Transparent MgAl<sub>2</sub>O<sub>4 </sub>ceramic could be found in a wide range of applications for both military and civil sector due to its high melting point, good mechanical properties, small refractive index (1.71) and its ability to allow light in range from UV to mid-IR to pass through. In the present work, transparent MgAl<sub>2</sub>O<sub>4</sub> was fabricated from metal nitrates via two steps. Firstly, the MgAl<sub>2</sub>O<sub>4</sub> nanopowder was synthesized via solution combustion synthesis from the metal nitrates. Secondly, the powder was then consolidated by Pulsed Electric Current Sintering (PECS) technique to fabricate transparent ceramic. XRD patterns of the obtained powder showed the peaks of only MgAl<sub>2</sub>O<sub>4</sub> phase. Besides, the atomic compositions of magnesium, aluminium and oxygen determined by EDX analysis were approximately corresponded to 1:2:4 of the molecular formula of MgAl<sub>2</sub>O<sub>4</sub>. After deagglomerating for 48 hours using soft ball-milling, the powder had the average particle of 27 nm. Transparent MgAl<sub>2</sub>O<sub>4</sub> samples, which were sintered with two-step sintering mode of 1050<sup>o</sup>C/60 minutes-1400<sup>o</sup>C/20 minutes, permitted the transmission of visible and infrared light with the transmittance up to 80%, Vickers hardness of 14.2 GPa, and fracture toughness of 1.1 MPa.m<sup>1/2</sup>. The results are a critical step toward fabrication of high-quality transparent ceramics from metal nitrates.
Transparent MgAl2O4 ceramics were fabricated by pulsed electric current sintering (PECS) employing two-step sintering mode. First, nanoscale MgAl2O4 powders were produced by solution combustion synthesis from hydrated nitrate compounds and urea. Subsequently, the synthesized powders were sintered by PECS with a heating rate of 100oC/min under an applied pressure of 100 MPa. The sintering process was conducted according to two-step heating profile. At the first step, the temperature increased to 1050, 1100, and 1150oC, followed by a dwell time of 60 min. The second-step sintering was carried out at 1300, 1350, and 1400oC for 20 min. The transparent ceramics sintered at 1050oC/ 60 min – 1400oC/ 20 min exhibited transmittance over 80% in infrared range. In addition, transparent samples presented a Vickers hardness up to 30 GPa for sintering mode of 1150oC/ 60 min – 1400oC/ 20 min.
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