Estimation of the Parameters of the Porous Structure and Permeability of Monofraction Ceramics
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Vol. 61, No. 3, September, 2020
ESTIMATION OF THE PARAMETERS OF THE POROUS STRUCTURE AND PERMEABILITY OF MONOFRACTION CERAMICS Yu. N. Kryuchkov1,2 Translated from Novye Ogneupory, No. 5, pp. 66 – 67, May 2020.
Original article submitted April 24, 2020. A method for assessing the structure parameters of porous ceramic materials by porosity and particle size is presented. Based on it, a physically more rigorous than the well-known Cozeny formula is obtained, a formula for determining the average (hydraulic) radius of the capillaries of permeable materials. The presented results of the calculation of the average radius of the capillaries of porous ceramics based on electrocorundum according to the obtained formula are in better agreement with experimental data than the calculations by the Cozeny formula. Keywords: porous permeable ceramics, specific surface, sinuosity coefficient of capillaries, particle size, average radius of capillaries, permeability.
voluted non-intersecting cylindrical capillaries of length L can be found as:
Porous ceramic materials are used for filtering liquids, gases, metal melts, catalytic purification of liquids and gases from harmful substances, gas dispersion in liquids and metal melts, adsorption purification of liquids or gases, and so on. The structure of porous powder materials is chaotic. Capillaries have narrowing (throat) and expansions (in the areas of their intersection with each other). In this case, the direction of movement of liquid or gas in the capillaries may differ from the direction of filtration, which is accounted for by the sinuosity coefficient of the capillaries [1 – 4]. The permeability of ceramic materials and products depends mainly on the size of the initial particles, the porosity of the material and the three-dimensional structure of the porous space. The features of this structure in the study of permeable materials are often ignored or accounted for only roughly [3, 4], since they use not three-dimensional models of a porous material, but models in the form of non-intersecting capillaries. If we imagine the threshold space of a permeable ceramic material as a simple system of non-intersecting tortuous cylindrical capillaries with an average radius r, then the capillary sinuosity coefficient x (the ratio of the capillary length to the material thickness) will also affect the specific surface area of the material So and, accordingly, the radius r. This can be confirmed with the following analysis. Assume a material of thickness h has an area S and in it, N con1 2
L = hx,
(1)
where x is the coefficient of capillary sinuosity. Then the volume of all pores V, the porosity P and So (the surface of the capillaries in a unit volume of the material) is determined by the following expressions: V = Npr2L = Nr2xh,
(2)
P = Npr2L/Sh = Npr2x/S,
(3)
So = 2pNrL/Sh = 2pNrx/S.
(4)
From expression (4) is follows that, with the same porosity, the capillary sinuosity coefficient (increases the specific surface area So of porous materials. This must be taken into acco
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