Magnesium aluminate (MgAl2O4) spinel (MAS) is a synthetic material with cubic crystal structure and excellent chemical, thermal, dielectric, mechanical and optical properties. These properties made MAS an indispensable material for optically transparent windows, domes and armours, and for certain refractory applications. High processing cost of dense MAS ceramics is in the main responsible for its limited usage in certain important applications despite its excellent performance in them. The volume expansion (∼8%) associated with MAS phase formation from alumina and magnesia does not allow obtaining dense MAS bodies in a single-stage reaction sintering process. Therefore, dense MAS bodies are made by following a double stage firing process, which is expensive. The existing literature suggests that the processing cost of dense MAS ceramics could be reduced to a great extent by decisive selection of starting raw materials, powder processing and densification conditions, and by understanding the under...

A review on magnesium aluminate (MgAl2O4) spinel: synthesis, processing and applications

http://link.springer.com/content/pdf/10.1007/978-94-011-3836-9_11.pdf

Mechanical Behavior of Ceramics

A 50:50 vol% MgO–Y2O3 nanocomposite with ~150 nm grain size was prepared in an attempt to make 3–5 lm infraredtransmitting windows with increased durability and thermal shock resistance. Flexure strength of the composite at 21° Ci s 679 MPa for 0.88 cm 2 under load. Hardness is consistent with that of the constituents with similar grain size. For 3-mm-thick material at 4.85 lm, the total scatter loss is 1.5%, forward scatter is 0.2%, and absorptance is 1.8%. Optical scatter below 2 lm is 100%. Variable intensity OH absorption (~6% absorptance) is observed near 3 lm. The refractive index is ~0.4% below the volume-fraction-weighted average of those of the constituents. Thermal expansion is equal to the volumefraction-weighted average of expansion of the constituents. Specific heat capacity is equal to the mass-fraction-weighted average of heat capacities of the constituents. Thermal conductivity lies between those of the constituents up to 1200 K. Elastic constants lie between those of the constituents. The Hasselman mild thermal shock resistance parameter for the composite is twice as great as that of common 3–5 lm window materials, but half as great as that of c-plane sapphire.

https://ceramics.onlinelibrary.wiley.com/doi/pdf/10.1111/jace.12589

D.P.H Hasselman

Papers

Thermal stress resistance of engineering ceramics