Ceramic Biomaterials

Biomedical Materials Reference Data

Standard Reference Material, SRM 2910 Calcium Hydroxylapatite {Ca₁₀(PO₄)₆(OH)₂}

Material heterogeneity was assessed for each of the certified analytes or physical parameters by means of analysis of variance (ANOVA) [1]. Uncertainties were assessed by use of the CIPM approach [2]. The certified and reference values are expressed as mean value ± expanded uncertainty (U) [3].

https://srmors.nist.gov/view_detail.cfm?srm=2910

Special Notes on Properties: Heating Conditions Causing Partial Dehydroxylation of Hydroxylapatite

Drafted by Bruce Fowler and John Tesk

At temperatures above 900 °C in air, partial dehydroxylation of Hydroxylapatite (HA), Ca₁₀(PO₄)₆(OH)₂, to oxyhydroxylapatite (OHA), Ca₁₀(PO₄)₆(OH)_2-xO_0.5x, can occur. This is based on x-ray diffraction [28,29,30,31], gravimetric [32], and infrared data [31,33] that either indicates or is consistent with the premise that HA begins to lose hydroxide ions on heating in air in the 900 °C to 1000 °C range.

To easily identify dehydroxylation in HA, an infrared band at 434 cm-1 in the spectra of heated HA can be utilized. This 434 cm-1 band has been assigned to Ca₃⁺⁺O= stretching [34]; it results from thermal dehydroxylation of HA to form oxide and water ( OH^- + OH^- --> O⁼ + H₂O) and is specific for OHA. This band is recommended for use to identify OHA that has been formed in HA that has been heated.

Moreover, two of the above-cited articles display infrared spectra of HA heated in air. At 900 °C, the 434 cm-1 band was not observed but was observed for heating at 1050°C [31] and at 1000 °C [33].

Partial dehydroxylation of HA after heating at 1000 °C in air has also been reported in a publication on preparation of a HA reference material [35]. Partial dehydroxylation has also been observed in NIST SRM^® 2910 HA heated at 1000 °C in air at 50 % relative humidity based on the presence of the 434 cm-1 band [36]; reheating this partially dehydroxylated SRM^®2910 at 850°C in air at 50 % relative humidity resulted in rehydroxylation and concomitant loss of the 434 cm-1 band [36].

Consequently, when preparing HA for laboratory use, reduction of the preparation temperature from 1000 °C to 850 °C in air is strongly recommended to avoid partial dehydroxylation of the HA (850 °C is recommended rather than 900 °C to ensure the absence of dehydroxylation).

The heating treatments for preparation of HA are usually carried out in air at normal humidity, which is usually a relative humidity of about 30 % to 50 %. Because dehydroxylation of HA is water vapor pressure dependent, the dehydroxylation temperature will decrease at low humidity. About 20 % dehydroxylation occurred for HA heated in vacuum at pressure of 6.7 Pa (0.05 Torr) at 800 °C for 20 h and then cooling under the same pressure to 25 °C [34]; hence, there is the need to also ensure that there is relative humidity above about 30 %. Reference 34 has a Fig. 5 that shows the 434 cm-1 band as being absent in "pure" HA vs. the situation in which there is a presence of OHA. Reference 34 also gives additional data including shift and intensity changes of the 434 cm-1 band and of a relevant band of OHA with increasing dehydroxylation.

Put a space here

Fig 6 in reference 31 and Fig. 11 in reference 33 show conditions under which the 434 cm-1 band has been produced, demonstrating the presence of OHA.

Fig 7 from Reference 36 has data which further supports the comments given.

Fig. 7. Spectra of hydroxyapate specimens after three different heating conditions.
Specimen (A) is SRM^® 2910 after drying at 105 °C for 24 h and then heated at 850 °C for 142 h. Specimen (B) has been given the same treatment as Specimen (A) but with an additional heating at 1000 °C for 24 h, which shows a new band, 434 cm-1, indicating dehydroxylation. Specimen (C) has been given the same treatment as Specimen (B) but with an additional subsequent heating at 850 °C for 19 h; this shows disappearance of the 434 cm-1 band, indicative of rehydroxylation.
The relative humidity was about (30 to 50) % for all heating treatments.

