Cost-Efficient Fabrication of Ceramic Membranes through Co-Sintering: Reducing Energy Consumption and Enhancing Performance

Ceramic membranes can handle extreme conditions like high temperatures and exposure to harsh chemicals, which make them perfect for applications like water purification, gas filtration and cleaning up industrial waste. However, there’s a big challenge holding them back from wider use: they’re expensive to produce. One of the main reasons for this high cost is the sintering process, which is a crucial step in making these membranes. Sintering involves heating the membranes at extremely high temperatures to make sure they are strong and can hold up in tough conditions. However, this step is very energy-intensive and accounts for a large chunk of the total production cost. Moreover, the way to fabricate ceramic membranes is another problem compared with that of polymer membranes. Ceramic membranes require multiple layers to be built up as each one needs its own cycle of coating, drying, and sintering. On top of that, each layer must be sintered separately, which can sometimes lead to cracks or other defects that affect the quality of the final product. To tackle these problems, researchers have started looking into a process known as co-sintering so instead of sintering each layer individually. Co-sintering allows multiple layers to be processed at the same time that could potentially slash both the energy consumption and fabrication period. While this idea sounds like a game-changer, it still faces great challenges. The different materials used in the layers of ceramic membranes have different properties when they’re sintered—some might expand more than others, or shrink at different rates. This mismatch creates mechanical stress within the membrane, resulting in cracks or other structural problems. That’s exactly the challenge that a group of researchers from Nanjing Tech University, led by Professors Zhaoxiang Zhong and Yiqun Fan, set out to solve. Professor Yiqun Fan is one of the earliest scientists to develop co-sintering technique for the fabrication of ceramic membranes. He published a series of co-sintered ceramic membranes in Journal of Membrane Science (the most famous journal in the field of membranes) since 2006. These works made co-sintering preparation of ceramic membranes popular. They wanted to figure out how the co-sintering process could be optimized to avoid these issues and make ceramic membrane production more efficient and affordable. Their research focused on understanding how stress develops during the sintering process and finding ways to reduce it. By digging into the mechanics of how the materials behave under heat, they aimed to identify strategies that would allow for the creation of strong, high-performance membranes without the usual high costs. If successful, this work could make ceramic membranes a much more accessible option for industries that need reliable, durable filtration systems. They systematically summarized the works in the co-sintered ceramic membrane and published a review paper in Separation and Purification Technology

The team worked with two layers designed for microfiltration and used different ceramic powders for each layer, trying to create a final product that wouldn’t crack and would perform well. A big part of this was controlling how much each layer shrinks during the sintering process. The researchers played around with different particle sizes for the cordierite powders used in each layer, reasoning that if they could manage the shrinkage, they could reduce the stress on the membrane. After sintering the layers to 1200°C, they found that the difference in shrinkage between the two layers was only 0.59%. This small difference helped them to produce a crack-free membrane with a uniform pore size. This showed that they could lower the stress during sintering and make a more durable membrane by carefully choosing and controlling the size of the particles.

Afterward and building on this success, the team moved on to a more complicated structure: a “sandwich” membrane with multiple layers. They added a layer of silicon carbide (SiC) whiskers between an alumina layer and a macroporous support. These whiskers acted almost like a buffer, stopping the alumina particles from penetrating too deeply into the support layer, which helped to reduce filtration resistance. After sintering the entire structure at 1000°C, the produced membrane had excellent water permeance—645 liters per square meter per hour per bar of pressure (L·m⁻²·h⁻¹·bar⁻¹)—and stayed structurally sound. This experiment really showed how using the right materials, like the SiC whiskers, can help reduce stress between layers and create membranes that are both strong and efficient. Moreover, the authors experimented with a ceramic support made from fly ash, a low-cost material, and combined it with mullite whiskers and an alumina membrane layer. After sintering the entire structure at 1050°C, they found that adding mullite whiskers reduced the shrinkage difference between the support and the membrane, which made it less likely for the membrane to crack. The final product was highly effective at separating oil from water, with an average pore size of about 100 nanometers and a water permeance of 450 L·m⁻²·h⁻¹·bar⁻¹. This was a big win as it showed that even cheaper materials like fly ash, when paired with advanced techniques, could still produce high-quality ceramic membranes that perform well.

Not stopping there, the team pushed the boundaries even further by investigating the use of co-sintering to make ultrafiltration membranes from 50 nm to below 5 nm and these membranes are tricky to produce because they have very small pores and tend to shrink more during the sintering process. For example, the researchers worked with a bi-layer membrane made of alumina and zirconia, sintering it at a carefully controlled 1050°C. By closely managing the temperature, they were able to prevent the top layer from cracking and still achieved a water permeance of 650 L·m⁻²·h⁻¹·bar⁻¹. According to the authors, their experiment highlights how important it is to carefully control the temperature during sintering especially when dealing with materials that shrink at different rates.

We believe the real impact of the work of Associate Professor Dong Zou, Professor Zhaoxiang Zhong, and Professor Yiqun Fan comes from how it addresses a problem that’s been limiting the use of ceramic membranes for a long time: the cost of making them. What the researchers managed to do here is find a way to significantly lower the energy needed to manufacture these membranes, all without compromising their performance. The breakthrough comes from the fact that they figured out how to sinter multiple layers in a single step, instead of having to process each layer separately. This could make producing ceramic membranes much faster and cheaper, which in turn could open the door for more industries—like water purification and gas filtration—to start using them. These are industries where the durability of ceramic membranes is essential, and where polymer-based membranes simply can’t keep up. Moreover, the team also showed how they could maintain the quality of the membranes, even with the cost-saving methods they used. By controlling the sintering temperature and managing the stress between the layers, they were able to prevent defects like cracking, which is a common issue when sintering ceramic materials. This is a big deal because it means that these membranes aren’t just cheaper to make but they’re also better in terms of how they perform. We think the work of Nanjing Tech University scientists essentially sets the stage for new advancements in membrane design where we might see even more specialized membranes that can handle highly corrosive environments or filter out extremely fine particles, areas where polymer membranes fall short. What’s also really interesting is the use of low-cost materials like fly ash (a kind of typical  waste product) will have a positive environmental impact. This study aligns with the growing trend of industries looking to cut their environmental footprint while still maintaining efficiency and quality.