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N. J. Carr

Bio: N. J. Carr is an academic researcher from Queen's University Belfast. The author has contributed to research in topics: Malonate & Thermal decomposition. The author has an hindex of 3, co-authored 5 publications receiving 118 citations.

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TL;DR: A kinetic and mechanistic study of the thermal decomposition of copper(II) malonate has been completed in which the rate measurements have been complemented with microscopic and analytical observations for salt that was partly decomposed to various known extents as discussed by the authors.
Abstract: A kinetic and mechanistic study of the thermal decomposition of copper(II) malonate has been completed in which the rate measurements have been complemented with microscopic and analytical observations for salt that was partly decomposed to various known extents. Plots of the fractional reaction ($\alpha$) against time for the isothermal reactions were approximately sigmoid but were distorted by a significant diminution in rate at the half-way stage ($\alpha \approx$ 0.5). Microscopic observations gave evidence that local fusion occurred soon after the onset of reaction, so that the initial acceleratory behaviour cannot be ascribed to a solid-state nucleation and growth process. From analytical measurements it is concluded that decomposition proceeds to completion by two distinct reactions, involving a stepwise cation reduction: Cu$^{2+}\rightarrow$ Cu$^+\rightarrow$ Cu$^0$. The relatively slower rate of the second reaction accounts for the marked diminution in slope of the $\alpha$-time plots after $\alpha$ = 0.5. The first reaction, copper(II) malonate decomposition, is characterized by a prolonged acceleratory process that obeys the exponential equation ($\ln \alpha$ = kt). This is explained by autocatalytic behaviour in which anion breakdown is promoted by acetate, a reaction product, thus (d$\alpha$/d$t$) = $k\alpha$. Separate experiments confirmed that added copper(II) acetate accelerated the reaction. The decomposition of copper(II) malonate was accompanied by partial fusion, and gas evolution within the viscous melt resulted in the development of an intracrystalline froth-like texture. Such partial melting was, however, localized within the reactant and the sizes and shapes of crystallites did not change markedly during reaction, so that product particles were pseudomorphic with those of the reactant. The final, short deceleratory phase of the first reaction overlapped with the onset of the second reaction. The second reaction was deceleratory throughout and obeyed first-order kinetics. Product acetate was not formed and the decomposition was evidently not influenced by the concurrent breakdown (0.5 < $\alpha$ < 0.75) of acetate remaining after the first reaction. The froth-like structure of the coherent matrix of the residue was retained unchanged between 0.5 < $\alpha$ < 1.0. The immobile component of this residual material was identified as a carbonaceous phase, the product copper atoms possessed sufficient mobility to aggregate in the form of metallic crystallites. Reaction mechanisms to account for the observations are proposed and are discussed with reference to the complementary kinetic, microscopic, and analytical data.

50 citations

Journal ArticleDOI
TL;DR: The first reaction of copper(II) maleate was accompanied by anion isomerization to form predominantly copper(I) fumarate before the onset of the second reaction.
Abstract: Kinetic studies of the thermal decomposition reactions of copper(II) maleate and of copper(II) fumarate have been undertaken. The mechanistic interpretations of these observations are supported by complementary analytical measurements and microscopic observations for the reactants, the products and salt partially decomposed to appropriate known extents of reaction. Analytical evidence showed that both reactants decompose with stepwise reduction of the cation and reaction was completed through two distinct, consecutive rate processes. During these first reactions copper(II) was reduced to copper(I) by approximately the half-way stage. The second reactions, in which copper(I) reduction to the metal was completed, was, for both salts, the significantly slower process. The first reaction of copper(II) maleate was accompanied by anion isomerization to form predominantly copper(I) fumarate before the onset of the second reaction. Copper(II) fumarate, containing the more stable anion, underwent no such transformation. Electron microscopic observations gave strong evidence that the first reaction in the decomposition of copper(II) maleate was accompanied by at least partial melt formation. Enhanced reactivity within the fused salt explains the sigmoid-shaped product yields vs. time curve. The first reaction of copper(II) fumarate was predominantly deceleratory. The second reactions of both salts obeyed the first-order equation and reactivities are compared quantitatively with the decompositions of the copper(I) salts synthesized within the reaction vessel by heating the acid with excess copper(I) oxide. Mechanisms of the decompositions of both salts [and of copper(II) malonate] are discussed with reference to the kinetic observations and interpretations are complemented by a consideration of the microscopic and the analytical evidence.

28 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that the temperature at which copper(II) malonate decomposes is significantly reduced in crushed mixtures containing excess carboxylate, which is not influenced by the relatively rapid initial reaction, and the rate subsequently diminishes as the amount of reactant remaining diminishes.

