Dual-phase mixing

This simple mixing rule demonstrates satisfactory agreement with experimental evidence from experiments with binary fluid blends [. l Furthermore, it is similar in form with the result from a continuum theory approach by Davis [ ], applicable for IPN with dual phase continuity but which are not mixed on a molecular level. This last model involves an exponent equal to 1/5 instead of 1/2 and is quite successful in predicting the experimental evidence [1 ] from permanent networks. 

Fig. 10.1. Different membrane concepts incorporating an oxygen ion conductor (a) mixed conducting oxide, (b) solid electrolyte cell (oxygen pump), and (c) dual-phase membrane. Also shown is the schematics of an asymmetric porous membrane (d), consisting of a support, an intermediate and a barrier layer having a graded porosity across the membrane.

There are several advantages to using a dual-phase membrane over a singlephase mixed electronic ionic conductor. These include the fact that the ionic conductors such as YSZ are much more chemically and thermally stable compared to most perovskites. Thus, dual-phase membranes are Ukely to be able to tolerate the harsh conditions of an oxygen separation device. They also show good tolerance to both CO2 and steam. The difficulty comes in the selection of an electronically conducting material. The cost of noble metals makes their incorporation into commercial devices unlikely. Therefore, the electron-conducting phase is Umited to a... 

Cr, Mn, Fe, Co [4] (or the nontransition element, Ga [5]). An example of such a dual-phase mixture is Ceo,8Gdo,20i,9 mixed with Lao,6Sro,4Goo,2Feo,803 [6]. The ratio of the two phases is important in determining the overall properties of the material. 

Hil] Hildebrand, H., Heinzel, G., Schreiber, G., Characterization of Dual Phase/Dispersion Mixed Microstracture in a Fe-Nb-C Alloy , Prakt. Metallogr., 35(5), 255-266, (1998) (Experimental, Phys. Prop., 17)... 

The morphology of IPNs has been widely investigated via electron microscopy and dynamical mechanical spectroscopy. Many IPNs have dual-phase continuity, with phase domain sizes of the order of several hundred angstroms. For sound and vibration damping over broad temperature ranges, the two polymers are mixed in different extents in different parts of the material, usually in the submicron range. 

Balachandran et al. (2007) also showed several ways to increase the H2 production rate by H2O decomposition via MIEC membranes. Producing CGO/Ni membranes with a finer microstructure enlarged the triple-phase-boundary area and increased the H2 production rate to = 10 cm (STP)/min.cm. Using a single-phase, mixed-con-ducting membrane (SrFeCoo.50x(SFC2)) also produced higher H2 production rates relative to dual-phase cermet membranes. 

Although the morphology found by Kim et aL, Figure 6.4, is intuitively expected for a SIN, even having simultaneous gelation of both polymers does not necessarily guarantee molecular mixing or dual-phase continuity. 

Piezodialysis is a novel desalination technique in which salt is preferentially transported across the membrane and removed from a feed using pressure as the driving force.The theory requires the membrane to consist of two continuous phases, one anionic and one cationic/ A suitable material should have dual-phase continuity, but with a minimum of molecular mixing between the phases. The morphological features attainable with IPN formation fit these theoretical requirements. " ... 

In general, the use of the IPN concept yields better control over phase domain size and extent of molecular mixing. By various mechanisms, processibility is attained, yet the final products are all crosslinked. Because in many cases the phases interpenetrate to develop dual-phase continuity, a new type of bonding is achieved, to hold the two components in juxtaposition. 

Li, H., Zhu, X., Liu, Y., Wang, W., and Yang, W. (2014) Comparative investigation of dual-phase membranes containing cobalt and iron-based mixed conducting perovskite for oxygen permeation. /. Membr. ScL, 462,... 

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