Application of Atmospheric Pressure Atomic Layer Deposition on Long Tubular Ceramic Membranes
Mrinal Roy (TU Delft - Civil Engineering & Geosciences)
Sebastiaan Heijman – Mentor (TU Delft - Civil Engineering & Geosciences)
Ran Shang – Mentor (TU Delft - Civil Engineering & Geosciences)
Ralph Lindeboom – Mentor (TU Delft - Civil Engineering & Geosciences)
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Abstract
Recently, the use of atomic layer deposition (ALD) technique for depositing thin films of metal oxides on membrane substrates has proved to be an effective way to fabricate commercially available UF or NF membranes to get tight UF/NF ceramic membranes. The main advantage of this technique is controlled deposition of a monolayer of metal oxides. This project was done to study the effect of ALD on 0.5 m long tubular membranes. TiO2 was deposited on the membranes by means of atmospheric pressure atomic layer deposition (APALD). This is different from most of the reported studies that use vacuum-based ALD. TiCl4 and H2O were used as the main precursors for depositing TiO2 through 2, 3 or 4 cycles of APALD. The growth rate of the deposited layer per cycle under different experimental conditions was measured indirectly using silicon wafers through ellipsometry. The effect of ALD was determined by measuring the membrane permeability and molecular weight cut-off (MWCO) values of the membranes before and after coating. The results obtained showed a variation in growth rate per cycle (GPC) of the deposited layers for different experimental conditions. APALD was performed on 6 membranes and the GPC rate was acceptable for only 2 membranes (0.14 nm/cycle and 0.03 nm/cycle), whereas the GPC for the other membranes was very high (more than 1 nm/cycle). After deposition, the 2 membranes with acceptable GPC rate showed a decrease in MWCO value by 627 Da and 405 Da respectively. These results demonstrated that APALD could be used to fabricate ceramic membranes, but only at proper experimental conditions for TiO2 deposition. An improved Carman-Kozeny model was also developed based on the MWCO value and on the GPC value, in order to predict the porosity and the permeability of the membranes. The results of the model and the measured permeability were compared; for some membranes, the model predicted correctly the permeability after coating.