Equation of state of carbonated hydroxylapatite at ambient temperature up to 10 GPa: Significance of carbonate

Abstract

The incorporation of the carbonate ion into the crystal structure of hydroxylapatite results in the creation of vacancies, oxygen-loss, and disorder, with consequent changes in physical and chemical properties. High-pressure experimental investigation up to 10 GPa of two synthetic carbonated hydroxylapatite samples with up to 11 wt% CO 3 , using a diamond-anvil cell and synchrotron powder X-ray diffraction, provides the first rigorous assessment of the mechanical behavior of the carbonated hydroxylapatite. The pressure-volume data suggest that the isothermal bulk modulus of these carbonated hydroxylapatites has been significantly decreased by the presence of the carbonate (up to about 15%), which in turn will affect all the carbonated apatite-related reactions in the geosystem. Since hydroxylapatite is one of the major components of the bones and teeth, the incorporation of the carbonate in the hydroxylapatite weakens teeth and bones not only chemically, but also physically.

The effect of type-B carbonate content on the elasticity of fluorapatite

“…Incorporation of carbonate into the apatite structure can occur by substitution for both channel anion (type-A) and phosphate ion (type-B), as first suggested by McConnell (1938 1990) have shown a correlation between increased carbonate and decreased phosphate, with different effects on the unit-cell parameters (Knudsen and Gunter 2002). The response of the unit-cell parameters of apatite to accommodation of the carbonate ion is complicated (Elliott 2002;Liu et al 2011 (Ivanova et al 2001).…”

“…It is wellestablished that the incorporation of carbonate into the apatite structure has a destabilizing effect, resulting in increased solubility (LeGeros 1991). Whereas the structural details of FAP, CAP, and HAP are generally well-established, those of "carbonated" apatite are not yet very clear (Liu et al 2011;Yi et al 2013). Due to the importance of carbonate-bearing HAP in biomineralization (Elliott 2002), the incorporation of carbonate into apatite and its resulting physicalchemical changes have been investigated extensively and yet are still not well understood (McClellan 1980;Perdikatsis 1991;Elliott 1994;Regnier et al 1994;Nathan 1996;Wilson et al 1999Wilson et al , 2004Comodi and Liu 2000;Leventouri et al 2000;Ivanova et al 2001;Elliott et al 2002;Pan and Fleet 2002;, 2008aYi et al 2013).…”

“…With regard to the elastic behavior of apatites, several compression experiments are done (Brunet et al 1999;Comodi et al 2001;Matsukage et al 2004;Schouwink et al 2010;Liu et al 2011) in Table 1 to investigate the compressibility of synthetic and natural apatite. Literature results are listed in Table 1 to compare the bulk modulus and the volume variations between the previous studies for apatite species and our results for carbonate-bearing fluorapatite (CFAP).…”

“…More recently, Liu et al (2011) investigated the mechanical behavior of "carbonated" hydroxylapatite (CHAP) and studied the effect of carbonate ion on the compressibility of HAP. The incorporation of the carbonate oxy-anion (for both types A-B) into the structure of HAP results in the formation of vacancies, oxygen-loss and disorder, with consequent changes in the physical-chemical properties.…”

“…The incorporation of the carbonate oxy-anion (for both types A-B) into the structure of HAP results in the formation of vacancies, oxygen-loss and disorder, with consequent changes in the physical-chemical properties. Liu et al (2011) results were obtained using a diamond-anvil cell and synchrotron X-ray powder diffraction up to 10 GPa on two synthetic CHAP samples with up to 11 wt% CO . The results of their BM3 EoS data-fitting, reported in Table 1, suggest that carbonate content significantly reduces the isothermal bulk modulus of CHAP (up to about 15%).…”