Effect of salt concentration on the electrical and morphological properties of calcium phosphates obtained via microwave-induced combustion synthesis

- Calcium phosphates were obtained by salt-assisted solution combustion synthesis.
- The amount of salt used influences the final phase obtained.
- The amount of salt used plays an important role in the final powder morphology.
- The dielectric constant varies with the amount of salt.

Calcium phosphates (CaP) have been widely used in biomedical applications. One of the most versatile techniques for obtaining CaP is auto-combustion synthesis. This technique stands out because of its low cost and high efficiency; however, the difficulty of controlling the size and morphology of the product is its principal disadvantage. The aim of this study was to synthesize calcium phosphates through microwave-induced and salt-assisted solution combustion synthesis. The initial ratio of Ca/P was 1.5, employing urea as fuel and potassium chloride as an additive. The morphology and the electrical properties of CaP in relation to the amount of salt added were evaluated using scanning electron microscopy (SEM) and impedance spectroscopy, respectively. It was found that the inclusion of salt during the synthesis affects the morphology of calcium phosphates, creating whisker-like structures, with lengths approximately between 500 nm and 1 µm and widths between 30 nm and 300 nm, which depend on the salt concentration. Calcium pyrophosphate was the major phase of the synthetized product without the addition of salt, and hydroxyapatite (HAP) and chlorapatite (CAP) when salt was included. The dielectric constant exhibited lower values for the samples rich in calcium pyrophosphate and values between 16 and 32 for HAP and CAP at 1 kHz.

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