Thermal decomposition of ammonium fluoromanganates(III)

The thermal decomposition of ammonium fluoromanganates (III) has been investigated in air and argon by simultaneous thermogravimetry and differential thermal analysis. Chemical analysis, X-ray powder data, and infrared spectra have been employed to characterise the intermediate and final products. The thermal decomposition can be described by the sequence (NH₄₃MnF₆ → (NH₄)₂MnF₅ → NH₄MnF₄ → MnF₂. Although penta- and tetra-fluoromanganates are well-defined compounds, the intermediate states could not be separated. In addition, a high temperature form of ammonium hexafluoromanganate has been observed.     

The use of TG/DSC–FT-IR to assess the effect of Cr sorption on struvite stability and composition

Struvite (MgNH₄PO₄·6H₂O; MAP) can be recovered from animal and human wastes for use as fertilizer. This encourages the sustainable use of phosphorus (P), closing the human P cycle. The toxic metalloid chromium (Cr) is a common component of wastes, and can substitute for P in geochemical and biological systems. Thus, its sorption to, and effect on the stability and composition of recovered MAP requires assessment. MAP precipitated from solutions with 1?C100???M Cr(III) had higher Cr loadings compared to those reacted in the presence of Cr(VI), indicative of higher sorption affinity of the lower oxidation state. Simultaneous thermal analysis of unreacted MAP revealed an endothermic peak at 126?±?0.5?°C by DSC with a mass loss of 52.9% by TG. Sorption of Cr produced minimal effects on the transition temperature and overall mass loss. The inflection in the TG curve indicated that Cr increased the temperature of maximum decomposition, but also the mass loss at this point. Combining TG results with FT-IR spectra revealed that for initial concentrations of 10?C50???M Cr(III) and 1?C5???M Cr(VI), NH₄ ⁺ was added, and H₂O(s) lost from the MAP structure. The change in composition was consistent with substitution of Cr(III) or Cr(VI) into the MAP structure. The TG/DSC?CFT-IR technique confirmed that Cr contamination affects the MAP composition and may accelerate the release of nutrients upon mineral decomposition. This has implications for the use of MAP fertilizers and subsequent cycling of P and contaminants in agricultural systems.     

Textural and catalytic properties of the FexOy/Fe-KClO4 system

Selected properties of commercial iron powders, standardised in the atmosphere of hydrogen, have been studied. The reactivity of iron oxides in the thermal decomposition of KClO₄ in the solid-state mechanical mixture of Fe and KClO₄ containing 9, 13, 17, 21 and 25 wt.% of KClO₄, respectively, has been tested by the differential thermal analysis (DTA) and thermogravimetric analysis (TG). It has been established that the Fe₃O₄ phase on the surface of the iron powder act as an effective catalysts in the thermal decomposition of KClO₄.     

Production and decomposition of highly excited 2-butyl radicals by the addition of hot hydrogen atoms to but-2-ene. Cross section for the addition reaction

Highly excited 2-butyl radicals have been generated by addition of hot hydrogen atoms to but-2-ene. Atoms of initial energy 130 kJ mol^?1 and 161 kJ mol^?1 were produced by photolysis of H₂S. Rates of decomposition of the highly excited 2-butyl radicals were monitored by analysis of stabilization and decomposition products, and the extent of energy-loss of the hydrogen atoms in nonreactive collisions assessed by measuring the effect of added xenon on product yields. A model involving the cross-section for the addition reaction, energy transfer in nonreactive collisions between hydrogen atoms and but-2-ene, RRKM rate constants for decomposition of excited 2-butyl radicals, and collisional energy transfer from the radicals, has been used to calculate product yields for comparison with experimental values. It is concluded that the cross-section for addition of hydrogen atoms of energy about 130 kJ mol^?1 to but-2-ene is 0.055 ± 0.028 nm². This value is compatible with the A factor for the thermal addition reaction.     

Thermoanalytical studies of natural potassium, sodium and ammonium alunites

Dynamic and controlled rate thermal analysis (CRTA) has been used to characterise alunites of formula [M(Al)₃(SO₄)₂(OH)₆] where M⁺ is the cations K⁺, Na⁺ or NH₄ ⁺. Thermal decomposition occurs in a series of steps: (a) dehydration, (b) well-defined dehydroxylation and (c) desulphation. CRTA offers a better resolution and a more detailed interpretation of water formation processes 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 water formation reveal the subtle nature of dehydration and dehydroxylation.     

