Nitrogen-containing apatite

Two commercial hydroxyapatites were treated in dry ammonia at temperatures between 800 and 1300 degrees C for different times up to 30 h. Nitrogen was incorporated with a maximum content of 3.7 wt% in presence of graphite. X-ray diffraction studies show no important phase transformation by the incorporation of nitrogen up to 1200 degrees C. Treatments at temperatures above 1200 degrees C resulted in the formation of CaO or Ca(OH)(2). P-31 NMR studies indicate no direct bonding of nitrogen and phosphorous. Infrared spectra show increasing intensities of four new bands at 3250, 2016, 1966 and 700 cm(-1) with increasing nitrogen contents, while the OH-bands at 3570 and 630 cm(-1) vanish. Taking into account results of the carbon content, XRD, NMR and IR spectra it is suggested that nitrogen enters into the structure as [CN2](2-) ion, substituting [OH](-) groups, and forming cyanamidapatite Ca-10(PO4)(6)(CN2). (C) 1999 Elsevier Science Limited. All rights reserved.