Preparation and thermal stability of trioxalatocobaltates of bivalent metals KM2+ [Co(C2O4)3]·xH2O

Trioxalatocobaltates of bivalent metals KM²⁺[Co(C₂O₄)₃]·x H₂O, with M²⁺ = Ba, Sr, Ca and Pb, have been prepared, characterized and their thermal behaviour studied. The compounds decompose to yield potassium carbonate, bivalent metal carbonate or oxide and cobalt oxide as final products. The formation of the final products of decomposition is influenced by the surrounding atmosphere. Bivalent metal cobaltites of the types KM²⁺CoO₃ and M²⁺CoO_3—x are not identified among the final products of decomposition. The study brings out the importance of the decomposition mode of the precursor in producing the desired end products.     

Crystallization kinetics of calcium carbonate at a stoichiometric ratio of components

The formal kinetics of calcium carbonate crystallization in aqueous solutions is studied at a stoichiometric ratio of Ca²⁺ and CO₃^2- ions. The kinetics of the process was monitored by convenient and reliable methods (complexometric analysis for calcium in an aqueous solution and energy dispersive and microscopic measurement of solid particle sizes). The effect the temperature and degree of supersaturation have on the periods of induction and mass crystallization and the equilibrium concentration of calcium ions in solution is estimated at continuously controlled pH and solution ionic strength. The kinetic parameters (n, k, τ_1/2, E_a) of calcium carbonate crystallization are calculated. It is shown that calcium carbonate with a calcite structure formed at a stoichiometric ratio of reagents, and changes in the temperature (25–45°C) and the solution’s degree of supersaturation (2–6) within the considered range had no effect on the characteristics of the solid phase.     

Thermal decomposition of basic zinc carbonate in nitrogen atmosphere

Dynamic kinetic analyses were performed on basic zinc carbonate using TG and DTA measurements in N₂. The thermal behavior and the kinetics of decomposition were studied. The effect of procedural variables on the kinetics was investigated. In this work, the procedural variables included heating rate and sample size. To estimate the activation energy of decomposition, the Friedman isoconversional method was applied. The activation energy (E_a) was calculated as a function of conversion (a).     

The solubility and kinetics of decomposition of ozone in aqueous solutions of nitrates

The influence of the concentration of NaNO₃ on the solubility of ozone in water was studied at 20, 30, and 40°C. The solubility coefficients of ozone were calculated, and the Henry constants and Sechenov coefficients determined. The Sechenov coefficients (K _c ) were found to decrease insignificantly as the temperature increased. The kinetics of dissolved O₃ transformations was analyzed. The decomposition of ozone was described by a pseudofirst-order equation with respect to salt concentration. The rate constant (k _c ) for the decomposition of ozone in the presence of NaNO₃ was found to be 3.5 × 10^?4 l mol^?1 s^?1.     

Studies on kinetics and mechanism of initial thermal decomposition of nitrocellulose

The thermal decomposition of nitrocellulose (NC) 12.1% N, has been studied with regard to kinetics, mechanism, morphology and the gaseous products thereof, using thermogravimetry (TG), differential thermal analysis (DTA), IR spectroscopy, differential scanning calorimetry (DSC) and hot stage microscopy. The kinetics of the initial stage of thermolysis ofNC in condensed state has been investigated by isothermal high temperature infrared spectroscopy (IR). The decomposition ofNC in KBr matrix in the temperature range of 142–151°C shows rapid decrease in O?NO₂ band intensity, suggesting that the decomposition of NC occurs by the rupture of O?NO₂ bond. The energy of activation for this process has been determined with the help of Avrami-Erofe'ev equation (n=1) and is ≈188.35 kJ·mol^?1. Further, the IR spectra of the decomposition products in the initial stage of thermal decomposition ofNC, indicates the presence of mainly NO₂ gas and aldehyde.     

