Influence of Ammonium Nitrate in the Synthesis of Alpha Tricalcium Phosphates (α-TCP) in One Step by Solution Combustion

Calcium phosphates are materials of wide interest in the medical and agricultural industries. Advanced in the standardization of protocols to obtain them by combustion in solution in a single step is highly desirable. This is particularly so for the alpha-tricalcium phosphate (α-TCP) phase, widely used in the development of bone cement. In this research, citrulline was used as a fuel for the first time in the one-step synthesis of calcium phosphates, and the effect of adding 0–15 g of ammonium nitrate (AN) as an extra oxidizer agent was studied, allowing the temperature of the reaction to increase from 648 to 950°C. The temperature was measured using low-cost equipment with infrared and type-K thermocouple and contrasted with the estimated theoretical values of adiabatic flame temperature. X-ray diffraction analysis showed the formation of a mixture of α-TCP and hydroxyapatite phases at the lowest combustion temperature, corresponding to 0 g of AN. When the amount of AN was increased, the XRD showed that α-TCP was obtained as a metastable phase, while the amount of hydroxyapatite decreased considerably. At higher combustion temperatures, the crystallite size estimated by Scherrer equation, in turn, increased to a value of 51.61 nm. The SEM images showed the presence of necks between particles in the powders that coincide with the estimation of high reaction temperatures.