Fabrication of Uniform Ceramic Membrane Coatings via Shear‐Minimized Dip‐Drain Process

ABSTRACT Ceramic membranes are widely used in water treatment and oil/water separation owing to their excellent chemical stability and long‐term durability. However, achieving a uniform coating layer on long or multichannel ceramic supports using conventional dip‐coating remains challenging, primarily owing to shear‐induced flow, gravitational slurry redistribution, and thickness gradients formed during substrate withdrawal, which significantly hinder scalability and reproducibility. Herein, a shear‐minimized dip‐drain process is proposed as an alternative method to fabricate uniform ceramic membrane layers on complex multichannel supports. Unlike conventional dip‐coating, the substrate remains stationary while the coating slurry is discharged at a controlled rate, minimizing relative motion and effectively suppressing shear flow and gravitational pooling. Systematic investigation of the drain rate revealed that increasing the discharge speed considerably reduced coating thickness and eliminated surface cracking, with an optimal condition at 2 mm/s. Microfiltration and ultrafiltration layers exhibited well‐defined pore structures (average pore sizes of ∼0.19 µm and 7–8 nm) while maintaining pure water permeability comparable to dip‐coated membranes. A cross‐sectional analysis showed minimal thickness variation, and oil/water separation tests confirmed that the oil rejection exceeded 99%. Overall, the dip‐drain process offers a practical solution to the limitations of conventional dip‐coating and has strong potential for industrial‐scale ceramic membrane manufacturing.