Thermal decomposition of zirconium hydroxide

The thermal decomposition of zirconium hydroxides prepared from aqueous ammonium hydroxide solutions on the addition of potassium fluorozirconate, K₂ZrF₆, under various conditions has been examined by thermogravimetry, differential thermal analysis, X-ray diffraction study and infrared spectrophotometry. As a result, it is found that the thermal decomposition of zirconium hydroxide proceeds according to

In this process, the transformation of amorphous ZrO₂ to either the metastable tetragonal or monoclinic form depends on the composition of the original starting material as an hydrated oxyhydroxide, ZrO_2−x (OH)_2x · y H₂O where x ⩽ 2 and y ⋍ 1.     

Thermal decomposition kinetics of strontium oxalate

The thermal decomposition behavior in air of SrC₂O₄ · 1.25H₂O was studied up to the formation of SrO using DTA-TG-DTG techniques. The decomposition proceeds through four well-defined steps. The first two steps are attributed to the dehydration of the salt, while the third and fourth ones are assigned to the decomposition of the anhydrous strontium oxalate into SrCO₃ and the decomposition of SrCO₃ to SrO, respectively. The exothermic DTA peak found at around 300°C is ascribed to the recrystallization of the anhydrous strontium oxalate. On the other hand, the endothermic DTA peak observed at 910°C can be attributed to the transition of orthorhombic-hexagonal phase of SrCO₃. The kinetics of the thermal decomposition of anhydrous strontium oxalate and strontium carbonate, which are formed as stable intermediates, have been studied using non-isothermal TG technique. Analysis of kinetic data was carried out assuming various solid-state reaction models and applying three different computational methods. The data analysis according to the composite method showed that the anhydrous oxalate decomposition is best described by the two-dimensional diffusion-controlled mechanism (D₂), while the decomposition of strontium carbonate is best fitted by means of the three-dimensional phase boundary-controlled mechanism (R₃). The values of activation parameters obtained using different methods were compared and discussed.     

Thermal decomposition of zinc carbonate hydroxide

This study is devoted to the thermal decomposition of two zinc carbonate hydroxide samples up to 400 °C. Thermogravimetric analysis (TGA), boat experiments and differential scanning calorimetry (DSC) measurements were used to follow the decomposition reactions. The initial samples and the solid decomposition products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and laser particle size analyzer. Results showed that zinc carbonate hydroxide decomposition started at about 150 °C and the rate of decomposition became significant at temperatures higher than 200 °C. The apparent activation energies (E_a) in the temperature range 150–240 °C for these two samples were 132 and 153 kJ/mol. The XRD analyses of the intermediately decomposed samples and the DSC results up to 400 °C suggested a single-step decomposition of zinc carbonate hydroxide to zinc oxide with not much change in their overall morphologies.     

Thermal decomposition of calcium and strontium peroxotitanates to metatitanates

Methods of DTA, TG, DSC, IR spectroscopy and X-ray phase analysis were used to study the thermal dehydration and decomposition of Ca²⁺ and Sr²⁺ peroxotitanates to the corresponding metatitanates. The stages of the process and the intermediate phases were identified. The information obtained was utilised to determine the optimum temperatures of heating of the initial peroxotitanates to yield metatitanates with a fairly high degree of crystallinity (for CaTiO₃ 680°C, and for SrTiO₃ 650°C).     

Monohydrates of strontium and barium hydroxide

The monohydrates of strontium and barium hydroxide have been prepared by decomposition, under vacuum, of the corresponding octahydrates. X-ray powder data for both compounds are reported, together with that for anhydrous strontium hydroxide; the latter is included in order to clarify an apparent anomaly in the literature.

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Zusammenfassung Es wurden die Monohydrate von Strontium und Bariumhydroxid im Vakuum aus den entsprechenden Octahydraten hergestellt. Röntgenographische Daten für beide Verbindungen sowie für wasserfreies Strontiumhydroxid wurden gegeben; für Letzteres, um gewisse Anom alien in der Literatur zu klären.

