Single oxides powder sintering

Electronic Transport, General Description. Magnesium Oxide (MgO). Electrical transport measurements on alkaline earth oxides encounter several difficulties, such as high resistance at low temperatures, a strong influence of surface layers, and high-temperature thermionic emission. The partly contradictory results depend considerably on the purity and nature of the samples (pressed porous powders, sintered samples, polycrystals, and single crystals) and on the experimental conditions. 

The first review of sintered ceramics obtained starting with sol-gel oxide powders was presented by Devi and Ganguli in a devoted chapter in the same handbook [22]. The review referred to ceramics derived from pure and doped single oxides, pure and doped binary oxides, multicomponent oxides, and composites. 

Zinc oxide and nickel oxide powders were pressed isostatically. Zinc oxide pellets were sintered in air at 900°C for 100 hr, resulting in compacts 85.5% theoretical density. Nickel oxide specimens were sintered in air at 1000°C for 120 hr, yielding compacts of only 78% theoretical density. The spheres of these oxides were obtained by crushing the pellets and then grinding them in a modified Jordan air-grinder ( ). The spheres thus obtained had diameters varying from 0.5 to 0.8 mm. In addition MgO single-crystal spheres of uniform diameter of 1 mm were employed. 

Yttrium—barium—copper oxide, YBa2Cu202 is a newly developed high T material which has been found to be fully superconductive at temperatures above 90 K, a temperature that can be maintained during practical operation. The foremost challenge is to be able to fabricate these materials into a flexible form to prepare wines, fibers, and bulk shapes. Ultrapure powders of yttrium—barium—copper oxide that are sinterable into single-phase superconducting... 

Most of the electrical and optical investigations on zinc oxide have been performed, not on single crystals, but on compressed powders, evaporated layers, and sintered samples, all of which constitute geometries of high potential surface-to-volume ratios. 

Nd2Ni04+5 powder was prepared by nitrate-citrate route as described by Courty, et a1. (1973). Stoichiometric amounts of neodymium and nickel oxides were dissolved in diluted nitric acid. After addition of a large excess of citric acid, the solution was dehydrated and heated until self-combustion of the precipitate to obtain submicronic precursor particles (Boehm, 2005). The final annealing was performed at 1000°C for 12 hours to obtain a single crystalline phase. The particles were then ball milled to obtain an average grain size (d0 5) of about 0.8 pm. A terpineol-based slurry was prepared from this powder and this was deposited on the electrolyte by screen printing and then sintered at 1100°C for three hours in air (Lalanne, 2008). 

The preparation of well-defined single-crystal surfaces of copper oxides in UHV or of well-sintered powders, starting from polycrystalline materials, is difficult. Consequently, structure-catalytic property correlations remain to be established. 

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