Filter pretreatment techniques

A major aspect of an SLS process may be conditioning of the slurry to improve its filterability. Table 11.4 summarizes common pretreatment techniques, and Table 11.5 lists a number of flocculants and their applications. Some discussion of pretreatment is in Section 11.3. 

Neither technique measures all the chlorides present in steel. The Bresle technique is estimated to have around 50% leaching efficiency the filter paper technique is somewhat higher. One could argue, however, that absolute values are of very limited use if chlorides are present in any quantity, they will cause problems for the paint. It does not perhaps matter at all that a measurement technique reports 200 mg/m, when the correct number was 300 mg/m. Both are far too high. This, indeed, is a weakness in the field of pretreatment quality control it is not known how much chlorides is too much. Although there is some consensus that the acceptable amount is very low, there is no consensus on what the cut-oflf value is [18-20]. 

Centrifugation alone is not sufficient to separate Np solid material from the solution (j) ). Thus, the Np solution concentrations and oxidation state analyses were determined from aliquots filtered through approximately 1.8 nm pore-size Centriflo membrane cones (Amicon Corp., Lexington, MA). Each filter cone was pretreated with an initial aliquot of the suspension to be filtered. Tests using successive filtration confirmed that no significant amounts of Np were being sorbed by the filter cones. The solutions were alpha counted by liquid scintillation techniques. Major cations in the solutions were determined by inductively coupled plasma spectrometry (ICP) analyses. 

Analysis of 02 as well as C02 in exhaust gas is becoming generally accepted and is likely to be applied as a standard measuring technique in bioprocessing. It is possible to multiplex the exhaust gas lines from several reactors in order to reduce costs. However, it should be taken into account that the time delay of measurements with classical instruments is in the order of several minutes, depending on the efforts for gas transport (active, passive) and sample pretreatment (drying, filtering of the gas aliquot). 

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