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With the goal to produce a hard and tough coating intended for tribological applications, CrAlN/TiSiN nanolayer coating was prepared by alternative deposition of CrAlN and TiSiN layers. In the first part of the article, a detailed study of phase composition, microstructure, and layer structure of CrAlN/TiSiN coating is presented. In the second part, its mechanical properties, fracture and tribological behavior are compared to the nanocomposite TiSiN coating. An industrial magnetron sputtering unit was used for coating deposition. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for compositional and microstructural analysis. Mechanical properties and fracture behavior were studied by instrumented indentation and focused ion beam techniques. Tribological properties were evaluated by ball-on-disk test in a linear reciprocal mode. A complex layer structure was found in the nanolayer coating. The TiSiN layers were epitaxially stabilized inside the coating which led to formation of dislocations at interfaces, to introduction of disturbances in the coating growth, and as a result, to development of fine-grained columnar microstructure. Indentation load required for the onset of fracture was twice lower for the nanolayer CrAlN/TiSiN, compared to the nanocomposite TiSiN coating. This agrees very well with their mechanical properties, with H3/E2 being twice higher for the TiSiN coating. However, the nanolayer coating experienced less severe damage, which had a strong impact on tribological behavior. A magnitude of order lower wear rate and four times lower steady state friction coefficient were found for the nanolayer coating.

Hydroxyapatite was used as the inert matrix for in-situ immobilization of strontium (Sr) radioactive isotopes at room temperature. A nano-emulsification method was applied to synthesize Sr-substituted calcium hydroxyapatite (Ca1−xSrx)10(PO4)6(OH)2. The concentration of incorporated Sr was in the range of 0 ≤ x ≤ 1. Immobilization of Sr was evaluated using a stable isotope instead of radioactive isotope. The effect of strontium concentration on the crystal structure was studied and the results have showed that in the whole concentration range, Sr forms solid solutions with the host hydroxyapatite crystal structure. Powders comprised of nanometre sized particles were obtained and their properties, such as crystallite and particle size, changes in lattice parameters as function of dopant content and thermal stability, were further examined. It was found that the crystal structure of obtained powders is thermally stable at high temperatures. No secondary phases were formed in as-prepared powders or during calcination. The results in this study showed that nano-emulsion strategy provides a simple pathway for synthesis of a single-phase Sr-substituted hydroxyapatite, which can be used for immobilization of Sr radioactive isotopes.

We have studied Ho-doped BiFeO 3 nanopowders (Bi 1−x Ho x FeO 3 , x = 0–0.15), prepared via sol-gel method, in order to analyse the effect of substitution-driven structural transition on dielectric and ferroelectric properties of bismuth ferrite. X-ray diffraction and Raman study demonstrated that an increased Ho concentration (x ≥ 0.1) has induced gradual phase transition from rhombohedral to orthorhombic phase. The frequency dependent permittivity of Bi 1−x Ho x FeO 3 nanopowders was analysed within a model which incorporates Debye-like dielectric response and dc and ac conductivity contributions based on universal dielectric response. It was shown that influence of leakage current and grain boundary/interface effects on dielectric and ferroelectric properties was substantially reduced in biphasic Bi 1−x Ho x FeO 3 (x > 0.1) samples. The electrical performance of Bi 0.85 Ho 0.15 FeO 3 sample, for which orthorhombic phase prevailed, was significantly improved and Bi 0.85 Ho 0.15 FeO 3 has sustained strong applied electric fields (up to 100 kV/cm) without breakdown. Under strong external fields, the polarization exhibited strong frequency dependence. The low-frequency remnant polarization and coercive field of Bi 0.85 Ho 0.15 FeO 3 were significantly enhanced. It was proposed that defect dipolar polarization substantially contributed to the intrinsic polarization of Bi 0.85 Ho 0.15 FeO 3 under strong electric fields at low frequencies.

