Ceramic films, preparation methods

Sasahara, K., Hyodo, T., Shimizu, Y., and Egashira, M. (2004) Macroporous and nanosized ceramic films prepared by modified sol-gel method with PMMA microsphere templates. /. Ear. Ceram. Soc., 24, 1961-1967. 

Because membranes appHcable to diverse separation problems are often made by the same general techniques, classification by end use appHcation or preparation method is difficult. The first part of this section is, therefore, organized by membrane stmcture preparation methods are described for symmetrical membranes, asymmetric membranes, ceramic and metal membranes, and Hquid membranes. The production of hollow-fine fiber membranes and membrane modules is then covered. Symmetrical membranes have a uniform stmcture throughout such membranes can be either dense films or microporous. 

Solution Deposition of Thin Films. Chemical methods of preparation may also be used for the fabrication of ceramic thin films (qv). MetaHo-organic precursors, notably metal alkoxides (see Alkoxides, metal) and metal carboxylates, are most frequently used for film preparation by sol-gel or metallo-organic decomposition (MOD) solution deposition processes (see Sol-GEL technology). These methods involve dissolution of the precursors in a mutual solvent control of solution characteristics such as viscosity and concentration, film deposition by spin-casting or dip-coating, and heat treatment to remove volatile organic species and induce crystaHhation of the as-deposited amorphous film into the desired stmcture. 

The above methods represent the most commonly employed methods for inorganic electronic thin film preparation. A variety of other methods, including Pechini,21 citrate,86 nitrate,23 and aqueous processes87 have also been used. For a discussion of these methods, the reader is referred to Refs. 5 through 12, which highlight these methods for the preparation of various electronic ceramic materials. 

Preparation of Pt-TiOx/Pd membranes. It was also desirable to prepare metalloceramic membranes in which the catalytic activity of the ceramic phase was enhanced through the addition of a noble metal. The very low surface area of the titania films prepared as described above made them difficult to impregnate with adequate dispersion by traditional incipient wetness techniques. Instead, finely ground titania (>200 mesh) was impregnated with platinum via the incipient wetness method with a chloroplatinic acid solution. This powder was then sprinkled onto the surface of a freshly dipped membrane, which was dried and heat treated as described. These materials were activated before use at 350°C in hydrogen for three hours. 

Adherent, conformal LPD ceramic film either crystalline (Method 2) or amorphous (Method 1) can be obtained on polyimides. This is in contrast to silanol-bearing surfaces (good for Method 1 only) or sulfonated surfaces (good for Method 2 only). The fact that the polyimides accommodate both titania preparations may be due to the partial hydrolysis of the polymer surface under oxide deposition conditions. This provides a mix of carboxylic acid and amide sites that anchor the titania by a combination of coulombic and chelation-based effects.22 An important lesson of this work is that the interaction of the polymer surface with the deposition solution may create oxide film anchoring sites. This does not negate activating the polymer surface. It recognizes that the polymer surface can react further under the deposition conditions. 

Nazeri-Eshghi et al. [32] were the first to report sol-gel processing of KNbOa ceramic powders. Their method was later adopted for the deposition of epitaxial thin films by Cheng et al. [38] The precursors used were KOC2H5 and Nb(OC2H5)5. The preparation procedure is fairly simple. Potassium metal is allowed to react with anhydrous ethanol, and the solution is then mixed with Nb(OC2H5)5. The solutions are usually stable for a few weeks. It was found that the addition of small amount of 2-ethylhexanoic acid helps to modify the... 

Electrochemical synthesis is an attractive method to prepare oxide ceramic films and powders, because it offers the several advantages such as low processing temperature, low cost, high purity, normal handling pressure, and controlled microstructure. In the electrochemical synthesis of oxide fine particles, both anodic... 

The chemical solution deposition method used for preparation of oxide films comprises the deposition of a liquid sol on a substrate and the conversion of gel films to ceramic films via heat treatment... 

CdS films and thin disks as a base material for the CdS-Cu S heterojunctions have also been prepared by sintering techniques. The preparation method for sintered films consisted in silk-screen printing on a ceramic substrate followed by a drying and sintering process at temperatures of about 600 C /15,16/. A different approach is based on compressing CdS powder in self supporting thin disks which are sintered at temperatures between 700 and 85o C. Grain sizes have been reported in this case of 5 to lO ym /16/. 

Fu G., Nazar L.F., Bain A.D. Aging processes of alumina sol-gel characterization of new aluminum polyoxycations by Al NMR spectroscopy. Chem. Mater. 1991 3 602-610 Furusaki T., Kodaira K. Preparation and properties of IniOs thin films by the sol-gel method. In High Performance Ceramic Film and Coatings. Elsevier Sdaice Pub, 1991, pp. 241-247 Furusaki T., Takahashi J., Takaha H., Kodaira K. Formation process ofSn02 thin films by sol-gel method. J. Ceram. Soc. Jpn. 1993 101 451 55 Furusaki T., Takahashi J., Kodaira K. Preparation ofTTO thin films by sol-gel method. J. CCTam. Soc. Jpn. 1994 102 200-205... 

Ohishi T., Maekawa S., Katoh A. Synthesis and properties of tantalum oxide films prepared by the sol-gel method using photo-irradiation. J. Non-Cryst. Sohds 1992 147 148 493-498 Ohishi T., Kato A. Photopatteming of tantalum oxide films by a sol-gel method using a KrF excimer laser. Br. Ceram. Trans. 1993 92 79-80... 

Fricke J. Aerogels and their applications. J. Non-Cryst. Solids 1992 147 148 356-362 Furusaki T, Kodaira K. Preparation and properties of In203 thin films by the sol-gel method. In High Performance Ceramic Films and Coatings, Vincenzini P., ed. Amsterdam Elsevier Science Publishers, 1991, 241-247... 

Hashimoto T, Yoko T., Sakka S. Third-order nonlinear optical susceptibihty of aFe203 thin film prepared by the sol-gel method. J. Ceram. Soc. Jpn 1993 101 64-68 Hatayama H., Swabe T, Kurokawa Y. Immobilization of urease on composite fiba- by using a gel formation of celluse acetate and titanium iso-propoxide. J. Sol-Gel Sci. Technol. 1996 7 13-17 Hattori A., Toda H. Highphotocatalytic activity of F-doped TiO film on glass. J. Sol-Gel Sci. Technol. 2001 22 47-52... 

Figure 15 depicts schematically a process for depositing a TiN film using dynamic mixing, carried out by a simultaneous operation of Ti evaporation and nitrogen ion implantation. The ceramic film deposited by dynamic mixing shows excellent adhesion because of the presence of a mixed layer formed between the film and substrate. Ceramic films such as TiN, ZrN, AIN, (Ti, Al) N, cBN, and TiC are prepared by this method. 

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