Phase Transformation of Calcium Phosphates by Electrodeposition and Heat Treatment
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INTRODUCTION
HYDROXYAPATITE ceramic (Ca10(PO4)6(OH)2, hereafter HAP) is used in orthopaedics and dental implant surgery, either alone or in combination with other materials or substrates, as a coating on metal implants[1,2] and to fill bone defects.[2–4] A lot of effort has been made in recent years to develop processing methods, such as plasma spraying,[5,6] electrophoretic methods,[7,8] and electrochemical methods,[9–12] for depositing calcium phosphate ceramics on the implant substrate alloys in order to have high strength, good processability, suitable specific density, and excellent corrosion resistance in the living body. Although the most widely applied HAP coating procedure is the plasma spray technique,[5,6] the major problem of the decomposition and phase transformation of HAP during the spray coating process still exists. Hence, the electrochemical deposition of calcium phosphate bioceramic coatings has attracted considerable attention[9–12] because of its many advantages. Specifically, composition and coating structure controls are WEI-JEN SHIH, Engineer, is with the Metal Industries Research and Development Center, Kaohsiung 81160, Taiwan R.O.C. MOO-CHIN WANG, Professor, is with the Head of Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, Kaohsiung 80782, Taiwan R.O.C. Contact e-mail: mcwang@kmu. edu.tw KUO-MING CHANG, Professor, CHENG-LI WANG, PhD Student, and SZU-HAO WANG, Engineer, are with the Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 80782, Taiwan R.O.C. WANG-LONG LI, Professor, is with the Institute of Nanotechnology and Microsystems Engineering, National Cheng Kung University, Tainan 70101, Taiwan R.O.C. HONG-HSIN HUANG, Professor, is with the Department of Electrical Engineering, Cheng Shiu University, Niaosong, Kaohsiung 83347, Taiwan R.O.C. Manuscript submitted July 8, 2009. Article published online October 5, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
possible due to the relatively low processing temperature, and highly irregular objects can be coated relatively quickly.[13] Since electrochemical deposition can be the result of increasing pH at the interface, which is attributed to electron incorporation to form OH– ions and H2 through water reduction, H2 gas evolution at the interface leads to a heterogeneous coating.[13] Recent work has used organic solutions to avoid the negative effects of H2 gas, and more homogeneous coatings have been reported by Chen et al.[14] In addition, Wang et al.[11] pointed out that when calcium phosphate coatings are deposited on a Ti-6Al-4V substrate using an electrolytic method under 80 Torr, bubbles quickly lift from the cathode surface, making the deposit regular and integrated. When the electrolyte contains Ca2+ and H2PO41–, it produces calcium phosphate powders, such as monocalcium phosphate monohydrate (MCPM, Ca(H2PO4)2Æ H2O), dicalcium phosphate dihydrate (DCPD, CaHPO4Æ 2H2O), octacalcium phosphate, amorphous calcium phosphate, and hydroxyapatite (HAP), depending on th
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