Smilja Marković

FTIR spectroscopy of framework aluminosilicate structures: carnegieite and pure sodium nepheline

Abstract In this work the spectroscopic studies of polymorph transformation of framework silicates containing six-membered rings and different Si/Al ratio were carried out. Two model systems with different stoichiometries (Na-LTA, Si/Al=1 and Na-FAU, Si/Al=1.23) were investigated. Thermally induced phase transformations of initial zeolites resulted in forming of stuffed derivatives of cristobalite (carnegieite) and tridymite (nepheline). Powder XRD method was used for the recognition of new phases. All obtained phases have framework structures built by single six-membered rings. The changes of middle range order (rings symmetry), which take place during transformations of Na-LTA and Na-FAU into low-temperature carnegieite, low-temperature carnegieite into pure sodium (ps) nepheline as well as ps-nepheline into high-temperature carnegieite, were investigated by IR spectroscopy. The rings symmetry is found to be dependent on a phase stoichiometry as well as on polymorph type.

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.

Hydrothermal Synthesis of Nanosized Pure and Cobalt-Exchanged Hydroxyapatite

Pure and cobalt-exchanged hydroxyapatite (HAp and CoHAp) powders were synthesized by hydrothermal method. X-ray diffraction (XRD), Raman spectroscopy, particle size analysis, inductively coupled plasma (ICP) emission spectroscopy, and scanning electron microscopy (SEM) were used to study the microstructural and unit cell parameters, average particle size, particle size distribution, chemical composition, and morphology of the synthesized powders. XRD and Raman spectroscopy confirmed that the samples were free from impurities and other phases of calcium phosphates. It has been found that the increase in the cobalt amount in the crystal structure of HAp reduces unit cell parameters, as well as average crystallite size (from XRD measurements). All of the powders were nano-sized with narrow particle distribution (from particle size analyses). SEM investigations indicated that nano-sized particles were organized in soft micro-sized agglomerates, whose sizes increased with the increase in the content of Co in HAp crystal structure.

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.

Influence of mechanical activation on microstructure and crystal structure of sintered MgO-TiO2 system

Mixtures of MgO-TiO2 were mechanically activated using high-energy planetary ball mill during 5, 10, 20, 40, 80 and 120 minutes. Sintering process was preformed in air at 1100 o -1400 o C for 2h. The decrease in powder’s particle size was noticed as the time of mechanical activation increased and confirmed by particle size analyzer. XRD analyses were performed in order to acquire the information about phase composition. Different ratio mixtures of MgTiO3 and Mg2TiO4 are present within all sintered samples. The effect of tribophysical activation on microstructure was investigated by scanning electron microscopy. The differential thermal gravimetric analysis has been performed in order to investigate thermal behaviour of the mixtures.

Structural and Dielectric Properties of BaTi1-xSnxO3 Ceramics

BaTi1-xSnxO3 (BTS) powders, with x ranging from 0 to 1, were synthesized by solid-state reaction technique. The powders were pressed into pellets and sintered at 1370 and 1420 oC. The structural characterization of sintered BTS samples was made at room temperature using X-ray diffraction and Raman spectroscopy measurements. The BTS samples were found to be singlephase solid solutions. Dielectric properties of sintered BTS samples were studied as a function of sintering temperatures and tin contents, too. For samples with x ranging from 0 up to 0.15, it has been found that the Curie temperature decreases while the maximum of the dielectric constant increases with increasing tin content. These samples have relatively high dielectric constants, contrary to x > 0.2 samples with very low dielectric constants. It is noticed that BTS ceramics sintered at 1420 oC exhibit better dielectric properties than those sintered at 1370 oC.

