Prof. Ivar E Reimanis
Colorado Center for Advanced Ceramics,
Metallurgical and Materials Engineering,
Colorado School of Mines
The title of this talk appears to be an oxymoron: most toughening mechanisms in ceramics require the presence of a second phase that leads to visible light scattering due to index of refraction mismatch. However, it is possible to stimulate toughening while retaining transparency if the second phase displays the same index of refraction as the matrix, or if the second phase particle size is significantly smaller than the wavelength of light. This talk reviews strategies to strengthen transparent ceramics. A focus is given to magnesium aluminate spinel (“spinel”), an important ceramic for windows, domes and armor. Attempts to toughen spinel by reinforcing with alumina show modest gains. This talk discusses efforts to design particle reinforced spinel via two methods, precipitation and dissolution. Dissolution, whereby alumina particles are dissolved into spinel at elevated temperature, is the most promising, leading to varying residual stresses that can increase crack resistance.