[CCoE Notice] Thesis abstract and announcement

[Knudsen, Rachel W]

The defense will be held on April 29th 1-3 pm in the MREB Room 126.




Low Temperature Synthesis of Sapphire or Ruby and

Their Applications

Chairman of the Committee: Dr. Stanko R. Brankovic, Professor Electrical and Computer Engineering


Committee Members:


Dr. Francisco C. Robles, Associate Professor Mechanical Engineering Technology

Dr. Yan Yao, Associate Professor Electrical and Computer Engineering

Dr. Jiming Bao, Associate Professor Electrical and Computer Engineering

Dr. Debora Rodrigues, Associate Professor Civil and Environmental Engineering

Dr. Suresh Khator, Associate Dean, Cullen College of Engineering

Dr. Alamgir Karim, Program Director Material Engineering Program



An Abstract of a Dissertation Presented to The faculty of the Material Science & Engineering Program University of Houston In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in Material Engineering

by Wenli Yang

May 2019


ABSTRACT

Sapphire or ruby as a single crystalα-Al2O3 phase is gaining a lot of attentionin recent

years due to its thermal, mechanical and opticalproperties. The current study presents a unique

method to synthesize sapphire or ruby, which optimizethe traditional synthesisprocess, and

explores some of their applications such as high refractive index thin film coating and stress

transferring material. In the synthesisprocess, pseudoboehmite (PB) is used as a precursor and

mechanical  milling  is  employed to  reduce  the  phase  transformation temperature  of

pseudoboehmite to sapphireor ruby. The phase transformation of the milled PB samples was

investigated by variouscharacterization techniques. XRD data showedthat PB structureis first

synthesized as raw material,followed by its room temperature transformation to χ-Al2O3.

Raman spectrum and HRTEM confirmed the presenceof α-Al2O3  and χ-Al2O3  phase in the

30hr  milled PB  sample.  Through the  proposed synthesis  method,  there is  a  significant

temperature reduction (approximately 200°C) for the complete transformation to sapphireor

ruby during annealing, which is confirmedfrom thermal analysis.This is due to sapphireor

ruby seeds are synthesized at room temperature in the milled sample and serve as hetero sites

for nucleation in the annealing process.


In addition, XPS and EELS analysis shows unique band gap effects,both of them are

consistent with theoretical value for two random choosing samples (PB milled 10hr and 30hr

samples). This indicates the reliability of XPS band gap results. It is found it is possible to tune

the band gap of aluminaduring mechanical milling through quantum confinement. FTIR result

shows that PB lose water content from its structure, which can releasesits surface strain during

the milling process,therefore cold welding induces the increase of PB grain size. The current

study also involvedthe application of sapphire or ruby thin films, which are deposited on

substrates through ion beam sputtering from the low temperature synthesized sapphireor ruby

target.
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