The samples with CaO to Ca12Al14O33 weight ratios of 75/25 and
90/10 (CA75MMand CA90MM)were prepared employing a microwave
assisted self-combustion method (MM) using urea excess in the presence
of ammonium nitrate. The precursors were aluminum nitrate
[Al(NO3)3·9H2O—Merck], calcium nitrate [Ca(NO3)2·4H2O—Merck],
urea [CO(NH2)2—Merck], and ammonium nitrate [NH4NO3—Merck].
Nitrates were chosen for synthesis because of their water solubility,
low fusion temperature, and low cost. Urea has the advantage of being
commercially available. It is relatively inexpensive and offers high heat
generation which is important for the crystallization of the desired
phases. The ammonium nitrate ensures reaction uniformity allowing
all the reactants to decompose at the same time. The MM method
could be of interest froman economical point of view(short preparation
time, energy gains) but implies the development of an appropriate
microwaves furnace for the preparation at an industrial scale.