Co-sintered ceramic membranes for separation applications: Where are we and where to go?

Owing to their high mechanical strength and thermal/chemical resistance, ceramic membranes play an important role in water treatment, gas separation, gas/solid filtration, and other applications. However, compared with the market share of polymer membranes, that of ceramic membranes is lower in industrial applications owing to high costs of materials and sintering consumption, which account for ∼ 20 % and ∼ 60 % of the total cost, respectively. Reducing the sintering consumption would widen the usage range of ceramic membranes. The co-sintering process, which combines several sintering processes into a single process, can lower the sintering consumption by drastically shortening the fabrication time. However, the mismatched sintering stress and sintering temperature between the two layers in the co-sintering process degrade the microstructure, integrity, and performance of the product. This review systemically investigated the three evolutionary stages of sintering processes (free sintering, constrained sintering, and co-sintering) and analyzed the sintering consumption, interfacial strength, and application areas of co-sintering. To provide deep insights regarding the co-sintering process of ceramic membranes, this review analyzed and discussed applications of co-sintering to solid oxide fuel cells and low-temperature co-fired ceramics processes. Finally, it discussed co-sintering processes for fabricating ceramic membranes, such as ceramic microfiltration and ultrafiltration membranes. Overall, this review can provide an important reference on ceramic membranes with low energy consumption for further industrial applications.