FTIR study of carbonate loss from carbonated apatites in the wide temperature range

Abstract

The mineral constituent of bone tissue is a carbonate-substituted apatite (CHA). The thermal stability of the CHA has been revealed to depend on the substitution type and degree, although relatively little is known about this behavior. The aim of this study was to investigate the carbonate loss from synthetic CHAs in equilibrium conditions in a wide temperature range. An approach based on FTIR spectroscopy of condensed gas phase was applied to evaluate the CO and CO2 release with increasing temperature. Four different CHAs were studied, which were prepared by either precipitation from solution or the solid-state interaction. The samples differ from each other by the substitution degree. In one of the samples calcium was partially substituted by magnesium. Decomposition was shown to start at surprisingly low temperature, about 400 degrees C, and the CO content increases monotonously with the increase of temperature. The CO2 content goes through a maximum due to its decomposition into carbon monoxide and oxygen, the temperature of this maximum being strongly dependent on the chemical synthesis route. Therefore, control of the sintering atmosphere with respect to the CO2/CO ratio is needed when preparing the carbonated apatite bioceramics.

The influence of foreign ions on the crystal lattice of hydroxyapatite upon heating

“…As the rate of mass loss (DTG=dm/dT) showed, about 5wt% was lost up to 550 C and the remainder up to 950 C. Such a mass loss in hydroxyapatite was observed earlier and usually associated with the loss of adsorbed water in the lower temperature range and of carbon dioxide above 550 C [5][6][7][8]. However, the mass loss below 550 C was also related to the release of structural water [6,10].…”

“…An easy way to introduce impurities is the conventional precipitation method. However, success in this way was limited because the role of incorporated counter-ions of parent compounds in the crystallization of hydroxyapatite is not yet fully understood [5][6][7][8]. Some aspects of this problem were studied in this work.…”

Application of carbonated apatite coating on a Ti substrate by aqueous spray method

“…Furthermore, it is important that the CO 2 molecule can be inserted into the apatite lattice. This is the first report of a CA film with CO 2 molecules inserted without any hydroxy groups in the apatite skeleton; however, there are several reports on apatite crystals with both inserted CO 2 molecules and hydroxy groups [36][37][38][39].…”

Crystal growth of apatite by replacement of an aragonite precursor

“…In addition, the IR spectrum shows carbonate related absorption bands in two different frequency regions. Bands in the region between 1300 and 1650 cm À 1 are due to the v 3 (CO 3 ) stretching modes and the band at 873 cm À 1 reflects the v 2 (CO 3 ) bending vibration [36][37][38][39][40]. Previous work has suggested that the occupancy of the v 2 sites occurs competitively between the OH and carbonate groups, while that of the v 3 sites between phosphate and carbonate molecules [37,38,41].…”