**4.1. Common synthetic techniques for the preparation of apatites**

The literature on the preparation of synthetic analogues of minerals from the supergroup of apatite8 (**Section 1.1**) is very extensive, but can be divided into three main categories [18],[21], [22],[23],[24]:

experiment [7]. ZAMBONINI and FERRUCIO [8] found that the fusion of Ca3(PO4)2 with CaCl2 produced apatite with very weak birefringence. Fusing Ca3(PO4)2 with an excess of NaCl gave crystals

By heating calcium phosphate with calcium chloride and water, under the pressure at 250°C, DEBRAY prepared chlorapatite [9]. WEINSHENK [10] also prepared chlorapatite by heating calcium chloride, ammonium phosphate and ammonium chloride at the temperature of 150 to 180°C in

sometimes exhibits the peculiarity of re-entrant pyramidal ends or phantom crystals. Spodio‐ site (Ca2(PO4)F) is orthorhombic, chlorspodiosite (Ca2(PO4)Cl [12],[13]) being much less developed along the *c*-axis than fluorspodiosite [14]. Chlorapatite was formed when dicalci‐ um phosphate was added in excess to molten calcium chloride. When precipitated calcium

The history of synthesis of various apatite compounds and substitution in the apatite struc‐ ture including the preparation of didymium bearing chlorapatite and chlorspodiosite is de‐ scribed in the work of ZAMBONINI and FERRUCIO [17]. The paper describes three of those

1:0.07:2.19 (1), 1:0.15:8.76 (2) and 1:0.67:2 (3). These mixtures were heated to the temperature of 1180, 1000 and 1100°C, respectively. Transparent, colorless apatite with the content of 3% DiPO4 results from the first experiment. The second experiment leads to the pale-violet crys‐ tal of chlorspodiosite3. The crystals of DiPO4 and only little amount of chlorapatite and

HENDRICKS et al [19] reported the preparation of hydroxylapatite by the hydrolysis of tricalci‐

 Chlorine analog of spodiosite [14]. Calcium chlorspodiosite is colorless crystalline compound structurally related to the mineral wagnerite (Mg2(PO4)F). It was reported by NACKEN in his study of the phase relationships which was obtained in the system CaCl2-CaO-P2O5 [12]. The synthesis of the compound by dissolving Ca3(PO4)2 in fused CaCl2 was reported by KLEMENT and GEMBRUCH [13]. Since the mineral was recognized as the mixture of fluorapatite, calcite and serpentine, it was

<sup>5</sup> Tricalcium phosphate was prepared by slow addition of Na3PO4 solution to the solution with the excess of Ca(NO3)2. The precipitate was washed with saturated solution of Ca3(PO4)2 until the filtrate was free of nitrates. The salt was then

Hydroxylapatite is very difficult to dehydrate, even at high temperature (**Section 1.5.2**). As a consequence of this, many

with neutral ammonium citrate. Oxoapatite was then prepared by the igni‐

was reported by HUTCHINS [15] and VOGHT [16] as present in lead-furnace slag [7].

CAMERON AND MCCAUGHEY [11] prepared fluorapatite by dissolving calcium

the cooled melt. Artificial fluorapatite

and CaCl2 in the weight ratio of

(Ca3(PO4)2·CaCl2, Ca2(PO4)Cl [14]) was obtained. Apatite

4

with the birefringence of 0.0050–0.0058.

phosphate was used, chlorspodiosite3

fluoride in fused disodium phosphate and lixiviating2

178 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

apatite syntheses using the mixture of Ca3(PO4)2, DiPO4

tion of hydroxylapatite to constant weight at 50°C.6

The method is described in **Section 4.1.1**.

discredited (IMA action 2003-03-B).

workers have mistaken it for oxyapatite [18].

dried at 50°C [19],[18].

chlorspodiosite with 9% of DiPO4 were recognized in the third mixture.

The separation techniques based on leaching of minerals from a solid by dissolving them in a liquid.

Didymium (Di) was recognized as the mixture of element of neodymium and praseodymium [18].

a sealed tube.1

um phosphate5

1

2

3

4

6

<sup>7</sup> Introduced as double salt of Na2Ca(CO3)2. Prepared mixtures were heated under the pressure of CO2 in the range from 55 to 100 and from 23 to 54 kg·cm−2 (kg·cm−2 = 98066.5 Pa) for binary and ternary system, respectively [20].

<sup>8</sup> In older literature termed as apatite-like substances.


Other methods (**Section 4.1.1**) such as microwave synthesis, combustion synthesis and high pressure method or deposition techniques are used much rarely.

The pressure-temperature ranges of these methods are shown in **Fig. 2**. Some of the most applied techniques are described in this chapter. The methods for the preparation of single crystals are described separately in the next **Section 4.2**.

**Fig. 2.** Pressure-temperature range for the material preparation [21].

<sup>9</sup> Various alternative names, such as Shake 'n Bake Methods or Beat 'n Heat, are used for the solid state synthesis (reaction) in literature [23].

<sup>10</sup>JAFFE [18] recognized the precipitation by metathesis and the precipitation by hydrolysis.

<sup>11</sup> Sometimes are included among high-pressure methods [24].
