Separation of adsorbed and intercalated hydrazine in hydrazine-hydrate intercalated kaolinite by controlled-rate thermal analysis

The thermal behavior of a low-defect kaolinite fully expanded with hydrazine-hydrate has been investigated in a nitrogen atmosphere at a constant, preset decomposition rate of 0.15 mg/min. Under controlled-rate thermal analysis (CRTA) conditions, it was possible to distinguish between loosely bonded (adsorbed) and strongly bonded (intercalated) reagent. The loosely bonded reagent 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 hydrazine-hydrate is connected to the kaolinite inner-surface OH groups by the formation of hydrogen bonds. Based on the thermoanalytical results, three different types of bonded reagent could be distinguished in the complex. Type I reagent (approximately 0.20 mol hydrazine-hydrate/mol inner-surface OH) is liberated between approximately 50 and 70 degreesC. Type 2 reagent is lost between approximately 70 and 85 degreesC, corresponding to a quantity of 0.12-0.15 mol hydrazine-hydrate/mol inner-surface CH. Type 3 reagent is lost in the 85-130 degreesC range, amounting to some 0.30 mol hydrazine/mol inner-surface OH. The quantity of this third type of reagent is independent of the conditions of sample pretreatment (drying). The liberation of bonded hydrazine-hydrate can be followed by FT-IR (DRIFT) spectroscopy in the OH and NH stretching ranges as well. When the complex is heated to 70 degreesC under CRTA conditions, a new reflection appears in the XRD pattern with a d-value of 9.6 Angstrom, in addition to the 10.3 Angstrom reflection. This new reflection disappears in contact with moist air and the complex re-expands to the original d-value of 10.3 A. The appearance of the 9.6 Angstrom reflection is interpreted as the expansion of kaolinite with hydrazine alone, while the 10.3 A one is due to expansion with hydrazine-hydrate.