Search

Apatites, being one of the most numerous mineral-like families of compounds, are considered as a matrix for binding lead ions, which is dangerous for the biosphere. The crystal-chemical (composition, structure) and thermophysical aspects (thermal expansion) are considered as the basis for analysing the properties of this kind of material. It is suggested that substances of the composition Pb5(AIVO4)2(BVIO4), Pb5(AIVO4)(CVO4)2 can be a perspective form of lead binding materials based on compounds with the structure of apatite (AIV = Si, Ge; BVI = S, Cr; CV = P). Such compounds, as it was shown by DTA and HTXRD experiments, are distinguished by the absence of polymerphism and the abnormal ordering of structure. Also, they have relatively low values of thermophysical indicators (the rate of change of linear thermal expansion coefficients is 0.02–0.03×106 K-1; values of the volume thermal expansion coefficients are 40–70×106 K-1). Compounds Pb5(SiO4)(PO4)2 (a = 9.78782(16) Å, c = 7.31084(16) Å, V = 606.555(23) Å3, R-bragg = 4.694 %) and Pb5(GeO4)(PO4)2 (a = 9.87697(12) Å, c = 7.33136(11) Å, V = 619.388(17) Å3, R-bragg = 1.730 %) were obtained, identified and crystallographically characterised for the first time.

Development of new non‐toxic pigments of a wide range of applications (from coloring of bone cements to aesthetic cosmetology, including tattooing) of blue and green shades is an urgent task. In the present work, colored compounds with apatite structure were synthesized by solid‐phase method. The obtained products were crystallized in hexagonal syngony of P63/m space group. The alloying elements – chromophores Mn5+ and Cr5+ in tetrahedrally coordinated positions – were responsible for sky‐blue and turquoise colors of the compounds, respectively. The conducted complex study (crystal structure, IR spectroscopy, color measurements, diffuse reflectance spectroscopy, electron paramagnetic resonance, cytotoxicity, surface morphology) of the colored compounds opens new opportunities for the development of alternative pigments of similar color range and expansion of the field of application of pigments based on compounds of apatite structural type. The results of in vitro study of cytotoxicity demonstrated the potential suitability of sky‐blue color compound (Mn‐containing apatite) for further creation of cold pigments on its basis for tattoo ink and bone cement coloring. [ABSTRACT FROM AUTHOR]

Hydroxyapatite was synthesized via sol-gel and solid-state reaction. Both compounds were investigated using high-temperature X-ray diffraction and differential scanning calorimetry. For sol-gel hydroxyapatite, we observed a phase transition, confirmed by character of changing of unit-cell parameters, thermal expansion coefficients and endothermic effect on DTA curve. In the process of obtaining ceramics using spark-plasma sintering both compounds manifested an unexpected shrinkage rate. All effects were explained on the basis of changings in crystal structure during distortion polymorphic transition.

This article presents the results of the optimization of solid-phase synthesis of oxysilicates of the composition SrREE4(SiO4)3O (REE: La–Lu, except Ce, Pm, Tm, Yb) having the structure of apatite. The new synthesis technique allows for reducing the temperature of the final stage and avoiding impurities of REEO(OH) and REE2O2CO3 in the final product. The crystal structure of SrEu4(SiO4)3O (a = 9.50029(37) Å, c = 7.02540(31) Å, V = 549.130(49) Å3, R-Bragg = 2.721%) was refined for the first time. This is a study of the thermal expansion of compounds in the temperature range of 173–373 K. The effect of the internal periodicity of changes in the linear and volumetric coefficients of thermal expansion in a number of studied compounds was revealed. [ABSTRACT FROM AUTHOR]

The paper describes methods for the preparation of compounds with an apatite structure containing only iodine atoms in the "halogen" position. The crystal structure of the compounds was refined by the Rietveld method. The resulting apatites have a structure with a space group P63/m and have the following unit cell parameters: Ba4f 1.78(2)Ba6h 2.75(2)(PO4)3I0.04(2) (a = 10.18609(34) Å, c = 7.71113(30) Å, V = 692.889(54) Å3, R = 5.448 %), Pb4f 1.82(2)Pb6h 2.75(2)(PO4)3I0.13(2) (a = 9.87882(18) Å, c = 7.43222(16) Å, V = 628.144(26) Å3, R = 8.533 %), Pb4f 1.90(2)Pb6h 2.68(2)(PO4)3I0.16(2) (a = 9.87058(48) Å, c = 7.41255(46) Å, V = 625.437(72) Å3, R = 5.433 %). The study of the crystal structure showed a relatively low efficiency of the binding of iodine in the apatite matrix. [ABSTRACT FROM AUTHOR]

Thorium silicate apatite with the formula [Ca3.84Th0.16]F[Ca2.79Th3.21]T(SiO4)6O2·x(H) was synthesized by solid-state reaction, and its structure refined in P63/m from powder X-ray diffraction (XRD) data using the Rietveld method (a = 9.50172(9) Å, c = 6.98302(8) Å, V = 545.98(1) ų; R-Bragg = 2.102%). It was found that thorium partitions strongly to the tunnel (T) 6h position rather than the framework (F) 4f site. Fourier transform infrared spectroscopy revealed only SiO4 tetrahedron, with SiO5 and SiO6 groups, sometimes observed in siliceous apatites absent, at least to the limit of detection of this technique. Thermal expansion of the thorium apatite determined by high-temperature XRD from 298-1173 K found Δa (0.87%) dilation to exceed Δc (0.73%) with increasing temperature consistent with other silicate apatites. [ABSTRACT FROM AUTHOR]

Development of new non‐toxic pigments of a wide range of applications (from coloring of bone cements to aesthetic cosmetology, including tattooing) of blue and green shades is an urgent task. In the present work, colored compounds with apatite structure were synthesized by solid‐phase method. The obtained products were crystallized in hexagonal syngony of P63/m space group. The alloying elements – chromophores Mn5+ and Cr5+ in tetrahedrally coordinated positions – were responsible for sky‐blue and turquoise colors of the compounds, respectively. The conducted complex study (crystal structure, IR spectroscopy, color measurements, diffuse reflectance spectroscopy, electron paramagnetic resonance, cytotoxicity, surface morphology) of the colored compounds opens new opportunities for the development of alternative pigments of similar color range and expansion of the field of application of pigments based on compounds of apatite structural type. The results of in vitro study of cytotoxicity demonstrated the potential suitability of sky‐blue color compound (Mn‐containing apatite) for further creation of cold pigments on its basis for tattoo ink and bone cement coloring. [ABSTRACT FROM AUTHOR]