Sol–gel derived alumina–hydroxyapatite–tricalcium phosphate porous composite powders Azade Yelten a , Suat Yilmaz a, * , Faik N. Oktar b,c a Istanbul University, Department of Metallurgical and Materials Engineering, 34320 Avcilar, Istanbul, Turkey b School of Health Related Professions, Radiology Department, Marmara University, Istanbul, Turkey c Nanotechnology and Biomaterials Research and Application Center, Marmara University, Istanbul, Turkey Received 23 June 2011; accepted 14 November 2011 Available online 22 November 2011 Abstract In this study, alumina–hydroxyapatite–tricalcium phosphate (a-Al 2 O 3 –HA–TCP) porous composite powders were produced and characterized. At first, boehmite sol (AlOOH) was obtained via sol–gel process by using aluminium isopropoxide (Al(OC 3 H 7 ) 3 ) as the starting material. Bovine hydroxyapatite (BHA) powders derived from deproteinized bovine bones were added as 10, 20, 30 and 50% weight of the starting material to each boehmite sol. Also Na-alginate was added to the boehmite sol as the dispersive agent. Subsequently, gelation for 3 h at 110 8C was applied to each sol mixture. Finally, gelated samples were heat treated for 2 h at 500, 800, 1000 and 1300 8C. DTA–TGA, XRD, FTIR and SEM-EDS analyses were used to characterize the obtained composite powders composed of a-Al 2 O 3 –HA–TCP phases. In order to investigate porosity properties, powders were pressed with hydraulic manual press and formed into pellets. Later these pellets were sintered for 2 h at 1300 8C. Apparent porosity and bulk density tests were applied to the pellets. The evaluation of these tests results indicate that a novel a-Al 2 O 3 –HA–TCP composite material with 38–44% apparent porosity has been produced. Crown Copyright # 2011 Published by Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Sol–gel processes; Composites; Al 2 O 3 ; Hydroxyapatite 1. Introduction Materials used in the regeneration or reparation of fully or partially damaged organs/tissues of the body are known as ‘‘biomaterials’’. Bioceramics, an important class of biomaterials, can be conveniently applied in orthopedic and dental surgery due to their remarkable properties such as high biocompatibility and stability [1–7]. Bioceramics are classified mainly into three groups on the basis of the interactions between the implant material and the tissues. These groups are called bioinert, bioactive and bioresorbable bioceramics respectively. Alumina and zirconia belongs to bioinert ceramics while hydroxyapatite (HA) to bioactive and tricalcium phosphate (TCP) to bioresorb- able ceramics [1,3,5,8–12]. Although alumina is famous for its high chemical and mechanical strength, it cannot form biochemical interfacial bonds with the tissues. HA is chemically and crystallographically similar to the mineral in human bones and teeth. On the contrary to alumina, HA has an ability of interfacial bonding to bone owing to its highly bioactive character. TCP can replace the body tissues when implanted depending on its bioresorbable properties and is one of the decomposition products of HA. These materials can be employed in different hard tissue applications like total hip joints, bone cement, tooth implants, etc. [11–19]. Recently, porous biocera- mic materials have drawn interest since pores in the structure provide prosperous spaces for the tissue and implant contraction which makes the materials potentially suitable for cell/tissue ingrowth/development [1,12]. HA can be obtained either from natural sources such as bovine bones, egg shells, sea shells, and corals or with chemical methods like hydrothermal precipitation, sol–gel technology, solid-state reactions. Several researchers have reported results about producing hydroxyapatite from natural sources [20–24] and in this experimental study, bovine hydroxyapatite (BHA) powders derived by Oktar et al. were used [23]. Sol–gel method is the most reliable way for providing alumina with very high purity [25–27]. Previous studies based on alumina–HA www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 38 (2012) 2659–2665 * Corresponding author. Tel.: +90 212 4737070x17692; fax: +90 212 4737180. E-mail address: syilmaz@istanbul.edu.tr (S. Yilmaz). 0272-8842/$36.00. Crown Copyright # 2011 Published by Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2011.11.032