SiC-slurries are aqueous suspensions produced at manufacturing of silicon wafers. In addition of suspended Si, SiC und SiO2 particles they also contain polyethylene glycol and tensides. The goal was to concentrate the produced slurry of the Si-wafer cleaning process and to use the filtrate in the washing process again. To solve the problem a prototype HPM-system with a ceramic membrane of 0.1 m2 membrane area and 1kD molecular weight cut-off was used. The system was operated at a system pressure of 0.15 MPa and a feed flow of 120 l/h. Because the solid fraction of the slurry varied very strongly, the membrane separation was operated with two synchronous operating flow initiators. As expected and because of the selected refinement of pores in the membrane a clear pH-neutral permeate was produced (see figure in the middle below).
To demonstrate the efficiency of flow initiators after a period of 2.5 hours the active DTE flow initiator was switched off. The diagram right below shows impressively the decrease of the permeate flow immediately afterwards. Additionally in the permeate container the permeate volume increases slowly. Then the prototype HPMT- system was operated as long as the membrane was blocked. After 7 hours this situation occurred. Subsequently, after the test run the complete blocked membrane was cleaned. However, only a tenth of the initial membrane water equivalent was reached. For conventional operating modes this result illustrates that already after short time the membrane is blocked irreversibly.
Advantages of HPM-systems are:
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Increase of membrane life time
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Stabilising of permeate flux at 75% of the initial value for the conditions given
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Avoidance of irreversible blocking of the membrane
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Saving of production equipment and auxillaries
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Competitive advantages at silicon wafer manufacturing
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Shape of solid matter particles in an aqueous silicon carbide slurry
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