Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Coating of Spinel Layers on Alumina by Electrostatic Spray Deposition (esd)(01. Izmir Institute of Technology, 2023) Demirkol, İrem; Akkurt, SedatMgAl2O4 spinel layer was coated on dense alumina pellets by advantageous ESD among the other deposition methods in terms of providing a simple, inexpensive setup and good control of the layer morphology. The main goals are successfull deposition of spinel layers on alumina pellets by ESD, to investigate the effect of ESD parameters (working distance, flow rate of precursors, applied voltage) on coating microstructure by conducting full factorial design experiments and to determine the best experimental conditions for a porous layer. Besides, MgCr2O4 layer was coated on dense alumina and MgAl2O4 layer was deposited on bisque-fired alumina pellet to extend the scope of the work. Alumina powders were compressed and sintered, respectively to obtain pellets. MgAl2O4 spinel precursor solution was sprayed on the alumina pellets by changing the parameters accordingly the full factorial design. MgAl2O4 and MgCr2O4 solutions were also sprayed on the bisque-fired and the dense alumina pellets with the parameters given the best porous layer. Elemental analysis of the residues obtained after evaporation of the solutions by energy dispersive X-ray spectroscopy (EDX), both unheated and post-heated residual powders of solutions by X-ray diffraction (XRD) and surface morphologies of coated pellets by scanning electron microscopy (SEM-EDS) were analyzed. Spinel layers on alumina pellets were successfully coated by ESD, which could provide variable surface morphologies. The optimum conditions for a porous layer were obtained as working distance of 15 mm, flow rate of 0.25 mL/h and applied voltage of 6 kV in this study. The coatings on the pellets before further heating were amorphous. Post-heating of the pellets were required to obtain crystalline spinel structure.Master Thesis Use of Metal Templates for Microcavity Formation in Alumina(Izmir Institute of Technology, 2011) Balkan, Sırma; Akkurt, SedatAlumina ceramics with microtunnels are produced by compressing submicron sized alumina powder and Ti, Cu or stainless steel wires in a metal die before firing the compacts at 1350oC for 4 hours. Diameters of wires ranged from 50 to 125 micrometers. Copper was found to completely melt and flow away from the compact leaving no trace of copper in alumina. Stainless steel diffused out into the alumina leaving few pores behind. Titanium, on the other hand, diffused into alumina at 20 to 30micrometers/hour and left plenty of Kirkendal porosity behind. The amount of porosity could have been increased further by applying intensive milling to the powder. But no milling was done in this study and hence a complete micro-tunnel was not obtained. The Kirkendal effect was observed to be effective in producing pores in the ceramic. Densification behavior of the ceramic was also investigated with a vertical dilatometer. Densities up to 93% were achieved in the ceramics. In some tests Ti metal plates were used as diffusion couples with alumina compacts. Similar diffusion behavior was observed with plates and wires.