Papers by Author: E. Suvaci

Abstract: In this study, textured α-SiAlON ceramic was produced by templated grain growth process. In order to enhance the alignment of the seeds, gated tape casting arrangement was utilized. Y-Ce codoped seeds were synthesized to induce the preferred orientation. For the production of the seeds, Ce3+ was used as a sintering additive due to its well-known effect on the formation of elongated α-SiAlON grains. In addition, Y3+ was used to stabilize Ce3+ in α-SiAlON structure. Gated tape casting arrangement was also used to enhance the alignment of the seeds in the green tape. After the lamination and sintering, preferentially aligned α-SiAlON grains were observed by the microstructural investigation. In addition, XRD results obtained from the planes parallel and perpendicular to the casting direction indicated the alignment of grains in α-SiAlON ceramics. Hardness measurements also confirmed that the alignment of the grains results in 8% increase in hardness value of the plane perpendicular to the casting direction with respect to that of the parallel one.

Abstract: Aqueous dispersions of SiAlON forming powders (Si3N4, AlN and Y2O3) were obtained. Dispersibility of powders was found to be improved by addition of sodium tripolyphosphate. Stable aqueous suspensions of SiAlON forming powders were prepared by using a phosphate ester, sodium tripolyphosphate (STPP, Na5P3O10). Effect of the STPP on rheological properties of the powder mixture was investigated by zeta potential measurements, sedimentation and milling studies. It has been shown that addition of the STPP to the aqueous SiAlON forming powder mixture improves the dispersion behavior significantly. These results suggest that STPP can be utilized as a dispersant in such ceramic systems.

Abstract: Electrophoretic deposition technique is a versatile coating method. With this method not only flat surfaces but also curved or rough surfaces can be coated in various thicknesses. In this study, BaTiO3 nanocrystals were synthesized with a novel nonaqueous method. In a simple one pot reaction process, the metallic barium is directly dissolved in benzyl alcohol at slightly elevated temperatures. After the addition of titanium isopropoxide and subsequent solvothermal treatment nearly spherical BaTiO3 nanocrystals typically 5 nm in diameter were obtained. The stability of the suspension in ethanol and nanocrystalline particle size distribution was measured by Malvern Nano-ZS. The BaTiO3 suspensions were directly used in an electrophoretic deposition process without any additional operation. Pt plated alumina was used as substrate. Various voltages were applied by altering the cathode to anode distance as well as deposition time for optimal process control. Because of the ethanol adsorbed on the surface of the nanoparticles, application of high voltages was possible without causing hydrolysis. The deposited surface coatings were dried in air atmosphere and sintered at different temperatures. SEM, EDX and XRD analysis were employed for the investigation of the coating.