Search

From a glass with the mol% composition 20.1 Na2O-3 Al2O3-23.1 BaO-23 TiO2-7.6 B2O3-17.4 SiO2-5.8 Fe2O3 cubic barium titanate was crystallized. Scanning and transmission electron microscopy micrographs of the prepared glass-ceramics show fine crystals agglomerated to globular particles. With increasing crystallization time, their volume concentration increases and the particles form interconnected aggregates. From electrical impedance measurements of selected glass ceramics, the electrical conductivity and the dielectric permittivity of the prepared materials were determined for temperatures from −-170 °C to 97 °C, and frequencies from 100 Hz to 100 kHz. The typical values of the resistance are in the order of 108 Ω and the dielectric constants in the order of 40 at 100 kHz at room temperature. The two diffuse relaxor type phase transitions observed from −-123 to −-73 °C and from −-33 to 0 °C are attributed to the transformation rhomboherdral - orthorhombic and orthorhombic - cubic BaTiO3, respectively.

Pulsed laser deposition (PLD) of thin carbon films on SiO2/Si substrates was performed and the resulting films were examined by X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), Raman spectroscopy and ellipsometry. The deposition process was accomplished by laser ablation with Nd:YAG laser (third harmonic λ = 355 nm, pulse width τ = 18 ns and a repetition rate of 10 Hz) on 320–420 nm SiO2/(001) Si substrates with surface area of 15 × 15 mm2. The laser ablation process was carried out in two different deposition regimes: i) continuous regime with a deposition time of 15–1800 s; and (ii) pulse mode. As a target, carbon microcrystalline graphite disks (OD 15 mm, thickness 0.5 mm) were used. We established that films consisting of graphite nanoparticles/graphene grains of 5 to 30 nm thickness were deposited by the continuous PLD process while films comprising one to few-layered nano-sized graphene were deposited by pulsed PLD. Some films have low resistance (ρ = (0.1–1.5) × 10−3 Ω·m) and consist predominantly of sp2 hybridized carbon with Raman spectrum, which resembles that of nano-sized graphene. Regardless of the PLD process used, we observed an interface film enriched with sp3 hybridized carbon, which could be related to C O, C H and other interface bonds.

Electrоdeposited Zn–Cr alloy coatings, containing 3.6, 5.4 and 9.4 mass % Cr were analysed by DSC and XRD. X-ray diffraction patterns of the samples show that when they are annealed to sele...

In this work, we report fabrication of highly porous metal-oxide nanostructures by pulsed laser deposition performed in air at atmospheric pressure. The attention was focused on the structure, morphology, and composition of ZnO, TiO2, SnO2 and MoO3 metal oxides. The technology applied leads to formation of nanostructures composed by nanoparticles. Additionally, a nanocomposite sample consisting of metal-oxide and noble-metal nanoparticles was fabricated. The nanostructures were produced in view of applications as gas sensors. Preliminary results on the gas-sensing properties of the metal-oxide nanostructures are reported.

A laser-based technology is presented for fabrication of oriented nanowires composed by nanoparticles. The nanowires were produced by nanosecond pulsed laser deposition in air at atmospheric pressure in the presence of an external magnetic field. The technology described is relevant to the preparation of nanowires of magnetic materials. Applying an external magnetic field during the deposition resulted in the formation of nanowires with lengths of a few microns oriented longitudinally to the magnetic field lines. The influence was investigated of the process parameters, namely, laser fluence, target-substrate distance, and wavelength used for ablation, on the morphology of the deposited samples. It was found that the degree of the nanowires’ orientation increased with the increase of the target-substrate distance. Also, the density of the deposited material was influenced by the laser fluence applied and by the wavelength used.