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Résumé Préparation des hydroxydes de strontium et de baryum monohydratés par décomposition dans le vide des octohydrates correspondants. Etude par rayons X de ces composés ainsi que de l'hydroxyde de strontium anhydre, dans le but, pour ce dernier, d'élucider certaines anomalies de la littérature.

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The authors wish to thank Mr. A. Miller for taking the X-ray powder photographs.     

Thermal decomposition of inorganic and organometallic compounds of tin-I. Triphenyltin hydroxide

The thermal decomposition of triphenyltin hydroxide in the temperature range 25–400°C has been studied. The decomposition products formed at each stage have been isolated and characterised. A decomposition scheme involving a reductive-elimination reaction is proposed. The proportions of this reaction and the accompanying reaction are dependent on the mode of heating.     

Thermal decomposition of ammonium uranates precipitated from uranyl nitrate solution with ammonium hydroxide

Thermal decomposition of ammonium uranates precipitated from uranyl nitrate solutions on addition of aqueous ammonium hydroxide under various conditions has been examined by thermogravimetry (TG), differential thermal analysis (DTA), infrared spectroscopy and X-ray diffraction study. The TG curves of all precipitates show the weight-loss corresponding to the calculated value as UO₃·NH₃·H₂O. The DTA curves of the precipitates give the endotherms at about 130, 210 and 590 °C and the exotherms at 340–420 °C. As a result, it is found that ammonium uranates thermally decompose to amorphous UO₃ at about 400 °C, and transform to U₃O₈ via β-UO₃.     

Thermal decomposition of chromium oxide hydroxide: I. Effect of particle size and atmosphere

The thermal decomposition process of α-HCrO₂ and β-HCrO₂ having various crystal habits and sizes was studied in an atmosphere of H₂O, O₂, and air by means of thermal gravimetry, high temperature X-ray diffraction analysis, and electrical conductivity measurement. In H₂O vapor both α-HCrO₂ and β-HCrO₂ were decomposed directly into crystalline Cr₂O₃ through the reaction 2HCrO₂ → Cr₂O₃ + H₂O. In the presence of O₂, however, the decomposition temperature was lower than that in H₂O vapor and a two-stepped thermal decomposition spectrum (two peaks) was obtained. Two steps were clearly separated on the β-HCrO₂ and assigned, respectvely, to the reactions $\text{2}\text{HCrO}{}_2\text{+}\text{1}\text{2}\text{O}{}_2\text{→ 2}\text{CrO}{}_2\text{+}\text{H}{}_2\text{O}$ and $\text{2}\text{CrO}{}_2\text{→}\text{Cr}{}_2\text{O}{}_3\text{+}\text{1}\text{2}\text{O}{}_2$. On the α-HCrO₂ samples the first reaction was newly found and followed by the second reaction at higher temperatures. The atoms in the crystal of α-HCrO₂ and β-HCrO₂ were found to start internal migration at about 200 and 250°C, respectively.     

Thermal analysis of lanthanum hydroxide

Lanthanum oxide (La₂O₃) is of great interest as catalyst material. When La₂O₃ particles are prepared from lanthanum hydroxide (La(OH)₃) by thermal processes under air, various oxycarbonate phases are formed which are resistant to thermal hydroxylation. This phenomenon has not yet been extensively investigated, even though oxycarbonate phases at the particle surfaces cause a change in lanthanum oxide??s catalytic activity. The carbonate phases formed cannot be detected by means of XRD or REM-EDX investigations due to their detection limits. Thermal analysis, particularly TG-FT-IR, allows not only for the detection of the carbonate phases in La(OH)₃, but also for the tracking of the entire dehydration process from La(OH)₃ via LaOOH to La₂O₃ as well as the correct interpretation of mass changes during the thermal transformations. Pursuant to the investigations here carried out, it was determined that carbonate-free lanthanum hydroxide compounds can only be prepared and stored in a CO₂-free protective gas atmosphere (e.g., argon).     

