Reactions of powdered silicon with some pyrotechnic oxidants

Thermogravimetry (TG) and differential scanning calorimetry (DSC) have been used to examine the thermal behaviour, in N₂ and in air, of the Si/Sb₂O₃, Si/KNO₃, Si/Fe₂O₃ and Si/SnO₂ pyrotechnic systems, in relation to the behaviour of the individual constituents.TG curves for Si powder, heated alone in air, showed that limited oxidation of Si occurred above 700°. In N₂, Sb₂O₃ sublimed completely between 500 and 900° and, in air, sublimation was accompanied by oxidation to Sb₂O₄. The Sb₂O₄ decomposed at higher temperatures. DSC curves for KNO₃ heated in N₂ showed the usual crystalline transition and melting endotherms followed by endothermic decomposition between 400 and 950°. DSC and TG curves of SnO₂and Fe₂O₃ revealed no thermal events when samples were heated to 1000° in either N₂ or air.For the Si/Sb₂O₃ system, the oxidation of Si by Sb₂O₃ between 590 and 700°, was complicated by sublimation of Sb₂O₃ in N₂ and also by the oxidation of Sb₂O₃ in air. No thermal events were observed for the Si/SnO₂and Si/Fe₂O₃ systems when heated under a variety of conditions in either N2 or in air, although these systems do sustain combustion on suitable ignition. In the Si/KNO₃ system, oxidation of Si occurs in a KNO₃ melt at temperatures above 560° in nitrogen and in air.

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Zusammenfassung Mittels TG und DSC wurde das thermische Verhalten der pyrotechnischen Systeme Si/Sb₂O₃, Si/KNO₃, Si/Fe₂O₃ und Si/SnO₂in N₂ und in Luft im Vergleich zum Verhalten der einzelnen Komponenten untersucht.TG-Aufnahmen über das Erhitzen von Si-Pulver in Luft zeigten eine begrenzte Oxidation von Silizium oberhalb 700°C. Sb₂O₃ sublimiert in Stickstoff vollständig zwischen 500 und 900°C, in Luft wird die Sublimation durch Oxidation zu Sb₂O₄ begleitet. Sb₂O₄ zersetzt sich bei höheren Temperaturen. DSC-Aufnahmen für KNO₃ in N₂ zeigen die gewohnten Umwandlungs- und Schmelzendothermen, gefolgt von einer endothermen Zersetzung zwischen 400 und 950°C. Die DSC- und TG-Kurven für SnO₂und Fe₂O₃ zeigen bei Erhitzen bis 1000°C weder in N₂ noch in Luft den Verlauf thermische Prozesse an.Bei dem System Si/Sb₂O₃ spielt sich neben der Oxidation von Si durch Sb₂O₃ zwischen 590 und 700°C auch eine Sublimation von Sb₂O₃ in N₂ sowie eine Oxidation von Sb₂O₃ in Luft ab. Für die Systeme Si/SnO₂und Si/Fe₂O₃ konnten durch Erhitzen unter einer Reihe von Bedingungen weder in Luft noch in N₂ Thermoprozesse nachgewiesen werden, obwohl diese Systeme nach geeigneter Zündung den Brennvorgang aufrechterhalten. Im System Si/KNO₃ erfolgt sowohl in N₂ als auch in Luft oberhalb 560°C die Oxidation von Si in der KNO₃-Schmelze.

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

Thermoanalytical investigation of someβ-manganese(IV)oxide-alkalimetalpersulfate systems

A TG and DTA investigation, under a static air atmosphere, of mixtures ofβ-MnO₂ and Na₂S₂O₈ or K₂S₂O₈ in different molar ratios is reported.β-MnO₂ lowers the initial decomposition temperatures of these persulfates by 25° through a catalytic effect. A mechanism is proposed for this effect. The X-ray diffractometry results in this investigation could be used to decide which type of semiconductorβ-MnO₂ should be used for the best activity.     