REFERENCES

[1] Neter, J.; Wasserman, W.; Kutner, M.H.; Applied Linear Statistical Models, 3rd Ed., Irwin, Boston (1990).

[2] Guide to the Expression of Uncertainty in Measurement, ISBN 92-67-10188-9, 1st Ed., ISO, Geneva, Switzerland (1993); see also Taylor, B.N.; Kuyatt, C.E.; Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results; NIST Technical Note 1297, U.S. Government Printing Office: Washington, DC (1994).

[3] Markovic, M.; Fowler, B.O.; Tung, M.S.; Lagergren, E.S.; Composition and Solubility Product of a Synthetic Calcium Hydroxyapatite. Chemical and Thermal Determination of Ca/P Ratio and Statistical Analysis of Chemical and Solubility Data; in: Mineral Scale Formation and Inhibition, Proceedings of Am. Chem. Soc. Symposium, Ed. Amjad, Z.; Plenum Press, NY, pp. 271-282 (1995).

[4] Taylor, B.N.; Guide for the Use of the International System of Units (SI); NIST Special Publication 811; U.S. Government Printing Office: Washington, DC (1995).

[5] McDowell, H.; Gregory, T.M.; Brown, W.E.; Solubility of Ca5(PO4)3OH in the System Ca(OH)2 - H3PO4 - H2O at 5, 15, 25, and 37 °C; J. Res. NBS, Vol. 81A, pp. 273-281 (1977).

[6] Markovic, M.; Fowler, B.O.; Tung, M.S.; Preparation and Comprehensive Characterization of Calcium Hydroxyapatite Reference Material; J. Res. NIST (2003) in press.

[7] Markovic, M.; Fowler, B.O.; Tung, M.S.; Preparation and Characterization of Monoclinic Calcium Hydroxyapatite; (in preparation).

[8] Kay, M.I.; Young, R.A.; Posner, A.S.; Crystal Structure of Hydroxyapatite; Nature, Vol. 204, pp. 1050-1052 (1964).

[9] Elliott, J.C.; Mackie, P.E.; Young, R.A.; Monoclinic Hydroxyapatite; Science, Vol. 180, pp. 1055-1057 (1973).

[10] Markovic, M.; Fowler, B.O.; Brown, W.E.; Octacalcium Phosphate Carboxylates; 2 Characterization and Structural Considerations; Chem. Mater., Vol. 5, pp. 1406-1416 (1993).

[11] Gee, A.; Deitz, V.R.; Determination of Phosphate by Differential Spectrophotometry; Anal. Chem., Vol. 25, pp. 1320-1324 (1953).

[12] Brunauer, S.; Emmett, P.H.; Teller, E.; Adsorption of Gases in Multimolecular Layers; J. Am. Chem. Soc., Vol. 60, pp. 309-319 (1938).

[13] Gregory, T.M.; Moreno, E.C.; Brown, W.E.; Solubility of CaHPO4·2H2O in the System Ca(OH)2 - H3P04 - H2O at 5, 15, 25, and 37.5 °C; J. Res. NBS, Vol. 74A, pp. 461-475 (1970).

[14] Gee, A.; Deitz, V.R.; Pyrophosphate Formation upon Ignition of Precipitated Basic Calcium Phosphates; J. Am. Chem. Soc., Vol. 77, pp. 2961-2965 (1955).

[15] Klug, H.P.; Alexander, L.E.; X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials; 2nd Ed., Chapter 9: Crystallite Size and Lattice Strains from Line Broadening; John Wiley and Sons, NY, pp. 618-708 (1974).

[16] Fowler, B. O.; Infrared Studies of Apatites. II. Preparation of Normal and Isotopically Substituted Calcium, Strontium, and Barium Hydroxyapatites and Spectra-Structure-Composition Correlations; Inorg. Chem., Vol. 13, pp. 207-214 (1974).

