Browsing by Author "Prout, E G"

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    The photolysis and co-irradiated decomposition of barium and strontium azides
    (1974) Shephard, Enid Gwendolyn; Prout, E G
    The effect of ultraviolet radiation on sieved powders and pellets of barium azide in the temperature range 27,0° - 135,0°C and of strontium azide in the temperature range 30,0° - l35,0°C has been studied. Decompositions in the temperature range 27,0°- 100,0°C for barium azide and 30,0° - 90,0°C for strontium azide have been termed photolytic decompositions, while reactions in the temperature range 110,0° - l35,0°C (the thermal decomposition temperature range) for both compounds have been termed co-irradiated decompositions. The ultraviolet light source used was a very high intensity 100 watt "point source" high pressure mercury arc lamp. The extent of decomposition was almost the same as a simple thermal decomposition. Kinetic analyses, activation energy determinations, studies of the dependence of reaction rates on light intensity, the effect of water vapour on the sample at various stages of reaction and the observance of the colour of the sample at various stages of reaction have been carried out. Analogous results were obtained for the two compounds. In the photolytic temperature range two distinct modes of decomposition are postulated to occur, the transition temperature occurring at 60,0°C for barium azide and at 50,0°C for strontium azide. During co-irradiation it is proposed that decomposition occurs via the expected thermal decomposition process and the photolytic mechanism or a slight variation thereof, above 60,0°C for barium azide and above 50,0°C for strontium azide.
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    The photolysis of calcium, barium, strontium and lithium azides and the co-irradiated decomposition of calcium azide
    (1978) O'Connor, Cyril Thomas; Prout, E G
    The effect of very high intensity ultraviolet radiation on powdered calcium, barium, strontium and lithium azides in the temperature range -80,0° - 35,0°C has been studied. Powdered and pelleted calcium azide was also irradiated with ultraviolet radiation in the temperature range 35,0° - 90,0°C and powdered lithium azide in the temperature range 24,0° - 170,0°C. All these decompositions were purely photolytic. Powdered and pelleted calcium azide was also subjected to ultraviolet radiation in the temperature range 110,0° - 140,0°C. This latter decomposition was termed co-irradiation due to the fact that both thermal and photolytic mechanisms were operative in this temperature range. Except at low temperatures, the extent of the decomposition was almost the same as that of a simple thermal decomposition. Kinetic analyses, determination of activation energies, studies of the dependence of reaction rates on light intensity, the effect of introducing water vapour to the sample at various stages of decomposition and the observance of the colour of the sample at various stages of reaction have been carried out. Analogous results were obtained for all four azides at low temperatures and the results obtained for calcium and lithium azides at ambient and higher temperatures were analogous to those obtained for barium and strontium azides under similar conditions by previous workers. During photolysis the activation energy undenvent transitions, in all four azides, in the region of 0°C and in the region of 60°C. Co-irradiation studies of calcium azide commenced at temperatures greater than 100°C. Similar studies were not carried out on lithium azide since even at temperatures in the region of 180°C the rate of photolytic decomposition was very much greater than that of a purely thermal decomposition at the same temperature.
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    The thermal decomposition of unirradiated and irradiated lithium azide
    (1969) Liddiard, Vernon Clive; Prout, E G
    The thermal decomposition in vacuo of lithium azide, in powder and pellet form, has been investigated. The temperature range was 160° - 220° C. The results obtained were highly reproducible, and a study of the reaction kinetics was made for both the pelleted and powdered forms of the azide. Mathematical analysis of the results obtained indicated that discrete nuclei are formed over the induction period which then grow two-dimensionally over the acceleratory period. The nuclei increase in number linearly with time and overlap and ingestion of the nuclei occurs during the acceleratory period. This was shown by the applicability of the Avrami-Erofeyev equation with the exponent n assuming the value 3, for the analysis of the acceleratory period p/t plot. The nuclei are formed mainly over the external surfaces of the decomposing particles. The effects produced by pre-irradiation with γ-, X- and U.V.- radiation on the subsequent thermal decomposition have been studied. These studies were largely on the powdered lithium azide, but some attention was also given to pre-irradiating the pelleted material. Pre-irradiation of the powdered material resulted in a marked shortening of the length of the induction period followed by an increased acceleratory rate, for the types of radiation employed. X- and U.V.-radiation did not have any significant effect on the decay period reaction rater The p/t plots were sigmoid, as found for the unirradiated azide. Applicability of the Avrami-Enofeyev equation in the analysis of the acceleratory period for the irradiated azide indicated that two-dimensional nuclei formed and grew on the surfaces of the particles, except in the case of γ-irradiated lithium azide when the reaction was largely confined to internal grain boundaries. Similar mechanisms operate over the induction periods for the unirradiated and irradiated azide. A change in the value of the activation energy for the acceleratory periods, indicated that the rate determining step for this stage of the reaction is altered after pre-irradiation. The same mechanism was applicable for the decay stages of the unirradiated and irradiated azide. The effects of pre-irradiation with all three types of radiation, resulted in a double-sigmoid p/t plot in the case of pelleted lithium azide. The initial reaction was confined to the surface of the pellet pre-irradiated with U.V., and occured throughout the bulk of the pellets pre-irradiated with γ- and X-rays.