Ljiljana Karanović

Synthetical bone-like and biological hydroxyapatites: a comparative study of crystal structure and morphology

Phase composition, crystal structure and morphology of biological hydroxyapatite (BHAp) extracted from human mandible bone, and carbonated hydroxyapatite (CHAp), synthesized by the chemical precipitation method, were studied by x-ray powder diffraction (XRD), Fourier transform infrared (FTIR) and Raman (R) spectroscopy techniques, combined with transmission electron microscopy (TEM). Structural and microstructural parameters were determined through Rietveld refinement of recorded XRD data, performed using the FullProf computing program, and TEM. Microstructural analysis shows anisotropic extension along the [00l] crystallographic direction (i.e. elongated crystallites shape) of both investigated samples. The average crystallite sizes of 10 and 8 nm were estimated for BHAp and CHAp, respectively. The FTIR and R spectroscopy studies show that carbonate ions substitute both phosphate and hydroxyl ions in the crystal structure of BHAp as well as in CHAp, indicating that both of them are mixed AB-type of CHAp. The thermal behaviour and carbonate content were analysed using thermogravimetric and differential thermal analysis. The carbonate content of about 1 wt.% and phase transition, at near 790 °C, from HAp to β-tricalcium phosphate were determined in both samples. The quality of synthesized CHAp powder, particularly, the particle size distribution and uniformity of morphology, was analysed by a particle size analyser based on laser diffraction and field emission scanning electron microscopy, respectively. These data were used to discuss similarity between natural and synthetic CHAp. Good correlation between the unit cell parameters, average crystallite size, morphology, carbonate content and crystallographic positions of carbonate ions in natural and synthetic HAp samples was found.

Crystal structure of cobalt-substituted calcium hydroxyapatite nanopowders prepared by hydrothermal processing

A series of cobalt-exchanged hydroxyapatite (CoHAp) powders with different Ca/Co ratios and nominal unit-cell contents Ca10−xCox(PO4)6(OH)2, x = 0, 0.5, 1.0, 1.5 and 2.0, were synthesized by hydrothermal treatment of a precipitate at 473 K for 8 h. Based on ICP (inductively coupled plasma) emission spectroscopy analysis, it was established that the maximum amount of cobalt incorporation saturated at ∼12 at.% under these conditions. The effects of cobalt content on the CoHAp powders were investigated using ICP emission spectroscopy, particle size analysis, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) analyses as well as X-ray powder diffraction (XRPD) including Rietveld analysis. According to XRPD, all the materials are single-phase HAp and CoHAp of low crystallinity. Rietveld analysis shows that Co enrichment causes the c cell parameter to decrease at a faster rate than the a cell parameter. A microstructural analysis showed anisotropic X-ray line broadening due to crystallite size reduction. In CoHAp there is significant crystal elongation in [001], and the average size decreases with increasing cobalt content. The crystallite morphology transforms from rod-like for the pure HAp to lamellae at the highest degree of Co substitution. The results of Rietveld refinement (symmetry, size and morphology of the crystallites) were confirmed by TEM and HRTEM analysis.

Mixed ligand Co(II), Ni(II) and Cu(II) complexes containing terephthalato ligands. Crystal structures of diaqua(2,2′-dipyridylamine)(terephthalato)metal(II) trihydrates (metal=cobalt or nickel)

Abstract A series of nine ternary Co(II), Ni(II) and Cu(II) complexes with some aromatic diamines and dianion of terephthalic acid (tpht) have been synthesized and characterized by elemental analysis, magnetic susceptibility measurements, IR and diffuse-reflectance spectroscopy. All compounds were obtained as microcrystalline solids, stable in air and insoluble in common solvents. Two of them, [M(tpht)(dipya)(H 2 O) 2 ]·3H 2 O [M=Co(II), Ni(II); dipya=2,2′-dipyridylamine], were obtained as single crystals and their crystal structures have been determined by X-ray structure analysis. Both structures consist of discrete [M(tpht)(dipya)(H 2 O) 2 ] 2+ complex units with two H 2 O molecules in the trans position. Three additional H 2 O molecules together with coordinated H 2 O and O atoms from COO groups make a three-dimensional network of hydrogen bonds. Terephthalato ligands are coordinated by only one COO group, which acts as a chelating ligand. Central metal ions are in a distorted octahedral environment. Based on the above-mentioned analysis and known crystal structures, the possible structures and geometry of the complexes are discussed. All Co(II) and Ni(II) complexes are pseudooctahedral and mononuclear, with only one of the tpht COO groups coordinated in a chelate mode. Cu(II) complexes have probably distorted octahedral geometry with bridging role of tpht ions and monodentate or strongly asymmetric coordination of COO groups.

