![Fig. 5.SEM images of SiC porous microstructures: (a) asymmetric membrane with a top layer [ 67]; (b) top layer containing SiC nanofibers [28]; and (c) SiC hollow fiber [48].](/figures/fig-5-sem-images-of-sic-porous-microstructures-a-asymmetric-1u1472rg.webp)
![Fig. 14.SiC membranes for wastewater treatment (a) as tube assembled in a stainless steel module [ 86], (b) flat sheet membrane assembly [ 87] and (c) multi-channel tube [88]. Figs. a, b and c reprinted under copyright permission by Alsys, Cembrane and Saint -Gobain, respectively.](/figures/fig-14-sic-membranes-for-wastewater-treatment-a-as-tube-6r20qnn4.webp)
![Fig. 13.(a) Simplified schematic of filters and catalytic filters, and (b) image of SiC diesel particulate filters (DPFs) [ 110]. Figs. b reprinted under copyright permission by Ibiden.](/figures/fig-13-a-simplified-schematic-of-filters-and-catalytic-312nhwm2.webp)
Q2. What is the effect of sintering on the membrane?
Upon sintering, the top layer attains the required pore size control enabling the membrane to separate gas/liquid generally by size exclusion, though sorption/diffusion can also affect the separation of molecules.
Q3. What is the common approach to improve hydrothermal stability?
A common approach to improve hydrothermal stability is to embed metal oxide with the thin-film matrix, a technique widely used for the preparation of SiO2 membranes [94,95].
Q4. What are the steps of the fabrication of porous substrates?
The fabrication processing steps of porous substrates include raw materials synthesis and beneficiation, shaping into green bodies, as well as intermediate and final thermal treatments.
Q5. What is the importance of the industrial deployment of SiC filters and membranes?
Thermal and chemical stability is also addressed in view of the importance of the industrial deployment of SiC filters and membranes.
Q6. What are the characteristics of siC filters and porous membranes?
SiC filters and porous membranes have unique characteristics when compared to their oxide counterparts, including high temperature resistance and, in some applications, improved chemical stability.
Q7. What are the common ingredients used for a pre-sintering conditioning of substrates?
Thermal treatment temperatures varied from low as 450 �C to as high as 2250 � C. Lower temperatures are generally applied for a pre-sintering conditioning of substrates.
Q8. What is the reason that many SiC-based composites were sintered at temperatures in excess?
mechanical strength is the reason that many α-SiC-based composite substrates were sintered at temperatures in excess of 1700 � C, though the trade-off is densification, which must be counteracted by the purpose of producing porous substrates.
Q9. What was used as a binding agent for the production of composites?
Glass frit was employed as an alternative α-SiC (4.5, 6.7, 14.5),Kaolin (2.1) a , Methyl cellulose (MC) b , Water d SiC (0.5, 3, 30), SodiumExtrusion 16 channelsFlat tubes (200 �50 � 4)Extrusion Plaques400 � C/4 h; 1200–1500 � C/1 h in air800-1100[43–45][46,47]sintering aid for the production of composite substrate, though as a silica-based glass powder, it was also used as a binding agent.
Q10. What was the common method used to deposit top layers on substrates?
The majority of the methods used to deposit top layers on substrates were slip casting or dip coating, though spray coating was also reported.
Q11. What are the advantages of sintering ceramics at high temperatures?
These high temperatures allow for the formation of necks in ceramic particles during sintering, thus strengthening the mechanical stability of the SiC or SiC composite substrate.
Q12. How many publications are available for He/N2 permselectivity using SiC?
As CH 4 concentration is likely to be very low at the back end of the natural gas processing plant, currently there is limited number of publications for He/N2 permselectivity using SiC membranes and best results are 21.
Q13. How much mass gain was observed in the alumina-doped support?
At 600 � C, the alumina-doped support showed mass gain of 1.3 mg cm �2, while the non-doped support showed mass gain of 0.7 mg cm 2.
Q14. What is the main reason for the increase in permeation of the smaller gases?
Another important aspect of these high quality SiC membranes is that¼the permeation of the smaller gases increases with temperature while the permeation of the large gases decreases or remains constant with temperature.
Q15. What is the principle of multi top layer coating and sintering?
This practice of multi top layer coating and sintering [68] follows a principle of reducing coating defects on thin films, which are susceptible to defect formation due to porous substrate surface roughness, environmental dust and other factors.
Q16. How did Han et al. test the mechanical strength of SiC porous filters?
Han et al. [30] tested SiC porous filters from 30 to 800 �C and reported that the mechanical strength decreased from ~10 to ~4MPa after 6 cold-hot cycles for non-reinforced SiC samples.
Q17. What is the effect of Fick’s law on the transport of liquids through SiC?
Fick’s law is also applicable for the transport of liquids through SiC membranes, which can be simplified (Eq. (2)), where the flux equals to the mass transfers coefficient times the pressure gradient applied through the membrane (J PΔp).
Q18. What is the yard stick to compare the performance of mem-branes?
Another excellent yard stick to compare the performance of mem-branes is a gas selective factor (SA/B), also known as permselectivity.
Q19. What is the way to avoid fouling?
Fouling studies could be accompanied by designing surface patterns to avoid fouling in tandem with computer fluid dynamic (CFD) modeling and validation.
Q20. What is the way to measure the stability of SiC membranes?
Within a reasonable pH operation, SiC filters and membranes are stable, but at very low or very high pH their stability is greatly reduced.
Q21. What is the equation for the flux of liquids through the membrane?
This equation shows that the flux of liquids through the membrane increases proportionally as a function of the pressureJx ¼�DK e dpdx(Eq. 4) gradient.
Q22. What is the role of siC in the separation of gas and liquid?
SiC filters and membranes are becoming integral part of separation of gas and liquid in processing industries such as wastewater, energy, gas cleaning, gas separation, food and pharmaceutical.
Q23. What is the main reason why ceramic membranes are more cost competitive?
ceramic membranes have become more cost competitive and are likely to continue the downward trend in price for the same reasons as polymeric membranes did in the past.
Q24. How does Darcy’s permeability change with the pore size?
Fig. 6b also shows that Darcy’s permeability increases as a function of the pore size, although there is a significant variation, as results are scattered by up to two orders of magnitude.