Stress and cracking in membranes during drying

Extensive stress measurements has been reported in mesoporous alumina [13,26], titania and alumina-titania composite membranes [13,27] supported by 

The membranes were synthesised from AlOOH (boehmite) sols with a typical (standard) concentration of 1 mol AlOOH/1, stabilised at pH = 4 with HNO3. Ti02 sols had a typical concentration of 0.3 mol Ti02/1, composite membranes of AlOOH and Ti02 were obtained by mixing the sols. 

In a number of cases polyvinylalcohol (PVA) with an average molecular weight of 72000 Dalton was added to the boehmite sol (35 g PVA/1 sol). Ti02 sols were sometimes mixed with 3.5 g hydroxy propylcellulose (HPC) with an average molecular weight of one million Dalton. 

The final membrane thickness was dependent on dipping time and is usually given after calcination at 600°C, resulting in Y-alumina or titania (anatase) membranes. 

Drying rates are varied by controlled changes of conditions in the drying chamber. The wind velocity has been varied between 3.25 m/s to 0.5 m/s (wind screens present). The last value corresponds with a mild drying regime and is used unless stated otherwise. 

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