Thermoanalytical investigations of thallous nitrate

Thallous nitrate was investigated using TG, DTA, and DSC in conjunction with gas chromatography and X-ray diffraction analysis. TG showed a weight loss beginning at 380° with a 50 percent loss by 520°. This weight loss was demonstrated to be caused by boiling rather than thermal decomposition. The DTA extrapolated onset temperature for the boiling was 467°. Two solid-solid transition points and the melting point were determined by DTA to be 77, 145, and 207°, respectively. Heat of transition values determined by DSC were 0.15 kcal/mole at 77°, 0.87 kcal/ mole at 145°, and 2.18 kcal/mole for the melting at 207°.

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Zusammenfassung Thallium(I)nitrat wurde mittels TG, DTA und DSC, mit Gaschromatographie und Röntgendiffraktionsanalyse gekoppelt, untersucht. TG zeigte einen beginnenden Gewichtsverlust ab etwa 380° und einen Verlust von 50% bis 520°. Es wurde gezeigt, daß dieser Gewichtsverlust eher vom Sieden als von der thermischen Zersetzung verursacht wird. Die aus DTA-Daten extrapolierte Anfangs-Siedetemperatur war 467°. Die Fest-festphasen Übergangspunkte und der Schmelzpunkt lagen, wie durch DTA ermittelt, bei 77, 145, bzw. 207°. Die mittels DSC bestimmten Wärmen der Übergangswerte betrugen 0.15 kcal/Mol bei 77°, 0.87 kcal/Mol bei 145° und 2.18 kcal/Mol für das Schmelzen bei 207°.

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Résumé On a étudié le nitrate de thallium(I) par TG, ATD et DSC conjointement à la Chromatographie en phase gazeuse et à l'analyse par diffraction des rayons X. La TG révèle une perte de masse à partir d'environ 380°, avec une perte de 50 p. c. à 520°. On montre que cette perte de masse est provoquée par l'ébullition plutôt que par la décomposition thermique. La température initiale de l'ébullition, extrapolée à partir des données ATD, est de 467°. Deux points de transition solide-solide ainsi que le point de fusion ont été déterminés par ATD et correspondent aux températures respectives de 77, 145 et 207°. Les valeurs des chaleurs de transition ont été déterminées par DSC: 0.15 kcal, mol^–1 à 77°, 0.87 kcal. mol^–1 à 145 et 2.18 kcal. mol^–1 pour la fusion à 207°.

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, , - . , 380° 50% 520°. , , . 467°. - , , 77, 145 207°. , , 0.15 / 77°, 0,87 / 145° 2.18 / 207°.

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The authors thank F. J. Conrad and W. J. Andrzejewski for gas analysis results and G. T. Gay for X-ray diffraction analyses.This work was supported by the United States Department of Energy.     

Thermoanalytical investigation of blood

The aim of this study is to understand some properties and thermal behavior of blood, giving a possible alternative tool which differs from the traditional blood diagnostic methods, and to improve investigations in hematology and artificial bloods. Wistar rat blood samples (WRBS); SHR rat blood samples (SHRBS) and human blood samples (HBS) were analyzed. TG curves showed two decomposition stages for HBS at around 100 and 230°C (T _onset), while three mass degradation stages for WRBS (70, 110, 270°C) and SHRBS (70, 120, 270°C) could be observed. DSC peaks showed five endotherms for HBS at 65, 82, 194, 201 and 309°C and three endotherms for WRBS at 83, 184 and 313°C.     

