Browsing by Author "Galwey, Andrew K."

Now showing 1 - 3 of 3

Decomposition Reactions of Nickel Formate, Nickel Malonate, Nickel Maleate and Nickel Fumarate in Oxygen
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Wheeler, Brian R.; Galwey, Andrew K.
Decomposition of nickel formate, nickel malonate, nickel maleate and nickel fumarate in oxygen yields nickel oxide and carbon dioxide only. The shape of each fractional reaction-time curve is comparable with that for the vacuum pyrolysis of the salt, there is no evidence that the product oxide provided a progressively increasing barrier to the progress of the oxidation process. The values of the activation energies for the decomposition reactions of all four salts are 150 ± 10 kJ mol–1 and different from those for reactions in vacuum. From the observations we conclude that the geometry of advance of the reactant/product interface, during nucleation and subsequent growth of the product phase, for reactions in oxygen and in vacuum are closely comparable, if not identical. The chemical processes occurring at the metal carboxylate/nickel oxide interface during the reaction in oxygen are discussed. It is suggested that the rate controlling process is largely determined by the surface and defect properties of the nickel oxide product phase.
Oxidation of a Pyrophoric Iron: Part 2. Direct Measurement of Self-heating Accompanying Chemisorption of Oxygen on the Finely Divided Iron-Carbon Substrate
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Galwey, Andrew K.; Gray, Peter
The self-heating accompanying the exposure to oxygen of a pyrophoric iron (here a finely divided iron-carbon preparation from an iron mellitate) has been studied quantitatively. In particular, temperature histories have been measured directly by means of a fine thermocouple located at the reactant centre. The dependence of the course of events on (i) initial temperature, from 193 to 720 K, (ii) oxygen pressure, from ca. 0.5 to 200 Torr and (iii) sample mass, from 16 to 40 mg has been investigated. Particular attention has been directed toward attaining really satisfactory reproducibility. All the phenomena observed correspond to sub-critical behaviour; ignitions have not been studied. The results are interpreted against the background knowledge (Part 1) of the kinetics of oxygen adsorption on this pyrophoric iron preparation. From the observations it is concluded that below 373 K and 4 Torr oxygen pressure, the extent of self-heating is determined by the rate of heat loss through the walls of the glass containing vessel. Above 4 Torr, the behaviour is more complex and is influenced by the occurrence of two distinct chemisorption reactions. Reaction above 500 K seems to be governed by gas diffusion processes and the overall temperature rise is moderated both by the containing vessel and by the diffusion of oxygen by inter- and intra-crystalline paths to the active surfaces within the particles of the reactant assemblage.
Thermal Decomposition of Manganese(II) Oxalate in Vacuum and in Oxygen
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (07), 1974) Brown, Michael E.; Dollimore, David; Galwey, Andrew K.
Comparative studies of the kinetics of thermal decomposition of anhydrous manganese(ll) oxalate in vacuum and in oxygen are reported. Reaction rates were appreciably influenced by the conditions of salt dehydration : both decompositions were more rapid for vacuum-dehydrated react ant than for salt dehydrated in air. The shapes of product yield against time curves were not detect- ably changed by the presence of oxygen. The solid product from the oxidation reaction was largely Mn;O3 and the activation energy was significantly lower than previously reported values for the vacuum decomposition which yields MnO. Mechanistic interpretation of the kinetic data was supplemented where appropriate by observations from electron micrographs. Product gas analyses, during the course of decomposition reactions, indicated the initial formation of products containing Mn3+, though this was subsequently reduced. Reaction mechanisms involving the participation of Mn3+ in both decomposition and oxidation of manganese(II) oxalate arc proposed.