Hydrothermal Method for Preparation of Crystal

Hydrothermal Method for Preparation of Crystal

Hydrothermal method: When water is heated in a closed vessel (autoclave) the pressure inside is increased and water remains as liquid above its normal boiling point. This condition is called hydrothermal. The heating of reactants in ‘super-heated water’, (also known as supercritical water; >373 K) has received much attention in synthesising crystals, particularly in mineralogy.

Hydrothermal techniques can be used to synthesize a wide variety of materials

– zeolites and aluminophosphates

– optical materials like KTP (KTiOPO4)

– BaTiO3 (widely used ferroelectric)

Hydrothermal synthesis of quartz

Uses a temperature gradient to dissolve the reactant at higher temperature, which is transported up the reaction tube by convection, then crystallizes out at a lower temperature.

Example: Hydrothermal synthesis of CrO2

Cr2O3 is the stable oxide of chromium at normal conditions.

Cr2O3 + CrO3 → 3CrO2

CrO3 → CrO2 + ½ O2

3 CrO3 + Cr2O3 → 5 CrO2 + O2