[17] Chung, F.H.; Quantitative Interpretation of X-ray Diffraction Patterns. I Matrix-Flushing Method for Quatitative Multi-component Analysis; J. Applied Cryst., Vol. 7, pp. 519-525 (1974).

[18] Chung, F.H.; Quantitative Interpretation of X-ray Diffraction Patterns. II Adiabatic Principle of X-ray Diffraction Analysis of Mixtures; J. Applied Cryst., Vol. 7, pp. 526-531 (1974).

[19] Eanes, E.D.; Gillessen, I. H.; Posner, A.S.; Intermediate States in the Precipitation of Hydroxyapatite; Nature, Vol. 208, pp. 364-367 (1965).

[20] Eanes, E.D.; Meyer, J.L.; The Maturation of Crystalline Calcium Phosphates in Aqueous Suspensions at Physiologic pH; Calcif. Tiss. Res., Vol. 23, pp. 259-269 (1977).

[21] Cline, J.P.; Schiller, S.B.; Liu, H-K.; Trahey, N.M.; Certificate, SRM 676 Alumina Internal Standard for Quantitative Analysis by X-ray Powder Diffraction; NIST, Gaithersburg, MD 20899 (1992).

[22] Cline, J.P.; NIST XRD Standard Reference Materials: Their Characterization and Uses; Proceedings of the International Conference: Accuracy in Powder Diffraction II; NIST Special Publication 846; U.S. Government Printing Office: Washington, DC (1992).

[23] Larson, A.C.; Von Dreele, R.B.; General Structure Analysis System (GSAS); Los Alamos National Laboratory Report LAUR, pp. 86-748 (1994).

[24] Thompson, P.; Cox, D.E.; Hastings, J.B.; Rietveld Refinement of Debye-Scherrer Synchrotron X-ray Data from A12O3, J. Applied Cryst., Vol. 20, pp. 79-83 (1987). SRM 2910 Page 8 of 9 SRM 2910 9

[25] Caglioti, G.; Paoletti, A.; Ricci, F.P.; Choice of Collimators for a Crystal Spectrometer for Neutron Diffraction; Nuclear Instrumentation, Vol. 3, pp. 223-228 (1958).

[26] Hubbard, C.R.; Zhang, Y.; McKenzie, R.L.; Certificate of Analysis, SRM 660 Instrument Line Position and Profile Shape Standard for X-ray Powder Diffraction; NIST, Gaithersburg, MD 20899 (1989).

[27] Von Dreele, R.B.; Cline, J.P.; The Impact of Background Function on High Accuracy Quantitative Rietveld Analysis (QRA): Application to NIST SRMs 676 and 656; Adv. X-ray Anal., Vol. 38, pp. 59-68 (1994).

[28] Trombe, J.C. and Montel, G. J. inorg. nucl.Chem. 40,15-21 (1978).

[29] Verbeeck, R.M.H., Heiligers, H.J.M., Driessens, F.C.M. and Schaeken, H.G. Z. anorg. allg. Chem.,466, 76-80 (1980).

[30] Wang, Pauchiu E. and Chaki, T.K. J. Mater. Sci.:Mater. Med. 4, 150-158 (1993).

[31] Kijima, Tsuyoshi and Masayuki, Tsutsumi J. Am. Ceram. Soc. 62(9-10) 455-460 (1979).

[32] Cihlar, J., Buchal, A. and Trunec, M. J. Mater. Sci. 34, 6121-6131 (1999).

[33] Hartmann, P., Jager, C., Barth, St., Vogel, J. and Meyer, K. J. Solid State Chem. 160, 460-468 (2001).

[34] Kuroda, S. and Fowler, B.O. Calcif. Tissue Int. 36, 361-369 (1984).

[35] Markovic, M., Fowler, B.O., Tung, M.S. and Lagergren, E.S. In: Mineral Scale Formation and Inhibition, Plenum Press, New York, 1995, pp 271-282.

[36] Fowler, B.O., unpublished raw data (figure) results.

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Date created: 04 December 2003
Last updated: 23 July 2004

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