3 citations

Journal ArticleDOI
TL;DR: The first reaction of copper(II) maleate was accompanied by anion isomerization to form predominantly copper(I) fumarate before the onset of the second reaction as mentioned in this paper.
Abstract: Kinetic studies of the thermal decomposition reactions of copper(II) maleate and of copper(II) fumarate have been undertaken. The mechanistic interpretations of these observations are supported by complementary analytical measurements and microscopic observations for the reactants, the products and salt partially decomposed to appropriate known extents of reaction. Analytical evidence showed that both reactants decompose with stepwise reduction of the cation and reaction was completed through two distinct, consecutive rate processes. During these first reactions copper(II) was reduced to copper(I) by approximately the half-way stage. The second reactions, in which copper(I) reduction to the metal was completed, was, for both salts, the significantly slower process. The first reaction of copper(II) maleate was accompanied by anion isomerization to form predominantly copper(I) fumarate before the onset of the second reaction. Copper(II) fumarate, containing the more stable anion, underwent no such transformation. Electron microscopic observations gave strong evidence that the first reaction in the decomposition of copper(II) maleate was accompanied by at least partial melt formation. Enhanced reactivity within the fused salt explains the sigmoid-shaped product yields vs. time curve. The first reaction of copper(II) fumarate was predominantly deceleratory. The second reactions of both salts obeyed the first-order equation and reactivities are compared quantitatively with the decompositions of the copper(I) salts synthesized within the reaction vessel by heating the acid with excess copper(I) oxide. Mechanisms of the decompositions of both salts [and of copper(II) malonate] are discussed with reference to the kinetic observations and interpretations are complemented by a consideration of the microscopic and the analytical evidence.

Cited by
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Journal ArticleDOI
TL;DR: In this paper, the model-free and model-fitting approaches have been applied to data for nonisothermal and isothermal thermal decompositions of HMX and ammonium dinitramide.

1,168 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compare the performance of isothermal and nonisothermal experiments for the decomposition of ammonium dinitramide (ADN) and show that the identical dependencies of activation energy on the extent of conversion are not obtained for isothermal or non-isothermal data.
Abstract: Thermogravimetric data for the decomposition of ammonium dinitramide (ADN) have been obtained under isothermal and nonisothermal conditions in order to determine the efficacy of different methods for analyzing the kinetics of solid-state reactions. A widely used model-fitting method gives excellent fits to the experimental data but yields highly uncertain values of the Arrhenius parameters when applied to nonisothermal data because temperature and extent of conversion are not independent variables. Therefore, comparison of model fitting results from isothermal and nonisothermal experiments is practically meaningless. Conversely, model-free isoconversional methods of kinetic analysis yield similar dependencies of the activation energy on the extent of conversion for isothermal and nonisothermal experiments. Analysis of synthetic data generated for a complex kinetic model suggests that, in the general case, the identical dependencies are unlikely to result from experiments obtained under isothermal and noni...

241 citations

Journal ArticleDOI
TL;DR: In this paper, a new computational technique (advanced isoconversional method) has been used to determine the dependence of the effective activation energy (Eα) on α for isothermal and nonisothermal TGA data.
Abstract: The methods of thermogravimetric analysis (TGA) and differential scanning calorimettry (DSC) have been used to study the thermal decomposition of ammonium perchlorate (AP). TGA curves obtained under both isothermal and nonisothermal conditions show a characteristic slowdown at the extents of conversion, α = 0.30−0.35. DSC demonstrates that in this region the process changes from an exothermic to an endothermic regime. The latter is ascribed to dissociative sublimation of AP. A new computational technique (advanced isoconversional method) has been used to determine the dependence of the effective activation energy (Eα) on α for isothermal and nonisothermal TGA data. At α > 0.1, the Eα dependencies obtained from isothermal and nonisothermal data are similar. By the completion of decomposition (α → 1) the activation energy for the isothermal and nonisothermal decomposition respectively rises to ∼110 and ∼130 kJ mol-1, which are assigned to the activation energy of sublimation. The initial decomposition (α → ...

240 citations

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TL;DR: In this paper, the role of extended crystallographic structures in controlling the course of the bond rearrangements that occur during the conversion of a solid reactant into solid products is discussed.

212 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that the energy distribution among the immobilized constituents of a crystalline reactant is not represented by the Maxwell-Boltzmann equation. And the existence of such interface energy levels, with a limited range of energies, would also allow for the variation of apparent activation energy with extent of reaction, and also with temperature, reported for many complex solid state reactions.

197 citations