Solution combustion synthesis of bioceramic calcium phosphates by single and mixed fuels—A comparative study S. Sasikumar, R. Vijayaraghavan * Chemistry Division, School of Science and Humanities, VIT University, Vellore 632014, Tamil Nadu, India Received 22 January 2007; received in revised form 15 February 2007; accepted 2 March 2007 Available online 10 April 2007 Abstract Calcium phosphate based bioceramics have been synthesized by a modified combustion synthetic route using both citric acid and succinic acid separately and in mixture as fuels and nitrate and nitric acid as oxidants. Calcium nitrate and diammonium hydrogen phosphate were used as calcium and phosphate sources. The effects of citric acid to succinic acid ratio on the phase formation have been investigated. The precursors and the calcined products have been characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy. Succinic acid has been used as a fuel for the first time to synthesize hydroxyapatite. Hydroxyapatite phase is formed when either citric acid or succinic acid is used as a fuel and b-tricalcium phosphate phase is formed when a mixture of citric acid and succinic acid is used as a fuel as revealed by powder X-ray diffraction. The average crystallite size of the synthesized powder determined by Debye–Scherrer formula is found to be in the range of 55–65 nm. Surface morphology of the samples was imaged using scanning electron microscope. Chemical analysis shows that the Ca:P ratio in synthesized ceramics is 1.67. Results are discussed in terms of the phases present in the precursors formed during single and mixed fuel approaches and also its carbonate content present in hydroxyapatite products. # 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Powders: chemical preparation; B. Spectroscopy; D. Apatite; E. Biomedical applications 1. Introduction Out of several calcium phosphate bioceramics, hydroxya- patite (HAP) and tricalcium phosphate (TCP) are the most commonly used constituents for bone replacement due to its less solubility in physiological environment. Composites of b- TCP and HAP, not only mimic that of human bone but also posses very good osteoconductivity and excellent biocompat- ibility [1]. The percentage of b-TCP in the composite is decided based on the characteristics required for the specific applica- tion. The function of b-TCP in the composite is to help the rapid bonding of artificial bones to natural ones by means of its fast resorbable nature in physiological pH. It is reported that most of the TCPs are resorbed within 6 weeks after implantation. The various applications of these composites are defect filling in total hip revision, spinal fusion, hand and foot surgery, fracture repair and joint reconstruction. Synthesis of HAP/TCP composite especially in nanosized forms has been an active area of research by various groups. Hydroxyapatite and b-TCP have been synthesized by the traditional solid-state reaction and wet chemical methods such as co-precipitation and sol–gel methods [2–4]. The problem associated with the solid-state reaction is its high temperature calcination and the large particle size of the resultant product [5]. The co-precipitation method improves reactivity of the components but the incomplete precipitation results in the alteration of stoichiometry which results in undesirable impurities [6]. The sol–gel method can reduce the segregation of metal elements and improve the chemical homogeneity during the decomposition of the polymeric precursors at high temperatures but the major disadvantages of the sol–gel process is the high cost of the starting material (metal alkoxides) and sometimes (or) often the precursor formed is extremely moisture sensitive [7]. However, sol–gel method has been employed to synthesize a variety of materials using cheap organic compounds as gelling agents cost effectively [8–10]. Recently, there has been a growing interest in synthesizing ceramic materials by self-propagating combustion synthesis www.elsevier.com/locate/ceramint Ceramics International 34 (2008) 1373–1379 * Corresponding author. Tel.: +91 416 2202338; fax: +91 416 224 3092. E-mail address: rvijayaraghavan@vit.ac.in (R. Vijayaraghavan). 0272-8842/$34.00 # 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2007.03.009