Ultrathin-film composites, reaction

Nodular structures were found not only in the ultrathin and asymmetric membranes but also at the surface of thin film composite (TFC) membranes. Cadotte reported that nodules were closely packed at the surface of a fully aromatic polyamide TFC membrane prepared by the in situ polycondensation reaction between m-phenylene diamine and trimesoyl chloride [3,4]. 

We have developed the use of ultrathin-film multilayer composites, illustrated in Figure 1, as the starting point for the formation of amorphous intermediate states. Ultrathin-film multilayer composites offer several unique advantages over other methods of preparing amorphous solids. These include the ability to monitor the progress of the reaction by X-ray diffraction and scanning calorimetry, the ability to separate the processes of diffusion and phase nucleation, and the ability to obtain thermodynamic data as the reaction progresses. 

Amorphous networks, 4-5 nAmorphous solid synthesis via ultrathin-film multilayer composites analysis of solid-state reaction mechanisms, 357,358/ application to synthesis of metastable ternary compounds, 366 control of crystallization of amorphous aUoy, 360,363,365-367/ control of formation of homogeneous amorphous alloy, 360,361-36 differential scanning calorimetric procedure, 359-360 grazing measurement procedure, 359 lugb-angje XRD procedure, 359 length sddes vs. course of solid-state reactions, 360,361-362/363 quantitative analysis of interdiffiision reaction, 356-357... 

Hardacre el al. (7 75, 174) investigated the properties, structure, and composition of cerium oxide films prepared by cerium deposition on Pt(lll), finding that the activity for CO oxidation is enhanced on Pt(lll) that is partially covered by ceria. It was suggested that new sites at the Pt-oxide interface become available for reaction. A remarkable observation is the high activity for CO oxidation when the Pt(lll) sample is fully encapsulated by ceria (Pt was undetectable by XPS and AES). It was proposed that an ultrathin, disordered ceria film becomes the active catalyst. It was also demonstrated by XPS and AES that Pt dramatically increases the reducibility of cerium oxide that is in intimate contact with Pt. This result suggests that intimate contact between the noble metal and oxide phases is indeed crucial to facile oxygen release from ceria. High-resolution electron microscopy demonstrated the presence of direct contact between ceria and noble metal for supported Pt-Rh catalysts (775). Hardacre et al. (173,174) related the catalytic activity of the ceria phase to partially reduced cerium oxide. 

Different authors have shown that compositionally modulated 3D metallic alloys can be electrochemically deposited using cyclic polarization conditions and multicomponent electrolytes [6.108, 6.109, 6.113, 6.114]. Alloy formation takes place alternately by diffusion and charge transfer control of the deposition reactions of different metal components. Similar conditions have been used for the deposition of ultrathin metal films and heterostructures (cf. Section 6.4). 

There are several potential routes to the preparation of composite reverse osmosis membranes, whereby the ultrathin semipermeable film is formed or deposited on the microporous sublayer.1 2 The film can be formed elsewhere, then laminated to the microporous support, as was done in the earliest work on this membrane approach. Or it can be formed in place by plasma polymerization techniques. Alternatively, membrane polymer solution or polymer-forming reactants can be applied in a dipcoating process, then dried or cured in place. The most attractive approach from a commercial standpoint, however, has been the formation of the semipermeable membrane layer in situ by a classic "non-stirred" interfacial reaction method. Several examples of membranes made by this last approach have reached commercial status. 

BasUe et aL [116] studied the WGS reaction using a MR consisting of a composite palladium-based membrane realized with an ultrathin palladium film ( 0.1 pm) coated on the inner surface of a porous ceramic support (y-Al203) by the co-condensation technique. The authors pointed out the benefit of applying a palladium MR, taking into account that, at 320°C and 1.1 bar, the thermodynamic equilibrium of CO conversion is around 70%, while the authors obtained with the MR CO conversion of around 100%. Moreover, the same authors illustrated that a complete CO conversion could be reached by using a composite membrane with a thinner palladium layer (10 pm Pd film coated on a ceramic support) [117]. 

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