Thermal and structural investigation of some oxalato-niobium complexes

Strontium tris(oxalato)oxoniobate, Sr₃[NbO(C₂O₄)₃]₂ · 8 H₂O has been synthesized and characterized by elemental analysis, infrared spectroscopy and powder X-ray diffraction. A mechanism of thermal decomposition is suggested on the basis of differential thermal analysis. The conditions of strontium metaniobate formation, as final product of the thermal decomposition, have been established.     

Investigation of bismaleimide containing naphthalene unit. II. Thermal behavior and properties of polymer

Crosslinking of 2,7-bis(4-maleimidophenoxy)naphthalene (BMPN) and 4,4-bismaleimi-dophenylmethane (BMPM) was investigated in the presence of 4,4-diaminodiphenylmethane (DDM) at the 2/1 molar ratio of bismaleimide/DDM. Their curing behaviors were characterized by infrared spectroscopy and differential scanning calorimetry. The presence of a naphthalene group in the backbone of the bismaleimide increased the curing temperature and reduced the polymerization reactivity. The exotherm was shifted to a lower temperature as the amine addition lead to chain extension. Thermal behavior and properties of cured products were investigated by thermogravimetric analyses and dynamic mechanical analyses. Also, at this molar ratio, the properties of the BMPN/DDM showed better T_g, thermal decomposition temperature, and moisture resistance than the epoxy derived from 2,7-dihydroxynapthalene cured with DDM system (DGEDN/DDM). © 1996 John Wiley & Sons, Inc.     

Correlation Between the Surface Acid-base Nature of Solid Metal Oxides and Temperature of CaSO4 Decomposition

By means of the combined use of scanning electron microscopy+energy dispersive spectrometry(SEM+EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetry (TG), the thermal decomposition of gypsum and gypsum bonded investment used for casting jewellery products has been studied in order to gain a further insight into the origin of the gas porosity in gold-based alloys produced via lost wax casting. The occurrence of the defect is related to the thermal decomposition of CaSO₄ that constitutes with silica the investment material and the decomposition of which takes place at a temperature very close to the casting temperature of some typical gold alloys. The decrease of the thermal decomposition temperature of gypsum is induced by the presence of silica and is related to the surface acid-base interaction between SiO₂ and CaSO₄. On the base of these results, the solid state thermal decomposition of calcium sulphate in the presence of other metal oxides characterised by different acid-base nature has been investigated and a correlation between the surface acid-base properties measured as isoelectric point of the solid surface (IEPS) and via XPS analysis and the temperature of CaSO₄ thermal decomposition is observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermoanalytical studies of silver and lead jarosites and their solid solutions

Dynamic and controlled rate thermal analysis has been used to characterise synthesised jarosites of formula [M(Fe)₃(SO₄)₂(OH)₆] where M is Pb, Ag or Pb–Ag mixtures. Thermal decomposition occurs in a series of steps. (a) dehydration, (b) well defined dehydroxylation and (c) desulphation. CRTA offers a better resolution and a more detailed interpretation of water formation processes 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 water formation reveal the subtle nature of dehydration and dehydroxylation. CRTA offers a better resolution and a more detailed interpretation of the decomposition processes 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 separation of the dehydroxylation steps, since in these cases a higher energy (higher temperature) is needed to drive out gaseous decomposition products through a decreasing space at a constant, pre-set rate.     

The Thermal Conversion of Lepidocrocite (γ-FeOOH) Revisited

The thermal conversion of lepidocrocite (γ-FeOOH) into maghemite (γ-Fe₂O₃)and hematite (α-Fe₂O₃) has been studied by dynamic (DSC) and static heating experiments. Dynamic heating defines two main regions: conversion of lepidocrocite to maghemite (endothermal signal peaking at 255°C) and conversion of maghemite to hematite (exothermal signal peaking at 450°C). In addition, an exotherm following the lepidocrocite to maghemite endotherm is observed. The maghemite phase appears as porous aggregates of nanocrystals characterized by an extensive spin-canting. We suggest that the additional exotherm is associated with structural changes and a decreasing extent of spin-canting in the maghemite phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on energetic compounds

