| Popis: |
The permeability towards various gases of fabricated beryllia, ranging from 80–95 % theoretical density, has been measured. Permeability coefficients, B o and K o , are calculated from the Carman equation and gas flow through beryllia is compared with that through graphite. The viscous permeability—density relationship for hot pressed beryllia is shown to be similar to that for metal powder compacts, and rapidly decreases to a negligible value at ≈ 95 % theoretical density. Information on pore properties (number, size and tortuosity) is obtained from permeability equations. For the specimen examined, the pores are ≈ 1 μ diameter, tortuous and relatively few in number. Comparison is made with graphite, and the pore structure of beryllia is discussed. A minimum is observed in the plot of permeability coefficient ( K ) against mean pressure ( p ) and an explanation is given in terms of pore size distribution for this and another type of observed plot. |
