Effect of LiF additive on combustion synthesis of MgAl2O4

Abstract

Due to the excellent mechanical properties and high transparency from near-UV to mid-IR (190<λ<6000nm), MgAl2O4 has been used for optical engineering applications, such as armored window systems, high energy laser windows and lightweight armor. In order to fabricate high quality transparent ceramics, high quality starting powder is necessary. So we focused on the combustion synthesis method which has recently drawn the attention of researchers due to multiply advantages. But the combustion synthesis method still have some disadvantages need to be overcome. Based on the mechanism of spinel formation, we decided to introduce some additive to improve this method. After calculation, the promising of LiF additive was certified. With different amount of LiF, combustion synthesis of MgAl2O4 (MAS) was investigated in relation to the synthesis conditions, powder properties, thermodynamic aspects and sinterability. Using citric acid as a single fuel, only hard-agglomeration MAS was obtained with high carbon contamination and poor sinterability which cannot be used as transparent ceramic raw materials. However, by introducing LiF, good property MAS powder can be synthesized. This is because LiF can effectively reduce the formation energy of MAS, remove the residue carbon, reduce agglomeration degree and promote the crystal growth during the combustion reaction. Through 2-steps calcination, the as-obtain high purity powders have been consolidated into transparent ceramics (T=81.0%) by SPS at T=1200℃ for 20min holding under P=80MPa