Preparation and Characterization of an 8.4 Hydrate of Kaolinite

-A stable 8.4/~ hydrate of kaolinite was prepared by exchanging ethylene glycol for water in the 10.8 A intercalate of ethylene glycol in kaolinite. The hydrate of kaolinite was characterized by XRD, FTIR and TGA/DSC. From the TGA data, one can estimate that there is 0.60 water molecule per A12Si20~(OH)4 units. The IR data suggest a similarity of the local environment of the intercalated water in this 8.4 A hydrate of kaolinite and the 8.4 A hydrate of nacrite previously described by Wada (1965). Key Words--Ethylene glycol, Hydrate of kaolinite, Intercalation, Kaolinite, Organo-day. I N T R O D U C T I O N Interlayer water in the kaolin minerals has attracted considerable attention over the years (Giese, 1988). Halloysite is known to readily intercalate water to yield a 10 A hydrated phase and an 8.35 A hydrate ofnacrite has been prepared by first intercalating with potassium acetate and then washing with water (Wada, 1965). Kaolinite does not naturally exist in a hydrated form, and hydrates that may be formed by displacing a previously intercalated species by washing with water are not stable and quickly decompose. Costanzo and coworkers have prepared various synthetic hydrates of kaolinite by first treating the KaoDMSO intercalate with ammonium fluoride to exchange some of the interlamellar hydroxyl groups with fluoride and then washing with water (Costanzo and Giese, 1985, 1990; Costanzo et al., 1984; Costanzo et al., 1982). They succeeded in forming both 8.4 A and 8.6 A monohydrates of kaolinite as well as two types of 10 /~ dihydrates. The stable 8.4 /~ hydrate could only be formed if20% or more of the surface hydroxyls could be replaced with fluorine. The water molecule in the 8.4 A hydrate was found to be keyed into the silicate sheet and was termed "hole water." Water in the 10 A hydrate was found in both the "hole" environment and the more weakly bound "associated" environment. In the course of our work involving the relationship between two ethylene glycol organokaolinite phases (Kao-EG 9.4 ~, and Kao-EG 10.8 ~) (Tunney and Detellier, 1994), a stable 8.4 A hydrate of kaolinite was prepared without first replacing some of the interlamellar hydroxyl groups with fluorine. This was then characterized by XRD, FTIR and TGA/DSC.