Hazardous residues from ferronickel production and glass cullet were mixed and vitrified. After low-cost heat-treatment the obtained glass was transformed in a fine-crystalline glass-ceramic. The evolution of structure during the crystallization cycle is studied by XRD and SEM-EDS. Finally, the morphology of final glass-ceramic was elucidated by TEM and FESEM. Due to the elevate amounts of iron and magnesium oxides and the presence of ∼2 wt % chromium oxides in the composition, the crystallization process is peculiar and the final structure of glass-ceramic is complex. Some preliminary Fe-Mg-Cr spinel crystals with size of few microns precipitate during the melt cooling. Then, these crystals act as centres for the growth of a pyroxene phase; thus, 15–20 vol% of the glass-ceramic structure is formed. The major amorphous phase, where Cr2O3 concentration becomes negligible, is characterized with a high immiscibility trend, leading to the formation of Fe-rich droplets with size of 50–70 nm. Subsequently, these droplets are transformed into nano magnetite crystals, which provoke crystallisation of the main pyroxene phase. This “second” new pyroxene phase differs by the one, already formed on the preliminary Fe-Mg-Cr spinel, and is composed by mono-crystals with size of 150–200 nm.

Glasses were prepared in the system (100 − x)(0.16Na2O/0.10MnO/0.74SiO2)/xFe2O3 (x = 15 and 25 in mol%) by the traditional melt-quenching technique. Some of them were subsequently crystallized at temperatures in the range from 520 to 700 °C for times from 10 min to 100 h. The valence states of Fe and Mn in selected glasses and glass-ceramics were investigated by X-ray photoelectron spectroscopy (XPS) and showed the presence mostly of Mn2+ while Fe occurs as both Fe2+ and Fe3+. X-ray diffraction (XRD) analyses of the 15 mol% Fe2O3 samples revealed that at lower temperatures and for short heat treatment times a solid solution with a spinel structure and a chemical composition between MnFe2O4 (jacobsite) and Fe3O4 (magnetite) crystallizes, while aegirine (NaFe(SiO3)2) additionally occurs at higher temperatures and for longer annealing times. Here the average crystallite size of the jacobsite-based phase varies between 4 and 10 nm, as determined by XRD. The XRD analysis of the 25 mol% Fe2O3 samples which spontaneously crystallize when quenching the melt only show the precipitation of the jacobsite–magnetite solid solution. The microstructure was investigated by scanning and transmission electron microscopy (SEM and TEM) as well as electron-backscatter diffraction (EBSD). The EBSD analyses show that the cubic crystals grow via the polygon as well as the dendritic growth mechanisms. The individual grains show independent orientations and inclusions of residual glass while a global crystallographic texture could not be detected. The obtained magnetization curves of the 25 mol% Fe2O3 samples show hysteresis and a Curie temperature of approximately 480 °C which supports the XRD results. The samples with 15 mol% Fe2O3 crystallized at 650 and 700 °C exhibit superparamagnetic behaviour and thin S-shaped magnetization curves with zero coercivity.

Glasses with the mol % composition 20.1Na2O/23TiO2/23.1BaO/3Al2O3/7.6B2O3/17.4SiO2/5.8Fe2O3 were synthesized. During heat treatment at 550°C for 5 min to 7 h, cubic BaTiO3 crystallized. The microstructure of the glass-ceramics was studied by scanning electron microscopy. The average size of the crystalline particles varied from 190 to 790nm, depending on the crystallization time. Impedance measurements of selected glass-ceramics at temperatures from -183 to 97°C using frequencies from 100Hz to 1MHz witness insulating properties. The ac-conductivity at 100Hz increases with temperature from 10−10 S/m at -183°C to 10−6 S/m at 97°C. The ac-conductivity is established predominantly in the glass phase with Na+-ions as charge carriers and could be well fitted by the universal as well as by the modified Jonscher power law. However, for the intermediate temperature range, the modified Jonscher equation seems to better explain the physical mechanisms of conduction dispersion with frequency. In the whole studied temperature range, the power “s” in the dispersion equation slightly varies with the glass-ceramics’ thermal history but shows a relatively large decrease with increasing temperature. The higher conductivity of the sample with the highest BaTiO3 volume fraction is associated with the lowest s-value and largest number of non-bridging oxygen ions in the structure.

We report results from an experimental and modeling study of the far-from-equilibrium electrodeposition of Ni–Cu alloys by changing systematically the current density with focus on the surface structuring and surface content of the elements. General finding is that Cu prevails in the convex regions of the deposit, while Ni prevails in the concave ones. No deposition of a monophase is observed by the XRD analyses—in all samples are registered two phases under the form of solid solutions of Cu and Ni. With the increasing current density, the percentage of the major component increases towards deposition of pure Cu and Ni. Some oscillations of the overpotential with the current density are correlated with the Cu content in the Cu-rich solid solution. An original model based on Cellular Automata (CA) rationalizes the hypothesis that during their simultaneous deposition, Cu preserves the diffusion-limited growth mode, while the Ni discharges in a kinetically controlled one. The model is expected to be valid for lower current densities.

