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 that used for 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.
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:
- A silicon carbide mix is made.
- The silicon carbide mix is extruded into the ceramic membrane substrate.
- The coating is added to the membrane substrate.
- The membrane is sintered, and now this is a ceramic membrane ready for application.
However, there are many more details to the four steps, 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.
In the second phase, the silicon carbide mix is extruded to the correct shape and cut at the right length. It is imperative to extrude the coarse membrane support when the mix is wet to produce even the most complex geometries. The membrane substrate can be extruded in customized geometries, making it useful for various filtration applications. Likewise, it is essential that the membrane support is 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 full dryness to have a stable and firm ceramic membrane substrate.
In the third step, a layer of coating 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 is to operate within. Moreover, more layers can be added to produce upper layers with higher selectivity. Typically, up to four layers of coating 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 layer of coating because an uneven layer will make different parts of one membrane perform differently.
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.
During all the production processes, it is crucial to have quality controls in order 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, leading to reduced OPEX through a more efficient operation with low maintenance costs. Simultaneously, the membranes support a green transition as they enable efficient and sustainable water management.
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