Ca,o-xAg,(PO,),(OH),_,CI, apatites Ann. Chim. Sci. Mat, 1998, 23, pp. 61-64

SYNTHESIS AND PHYSICAL AND CHEMICAL CHARACTERIZATION OF Calp-xAgx(P04)6(0H)2.x0, APATITES

L. BADROUR’, A. SADEL’, M. ZAHIR’, L. KIMAKH’T~, A. EL HAJBI*

1 Laboratoire de Physico-Chimie des Matkriaux, Universid Chow&% Doukkali, Facult6 des Sciences, B.P. 20, El Jadida, Maroc

2 Laboratoire de Chimie Physique, Universitk Chouaib Doukkali, Facultt des Sciences, B.P. 20, El Jadida. Maroc .

ABSTRACT: The synthesis of calcium-silver hydroxyapatites of composition Car,,.~Ag@O&(OH)zW~& is discussed, together with their physical and chemical properties. Samples prepared both by dry process and by double decomposition were characterized using a variety of analytical techniques (chemical analysis, X-ray diffraction, infrared spectroscopy). The lattice parameters a and c increase linearly with the amount of silver added The increase is attributed to the preferential substitution of the silver ion in site Me (I) of these apatites.

RESUME : Svnthkse et caract&isation nhvsico-chirniaue des aoatites de tvntz

@iO-xAgx~h)6(0H)2-x0,.

Ce travail est consacre P la synthese et a l’etude physicochimique des hydroxyapatites calcium- argent de formule: Cal~~A~(P036(OH)z-~~. Les echantillons, preparks a la fois par voie Gche et par double decomposition sont caracterkes par diff&entes techniques (analyse chimique, diffkaction des rayons X, spectroscopic infrarouge). Les parametres cristallographiques a et c varient lin6airement en fonction du taux d’argent ajoute. Cette augmentation est like P la substitution preferentielle de l’ion argent dans le site Me(l) de la structure de ces apaatites

I INTRODUCTION

Hydroxyapatite ceramics are widely used in biomedical applications [1,2]. Synthesis of these ionocovalent solids is therefore very important. However, there is little information in the literature concerning physical and chemical study of apatites in which calcium is replaced by a noble metal. In this paper we discuss

the efkt which substkution of silver for calcium has on apatite crystslhzation, with 0 < x CO.22 in the case of dry synthesis and 0 <x CO.55 for wet synthesis.

2 EXPERIMENTAL PROCEDURE

Dry synthesis of these compounds has been described by L.Badrour [3]. For wet synthesis, we used the method known as double decomposition [4] in a basic enviromnent @H = 10-l 1).

Remin& L. BADROUR’, Universti Chouaib Doukkali, Faculte des Sciences, B.P. 20, El Jadida, MOMCCO

62 L. Badrour et al.

The apatite was precipitated from a solution of phosphate (NaJ-IPO-;) and a mixture of solution of calcium nitrate Caf,N0&,4HrO and of silver nitrate AgNO, in stoechiometric proportions. Chemical analysis was performed by the central analytical department of Vemaison, France. Phosphorus content was analysed using the Gee and Deitz calorimetry method [S]

3 RESULTS

3.1 Chemical analvsis

The results of the chemical analysis obtained for both forms of synthesis are shown in table 1 .They show that the phases obtained are in good agreement with the formulae adopted.

Table 1: Chemical analysis of Car~,Ag#O.&(OH)~,l& hydroxyapatites prepared by the two methods of synthesis

1 wet process

t

dti process

3.2 X-rav diffraction

X-ray diffraction diagrams of the samples prepared by the wet process are shown in figure 1. For x i 0,55, the products obtained consist of a single apatite phase. Figure 2 and table 2 show the values of the lattice parameters of the solid solution series (0 c x < 0.55) for the two methods of synthesis.

Table 2: Lattice parameters a and c and cell volume v of the samples prepared by the two methods of synthesis

At a silver ion content higher than 0.55, the appearance of the difkctograms changes. The first change is the broadening of the apatite diffraction rays, followed by the appearance of the silver orthophosphate phase Ag3P04 which increases in proportion as the ratio w(Ca+ Ag) increases

Ca,,,Agx(PO,)s(OH),U, apatites 63

Figure1 0.55

0.46

0.30

0.20

0

Figure 2

Finurel: Diffractograms of Ca,o.xAg~~04)6(0H)2,0,.conlpounds prepared by the wet process for different amounts of silver 0 < x < 0.55

Fimrre2: Variation of the parameters a, c and v with silver content of the compounds prepared by the two methods of synthesis ( n :wet, A :dry)

3.3 Infrared snectra

The spectra of the hydroxyapatites Ca,o.lAg,(POS,(OH),,u,.(x<0.55) differ little from one another. They ressemble the spectra of the hydroxyapatite Ca,0(P04)6(0H)2, The absence of other bands indicates the fixation of the silver in the sites I of the lattice, at least in part [3].