Synthesis and deposition of ZnO based particles by aerosol spray pyrolysis

Abstract Spray pyrolysis was used for the deposition of well defined submicronic to nanosize particles based on ZnO. The influence of the temperature in the range from 345 to 1165 K, solution concentration (0.004 and 1.5 mol dm−3) and the residence time on the particle morphology is discussed. X-ray diffraction, differential scanning calorimetry and scanning electron microscopy were used in particle characterization. With the presumption that certain particle morphology is formed during the evaporation/drying stage of spray pyrolysis, the corresponding mathematical model for droplets evaporation is developed and correlated with the empirical results.

Disodium hexaaquacobalt(II) bis[dihydrogen 1,2,4,5-benzenetetracarboxylate(2 –)] tetrahydrate

The title structure, Na 2 [Co(H 2 O) 6 ](C 10 H 4 O 8 ) 2 .4H 2 O, consists of [Co(H 2 O) 6 ] 2+ and Na + cations, dihydrogen 1,2,4,5-benzenetetracarboxylate(2-) (H 2 btc) anions and water of crystallization. The [Co(H 2 O) 6 ] 2+ and H 2 btc ions, as well as the water molecules, are linked together by a three-dimensional network of hydrogen bonds. A short symmetrical intramolecular hydrogen bond between the COO and COOH groups is found to exist in the H 2 btc ions.

Solid state synthesis of extra phase-pure Li4Ti5O12 spinel

Extra phase-pure Li4Ti5O12 spinel with particle sizes less than 500 nm was synthesized by solid state reaction of mechanochemicaly activated mixture of nano anatase and Li2CO3 for a very short annealing time, 4 h at 800 °C. Structural and microstructural properties, the mechanism of solid state reaction between anatase and Li2CO3 as well as thermal stability of prepared spinel were investigated using XRPD, SEM and TG/DSC analysis. The mechanism of reaction implies decomposition of Li2CO3 below 250 oC, formation of monoclinic Li2TiO3 as intermediate product between 400 and 600 °C and its transformation to Li4Ti5O12 between 600–800 oC. The spinel structure is stable up to 1000 oC when it is decomposed due to Li2O evaporation.

Sr, Ba and Cd arsenates with the apatite-type structure.

X-ray diffraction analysis of single crystals of three new arsenates adopting apatite-type structures yielded formula Sr(5)(AsO(4))(3)F for strontium arsenate fluoride, (I), (Sr(1.66)Ba(0.34))(Ba(2.61)Sr(0.39))(AsO(4))(3)Cl for strontium barium arsenate chloride, (II), and Cd(5)(AsO(4))(3)Cl(0.58)(OH)(0.42) for cadmium arsenate hydroxide chloride, (III). All three structures are built up of isolated slightly distorted AsO(4) tetrahedra that are bridged by Sr(2+) in (I), by Sr(2+)/Ba(2+) in (II) and by Cd(2+) in (III). Compounds (I) and (II) represent typical fluorapatites and chlorapatites, respectively, with F(-) at the 2a (0, 0, {1/4}) site and Cl(-) at the 2b (0, 0, 0) site of P6(3)/m. In contrast, in (III), due to the requirement that the smaller Cd(2+) cation is positioned closer to the channel Cl(-) anion (partially substituted by OH(-)), the anion occupies the unusual 2a (0, 0, {1/4}) site. Therefore, Cl(-) is similar to F(-) in (I), coordinated by three A2 cations, unlike the octahedrally coordinated Cl(-) in (II) and other ordinary chlorapatites. Furthermore, in (III), using FT-IR studies, we have inferred the existence of H(+) outside the channel in oxyhydroxyapatites and provided possible atomic coordinates for a H atom in HAsO(4)(2-), leading to a proposed formulation of the compound as Cd(5)(AsO(4))(3-x)(HAsO(4))(x)Cl(0.58)(OH)(0.42-x-(y/2))O(x+(y/2))(y/2).

