Sintering and mechanical properties of the alumina–tricalcium phosphate–titania composites Siwar Sakka ⁎, Jamel Bouaziz, Foued Ben Ayed Laboratory of Industrial Chemistry, National School of Engineering, Box 1173, 3038 Sfax, Sfax University, Tunisia abstract article info Article history: Received 28 September 2013 Received in revised form 18 February 2014 Accepted 18 March 2014 Available online 26 March 2014 Keywords: Biomaterials Tricalcium phosphate Alumina Titania Sintering Mechanical properties The objective of this study was to determine the effect of the content of titania and the sintering process on the transformation phase, the densification, the rupture strength and the microstructures of the alumina–10 wt.% tricalcium phosphate composites. After the sintering process, the samples were examined by using 31 P and 27 Al magic angle scanning nuclear magnetic resonance, X-ray powder diffraction and scanning electron micros- copy analysis. The Brazilian test was used to measure the rupture strength of the samples. The present results provide new information about solid-state reactivity in the ternary system α-alumina-β-tricalcium phos- phate–anatase–titania. The differential thermal analysis of the α-alumina-β-tricalcium phosphate–titania composites shows two endothermic peaks, at 1360 °C and at 1405 °C, which are caused by the reactions between titania/alumina and titania/tricalcium phosphate, respectively. Thus, the presence of titania in the alumina– 10 wt.% tricalcium phosphate leads to the formation of β-Al 2 TiO 5 at 1360 °C. At 1600 °C, the alumina–10 wt.% tricalcium phosphate–5 wt.% titania composites displayed the highest rupture strength (74 MPa), compared to the alumina–10 wt.% tricalcium phosphate composites (13.5 MPa). Accordingly, the increase of the rupture strength is due to the formation of the new β-Al 2 TiO 5 phase. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Biomaterial research is defined and explained through the introduc- tion of biotechnology and advances in the understanding of the compat- ibility of human tissues [1]. Among the biomaterials used in different areas, bioceramics are widely used in medical applications, notably for implants in orthopedics, maxillofacial surgery and dental implants [2]. Special attention has been given to β-tricalcium phosphate (β-Ca 3 (PO 4 ) 2 )(β-TCP) due to its outstanding biological responses to physiological environments [3,4]. The use of β-TCP in the human body has been limited due to its poor mechanical properties [5,6]. Much research has been interested in enhancing the mechanical resistance of β-TCP by the inclusion of several additives [5,7–12]. Metal oxide ceramics, such as alumina (Al 2 O 3 ), have been widely studied due to their chemical inertness, excellent tribological properties, high wear resistance, fracture toughness and high strength [13]. Alumina is bio- inert with human tissues [9,14,15]. Thus, the study conducted by Sakka et al. [16] has recently been concerned with the alumina/ tricalcium phosphate system elaborated by researchers interested in producing Al 2 O 3 –TCP composites with different percentages of β-TCP (10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% and 50 wt.%). As a result of this study, the best mechanical properties of the alumina–10 wt.% tricalcium phosphate composites reached 13.5 MPa after a sintering process at 1600 °C for 1 h [16]. In such cases, and in order to improve the mechan- ical resistance of these composites, it is necessary to introduce a reinforc- ing agent, i.e. ceramic oxide or metallic dispersion. Among the ceramic oxide agents used for reinforcement, titania (TiO 2 ) has been used in orthopedic applications especially because of its excellent mechanical resistance, its biocompatibility, its chemical stability in aqueous envi- ronments and its chemical inertness [17–22]. Therefore, and due to its properties, we have chosen titania as the agent of reinforcement to be added to the Al 2 O 3 –10 wt.% TCP composites. We will later discuss the influence of titania on the phase transformation, densification, rupture strength and microstructures of those composites. Within this context, we are interested in examining the effect of TiO 2 (2.5 wt.%; 3 wt.%; 4 wt.%; 5 wt.%; 7.5 wt.% and 10 wt.%) on the Al 2 O 3 –10 wt.% TCP composites sintered at various temperatures (1500 °C, 1550 °C and 1600 °C) for different sintering lengths of time (0 min, 30 min, 60 min, 90 min, 120 min and 180 min). After sintering, the characteristics were examined by X-ray diffraction, magic angle scanning nuclear magnetic resonance ( 31 P and 27 Al) and scanning electron microscopy. 2. Materials and methods Commercial alumina (Riedel-de Haёn), commercial titania (Riedel- de Haёn) and synthesized tricalcium phosphate (β-TCP) were used in this study. The β-TCP powder was synthesized by solid-state reaction from calcium carbonate (CaCO 3 ) and calcium phosphate dibasic anhy- drous (CaHPO 4 ) [15]. Stoichiometric amounts of high purity powders, Materials Science and Engineering C 40 (2014) 92–101 ⁎ Corresponding author. Tel.: +216 21 221 104; fax: +216 74 275 595. E-mail address: sakka.siwar@yahoo.fr (S. Sakka). http://dx.doi.org/10.1016/j.msec.2014.03.036 0928-4931/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec