Jaroslav Briančin

Mechanochemical route for sulphide nanoparticles preparation

Abstract Well-crystallized ZnS, CdS and PbS nanoparticles were successfully synthesized by the mechanochemical route from the corresponding acetates and Na 2 S. X-ray powder diffraction and scanning electron microscopy were used to characterize the as-obtained products. The SEM measurements show the aggregates of small nanocrystals in which particle sizes of 5–18 nm were estimated by Scherrers formula. Simple flow chart of the preparation of sulphide nanoparticles was presented.

Effect of PMN modification on structure and electrical response of xPMN–(1−x)PZT ceramic systems

The structural and electrical properties of xPb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr,Ti)O3 ternary ceramic system with the composition near to the morphotropic phase boundary (MPB) and of xPb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr0.47Ti0.53)O3 ceramics were investigated as a function of the Pb(Mg1/3Nb2/3)O3 (PMN) content by scanning electron microscopy (SEM), X-ray diffraction (XRD), dielectric and piezoelectric spectroscopy and polarization-electric field measurement technique. Studies were performed on the samples prepared by a columbite precursor method for x=0.125, 0.25 and 0.5. Room temperature SEM investigations revealed common trends in the grain structure with increasing PMN content. XRD analysis demonstrated that with increasing PMN content in xPb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr0.47Ti0.53)O3, the structural change occurred from the tetragonal to the pseudocubic phase at room temperature. Changes in the dielectric and ferroelectric behavior were then related to these structural trends and further correlated with the piezoelectric properties. The results of ferroelectric hysteresis measurements, in conjunction with dielectric spectroscopy, demonstrated an intermediate, relaxor-like behavior between normal and relaxor ferroelectrics in the solid solution system, depending on the PMN content.

Dielectric properties and phase transition behavior of xPMN-(1 - x)PZT ceramic systems

The dielectric properties and phase transition behavior of the pseudo-ternary xPb(Mg1/3Nb2/3)O3-(1 − x)Pb(Zr,Ti)O3 solid solution system were investigated as a function of the Pb(Mg1/3Nb2/3)O3 (PMN) content and Ti/Zr ratio for selected compositions. The investigations have demonstrated a general trend in broadening of the phase transition and increasing diffusivity with increasing PMN content. For the morphotropic phase boundary (MPB) compositions, the dielectric permittivity maximum, its temperature (Tm) and the Curie-Weiss constant were found to decrease with increasing Mg1/3Nb2/3 concentration. When a Ti/Zr ratio was constant and equal to 53/47, temperature-dependent investigations demonstrated that the dielectric parameters involved in a modified Curie-Weiss law increase monotonically with increasing PMN content and Tm moves toward room temperature with average rate of ≈ −4.1°C/mol% as well. A phase transition in 0.5PMN-0.5Pb(Zr0.47Ti0.53)O3 and 0.25PMN-0.75Pb(Zr0.60Ti0.40)O3 ceramic systems exhibited a diffused behavior with a characteristic frequency dependence of Tm. From pyroelectric measurement, an unusual spontaneous polarization behavior at about 215 K is reported for some MPB compositions.

Non-oxidative leaching of mechanically activated stibnite

Abstract The results obtained by leaching stibnite with a basic solution of sodium hydrogen sulphide are presented in this paper. The intensification of leaching by the mechanical activation produced by grinding the mineral in a planetary mill for 20 min brings about acceleration of the process by tenfold. The non-oxidative leaching of stibnite is a structure-sensitive process and the structure sensitivity decreases if assemblages of particles, i.e., agglomerates arise. The activation energy calculated from the temperature dependence of leaching in the region 293–345 K had the value E=28 kJ mol−1 for a non-activated sample (standard) and E=13 kJ mol−1 for a sample activated for 20 min. This suggests that the rate-determining step must have been changed. The SEM investigation of the residues after leaching documents the morphological non-uniformity of the leaching process.

