐, middle‐, and high‐temperature melting endotherms, respectively. The independence of endotherm III to the crystallization temperature, the existence of an exothermic crystallization peak just below the endotherm III, and the heating rate dependence of endotherm III indicated that endotherm III was due to the remelting of recrystallized lamellar during a heating scan. The influence of crystallization time on the melting behavior of PBSA showed that endotherms II and III developed prior to endotherm I; endotherm III developed rather simultaneously with endotherm II. Further investigation showed that the peak temperature of endotherm I increased linearly with the logarithm of the crystallization time. It suggested that endotherm II was attributed to the melting of the primary lamellae, while endotherm I was due to the melting of secondary lamellae. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3077–3082, 2005     

Melting behavior of poly(butylene succinate) during heating scan by DSC

The melting behavior of isothermally crystallized poly(butylene succinate) (PBS) has been investigated using differential scanning calorimetry (DSC) and wide‐angle X‐ray analysis. The samples crystallized between 80°C to 100°C show middle endotherm at the position just before the high exotherm, while the others under 80°C show two endotherms (low and high). From the results of the melting peak vs. crystallization temperature plot, it was suggested that the middle endotherm corresponds to the melting process of the original crystallites and the high endotherms to the melting process of the recrystallized ones. As the DSC heating rate was increased, the peak temperature of the low and middle endotherms increased and that of the high endotherm decreased, indicating that the low endotherm was due to the original crystallites as well as the middle endotherm. Consequently, in the heating scan of PBS, the existence of two kinds of morphologically different crystallites as well as the process of melting and recrystallization becomes evident. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1357–1366, 1999     

Design and performance of an evolved gas analysis ion attachment mass spectrometer

We designed a simple evolved gas analysis (EGA) system to act as a sampler between solid samples at atmospheric pressure and the high vacuum inside a mass spectrometer. The newly designed stainless steel system is simple, small and rugged and fulfills all the basic requirements for EGA. The temperature is programmable with 60°C/min as the maximum heating rate and the temperature range is up to 600°C. With this system coupled with lithium ion attachment mass spectrometry (IAMS), it is possible to study the temperature‐programmed decomposition of a number of solid materials by detecting any chemical species on a real‐time basis. For illustrative purposes, EGA‐IAMS experiments of polyethylene polymers have been conducted. Copyright © 2010 John Wiley & Sons, Ltd.     

Evolved gas analysis (EGA) of brick clays

Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday     

Kinetic analysis of complex decomposition reactions using evolved gas analysis

For complex decomposition reactions, traditional methods, such as TG and DSC cannot fully resolve all of the steps in the reaction. Evolved gas analysis (EGA) offers another tool to provide more information about the decomposition mechanism. The decomposition of sodium bicarbonate was studied by TG, DSC and EGA using a simultaneous thermal analysis unit coupled to a FTIR. The decomposition of sodium bicarbonate involves two reaction products H₂O and CO₂, which are not evident from either TG or DSC measurements alone. A comparison of the reaction kinetics from TG, DTG and EGA data were compared.     

Conditions for the α1-α2 transition in isotactic polypropylene samples

Transitions between structural modifications of isotactic polypropylene, characterized by increasing degrees of order in respect to the up and down positioning of the chains, have been studied for samples having different previous thermomechanical histories or containing small amounts of ethylenic units. The annealing temperature ranges, in which such transitions are observed, are strictly related to the positions of the melting endotherm positions for the various samples. For all the recrystallized samples, the same relation has been found between the increases in the melting peak positions and the increases in the parameter selected as a measure of the up-down degree of order.     

Thermal decomposition of [Cd(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

Thermal decomposition of [Cd(NH₃)₆](NO₃)₂ was studied by thermogravimetry (TG) with simultaneous differential thermal analysis (SDTA) for two samples and at two different sets of measurement parameters. The gaseous products of the decomposition were on-line identified by evolved gas analysis (EGA) with a quadruple mass spectrometer (QMS). The decomposition of the title compound proceeds, for both cases, in the three main stages. In the first stage, deammination of [Cd(NH₃)₆](NO₃)₂ to [Cd(NH₃)](NO₃)₂ undergoes by three steps and 5/6 of all NH₃ molecules are liberated. At second stage the liberation of residual 1/6NH₃ molecules and the formation of Cd(NO₃)₂ undergoes. However, during this process simultaneously a two-step oxidation of a part of ammonia molecules also takes place. In a first step as a result a mixture of ammonia, water vapour and nitrogen is formatted. At the second step, subsequent oxidation of a next part of NH₃ molecules undergoes. As a result, a mixture of nitrogen oxide, nitrogen and water vapour is formatted, what for these both steps clearly indicates the EGA analysis. The third stage of the thermal decomposition is connected with the melting and subsequent decomposition of residual Cd(NO₃)₂ to oxygen, nitrogen dioxide and solid CdO. Additionally, third sample was measured by differential scanning calorimetry (DSC) and the results are fully consistent with those obtained by TG.     

