Unwanted Phases

Unwanted phases snch as liqnid sings, tramp metal, etc., can damage dry flame arrester elements so that they have to be replaced, or they can also block or ping the arrester free-area. ft is not always obvions when an arrester will be impacted by a liqnid sing or tramp metal. However, when this is snspected or has already occnrred in a process, several things can be done to avoid the problem as follows  

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Multi-channel compression systems divide the speech spectrum into several frequency bands, and provide a compression amplifier for each band. The compression may be independent in each of the bands, or the compression control signals and/or gains may be cross-linked. Independent syllabic compression has not been found to offer any consistent advantage over linear amplification [Braida et al., 1979][Lippmann et al., 1981][Walker et al., 1984], One problem in multi-channel compression systems has been the unwanted phase and amplitude interactions that can occur in the filters used for frequency analysis/synthesis [Walker et al., 1984] and which can give unwanted peaks or notches in the system frequency response as the gains change in each channel. 

The maximum additive concentration (MAC) is defined as the maximum amount of solubilisate, at a given concentration of surfactant, that produces a clear solution. Different amounts of solubilisates, in ascending order, are added to a series of vials containing the known concentration of surfactant and mixed until equilibrium is reached. The maximum concentration of solubilisate that forms a clear solution is then determined visually. This same procedure can be repeated for the different concentrations of surfactant in a known amount of solubilisate in order to determine the optimum concentration of surfactant (Figure 4.24). Based on this information, one can construct a ternary phase diagram that describes the effects of three constituents (i.e., solubilisate, surfactant, and water) on the micelle system. Note that unwanted phase transitions can be avoided by ignoring the formulation compositions near the boundary. In general, the MAC increases with an increase in temperature. This may be due to the combination of the increase of solubilisate solubility in the aqueous phase and the micellar phase rather than an increased solubilization by the micelles alone. 

In a bioprocess the desired end product may be present as whole cells or intracellular or extracellular material at the end of a fermentation. Therefore in this first bioseparation stage, it may be necessary to recover either the solid or aqueous phase, with as much of the unwanted phase removed as possible, and with minimal loss of the desired material to maximize product yield. 

The alcohol cosolvents or cosurfactants may partition between aqueous and oil phases in different proportions than the primary surfactant, and therefore, grouping these components in the surfactant pseudocomponent is inappropriate. Chromatographic separation of the components may occur during flow in the reservoir, and unwanted phases may form. 

In the latter approach, a chemical reaction or com-plexation takes place in a mixing-reaction coil, resulting in an extractable component segmented with an organic immiscible solvent steam at the phase segmenter, where small reproducible droplets of one phase are formed in the other. The phase containing the analytes of interest can be monitored by a flow-through detector, and the unwanted phase is directed to waste. 

Another way to avoid unwanted phase separation is to force the solvent system to be saturated in one component. For example, a distinct water layer is put in contact with water-saturated hexane and the solution is continuously stirred to ensure that the hexane will remain water-saturated. Unfortunately, the solubility is still temperature dependent, so that the solvent/colunnn system must be temperature regulated to guarantee stable and reproducible chromatographic results. 

For industrial appHcations, Alilii is an unwanted phase because of the deterioration of mechanical and corrosion properties of the Al(Li) alloy. The characteristic feature of AliLii phase formation is that around the AliLii phase regions there is no metastable AI3 Lii phase. It is also found experimentally that the elastic modulus increase is well related to the presence of the intermediate metastable AliLii phase [70, 77-79]. It would be interesting to define whether it is possible to stabilize the metastable AliLii phase because of small particles or some other way. The basic results of this section were published first in [58, 59, 66]. 

The compositions of the materials of interest consisted of SiC, Si, Al, and Ti in some combination. SiC Si composites were made initially with varying amounts of carbon present in the perform. Specifically, four carbon levels were used, nominally 2, 5, 7, and 8 wt.% of the preform. Secondly, SiC Si-Ti samples were made with 8, 11, and 18 volume % Ti in the alloy. One sample was generated for each separate combination. These numbers were chosen based on the phase diagram of Si Ti and the ability to make fully infiltrated parts with limited solidification porosity. SiC Si-AI samples were made with volume percents of 8, 18, and 37 Al in the alloy. In addition a SiC Si-Al-Ti sample was created. This may allow for additional reaction formed SiC in the SiC Si-AI samples as the Al reacts with C to form AI4C3 which is an unwanted phase. Example microstructures are provided in Figure I. 

Pyrex-type glasses fit this demands. Na ions provide the electrical conductivity, but the glass also contains small amounts of AI2O3 which prevents the unwanted phase separation (see Sect. 1.1.6). The homogeneous microstructure of a Pyrex glass is shown in Fig. 1.37. 

The process results in some loss of boron in the form of boron oxide which causes the formation of non-stoichiometric boride and presence of residual carbon in the product. Sometimes ZrC or HfC phases are also present in the final product. These unwanted phases can be avoided by using excess B C in the charge (Guo et al., 2009 Zhang et al., 2009). 

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