Thermoanalytical investigation of calcium chromate

Thermoanalytical methods have been used to study calcium chromate (CaCrO₄) samples. Thermal decomposition temperatures determined by TG in vacuum and by DTA in air could not be successfully used for screening purposes. Other thermogravimetry studies in air indicate that TG can be an effective quality control tool in screening out samples which have an assay value below 97.0% CaCrO₄. More complete analyses using TG in an argon atmosphere gave good results for CaCO₃ and H₂O content as well as for total CaCrO₄. Reliable measurement of Ca(OH)₂ was not achieved. Effluent gas analysis—mass spectrometry was used to identify gaseous products as a function of temperature, in order to verify interpretation of TG curves.Thermogravimetry, differential scanning calorimetry, nuclear magnetic resonance, and mass spectrometry have been used in an effort to explain the unusual weight loss observed between 400 and 600°C for many CaCrCO₄ samples. Ca(OH)₂ decomposition is not the primary cause of this weight loss, as originally suspected, but instead the loss appears to be due to volatization of H₂O trapped in the CaCrO₄ crystal.     

Thermoanalytical studies of some sweeteners

The thermal decomposition behavior of acesulfame-K (ACK), aspartame (ASP), sodium cyclamate (SCL), saccharine (SAC), and sodium saccharine (SSA) were investigated. After re-crystallization of the commercial samples the compounds were characterized by using elemental analysis, IR spectroscopy and thermoanalytical techniques (TG/DTG, DTA, and DSC). Evidences of hydrate water loss were observed for SSA and ASP. Melting was detected for SSA and SAC. Each compound decomposed in a characteristics way. The decomposition of APS and SAC took place completely, while ACK, SCL and SSA resulted in K₂SO₄, Na₂SO₄, and Na₂SO₄, as residues respectively. The Flynn-Wall-Ozawa method for kinetic calculations was applied for the volatilization of saccharine resulting in E _a = 80 ± 1 kJ mol⁻¹ and log A = 7.36 ± 0.07 min⁻¹.     

Ageing studies of magnesium–sodium nitrate pyrotechnic compositions

The ageing characteristics of pyrotechnic compositions are influenced not only by temperature, but also by surrounding effects as humidity and vibrations. In this paper the thermal stability of the pyrotechnic system magnesium–sodium nitrate will be investigated. In an inert helium atmosphere two steps of mass loss, which were not completely separated from each other, were observed in the temperature range from 65 to 265°C: a mass loss of about 15% between 65 and 160°C and about 34% between 160 and 265°C. It is assumed that these two steps are caused by different processes. The separation between the two steps was not or hardly detectable for measurements that were performed in a nitrogen atmosphere. Using MS and FTIR (mass spectrometry/Fourier transform infrared spectroscopy) the evolved gases were analysed. Only above about 170°C evolving gases were detected (which means that during the first step no gases were detectable). The detected gas mainly consists of CO₂, CO and N₂O, with smaller amounts of NO₂, NO and possibly HCN. A third step of mass loss (8–9%) was observed above 314°C. The process which caused this step of mass loss is considered not to contribute significantly to the ageing of the material at much lower temperatures of maximum 80°C, which is of interest in view of the use of the materials.     

Thermoanalytical studies of intumescent systems

Fire retardant intumescent coatings which produce a swollen char on heating are being frequently used to protect buildings containing structural steel from the effects of exposure to high temperatures caused by fire. This paper contains details of a study carried out using thermal analysis techniques to elucidate the mechanisms of the development of intumescent chars during the heating of an intumescent coating system based on ammonium polyphosphate, pentaerythritol and melamine. In particular, the role of melamine as the spumific agent has been studied. The melamine is shown to react chemically with the ammonium polyphosphate in addition to carrying out its role as the spumific, or blowing agent.     

