Influences of product gases on the kinetics of thermal decomposition of synthetic malachite evaluated by controlled rate evolved gas analysis coupled with thermogravimetry

An instrument of controlled rate evolved gas analysis (CREGA) coupled with TG‐DTA was constructed for analyzing the influences of product gases on the kinetics and mechanism of the thermal decomposition of solids that produce more than one gaseous products at the same stage of reaction. The thermal decomposition of synthetic malachite, Cu₂(OH)₂CO₃, was subjected to the measurements of CREGA‐TG under controlled concentrations of H₂O and CO₂ in the reaction atmosphere with taking account of self‐generated H₂O and CO₂ during the course of reaction. By a series of CREGA‐TG measurements carried out under various atmospheric conditions, it was reconfirmed that the reaction is accelerated and decelerated by the effects of atmospheric H₂O and CO₂, respectively. From the kinetic analysis of the CREGA‐TG curves and results of high temperature X‐ray diffraction measurements under various reaction atmospheres, it was revealed that the anomalous effects of atmospheric H₂O on the reactivity and on the reaction rate of the thermal decomposition of synthetic malachite appear at the early stage of the reaction. Usefulness of the CREGA‐TG technique for measuring the kinetic rate data for the thermal decomposition of solids was demonstrated in the present study, by emphasizing the importance of quantitative control of self‐generated reaction atmosphere. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 346–354, 2005     

Effect of atmosphericwater vapor on the kinetics of thermal decomposition of copper(II) carbonate hydroxide

The effect of atmospheric water vapor on the kinetic rate behavior of the thermal decomposition of copper(II) carbonate hydroxide, Cu₂CO₃(OH)₂, was investigated by means of TG-DTA coupled with a programmable humidity controller. With increasing water vapor pressure p(H₂O) from 0.8 to 10.6 kPa, a systematic reduction of the reaction temperature of the thermal decomposition was observed as the continuous trend from the previous works at the lower p(H₂O). Through a comparative kinetic analysis of the reaction at different p(H₂O), a catalytic action of the atmospheric water vapor on the nucleation process at the first half of the reaction was identified as the possible origin of the reduction of the reaction temperature.     

Thermal decomposition of copper(II) and zinc carbonate hydroxides by means of TG-MS

Summary For the quantitative analyses of evolved CO₂and H₂O during the thermal decomposition of solids, calibration curves, i.e. the amounts of evolved gases vs. the corresponding peak areas of mass chromatograms measured by TG-MS, were plotted as referenced by the reaction stoichiometry of the thermal decomposition of sodium hydrogencarbonate NaHCO₃. The accuracy and reliability of the quantitative analyses of the evolved CO₂and H₂O based on the calibration curves were evaluated by applying the calibration curves to the mass chromatograms for the thermal decompositions of copper(II) and zinc carbonate hydroxides. It was indicated from the observed ratio of evolved CO₂and H₂O that the compositions of copper(II) and zinc carbonate hydroxides examined in this study correspond to mineral malachite, Cu₂CO₃(OH)₂, and hydrozincate, Zn₅(CO₃)₂(OH)₆, respectively. Reliability of the present analytical procedure was confirmed by the fairly good agreement of the mass fraction of the evolved gases calculated from the analytical values with the total mass-loss during the thermal decompositions measured by TG.     

Kinetic Analysis of the Thermal Decomposition of Synthetic Malachite by CRTA

The kinetic behavior of the thermal decomposition of synthetic malachite was investigated by means of CRTA under different conditions of reduced pressure, flowing gases and quasi-isobaric atmospheres. The thermal decomposition was found to proceed at lower temperatures under the influence of the self-generated gases, CO₂ and H₂O. From a viewpoint of chemical equilibrium, the normal and opposite effects on the overall kinetics were observed for the self-generated CO₂ and H₂O, respectively. The complexity of the present reaction is also reflected by the variations of the apparent kinetic parameters which depend on the applied and self-generated atmospheric conditions. The practical usefulness of CRTA when applied to a complicated thermal decomposition is discussed as exemplified by the kinetic approaches to the present reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Infrared evolved gas analysis during thermal investigation of lanthanum, europium and samarium carbonates

The characterisation of rare earth elements carbonates (REECs) was performed by thermal analysis (TG-DTG) combined with simultaneous infrared evolved gas analysis-Fourier transform infrared (EGA-FTIR) spectroscopy. The TG-DTG curves were obtained using the Perkin-Elmer PC series TGA-7 thermogravimetric analyser in the temperature range 25-800 °C both in dynamic air and nitrogen atmosphere.La₂(CO₃)₃·nH₂O, Eu₂(CO₃)₃·nH₂O and Sm₂(CO₃)₃·nH₂O were analysed, the dehydration and decarbonation steps were investigated and the water content was calculated. The trace rare earth elements in lanthanum, europium and samarium carbonates were determined by Philips PU 7000 inductively coupled plasma atomic emission spectrometry (ICP-AES) and the concentration of REE ranged from 6.2×10⁻⁵ to 4.2×10⁻⁴% (w/w).     

