A modified model for alumina membranes formed by gel-casting followed by dip-coating

α-Al2O3 membrane coating (top layer) was formed by dip-coating and investigated based on full factorial design of experiments. Statistical analysis showed that the effects of two variables; dipping time and withdrawal speed of the substrate, were highly significant in determining the thickness of the top layers (α<0.001). A modified model was developed to interpret quantitatively the formation process of the top layers onto the porous substrate during dip-coating. In this model, the effects of all variables affecting the top layer thickness were considered simultaneously. The experimental data corresponding to α-Al2O3 membranes obtained from suspensions with different volume fractions of ceramic powder showed good agreement with the model. The root mean square deviation was less than 0.02.