Gas Permeability of Dense Shaped Refractory Products - Test Method - BS EN 993-4:1995, BS 1902-3.9:1995
Methods of test for dense shaped refractory products. Determination of permeability to gases.
The permeability of a material is related to the distribution of its pores and because of this, is very sensitive to variations in texture. It is not directly related to the apparent porosity and it shows, within the same piece and even more so from one piece to another within the same batch, a much greater variation than does the porosity.
It should be noted that, unlike density and porosity, permeability is a property that varies according to the direction in which the measurement is made and even, in certain cases, according to the sense in that direction in which the gas is flowing.
It is therefore essential to make quite a number of measurements in order to judge the quality of a batch, or to know the variation of permeability as a function of the direction of gas flow. As with all volumetric measurements, it is essential to keep the apparatus away from air currents and sources of heat.
Measurement is made of the rate of flow of a dry gas of known dynamic viscosity through a test piece of known dimensions under the action of a known pressure difference. The gas flow rate is measured either by a rotameter or by the displacement of air by water in a measuring cylinder. In the second case a correction is made if the air is not dried before passing through the test piece.