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Dna Adsorption on Silica, Alumina and Hydroxyapatite and Imaging of Dna by Atomic Force Microscopy
(Izmir Institute of Technology, 2013) Yetgin, Senem; Balköse, Devrim; Balköse, Devrim
The scope of the study is to investigate calf thymus DNA adsorption process on solid powders such as silica, alumina and hydroxyapatite (HAP) to improve DNA solid phase extraction efficiency and to visiulize DNA adsorption by atomic force microscopy (AFM). The equilibrium and kinetics of the DNA adsorption were investigated in batch adsorption on a commercial silica gel and a synthesized silica aerogel, commercial alumina and HAP powders from aqueous DNA solution. Commercial DNA extraction kit adsorbents were also characterized and used for adsorption. Adsorbed DNA was imaged in ambient air on flat surfaces of mica, silica and alumina wafers and HAP particles coated glass surfaces and a HAP pellet surface by AFM. Effects of ambient air, nitrogen flow and freeze drying methods on DNA morphology on the releted surfaces were also investigated. Adsorption of DNA on silica, alumina and HAP increased with the decrease of pH from 9.0 to 2.0. Enhancements of the adsorption capacities of adsorbents were obtained with the addition of MgCl2. It was found that the Van der Waals and the hydrogen bonds rather than the surface charge were the cause of the adsorption. The adsorption isotherms of DNA on silica, alumina and HAP were fitted to Langmuir model in pH range 2-9. The adsorption kinetics obeyed pseudo second order model. The sharpest image of DNA by AFM was obtained by freeze drying method on alumina surface. Dispersed DNA in water was adsorbed on the surfaces not as single molecules but as supercoils consisting of many molecules.
Sintering, Co-Sintering and Microstructure Control of Oxide Based Materials: Zirconia, Alumina, Spinel, Alumina-Zirconia and Spinel-Alumina
(Izmir Institute of Technology, 2010) Yalamaç, Emre; Akkurt, Sedat
Densification and microstructural evolution during co-sintering of alumina (Al2O3) . zirconia (Y-ZrO2) and alumina . spinel (MgAl2O4) co-pressed bimaterials were investigated. First high purity submicron powders of monomaterials of alumina, spinel and zirconia were pressed at 100 to 250 MPa with different dry pressing techniques like UP (uniaxial pressing) and CIP (cold isostatic pressing). The latter was found to provide higher green densities. Before co-sintering of bi-materials, sintering behaviors of their end-members were studied by vertical dilatometer to determine the degree of shrinkage mismatches between the end-members. The effects of precoarsening and two-step sintering on the densification and microstructure of spinel ceramics were tested. Samples were etched both chemically and thermally to better understand their structure. Crack-free bonds were observed in alumina-spinel bi-materials after compaction by UP+CIP. Interfaces between alumina and spinel after treatment at 1400-1500 C were investigated by SEM, EDS, WDS, EBSD. A spinel interlayer with columnar grains of up to 40 .m length and 5 .m width was observed after 16 hours at 1500 C. Growth rate of this interlayer from spinel toward alumina was found to follow parabolic kinetics, controlled by a diffusion mechanism of probably lattice diffusion of O2- ions. Two isothermal steps co-sintering at 1400 C and 1500 C on the interlayer formation was tested. Two separate areas formed in the interlayer spinel. Diffusion couple tests of spinel and alumina produced the same columnar spinel grains at the interface with the same kinetics as in co-sintering experiments. Phase boundaries between the columnar spinel and alumina grains had a characteristic center of curvature located in alumina which was further indication of the direction of growth of the interlayer.

Phd Degree / Doktora

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