Influence of Spark Plasma Sintering ( SPS ) Conditions on Transmission of MgAl 2 O 4 Spinel

The effects of the spark plasma sintering ( SPS ) parameters, such as heating rate α, temperature T and soak time t s , and impurities on in‐line transmission T in were examined in MgAl 2 O 4 spinel. The SPS processing at T = 1300°C for t s = 20 min with a low heating rate of α = 10°C/min is a preferable condition for attaining higher T in . For the higher T or the longer t s , grain coarsening enhanced the coalescence of residual pores and second phase precipitation, resulting to the limited T in even at the slow α. Although the lower T and longer t s attained fine and dense microstructure simultaneously, the maximum T in was limited to about 50%. The limited transmission, particularly in the visible range, can be ascribed to the discoloration caused by the carbon contamination. The carbon contamination arose from the preexisting trace CO 3 impurities, irrespective of the SPS conditions. For the higher α, which is the primary advantage of the SPS technique, the additional carbon contamination occurred from the paper/die and remained as glassy carbon in the matrix. To attain higher T in by the SPS technique, the lower α and T , and the shorter t s should be utilized after removing the impurities.