Thermal analysis of magnesium hydroxide

Natural brucite and two precipitated Mg(OH)₂ samples were analysed in a simultaneous TG-DTG-DSC analyser. The initial dehydroxylation temperature of natural brucite is lower than those of the precipitated samples, but the maximum and final temperatures of the former are higher than those of the latter. The maximum temperatures of individual samples obtained from DTG and DSC curves are almost the same. Heats of reaction derived from peak areas for the three samples are not exactly the same, as they are influenced by the specific surface area of the individual sample. Activation energies deduced by Freeman and Carroll's method are very different from one another. This is attributed to the difference in pressure when the sample is crimped. A linear relationship is observed between the deduced activation energy and the specific height of the DSC peak.

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Zusammenfassung Natürlicher Brucit und zwei gefällte Mg(OH)₂-Proben wurden in einem simultanen TG-DTG-DSC-Analysator geprüft. Die Anfangstemperatur der Dehydroxylierung des natürlichen Brucits ist niedriger als die der gefällten Proben, doch sind Maximal- und Endtemperaturen des ersteren höher als jene der letzteren. Die an Hand von DTG und DSC-Kurven erhaltenen Maximaltemperaturen der einzelnen Proben sind fast identisch. Die aus den Peakflächen der drei Proben errechneten Reaktionswärmen sind nicht genau dieselben, da sie von der spezifischen Peakfläche der einzelnen Proben beeinflußt werden. Die mittels der Methode von Freeman und Carroll abgeleiteten Aktivierungsenergien sind von einander sehr verschieden. Sie werden den Unterschieden im Druck bei dem Schrumpfen der Probe zugeschrieben. Ein linearer Zusammenhang zwischen der abgeleiteten Aktivierungsenergie und der spezifischen Höhe der DSC-Peaks wurde beobachtet.

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Résumé La brucite naturelle et deux échantillons de Mg(OH)₂ précipités ont été étudiés par TG-TGD et DSC simultanées. La température initiale de la déshydroxylation de la brucite naturelle est plus faible que celle des deux échantillons précipités, mais les températures maximale et finale de déshydroxylation de la brucite sont plus élevées que celles des échantillons précipités. Les chaleurs de réaction déduites de l'aire des pics DSC des trois échantillons ne sont pas exactement les mêmes, puisqu'elles sont influencées par l'état de surface des échantillons individuels. Les énergies d'activation trouvées en appliquant la méthode de Freeman et Carroll sont très différentes les unes des autres. Elles sont attribuées à la différence de pression au niveau de l'échantillon. On a observé une relation linéaire entre l'énergie d'activation déduite et la hauteur spécifique du pic DSC.

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The authors wish to thank Dr. T. C. W. Mak, Department of Chemistry, The Chinese University of Hong Kong, for taking the X-ray diffraction data.     

Preparation and thermal decomposition of indium hydroxide

Summary Indium hydroxides were prepared by the mixing of aqueous indium nitrate solution with sodium or ammonium hydroxide solutions under various conditions. The thermal decomposition of the resulting materials was examined by thermogravimetry, differential thermal analysis, X-ray diffraction study and infrared spectroscopy. It has been found that sodium hydroxide solution is more suitable than the addition of ammonium hydroxide solution to prepare indium hydroxide in well crystallization; the thermal decomposition of indium hydroxide, in which the composition is In(OH)₃·xH₂O where x￡2, proceeds according to the following process: In(OH)₃·xH₂O?cubic In(OH)₃?cubic In₂O₃     

The coirradiated decomposition of barium and strontium azides

The coirradiated decomposition of barius and strontium azides using high intensity UV light has been studied in the temperature range 190–135°C. Activation energies have been determined for different light intensities. It is proposed that thermal and photolytic decomposition occur concurrently during all stages of decomposition.     

