Synthesis and characterization of titanium sol–gels in varied gravity
Two unique test systems were designed and built to allow the effects of varied gravity (high, normal, reduced) during synthesis of titanium sol–gels to be studied. A centrifuge capable of providing high gravity environments of up to 70 g for extended periods while applying a 100 mbar vacuum and a temperature of 40–50 °C to the reaction chambers was developed. The second system was used in the QUT Microgravity Drop Tower Facility also provided the same thermal and vacuum conditions used in the centrifuge, but was required to operate autonomously during free fall.
Through the use of post synthesis instrumental characterization, it was found that increased gravity levels during synthesis, had the greatest effect on the final products. Samples produced in reduced and normal gravity appeared to form amorphous gels containing very small particles with moderate surface areas. Whereas crystalline anatase (TiO2), was found to form in samples synthesized above 5 g with significant increases in crystallinity, particle size and surface area observed when samples were produced at gravity levels up to 70 g.
It is proposed that for samples produced in higher gravity, an increased concentration gradient of water is forms at the bottom of the reacting film due to forced convection. The particles formed in higher gravity diffuse downward toward this excess of water, which favors the condensation reaction of remaining sol–gel precursors with the particles promoting increased particle growth. Due to the removal of downward convection in reduced gravity, particle growth due to condensation reaction processes are physically hindered hydrolysis reactions favored instead. Another significant finding from this work was that anatase could be produced at relatively low temperatures of 40–50 °C instead of the conventional method of calcination above 450 °C solely through sol–gel synthesis at higher gravity levels.
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|Item Type:||Journal Article|
|Keywords:||nanomaterials, gravity, reduced gravity, hyper graviity, microgravity, titania sol gels, sol gels|
|Subjects:||Australian and New Zealand Standard Research Classification > PHYSICAL SCIENCES (020000)
Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000)
Australian and New Zealand Standard Research Classification > ENGINEERING (090000)
|Divisions:||Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
|Copyright Owner:||Copyright 2014 Elsevier B.V.|
|Copyright Statement:||NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Non-Crystalline Solids. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Non-Crystalline Solids, [Volumes 396–397, (1 August 2014)] DOI: 10.1016/j.jnoncrysol.2014.04.010|
|Deposited On:||03 Jun 2014 22:30|
|Last Modified:||06 Sep 2016 06:06|
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