Colloidal spray deposition

A significant recent advance has been the development of microfiltration and ultrafiltration membranes composed of inorganic oxide materials. These are presently produced by two main techniques (a) deposition of colloidal metal oxide on to a supporting material such as carbon, and (b) as purely ceramic materials by high temperature sintering of spray-dried oxide microspheres. Other innovative production techniques lead to the... 

A very recent development is encapsulation of actives in colloidosomes [16, 41]. The method is analogous to liposome entrapment. Selectively permeable capsules are formed by surface-tension-driven deposition of solid colloidal particles onto the surface of an inner phase or active ingredient in a water-in-oil or an oil-in-water emulsion composed of colloidal particles. Initially synthetic polymer microparticles were used but more recently a natural alternative has been described based on small starch particles. After spray-drying, redispersible emulsions can be formed. 

The design of the interstices filling in colloidal crystals with appropriate media and subsequently fluid-solid transformation is central to the whole synthesis. Fluid precursors in the voids of crystal arrays can solidify by polymerization and sol-gel hydrolysis. More recently, many methods have been developed including salt precipitation and chemical conversion, chemical vapor deposition (CVD), spraying techniques (spray pyrolysis, ion spraying, and laser spraying), nanocrystal deposition and sintering, oxide and salt reduction, electrodeposition, and electroless deposition. 

Several other approaches to thin-film deposition into porons materials from the liquid phase have been attempted, most notably the deposition of CnlnSe2 and CuInS2 from colloidal solutions by Czekelius et al. (1999), and of InP by Zaban et al. (1998). Spray pyrolysis of CuInS2 from liquid precursor solutions onto strnctnred substrates has been explored by Krunks et al. (1999, 2001). 

A closely related second method to achieve an even denser metallic layer involves the introduction of tin ions instead of silver followed by a spray of water-based silver-ammonia complex, freshly mixed with reducer. The tin catalyzes the deposition of silver, resulting in the formation of colloidal metallic silver. Upon drying, a very regular, shiny metallic silver layer with a thickness ranging from 10 to 600 atoms is produced as indicated formally below ... 

Hence a volmnetric three-dimensional region has to be provided for the reaction. The most common methods of applying the electrode layer on the electrolyte are plasma spraying, vapor deposition, solution coating and colloidal ink methods. 

Pesticides are substances that repel, kill or otherwise control unwanted animals or plants. Examples include insecticides, fungicides and herbicides. The formulation of pesticides is significant in terms of product stability and product performance. The current trend in crop protection is towards products that are more potent, safer to user, having less impact on the environment, more convenient to use and improved efficiency of the apphed product [85]. In the case of sprayed products, colloid and interface science impacts all aspects of apphcation. First, spray droplets impact the leaf surface, creating a fohar deposit from which the pesticide moves into the leaf or contacts the pest (see Figure 13.7) [85]. The spray pattern is influenced by the applicator nozzle hydrodynamics, the physical properties of the spray fluid and the movement of sprayer vehicle. 

The use of pneimiatically assisted nebulization (PAN) was explored by depositing the colloidal silver solution over the samples. Contaminated samples were generated by depositing 10 pL of a 10 M solution of adenine in methanol over a silicon plate. The colloid was sprayed for 30 s at a distance of... 

Relatively recently electrochemistry has turned its attention to colloidal solutions of organic polymers. A new line of processes of industrial importance has thereby been opened up, that of electrophoretic deposition of paints and plastic coatings, which provide improved adherence and has technological advantages over classical spraying processes[4]. 

Recently, the flat spray technique has been applied successfully on pilot scale for the homogeneous deposition ofAu colloid containing lead silicate glass coatings on 1 m size float glass panes (Fink-Straube, 1998/2002). The appropriate coating line (producer Venjakob) is shown in Figure 29-7. 

Figure 29-7. Flat spray coating line (Venjakob) for the deposition of metal colloid containing coatings on flat glass.

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