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Production and Characterization of Ceramic Components Via Current Sintering Techniques
(01. Izmir Institute of Technology, 2023) Karacasulu, Levent; Ahmetoğlu, Çekdar Vakıf; Adem, Umut
This dissertation aims to utilize contemporary advanced sintering techniques such as cold sintering, reactive hydrothermal liquid phase densification, fast firing, flash sintering, and ultrafast high-temperature sintering for sintering of various ceramic materials. The ceramics produced through these methods are compared with their traditional counterparts in terms of processing-structure-property relationships. In the first section, a brief overview of the advanced sintering techniques used is provided. Chapters 2-7 give a review study on low-temperature densification techniques, and the studies conducted using the cold sintering process and reactive hydrothermal liquid phase densification process, namely cold sintering techniques, which allow densification below 400 °C. Chapters 8&9 presents research related to ceramic materials produced via the fast-firing technique with rapid heating rates compared to conventional sintering, widely employed in the industry. Chapters 10-12 cover sintering studies conducted utilizing joule heating based sintering techniques allowing very fast heating rates such as flash sintering and ultrafast high-temperature sintering. Chapter 13 presents a comparison of current sintering techniques used in terms of applicability, equipment, materials, and so on. The pros and cons of such techniques were explained. In conclusion, there may be no guarantee that every ceramic material will yield successful results in all sintering processes. It is essential to recognize that each sintering process occurs within distinct sintering mechanisms. The selection of the appropriate advanced sintering method and conditions should be based on an assessment of the specific material's characteristics and the desired properties in the final product.
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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