How is a ceramic membrane made?

Producing ceramic membranes involves several complex processes, including high temperatures of more than 2100 ˚C and inert atmosphere. Therefore, special manufacturing equipment, expertise, carefulness, and clearly defined precautionary and security protocols are required. Let us dive into how a ceramic membrane is made.

Membrane technology can be produced utilizing various materials and methods. Still, the material silicon carbide provides some unique membrane features such as extreme durability, enhanced chemical and mechanical stability, the highest flux, and lastly, it is among the best materials when it comes to fouling resistance. This is due to the material's extreme strength, as it is the second hardest material in the world, solely surpassed by diamonds. Therefore, silicon carbide is also applied in industrial applications more frequently. Learn more about the unbreakable material silicon carbide here. However, this material also demands high sintering temperatures compared to other materials, such as polymeric membranes. Yet, this is compensated by an extremely durable membrane with a long lifetime, delivering reduced operational and maintenance costs. Silicon carbide provides high endurance and small pores, which is crucial as the secret behind a successful membrane lies in the pores' size, shape, and chemistry. Read more about why you should utilize ceramic membranes here.

Production Steps Ceramic Membrane

The Production Steps

Ceramic membranes are produced in a multi-step process, and each step plays a crucial role in achieving durable, high-quality ceramic membranes. Basically, ceramic membranes are produced in four overall steps:

  1. A silicon carbide mix is made.
  2. The silicon carbide mix is extruded into the ceramic membrane substrate, and the coating is added to the membrane substrate.
  3. The membrane is sintered, and now this is a ceramic membrane ready for application.

However, the four steps have many more details, so let us dive into the details. 

1) Silicon Carbide Mix

In the first phase, a paste is made with a mixture of multiple raw materials, which contains silicon carbide powder, dispersant, and solvent. It is crucial to use the correct raw materials and quantities to obtain consistent, high-quality membranes. The mix is homogenized thoroughly before a binder is added to strengthen the mechanical stability of the membrane.

2) Extrusion

The silicon carbide mix is extruded to the correct shape and cut at the right length in the second phase. It is imperative to extrude the coarse membrane support to produce even the most complex geometries when the mixture is wet. The membrane substrate can be extruded in customized geometries, beneficial for various filtration applications. Likewise, the membrane support must be smooth and homogeneous in order to obtain high flux and mechanical strength. Once the correct geometry is obtained, the membrane substrate should dry. If it is not dried sufficiently, the membrane shape might be damaged, which will lead to a malfunctioning membrane. Thus, it is essential to obtain complete dryness to have a stable and firm ceramic membrane substrate.

3) Coating

In the third step, a coating layer is added to the membrane substrate. The coating controls the membrane pore size, and thus, the selectivity. Furthermore, the coating provides ruggedness and durability. Learn more about what the ceramic membrane coating layer does here. The coating can be added by utilizing three methods, which are 1) spray coating, 2) dip coating, and 3) slip coating. However, dip-coating is the most preferred method due to its simplicity. Still, the selected method should be chosen with care as it affects the thickness of the layer. For instance, the dip-coating technique delivers layers within the range of 0.16-100 microns, while the spray coating technique delivers layers within 60-200 microns.

Thus, the method should be chosen based on its simplicity, the membrane geometry, and the filtration range the membrane operates within. Moreover, more layers can be added to produce upper layers with higher selectivity. Typically, up to four coating layers can be added to the membrane substrate.

Afterward, the membrane should dry again to obtain a consistent coating layer. It is essential to get an even coating layer because an uneven layer will make different parts of one membrane perform differently.

4) Sintering

In the fourth step, the ceramic membrane is burned in a high-temperature furnace with an inert atmosphere of up to 2100 ˚C for 2-3 days. This process provides durable physical and chemical properties.

In comparison, oxide-based membranes are merely sintered in a furnace of 1200-1600°C. It is the high sintering temperature of up to 2100 ˚C as well as the duration of 2-3 days that heavily add to the production costs of ceramic membranes and make the industrial-scale production of SiC membranes costly. Still, the high sintering temperature is necessary to achieve the desired physical and chemical properties of a SiC membrane.

Ceramic Membrane Quality Testing

Quality Testing

It is crucial to have quality controls during all the production processes to secure an excellent standard of membrane technology. Likewise, the ceramic membranes are quality tested once produced to ensure a well-functioning, high-quality, and extremely durable ceramic membrane. If a ceramic membrane is made correctly, it has a long lifetime and requires minimum maintenance, reducing OPEX through a more efficient operation with low maintenance costs. Simultaneously, the membranes support a green transition, enabling efficient and sustainable water management.

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Read about ceramic membranes and how they enable an extremely efficient and durable liquid filtration process, ensuring compliance with even the strictest environmental regulations and discharge limits. 

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