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.     

Thermal decomposition of natural iowaite

The thermal decomposition of natural iowaite of formula Mg₆Fe₂(Cl,(CO₃)_0.5)(OH)₁₆·4H₂O was studied by using a combination of thermogravimetry and evolved gas mass spectrometry. Thermal decomposition occurs over a number of mass loss steps at 60°C attributed to dehydration, 266 and 308°C assigned to dehydroxylation of ferric ions, at 551°C attributed to decarbonation and dehydroxylation, and 644, 703 and 761°C attributed to further dehydroxylation. The mass spectrum of carbon dioxide exhibits a maximum at 523°C. The use of TG coupled to MS shows the complexity of the thermal decomposition of iowaite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition of the synthetic hydrotalcite woodallite

The thermal stability and thermal decomposition pathways for synthetic woodallite have been determined using thermogravimetry in conjunction with evolved gas mass spectrometry. Chemical analysis showed the formula of the synthesised woodallite to be Mg_6.28Cr_1.72Cl(OH)₁₆(CO₃)_0.36⋅8.3H₂O and X-ray diffraction confirms the layered LDH structure. Dehydration of the woodallite occurred at 65°C. Dehydroxylation occurred at 302 and 338°C. Both steps were associated with the loss of carbonate. Hydrogen chloride gas was evolved over a wide temperature range centred on 507°C. The products of the thermal decomposition were MgO and a spinel MgCr₂O₄. Experimentally it was found to be difficult to eliminate CO₂ from inclusion in the interlayer during the synthesis of the woodallite compound and in this way the synthesised woodallite resembled the natural mineral.     

Thermal decomposition of synthetic hydrotalcites reevesite and pyroaurite

A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of synthetic hydrotalcites reevesite (Ni₆Fe₂(CO₃)(OH)₁₆·4H₂O) and pyroaurite (Mg₆Fe₂(SO₄,CO₃)(OH)₁₆·4H₂O) and the cationic mixtures of the two minerals. XRD patterns show the hydrotalcites are layered structures with interspacing distances of around 8.0. Å. A linear relationship is observed for the d(001) spacing as Ni is replaced by Mg in the progression from reevesite to pyroaurite. The significance of this result means the interlayer spacing in these hydrotalcites is cation dependent. High resolution thermal analysis shows the decomposition takes place in 3 steps. A mechanism for the thermal decomposition is proposed based upon the loss of water, hydroxyl units, oxygen and carbon dioxide.     

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.     

Thermal properties of epoxy resin nanocomposites based on hydrotalcites

Epoxy resin nanocomposites containing home-made hydrotalcites (HTlc) have been prepared and their properties have been studied and compared with those of montmorillonite (MMT)-type layered silicates-based nanocomposites. Nanofiller dispersion in the polymer matrix has been evaluated by transmission (TEM) electron microscopy and wide angle X-ray diffraction (WAXD), while nanocomposite thermal properties have been studied in detail by thermogravimetric analysis (TGA/DTG) and cone calorimeter tests.The morphological studies have shown that the compatibilisation of the above two type of nanofillers allowed us to obtain nanostructured materials. As far as thermal properties are concerned, nanocomposites based on HTlc are found to decompose, both in air and nitrogen, following a trend similar to that of the neat polymer matrix, while in the case of the nanocomposite based on the organophilic MMT a slight improvement was found in air. Conversely, cone calorimetric tests have demonstrated that only the organophilic hydrotalcite was capable of decreasing the peak of the heat release rate in a relevant way.     

