Abstract
A citrate sol-gel method has been used to synthesize mayenite (Ca12Al14O33). X-ray powder diffraction data show that the samples synthesized using the citrate sol-gel method contained CaAl2O4 and CaCO3 along with mayenite when fired ex-situ in air at 800˚C but were single phase when fired at 900˚C and above. Using high temperature x-ray diffraction, data collected in-situ in air at temperatures of 600˚C and below showed only amorphous content; however, data collected at higher temperatures indicated the first phase to crystallize is CaCO3. High temperature x-ray diffraction data collected in 4% H2/96% N2 does not show the presence of CaCO3, and Ca12Al14O33 starts to form around 850˚C. In comparison, x-ray powder diffraction data collected ex-situ on samples synthesized using traditional solid-state synthesis shows that single phase was not reached until samples were fired at 1350˚C. DTA/TGA data collected either in a nitrogen environment or air on samples synthesized using the citrate gel method suggest the complete decomposition of metastable phases and the formation of mayenite at 900°C, although the phase evolution is very different depending on the environment. Brunauer-Emmett-Teller (BET) measurements showed a slightly higher surface area of 7.4 ± 0.1 m2/g in the citrate gel synthesized samples compared to solid-state synthesized sample with a surface area of 1.61 ± 0.02 m2/g. SEM images show a larger particle size for samples synthesized using the solid-state method compared to those synthesized using the citrate gel method.