Thermoanalytical investigation of layered titanium salts

The investigated materials have similar routes of thermal decomposition; i.e. they lose their crystal water first, then at a higher temperature their structural one. At least the result TiP₂O₇ goes through a phase change at about 1000 K. The amorphous titanium phosphate lost its crystal and structural water at higher temperature than those of crystalline forms. Both α- and γ-titanium phosphates and also their transition metal containing forms have layered structure. In case of α- and γ-forms after the loss of crystal water a phase change occurs which is followed by the decomposition of the molecule. Various transition metals containing γ-titanium phosphates lose their crystal water at the same temperature, with the exception of Ni containing ones. The process is finished in this case at temperature 90 K higher than that of the others. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermoanalytical investigation of crystallin cerium phosphate

The crystalline cerium bis-monohydrogen phosphate Ce(HPO₄)₂·1.33 H₂O was synthetized and identified by X-ray and analytical methods.The thermal decomposition was investigated by simultaneous TG, DTG and DTA measurements. As a result of investigations four endothermic processes with weight loss were found; the first two, nearly equal peaks at 373 and 423 K, the third at 653 K and the last at 1053 K. The material after heating over 1273 K was investigated with the same analytical methods. In connection with these data we supposed that the weight losses may be identified as water and oxigen losses. The thermal analysis was supported by X-ray measurements. Collecting the results of thermal and X-ray analysis crystalline water bound in the molecule in various ways can be quantitatively distinguished. It was found that this phenomena have definite influence on the layer distance.By the X-ray measurements the change of the crystal structure taking place during the heating process could be followed.

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Zusammenfassung Das kristalline Cer-bis-phosphat [Ce(HPO₄)₂.1.33 H₂O] wurde synthetisiert und durch Röntgen- und analytische Methoden identifiziert.Die thermische Zersetzung wurde durch simultane TG-, DTG- und DTA-Messungen untersucht. Als Ergebnis der Untersuchungen wurden vier endotherme Vorgänge mit Gewichtsverlust gefunden: die ersten zwei annähernd gleichen Peaks bei 373 und 423 K, der Dritte bei 635 K und der Letzte bei 1053 K. Nach Erhitzen über 1273 K wurde die Substanz mit den gleichen analytischen Methoden untersucht. Im Zusammenhang mit diesen Angaben wurde angenommen, dass die Gewichtsverluste der Abgabe von Wasser und Sauerstoff zugeordnet werden können. Die Thermoanalyse wurde durch Röntgenuntersuchungen unterstützt. Durch gemeinsame Auswertung der Ergebnisse der Thermo- und Röntgenanalyse konnte das im Molekül auf verschiedene Arte gebundene Kristallwasser quantitativ unterschieden werden. Es wurde gefunden, dass dieses Phänomen einen ausgeprägten Einfluss auf den Abstand der Schichtenentfernung hat.Durch Röntgenmessungen konnten die während des Aufheizvorganges stattfindenden Veränderungen der Kristallstruktur verfolgt werden.

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Résumé Le bis(monohydrogéno)phosphate de cérium [Ce(HPO₄)₂.1,33 H₂O] cristallin a été synthétisé et identifié par les méthodes analytiques et par rayons X.La décomposition thermique a été suivie par TG, TGD et ATD simultanées. Les résultats des essais ont mis en évidence quatre processus endothermiques avec perte de poids: les deux premiers, avec des pics sensiblement égaux à 373 et 423 K, le troisième à 653 K et le dernier à 1053 K. AprÊs chauffage au-dessus de 1273 K le matériau a été étudié à l'aide des mèmes méthodes analytiques. D'aprÊs ces données, les pertes de poids peuvent sans doute Être attribuées à des pertes d'eau et d'oxygÊne. L'analyse thermique a été étayée par examen aux rayons X. Le rapprochement des résultats a permis de distinguer de faÇon quantitative divers modes de liaison de l'eau de cristallisation dans la molécule. On établit que ce phénomène a une influence définie sur la distance des couches.Les mesures aux rayons X ont permis de suivre le changement de la structure cristalline pendant le chauffage.

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- [/_4/2·1.33 ₂ . , . , : , , 373 423 , — 653 — 1053 . 1273 . , . . , . , . , .