Isothermal and rising temperature kinetic studies of doped nonstoichiometric basic nickel carbonate

The techniques of thermal analysis are used to determine the mode of decomposition of nickel carbonates doped by the method of coprecipitation. Nickel carbonate prepared by this method is basic in nature with the stoichiometryxNiCO₃·yNi(OH)₂·zH₂O. Isothermal Thermogravimetry was applied to determine the mechanism of decomposition. Rising temperature Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) were used to study the effects of doping on the kinetics of the decomposition. Doping was found to strongly influence the kinetics of the decomposition. The kinetics of thermal decomposition of the doped carbonates were compared with conductivity studies. A compensation effect has been observed and is discussed, in the thermal decomposition of the doped nickel carbonates. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Cadmium complex possessing simultaneously silanethiolato- and dithiocarbamato-ligands. A novel single-source precursor of cadmium sulfide

Thermal decomposition of suitable coordination compounds may be used as efficient route for fabrication of semiconducting layers. A new potential CdS precursor—a cadmium complex with all-sulfur Cd-coordination sphere [Cd{μ-SSi(OBu ^t )₃}(S₂CNC₄H₈)]₂ 1—has been prepared, and its properties are investigated. The complex was obtained in the reaction between dimeric bis(tri-tert-butoxysilanethiolato)cadmium(II) [Cd{SSi(OBu ^t )₃}₂]₂ and ammonium N,N-tetrametylene-dithiocarbamate and characterized by spectral methods (IR, UV–Vis, MS, and NMR). X-ray structure analysis revealed the complex as molecular and dimeric in solid state with each of chelating dithiocarbamate ligands bonded to one Cd center and sulfur atoms from two tri-tert-butoxysilanethiolato ligands bridging metallic centers and thus completing the CdS₄ coordination sphere. Thin film of the precursor prepared on SiO₂ substrates via spin-coating technique was analyzed by AFM. Its decomposition was studied by thermal analysis methods (TG, DSC, and TG-FTIR). After melting at 227 °C, [Cd{μ-SSi(OBu ^t )₃}(S₂CNC₄H₈)]₂ undergoes endothermic decomposition leading to CdS as the only solid product further identified by XRD, EDS, FIR as hexagonal CdS form. Its morphology is characteristic and may be described as “micro-noodles”.     

Trimellitate complexes of divalent transition metals with hydrazinium cation

New dihydrazinium divalent transition metal trimellitate hydrates of empirical formula (N₂H₅)₂M(Html)₂·nH₂O, where n = 1 for M = Co or Ni, and n = 2 for M = Mn, Zn, or Cd (H₃tml = trimellitic acid), and monohydrazinium cadmium trimellitate, [(N₂H₅)Cd(Html)_1.5·2H₂O] have been prepared and characterized by physico-chemical methods. Electronic spectroscopic, and magnetic moment data suggest that Co and Ni complexes adopt an octahedral geometry. The IR spectra confirm the presence of monodentate carboxylate anion (Δν = ν_asy(COO^?) ? ν_sym(COO^?) > 190 cm^?1) and coordinated N₂H₅ ⁺ ion (ν_N–N 1015 ? 990 cm^?1) in all the complexes. All the complexes undergo endothermic decomposition eliminating CO₂ in the temperature region 200–250 °C, followed by exothermic decomposition (in the range of 500–570 °C) of organic moiety to give the respective metal carbonate as the end products except nickel and cobalt complexes, which leave respective metal oxides. X-ray powder diffraction patterns reveal that Ni and Co complexes are isomorphous as are those of, Zn(II) and Cd(II) of the type, (N₂H₅)₂M(Html)₂·2H₂O.     

Solid-state decomposition studies on fluoroperoxo species of transition metals: Part XIII. Kinetics of isothermal decomposition of K2[V2O3(O2)F2] and K3[Ta(O2)2F4]

The kinetics of isothermal decomposition of K₂[V₂O₃(O₂)₂] and K₃[Ta(O₂)₂F₄] have been investigated in the temperature range 413–493 K using a constant volume apparatus. The α vs. time plots for both these solids are sigmoidal in nature. The kinetics obey the Avrami-Erofeev equation (n = 2) for the initial stage of the decomposition. The contracting volume equation fits well for the deceleratory region. The activation energies are 164.8 and 105.4 kJ mol⁻¹ for K₂[V₂O₃(O₂)₂F₂], and 85.2 and 76.6 kJ mol⁻¹ for K₃[Ta.(O₂)₂F₄].The absence of lattice water in these two solids may be responsible for the appearance of a short induction, followed by an acceleratory region in pristine solids, in contrast to hydrated fluoroperoxo zirconates, wherein the dehydration step preceding peroxide decomposition leads to facile nucleation and a deceleratory nature of decomposition.The kinetic characteristics of the decomposition of fluoroperoxo species so far studied are summarized and discussed.     

