IMPROVEMENT OF ROOM TEMPERATURE MECHANICAL PROPERTIES OF VARIOUS AMOUNT OF METAL OXIDE DOPING CUBIC ZIRCONIA (c-ZrO2) USED AS ELECTROLYTE MATERIAL FOR SOLID OXIDE FUEL CELLS

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Thesis Type: Postgraduate

Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2007

Student: TUĞBA BOYACIOĞLU

Supervisor: SÜLEYMAN TEKELİ

Open Archive Collection: AVESIS Open Access Collection

Abstract:

In this study; the effect of various amount of SiO2 and TiO2 additions on room temperature mechanical properties of cubic zirconia (c-ZrO2) was investigated. The c-ZrO2 specimens doped up to 10 wt% SiO2 and TiO2 were pressurelles sintered at 1450 oC. XRD results showed that when the TiO2 amount was less than 5 wt %, the specimens were entirely in single cubic phase; further addition of TiO2 (5 wt% or more) destabilized cubic zirconia phase and caused the formation of tetragonal phase. Also, the amount of tetragonal phase increased with increasing TiO2 content in cubic zirconia matrix. With SiO2 addition, there was no change in crystal structure. Also, the reaction phase between SiO2 and c-ZrO2 was not seen. It was observed that how these additions effected the room temperature mechanical properties of hardness, fracture toughness and flexural strength. While the hardness values decreased with SiO2 addition, the TiO2 addition increased the hardness reaching 12 GPa. With increasing amount of SiO2 and TiO2 additions, the fracture toughness values determined by Vickers hardness measurement technique increased. While the fracture toughness value of undoped c-ZrO2 was 1,5 MPa.m1/2, this value was 3,64 MPa.m1/2 for 10 wt% SiO2 doped c-ZrO2 and 3,3 MPa.m1/2 for 10 wt% TiO2 c-ZrO2. In other work, it was observed that the flexural strength was not effected by SiO2 addition. But the TiO2 addition improved the flexural strength reaching the value of 375 MPa from 275 MPa.