Influence of Spark Plasma Sintering (SPS) Conditions on Transmission of MgAl2O4 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 MgAl₂O₄ 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 CO₃ 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.