We have been carrying out investigation for some problems concerning gas permeability and application of their clarification technologies to refractories by a new gas permeability measuring apparatus. １）It is thought that the gas stream in refractories flows not as a laminar flow but as a calm turbulent flow, and gas density is thought to influence the permeability measurements under high pressure conditions. ２）Two types of samples were taken from the MgO-C brick. One type was taken from the side to which pressure was applied during manufacturing and other type was taken from the side perpendicular to the direction to which pressure was applied. There was a clear difference in the permeability which was caused by orientation of the graphite between the two types of samples used. ３）Permeability of refractories was found to increase with pore diameter. However, pores generated by the heating and dehydrating of castable are small with diameters of 10nm - 100nm.

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