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Transparent armour ceramics: Spinel vs. Sub-µm Al2O3

Transparente schusssichere Keramik: Gegenüberstellung von Spinell mit Submikron-Al2O3
: Krell, A.; Hutzler, T.; Klimke, J.

Heinrich, J.G. ; Deutsche Keramische Gesellschaft e.V. -DKG-; European Ceramic Society:
10th International Conference and Exhibition of the European Ceramic Society, ECerS 2007. Proceedings : Berlin, June 17-21 2007
Baden-Baden: Göller, 2007
ISBN: 3-87264-022-4
European Ceramic Society (International Conference and Exhibition) <10, 2007, Berlin>
Conference Paper
Fraunhofer IKTS ()
transparent armour; light transmission; defect-free processing; alumina Al2O3; spinel MgO.Al2O3; Aluminiumoxid; Magnesiumaluminiumspinell; Submikronkorn; Sintern; Schlickergießen; Gel; transparente Keramik; Vickers-Härte; optische Durchlässigkeit; Beschussprüfung; Gelcasting-Verfahren

Sintered sub-µm Al2O3 is the hardest of all transparent materials for compact windows, and a high hardness is important for the ballistic performance. However, visible light transmission of sintered alumina is limited by birefringent scattering to a real in-line transmission RIT of only 70-75 % of the theoretical maximum (at 0.8-1 mm thickness). These losses increase with thickness whereas a safe ballistic performance requires 1.5-2 mm at least. Slip casting brings RIT closer to the limit with grain sizes of 0.3 µm (at 0.8 mm thickness: 84-93 % of the theoretical maximum) but these results give again rise to doubt that it will ever be possible to manufacture larger and thicker Al2O3 windows with a sufficiently high transparency. On the other hand, new fine-grained spinel associates an RIT close to the theoretical maximum with a hardness that approaches sapphire. In first ballistic tests this spinel outperformed sapphire. It is, therefore, suggested that sub-µm Al2O3 may be good for IR windows or as armour for low threat applications (where thinner tiles can be used). For thicker windows, however, the new spinel appears as a most favourable candidate.