Publications

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Solution-based synthesis is a powerful approach for creating nano-structured materials. Although there have been significant recent successes in its application to fabricating nanomaterials, the general principles that control solution synthesis are not well understood. The purpose of this LDRD project was to develop the scientific principles required to design and build unique nanostructures in crystalline oxides and II/VI semiconductors using solution-based molecular self-assembly techniques. The ability to synthesize these materials in a range of different nano-architectures (from controlled morphology nanocrystals to surface templated 3-D structures) has provided the foundation for new opportunities in such areas as interactive interfaces for optics, electronics, and sensors. The homogeneous precipitation of ZnO in aqueous solution was used primarily as the model system for the project. We developed a low temperature, aqueous solution synthesis route for preparation of large arrays of oriented ZnO nanostructures. Through control of heterogeneous nucleation and growth, methods to predicatively alter the ZnO microstructures by tailoring the surface chemistry of the crystals were established. Molecular mechanics simulations, involving single point energy calculations and full geometry optimizations, were developed to assist in selecting appropriate chemical systems and understanding physical adsorption and ultimately growth mechanisms in the design of oxide nanoarrays. The versatility of peptide chemistry in controlling the formation of cadmium sulfide nanoparticles and zinc oxide/cadmium sulfide heterostructures was also demonstrated.

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Polyoxoniobate chemistry, both in the solid state and in solution is dominated by [Nb{sub 6}O{sub 19}]{sup 8-}, the Lindquist ion. Recently, we have expanded this chemistry through use of hydrothermal synthesis. The current publication illustrates how use of heteroatoms is another means of diversifying polyoxoniobate chemistry. Here we report the synthesis of Na{sub 8}[Nb{sub 8}Ti{sub 2}O{sub 28}] {center_dot} 34H{sub 2}O [{bar 1}] and its structural characterization from single-crystal X-ray data. This salt crystallizes in the P-1 space group (a = 11.829(4) {angstrom}, b = 12.205(4) {angstrom}, c = 12.532(4) {angstrom}, {alpha} = 97.666(5){sup o}, {beta} = 113.840(4){sup o}, {gamma} = 110.809(4){sup o}), and the decameric anionic cluster [Nb{sub 8}Ti{sub 2}O{sub 28}]{sup 8-} has the same cluster geometry as the previously reported [Nb{sub 10}O{sub 28}]{sup 6-} and [V{sub 10}O{sub 28}]{sup 6-}. Molecular modeling studies of [Nb{sub 10}O{sub 28}]{sup 6-} and all possible isomers of [Nb{sub 8}Ti{sub 2}O{sub 28}]{sup 8-} suggest that this cluster geometry is stabilized by incorporating the Ti{sup 4+} into cluster positions in which edge-sharing is maximized. In this manner, the overall repulsion between edge-sharing octahedra within the cluster is minimized, as Ti{sup 4+} is both slightly smaller and of lower charge than Nb{sup 5+}. Synthetic studies also show that while the [Nb{sub 10}O{sub 28}]{sup 6-} cluster is difficult to obtain, the [Nb{sub 8}Ti{sub 2}O{sub 28}]{sup 8-} cluster can be synthesized reproducibly and is stable in neutral to basic solutions, as well.

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This report summarizes research on the aging of Class I components in environments representative of nuclear power plants. It discusses Class IE equipment used in nuclear power plants, typical environments encountered by Class IE components, and aging techniques used to qualify this equipment. General discussions of radiation chemistry of polymers and accelerated aging techniques are also included. Based on the inadequacies of present aging techniques for Class IE equipment, a proposal for an experimental program on electrical cables is presented. One of the main purposes of the proposed work is to obtain relevant data in two areas of particular concern--the effect of radiation dose rate on polymer degradation, and the importance of synergism for combined thermal and radiation environments. A new model that allows combined environment accelerated aging to be carried out is introduced, and it is shown how the experimental data to be generated can be used to test this model.