     

Thermoanalytical and thermogastitrimetric investigation of oil-shales

From thermoanalytical curves (DTG, TG) recorded in an oxygen atmosphere, the moisture and carbonate contents of oil-shales were determined with acceptable accuracy. The nature of the carbonates was predicted from the shape of the DTG curves above 550°C Dolomite (ankeritc) as found in Gérce oil-shale, and calcite in Pula-9 oil-shale. The clay content was determined from the signal of a water-detector recorded in a nitrogen atmosphere. The peaks at 80°C and 150°C for Gérce oil-shale were attributed to montmorillonite, and the sharp peak at 525°C for Pula-9 oil-shale to kaolinite.The volatile and fixed carbon contents of the oil-shales were calculated from the thermogastitrimetric curves.

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Zusammenfassung Feuchtigkeits- und Carbonatgehalt von Ölschiefern werden aus in Sauerstoffatmosphäre aufgenommenen thermoanalytischen Kurven (DTG, TG) mit annehmbarer Genauigkeit bestimmt. Die Natur der Carbonate wurde aus dem Verlauf der DTG-Kurve oberhalb 550 °C vorausgesagt. Dolomit (Ankerit) wurde im Gérce-Ölschiefer, Calcit im Pula-9-Ölschiefer gefunden. Der Gehalt an Tonen wurde aus dem in Stickstoffatmosphäre erhaltenen Signal eines Wasserdetektors bestimmt. Die Peaks bei 80 und 150 °C in der DTG-Kurve des Gérce-Ölschiefers werden Montmorillonit, der scharfe Peak bei 525 °C im Falle von Pula-9-ölschiefer Kaolinit zugeschrieben. Die Gehalte der Ölschiefer an flüchtigem und fixiertem Kohlenstoff werden aus gastitrimetrischen Kurven berechnet.

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(, ) , , . 550°. (), -9-. . , 80 150° , 525° -9 — . , .

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The authors are indebted to J. Kristóf (Dept. of Anal. Chem., Univ. of Veszprém) for carrying out the continuous water measurements; to K. Labdy (Central Laboratory, Univ. of Veszprém) for the elemental analysis results; to I. Vassányi (Dept. of Mineralogy, Univ. of Veszprém) for the diffractometric results; and to I. Koncz (Hydrocarbon Research and Development Institute, Nagykanizsa) for donating the oil-shale samples.     

Thermoanalytical investigation of drug–excipient interaction

Piroxicam–excipient (chitosan or cellulose) mixtures after mechanical activation were investigated using DSC. Crystallization of amorphous piroxicam was detected near 80°C in the mixtures of the components activated separately. If the components in the mixture are activated together, amorphous piroxicam does not crystallize at heating. Both excipients interact with piroxicam, decreasing its melting point and enthalpy of melting. Mechanical activation intensifies the interaction, decreasing the melting point by 8°C and reducing the enthalpy of melting two times.     

Thermoanalytical investigation of high-temperature transformations of polyimides

The results of thermoanalytical investigations of polyimides are considered. It is shown that combined application of methods of thermal analysis makes it possible not only to determine the thermal and structural characteristics of polyimide articles but also to observe the formation of polyimides, their thermal degradation and transformation into new structures under the influence of high temperatures.     

Thermoanalytical investigation of some alkaline earth hydroxide hydrates on application as latent heat storage materials

Owing to their high specific melting enthalpy and the range of the melting temperatures the alkaline-earth hydroxide hydrates Ba(OH)₂·8H₂O and Sr(OH)₂·8H₂O are promising latent heat storage materials. The investigations of the melting and solidification behaviour of Sr(OH)₂·8H₂O and its mixtures with Ba(OH)₂·8H₂O, which had been performed by means of DTA and DSC methods in the closed system with a constant gross composition lead to statements on the melting temperature and specific melting enthalpyvs. concentration. Theoretical storage densities of 532 MJ/m³ are obtained for the mixture of Ba(OH)₂·8H₂O and Sr(OH)₂·8H₂O (80/20) and a value of 655 MJ/m³ can be achieved for Sr(OH)₂·8H₂O. The kinetics of rehydration to the octahydrates has a great influence on the storage temperature and storage density.     

