Influence of LiF on the Infrared Transmissivity of Magnesia Alumina Spinel Transparent Ceramics

The influence of LiF as a sintering aidditive on the infrared transmissivity of magnesia alumina spinel(MgAl2O4;spinel,briefly) transparent ceramics was investigated.Spinel powders prepared by Sol-Gel method,were mixed with LiF of 0-2.5wt%,and then ball milled,tested by XRD for their phase compositions.Hot press(HP) or hot press combined with hot isostatic press(HP/HIP) technique was applied to sintering the powder mixtures into spinel ceramics,while HP under 32 MPa at 1550℃,and HIP under 150 MPa at 1700℃.The structures and infrared transmissions of the ceramic bodies were examined by SEM and IR spectrometer,respectively.Li contents in the spinel powder mixtures and in the resulted ceramics were detected by inductively coupled plasma(ICP) technique.The incorporation of LiF in the starting spinel powders facilitates the growth of grains and the expulsion of pores during sintering.And it shows LiF promotes the sintering of spinel ceramics.Spinel ceramics with LiF contents of 1.0wt%-1.5wt% exhibit optimal infrared transmissivity.While excess LiF acts adversly on the optical performances of spinel ceremics due likely to its remnant or derivative in the ceramic bodies.