Dj. Janaćković

Synthesis of mullite nanostructured spherical powder by ultrasonic spray pyrolysis

In this paper the synthesis of nanostructured spherical particles of mullite powders by ultrasonic spray pyrolysis is presented. The mullite crystallization and the nanostructure development during heating were examined by infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscope analysis. Comparative analysis of experimentally determined and theoretically calculated particle size distribution, obtained on the basis of three-dimensional (3D) model of spherical/ellipsoidal waves generated by incident ultrasonic field, confirmed that the process of aerosol/powder particle synthesis can be regarded as deterministic process.

Synthesis, morphology, and formation mechanism of mullite particles produced by ultrasonic spray pyrolysis

Submicrometer spherical particles of mullite powder were synthesized by ultrasonic spray pyrolysis of emulsion and solutions, using tetra-ethyl-orthosilicate (TEOS) or silicic-acid and Al(NO 3 ) 3 · 9H 2 O as initial compounds. Crystallization of mullite phase was determined by differential thermal (DT), thermogravimetric (TG), infrared (IR), and x-ray analyses. The synthesis of mullite from TEOS emulsion occurs by crystallization of γ–Al 2 O 3 (or Al, Si-spinel) from the amorphous phase and its subsequent reaction with amorphous SiO 2 , as well as by crystallization of pseudotetragonal mullite below 1000 °C and its subsequent phase transformation into orthorhombic mullite. In the powders produced from silicic acid solutions, synthesis of mullite occurs only by crystallization of γ–Al 2 O 3 between 900 and 1000 °C and its further reaction with amorphous SiO 2 between 1100 and 1200 °C. Particle formation mechanism depended directly on the initial emulsion or solution preparation, i.e., on the phase separation in the emulsion and on the silicic-acid crosslinking conditions.

Influence of synthesis parameters on the structure of boehmite sol particles

Abstract Influence of the type and amount of acid, used for aluminium hydroxide peptization, on the crystallinity and specific surface area of the dispersed phase of boehmite sols as well as the pH of sols, was investigated. The ratio n (HCl)/ n (Al(OH) 3 )=0.1 was found to be optimum for aluminium hydroxide peptization. Higher acid to aluminium hydroxide ratio leads to a decrease in specific surface area and crystallinity of the solid phase as well as in pH of sols. Increase in counter ion (Cl − ) concentration causes a shift in d values of (020) crystallographic plane, from the value corresponding to boehmite to that for pseudoboehmite, and a decrease in specific surface area of the sol solid phase. Using HNO 3 as a peptizing agent, greater crystallinity and higher specific surface area values of the solids were registered.

Surface Properties of HAp Particles Obtained by Hydrothermal Decomposition of Urea and Calcium-EDTA Chelates

In this paper surface properties of calcium-hydroxyapatite, synthes ized by modified hydrothermal reaction of urea and Ca(EDTA) 2– in phosphate solutions, as well as the dependence of calcium hydroxyapatite dispersion stability on pH were determined. T he specific surface area of calcium-hydroxyapatite was experimentally found to be 67 m /g. The point of zero charge (PZC) of indifferent KCl electrolyte of 6.8 ± 0.1 was determined by the batch equilibration method. From the dependence of surface charge density on pH and electrolyte concentrati on, the intrinsic equilibrium constant of surface groups p a2 K was determined to be 8.3 ± 0.1, while p int a1 K , calculated from the p int a2 K and point of zero charge values, is 5.3 ± 0.1. Hy droxyapatite suspension stability was investigated, in the pH range from 7 to12, it was r evealed that the most stable dispersion at pH 10. Introduction Hydroxyapatite is one of the main constituent compo unds of bones and teeth. Knowledge of the hydroxyapatite surface chemistry is very important from the point of view not only of bone tissue formation but also of HAP solubility, due to its in teraction with the surrounding fluid. Solubility of apatites is directly connected with various illness es uch as decalcination of bones (osteoporosis) and dental caries[1-2]. Behavior of the aqueous dispersion of hydroxyapatit e depends on the interfacial chemistry of the solid phase and dispersive medium. Surface charge o f hydroxyapatite in aqueous systems plays one of the main roles in determination of its colloidal and sorption properties [3]. The studies of the point of zero charge (pH PZC) and surface charge characteristics of apatites in dicate that H + and OH are potential-determinig ions and that the surface charge development at the apatite-water interface could be described by amphoteric dissociation react ions of surface functional groups [4,5]. In this paper, behavior and surface properties such as specific surface area, presence of particular surface groups, point of zero charge, surface charg e density, and intrinsic equilibrium constants of carbonate HAP obtained by hydrothermal decompositio n of urea and Ca-chelate, were reported. Methods and Materials Synthesis of carbonate hydroxyapatite was performed by a modified method of Fujishiro et al.[6-8], and was described earlier [9]. Specific surface area of HAP was determined by the B.E.T. (Brunauer – Emett – Teller) method, the sample was previously degassed in vacuum for 2 hour s at 150°C. The point of zero charge of HAP was determined by t he batch equilibration method described by one of the authors[10]. The adopted technique is as follows: KCl of different ionic strengths, 0.1 and 0.01 mol/ dm, was used as an electrolyte. First set of measurements included 12 samples with 25 cm 3 KCl of 0.1 mol/dm ionic strength. The initial pH (pHi) values, from 3 to 10, were adjusted by adding sm all volumes of 0.1 mol/dm 3 HCl or KOH to Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 437-440 doi:10.4028/www.scientific.net/KEM.240-242.437

Influence of aerosol formation mechanism by an ultrasonic field on particle size distribution of ceramic powders

Abstract Aerosol droplet genesis by ultrasonic atomization has been theoretically studied using a model for three-dimensional spherical/ellipsoidal waves generated by excitation of a system of given geometry by forced frequency of an ultrasonic oscillator. Analyzing the harmonic function of the rate potential, an equation has been derived that defines the mean diameter and the distribution spectrum of aerosol droplets formed at the surface of a liquid. Comparison has been made between the calculated values for the mean particle sizes and their distribution with those obtained experimentally for Al 2 O 3 , mullite and cordierite powders synthesized from different precursors.

