Avaliação do tipo de combustível na síntese por reação de combustão na obtenção de fosfatos de cálcio.

Abstract

This research proposed to evaluate the influence of the fuel type on the synthesis by combustion reaction at the temperatures 500 and 800 oC, aiming at obtaining calcium phosphates for biomedical applications. The fuels used were: glycine, urea, citric acid, aniline and carbohydrazide. The amounts of oxidizing and reducing reactants were calculated according to the theory of propellants and explosives. The samples were obtained by the process of synthesis by combustion reaction in solution, at temperatures of 500 and 800 ° C. During the syntheses the temperature and the combustion time were measured, and the products of the reactions were characterized by X-ray diffraction with phase quantification through Rietveld's refinement, density, Fourier transform infrared spectroscopy, textural analysis, scanning electron microscopy and particle size distribution. The experimental density values were equivalent to the theoretical data according to the diffractometric standards of the Inorganic Crystal Structure Database (ICSD). In view of the obtained results, it was possible to synthesize nanocrystalline calcium phosphates successfully, through the combustion reaction at the synthesis temperatures of 500 and 800 oC using different fuels. With the exception of glycine fuel, all the samples under study presented the majority phase of the hydroxyapatite associated with a second crystalline phase, the tricalcium phosphate (ȕ-TCP). The samples obtained with glycine presented a third phase, known as anhydrous dicalcium phosphate or monetite (DCPA). The increase in temperature favored the increase of the particle size and consequently decrease of the surface area for the powders obtained with citric acid and aniline. On the other hand, the carbohydrazide, glycine and urea fuels presented higher porosity, due to the large amount of gases released, and for this reason higher surface area values. The samples presented a finer morphology formed by agglomerates in the form of skeins, typical of samples of calcium phosphates without calcination, presenting a narrow, symmetrical and monomodal distribution. Therefore, the results validate the efficacy of the synthesis by

combustion reaction to obtain calcium phosphates, especially hydroxyapatite and ȕ- TCP, for applications such as biomaterials. Considering the above, the sample with

the highest amount of hydroxyapatite was An800 obtained with the aniline fuel at a temperature of 800 ° C.