Raman spectroscopy of synthetic and natural iowaite

The chemistry of a magnesium based hydrotalcite known as iowaite Mg6Fe2Cl2(OH)16.4H2O has been studied using Raman spectroscopy. Iowaite has chloride as the counter anion in the interlayer. The formula of synthetic iowaite was found to be Mg5.78Fe2.09(Cl,(CO3)0.5)(OH)16.4H2O. Oxidation of natural iowaite results in the formation of Mg4FeO(Cl,CO3) (OH)8.4H2O. X-ray diffraction (XRD) shows that the iowaite is a layered structure with a d(001) spacing of 8.0 angtsroms. For synthetic iowaite three Raman bands at 1376, 1194 and 1084 cm(-1) are attributed to CO3 stretching vibrations. These bands are not observed for the natural iowaite but are observed when the natural iowaite is exposed to air. The Raman spectrum of natural iowaite shows three bands at 708, 690 and 620 cm(-1) and upon exposure to air, two broad bands are found at 710 and 648 cm(-1). The Raman spectrum of synthetic iowaite has a very broad band at 712 cm(-1). The Raman spectrum of natural iowaite shows an intense band at 527 cm(-1). The air oxidized iowaite shows two bands at 547 and 484 cm(-1) attributed to the (CO3)(2-)nu2 bending mode. Raman spectroscopy has proven most useful for the study of the chemistry of iowaite and chemical changes induced in natural iowaite upon exposure to air.     

Thermal decomposition of the hydrotalcite

Summary A combination of thermogravimetry and hot stage Raman spectroscopy has been used to study the thermal decomposition of the synthesised zinc substituted takovite Zn₆Al₂CO₃(OH)₁₆·4H₂O. Thermogravimetry reveals seven mass loss steps at 52, 135, 174, 237, 265, 590 and ~780°C. MS shows that the first two mass loss steps are due to dehydration, the next two to dehydroxylation and the mass loss step at 265°C to combined dehydroxylation and decarbonation. The two higher mass loss steps are attributed to decarbonation. Raman spectra of the hydroxyl stretching region over the 25 to 200°C temperature range, enable identification of bands attributed to water stretching vibrations, MOH stretching modes and strongly hydrogen bonded CO₃^2--water bands. CO₃^2- symmetric stretching modes are observed at 1077 and 1060 cm^-1. One possible model is that the band at 1077 cm^-1is ascribed to the CO₃^2- units bonded to one OH unit and the band at 1092 cm^-1is due to the CO₃^2- units bonded to two OH units from the Zn-takovite surface. Thermogravimetric analysis when combined with hot stage Raman spectroscopy forms a very powerful technique for the study of the thermal decomposition of minerals such as hydrotalcites.</o:p>     

Thermal decomposition and non-isothermal decomposition kinetics of carbamazepine

The thermal stability and kinetics of isothermal decomposition of carbamazepine were studied under isothermal conditions by thermogravimetry (TGA) and differential scanning calorimetry (DSC) at three heating rates. Particularly, transformation of crystal forms occurs at 153.75°C. The activation energy of this thermal decomposition process was calculated from the analysis of TG curves by Flynn-Wall-Ozawa, Doyle, distributed activation energy model, ?atava-?esták and Kissinger methods. There were two different stages of thermal decomposition process. For the first stage, E and logA [s^?1] were determined to be 42.51 kJ mol^?1 and 3.45, respectively. In the second stage, E and logA [s^?1] were 47.75 kJ mol^?1 and 3.80. The mechanism of thermal decomposition was Avrami-Erofeev (the reaction order, n = 1/3), with integral form G(α) = [?ln(1 ? α)]^1/3 (α = ～0.1–0.8) in the first stage and Avrami-Erofeev (the reaction order, n = 1) with integral form G(α) = ?ln(1 ? α) (α = ～0.9–0.99) in the second stage. Moreover, ΔH ^≠, ΔS ^≠, ΔG ^≠ values were 37.84 kJ mol^?1, ?192.41 J mol^?1 K^?1, 146.32 kJ mol^?1 and 42.68 kJ mol^?1, ?186.41 J mol^?1 K^?1, 156.26 kJ mol^?1 for the first and second stage, respectively.     