The effect of Sn for Ti substitution on the average and local crystal structure of BaTi1−xSnxO3 (0 ≤ x ≤ 0.20)

The effect of Sn for Ti substitution on the crystal structure of a perovskite, barium titanate stannate (BTS), BaTi1−xSnxO3 for x = 0, 0.025, 0.05, 0.07, 0.10, 0.12, 0.15 and 0.20, was investigated. The powders were prepared by the conventional solid-state reaction technique. The structural investigations of the BTS powders were done at room temperature by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected-area electron diffraction (SAED) and Raman spectroscopy analyses. Rietveld refinement of XRD data indicates that gradual replacement of titanium by tin in BaTiO3 provokes a phase transition from tetragonal for 0 ≤ x ≤ 0.07 to cubic for x = 0.12, 0.15 and 0.20. The coexistence of tetragonal (P4mm) and cubic (Pm\overline 3m) crystal phases was established in powder with nominal composition BaTi0.9Sn0.1O3. The crystal phases determined by Rietveld refinement were confirmed by HRTEM and SAED analyses. The crystal structures of the BTS powders at short-range scale were studied by Raman spectroscopy, which shows tetragonal (P4mm) and a small fraction of orthorhombic (Pmm2) crystal phases for all the examined BTS powders, implying a lower local ordering when compared to the average symmetry.

Dielectric and Ferroelectric Properties of BaTi1-xSnxO3 Multilayered Ceramics

Multilayered BaTi1-xSnxO3 (BTS) ceramics with different Ti/Sn ratios were produced by pressing and sintering at 1420 oC for 2 hours. X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy were used for structural, microstructural and elemental analysis, respectively. The dielectric and ferroelectric behavior of sintered samples was studied, too. It is found that in ingredient materials, with increasing Sn content, the tetragonality decreases; Curie temperature moves towards room temperature, while the maximum of the dielectric constant increases, and also, they becomes less hysteretic. It is noticed that multilayered BTS ceramics with different Ti/Sn contents have a broad transition temperature and show a relatively high dielectric constant in a wide temperature range. It is shown that dielectric properties of these materials may be modified by a combination of different BTS powders as well as layers number.

Processing and characterization of UHMWPE composite fibres with alumina particles in poly(ethylene-vinyl acetate) matrix:

Processing of hybrid composites represents a challenge for engineers where the aim is to establish compatibility among several materials. The aim of this study is to evaluate the effects of different sizes and morphologies of alumina fillers on the mechanical and thermal properties of the composite fibres based on ultra-high molecular weight polyethylene fibres (UHMWPE). These fibres have an outstanding elastic modulus and they are compatible with nonpolar sequences of the poly(ethylene-co-vinyl acetate) (EVA) matrix. Compared to the fibres, inferior mechanical properties of the matrix can be improved using alumina particles. Commercial aluminium oxide (Al2O3) nanoparticles, commercial whiskers and synthesized particles of Al2O3 doped with iron oxide, incorporated in different weight percentages, were used as fillers. The UHMWPE fibres were impregnated using the solution of EVA in toluene with dispersed particles. Fourier transform infrared spectroscopy and field emission scanning electron microscope were used for structural examination. Tensile testing revealed increasing of modulus of elasticity and strengths of obtained hybrid composite fibres. Thermal gravimetry showed improved thermal stability up to 350°C of the hybrid composite fibres with alumina particles doped with iron oxide. Results of tested samples showed that the best mechanical properties were for hybrid composite fibres with 1 wt% of iron doped alumina filler.

Mechanochemical treatment and structural properties of lead adsorption on kaolinite (Rudovci, Serbia)

In the present work, remediation of lead-containing solution using raw and modified kaolinite has been presented. The micro and nanostructure of samples has been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Laser diffraction and scattering (LDS), was analyzed by particle size analyzer based on laser diffraction and particle size distribution (PSD) was done. The degree of metal adsorption was evaluated analyzing the Pb(II) contaminated samples by inductively coupled plasma atomic emission spectrometry (micro- and nanostructure on immobilization efficiency correlCP AES). The results show the impact of immobilization efficiency and ation between micro- and nanostructure. The thermodynamic data (ΔH°, ΔS°, ΔG°) are calculated from the temperature-dependent sorption isotherms. The results suggest sorption process of Pb(II) on kaolinite as spontaneous and endothermic.