A study of water sorption isotherms on charcoal coated with different amounts of variously disposed chemisorbed oxygen shows that it is the oxygen disposed as COa which enhances the sorption capacity of charcoal and not the rest of the combined oxygen. The area of the hysteresis loop also increases with increase in the amount of this oxygen. An appreciable amount of water, representing about one mole per mole of C02, is held so firmly by charcoal that it is not desorbed even on drying to zero humidity. This enhances the hysteresis effect, which, however, persists though to a smaller extent, even on complete elimination of the combined oxygen.The work of Lawson1 and King and Lawson2 shows that the presence of chemisorbed oxygen in charcoal increases the low pressure sorption of water by charcoal and shifts the isotherms to lower pressures than those corresponding to the same amount of sorption in the absence of any such oxygen. Similar results have been reported in more recent papers by Emmett,3 Dubinin and Zaverina,4 Healey, et al.,5 Anderson and Emmett6 and Mc-Dermot and Amell.7 8Smith, et al.f are of the view that the increase is due to an extensive reaction of water with oxygen complex producing a new surface complex. McDermot and Amell7 believe that the oxygen provides isolated active centers at which the sorption proceeds in the form of "clumps" or "clusters"9 of water molecules which grow in size by a mechanism, of hydrogen bonding until they merge, at a higher relative pressure, to fill the smaller pores. Capillary condensation occurs whenever a cluster reaches sufficient size to bridge the walls of a pore.
Zinc sulphide (ZnS) i~ an important II-VI compound well-known for the electrooptic applications. It is also one of the moJt suitable materials for the fabrication oflR transmitting domes and windows because ofits transmission in the IR region (2-12 ~) of the spectrum as well as its excellent thermo-mechanical properties. The ZnS domes and vorindows Je prepared by hot pressing or hot isostatic pressing (ffiP) of opti"cal quality grade ZnS powder" This paJ!!er describes the preparation of optical quality grade ZnS powder using a modified acid process maintainihg a constant pH, The resulting ZnS powder is subjected to thermal treatment in different atmospheres and at different tdmperatures. The ZnS powder thus obtained has been characterised by chemical analysis, part'ical ~le measurement, IR spectrophotomeny .XR-D apd XR-F analysis. The role of various experimental parameters involved, e.g., concentration of ZnSO4 solution. firing temperature and firing atmospheres is investigau:d. A transmission of 69 per cent was achieved after lflP of the ZnS powder prepared
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