CHARACTERISTICS OF FINE PORES IN SOME HALLOYSITES

Isotherms were obtained for nitrogen adsorption and desorption on seve n halloysite-rich samples from New Zealand and Western Australia. Calc ulations from these isotherms indicate that halloysites with mainly sm all particles (< c. 0.08 mu m in width) had abundant cylindrical pores with narrow size distributions in the 5-15 nm range. They also indica te that halloysites with mainly large particles (> c. 0.1 mu m in widt h) had few if any pores in the mesopore range (2-50 nm). Transmission electron microscopy (TEM) shows that cylindrical pores originate from the central holes in tubular particles. The TEM also suggests that sli t-shaped pores can originate from the shrinkage of blocks of layers up on dehydration of halloysite.