Adaptive Ceramic Filters Based on Electrochemically Produced Membranes

What are e-membranes?

Ceramic filtration membranes offer several advantages over polymer membranes: they exhibit good chemical and abrasion resistance and can be regenerated through thermal treatment. In addition to the conventional powder-based manufacturing route, electrochemical processing also enables the production of ceramic membranes with unique properties – electrochemically produced membranes or “e-membranes”.

Manufacturing and properties

Electrochemical oxidation (anodization) is an established industrial process for surface treatment of aluminum materials. It produces an oxide layer on the aluminum surface with a thickness ranging from less than one micrometer to several hundred micrometers and with a directional pore structure (Figs. 1 and 2). In a second electrochemical process step, the oxide layer is fully and non-destructively detached from the aluminum surface, yielding a free-standing, highly porous aluminum oxide membrane.

The pore diameter (10–400 nm), pore density (10⁸–10¹⁰ cm^-²) and membrane thickness (0.1–600 μm) can be precisely adjusted by selecting appropriate process conditions. In trials carried out to date, e-membranes were produced with sizes up to 20 cm², and there is potential for even larger areas.

Application potential

Despite their very uniform pore size distribution and high porosity, e-membranes have not yet been used in filtration applications. One contributing factor here is their low membrane thickness, which limits mechanical stability. However, initial tests demonstrate their potential for particle filtration from aqueous media (Fig. 3), as shown here with a TiO₂ suspension. The e-membranes were stable under pressures of several bar, although the full performance range has not yet been explored.

Potential applications in the ultra- to microfiltration range include the separation of inorganic particles and microplastics, and in the case of e-membranes with very small pore diameters, the separation of complex organic molecules. Since they have relatively hydrophobic surface properties, they can also be used for treating organic-rich media. Beyond filtration, e-membranes offer promising possibilities in such areas as sensors, catalysis, energy storage, material separation and microbiology.

Services offered
 

• Manufacturing of anodization layers and e-membranes with tailored properties
• Collaborative research projects to develop practical applications of e-membranes