In this work, ZnO nanostructures were fabricated on noble-metal (Au, Ag and Au–Ag alloys) coated silicon substrates by applying pulsed laser deposition. The samples were prepared at a substrate temperature of 550 °C, an oxygen pressure of 5 Pa, and a laser fluence of 2 J cm−2 – process parameters usually used for deposition of smooth and dense thin films. The metal layer's role is substantial for the preparation of nanostructures. Heating of the substrate changed the morphology of the metal layer and, subsequently, nanoparticles were formed. The use of different metal particles resulted in different morphologies and properties of the ZnO nanostructures synthesized. The morphology of the ZnO nanostructures was related to the Au–Ag alloy's content of the catalyst layer. It was found that the morphology of the ZnO nanostructures evolved from nanorods to nanobelts as the ratio of Au/Ag in the alloy catalyst was varied. The use of a small quantity of Ag in the Au–Ag catalyst (Au3Ag) layer resulted predominantly in the deposition of ZnO nanorods. A higher Ag content in the catalyst alloy (AuAg2) layer resulted in the growth of a dense structure of ZnO nanobelts.

Nb modified mesoporous SBA-15 and HMS materials were synthesized and studied as a support of NiMo. Calcined co-impregnated NiMo catalysts were prepared using ammonium heptamolybdate and nickel nitrate. Moreover, NiMo catalysts prepared in this manner were treated with thioglycolic acid (TGA). For comparison, NiMo catalysts were prepared by a simultaneous impregnation of the supports with Ni, Mo precursors and TGA. The TGA:Mo molar ratio was 4.0. The supports and NiMo catalysts were characterized by N 2 physisorption, small- and wide-angle XRD, TPD-NH 3 , SEM, UV–vis DRS, FTIR and XPS. Catalyst activity was examined in hydrodesulfurization (HDS) reactions of 1-benzothiophene and thiophene at 350 °C. It was found that simultaneous impregnation by Ni, Mo and TGA led to higher HDS activities than the sequential treatment of the calcined NiMo catalysts by TGA.

The crystal and magnetic structures of the frustrated Co3O4 spinel oxide have been studied by means of neutron diffraction at high pressures up to 8.7 GPa in the temperature range 5–300 K. At ambient pressure, a coexistence of the long range ordered antiferromagnetic (AFM) phase and short range disordered phase below TN = 33 K was observed. At pressures above 2 GPa, a suppression of the magnetically disordered phase and stabilization of the AFM phase, characterized by rapid increase of the Neel temperature in 1.5 times from 33 to 51 K with a pressure coefficient dTN/dP = 2.1 K/GPa occur. The observed phenomena are analyzed in terms of the competing nearest neighbor and next nearest neighbor magnetic interactions. In addition to the A-O-B-O-A nearest neighbor superexchange, an important role of the A-O-O-A next nearest neighbor superexchange interactions in magnetic behavior of Co3O4 is pointed out.

Bulk glasses with a composition 20.1Na2O/23.1BaO/23.0TiO2/7.6B2O3/17.4SiO2/3Al2O3/5.8Fe2O3 containing less than 30 mol% glass-forming oxides are synthesized. Information on the valency of the glass constituents is obtained by x-ray photoelectron spectroscopy and it is concluded that all species are predominantly present in their oxidized state. Glassy samples are annealed above the glass transition temperature which leads to the crystallization of BaTiO3 for all time-temperature applied schedules. The phase composition of the glass-ceramics is studied by x-ray diffraction and the formation of cubic BaTiO3 is suggested. Temperature-dependent Raman spectroscopy confirms the presence of solely cubic BaTiO3. The microstructures of all annealed samples are similar and consist of globular interconnected particles in which nanosized BaTiO3 crystals grow randomly. The mean size of the spherical formations increases with the increasing annealing time from 200 to 600 nm. Electron microscopy suggests that during the annealing process first phase separation and then crystallization of BaTiO3 occurs.