Thermal decomposition study of HAuCl4·3H2O and AgNO3 as precursors for plasmonic metal nanoparticles

Thermal decomposition of HAuCl₄·3H₂O and AgNO₃, as precursors for Au and Ag nanoparticles, respectively, was monitored by coupled TG–DTA with TG/EGA–FTIR and EGA–MS techniques in a flowing 80 %Ar + 20 %O₂ and Ar atmospheres in the temperature range of 30–600 °C. The intermediate and final products of thermal decomposition were analysed by ex situ XRD and FTIR techniques. The thermal degradation of HAuCl₄·3H₂O starts immediately after melting at 75 °C and takes place in three steps in the temperature range of 75–320 °C with total mass loss of 49.4 and 49.7 % in artificial air and Ar atmospheres, respectively. EGA by MS and FTIR revealed a simultaneous release of H₂O and HCl in the temperature range of 75–235 °C. EGA by MS revealed a release of Cl₂ at around 225 °C and in the interval of 250–320 °C. According to the XRD analysis, the main solid product in the end of the first decomposition step at 190 °C is AuCl₃; in the end of the second decomposition step at 240 °C is AuCl and the final product at 320 °C is Au. The thermal decomposition of AgNO₃ takes place in a single step in the temperature range of 360–515 °C with a total mass loss of 39.0 and 37.8 % in flowing artificial air and Ar atmospheres, respectively. According to EGA–MS and EGA–FTIR the main evolved gases are NO₂, NO and O₂. The final product of the thermal decomposition at 600 °C is Ag irrespective of the atmosphere.     

Combined use of ion beam slope cutting and scanning electron microscopy for the investigation of the 3-dimensional micro-structure of alterated mediaeval glass

Ion beam slope cutting (IBSC) has been developed as a preparation method for SEM and TEM to avoid the problems which occur using the common mechanical preparation techniques. IBSC has been practised on metals, plastic composites ceramics and alterated mediaeval glass, too. For the investigation of the 3-dimensional microstructure of the glass samples, IBSC has been the only method, which will enable a small cut without destroying the valuable cultural heritage. By SEM investigations of the ion beam cut, the alteration process of mediaeval glass has been observed starting on the surface and spreading into deeper zones of glass. Vertical and lateral cracks are only developing and spreading in the surroundings of crater erosions. The cracks cause splitting of parts near the surface of glass. Inside the cracks, harmful atmospheric gases, like SO₂ and CO₂, are reacting with the main glass components to alterations salts, which will build up a white and black crust on the surface and in zones near the surface.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Thermal Analysis And Powder X-Ray Diffraction Study of Terpin: Evidence of a eutectic ‘hydrate/anhydrous form’

When the DSC analysis of different samples of terpin hydrate is carried out, a non identified small endotherm is observed at about 100°C, just before the melting endotherm. This phenomenon is detected whatever the experimental conditions are.After some trials, this endotherm was identified as an eutectic formed with terpin hydrate and desolvated terpin (17/83).The importance of the experimental conditions is preponderant. In an open pan, the desolvation occurs and the melting endotherm of the anhydrous form can be observed at 105°C. In a closed pan, no desolvation is detected and the melting endotherm at 120°C is that of the terpin hydrate.The eutectic exhibits a good compression ability and a fast dissolution. Its stability is correct. Its use in therapeutic tablets can be envisaged.The eutectic structure could be, more generally, favourable to compression owing to the isotropic texture of this particular solid state.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal behaviour of mechanically amorphized colemanite

The effect of mechanical treatment on the thermal decomposition of calcium borate, colemanite — Ca₂B₆O₈(OH)₆·2H₂O was studied by means of XRD, FTIR, SEM and thermal analysis methods. Grinding of colemanite causes the solid-state amorphization of this mineral, as a result of the destruction of its structure along the cleavage plane. The decrease in the particle size of the original material and the increase in its internal structural disorder affect the temperatures and the magnitudes of the thermal effects accompanying the processes of dehydration and dehydroxylation. The diminishing values of the enthalpies of these processes may be a quantitative measure of the degree of amorphization of colemanite.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthdayThe author is grateful to Professor L. Stoch for helpful discussions.Support for this work was provided by the Polish Committee for Scientific Research (KBN) — Grant No. 3 P407 034 06.     

Irreversible formation of a network during melting/dissolution of nascent PE

A high temperature endotherm has been reported recently for PE samples during a slow T ramp which has been associated with a phase change in strained chains. From comparison of NMR and calorimetric data on nascent and melt/recrystallized samples, the following origin of the strain is now proposed. Nascent PE is a homogeneous material which contains a sizeable proportion of short-range ordered chains interrupted by loose knots. Due to expansion during melting, the knots become tighter and a physical network which encompasses a fraction of the chains is produced. The network so formed interrupts the melting process in the ordered chains. In PE and other polyolefins, melting resumes at higher T. The high T endotherms of physical and chemical networks are compared. The consequences of this network for polymer properties as well as its general occurrence are discussed briefly. © 1993 John Wiley & Sons, Inc.     

