A compact layer of alumina modified by CaCl sub(2): The influence of composition and porous structure on water transport

This paper reports a target-oriented synthesis of the compact layer of alumina and its modification by a calcium chloride. The layer preparation procedure with the use of binder has been developed which makes it possible to widely vary the layer porous structure. The effect of the layer structure and composition on water vapor transport in it has been studied by NMR imaging. The effects of the size of the primary alumina grains, the amounts of the binder and the guest salt on the porous structure of the layer and the mechanism of vapor transport in the layer have been investigated. Variation of these parameters has been shown to alter the relative contributions of the diffusional resistances in the intergrain macropores and in the intragrain mesopores and to permit an intentional transition between the different diffusional regimes of water sorption. If the sorption rate is limited by the diffusion of water in the intergrain voids, an adsorption front is formed in the sample and is propagating into the layer. The penetration depth depends on time as t super(0.5). If the water sorption in the primary grains is the slowest process, the water uptake uniformly increases over the entire layer.