The synthesis of invert glasses in the system Na2O/TiO2/BaO/Al2O3/B2O3/SiO2/Fe2O3 is reported for different [Na2O]/[Al2O3]-ratios and glass-former concentration less than 30 mol%. During annealing in the glasses cubic and tetragonal BaTiO3 crystals are simultaneously crystallized as proved by X-ray diffraction. Scanning electron microscopy micrographs show that during isothermal heat-treatment globular crystals with sizes from 100 nm to 1 μm are formed. The dielectric properties of the glass-ceramics are studied at room temperature by impedance spectroscopy using two contact points measurement and gold electrodes. The impedance and the phase angle are measured in the frequency range from 0.1 Hz to 1 MHz. The obtained impedance spectra are simulated using an appropriate equivalent circuit in order to extract information on the bulk resistance and capacitance of the sample. Measurements of the capacitance at fixed frequencies are carried out and the dielectric constants are calculated. High dielectric constants in the order of 1000 at a frequency of f = 13 Hz are estimated, which increase with the increasing annealing times and decrease with increasing frequencies.

Glass powders, obtained after vitrification and milling of iron-rich Municipal Solid Waste Bottom Ashes (MSWA), were studied towards manufacture of sintered glass-ceramic material. The crystallization kinetics was investigated both in air and argon atmospheres by non-isothermal Differential Thermal Analysis (DTA). The densification behaviors at different temperatures were studied with optical dilatometry. The formed crystal phases were evaluated with X-ray diffraction (XRD) and the microstructure of samples were observed by scanning electron microscopy (SEM). The investigated composition is characterized with a high crystallization trend and formation of pyroxene solid solutions and melilite solid solutions. Due to additional nucleation process and lower viscosity (because of the lack of Fe2 + oxidation) the phase formation in inert atmosphere is accelerated and is carried out at lower temperature. In the interval 800–900 °C the densification in both atmospheres is inhibited by the intensive phase formation. However, after increasing the sintering temperature up to 1120–1130 °C secondary densification is carried out, resulting in material with zero water absorption, low closed porosity and high crystallinity. Some decreasing of sintering temperature and finer crystal structure are predicted at densification in inert atmosphere.

Two series of Fe-doped (5, 10 and 20 wt% Fe 2 O 3 ) ceria oxides were synthesized by mechanochemical mixing (MM) and impregnation (IM) methods. The Au catalysts (3 wt%) supported on these mixed oxides were tested in WGSR and PROX. Gold catalysts on supports prepared by IM exhibited WGS activity lower than that of gold on undoped ceria. Significantly better WGS performance was demonstrated over gold catalysts on supports synthesized by MM. The observed differences in the catalytic behavior were explained by the crucial role of the gold dispersion depending on the preparation method. The highest WGS activity of Au5FeCeMM catalyst was attributed to the cooperative catalytic work of Fe-modified ceria and magnetite with the highest extent of non-stoichiometricity. In contrast to WGSR, the catalytic behavior in PROX over gold catalysts on supports prepared by both methods did not differ significantly. Fe likely acted as a ceria modifier because no changes in Fe-phases and Fe valence state were observed upon reaction. The nanosized hematite particles covering the ceria grains in the case of the IM method could diminish the ceria basicity explaining the observed good and stable PROX performance over Au10FeCeIM catalyst in the presence of CO 2 and water.

Three new ceramic batches with no traditional fluxes and 30, 50 and 70 wt.% blast furnace slag were studied. The processes of phase formation and densification were estimated in non-isothermal conditions by differential thermal analysis and dilatometry, respectively. After that the degrees of sintering, obtained after heat-treatment at different temperatures and times, were evaluated measuring the variations of linear shrinkage and water absorption. The structures of final materials and their phase compositions were studied with scanning electron microscopy, pycnometry and X-ray diffraction. Mechanical properties of the final ceramics were also measured. The obtained ceramics are characterized with a narrow sintering interval at 1200–1220 °C and good degrees of densification. Due to the formation of pyroxene and anorthite solid solution the new materials show high crystallinity. As a result, the measured bending strength and hardness surpass the values of traditional building and tiling materials.