Summary Bis(propylenediamine)metal perchlorate (BPMP) complexes like [M(pn)₂](ClO₄)₂ (where M=Cr, Mn, Ni, Cu, Zn and pn=propylenediamine) have been prepared and characterized by gravimetric methods, infrared and elemental analysis. Thermal properties have been studied using simultaneous thermogravimetry-differential thermal analysis in atmospheres of nitrogen and air to examine the effect of atmospheric change on thermal decomposition of these complexes. Changing of the atmosphere does not cause any measurable changes in the decomposition of complexes. However, as indicated by thermoanalytical techniques, the thermal stability of present complexes decreases in the order: [Cr(pn)₂](ClO₄)₂>[Mn(pn)₂](ClO₄)₂>[Zn(pn)₂](ClO₄)₂>[Ni(pn)₂](ClO₄)₂>[Cu(pn)₂](ClO₄)₂. Isothermal thermogravimetry, over the temperature range of decomposition has been done for all the complexes. An analysis of the kinetics of thermal decomposition was made using a model fitting procedure as well as an isoconversional method, independent of any model. The results of both kinetic approaches have been discussed critically. The explosion delay (D_E) was measured to investigate the trend of rapid thermal analysis.     

Thermal decomposition of rare earth complexes withm-aminobenzoic acid

The conditions of thermal decomposition of the m-aminobenzoates of Y, La, Ce(III), Pr, Nd and Sm-Lu, Ln(C₆H₄NH₂COO)₃.nH₂O (n=4–6), have been studied.The hydrated compounds lose all molecules of crystallization water in one stage at 333–413 K. The anhydrous compounds are stable up to 570 K and are then decomposed exothermically to oxides.

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Zusammenfassung Es wurden die Bedingungen für die thermische Zersetzung derm-Aminobenzoate Ln(C₆H₄NH₂COO)₃.nH₂O (n=4–6) von Y, La, Ce(III), Pr, Nd und Sm-Lu untersucht. Alle Verbindungen geben ihr Kristallwasser in einem Schritt bei einer Temperatur zwischen 333 und 413 K ab. Die wasserfreien Verbindungen sind bis 570 K stabil und zersetzen sich dann exotherm unter Entstehung von Oxiden.

     

Studies on the thermal decomposition of the silver group of alkali metal nitritocobaltates(III)

The thermal decomposition of nitritocobaltate(III) of the silver group of general formula M₂Ag[Co(NO₂)₆] (where M = K⁺, NH⁺₄, Rb⁺ or Cs⁺) has been investigated. Based on the thermal curves of the investigated compounds and chemical and diffractometric analysis, the mechanism of thermal decomposition has been determined. The results obtained indicate that the decomposition proceeds in three stages. As a result of decomposition in the first stage (300°C), nitrates of alkali metals, metallic silver and Co₃O₄ are formed. In the second stage (500°C), a partial decomposition of nitrates to alkali metal oxides occurs, and in the third stage the products are alkali metal oxides, silver and Co₃O₄. This paper also presents the dependence of the decomposition temperature of nitritocobaltates(III) of the silver group on the ionic radius of the outer-sphere cation.     

Thermal behavior of Mannich base N,N′-tetra(4-antipyrylmethyl)-1,2-diaminoethane (TAMEN) and its complexes

The thermal decomposition in air and in nitrogen atmosphere of binuclear complex compounds of Cu(II) and Co(II) containing the Mannich base N,N′-tetra(4-antipyrylmethyl)-1,2 diaminoethane (TAMEN) as a ligand, Cu₂(TAMEN)Cl₄ and Co₂(TAMEN)Cl₄, were investigated. X-ray powder diffractometry, infrared spectroscopy and simultaneous thermogravimetry-differential thermal analysis (TG-DTA), have been used to characterize and to study the thermal behavior of these compounds. The results provided information concerning the stoichiometry, crystallinity, thermal stability and decomposition mechanism of the compounds.     

