Browsing by Author "Gray, P."

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Self-heating and Spontaneous Ignition in the Oxidation of Gaseous Hydrazine
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (3), 1972) Gray, P.; O’Neill, E. P.
The spontaneous ignition of gaseous mixtures of oxygen and hydrazine has been investigated in a 1 1. spherical vessel over the temperature range 690-770 K. Emphasis is placed on direct detection of prc-cxplosivc sclf-hcating in the reacting gas. Very fine thermocouples (made from 0.025 mm Pt and Pt-Rh wires) arc used to follow temperature changes, and to map temperature-position profiles during oxidation: N2H4H+O2 ->N2+2H2O, H = -138 kcal mol-1. Unusually among gas-phase oxidations, this spontaneous ignition is clearly thermal in character. Strong self-heating is always observed. In accordance with a conductive theory of heat losses, temperatures arc not uniform throughout the reactant but depend on the distance from the vessel centre, being greatest at the centre and least at the walls. The (approximately) parabolic form and the absence of any significant temperature-step at the walls confirm the absence of convection at the pressures concerned. A critical centre temperature rise exists above which stable reaction is impossible and ignition inevitable. Thermal theory predicts a critical value of 1.61 RT^E, i.c., about 70 K, under circumstances where reactant coirsumption can be ignored, and a value of 116 K when it is taken into account: the value observed here is 120 K. The hydrazine-boxygen system is more difficult to handle than some systems previously investigated and catalysis at the thermocouple is harder to eliminate. These effects, and the consequences of employing thermocouples of finite heat capacity, are also discussed.
Thermal Conductivities of Gaseous Mixtures Containing Hydrocarbons: Part 1.—n-Butane, iso-Butane, iso-Pentane and neo-Pentane, and Their Binary Mixtures With Argon
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (6), 1972) Parkinson, C.; Gray, P.
Thermal conductivities of the four pure gases n-butane, iso-butane, iso-pentanc and nco-pentane and of their binary mixtures with argon have been measured at 50 and 100°C. The thermal conductivities of all four polyatomic gases lie close together and there arc marked similarities in the conductivity against composition curves for their binary mixtures with argon. Thermal conductivities less than molar average values are found at both 50 and 100 C for each mixture. These “ negative deviations ” arc greatest at 50nC and result in broad minima in each case. At 100 C minima arc less pronounced and arc confined to the n-butane, iso-pentane and neo-pcntanc mixtures. Points of inflexion develop in all the conductivity against composition curves at this temperature. We believe that negative deviations are generally to be associated with binary mixtures of a monatomic with a non-polar polyatomic gas, and minima can be manifested when the ratio of thermal conductivities for the pure components (Xj/X/) is not far from unity. The formal condition is AjjAji > where Ay and Aji arc coefficients of the Suthcrland-Wassiljcwa equation and subscript i denotes the component with the lower thermal conductivity. The data arc used to test predictions of thermal conductivities of gas mixtures both by approximations to rigorous kinetic theory (Hirschfelder-Eucken, and Monchick, Pereira and Mason) and by the empirical relationship of Lindsay and Bromley. All three methods predict thermal conductivities which arc in reasonable agreement with experimental measurements, but the Hirschfelder-Eucken approximation is found to be most satisfactory (mean deviation 1.27 % from 74 compositions) for these mixtures.
Thermal Conductivities of Gaseous Mixtures Containing Hydrocarbons: Part 2.—Cyclopropane, Propene, But-l-ene and trans-But-2-ene, and Their Binary Mixtures with Argon
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (6), 1972) Parkinson, C.; Mukhopadhyay, P.; Gray, P.
Thermal conductivities of the four pure gases cyclopropane, propene, but-l-ene and trans-but-2- ene and their binary mixtures with argon have been measured at both 50 and 100°C. The thermal conductivities of the pure polyatomic gases lie close together and strong similarities exist in the conductivity versus composition curves for each binary mixture. At 50°C thermal conductivities of the mixtures arc less than the molar average values and a broad minimum results in each case. At 100°C negative deviations are much reduced and only the trans- but-2-cne with argon system displays a minimum. Points of inflexion develop for the cyclopropane, propene and but-l-enc mixtures at this temperature and thermal conductivities slightly above molar average values arc seen in regions of high hydrocarbon concentration. Thermal conductivities of the binary mixtures calculated on the basis of an empirical equation and from approximations to rigorous kinetic theory (Hirschfelder-Euckcn and Monchick, Pereira and Mason) arc compared with the experimental results. All three methods of calculation are found to give reasonably good agreement with experiment, but the Hirschfcldcr-Eucken approximation is the most satisfactory (mean deviation 0.89 % from 72 compositions) for these mixtures.