Aalborg Universitet
Tailoring glass surfaces via internal cationic diffusion
Yue, Yuanzheng; Smedskjær, Morten Mattrup
Publication date:
2009
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Citation for published version (APA):
Yue, Y., & Smedskjær, M. M. (2009). Tailoring glass surfaces via internal cationic diffusion: An invited talk.
Abstract from International Conference on Materials for Advanced Technologies 2009, Singapore, Singapore.
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Submission ID : ICMATA02633-04515
Presentation Type : Invited Speaker
Topic/Symposium : D) Functional Ceramic Materials, Oxide Thin Films and Heterostructures
Keywords : Surface Characterization; Thin Films; Nanofabrication
Tailoring glass surfaces via internal cationic diffusion
Yuanzheng Yue; Morten M. Smedskjaer
Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University,
Aalborg, Denmark
In this paper, we report a new way to create functional surfaces on the transition metal
containing oxide glasses. In terms of chemistry and structure, the created surfaces are classified
into two groups. One group is the nano-crystalline surface layer enriched in earth alkaline
oxides, and the other is the nano-amorphous surface layer enriched in silica. The nanocrystalline surface is generated by subjecting the glass to an oxidation process in atmospheric
air at the glass transition temperature for a certain duration. During this process, a fraction of
the transition metal ions will be transformed from low to high valence state, and this causes
electron holes to migrate from the glass surface towards the glass interior. To maintain the
charge neutrality, the network modifying ions must diffuse from the interior towards the
surface, i.e., the so-called outward diffusion occurs. At the surface, the modifying cations react
with oxygen ions to form the corresponding oxides, the formation of which is driven by the
negative Gibbs free energy of the reaction. It is found that the magnesium ions are the most
mobile, and hence, the formed periclase (MgO) is the predominant nano-crystalline phase in
the surface layer. The origin of this phenomenon is discussed in the present work. As a mirror
effect, the nano-amorphous surface layer enriched in silica is generated by subjecting the glass
to a reduction process. The direction of the cationic diffusion during reduction is just the
opposite of that of the outward diffusion, i.e., the so-called inward diffusion occurs. However,
whether the inward diffusion happens strongly depends on the partial pressure of the reducing
gas (e.g. hydrogen). The fascinating part of the new approach is that both the direction and the
extent of the diffusion are controllable, and hence, the thickness of both types of layers can be
tailored. The formation of the nano-layers can considerably contribute to improving physical
and chemical functions of glassy materials. We clarify the kinetic and thermodynamic
mechanisms of both outward and inward diffusion. We also describe the perspectives of our
new approach, in particular, with respect to the potential applications of the approach in
creating functional surfaces on non-oxide glasses, and even on crystalline materials.
References:
1. Y. Z. Yue, M. Korsgaard, L. F. Kirkegaard and G. Heide: Formation of a nanocrystalline
layer on the surface of stone wool fibers, J. Am. Ceram. Soc. 92 [1] (2008) 62-67.
2. M. M. Smedskjaer, J. Deubener and Y. Z. Yue: Inward cationic diffusion and formation of
silica-rich surface nanolayer of glasses, Chem. Mater. (2009) (in press)