Determination of the porosity characteristics by pycnometric methods

Data on pore size distribution in solids are obtained by pycnometric density-based methods for measuring the pore structure of materials. The results of measuring open porosity by weighing a dry sample followed by evacuation and saturation with distilled water at atmospheric pressure, impregnation with water under pressure using a hydrostat and mercury porosimetry are presented. The samples of porous nickel obtained using powder technology by sintering of the compacts from mixtures of nickel nanopowder with powder ammonium bicarbonate NH4HCO3 (a blowing agent), the volume fractions of which were 80 and 20%, respectively, were studied. A powder blowing agent with a particle size of 63 – 125, 140 – 200, and 250 – 315 μm was used. A theoretical estimation of the pore size available for the penetration of the impregnating liquid was carried out for three methods used for the determination of open porosity. It is shown that upon water saturation after evacuation the liquid can penetrate only into pores larger than 3 μm. Moreover, in porous structures with a large fraction of submicron pores, the actual values of the open porosity are significantly underestimated when using the method of saturation with distilled water after evacuation. The higher the fraction of fine pores in the material, the lower the open porosity value. The difference between the open porosity values determined by methods of water impregnation using a hydrostat and mercury porosimetry was negligible. It has been established that among three considered methods for measuring open porosity, only the method of saturation with distilled water after evacuation cannot be used in analysis of structures with submicron pores. The results obtained can be used to develop porous functional materials and products with a given porosity structure.

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