Thermal decomposition of hydrotalcite with hexacyanoferrate(II) and hexacyanoferrate(III) anions in the interlayer

The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. The thermal decomposition of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer has been studied using controlled rate thermal analysis technology. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 10.9 and 11.1 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. Calculations show dehydration with a total loss of 7 moles of water proving the formula of hexacyanoferrate(II) intercalated hydrotalcite is Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.5·7H₂O and 9.0 moles for the hexacyanoferrate(III) intercalated hydrotalcite with the formula of Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.66·9H₂O. CRTA technology indicates the partial collapse of the dehydrated mineral. Dehydroxylation combined with CN unit loss occurs in two isothermal stages at 377 and 390°C for the hexacyanoferrate(III) and in a single isothermal process at 374°C for the hexacyanoferrate(III) hydrotalcite.     

Thermal decomposition of hydrotalcites with variable cationic ratios

Thermal analysis complimented with evolved gas mass spectrometry has been applied to hydrotalcites containing carbonate prepared by coprecipitation and with varying divalent/trivalent cation ratios. The resulting materials were characterised by XRD, and TG/DTG to determine the stability of the hydrotalcites synthesised. Hydrotalcites of formula Mg₄(Fe,Al)₂(OH)₁₂(CO₃)·4H₂O, Mg₆(Fe,Al)₂(OH)₁₆(CO₃)·5H₂O, and Mg₈(Fe,Al)₂(OH)₂₀(CO₃)·8H₂O were formed by intercalation with the carbonate anion as a function of the divalent/trivalent cationic ratio. XRD showed slight variations in the d-spacing between the hydrotalcites. The thermal decomposition of carbonate hydrotalcites consists of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation and decarbonation of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where the first step is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting with the interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding metal oxides and spinels, including MgO, MgAl₂O₄, and MgFeAlO₄.     

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.     

Thermal Decomposition of Barium Dioxodiaquaperoxyoxalato Uranate(VI) Hydrate

Barium dioxodiaquaperoxyoxalatouranate was obtained by reaction of uranyl nitrate with oxalic acid and then hydrogen peroxide in the presence of barium ion. The complex was subjected to chemical analysis. The thermal decomposition behaviour of the complex was studied using TG, DTG and DTA techniques. The solid complex salt and the intermediate product of its thermal decomposition were characterized using IR absorption and X-ray diffraction spectra. Based on data from these physico-chemical investigations the structural formula of the complex was proposed as Ba[UO₂(O₂)(C₂O₄)(H₂O)₂]⋅H₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of mechanism of thermal decomposition of Mg,Ca and Zn hydrazidocarbonates by evolved gas analysis

Hydrazo-carbonates are complex compounds and products of the reactions between solutions of metal ion and solutions of hydrazido-carbonic acid. The decomposition of Mg(N₂H₃COO)₂. 2H₂O, Ca(N₂H₃COO)₂·H₂O and Zn(N₂H₃COO)₂ in inert atmosphere were studied. By classical thermoanalytical methods and data on the composition of the intermediates and final products the mechanisms of the thermal decomposition could not be resolved therefore also evolved gas analysis was used (EGA). The first step of thermal decomposition of Ca and Mg hydrazidocarbonates is dehydration. With the heating the decomposition of the hydrazido-carbonates proceeds under evolution of the ammonia, carbon monoxide and/or nitrogen and carbon dioxide giving as the intermediates for calcium and magnesium compounds the corresponding carbonates oxides as the final products. The zinc compound decomposes to the oxide, ZnO but also zinc cyanamide was detected during to the thermal treatment.     

Thermal decomposition of the synthetic hydrotalcite iowaite

The thermal stability and thermal decomposition pathways for synthetic iowaite have been determined using thermogravimetry in conjunction with evolved gas mass spectrometry. Chemical analysis showed the formula of the synthesised iowaite to be Mg_6.27Fe_1.73(Cl)_1.07(OH)₁₆(CO₃)_0.336.1H₂O and X-ray diffraction confirms the layered structure. Dehydration of the iowaite occurred at 35 and 79°C. Dehydroxylation occurred at 254 and 291°C. Both steps were associated with the loss of CO₂. Hydrogen chloride gas was evolved in two steps at 368 and 434°C. The products of the thermal decomposition were MgO and a spinel MgFe₂O₄. Experimentally it was found to be difficult to eliminate CO₂ from inclusion in the interlayer during the synthesis of the iowaite compound and in this way the synthesised iowaite resembled the natural mineral.     

