FTIR and XRD evaluation of carbonated hydroxyapatite

powders synthesized by wet methods

Anna Slosarczyka, Zofia Paszkiewicza, Czesława Paluszkiewicza,b,*

aAGH—Faculty of Material Science and Ceramics, University of Science and Technology, 30-059 Krakow, Al. Mickiewicza 30, PolandbJagiellonian University, Regional Laboratory, 30-060 Krakow, ul. Ingardena 3, Poland

Received 10 November 2004; accepted 30 November 2004

Available online 11 January 2005

Abstract

Carbonated hydroxyapatite powders were obtained by wet method. The CO2K3 ions were introduced using NH4HCO3 and NaHCO3 in the

amount of 0.1 or 0.05 M. It was found by FTIR and X-ray studies that fraction of CO2K3 substitutions in the HAp structure and thermal

stability of CHAp depends on the amount and type of carbonate additives. The significant decomposition of carbonated hydroxyapatite

powders is observed when they are heated at the temperature of 800 8C.

q 2004 Elsevier B.V. All rights reserved.

Keywords: Carbonated hydroxyapatite; FTIR; XRD

1. Introduction

Biological apatites present in natural bone, dentin and

enamel contain different amounts of carbonate: 7.4, 5.6 and

3.5 wt%, respectively. Synthetic CO3 apatite (CHAp) has

been classified as type A or B depending on the mode of

carbonate substitution: CO2K3 for OHK (type A) or CO2K

3 for

PO3K4 (type B). Biological apatites are principally type B [1].

In synthetic powders prepared by wet methods some

fractions of PO2K4 as well as OHK groups are replaced by

CO2K3 groups (type AB). Among the variety of hydro-

xyapatite-based bioceramics carbonate hydroxyapatite

seems to be a promising material for bioresorbable bone

substitution. Sintering time, temperature and the atmosphere

are important parameters to control the level and type of

carbonate substitution. The presence of CO2K3 in

hydroxyapatite structure influences the decomposition,

sinterability, solubility and biological reactivity of CHAp

implantation materials. Development of synthesis methods

for CHAp initial powders with suitable characteristics, i.e.

chemical composition, morphology, resorption and/or

dissolution rate is of a great importance [2–4].

0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.molstruc.2004.11.078

* Corresponding author. Tel.: C48 12 617 2487; fax: C48 12 633 7161.

E-mail address: ucpalusz@cyf-kr.edu.pl (C. Paluszkiewicz).

FTIR spectroscopy and XRD methods are used in the

investigations of structural changes and thermal stability of

the calcium phosphate-based materials [5–9]. The aim of the

present work was to apply FTIR and XRD techniques in

the assessment of carbonated HAp powders preparation.

2. Materials and methods

In our studies carbonated hydroxyapatite powders were

produced by wet method. In syntheses CaO, Ca(NO3)2$4H2O

or Ca(CH3COO)2$H2O as calcium reagents and H3PO4 or

(NH4)2HPO4 as a source of phosphorous were used. The Ca/P

molar ratio was equal to 1.67. Ammonium hydrogen

carbonate (NH4HCO3) and sodium hydrogen carbonate

(NaHCO3) were applied in the amounts of 0.1 or 0.05 M as

reactants introducing CO2K3 groups. The syntheses carried out

were classified into four groups: I–IV (Table 1). In each group

the hydroxyapatite powder without any additives was

synthesized as a reference. During synthesis the pH of the

reaction medium was stabilized at O11 using ammonium

hydroxide solution. The suspensions were aged for 24 h at

room temperature and decanted. The resultant precipitates

after washing with deionized water were dried at 90 8C,

ground and calcined at 400, 800, 900 and 1250 8C.

Journal of Molecular Structure 744–747 (2005) 657–661

www.elsevier.com/locate/molstruc

Table 1

Reagents used in the individual synthesis the carbonated hydroxyapatite

powders

No. of

group

Symbol

of synthesis

Reagents

Ca2CPO3K

4 CO2K3

I H CaO H3PO4 –

H/C-1 CaO H3PO4 0.1 M

NH4HCO3

II HN CaO (NH4)2HPO4 –

HN/C-2 CaO (NH4)2HPO4 0.1 M

NH4HCO3

HN/C-3 CaO (NH4)2HPO4 0.1 M

NaHCO3

HN/C-4 CaO (NH4)2HPO4 0.05 M

NH4HCO3

III HA Ca(NO3)2$4H2O (NH4)2HPO4 –

HA/C-5 Ca(NO3)2$4H2O (NH4)2HPO4 0.1 M

NaHCO3

IV HO Ca(CH3COO)2 (NH4)2HPO4 –

HO/C-6 Ca(CH3COO)2 (NH4)2HPO4 0.1 M

NH4HCO3

A. Slosarczyk et al. / Journal of Molecular Structure 744–747 (2005) 657–661658

Phase composition of the powders was determined by the

X-ray diffraction method in the range of 2q from 0 to 708

using a Philips diffractometer. Fourier transform infrared

spectroscopy (FTIR) studies were carried out on the Digilab

FTS 60 v spectrometer in the range of 400–4000 cmK1. The

transmission technique was applied and the samples were

prepared as standard KBr pellets. For selected spectra the

ratios of integrated intensities as well as integrated areas of

the bands corresponding to CO2K3 groups in the range of

1380–1580 cmK1 and those due to PO3K4 at 900–1300 cmK1

were calculated.

