Kinetics of nanocrystalline phase transformations in spray pyrolysed ZnO particles

The thermal behavior of ZnO powder obtained by ultrasonic spray pyrolysis of nitrate solution (c=0.8mol/dm3, D0=2.695µm, Tmax=6000C, FG=1.2dm3/min) was investigated using non-isothermal differential scanning calorimetry (DSC, heating rates 5, 10, 15, 20O/min). The exothermic heat effects at the temperature range from 350 to 5000C were linked to particles structural data obtained by XRD, SEM and TEM analysis. Produced particles are characterized by uniform submicronic size (D=800nm, BET=4.94m2/g), high phase purity and granular or circular “open” surface due to the presence of primary crystallites (d= 20nm). Observed structural changes during heating of this powder were attributed to simultaneous processes of nucleation and growth of primary crystallites inside the produced particles

The synthesis: Structure relationship in the ZnO-Cr2O3 system

In this work the development of the spinel phase in the ZnO-Cr2O3 system was discussed from the viewpoint of the synthesis-structure relationship. The nanostructure evolution in particles obtained either via solution-based (spray pyrolysis) or solid-state (mechanical activation) synthesis procedures were investigated by XRD analysis. A detailed structural analysis of the spinel phase lattice parameters, average primary crystallite sizes and micro strains were performed in accordance with a procedure based on the Koalariet-Xfit program. Due to the importance of spinel-phase cat ion distribution for chemical and physical properties, a study of the site occupation factors, i.e. changes in the stoichiometric, of ZnCr2O4 spinals was undertaken. The calculation based on atomistic methods for the description of both perfect and defect spinel ZnCr2O4 crystal lattices has been applied and the presence of individual structural defects was determined

Hemolytic activity of bioactive nanocomposites

Huge range of tested biomaterials in recent decades has emerged as an ideal scaffold for cell growth, but few have demonstrated clinical efficacy. Among them, synthetic hydroxyapatite (HAp, Ca10(PO4)6(OH)2) is the most promising because of its biocompatibility, bioactivity, and osteoconductivity. Biocompatibility represents the primary concern for any material to be used as a substitute for natural tissue. Hydroxyapatite particles interact with numerous cellular systems in vivo, and some of these interactions may lead to cell damage and to stimulate platelet activation, coagulation and thrombus formation. The aim of this work was to examine the hemocompatibility of nanocalcium hydroxyapatite substituted with 5% and 12% cobalt (Ca /CoHAp) and hydroxyapatite/polylactidcoglicolid (HAp / PLGA) in relation to pure HAp by testing their hemolytic activities. The results show the discrepancy in hemolytic activity of implanted matherials. The degree of crystallinity of samples had a more dominant influence on hemolysis than the percentage of substituted cobalt. Hemolysis ratios of the nanocalcium hydroxyapatite substituted with cobalt samples were below 3%, indicating good blood compatibility and that they are promising for medical application

RESEARCH ON LONG–TERM COLONIZATION OF GOOSANDER (MERGUS MERGANSER LINNEAUS, 1758) WITH REFERENCE TO HABITAT AVAILABILITY

Abstract — This article presents data on long-term colonization of goosander in Western Serbia and Eastern Republic of Srpska (on five oligotrophic reservoirs formed by the Drina River) based on continuous counting since the first observation of nesting in 1987. The total number of breeding pairs and their distribution in neighboring habitats continuously increased from year to year, suggesting that expansion of the population is still below the limit of the habitat. The decrease in population which occurred in certain years was due to environmental or anthropogenic influence

Synthesis of thin films by the pyrosol process

Among many aerosol routes, the Pyrosol process, due to its simplicity, low cost and quality of obtained films, represents a promising technique for the synthesis of thin films. The pyrosol process is based on the transport and pyrolysls of an aerosol of processor solution, generated in an ultrasonic atomizer, on a heated substrate. The theoretical principles of the pyrosol process are presented in this paper, as well as the influence of some synthesis parameters on the deposition of SnO2 thin films

Evolution of the microstructure of disperse ZnO powders obtained by the freeze-drying method

Freeze-drying, as a cryochemical powder processing method is applied in the synthesis of ZnO submicrometer to narrosized powders. The process involves rapid freezing of the sprayed precursor solution, drying under vacuum by sublimation of the Solvent and salt decomposition to oxide by thermal treatment. Calcination of dehydrated Zn(NO3)(2) was performed through destruction of the primary crystal structure, i.e. through accumulation of different defect complexes and based on this, the formation of a new state of the ZnO crystal lattice. An analysis of the microstructure evolution of zinc oxide particles in the temperature range from 548 to 898 K is described. The research was performed using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), electronic paramagnetic resonance (EPR) and infrared spectroscopy (IR). It was shown that the least ("primary") coherent scattering region (580 Angstrom) and the most defective state were ZnO obtained at the lowest calcination temperature (T-c = 548 K). Increase of the calcination temperature (T-c > 548 K) favors uniting of eight closest "primary" domains into "secondary" ones. Unification is accompanied by a pronounced increase in microstrainin "secondary" domains, whose size practically does not depend on the calcination temperature in the region 573-898 K

Nanocrystalline functional materials and nanocomposites synthesis through aerosol routes

This paper represents the results of the design of functional nanocrystalline powders and nanocomposites using chemical reactions in aerosols. The process involves ultrasonic aerosol formation (mist generators with the resonant frequencies of 800 kHz, 1.7 and 2.5 MHz) from precursor salt solutions and control over the aerosol decomposition in a high-temperature tubular flow reactor. During decomposition, the aerosol droplets undergo evaporation/drying, precipitation and thermolysis in a single-step process. Consequently, spherical, solid, agglomerate-free submicronic particles are obtained. The particle morphology, revealed as a composite structure consisting of primary crystallites smaller than 20 nm was analysed by several methods (XRD, DSC/DTA, SEM, TEM) and discussed in terms of precursor chemistry and process parameters. Following the initial attempts, a more detailed aspect of nanocrystalline particle synthesis was demonstrated for the case of nanocomposites based on ZnO-MeO (MeO=Bi Cr+), suitable for electronic applications, as well as an yttrium-aluminum base complex system, suitable for phosphorus applications. The results imply that parts of the material structure responsible for different functional behaviour appear through in situ aerosol synthesis by processes of intraparticle agglomeration, reaction and sintering in the last synthesis stage