Melting behaviour and evolved gas analysis of xylose

Two enantiomeric forms of xylose were identified as α-D-xylopyranose and α-L-xylopyranose by powder diffraction. Their melting behaviour was studied with conventional DSC and StepScan DSC method, the decomposition was studied with TG and evolved gases were analyzed with combined TG-FTIR technique. The measurements were performed at different heating rates. The decomposition of xylose samples took place in four steps and the main evolved gases were H₂O, CO₂ and furans. The initial temperature of TG measurements and the onset and peak temperatures of DSC measurements were moved to higher temperatures as heating rates were increased. The decomposition of L-xylose started at slightly higher temperatures than that of D-xylose and L-xylose melted at higher temperatures than D-xylose. The differences were more obvious at low heating rates. There were also differences in the melting temperatures among different samples of the same sugar. The StepScan measurements showed that the kinetic part of melting was considerable. The melting of xylose was anomalous because, besides the melting, also partial thermal decomposition and mutarotation occurred. The melting points are affected by both the method of determination and the origin and quality of samples. Melting point analysis with a standardized method appears to be a good measure of the quality of crystalline xylose. However, the melting point alone cannot be used for the identification of xylose samples in all cases.     

Kinetic parameters of unsaturated polyester resin modified with poly(ε -caprolactone)

The mineral sabugalite (HAl)_0.5[(UO₂)₂(PO₄)]₂⋅8H₂O, has been studied using a combination of energy dispersive X-ray analysis, X-ray diffraction, dynamic and controlled rate thermal analysis techniques. X-ray diffraction shows that the starting material in the thermal decomposition is sabugalite and the product of the thermal treatment is a mixture of aluminium and uranyl phosphates. Four mass loss steps are observed for the dehydration of sabugalite at 48°C (temperature range 39 to 59°C), 84°C (temperature range 59 to 109°C), 127°C (temperature range 109 to 165°C) and around 270°C (temperature range 175 to 525°C) with mass losses of 2.8, 6.5, 2.3 and 4.4%, respectively, making a total mass loss of water of 16.0%. In the CRTA experiment mass loss stages were found at 60, 97, 140 and 270°C which correspond to four dehydration steps involving the loss of 2, 6, 6 and 2 moles of water. These mass losses result in the formation of four phases namely meta(I)sabugalite, meta(II)sabugalite, meta(III)sabugalite and finally uranyl phosphate and alumina phosphates. The use of a combination of dynamic and controlled rate thermal analysis techniques enabled a definitive study of the thermal decomposition of sabugalite. While the temperature ranges and the mass losses vary due to the different experimental conditions, the results of the CRTA analysis should be considered as standard data due to the quasi-equilibrium nature of the thermal decomposition process. The online version of the original article can be found at     

Dynamic and controlled rate thermal analysis of hydrozincite and smithsonite

The understanding of the thermal stability of zinc carbonates and the relative stability of hydrous carbonates including hydrozincite and hydromagnesite is extremely important to the sequestration process for the removal of atmospheric CO₂. The hydration-carbonation or hydration-and-carbonation reaction path in the ZnO-CO₂-H₂O system at ambient temperature and atmospheric CO₂ is of environmental significance from the standpoint of carbon balance and the removal of green house gases from the atmosphere. The dynamic thermal analysis of hydrozincite shows a 22.1% mass loss at 247°C. The controlled rate thermal analysis (CRTA) pattern of hydrozincite shows dehydration at 38°C, some dehydroxylation at 170°C and dehydroxylation and decarbonation in a long isothermal step at 190°C. The CRTA pattern of smithsonite shows a long isothermal decomposition with loss of CO₂ at 226°C. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of zinc carbonate minerals via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. The CRTA technology offers a mechanism for the study of the thermal decomposition and relative stability of minerals such as hydrozincite and smithsonite.     

Energetic calcium(II) complexes of 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)1,2,4,5-tetrazine: synthesis,crystal structure,and thermal properties

We synthesized two calcium salts of 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz): [Ca₂(BTATz)₂(H₂O)₈·6H₂O] (1) and Ca(BTATz)(phen)(H₂O)₅·4H₂O (2). Complexes 1 and 2 were characterized by elemental analysis, Fourier transform infrared spectrometry, and single-crystal X-ray diffraction. Structural analysis revealed that Ca(II) was present in different coordination structures in the two complexes. Complex 1 exhibited a symmetric octahedral coordination that included three nitrogens and five water molecules. Complex 2 formed an asymmetric seven-coordinate structure with calcium connected to nitrogen in BTATz and to oxygens. The thermal behaviors of 1 and 2 were characterized via differential scanning calorimetry and thermogravimetry–differential thermal gravimetry. The peak thermal decomposition temperatures of 1 and 2 was 557.39 and 573.86 K, respectively. The kinetic equations of the main exothermic decomposition reaction were also derived. Moreover, the thermal safety of the complexes was evaluated by calculating some important thermodynamic parameters, such as self-accelerated decomposition temperature, thermal ignition temperature, and critical temperature of thermal explosion. Results indicated that both complexes exhibit good potential as a propellant component.     

Thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O: II. Identification of the gaseous products

The main goal of the presented work was to verify the previously assumed decomposition stages of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O (HACOT) [Thermochim. Acta 354 (2000) 45] under different atmospheres (inert, oxidising and reducing). The gaseous products of the decomposition were qualitatively and quantitatively analysed by mass spectrometry (MS) and Fourier-transformed infrared spectroscopy (FT-IR). It was confirmed that the gaseous products of HACOT decomposition under studied atmospheres there were H₂O (stage I) and NH₃, CO₂ (stage II). The main gaseous products in the third stage in argon and hydrogen (20 vol.% H₂/Ar) were CO and CO₂, whereas in air (20 vol.% O₂/Ar) only CO₂ was identified. Under the oxidising as well as reducing atmospheres the influence of secondary reactions on the composition of both, solid and gaseous products was found particularly strong during the third stage of the process. The studies of the multistage decomposition of HACOT, additionally complicated by many secondary reactions, required application of the hyphenated TA-MS or TA-FT-IR techniques combined with the pulse thermal analysis PTA^® allowing quantification of the spectroscopic signals and investigation of gas-solid and gas-gas reactions in situ.     

Thermal Analysis of Manganese(II) Complexes With Glycine

The thermal decomposition behaviour of the manganese(II) complexes with glycine: Mn(gly)Cl₂(H₂O)₂, Mn(gly)₂Cl₂, Mn(gly)Br₂(H₂O)₂, Mn(gly)₂Br₂(H₂O)₂ was investigated by means of TG-DTG-DTA, Hi-Res-TA and DSC techniques. The evolved gas analysis was carried out by means of the coupled TG-FTIR system. Heating of the complexes results first in the release of water molecules. Next, the multi-stage decomposition process with degradation of glycine ligand occurs. Water, carbon dioxide and ammonia were detected in the gaseous products of the complexes decomposition. The temperature of NH₃ evolution from the complexes is higher than from free glycine. The final residue in the air atmosphere is Mn₂O₃ which transforms into Mn₃O₄ at 930°C. In a nitrogen atmosphere, the complexes decompose into MnO. This revised version was published online in August 2006 with corrections to the Cover Date.     

热分析与气相色谱联用研究一水合草酸氢钾

用热分析与气相色谱联用技术(TA-GC)研究KHC₂O₄·H₂O的热分解表明,在空气和氦气当中,开始时缓慢分解,放出结晶水。接着KHC₂O₄快速分解成K₂C₂O₄,并释放出一些气体产物：O₂(分解初期)、CO、CO₂和H₂O。讨论了KHC₂O₄的分解机理。     

Controlled rate thermal analysis of hydromagnesite

The reaction of magnesium minerals such as brucite with CO₂ is important in the sequestration of CO₂. The study of the thermal stability of hydromagnesite and diagenetically related compounds is of fundamental importance to this sequestration. The understanding of the thermal stability of magnesium carbonates and the relative metastability of hydrous carbonates including hydromagnesite, artinite, nesquehonite, barringtonite and lansfordite is extremely important to the sequestration process for the removal of atmospheric CO₂. This work makes a comparison of the dynamic and controlled rate thermal analysis of hydromagnesite and nesquehonite. The dynamic thermal analysis of synthetic hydromagnesite proves that dehydration takes place in two steps at 135 and 184°C, dehydroxylation at 412°C and decarbonation at 474°C. Controlled rate thermal analysis shows the first dehydration step is isothermal and the second quasi-isothermal at 108 and 145°C, respectively. In the CRTA experiment both water and carbon dioxide are evolved in an isothermal decomposition at 376°C. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of magnesium carbonates such as nesquehonite via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal partial nesquehonite structure.     

Zum thermischen Verhalten von Aluminiumfluoridhydroxidhydrat AlF2,3(OH)0,7(H2O)

The Thermal Behaviour of Aluminium Fluoridehydroxide Hydrate AlF_2.3(OH)_0.7(H₂O) The thermal decomposition of AlF_2,3(OH)_0,7(H₂O) depends strongly on the partial pressure of the gaseous reaction products and proceeds in three overlapping steps, namely dehydratation, formation of x-ray amorphous Al₂O₃ and metastable β-AlF₃, and formation of α-AlF₃ and α-Al₂O₃. Beside that an exchange of F/OH takes place. The vaporization is mainly determined by the crucible type and pressure conditions, as shown by simultaneous TG-MS measurements too. Main gaseous species are H₂O and HF. The gas complexes HAlF₄, and H₂AlF₅ are observed.