From nanoporous to transparent MgAl2O4 spinel—Nanostructural flexibility by reaction densification of metastable powders

•The reaction kinetics of γ-Al2O3 – nano-MgO to form MgAl2O4 was analyzed for the first time. The reaction/densification kinetics of these metastable, nano-sized reactants were enhanced (reaction constant 6 orders of magnitude higher) compared to stable α-Al2O3 – micron-sized MgO.•Using the same starting powder, the processing procedure can produce a wide range of microstructures leading to nanoporous high temperature energy absorbing materials and highly dense optically transparent spinel.•These materials have implications for the design of light weight high temperature resistant applications as well as optical materials for harsh environments.