Preparation and thermal degradation kinetics of terpolymer poly(?-caprolactone-co-1,2-butylene carbonate)

Poly(?-caprolactone-co-1,2-butylene carbonate) (PBCCL) was successfully synthesized via terpolymerization of carbon dioxide, 1,2-butylene oxide(BO) and ?-caprolactone (CL). A polymer-supported bimetallic complex (PBM) was used as catalyst. The influences of various reaction conditions such as reaction content, reaction time and reaction temperature on properties of terpolymers were investigated. When CL content increased, the viscosity-average molecular weights (M_v), glass transition temperature (T_g) and decomposition temperature (T_d) of PBCCL improved relative to those of poly(1,2-butylene carbonate) (PBC). Prolonging the reaction time resulted in increase in M_v and T_g. As reaction temperature increased, the molar fractions of CL (fCL) increased obviously. When the reaction temperature went beyond 80 °C, the resulting copolymers tended to be crystalline. The thermal properties and degradation behaviors of PBCCL were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The apparent activation energy and thermal degradation model of PBCCL was estimated by means of Ozawa-Flynn-Wall method and Phadnis-Deshpande method, respectively. The results showed that T_g and T_d of the terpolymer PBCCL were much higher than those of PBC. The thermal degradation behavior of PBCCL was evidenced by one-step thermal degradation profile. The average apparent activation energy is 77.06 kJ/mol, the thermal degradation kinetics follows the power law thermal decomposition model.     

Activation energy of thermal decomposition of LaC2O4Br

The activation energy of the thermal decomposition of finely ground LaC₂O₄Br was determined according to the method of Ozawa asE _a=203.83 kJ mol^?1. As compared to the value for the parent oxalate La₂(C₂O₄)₃ E _a=130 kJ/mol), this value is higher by about 70 kJ/mol, which is consistent with the increased interaction between the metal and oxalate ions. The substitution of Br by Cl does not affect the decomposition kinetics profoundly.     

Stabilization of ammonium dinitramide in the liquid phase

The kinetics of accumulation of the main products of thermal decomposition of ammonium dinitramide in the melt was investigated. The isotope composition of nitrogen-containing gases evolved by the decomposition of ¹⁵NH₄N(NO₂)₂ and NH₄ ¹⁵N(NO₂)₂ was found. Easily oxidized salts, amines, amides, iodides, and other compounds soluble in the melt interfere with the liquid-phase decomposition of ammonium dinitramide.     

Thermal decomposition of [Co(NH3)5Cl]Cl2

The thermal decomposition of [Co(NH₃)₅Cl]Cl₂ was studied under non-isothermal conditions, in dynamic air and argon atmospheres. The kinetics of the particular stages of [Co(NH₃)₅Cl]Cl₂ thermal decomposition were evaluated from the dynamic weight loss data by means of the modified Coats-Redfern method. TheD _n andR _n models were selected as the models best fitting the experimental TG curves. These models suggest that the kinetics and macromechanism of [Co(NH₃)₅Cl]Cl₂ decomposition can be governed by diffusive and/or phase boundary processes. The values of the activation energy,E _a, and the pre-exponencial factor,A, of the particular stages of the thermal decomposition were calculated.     

Thermal decomposition of Cd(CH3COO)2·2H2O studied by a coupled TG-DTA-MS method

The thermal decomposition of cadmium acetate dihydrate in helium and in air atmosphere has been investigated by means of a coupled TG-DTA-MS method combined with X-ray diffraction analysis. Dehydration of Cd(CH₃COO)₂·2H₂O is a two-stage process with Cd(CH₃COO)₂·H₂O as intermediate. The way of Cd(CH₃COO)₂ decomposition strongly depends on the surrounding gas atmosphere and the rate of heating. CdO, acetone and CO₂ are the primary products of decomposition in air. In helium decomposition goes by two parallel and consecutive reactions in which intermediates, Cd and CdCO₃, are formed. Metallic cadmium oxidizes and cadmium carbonate decomposes giving CdO. Some of the metallic cadmium, depending on the heating rate and the concentration of oxygen, evaporates. Acetone is partially oxidized in secondary reactions with oxygen. This revised version was published online in July 2006 with corrections to the Cover Date.     

Decomposition of cyclic acetone peroxides in acid media

The kinetics and stoichiometry of the formation of active oxygen (AO) in the acidic decomposition of trimeric (TATP) and dimeric (DADP) cyclic acetone peroxides are considered. Fe(III) produced as a result of Fe(II) oxidation with active oxygen has been determined using rhodanide procedure. The kinetics of the formation of active oxygen is described by a first order equation. The effective rate constant of TATP decomposition depends on the Hammett acidity function H ₀: log k _eff = ?H ₀ ? 2.6 (k _eff is in s^?1). Consequently, the decomposition rate of TATP is limited by protonation. In the HCl and H₂SO₄ concentration range from 0.006 to 2.9 mol/L, the decomposition of DADP occurs with k _eff = 0.0010 ± 0003 s^?1 at a Fe(II) concentration of 3.5 mmol/L and k _eff depends linearly on the concentration of Fe(II).     

