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Proceedings Paper

Effects and elimination of nanoporosity in transparent sintered spinel (MgAl[sub]2[/sub]O[sub]4[/sub])
Author(s): Andreas Krell; Katja Waetzig; Jens Klimke
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Paper Abstract

MgAl2O4 is a candidate for sintered windows, domes and lenses for UV, visible, and IR applications. However, exact Mie calculation shows that for imaging uses with a window thickness of e.g. 5 mm even IR transmission will not tolerate smallest amounts of 0.01% of 50-100 nm small pores, and the impact of such pores is even worse at shorter wave lengths. Principles of solid state sintering suggest that smallest pores should be eliminated more easily than larger ones. It is, however, observed that a significant population of 50-100 nm small nanopores exists in undoped transparent spinel ceramics after hot-isostatic pressing with the higher concentration the finer the particles of the raw spinel powder are. On the other hand, it is demonstrated that sintering densification is governed not only by the size of the ceramic powder particles and the homogeneity of their mutual coordination but also by the state of the crystal lattice. Taking advantage of this latter effect, sintered spinel ceramics were derived by reactive sintering of undoped MgO/Al2O3 mixtures resulting in an in-line transmittance which fits comparable spinel single crystals from 200nm wave length up to the IR range.

Paper Details

Date Published: 20 May 2011
PDF: 10 pages
Proc. SPIE 8016, Window and Dome Technologies and Materials XII, 801602 (20 May 2011); doi: 10.1117/12.883958
Show Author Affiliations
Andreas Krell, Fraunhofer-Institut für Keramische Technologien und Systeme (Germany)
Katja Waetzig, Fraunhofer-Institut für Keramische Technologien und Systeme (Germany)
Jens Klimke, Fraunhofer-Institut für Keramische Technologien und Systeme (Germany)

Published in SPIE Proceedings Vol. 8016:
Window and Dome Technologies and Materials XII
Randal W. Tustison, Editor(s)

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