Sintering Behaviour of Nanosized HAP Powder

The influences of temperature and time on sintering behaviour of nanosized HAP powder were investigate in this paper. The calcium hydroxyapatite powder, with the average crystallite size of 34 ± 1 nm, was uniaxially pressed at a pressure of 500 MPa. Obtained green compacts were sintered at temperature ranging from 1000°C to 1200°C in air atmosphere at various times. According to the results of scanning electron microscopy, X-ray and FTIR analyses, it is shown that HAP compacts with dense microstructure and average grain size below 250 nm is obtained.

The influence of silicon substitution on the properties of spherical- and whisker-like biphasic α-calcium-phosphate/hydroxyapatite particles

In this work, the influence of the morphology of hydroxyapatite particles on silicon substitution through hydrothermal synthesis performed under the same conditions was investigated. Spherical- and whisker-like hydroxyapatite particles were obtained starting from calcium-nitrate, sodium dihydrogen phosphate, disodium-ethylenediaminetetraacetic acid and urea (used only for the synthesis of whisker-like particles) dissolved in aqueous solutions. Silicon was introduced into the solution using tetraethylorthosilicate. X-ray diffraction, infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and transmission electron microscopy indicate that silicon doping induce different phase compositions and bioactivity of spherical- and whisker-like hydroxyapatite particles obtained under the same hydrothermal conditions. Silicon-substituted, spherical hydroxyapatites particles showed greater phase transformation to silicon-substituted α- calcium-phosphate compared with whiskers-like hydroxyapatite particles synthesized with the same amount of added silicon. Metabolic activity assay performed with SaOs2 osteosarcoma cells showed better biocompatibility of annealed biphasic spherical-like particles compared with annealed whiskerlike particles while dried spherical-like particles induce high cytotoxicity effect.

Modeling of nanostructural design of ultrafine mullite powder particles obtained by ultrasonic spray pyrolysis

Abstract In this paper, a model of substructure design of mullite powder particles obtained by spray pyrolysis in the field of ultrasound excitation is described. Based on this model, the size of subparticles (nanoparticles) constituting the substructure of so obtained powder is described and compared to experimentally determined values. High agreement between theoretical and experimental values confirmed the value of the theoretical model and its wide applicability in estimation of particle substructure for mullite powder obtained under the conditions of the periodical physical field activity.

Synthesis of nanostructured mullite from xerogel and aerogel obtained by the non-hydrolytic sol-gel method

Abstract Synthesis and nanostructure evolution of mullite (3Al2O3.2SiO2) from xero- and aerogels, obtained by the non-hydrolytic sol-gel process are described. Mullite crystallization and gel nanostructure evolution after heat treatment were studied by differential-thermal, x-ray diffraction, infrared and thermomicroscopic analysis as well as by scanning electron microscopy. Crystallization of mullite from both gels starts at 900 °C and further increase in temperature increases the size of crystallites formed from 32 to 100 nm and 12 to 20 nm in the case of xero- and aerogels, respectively. Accelerated sintering of aerogels in the temperature range 900 to 1000° C is a consequence of the viscous flow of the amorphous SiO2 phase.

Double-Layer Bioactive Glass Coatings Obtained by Pulsed Laser Deposition

Pulsed laser deposition was used to obtain functionally graded bioactive glass coatings on titanium substrates. An UV KrF* (λ=248 nm, τ>7 ns) excimer laser was used for the multi-pulse irradiation of the targets. The depositions were performed in oxygen while keeping substrate temperature at 400°C. We used sintered glass targets in the system SiO2-Na2O-K2O-CaO-MgOP2O5 that differed in SiO2 content, which was either 57 wt.% (6P57) or 61 wt.% (6P61). A glass 6P61 was used as the first layer in direct contact with the metallic substrate, while the outer bioactive layer was made of glass 6P57. Both the bioactive coatings and the bulk glasses were analyzed by Fourier transform infrared spectrometry (FTIR), grazing incidence X-ray diffraction (GIXRD), and scanning electron microscopy (SEM). The FTIR spectra of the glass powders and glass coatings showed the main vibration modes of the Si-O-Si groups. GIXRD analysis confirmed that the glass coatings had an amorphous structure. The SEM micrographs of the glass coatings showed the films to consist of droplets with diameters ranging from 0.2 to 5 μm. SEM was used to determine the rate of apatite formation on the coating when exposed to simulated body fluid (SBF) solution for 7 days. We demonstrated that pulsed laser deposition leads to good glass-metal adhesion on the substrate and well attached bioactive particles on the surface. We consider therefore this method appropriate for forming implants that can develop an apatite layer after immersion in SBF.