Surface and bulk properties of mechanically activated zinc sulphide

BET, scanning electron microscopy, X-ray photoelectron, infrared, X-ray diffraction and Mössbauer spectroscopy methods were used to identify changes in surface, structural and spectroscopic properties of sphalerite produced by mechanical activation. Activated samples exhibit amorphization of crystallographic structure of the mineral, as well as of hyperfine structure of the accessory manganese. The presence of a new magnetic phase was disclosed in the samples activated for longer periods of time. Changes in structure are accompanied by mechanochemical oxidation of the surface layer of sphalerite.

Study of controlled tetracycline release from porous calcium phosphate/polyhydroxybutyrate composites

Porous calcium phosphate ceramics were prepared by sintering of mixtures of nanocrystalline apatitic calcium phosphate and fibrous natural cotton cellulose after pressing at temperatures of 1150 °C and 1250 °C. Micro-and macropores were present in microstructures of ceramic samples. The microstructures of porous ceramics were similar to those observed in bone tissues and fiber-like randomly oriented texture was observed in ceramics. Polyhydroxybutyrate (PHB) biopolymer layers are distributed homogeneously in the samples after evaporation of the diluent (chloroform) from the PHB vacuum impregnated porous samples. The tetracycline (TTC) release rate decreases with the content of polyhydroxybutyrate in the ceramic samples, which corresponds to the rise in amount of biopolymer displaced in the pores of ceramics. The concentration of TTC in the phosphate buffer saline solution varies almost linearly with time after the first seven hours from the start of the release of the calcium phosphate ceramic samples with 2.4 mass % of polyhydroxybutyrate. The initial burst effect was significantly depressed by the preparation method used.

Properties of mechanochemically pretreated precursors of doped BaTiO3 ceramics

The properties of doped BaTiO3 ceramics prepared from mechanically activated precursors (BaCO3, TiO2, PbO), dopant (Sb) and admixtures (SiO2, Al2O3) were investigated. Mechanical activation of the mixture 1.00 BaCO3 + 1.15 TiO2 + 0.10 PbO brings about an increase in its specific surface and partial amorphization of BaCO3; Ba, O and C occur in the surface of this mixture in at least two chemically different states. BaTiO3 obtained from the above mentioned mechanically activated precursors by high-temperature solid-state synthesis at 1100 ° C consists of homogeneous particles with a narrow particle size distribution.

Feasibility of a Thiobacillus ferrooxidans bacterial leaching of a chemically preleached chalcopyrite

Abstract In this paper the changes of the chalcopyrite, chemically preleached with the solution of iron (III) sulfate, are described and the possibilities of its subsequent leaching by the bacteria Thiobacillus ferrooxidans are examined. It has been found that a layer of elemental sulfur is created on the surface of samples and its amount linearly increases with time during chemical preleaching. At the same time, the volume of chalcopyrite changes, which is characterized by a decrease in values of the lattice parameters. The rate of bacterial leaching of the chemically preleached chalcopyrite is a function of the specific surface area of the preleached samples and decreases with increasing amount of the sulphur created on the surface. The presented results suggest that it would be feasible to combine chemical and bacterial leaching at least in closed-device experiments to improve or to increase total copper recovery.

Ultrafast mechanochemical synthesis of copper sulfides

Covellite, CuS and chalcocite, Cu2S were prepared within a few seconds by ball milling of the elemental precursors. The morphology of the used copper, related to its preparation method, was found to be the key factor for the ultrafast reaction. The explosive character of the reaction was monitored by the gas pressure changes in the milling vessel and the reaction progress was pursued by X-ray diffraction analysis and Soxhlets extraction. The local temperature at the contact site between the milling media and the milled mixture at the time of explosion was calculated as 950 °C for CuS and 700 °C for Cu2S. The mean crystallite size of the prepared products was 15 nm for CuS and 65 nm for Cu2S.

Properties and reactivity of Mn-doped ZnS nanoparticles

Abstract The physico-chemical properties and reactivity of ZnS:Mn (1% Mn) nanoparticles were investigated. ESR, XRD, specific surface area and reactivity in H 2 SO 4 were studied in order to elucidate the degree of distribution of Mn atoms. There is a strong correlation between preparatory history, the shape of ESR spectra and reactivity of ZnS:Mn nanoparticles.