The anodic behavior, corrosion resistance and protective ability of Zn and alloyed Zn–Co (∼3 wt.%) nanocomposite coatings were investigated in a model corrosion medium of 5% NaCl solution. The metallic matrix of the layers incorporates core–shell nano-sized stabilized polymeric micelles (SPMs) obtained from poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) block co-polymers. The protective properties of the composite coatings were evaluated using potentiodynamic polarization technique, polarization resistance measurements and powder X-ray diffraction. The sizes and distribution of the stabilized polymeric micelles in the starting electrolytes used as well as in the metal matrices of the layers were investigated using scanning and transmission electron microscopy. The results obtained are compared to those of electrodeposited Zn and Zn–Co (∼3 wt.%) alloy coatings at identical conditions and demonstrate the enhanced protective characteristics of the Zn nanocomposites during the investigating period. The influence of the SPMs on the corrosion resistance of the nanocomposite layers is commented and discussed.

Gold supported catalysts on ceria-alumina, prepared by different methods have been studied in the WGS reaction. For the synthesis of the mixed ceria-alumina support two methods were applied—a new method of mechanochemical activation and well known ceria washcoating on alumina. Gold catalysts on ceria-alumina, prepared by mechanochemical activation show a high and stable WGS activity. A correlation between redox activity of the catalysts, estimated by TPR and the catalytic activity of the samples was observed. The introducing of alumina to ceria by mechanochemical activation causes formation of oxygen vacancies, located mainly on the catalyst surface. In the freshly prepared catalysts an optimum between a part of positively charged nano-gold particles, Ce 3+ and oxygen vacancies should be the crucial factor for the good performance of WGS catalysts. In the course of redox reaction the active complex is being changed because of the electron transfer between gold and ceria through oxygen vacancies. A positive effect of alumina on the catalysts stability with respect to avoiding gold and ceria particles agglomeration was confirmed, as well.

The thermolysis of the ill-known γ-MnC2O4·2H2O is investigated applying DTA, TG, DSC, FT-IR, SEM, BET and Rietveld XRD phase analyses for thorough characterization of the starting compound and its calcined products. The dehydration proceeds in one step with ∆H = 149 kJ mol−1 (reported for the first time). Primary decomposition product is Mn3O4 ([Mn2+Mn2 3+]O4) with high specific surface area. During its formation, the oxidation of Mn3+ species to Mn4+ starts, followed by oxidation of Mn2+–Mn3+, thus leading to formation of metastable Mn5O8 ([Mn2 2+Mn3 4+]O8) and Mn2O3. Before complete precursor decomposition under non-isothermal conditions, the reduction of Mn4+–Mn3+ occurs, forming an additional amount of Mn3O4. After isothermal annealing of γ-MnC2O4·2H2O in the range of 573–823 K, Mn3O4 is detected as a major product in all samples. Mn5O8 is identified after calcination at 573, 673, 723 K, and its amount decreases gradually in this order. Cubic Mn2O3 appears after heat treatment at 673 K; its content varies between 13 and 23 % in the range of 673–773 K and becomes close to that of Mn3O4 at 823 K. The application of the same experimental conditions as in the investigation of α-MnC2O4·2H2O and MnC2O4·3H2O allows an objective comparison of the nature and the peculiarities of the thermal decomposition of different crystal forms of manganese oxalate.

Temporary scaffolds that mimic the extracellular matrix’s structure and provide a stable substratum for the natural growth of cells are an innovative trend in the field of tissue engineering. The aim of this study is to obtain and design porous 2D fibroin-based cell matrices by femtosecond laser-induced microstructuring for future applications in muscle tissue engineering. Ultra-fast laser treatment is a non-contact method, which generates controlled porosity—the creation of micro/nanostructures on the surface of the biopolymer that can strongly affect cell behavior, while the control over its surface characteristics has the potential of directing the growth of future muscle tissue in the desired direction. The laser structured 2D thin film matrices from silk were characterized by means of SEM, EDX, AFM, FTIR, Micro-Raman, XRD, and 3D-roughness analyses. A WCA evaluation and initial experiments with murine C2C12 myoblasts cells were also performed. The results show that by varying the laser parameters, a different structuring degree can be achieved through the initial lifting and ejection of the material around the area of laser interaction to generate porous channels with varying widths and depths. The proper optimization of the applied laser parameters can significantly improve the bioactive properties of the investigated 2D model of a muscle cell matrix.