John Engell

Fabrication of Nasicon electrolytes from metal alkoxide derived gels

Abstract Clear gels corresponding to several compositions in the Nasicon solid solution series have been prepared from dry phosphoric acid, tetraethylorthosilicate, zirconium propoxide and sodium methoxide all dissolved in propanol. The effects on the polymerization and gel formation of temperature, time, addition of water and order of mixing of the components have been studied. The crystallization of these gels and their usefulness as raw materials for the fabrication of dense ceramics of Nasicon have been investigated. For a Zr-poor Nasicon composition 97% of the theoretical density has been obtained at temperature below 1000°C. For a fixed ratio between Si and P, the temperatures needed to densify the ceramics increase with the Zr-content. The high temperature phase relations relevant to Nasicon have also been studied.

Adsorption of polar aromatic hydrocarbons on synthetic calcite

The wettability of hydrocarbon reservoirs depends on how and to what extent the organic compounds are adsorbed onto the surfaces of calcite, quartz and clay. A model system of synthetic calcite, cyclohexane and the three probe molecules: benzoic acid, benzyl alcohol and benzylamine, have been studied by adsorption experiments. The results clearly demonstrate the differences in the adsorption behaviour between probes with different functional groups of varying polarity and acidity. The maximum adsorption decreases in the order: benzoic acid, benzyl alcohol and benzylamine. The order of magnitude of ΔG° for the adsorption process implies the formation of a strong bond between the calcite surface and the adsorbate molecules.

Properties of nasicon electrolytes prepared from alkoxide derived gels: Ionic conductivity, durability in molten sodium and strength test data

Abstract Nasicon ceramics have been prepared from gel-derived raw materials both by conventional sintering and by hot-pressing. For several compositions the ionic conductivity have been determined by the AC-method. The properties of ceramics based on the ZrO2-poor composition Na2.94Zr1.49P0.8Si2.2O10.85 have been studied in greater detail. Durability test in Na/Na-cells so far indicate good stability at 300°C, and corrosion tests in molten sodium (400°–700°C) indicate that at 400°, 350° and 300°C it will take respectively at least 100 h, 7 weeks and 3 years to dissolve a 1 micron thich layer of the ceramic. The fracture strenght of the ceramics have been determined by the three point bending method. Weibul statistics indicate an average fracture strength of 168 MPa and a m-value of 8.3 (sample vol. 0.07 cm3) for the best ceramics prepared so far.

Effect of sintering atmosphere on the pore-structure stability of cerium-doped nanostructured alumina

Pore-structure stability of pure and Ce-doped alumina in air and argon atmospheres was studied using DTA, TGA, N2 ads./des. and XRD with a view to understand the importance of the ionic size of the dopant cation on the pore-structure stability of alumina. The ionic size effect was studied by heat treating the Ce-alumina system in both oxidizing and reducing atmospheres to have Ce4+ (87 pm) and Ce3+ (106 pm) respectively. No compound formation between Ce and alumina was observed. In the case of pure alumina there is a drastic reduction in porosity during the transformation to α-alumina. Ce-doped alumina has a higher DSC transformation temperature corresponding to the α-alumina transformation compared to pure alumina. Ce-doped alumina showed higher pore-structure stability compared with pure alumina and the stability was relatively higher in reducing atmosphere (higher Ce3+/Ce4+ ratio, higher effective ionic size) compared with oxidizing conditions (lower Ce3+/Ce4+ ratio, lower effective ionic size).

BaZrO3: Synthesis, properties and compatibility with Ba2YCu307 − X

Abstract Homogeneous powders of BaZrO 3 have been prepared by a sol-gel route involving mixing of Ba-hydroxide dissolved in methanol and Zr-propoxide. Drying at 110 °C results in the formation of an agglomerated amorphous powder, which is milled prior to calcination. Calcination at temperatures above 620 °C results in single phase BaZrO 3 . BaZrO 3 ceramics were fabricated in order to investigate the interaction with Ba 2 YCu 3 O 7 − X in the temperature range 945 °C–1095 °C. The results show that BaZrO 3 is a promising material for use as substrates for thin films and as container material for bulk samples of the Ba 2 YCu 3 O 7 − X superconductor.

Preparation of CuZr2P3O12 from alkoxide-derived gels : phase formation as a function of heat treatment

AbstractThe phase formation in alkoxide gels with composition corresponding to CuZr2P3O12 has been studied as a function of gel preparation and heat treatment. Two preparational methods have been examined. The chemicals used include Cu(NO)3 · 3H2O, Zr(n-OC3H7)4 and either P2O5 or H3PO4, respectively. The P2O5 method results in the formation of di-phase gels. Heat treatment of these invariably gives multi-phase materials. Gels prepared by the H3PO4 method are completely amorphous and can be converted into porous glasses by heating to 500 °C. Calcination in the range 650 to 750 ° C results in the formation of a new CuZr4P6O24 phase (

Metastable Liquid Immiscibility in Nuclear-Waste-Glasses

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Intercutaneous implant device

. Later, this prevents formation of mono-phase materials during heating to 1200 ° C. It is suggested that this behaviour is related to mixing of Cu2+ and Zr4+ in the normal copper and zirconium positions in the low-temperature