Use of sol-gels in the application of ceramic oxide thin films

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Paulson, Bradley
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Chemical and Biological Engineering

The function of the Department of Chemical and Biological Engineering has been to prepare students for the study and application of chemistry in industry. This focus has included preparation for employment in various industries as well as the development, design, and operation of equipment and processes within industry.Through the CBE Department, Iowa State University is nationally recognized for its initiatives in bioinformatics, biomaterials, bioproducts, metabolic/tissue engineering, multiphase computational fluid dynamics, advanced polymeric materials and nanostructured materials.

The Department of Chemical Engineering was founded in 1913 under the Department of Physics and Illuminating Engineering. From 1915 to 1931 it was jointly administered by the Divisions of Industrial Science and Engineering, and from 1931 onward it has been under the Division/College of Engineering. In 1928 it merged with Mining Engineering, and from 1973–1979 it merged with Nuclear Engineering. It became Chemical and Biological Engineering in 2005.

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1913 - present

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  • Department of Chemical Engineering (1913–1928)
  • Department of Chemical and Mining Engineering (1928–1957)
  • Department of Chemical Engineering (1957–1973, 1979–2005)
    • Department of Chemical and Biological Engineering (2005–present)

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Metal oxide sol-gels were produced through a controlled hydrolysis-condensation reaction of the metal alkoxide in alcohol using nitric acid as a catalyst. In obtaining sols of niobia, tantala, and titania, increasing either the water content or the system concentration increased the rate of gelation. However, while a sufficient amount of nitric acid was required to promote the condensation of the metal oxide and inhibit the precipitation, increasing the amount of nitric acid beyond that point slowed the gelation rate. A sufficient excess of water also lead to precipitation. These systematic parameter investigations were used to obtain sols of bismuth oxide, germania, yttria, and zirconia;The single component sols were characterized and used to make thin films on silicon wafers. The empirical equation, d = (2000 log([mu]) + 350) (w)[superscript]-0.5, was obtained, which adequately describes the thickness of the sintered films, independent of the ceramic oxide, solvent, concentration, sol age, and reaction conditions;The single component sols were used to make binary oxide sols--barium titanate, lithium niobate, and lithium tantalate. A barium solution can be added to the titania sol to produce a barium titanate compound of the desired composition, including Ba[subscript]2Ti[subscript]9O[subscript]20 and BaTi[subscript]5O[subscript]11. Mixing a lithium solution into either a niobia or a tantala sol yielded the desired compound along with a heavy metal oxide (either lithium niobate with niobium oxide or lithium tantalate with tantalum oxide). However, dissolving lithium methoxide with the ethoxide of niobium or tantalum in ethanol, prior to hydrolysis, did produce the desired binary oxide (lithium niobate or lithium tantalate) without any uncombined metal oxide;By altering the stoichiometric ratios of the constituent cations, different compounds were produced for dielectric characterization with an AC bridge circuit. In the case of the barium titanates, these calculated constants ranged from a high of 26.0 for TiO[subscript]2, to a low of 11.9 for BaTi[subscript]5O[subscript]11. The range for lithium tantalate was from a high of 21.6 for a stoichiometry of Li[subscript]7TaO[subscript]6, to a low at 8.4 for LiTaO[subscript]3. Lithium niobate ranged from a high at 21.1 for Nb[subscript]2O[subscript]5, to a low at 8.9 for Nb[subscript]2O[subscript]5 at a stoichiometry of Li[subscript]2Nb[subscript]32O[subscript]81.

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Thu Jan 01 00:00:00 UTC 1987