Thermal decomposition of aqueous manganese nitrate solutions and anhydrous manganese nitrate. Part 3. Isothermal kinetics

The kinetics of the thermal decomposition of aqueous manganese nitrate solutions and anhydrous manganese nitrate in air were established from isothermal experiments. By heating the solution, first most of the water evaporates to a composition of equimolar amounts of water and manganese nitrate; this concentrated solution then decomposes to γ-Mn(NO₂, NO₂ and water, usually in two steps. The first step can be described best by the model [?ln(1 ? α)]^{$\text{1}\text{2}$} = 8.9 × 10¹¹ exp(?121000/RT)t, whereas the second step is described equally well by several models. The kinetic parameters of these models are quite similar, the average activation energy being 141 kJ mole^?1.The decomposition of anhydrous Mn(NO₃)₂, which proceeds in a single step, can also be described with several similar models. In this case the average activation energy is about 92 kJ mole^?1.     

Preparation, thermal decomposition and lifetime of Eu(III)-phenanthroline complex doped xerogel

The main purpose of this work is proposing a new method of using non-isothermal formal kinetics analysis to predict the lifetime of luminescent complex materials. The Eu(III)-phenanthroline complex doped xerogel has been in situ synthesized by a catalyst-free sol-gel method. The photoluminescence spectra and TG curves of the xerogel verify the formation and decomposition of Eu(III)-phenanthroline complex in xerogel. The decomposition of the xerogel formally occurs in three steps. The Friedman and FWO isoconversional methods and multivariate non-linear regression method are used for formal kinetic analysis. The overall decomposition process below 800 °C is fitted by three-step consecutive reaction. The best fitted model for each step is F_n (n order reaction, the corresponding function f(α) is (1 − α)ⁿ). Correlation coefficient is 0.99956. The lifetime values of xerogel at different temperatures are predicted based on non-isothermal kinetic models by the 5% decomposition of europium organic complex.     

Thermal decomposition reaction kinetics of complexes of [Sm(o-MOBA)3bipy]2·H2O and [Sm(m-MOBA)3bipy]2·H2O

The complexes of [Sm(o-MOBA)₃bipy]₂·H₂O and [Sm(m-MOBA)₃bipy]₂·H₂O (o(m)-MOBA = o(m)-methoxybenzoic acid, bipy-2,2′-bipyridine) have been synthesized and characterized by elemental analysis, IR, UV, XRD and molar conductance, respectively. The thermal decomposition processes of the two complexes were studied by means of TG–DTG and IR techniques. The thermal decomposition kinetics of them were investigated from analysis of the TG and DTG curves by jointly using advanced double equal-double steps method and Starink method. The kinetic parameters (activation energy E and pre-exponential factor A) and thermodynamic parameters (ΔH ^≠ , ΔG ^≠ and ΔS ^≠) of the second-step decomposition process for the two complexes were obtained, respectively.     

Bond energies and thermal decomposition of [Pt(X)(CH3)(P(C2H5)3)2] complexes

The thermal decomposition of the complexes trans-[Pt(X)(CH₃)L₂] (L  P(C₂H₅)₃; X  Cl, Br, I, CN) in decalin at 170 and 200°C affords methane platinum metal and [Pt(X)₂L₂]. The kinetics of the decomposition of the complexes were determined by monitoring the appearance of methane by GLC. The observed first-order rate constant was found to be independent on the nature of the ligand X. The thermal decomposition of the trideuteriomethyl complexes [Pt(X)(CD₃)L₂] (X  I, CN) in decalin-d₁₈ at 170 and 200°C was studied by GLC/MS. The thermolysis affords CD₃H and CD₄ in ratios which are independent of the nature of X and of the temperature used. The mass spectra of the complexes were also examined. A relative scale of platinum-to-methyl bond dissociation energies has been established by measuring the appearance potential of the fragment ion [Pt(X)L₂]⁺ and the ionization energies in the series [Pt(X)(CH₃)L₂]. Ionization potentials and PtCH₃ bond energies show a clear dependence on the nature of X which is not reflected in corresponding changes in the decomposition rates.