4 DISCUSSION Apatites have a crystal lattice of generally hexagonal symmetry (P63/m) [ 6-91. The plots of the lattice

parameters a and c as a function of changes in the silver content obtained for the solid solution series Ca,,,A~(POJ)6(O~)z.,0, show similar behavior for samples prepared by both methods, wet and dry [3]. Figure 2 shows an appreciable linear increase in lattice parameters a and c as the silver content of the hydroxyapatites rises. These plots therefore follow Vega& law [IO]. The simultaneous increase in the lattice parameters can be interpreted by refering to the difference in the ionic radius of the calcium and the silver ions, respectively 0.99 A and 1.28 A [ll]. Substitution of the Ca ” ions by the larger Ag’ ions leads to a greater increase in the parameter c than in the parameter n. It appears therefore that we have succeeded in preparing hydroxyl apatites containing ions Ag’ in the range of the atomic ratio Ag/ (Ag+Ca) between 0 and 0.055. At a value > 0.055, the crystalline structure is preserved, but the content of silver orthophosphate AgjP04 increases.

Attempts to increase the solubility of the silver ion by either the dry or the wet method did not make it possible to obtain wholly apatite compoundsThe same phenomenon has been observed in the system AhO& radioactive silver [12-141. Although the ionic radius of aluminum (0.57 A) is less than that of silver (1.28 A), we measured slight solubility of this element, Silver is a very different cation from those previously studied in apatites. It is a noble element, and is therefore hardly susceptible to oxidization. This has led us to consider the influence of the effect of size, of the chemical nature of silver and of the presence of the different sites or defects in the apatite lattice, These conditions are necessary to fix the silver in certain of the calcium sites. Ait may be noted that the same phenomenon has been observed in ihe compounds Ca,,,Na,Nd,(PO&F,.[ 151. A similar study of the apatites Pb 10-2xLnxAg?r(PO&F2 showed that the cell contracts as the silver content increases, since the mean ionic radius of the couplets Ag’, Lr?’ is lower that the size of the ion Pb2*, whatever the nature of Ln” [16]. However, in ionic solids, these effects are related not only to the size of the atoms, but also to their charge. This relationship can be linked to the observations described by Peterson [17,18] who explains this phenomenon qualitatively, by suggesting that the d elements contain certain polarisable electronic layers, and that this feature becomes proportionately more significant as the ionic radius increases, When the polarisability is high, the energy needed to cross the site is weaker. Peterson also points out that the polarisability of an ion may also be a function of its local environment and

64 L. Bach-our et a/.

that in the ionic compounds, the e&ct of size applies only to ions bearing the same charge. Consequently the effect of size associated with polarisability cannot account filly for the behavior of elements such as sodium containing 111 inner layers which are not polarisable (am=2 1.62 Asa ~,+=2.25 A3) [19]. We may therefore suggest that the substitution is related not only to the issues discussed above, but also to a further disruption, namely the chemical behavior of silver. In order to understand these phenomena, we have to consider the interactions between the solutes and the defects in the host lattice. In taking account of these different considerations:effects of size, polarisability, charge and the chemical behavior of silver and its local environment, and in supposing behavior similar to that described by I. Mayer [lO,l l] and that found in our own studies, it appears that the Ca(I) sites along the c axis are the sole positions in the lattice and that the high polarisability of silver enables greater distortion and thus better diffusion within these sites.

These results agree well with those obtained by infrared spectroscopy. We did not tind any displacement of the band v.(OH) as the silver content increased However , a displacement of this kind has been observed in materials containing the sodium ion and with the formula Ca,,,Na,,(PO,),,(CO,),oy(oH),f~~) [20]. These authors found that at 1 lOO”C, the absorption band of the hydroxyl ions (3570 cm“) disappears, and is replaced by another band at 3520 cm-‘. They claim that these disruptions of the band can only be attributed to the presence immediately adjacent to the hydroxyl ions in the lattice of Nai ims, which thus fix themselves in the Ca(II) sites.

5 CONCLUSION

In this paper, we have discussed the substitution of silver ions in Ca,,,Ag,(PO,),(O~.,r?, .We conclude that substitution of this ion takes place preferentially in the Ca(I) site, and that this leads to sign&ant changes in the parameters a and c. Similar studies of substitution of OH-, ions by F and Cl- in this hydroxyapatite will be needed to clarify the role of silver in these biomaterials. We are convinced that the application of the silver ion in the hydroxyapatites Ca,,&(PO&(Y)&X (Y= OH, F’, Cr) will prove to be extremely usell in the next few years because of the antibiotic properties of silver nitrate [2 1,221.

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111 PI r31 141 151 VI [71 PI

PI

DOI Ull u21 Cl31

u41 u51 [I61 u71 U81 u91 PO1 PI WI

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