| Transparent MgAl2O4 Spinel Fabricated by Sinter-HIP process |
| Ha-Neul KIM |
| Korea Institute of Materials Science |
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Keywords: Transparent, MgAl2O4, HIP, Spinel
Magnesium aluminate spinel (MgAl2O4) have been considered as a leading candidate for optical ceramics applications, since it had been developed as translucent bulks by R.J. Bratton[1]. For highly transparent (>80%) MgAl2O4, total volume porosity should be less than 50ppm, and nano-size pores with 40~70nm (one-tenth of visible wavelength range) also should be minimized according to the Mie-scattering theory[2]. In order to realize that, various different sintering methods have been applied such as hot-press[3], hot-press/hot isostatic press (HIP)[4, 5], spark plasma sintering (SPS)[6,7], and sinter-HIP[8,9]. For the armor application, it is important to make sub-um grained bulks for enhancing the hardness, so that improves the ballistic resistance. Until now, it is reported that only sinter-HIP process can meet both the high transmittance (>80%) and the fabrication of large MgAl2O4 bulk with sub-um grain.
In this study, highly transparent MgAl2O4 spinel was fabricated by sinter-HIP process. Commercial MgAl2O4 nanopowder which has 30m2/g of surface area (primary pariticle size = ~55nm), was effectively disintegrated into nano-dispersed slurry (D50<150nm) via microfluidization method. Uniform compacts with narrow pore size distribution, were made from the slurry via slip-casting process. The compacts were sintered under air atmosphere in the range of 1400oC ~ 1600oC in order to analyze the sintering behavior and remove open pores prior to HIP process. Selected air-sintered samples were HIPed at 1450oC for 5hrs to achieve transparent MgAl2O4. The in-line transmittance of a fabricated MgAl2O4 with 1mm of thickness, was close to the theoretical transmittance (~86.9%), 85.1% at 550nm and over 80% even at 300nm (UV wavelength). It is considered that the high in-line transmission is related to the delicate ceramic processing technique (especially microfluidization), and a small amount of Ca impurities from gypsum mold.
References:
[1] R.J. Bratton, J. Am. Ceram. Soc. 57[7] (1974) p.283.
[2] R.Apetz et al., J. Am. Ceram. Soc. 86[3] (2003) p.480
[3] L. Eposito et al., J. Eur. Ceram. Soc. 33 (2013) p.737
[4] A.C. Sutorik et al., J. Am. Ceram. Soc. 95[2] (2012) p.636
[5] http://www.techassess.com
[6] G. Bonnefont et al., Ceram. Int. 38 (2012) p.131
[7] K. Morita et al. J. Am. Ceram. Soc. 92[6] (2009) p.1208
[8] A. Krell et al. J. Am. Ceram. Soc. 93[9] (2010) p.2656
[9] A. Goldstein et al. J. Ceram. Soc. Jpn. 117[11] (2009) p.1281 |
| Acknowledgements : This work was supported by the MCTD (Materials & Components Technology Development) Program (PN : 10047010, Development of 80% Light-Transmitting Polycrystalline Ceramics for Transparent Armor•Window Applications) funded By the Ministry of Trade, industry & Energy (MI, Korea). |
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