Synthesis of ZnO-based varistor precursor powders by means of the reaction spray process

High-purity, fine-grained oxide ceramic powders that are commonly used for ZnO-based varistors were synthesized by means of the reaction spray process. Processing steps included formation of the solutions of zinc nitrate and/or certain metal additives and spraying of the solution into a heated reaction column using a two-phase nozzle. After water evaporation from the droplets, the precursor salts were decomposed at elevated temperatures (up to 1473 K) in order to obtain homogeneous oxide powders with complex compositions corresponding to the final multicomponent varistor system. The decomposition behaviour of the precursors, as well as the characteristics of the resulting powders: crystallinity, phase composition, particle shape, morphology and particle-size distribution, were examined. It was shown that the characteristics of the reaction spray-derived powders can be controlled by adjusting the system and the solutions parameters.

Structure refinement of natural robinsonite, Pb 4 Sb 6 S 13 : cation distribution and modular description

Crystal structure of robinsonite from the locality Male Zelezne, Nizke Tatry Mountains, Slovakia, has been refined using single-crystal data (MoKa X-ray diffraction, CCD area detector) to the conventional R-factor: R 1 = 0.045. Robinsonite crystallizes in the space group 12/m, with a = 23.642(4), b = 3.9761(6), c = 24.420(4) A, β = 93.808(3)° and Z = 4. X-ray diffraction and chemical analysis resulted in comparable formulae, Pb 4 . 0 3 Sb 5 . 9 7 S 1 3 and Pb 3 . 9 3 Sb 5 . 7 7 S 1 3 , respectively, which are close to the ideal formula Pb 4 Sb 6 S 1 3 . Robinsonite is a member of a large family of rod-based sulphosalts, composed of rods of SnS (or TII) archetype. In robinsonite, two types of rods, respectively 2 and 3 Sb coordination pyramids broad, combine. Their arrangement results in two types of rod-layers, denoted according to their inter-rod connections as Type 1 and Type 4, respectively. In the former case, a tightly bonded double-layer continues from one rod into the other. In the latter, the rods are interconnected by the smallest possible fragment of SnS-like configuration that is rotated 90° in respect to the SnS-like (TIl-like) arrangement in the rod interiors. The mixed cation sites are the main characteristic of the robinsonite structure. The present study is the second one performed on natural robinsonite and the first in which all mixed positions are successfully refined. The mixed sites are concentrated in slabs parallel to [010]. The composition of these slabs can be explained by the necessity to match dimensions of the structure motifs across a noncommensurate interspace. Comparison with monoclinic boulangerite shows many similarities in distribution of mixed cation sites.

Crystal structure of nobleite, Ca[B6O9(OH)2].3H2O, from Jarandol (Serbia)

Crystal structure of nobleite from locality Jarandol (Serbia) has been refined using single-crystal data (Mo K α radiation, CCD area detector) to the conventional R 1 factor 0.0324 for 2432 reflections having I > 2σ( I ) and 0.0540 for all 3383 data. Hydrogen atoms were found in difference Fourier maps and were refined isotropically with no constraints. Nobleite is monoclinic, space group P 2 1 / a, a = 14.580(1), b =8.0240(7), c =9.8486(8) A, β = 111.801(2) °, V =1069.7(2) A 3 and Z =4. The chemical composition calculated from the chemical analysis corresponds to the formula Ca 0.97 Mg 0.01 Sr 0.01 [B 5.89 O 9 (OH) 2 ]·3H 2 O based on 14 O atoms. Nobleite belongs to M 2+ O·3B 2 O 3 · x H 2 O, i.e. to 1·3· x group of borates, with x = 4 and M = Ca, i.e. its nominal composition is CaO·3B 2 O 3 ·4H 2 O or Ca[B 6 O 9 (OH) 2 ]·3H 2 O. The fundamental building block ( FBB ) of nobleite structure contains three BO 4 -tetrahedra and three BO 3− coordination triangles. The three tetrahedra share one corner denoted by [Φ] in the designation for the FBB. The FBB in nobleite is [Φ] | |, which means that it is composed of three rings. Each six-membered B-O ring is formed by sharing corners among two tetrahedra, 2□, and one triangle, Δ. The FBB s are further polymerized into sheets, parallel to the 100 plane, with Ca cations in the holes of the sheets and water molecules between them. The Ca atom is coordinated by six oxygens from FBB s and three water molecules. The Ca-polyhedron with coordination number 9 can be described as a distorted hexagonal bipyramid with one vertex split. All hydroxyl groups and water molecules form hydrogen bonds located mainly between sheets. Present results show that nobleite is not structurally identical to tunellite.