Thermal decomposition ofC-iodotetrazoles

Thermal decomposition of 1-substitutedC-iodotetrazoles in melt and solutions has been investigated. Thermal stabilities, kinetic and activation parameters, and compositions of products of thermolysis ofC-iodotetrazolcs depend on the substituent nature. The scheme of thermolysis ofC-iodotetrazoles has been suggested.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 68–71, January, 1996.     

Thermal decomposition of benzotrifuroxane

The thermal decomposition of benzotrifuroxane proceeds through cleavage of the C-C and O-N(O) bonds of the furoxane ring with formation of dinitriloxodifuroxanyl.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1914–1915, August, 1991.     

Thermal decomposition of dicyanofuroxane

The thermal decomposition of dicyanofuroxane (DCFO) proceeds through cleavage of the O-N(O) and C-C bonds of the furoxane ring with formation of dicyanogen N-oxide. The autocatalytic reactions of this N-oxide with DCFO lead to a pentamer, most likely, with 1,2,4-oxadiazole structure.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1916–1918, August, 1991.     

Thermal decomposition of hydromagnesite

Non isothermal decomposition of synthetically prepared hydromagnesite phase with two different morphologies (2-D micro sheets and nests) was studied in dynamic nitrogen atmosphere by thermogravimetric analysis, differential thermogravimetric analysis, and differential scanning calorimetric techniques. Two different kinetic models, i.e. the Friedman isoconversion and the Flynn–Wall methods were employed for the analysis of thermal decomposition. The apparent activation energy (E _a) of the hydromagnesite phases having 2-D micro sheet and nest morphology were calculated and compared. The activation energy of nest morphology was found to be relatively higher than 2-D micro sheets. The higher activation energy for the relatively close packed ‘nest’ morphology is attributed to the difficulty of thermal transport in the core.     

Thermal decomposition of pyrite

Thermal decomposition of natural pyrite (cubic, FeS₂) has been investigated using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. X-ray diffraction analysis of pyrite ore from different sources showed the presence of associated minerals, such as quartz, szomolnokite, stilbite or stellerite, micas and hematite. Hematite, maghemite and pyrrhotite were detected as thermal decomposition products of natural pyrite. The phase composition of the thermal decomposition products depends on the temperature, time of heating and starting size of pyrite crystals. Hematite is the end product of the thermal decomposition of natural pyrite.     

Thermal decomposition of stichtite

The mineral stichtite was synthesised and its thermal decomposition measured using thermogravimetry coupled to an evolved gas mass spectrometer. Mass loss steps were observed at 52, 294, 550 and 670°C attributed to dehydration, dehydroxylation and loss of carbonate. The loss of carbonate occurred at higher temperatures than dehydroxylation.     

Thermal decomposition of methylxanthines

The thermal decomposition of theophylline, theobromine, caffeine, diprophylline and aminophylline were evaluated by calorimetrical, thermoanalytical and computational methods. Calorimetrical studies have been performed with aid of a heat flux Mettler Toledo DSC system. 10 mg samples were encapsulated in a 40 μL flat-bottomed aluminium pans. Measurements in the temperature range form 20 to 400°C were carried out at a heating rate of 10 and 20°C min⁻¹ under an air stream. It has been established that the values of melting points, heat of transitions and enthalpy for methylxanthines under study varied with the increasing of heating rate. Thermoanalytical studies have been followed by using of a derivatograph. 50, 100 and 200 mg samples of the studied compounds were heated in a static air atmosphere at a heating rate of 3, 5, 10 and 15°C min⁻¹ up to the final temperature of 800°C. By DTA, TG and DTG methods the influence of heating rate and sample size on thermal destruction of the studied methylxanthines has been determined. For chemometric evaluation of thermoanalytical results the principal component analysis (PCA) was applied. This method revealed that first of all the heating rate influences on the results of thermal decomposition. The most advantageous results can be obtained taking into account sample masses and heating rates located in the central part of the two-dimensional PCA graph. As a result, similar data could be obtained for 100 mg samples heated at 10°C·min⁻¹ and for 200 mg samples heated at 5°C min⁻¹.