Release:
2019, Vol. 5. №1About the authors:
Zoya A. Ishkova, Associate, Earth Cryosphere Institute, Tyumen Scientific Centre of the Siberian Branch of the Russian Academy of Sciences; z.ishkova@yandex.ruAbstract:
Studies of the porous structure of solids are based on analytical methods, the number of which is currently over 60. Those methods are built on the physical principles of the porous structure parameters measure.
The following methods are used to determine the properties of microfiltration membranes: scanner electron microscopy, the “bubble-point” method, mercury porometry, and permeability measurements. The first three methods are used for the structural parameters, the last one — for the mass transfer characteristics. The method of determining the “bubble point” of flat membranes measures the minimum pressure at which the gas slips through the pores of the sample filled with liquid. The discrepancy between the results of the experiment when using different saturated liquids is a disadvantage of this method. In addition, the results of experiments can be affected by the rate of increase in pressure, size, length, and pore morphology. With an increase in pressure, a sample may fail, since the method is based on the mechanical action on the sample.
The authors have proposed a method for the “crystallization-onset” of water, which is an analogue of the method for determining the “bubble point” and refers to capillary methods. Testing of this method took place on samples of ceramics of various porosities and showed a stable relationship between the values of the pressure of the “bubble point” and the temperature of the beginning of crystallization of water. In this regard, it was decided to apply this method to determine the size of maximum through pores for various types of membranes.
The authors carried out a series of experiments to determine the critical temperature — the “crystallization-onset” method — and the pressure of the first bubble overshoot — the “bubble-point” method for ceramics and for Vladipor membranes. They have developed linear correlation dependences and compared the results studying the effect of filters height on the experiments results. Repeated experiments showed reproducibility of experimental data and the effect of re-freezing on the stability of membrane properties.
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