Fluor-apatite

In conclusion, the solubility data indicate that upon precipitation from aqueous solutions which have a F/OH molar ratio less than a certain value, slightly fluoridated hydroxyapatites will be formed (x .0.15), and above that ratio nearly pure fluor-apatite will be formed. Usually the F/OH ratio varies so that intimate mixtures of hydroxyapatite and fluorapatite will result (64). The effect of fluoride on teeth and bones are discussed elsewhere (52, 57). 

Analyses revealed a fluor-apatite composition with an average formula. 

C. B. Baddiel, E.E. Berry, Spectra-structure correlations in hydroxyapatite and fluor-apatite, Spectrochim. Acta 22 (1966) 1407-1416. 

The natural fluor-apatites in our study consisted of 75 samples from a variety of geologic environments. Concentrations of potential luminescence impurities in several samples are presented in Table 4.4. 

For the correct interpretation of the luminescent bands, artificial apatite standards have been investigated, as nominally pure, as activated by different potential luminogen impurities. Natural carbonate-fluor-apatites not containing REE were heated with 1 - 5 wt. % of oxides of Eu, Pr, Sm and Dy at 900 °C in air and in vacuum. By changing the activation conditions the differentiation between isomorphous substitutions in different Ca-sites has been achieved. Under vacuum the compensation of the excessive positive charge by substitution of E by 0 is impossible and the luminescence centers in Ca(ll) sites may be less preferential. After heating at this temperature carbonate-fluor-apatite loses its carbonate content and becomes very similar to natural fluor-apatite. 

Sedimentary carbonate-fluor-apatite Cas(P04,003)3 is not luminescent under X-rays, and under UV lamp excitation it is characterized by broad structureless bands which are very similar to those encountered in many sedimentary minerals. It was concluded that this luminescence is due to different kinds of water-organic complexes (Tarashchan 1978). For this reason the luminescence properties of the sedimentary apatites is much less informative compared to magmatic apatite and attracted not much attention. 

Carbonate-fluor-apatite accommodates large quantities of trace elements, mainly uranium, which are potential luminescence centers. It has been proposed that uranium may occur in phosphorites in the following forms as a separate uraninite phase as an adsorbed or structurally incorporated uranyl ion as a dominantly replacement for Ca +, to be structurally incorporated... 

In humid environments, hydroxyapatite (Ca5(P04)30H), the main component of the inorganic bone and tooth matrix, is transformed into the more stable fluor-apatite (Ca5(P04)3F). In an idealized sample, fluorine uptake from the environment leads to a U-shaped concentration profile, which slowly develops into the bulk from the outer surface and from the marrow cavity inwards according to Fick s second law... 

Fluorine occurs in nature in minerals such as fluorite, Cap2 fluor-apatite, Ca.(PO )3F, which is a constituent of bones and teeth and cryolite, Na3AlF<. and in small quantities in sea water. Its name fluorine, from Latin finere, to flow, refers to the use of fluorite as a flux (a material which forms a melt with metal oxides). 

Fluorine fluorite fluor-apatite cryolite hydrogen fluoride hydrofluoric acid silicon tetrafluoride sodium fluoride oxygen fluoride. 

Figure 21 Ion activity product of carbonate fluor-apatite as a function of carbonate content as determined from oversaturation (pH stat experiments) and undersaturation (dissolution experiments) by Jahnke (1984). Despite divergence of the two data sets, the trend of increasing solubiUty with increasing carbonate content is apparent.

Fluor kann in Form von Fluorid-Ionen (F ) in Knochen und Zahne eingebaut werden (Fluor-apatit), spielt aber ansonsten im Organismus keine essentielle Rolle. 

The atomic structure of fluor-apatite and its relation to that of tooth and bone materials. Miner. Mag., 27, 254- 257. 

McClellan, G.H., 1980. Mineralogy of carbonate fluor-apatites. J. Geol. Soc. London, 137, 675-681. 