3. Results and discussion

X-ray diffraction studies have shown that HAp is the only

crystalline phase when all the powders containing

Fig. 1. X-ray diffraction pattern of HN

NH4HCO3 and NaHCO3 as additives are calcined at

400 8C. Calcination at 800 8C leads to the appearance in

the systems of a small amount of free calcium oxide whose

content grows as the temperature increases to 1250 8C

(Figs. 1–3). Decomposition of HAp has not been observed

in the case of powders synthesized without any additives.

This proves that the presence of carbonate ions in the

structure lowers thermal stability of HAp resulting in its

decomposition and the appearance of CaO as the secondary

phase.

FTIR studies have shown that independently of the

starting reagents and the type of carbonate additive,

carbonated apatites have been obtained in all syntheses

carried out by the wet method. Fig. 4 presents second

derivatives of the spectra corresponding to different kinds of

carbonated apatites. They can be classified as apatites of

type B which give the bands originating from stretching

vibrations of CO2K3 ions at ca. 1415 and 1450 cmK1 or type

AB which show the additional band at 1515 cmK1. The

band at 1550 cmK1 is characteristic for both, type B and

type A apatites [4].

It has been found that the reference sample synthesized

without any carbonate additives has also contained a small

fraction of CO2K3 substitutions (Fig. 5). FTIR spectrum of

the reference sample shows characteristic bands due

to PO3K4 ions (n1—963 cmK1, n3—1036 and 1095 cmK1,

n4—568 and 600 cmK1), OHK groups (stretching vibration

at 3570 cmK1 and libration mode at 630 cmK1). Addition-

ally, the bands at about 1400 cmK1 (n3) and 870 cmK1(n2)

due to CO2K3 can be seen. The bands assignments are

according to literature data [4,5,9].

The amount of carbonate additive as well as the

calcination temperature have influenced the share of CO2K3

substitutions. Thus, the HN/C-2 powder synthesised with a

double amount of NH4HCO3 with respect to that introduced

to HN/C-4 while preserving other synthesis parameters

identical, after calcination at 400 8C contained a markedly

/C-2 powder calcined at 400 8C.

Fig. 2. X-ray diffraction pattern of HN/C-2 powder calcined at 800 8C.

A. Slosarczyk et al. / Journal of Molecular Structure 744–747 (2005) 657–661 659

higher amount of CO2K3 (Fig. 6). This has been confirmed

by comparison of the integrated area ratios of the bands due

to carbonate (1380–1580 cmK1) and phosphate

(900–1300 cmK1) groups in the spectra of HN/C-2 and

HN/C-4 samples. In the case of the former sample this ratio

has been equal to 0.231, whereas for the latter one its value

has been 0.185. Thus, the relative ratio for the spectra of

these two samples has been equal to 1.25.

In the case of the spectrum of HN/C-2 powder the ratio of

integrated areas of the band at 1380–1580 cmK1 corre-

sponding to CO2K3 groups and that at 900–1300 cmK1

originating from PO3K4 groups has decreased ca. 8.5 times

after calcination of the powder at 900 8C with respect to the

spectrum of this sample calcined at 400 8C. Similar

calculations carried out for the spectrum of the HN/C-4

powder (with lower fraction of CO2K3 substitutions) have

shown only a threefold lowering. These results may indicate

different kinetics of CO2K3 substitutions from CHAp

structure in both cases corresponding to two different

Fig. 3. X-ray diffraction pattern of HN/

amounts of ammonium hydrogen carbonate added during

synthesis.

Analysis of the spectra presented in Fig. 7 shows that the

amount and thermal stability of carbonate substitutions in

HAp structure is also influenced by the source of CO2K3

groups. Thus, the CO2K3 substitution is facilitated when

ammonium hydrogen carbonate is used as their source.

Comparison of the spectra of the HN/C-3 and HN/C-2

powders after calcination at 900 8C indicates that the

substitutions prepared using sodium hydrogen carbonate

are more thermally stable at 900 8C (the relative ratio of the

appropriate integrated band areas in the spectra of both

samples has been equal to 2.26).

