The Effect of Secondary Phases and Birefringence on Visible Light Transmission in Translucent alpha'-SiAlON Ceramics
Technical Report,15 Sep 2010,14 Mar 2013
Pennsylvania State University University Park United States
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Transparent alpha-SiAlON ceramics have the potential to replace modern transparent ceramic ballistic windows such as AlON, spinel, and sapphire due to their superior hardness and lower density. Residual AlN-polytypoid and amorphous glass were observed as secondary phases in initial studies but through systematic composition studies we decreased the AlN-polytypoid concentration. UV-visible spectroscopy demonstrated that neither the amorphous glassy grain boundary phase nor AlN-polytypoids are the dominant light scattering sites in alpha-SiAlON ceramics. The effects of birefringent scattering on the light transmission were explored by analyzing the effect of grain size in alpha-SiAlON ceramics. Seeding with 17.13 wt excess alpha-Si3N4 powder of approximately 400 nm particle size resulted in an aluminum nitride deficient alpha-SiAlON grain size of 0.77 microns. T he excess Si3N4 sample shows better textual contrast than the AlN deficient samples, but UV-visible spectroscopy analyses show that the seeded samples have lower total transmission in comparison to the AlN deficient samples due to greater absorption processes from free Si. It was concluded that birefringence and absorption processes by free Si are the dominant sources of visible light transmission loss in alpha-SiAlON and that more work is needed is resolve these issues.
- Ceramics, Refractories and Glass