Morphology of the Interface

A remaining question is the morphology of the interface between the silica top-layer and the intermediate Y-AI2O3 support layer. In the dip-coating process the silica layer may either form an almost flat layer on top of the polished support surface or partly infiltrate the pores in the y-layer. With conventional techniques (SEM-EDS, or TEM) the microscopic geometry of this interface cannot be elucidated. With RBS analysis a more clear indication can be obtained on the depth distribution of the silicon atoms with respect to the y-alumina surface. 

Effective mass transfer is as important since product stability can be seriously compromised in colloids and suspensions, both liquid-solid and liquid-liquid phases, if the morphology of the interface is not properly formed, and interactions sufficiently developed. Phase separation is the major consideration in such complex systems, and is easily affected by poor process history. 

Several families of polymers may be used for this application, including cellulose acetates, aromatic polyamides and polysulfones, but progress remains to be made regarding the nature of membranes and their implementation to control the morphologies of the interface. 

The morphology of the interface allows equilibrium bonding of silanols with the surface. This requires a rigid or tacky (but not rubbery or flexible) polymer at the interface. 

The ellipsometric method was used to study adsorbed DNA for the first time by Humphreys and Parsons [222], Since that time the sensitivity of this method has appreciably increased [223], The measurement of x-ray reflection enabled studies of the structure of very thin layers (down to several A) and the morphology of the interface [224]. 

Although interfaces usually constitute a small fraction of the total volume of a composite, the effects of their properties on the bulk properties are large because of the large surface area of the interfaces. The properties of the interface depend on whether or not there has been a reaction at the interface, the type of bonding at the interface, and on the nature (crystalline or amorphous) and morphology of the interface material. The consequences of having a smooth versus a rough interface are far more important in structural applications where one phase, such as a fiber, must be able to slide out of the matrix to some extent, in order to achieve optimum mechanical behavior. 

In this regard, there is an excellent review article on MMMs for gas separation, with a detailed discussion on the morphology of the interface between the inorganic particles and the polymer matrix (Chung et al. 2007). Unlike many other articles, this deals with asymmetric membranes for both flat sheets and hollow fibers aimed at the formation of an ultrathin defect-free mixed-matrix skin layer. 

The nature of bonding in the carbides is known to be a mixture of covalent and metallic with little ionic tendency. If solid solutions were formed, Ta from TaSi substimted the transition metal atoms in the carbide lattice. This may occur either by cations diffusion or by solntion-precipitation. Given the low diffusion coefficient of this class of materials, it is presumed that lattice diffusion can occur only at very high temperature. Indeed, solution re-precipitation seems to be the dominant mechanism, in light of the sintering behaviour characterized by a relatively low T, 1400-1600°C (Table 2). The well-defined boundary between core and shell and the morphology of the interface between them also put forward a re-precipitation from liquid phase over a diffusion process. 

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