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Item Viscosities of Gaseous Nitric Oxide, Nitrous Oxide and Sulphur Dioxide at High Temperatures(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (05), 1981) Clifford, Anthony A; Gray, Peter; Scott, Alan CThe viscosities of nitric oxide (372–1015 K), nitrous oxide (372–733 K) and sulphur dioxide (321–1300 K) have been measured using a capillary-flow viscometer in a comparative mode. Smoothed viscosity tables have been produced using recommended nitrogen viscosities.Item Lennard-Jones 12:6 Parameters for Ten Small Molecules(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (2), 1977) Clifford, Anthony A.; Gray, Peter; Platts, NormanYalucs for Lennard-Jones parameters, calculated from recently measured viscosity data for temperatures between 200 and 500 K, are reported for ten small molecules.Item Explosive Oxidation of Hydrogen Sulphide: Self-heating, Chain-branching and Chain-thermal Contributions to Spontaneous Ignition(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (12), 1974) Gray, Peter; Sherrington, Malcolm E.The spontaneously explosive oxidation of hydrogen sulphide in a 290 cm3 vessel has been investigated over a temperature range 280–360°C and between pressures of 10 and 120 mmHg. Conditions for ignition have been mapped on a p,T diagram. Very fine thermocouples (25 µm Pt–Pt/Rh) have been used to detect and measure self-heating, and special emphasis has been laid on the direct measurement of the size and form of the temperature against time histories for different initial conditions or locations on the ignition diagram. The effects of reactant proportions and of added diluents (with different thermal conductivities) on the second and third ignition limits have also been studied. Although the reaction exhibits many features traditionally associated with purely branched chain explosions, the direct temperature measurements have revealed extensive self-heating under very varied conditions of pressure and temperature. Boundaries may be drawn on the ignition diagram that separate the regions where a combined chain-thermal mechanism is responsible for explosions (I) from those which may be considered as purely thermal (II) or isothermal branched chain (III) in nature. The measured temperature against time histories provide novel experimental support for the unified theoretical treatment of chain and thermal explosions of Gray and Yang. Critical temperature rises are smaller than would be expected on a purely thermal basis, and induction times are longer. In the chain-thermal region, the rate of self-heating immediately prior to ignition is not always rapid; indeed, temperature excesses may be relatively steady or even decreasing when spontaneous explosion takes place. We should expect similar behaviour in the hydrogen-oxygen reaction.Item Self-heating and Spontaneous Ignition in the Combustion of Gaseous Methylhydrazine(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Gray, Peter; Sherrington, Malcolm E.The exothermic oxidation of gaseous monomethylhydrazine (CH3NHNH2) has been investigated in the gas phase over a temperature range 370–510°C in a 1-litre vessel. Critical conditions of pressure, temperature and reactant proportions for spontaneous ignition, and the effects of inert diluents have been examined. CH3NHNH2+ 2.5 O2→N2+ CO2+ 3 H2O; ΔH=– 1340 kJ mol–1(–320 kcal mol–1) Temperature changes have been followed by means of very fine thermocouples (13 µm diam. Pt–Pt/Rh) coated to prevent surface catalysis. The reactant is always hotter than the vessel, and the temperature excess is greatest at the centre, in accord with conductive theory. Uncommonly among gas-phase oxidations, the combustion of methylhydrazine is dominated by thermal effects. As was previously found for hydrazine, large central temperature excesses (about 80 and 100°C) are common and have to be exceeded for ignition to occur. The critical temperature excesses are consistent with the effective activation energy (ca. 80 kJ mol–1 or 19 kcal mol–1) derived from critical pressure limits and taken together indicate that the critical increment in average temperature is between 1.1 and 1.2 RT2a/E. These values do not provide support for the theoretical treatment by Adler and Enig, which requires stable temperature excesses greater than 2.41 RT2a/E to be realisable for a second order reaction; they are consistent, however, with our recent analytical and computational predictions on the stability of such systems.Item 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, PeterThe 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.Item Thermal Conductivities of Ethene and its Fluorocarbon Analogues and of their Binary Mixtures with Argon(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Gray, Peter; Parkinson, ChristopherThe thermal conductivities of the five pure gases CH2CH2, CHFCH2, CF2CH2, CF2CHF and CF2CF2 together with their binary mixtures with argon, have been measured at both 50 and 100°C. At 50°C, negative deviations below the molar average value occur in the conductivity against composition curves for all five systems, and minima or signs of minima at intermediate compositions develop in the mixtures of CF2CH2, CF2CHF and CF2CF2 with argon. At 100°C, the latter three systems again show negative deviations, and minima are once more displayed by the mixtures of CF2CHF and CF2CF2 with argon. The system CHFCH2 plus argon exhibits evidence for a point of inflexion in the curve. This is the first time that minima have been observed in binary mixtures of a polar and a monatomic gas, though minima have been found with non-polar mixtures. Where minima develop, the formal condition AijAji[gt-or-equal]λj/λi is fulfilled, where Aij and Aji are coefficients of the Sutherland–Wassil-jewa equation, subscript i denoting the component with the lower thermal conductivity. The predictions of the empirical equation of Lindsay and Bronley are compared with experiment: the agreement is markedly less good than normally found, discrepancies being greatest in mixtures containing the most polar constituents. Outline comparisons with the Hirschfelder–Eucken approximation to rigorous theory are satisfactory.Item Reaction of Perfluoroethyl Radicals with Cycloalkanes(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Whytock, David A.; Clarke, John D.; Gray, PeterThe reactions of C2F5 radicals with C4 to C7 cycloalkanes have been studied using perfluoroethyl iodide as the source of free radicals. The Arrhenius parameters obtained for the reaction C2F5+ c-RH→C2F5H + c-R were (c-R = cycloalkyl): [graphic omitted] The Arrhenius parameters are compared with those for corresponding CF3 radical reactions. From the activation energies, values for the c-R—H bond dissociation energies are derived using the Evans–Polanyi method. Bond strengths for methylene groups in C5, C6 and C7 cycloalkanes are all close to that for the Pri—H bond dissociation energy in propane.