Khudolozhkin VO, Urasov VS, Kurash W (1974) Mossbauer study of the ordering of Fe in the fluor-apatite structure. Geochemlntl 11 748-750... 

Apatite composition. The compositions of metamorphic apatite typically fall along the F-OH join, although apatite with small amounts of Cl has been reported from metamorphic rocks (e.g., Kapustin 1987). Most, if not all, metamorphic apatite is dominated by the F end-member (i.e., fluor-apatite). A survey of analyses is shown in Figures 1 and 2. The F/(F+OH) typically ranges from 0.4 to 1.0 with a median value of 0.85 (Fig. la). Thus, it appears that the widespread presence of apatite in metamorphic rocks may be as much a function of the availability of F as it is the availability of P. (It should be noted that many published apatite analyses have reported F values in excess of the maximum permitted by stoichiometry, presumably due to analytical difficulties measuring F in apatite on the BMP as discussed by Stormer et al. 1993). 

Polycrystalline hydroxy/fluor apatite solid solutions are proton conductors at 250-500°C, due to enhanced proton movement between the OH groups in the channel structure (Chapter 13.1). 

Tooth enamel consists of hydroxyapatite, Ca5(P04)30H (Ksp = 6.8X 10 ). Fluoride ion added to drinking water reacts with Cas(P04)30H to form the more tooth decay-resistant fluor-apatite, Cas(P04)3F K p = 1.0X10 ). Fluoridated water has dramatically decreased cavities among children. Calculate the solubility of Cas(P04)30H and of Cas(P04)3F in water. 

P site, Mn in Ca(l), Ca(ll) sites and adsorption on carlxMiate-fluor-apatite surface reabsorption lines of molecular oxygen and water have been found and ascribed (Gaft et al. 1996 Gaft et al. 1997a, b, c) (Figs. 4.2, 4.3, 4.4, 4.5, 4.6 and 4.7). 

Gaft M, Reisfeld R, Panczer G et al (1996) Luminescence of Eu ", Pr " and Sm " in carbonate-fluor-apatite. Acta Phys Polonica A 90 267-274... 

Thus different luminescence takes place after activation in air and in vacuum. As it was already mentioned, in the apatite structure Ca5(P04)3F there are two types of Ca site Ca(l) with C3 symmetry and Ca(II) with Cs symmetry. The Dq- Fq transition has been reported to exist in cases where the site symmetry allows an electric dipole process Cs, C , Cnv This is consistent with the conclusion that the centers with the main line at 574 nm belongs to Ca(II) site with Cs symmetry, while the asymmetry of the crystal field is lower for the center with the main line at 618 nm. The ratio between Dq- Fo and Dq- F2 which are forced electric dipoles to Dq- Fi which is magnetic dipole tells us about the synunetry of the site in which Eu + is situated (Blasse and Grabmaier 1994 Reisfeld 1973). In fluor-apatite activated in air the ratio is higher meaning a lower synunetry Ca(II) site, while in namral fluorapatite or synthetic one activated in vacuum the ratio is lower... 

A relatively rare strong line appears in the luminescence spectrum of apatite near 544 nm (Fig. 4.3c). Spectrally it is similar to the line of Tb " ", but is characterized by much shorter decay time and its intensity is not correlated with other lines of Tb. By analogy with other hosts it is known that Er " " and Ho may generate luminescence in this spectral region. Artificial fluor-apatite activated by Er exhibits... 

Carbonate-fluor-apatite accommodates large quantities of trace elements, mainly uranium, which are potential luminescence centers. It has been proposed that uranium may occur in phosphorites in the following forms as a separate uraninite phase as an adsorbed or structurally incorporated uranyl ion as dominantly a U" replacement for Ca " " to be structurally incorporated appreciably as both and U (Altschuler 1980). The steady-state luminescence of water-organic comlexes is strong and conceales the weaker characteristic luminescence of uranium containing centers, which can be detected by the difference in decay times only. The reason is that the decay time of water-organic complexes is characterized by two time intervales less than 30 ns and more than 10 ms. Since... 

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