Bioaccessibility of some elements from wheatgrass (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) by in-vitro gastrointestinal digestion combined with neutron activation analysis using ammonium bicarbonate as an alternate base

Studies on bioaccessibility of elements were carried out by in-vitro gastrointestinal digestion simulation method combined with neutron activation analysis (NAA) using NH₄HCO₃ as an alternate base to commonly used base of NaHCO₃. The effect of two bases namely NaHCO₃ and NH₄HCO₃ on the bioaccessibility of the elements namely Br, Fe, K, La, Na, Rb, Sm and Zn from wheat seeds, fresh wheatgrass and commercial wheatgrass tablet was investigated. The bioaccessible concentrations of the elements were determined by neutron activation analysis (NAA). The bioaccessible concentrations of samples digested using NH₄HCO₃ were found to be higher by 10–15% for most of the elements than that observed using NaHCO₃. In the case of fresh wheatgrass, the differences were as high as 50%. The present study indicated that NH₄HCO₃ can be used as a base instead of NaHCO₃ in in-vitro gastrointestinal digestion simulation method.     

Oxidation of a carbon/glass reinforced cyanate ester composite

The decomposition/oxidation behaviour of a carbon/glass fibre reinforced thermosetting pre-impregnated material based on polymerized aromatic cyanate ester compounds (commercial name GURIT-PN900-C582-43) has been investigated. Experiments were carried out for thermally thick samples exposed in a preheated reaction chamber (temperatures between 650–950 K) and a continuous gas flow (inlet velocity between 0.6 and 4.2 cm/s). Temperature measurements indicate that, in air, the process takes place under a mixed kinetic-diffusive control with three main dynamic stages corresponding to oxidative decomposition, heterogeneous ignition delay and oxidation. The oxidative decomposition stage is always much faster than the total duration of the ignition delay and oxidation stages (factors of 60–85). SEM pictures show dramatic changes in the material structure with amounts of solid residue, at the conclusion of the conversion process, varying from about 62% (resin char, glass and carbon fibres) to 29% (essentially the glass fibres) (against 85–75% for thermal degradation). Also, with the aid of thermogravimetric curves measured in air for the composite material and a charred residue, a three-step oxidation mechanism is proposed consisting of the oxidative decomposition of the resin, the oxidation of the resin char and the oxidation of the carbon fibres with estimated activation energies of 95, 136 and 185 kJ/mol, respectively.     

Decomposition of methanol vapour over solid catalyst,measured by DSC

The activity of copper containing catalysts for the formation of methanol from CO and H₂ is investigated by DSC measurement of the methanol decomposition. Calibration of the DSC signal can be performed by melting experiments with tin under reaction conditions. Comparison of catalysts is well possible by measurement of the standard activity at 240°, the apparent activation energy for the methanol decomposition reaction and the aging of the catalyst samples.

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Zusammenfassung In DSC-Messungen an der Zersetzung von Methanol wurde die Aktivität von kupferhaltigen Katalysatoren für die Bildung von Methanol aus CO und H₂ untersucht. Das DSC-Signal kann mittels Zinn-Schmelzexperimenten unter Reaktionsbedingungen kalibriert werden. Ein Vergleich der Katalysatoren ist ohne weiteres durch die Messung der Standardaktivität bei 240°C, der scheinbaren Aktivierungsenergie der Methanol-Zersetzungsreaktion und des Alterns der Katalysatorproben möglich.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday     

Melting behavior of isotactic polystyrene

The melting behavior of isotactic polystyrene, crystallized from the melt and from dilute solutions in trans-decalin, has been studied by differential scanning calorimetry and solubility measurements. The melting curves show 1, 2, or 3 melting endotherms. At large supercooling, crystallization from the melt produces a small melting endotherm just above the crystallization temperature T_c. This peak originates from secondary crystallization of melt trapped within the spherulites. The next melting endotherm is related to the normal primary crystallization process. Its peak temperature increases linearly with T_c, yielding an extrapolated value for the equilibrium melting temperature T_c° of 242 ± 1°C as found before. By self-seeding, crystallization from the melt could be performed at much higher temperature to obtain melting temperatures as high as 243°C, giving rise to doubt about the value of T_c° found by extrapolation. For normal values of T_c and heating rate, an extra endotherm appears on the melting curve. Its peak temperature is the same for both melt-crystallized and solution-crystallized samples, and independent of T_c, but rises with decreasing heating rate. From the effects of heating rate and partial scanning on the ratio of peak areas and of previous heat treatment on dissolution temperature, it is concluded that this peak arises from the second one by continuous melting and recrystallization during the scan.