Laser ablation condensation of TiO2 and ZrO2: implications for the densification and coalescence of nanoparticles

by Tsai, Meng-Hsiu

Abstract (Summary)
This thesis is about the phase transformation, shape, size distribution and coalescence of TiO2 (part I) and ZrO2 (part II) nanopartilces produced by Nd-YAG laser ablation on metal targets under oxygen background gas, and characterized by analytical electron microscopy. The optimum laser ablation condition that satisfactory and routinely yield high-pressure phases of TiO2 (i.e. £\-PbO2-type and fluorite-related structures) and ZrO2 with high residual stress were reported. Part I-1 focuses on physical coagulation, by Van der Waals force, of the TiO2 condensates at temperatures up to about 1000 K as a result of post-condensation radiant heating. In part I-2, imperfect oriented attachment of nanoparticles over specific surfaces is rationalized to cause accretion and defects for the rutile condensates. Brownian motion may proceed above a critical temperature for anchorage release at the interface of imperfect attached nanoparticles until an epitaxial relationship is reached. Part I-3 deals with further the Brownian-type rotation of the imperfectly impinged £\-PbO2-type TiO2 and rutile nanocondensates until interfacial-energy cusp was reached. In part I-4 laser ablation condensation synthesis of dense TiO2 polymorphs and their phase transformations were documented. Part II-1 is about dense tetragonal (t)-ZrO2 and cubic (c-) nanocondensates which were synthesized under very rapid heating and cooling by pulsed Nd-YAG laser ablation with oxygen background gas. The t-ZrO2 nanoparticles were found to form deformation twins/faults and followed unique transformation path upon local electron dosage. Electron diffraction indicated that the dense c- and t- phase with specific size and residual stress were allowed to relax and/or kinetically phase change into lower-energy state as constrained by the intersections of the internal energy vs. cell volume plots calculated for the two polymorphs (Part II-2).
Bibliographical Information:

Advisor:Gan, Der shin; Chen, Shueiyuan; Hsieh, Ker-Chang; Hwang, S.L.; Shen, Pouyan; Kao Po-We

School:National Sun Yat-Sen University

School Location:China - Taiwan

Source Type:Master's Thesis

Keywords:tio2 laser ablation nca phase transformation coalescence zro2


Date of Publication:07/12/2005

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