Evaporation-calcination techniques

Pure and NaP-modified MnOx-catalysts were used in our study. Due to easy visualization by AFM, the MnOx layer was placed on a Si-wafer substrate (1 cm x 1 cm plate), by a reactive deposition technique. The sample preparation was carried out in a vacuum installation equipped with an resistance evaporator. Metallic manganese (99.8%) as a source and a Si wafer with a surface orientation (111) and resistivity of 7.5 ohm/cm as support, were used. During MnOx deposition, an oxygen partial pressure of ca 10 torr, in dynamic mode, was maintained. Before used for the catalytic purpose, MnOx samples were calcined in air at 700°C for 60min. In order to prepare the NaP-modified catalyst, the MnOx samples were impregnated in a diluted Na4P20 solution (5 wt %), dried and finally calcined at 500° C, in air during 30 min. The interaction with methane was performed in a quartz reactor in a methane atmosphere at 700° 5° C. 

The synthesis of lithium aluminates for tritium production requires formation of nanostructured phases. These can be made by solid-state reaction, by appropriate mixing of oxide powders [84] or by sol-gel methods [80, 85-87], One technique is the peroxide route where y-Al203 and LiC03 are dissolved in a peroxide (H202) solution. Evaporation of water and calcining the solid residue results in nanophase LiA102. 

A complete range of metastable cerium-zirconium mixed metal oxide powders (CexZr(i.x)Oy, 0 < X < 1) were prepared through a similar hydroxide precipitation technique reported by Hori, et al. [11]. Cerium (IV) ammonium nitrate and zirconium oxynitrate precursors are completely dissolved in de-ionized water with mild heat and precipitated through the addition of excess ammonium hydroxide (-100 vol%). The ceria-zirconia is thoroughly washed with excess distilled water and allowed to evaporate to dryness overnight. The ceria-zirconia system is calcined in atmosphere for 1 hour at 773 K and subsequently milled into a fine powder. The model ceria-zirconia catalysts are prepared from the ground cerium-zirconium oxide powders using a 13 mm diameter pellet die and hydraulic press. 

Precipitation from a concentrated solution of cations can be performed by solvent evaporation. To ensure that the particle size remains small, the concentrated solution may be atomised at high pressure into fine droplets of 100-500 pm diameter the solvent is rapidly evaporated by an upward stream of hot gas. The particles obtained, which can be as small as 100 nm, are compacted and calcined to produce the ceramic. A schematic representation of the spray-drying process is shown in Fig. 3.4. Several alternative methods are currently under development they are known as aerosol synthesis, aerosol pyrolysis or mist pyrolysis, depending on the specific technique to produce the gaseous suspension of fine particles aerosols are produced in high pressure nozzles and mists are obtained by means of nebulisers. YIG particles (0.25 pm) have been obtained by mist pyrolysis (Matsumoto et ai, 1991) by nebulising an aqueous solution of... 

Liquid mixture technique can be used to obtain the composite precursor. It consists of the evaporation of a dispersion of YSZ powder in a solution of nickel acetate tetrahydrate and ethanol, followed by calcination at 450°C/5 h to eliminate the organic material [28]. 

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