Application of krypton and nitrogen isotherms to characterisation of hydrophobized fine dispersional limestone material

The knowledge about the sorptive character of porous materials is important during their manufacturing, checking their quality and exploitation. In the case of hydrophobized materials such characterisation may be useful not only for description of porous structure but also for measurement of their hydrophobization degree. Two grain fractions of fine dispersional limestone of grain diameter in accordance with the manufacturer's data (Limestone Mine Czatkowice) equals less than 80 mu m for lime meal and 100-400 mu m for lime sand were investigated. The techniques of limestone powder hydrophobization were carried out in apparatuses of own design and are described in previous works of authors (Vogt, Opaliski, Chem. Engineer. Trans. 17:1711-1716, 2009; Vogt, Pol. J. Environ. Stud. 20:801-804, 2011; Vogt, Pol. J. Chem. Technol. 10:49-51, 2008; Buczek, Vogt, Polish Patent. PL 396668, 2013). All modified samples acquired the hydrophobic character but hydrophobic degree of materials was measured with the use of various techniques, therefore it was difficult to compare obtained results. It is the reason why the authors used the adsorption measurements as a method to characterize the hydrophobic properties of materials. In the adsorption measurement two gases: nitrogen and krypton were used as adsorbats. The adsorption isotherms were determined for both raw and modified by commercial modifiers (stearic acid, silicone preparation and bituminous preparation) fine dispersional limestone material. The volume of pores, specific surface area were calculated from the experimental adsorption isotherms (Rouquerol et al., Adsorption by powders and porous solids, Academic press, London, 1999; Gregg, Sing, Adsorption, Surface Area and Porosity, Academic Press, London, 1982). The adsorption value obtained for hydrophobized materials is generally lower than for raw materials. Obtained results enable us to make characterization of the fine dispersional limestone after the hydrophobization process. Regardless of the gas (nitrogen or krypton) used the adsorption value obtained for hydrophobized materials is in principle lower than for raw materials. However, it is more important that the mutual position of the isotherms obtained for materials modified with the use of individual modifiers is the same for both used adsorbs, krypton and nitrogen. This fact makes it possible to determine the degree of hydrophobization of the lime material modified with the use of various modifiers.