Thermoanalytical investigation of lignite humic acids fractions

Differential scanning calorimetry (DSC) and thermogravimetry (TG) studies of humic acids (HA) sequentially extracted at pH 7, 8, 9 and 10 by phosphate and pyrophosphate buffers have been carried out. Supplement information were provided by elementary analysis and FTIR spectroscopy to characterize and evaluate in details the thermooxidative behavior of HA fractions. The exothermic DSC profiles of the HA samples extracted by phosphate buffers or by pyrophosphates were shifted to lower temperatures in comparison with the original sample and showed narrow distribution of humic molecules. Experimental data showed dependency of HA fraction composition on the pH used during extraction. DSC experimental data showed 1 endothermic and from 2-5 exothermic peaks associated with mass loss recorded by TG measurement. Higher degree of aliphaticity observed on samples extracted at lower pH did not remarkably affect the DSC peak temperature of the first decomposition step associated with aliphatic moieties and functional groups decomposition and recombination reactions. On the other hand, such dependency was observed in higher temperature range where destruction of aromatic structures took part. The behavior of HA samples (even after separation of specific fractions) showed high complexity of system, which resulted in complicated physical and chemical processes occurred during thermooxidation. Observed stability and released heat were affected by many factors, among them evaporation of volatile part of humic matter and a slight contribution of weak interactions among humic molecules were considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermoanalytical investigation of crystalline layered hafnium salts

Transition metal containing hafnium phosphates forms has layered monoclinic structure. In general these materials have similar route of thermal decomposition; i.e. they loss their crystal water first then at a higher temperature their structural one. At least the result HfP₂O₇ goes through phase change at about 1000 K. In detail among their thermal decomposition some differences occur. The Mn and Zn containing samples have similar behaviour as pure hafnium phosphate. The Cu and Ni containing materials have an additional exo-process connected with the transition metal oxide forms. In case of Co containing sample similar to that of Zn containing one (but very weak) processes were observed.     

Thermoanalytical study of some anti-inflammatory analgesic agents

Thermogravimetry (TG), differential thermal analysis (DTA), differential scanning calorimetry (DSC) as well as X-ray diffraction powder (DRX) patterns and Fourier transformed infrared spectroscopy (FTIR) were used to study ketoprofen, ibuprofen, and naproxen. The chemical or physical properties of the studied compounds were established and when possible by X-ray powder diffractometry and/or infrared spectroscopy were used. In this investigation, quantum chemical approach was used to determine the molecular structures using Becke three-parameter hybrid method and the Lee–Yang–Par (LYP) correlation functional. The performed molecular calculations in this work were done using the Gaussian 03 routine. Theoretical calculations help in interpretations of FTIR spectra supplying structural and physicochemical parameters.     

Thermoanalytical behaviour of some coating free films

Differential scanning calorimetry (DSC) was used in the investigation of the behaviour of coating free films. The films were produced from two film-forming polymers which are chemically different but equally used for producing controlled-release dosage forms: Eudragit NE 30 D (synthetically produced polymethacrylate copolymer) and LustreClear product (mixture containing natural and semi-synthetic components: microcrystalline cellulose, hydroxy-ethyl cellulose, carrageenan and polyethylene glycol). During their comparative analysis the characteristic parameters of the DSC curves obtained with dynamic measurement method were used and their changes as a function of storage conditions and storage time were observed. It was found that the thermoanalytical behaviour of the examined methacrylate-based Eudragit NE and cellulose-based LustreClear films was different. The specific enthalpy change of Eudragit NE fresh films was very little, but it increased considerably during storage. The specific enthalpy change of LustreClear films was much greater but its value shows only a slight further increase during storage. The results obtained help to choose the proper temperature for coating and drying.