Hydrazine-hydrate intercalated halloysite under controlled-rate thermal analysis conditions

The thermal behaviour of halloysite fully expanded with hydrazine-hydrate has been investigated in nitrogen atmosphere under dynamic heating and at a constant, pre-set decomposition rate of 0.15 mg min(-1). Under controlled-rate thermal analysis (CRTA) conditions it was possible to resolve the closely overlapping decomposition stages and to distinguish between adsorbed and bonded reagent. Three types of bonded reagent could be identified. The loosely bonded reagent amounting to 0.20 mol hydrazine-hydrate per mol inner surface hydroxyl is connected to the internal and external surfaces of the expanded mineral and is present as a space filler between the sheets of the delaminated mineral. The strongly bonded (intercalated) hydrazine-hydrate is connected to the kaolinite inner surface OH groups by the formation of hydrogen bonds. Based on the thermoanalytical results two different types of bonded reagent could be distinguished in the complex. Type I reagent (approx. 0.06 mol hydrazinehydrate/mol inner surface OH) is liberated between 77 and 103degreesC. Type 2 reagent is lost between 103 and 227degreesC, corresponding to a quantity of 0.36 mol hydrazine/mol inner surface OH. When heating the complex to 77degreesC under CRTA conditions a new reflection appears in the XRD pattern with a d-value of 9.6 Angstrom, in addition to the 10.2 Angstrom reflection. This new reflection disappears in contact with moist air and the complex re-expands to the original d-value of 10.2 A in a few h. The appearance of the 9.6 Angstrom reflection is interpreted as the expansion of kaolinite with hydrazine alone, while the 10.2 Angstrom one is due to expansion with hydrazine-hydrate. FTIR (DRIFT) spectroscopic results showed that the treated mineral after intercalation/deintercalation and heat treatment to 300degreesC is slightly more ordered than the original (untreated) clay.