The influence of the UV-radiation on the thermal stability of the AgCl

Silver chloride is widely used as light-sensitive element of photographic emulsions in photo materials. Despite widespread use of silver chloride such important photochemical characteristic as influence of ultra-violet radiation on its physicochemical characteristics is not widely explored. The work is aimed to define the influence of ultraviolet radiation on thermal stability (sublimation energy) of silver chloride. Mercury-quartz lamp of high pressure with maximal intensity on wave-length 365 nm was used as an emitter. Samples of AgCl were placed in Petri dish and were put under the ultraviolet lamp. According to the experiments, crystals of silver chloride were differed depending on synthesis conditions: silver chloride synthesized in excess of silver ions was characterized by heat of sublimation about 6813 J/g, what meant that its heat of sublimation rises by 1.8 times. At the same time silver chloride, synthesized in excess of chloride ions was characterized by decrease of heat of sublimation by ~ 2 times. It is known that presence of chloride ions in the lattice decreased speed of photolysis during irradiation. Apparently a solid surface film of metallic silver was formed on surface of silver chloride synthesized in excess of silver chloride during time of irradiation, while there was no film on surface of silver chloride synthesized in excess of chloride ions. The presence of the solid surface film of silver with melting temperature of 960° С obstructed evaporating of silver chloride: temperature of intensive vaporization of original sample was ~ 800 °С, while after irradiation it decreased to ~ 750 °С. Temperature of intensive sublimation of sample synthesized in excess of chloride ions was ~ 800 °С and changed insignificantly after irradiation. Growth of heat of sublimation of silver chloride with excess of silver ions is, seemingly, connected with energy expenditure on sublimation due to decrease in proportion of surface which is not covered with silver. Reduction of heat of sublimation of silver chloride with excess of chloride ions was explained by absence of the solid surface film of silver and catalytic effect of silver agglomerates formed during the process of irradiation.

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