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Abstract  

Ibuprofen has been subjected to a TG/DTA study over the temperature range of 30 to 350°C in a flowing atmosphere of nitrogen. The heating rate and the flow rate were varied. The DTA shows a melting at around 80°C and boiling point range from 212 to 251°C depending upon the heating rate. The mass loss in the TG data confirms the evaporation of Ibuprofen between them.p. and the normalb.p. Evaporation is limited to the surface area, which is a constant in the crucible holding the sample. The DTG plot shows clearly a zero order process which is consistent with the process of evaporation. The enthalpy of vaporization (Δvap H) calculated by Trouton's rule is found to be in the range of 42.7–46.1 kJ mol−1. TheE act for the zero order reaction is in the range of 81.8–87.0 kJ mol−1 and is calculated by use of the derivative method. The value ofE act is about twice that for ΔH vap in Ibuprofen and differs from other compounds, whereE act ≈Δ H vap. It is suggested that the Ibuprofen molecule is existing as a dimer in the liquid state and dissociates to a monomer in the vapor state.

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Abstract  

The kinetics of the anodic dissolution of metallic uranium in 1, 2, 3, and 4 mol.l-1 HNO3 solutions at 30 °C were studied by potentiostatic polarization. The dissolved uranium was determined by polarography and the anodic dissolution rates by the initial rate method. It was observed that the dissolution rate increases with the applied potential, but is independent of the HNO3 concentration, because it is a zero order reaction. A mechanism for the anodic reaction was proposed based on the adsorption theory.

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Journal of Thermal Analysis and Calorimetry
Authors: Agna Hélia de Oliveira, Elisana Afonso de Moura, Márcia Ferraz Pinto, José Valdilânio Virgulino Procópio, Valmir Gomes de Souza, Fábio Santos de Souza, and Rui Oliveira Macêdo

Abstract

This work studied the thermal characterization of the pentoxifylline raw material through thermoanalytical techniques (TG, DSC, DSC-photovisual) and analysis of degradation products by Pyr-GC/MS. The picture obtained with DSC-photovisual showed the total vaporization of pentoxifylline at 230.0 °C. The TG dynamical curve presented only one step for the loss of mass evidencing to be a kinetic process of zero order reaction. The pyrograms obtained for pentoxifylline sample in the solid state and solution in the temperatures of 250.0, 300.0, and 400.0 °C, showed only one peak identifying the pentoxifylline.

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Kinetic parameters were determined for the decomposition reactions of some com plexes of cobalt, nickel, manganese, copper and cadmium halides and pseudohalides with ammonia, pyridine and substituted pyridines. For the zero order reactions, the values of the pre-exponential factors calculated assuming as limiting step the diffusion of the volatile component through the layer of the decomposed substance, are in satisfactory agreement with the experimental values.

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Journal of Thermal Analysis and Calorimetry
Authors: Vadim V. Krongauz, Yann-Per Lee, and Anthony Bourassa

sublimation of solids is zero-order reaction with f (α) ≡ 1 and linear α dependence on the reaction time. Then, to obtain E a the rate of reaction could be measured as a function of temperature at any α due to constant slope of kinetic curves [ 54 and ref

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Journal of Thermal Analysis and Calorimetry
Authors: José Valdilânio Virgulino Procópio, Valmir Gomes de Souza, Rodrigo Albuquerque da Costa, Lidiane Pinto Correia, Fábio Santos de Souza, and Rui Oliveira Macêdo

showed a kinetic process with zero order reaction for all samples in first and main step of decomposition. The activation energy values were different among the samples, where SVA presented E a about 73.10 kJ mol −1 , while SVB and SVC showed values

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.15) are close to those of AP decomposition. The second-stage reaction rate depends weakly on the conversion degree (0.4 < α < 0.8), which is characteristic of pseudo-zero order reactions.In this case, the expression for the rate constant is 5

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-8842(02)00195-5 . 16. Sarıkaya , Y , Ada , K , Önal , M . Applications of the zero-order reaction rate model and transition state theory on the intra-particle sintering of an alumina powder by using surface area measurements . J Alloy

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the equation bellow, considering zero order reaction [ 14 ]: 2 For small intervals in temperature and the same extension and reactions in a series of experiments using different heating rates, activation energy can be described as: 3

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specimens ( Fig. 9 c, d). Up to ∼0.30 α , oxidation of MS and SS specimens involved R 1 mechanism i.e., zero-order reaction kinetics indicating faster degradation of the specimens during α >0.05 to ∼0.30 α since during this stage the supply of free

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