Thermoanalytical investigations of 4-methylpiperazine-1-carbodithioic acid ligand and its iron(III), cobalt(II), copper(II) and zinc(II) complexes

The thermal decomposition studies on 4-methylpiperazine-1-carbodithioic acid ligand (4-MPipzcdtH) and its complexes, viz. [M(4-MPipzcdtH)_n](ClO4)_n (M=Fe(III) when n=3; M=Co(II), Cu(II) when n=2) and [Zn(4-MPipzcdtH)₂]Cl₂ have been carried out using non-isothermal techniques (TG and DTA). Initial decomposition temperatures (IDT), indicate that thermal stability is influenced by the change of central metal ion. Free acid ligand exhibits single stage decomposition with a sharp DTA endotherm. Complexes, [M(4-MPipzcdtH)_n](ClO₄)_n undergo single stage decomposition with detonation and give rise to very sharp exothermic DTA curves while the complex [Zn(4-MPipzcdtH)₂]Cl₂ shows three-stage decomposition patterns. The kinetic and thermodynamic parameters, viz. the energy of activation E, the frequency factor A, entropy of activation S and specific rate constant k, etc. have been evaluated from TG data using Coats and Redfern equation. Based upon the results of the differential thermal analysis study, the [M(4-MPipzcdtH)_n](ClO₄)_n complexes have been found to possess characteristic of high energy materials.     

Thermal behavior of Mannich base N,N′-tetra(4-antipyrylmethyl)-1,2 diaminoethane (TAMEN) and its binuclear complexes

The thermal decomposition of Mannich base N,N′-tetra(4-antipyrylmethyl)-1,2-diaminoethane (TAMEN), and its Ni(II), binuclear complex, Ni₂(TAMEN)Cl₄, in air and in nitrogen atmosphere, were investigated. X-ray powder diffractometry, infrared spectroscopy and simultaneous thermogravimetry-differential thermal analysis (TG-DTA), have been used to characterize and to study the thermal behavior of these compounds. The results provided information concerning the stoichiometry, crystallinity, thermal stability and decomposition mechanism of the compound.     

Studies on high-temperature thermal transformation and dielectric property of aluminum–chromium phosphates

High-temperature thermal transformation of aluminum–chromium phosphates has been investigated by means of DSC–TG, IR, and XRD analysis. The relative dielectric constant and thermal decomposition were measured and discussed. The results show that crystallization and thermal decomposition started at about 1,273 K, only AlPO₄ and Cr₂O₃ have been found at 1,873 K due to the decomposition of PO ₃ ^? , P₂O ₇ ^2? , and PO ₄ ^3? . The relative dielectric constant is fluctuant.     

Studies on the thermal decomposition kinetics and mechanism of ammonium niobium oxalate

Ammonium niobium oxalate was prepared and characterized by elemental analysis, XRD and FTIR spectroscopy analysis, which confirmed that the molecular formula of the complex is NH₄(NbO(C₂O₄)₂(H₂O)₂)(H₂O)₃. Dynamic TG analysis under air was used to investigate the thermal decomposition process of synthetic ammonium niobium oxalate. It shows that the thermal decomposition occurs in three stages and the corresponding apparent activation energies were calculated with the Ozawa–Flynn–Wall and the Friedman methods. The most probable kinetic models of the first two steps decomposition of the complex have been estimated by Coats–Redfern integral and the Achar–Bridly–Sharp differential methods.     

Some transition metal nitrate complexes with hexamethylenetetramine

Three hexamethylenetetramine (HMTA) metal nitrate complexes such as [M(H₂O)₄(H₂O-HMTA)₂](NO₃)·4H₂O (where M=Co, Ni and Zn) have been prepared and characterized by X-ray crystallography. Their thermal decomposition have been studied by using dynamic, isothermal thermogravimery (TG) and differential thermal analysis (DTA). Kinetics of thermal decomposition was undertaken by applying model-fitting as well as isoconversional methods. The possible pathways of thermolysis have also been proposed. Ignition delay measurements have been carried out to investigate the response of these complexes under condition of rapid heating.     

A new method of synthesis of BiFeO<Subscript>3</Subscript> prepared by thermal decomposition of Bi[Fe(CN)<Subscript>6</Subscript>]·4H<Subscript>2</Subscript>O

In order to investigate the formation of the multiferroic BiFeO₃, the thermal decomposition of the inorganic complex Bismuth hexacyanoferrate (III) tetrahydrate, Bi[Fe(CN)₆]·4H₂O has been studied. The starting material and the decomposition products were characterized by IR spectroscopy, thermal analysis, laboratory powder X-ray diffraction, and microscopic electron scanning. The crystal structures of these compounds were refined by Rietveld analysis. BiFeO₃ were synthesized by the decomposition thermal method at temperature as low as 600 °C. There is a clear dependence of the type and amount of impurities that are present in the samples with the time and temperature of preparation.