Effect of addition of poly-N-vinylpyrrolidone on the surface characteristics of zirconia gel

The surface characteristics of pure and poly-N-vinylpyrrolidone-containing zirconia gel were investigated by nitrogen adsorption at - 1960C. Structural and phase changes were studied by X-ray diffractometry and differential thermal analysis. The inclusion of poly-N-vinylpyrrolidone did not retard the appearance of the X-ray diffraction patterns of zirconia gel but only led to a decrease in their relative intensities. Surface characteristics were greatly affected by inclusion of the polymer in the gel, as evidenced by a remarkable increase in surface area, total pore volume and pore radii. The optimum increase was observed for the sample containing 5% of poly-N-vinylpyrrolidone. On thermal treatment at 3000C the pure sample exhibited an increase in the micropore volume which can be attributed to perforation of the gel during the evolution of a considerable amount of hydrated water. On the other hand, the inclusion of poly-N-vinylpyrrolidone led to a strengthening of the skeletal wall of the gel to withstand perforation. However, thermal treatment at 5500C led to a marked decrease in the surface area, especially for samples containing high percentage of poly-N-vinylpyrrolidone, e.g. 10%. This decrease may be attributed to shrinkage of the polymer at higher temperature which led to the disappearance of a great fraction of the area. (author)