In all the carbonated apatites prepared the lowering

of CO2K3 substitutions together with the successive increase

of ordering as treatment temperature grows have been

observed (Fig. 8). This process is particularly pronounced in

the temperature range of 800–900 8C (the bands due to

CO2K3 disappear and the bands at 630 cmK1 together with

C-2 powder calcined at 1250 8C.

Fig. 4. FTIR differential curves of HN/C-2 (B type apatite) and HN/C-3

(AB type apatite) after calcination at 400 8C.

Fig. 5. FTIR spectra of HAp powder (synthesized without any additives)

after calcinations at 400 8C.

Fig. 7. FTIR spectra of carbonated hydroxyapatite powders (HN/C-2,

HN/C-3) synthesized with 0.1 M of NH4HCO3 or NaHCO3 as additives

after calcination at 400 and 900 8C.

A. Slosarczyk et al. / Journal of Molecular Structure 744–747 (2005) 657–661660

that at 3570 cmK1 corresponding to OHK groups in the

HAp structure show up). Additionally, a weak band

at 3640 cmK1 in the spectrum of the powder calcined at

1250 8C can be assigned to the stretching vibrations of OH

Fig. 6. FTIR spectra of carbonated hydroxyapatite powders (HN/C-2,

HN/C-4) synthesized with different amounts of NH4HCO3 (0.1 or 0.05 M)

after calcination at 400 and 900 8C.

groups contained in Ca(OH)2. This compound is formed as

the result of HAp decomposition giving free CaO followed

by its reaction with water [7].

The results of our studies obtained by FTIR spectroscopy

and XRD studies have confirmed the influence of the

synthesis conditions on the effectiveness of CO2K3

substitution in HAp structure and on thermal stability of

obtained carbonated apatites.

4. Conclusions

All the conditions of the wet synthesis used in the present

work make it possible to obtain carbonated apatites. The

carbonated apatites prepared correspond to type B or AB. In

the latter case the substitution on the side of PO3K4 groups

prevails. The influence of carbonate substitution on phase

stability of CHAp is evident.

As the consequence of CO2K3 groups replacing the PO3K

4

ones accompanied by the increase in Ca/P O1.67 ratio, the

obtained non-stoichiometric carbonated apatites are

Fig. 8. FTIR spectra of carbonated apatites HO/C-6 after calcination at 400,

800, 900 and 1250 8C.

A. Slosarczyk et al. / Journal of Molecular Structure 744–747 (2005) 657–661 661

thermally less stable than that containing no substitutions.

They undergo a significant decomposition already in

the temperature range of 800–900 8C. This process results

in the formation of free CaO whose amount grows as the

treatment temperature is increased up to 1250 8C.

Fraction of CO2K3 substitutions in the HAp structure

depends on the amount and type of carbonate additive.

Thermal stability of carbonate substitutions is higher when

they are introduced using NaHCO3 than using NH4HCO3.

The increase of calcination temperature to 900 8C dramati-

cally lowers the content of CO2K3 groups in the synthetic

carbonated apatite structures. The influence of the synthesis

conditions on the effectiveness of CO2K3 substitution in HAp

structure and on thermal stability of carbonated apatites has

been established.

The usefulness of integrated FTIR and XRD studies in

evaluation of carbonated hydroxyapatite powders has been

confirmed.

References

[1] R.Z. Le Geros, Calcium Phosphates in Oral Biology and Medicine in:

H.M. Myers (Ed.), Karger, Basel, 1991.

[2] W.L. Suchanek, P. Shuk, K. Byrappa, R.E. Riman, K.S. Tentluis,

V.F. Janas, Biomaterials 23 (2002) 699–710.

[3] J.E. Barralet, S.M. Best, W. Bonfield, J. Mater. Sci. Mater. Med. 11

(2000) 719–724.

[4] J.C. Merry, J.R. Gibson, S.M. Best, W. Bonfield, J. Mater. Sci. Mater.

Med. 9 (1998) 779–783.

[5] A. Slosarczyk, C. Paluszkiewicz, M. Gawlicki, Z. Paszkiewicz,

Ceramics Int. 23 (1997) 297–304.

[6] S. Raynaud, E. Champion, D. Bernache-Assollant, Biomaterials 23

(2002) 1065–1072.

[7] L. Sun, C.C. Berndt, C.P. Grey, Mater. Sci. Eng. A360 (2003) 70–84.

[8] A. Rapacz-Kmita, A. Slosarczyk, Z. Paszkiewicz, Z. Paluszkiewwicz,

J. Mol. Struct. 704 (2004) 333–340.

[9] R.M. Wilson, J.C. Elliott, S.E.P. Dowker, L.M. Rodriquez-Lorenzo,

Biomaterials 26 (2005) 1317–1327.