Synthesis of zirconia microcrystals by hydrothermal method

• Main Author: Chen, Kenbin
• Other Authors: Gan Chee Lip
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Materials::Ceramic materials
• Online Access: http://hdl.handle.net/10356/64677
• Institution: Nanyang Technological University

A major drawback to the practical application of shape memory ceramics (SMCs) is the limited amount of strain it can sustain before cracking. This cracking is due to the large mismatch stresses between neighbouring grains that result due to the phase transformation in polycrystalline ceramics. In order to reduce these stresses, the size scale of the sample as well as the unstable grain boundary regions have to be minimized. This report serves to investigate the effectiveness of hydrothermal synthesis in producing fine scaled zirconia micro/nano-particles. For this study, 0.5M zirconyl nitrate hydrate and 5M sodium hydroxide were chosen as precursor materials and synthesized at 200°C. Hydrothermal medium composition and time parameters were varied to study their corresponding effects on zirconia particle morphology, shape and size. This project aims to ascertain the optimal conditions of hydrothermal synthesis so as to achieve zirconia particles of small volume structures, 500 nm to 1 µm in length with uniform aspect ratios. Yttrium nitrate additives were also varied at 3, 4 and 10 mol% to determine the ideal mole percentage for stabilization of the tetragonal zirconia phase. It was found that the sample with the reagent composition of 1:3, synthesized for 24 hours and an addition of 10 mol% yttria yielded rice grain like particles (525 x 180 nm) with tetragonal composition of 39.9 wt%. Theoretically, these dimensions are small enough to sufficiently eliminate the mismatch stresses. However, further study is needed to refine the hydrothermal process in order to attain complete phase stabilization and consequently, achieve superelastic properties in the ceramic. A thorough examination with reported results on the effects of the aforementioned experimental conditions on morphology as well as that of the additives on the phase stabilization of zirconia nanocrystals will be discussed at length.