Molecular size pores in beryllium oxide powders

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Abstract
BeO prepared by thermal decomposition of β-Be(OH)2in vacuo consists of porous aggregates of crystallites 30 Å. The aggregates are relics of individual hydroxide crystals which undergo a volume shrinkage on decomposition of only 30 % of that theoretically possible, and have a density 50 % that of dense BeO. Of the intra-aggregate pore volume, only 20 % is available to CCl4 and 50 % available to N2 and hence there is a substantial volume of pores 2 adsorption at low pressures and exhibit measurable He adsorption even at 100°C. Although of comparable molecular size to N2, H2O is able to penetrate most or all of the pores (due to the higher interaction energy to H2O with the oxide surface) and after desorption some of these become accessible to N2. Similarly, H2O adsorption and desorption increases the pore volume accessible to CCl4, and various H2O treatments (including decomposition of the hydroxide in the presence of H2O vapour) lead to a microstructure in which pores <6 Å are virtually absent.

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