Thermal behavior and decomposition kinetics of composite solid propellants in the presence of amide burning rate suppressants

The employment of burning rate suppressants in the solid rocket propellant formulation is long known. Different research activities have been conducted to well understand the mechanism of suppression, but literature about the action of oxamide (OXA) and azodicarbonamide (ADA) on the thermal decomposition of composite propellant is still scarce. The focus of this study is on investigating the effect of burning rate suppressants on the thermal behavior and decomposition kinetics of composite solid propellants. Thermogravimetric analysis (TG) and differential thermal analysis have been used to identify the changes in the thermal and kinetic behaviors of coolant-based propellants. Two main decomposition stages were observed. It was found that OXA played an inhibition effect on both stages, whereas the ADA acts as a catalyst in the first stage and as coolant in the second one. The activation energy dependent on the conversion rate was estimated by two model-free integral methods: Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) based on the TG data obtained at different heating rates. The mechanism of action of coolants on the decomposition of solid propellants was confirmed by the kinetic investigation as well.     

The thermal decomposition of Mg-Al hydrotalcites: effects of interlayer anions and characteristics of the final structure

The thermal decomposition of hydrotalcites (HTs) with different interlayer anions in the 298-523 K region has been investigated by using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and IR, 27Al MAS-NMR and X-ray absorption near-edge structure (XANES) spectroscopy. The thermal stability of the HT with interlayer oxalate was remarkably higher than that of HTs with interlayer carbonate; the onset temperatures for decomposition were 523 K and 473 K, respectively. It is proposed that the basicity of the interlayer anion is the key factor in the onset of dehydroxylation of the brucite-like layers: the lower the basicity, the more thermally stable the HT compound. After heat treatment at 723 K, small Mg(Al)O domains (approximately 5 nm) within the HT crystallites cause broadening of the XRD reflections. The electron diffraction pattern consists of spots and rings, due to nonrandomly oriented crystalline material. Formation of disordered bonds, caused by nonideal packing between the decomposing adjacent cation layers in the (111) direction, could explain the expanded d value in the resulting MgO-like phase observed with XRD and electron diffraction. The orientation of the Mg(Al)O domains in the heat-treated material may be crucial for the so-called "memory effect" of HTs.     

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 characteristic parameters for the outer material of composite hydrogen storage tank by cone calorimeter

This paper presents the investigation of Al₂O₃/PAG nanolubricant performance for a compact vehicle mobile air conditioning (MAC) system. The Al₂O₃/PAG nanolubricant in this study is prepared by using two-step preparation method and stabilized using 4-Step UV–Vis Spectral Absorbency Analysis. An enhancement in the coefficient of performance (COP), reduction in compressor work, and enhancement in the cooling capacity of MAC employing Al₂O₃/PAG nanolubricant are recorded up to 31%, 26% and 32%, respectively, for 0.010% volume concentration. The current MAC performance is compared with MAC employing SiO₂/PAG nanolubricant from previous study. The comparison shows that the Al₂O₃/PAG nanolubricant has better performance in term of cooling capacity, compressor work, and COP at an average of 6%, 8%, and 33%, respectively. Therefore, the finding from this study suggests Al₂O₃/PAG nanolubricant with a volume concentration of 0.010% as an optimum and best performance nanolubricant for MAC systems.

     

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 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 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 ethane

The decomposition of C₂H₆ in Ar was studied by laser-absorption and laser-schlieren measurements of the reaction rate behind incident shock waves with 1300 < T < 2500°K and 1.1 < ρ < 4.4 × 10^?6 mol/cm³. The experimental profiles were parameterized by suitable measures of reaction progress. Computer simulations using a 14-reaction mechanism were used to compare assumptions about rate constant expressions with the experimental parameters and to investigate the sensitivity of computed parameters to these assumptions. A rate constant expression k(cm³/mol˙sec) = 2 × 10¹¹¹ T^?25.26 exp(?80 320/T) was found for the primary dissociation step C₂H₆ + M ? CH₃ + CH₃ + M under the conditions studied; no difference in rate was discernable between M ? Ar and M ? C₂H₆. Rate constant expressions found to be suitable for the remaining reactions of the mechanism, to some of which the computed parameters were sensitive, were in accord with previous proposals. Our results and results from earlier investigations of the primary decomposition reaction, in both forward and reverse directions, were extrapolated, using RRK methods, to obtain low-pressure limiting rate constants and found to be concordant.