Investigations of the high-pressure sintered nanocrystalline mullite powder are presented. The synthesized mullite powder with crystallite size of 51 nm was densified by using high-pressure anvil-type with hollows apparatus at 4 GPa over the temperature range of 1100-1500 degrees C in 100 degrees C steps. The phase composition and structural parameters of the densified samples were studied as a function of densification temperature. The XRD analysis revealed the appearance of new phases, such as kyanite and corundum, whose development affected the densities of the sintered samples. High relative densities of the sintered samples were obtained because of the application of high pressure. The needle-like microstructure was developed owing to the anisotropic grain growth of mullite. The elongated mullite grains reached the length of approximately 5 mu m at 1400 degrees C, whereas the grains treated at 1500 degrees C became thicker preserving the same needle length. The Vickers microhardness of the developed microstructures increased with the increase of temperature up to 1400 degrees C, while at 1500 degrees C it was slightly reduced due to the grain coarsening. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Simple route was used for synthesis of nanostructured titania samples doped with 3 and 6 mol% of Cr3+ Titanium(IV)-isopropoxide and water were used as starting materials and as an agents for controlling hydrolysis and condensation reactions. The phase evolution of titania (TiO2) was followed by calcination at 400, 600 and 800 degrees C. The synthesized powders were examined by field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD). Single-phase anatase was obtained at low temperature (400 degrees C) in all cases. The photocatalytic activity of TiO2 doped nanopowders was evaluated by the photocatalytic degradation of crystal violet in aqueous solution. The present study indicates that this simple synthesis method can be an effective route to produce efficient photoactive doped anatase nanopowders. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Nanocrystalline manganites Ca1-xGdxMnO3 (x=0.05, 0.1, 0.15, and 0.2) were synthesized by a modified glycine-nitrate procedure and subjected to a systematic investigation regarding the effects of calcination and sintering on their structural, microstructural and magnetic properties. Thermal treatments of the green bodies were carried out by the conventional sintering (CS) method and the effects were monitored by different experimental techniques (XRD, ICP, FTIR, SEM, and EDS). The obtained results showed that induced structural/microstructural changes were not simple functions of the dopant concentration x and that they were influenced by different material-specific processes. Magnetism of the final bulk powders have been investigated by SQUID-magnetometry and correlated with samples composition and structural/microstructural properties. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Porous silica ceramics were obtained at low forming pressure and low sintering temperature by using diatomaceous earth as a silica source and boric acid as an inexpensive additive. The starting raw material, diatomite from surface coal mine Kolubara, Serbia, was purified from organic and inorganic impurities by using heat and chemical treatment. Boric acid was used as binding and sintering aid up to 2 wt%. Powder was compacted by using different pressures of 40, 60 and 80 MPa. The pressed samples were sintered at 850, 1000, 1150, and 1300 degrees C for 4 h in air. A relatively high porosity in the range of 60-70% is obtained for the samples pressed at 40, 60 and 80 MPa and sintered at 1000 degrees C. Median pore size diameters are in the range of macroporous up to 2 mu m in the samples sintered at 1150 and 1300 degrees C. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scaning electron microscopy (SEM) and mercury porosimetry measurements were employed to characterize the phases, functional groups, microstructure and pore size distribution of the obtained samples. In addition, measurements of densities and open porosities by immersion technique, according to Archimedes principle, were used. The relations between mechanical properties (Young modulus, Poisson ratio, and compressive strength) versus content of boric acid in the investigated samples were studied and disscussed. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Y-doped HfO2 nanopowders, produced by metathesis synthesis, exhibit ferromagnetism at room temperature. The X-ray diffraction and Raman measurements have shown that HfO2 nanopowders undergo phase transformation from monoclinic to tetragonal and cubic phase with increasing of Y content. The X-ray photoelectron spectroscopy and Raman analysis gave evidence that Y-doped HfO2 nanopowders are oxygen deficient. The ferromagnetic properties of Y-doped HfO2 nanocrystals are dependent on crystal structure changes. The structural transformation from monoclinic to tetragonal phase with Y doping is followed by increased ferromagnetic ordering because of the increased concentration of oxygen vacancies (V-O) in different charge states. Higher Y content favors the formation of cubic phase and the ferromagnetism significantly weakens. In cubic hafnia phase, yttrium can form (V-O-Y-Hf) defect complexes in different charge states. The appearance of these complexes can be responsible for the degradation of ferromagnetic ordering. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Fine tungsten carbide (WC) powder was prepared by solid state reaction between tungsten powder (W) and activated carbon cloth as a new carbon (C) source. The effect of temperature and time of heat treatment as well as the effect of C/W ratio on WC phase formation was studied. The results obtained by X-ray powder diffraction (XRPD) show that obtained powder is single WC. Microstructure and morphology was determinate by means of scanning electron microscopy (SEM). Brunauer-Emmett-Teller (BET) method was used for examining specific surface area and texture of obtained powders. It was found that WC powder was successfully synthesized in excess carbon after eight-hour heat treatment at relatively low temperature (1000 degrees C). (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Multidoped nanosized ceria powders were prepared by either modified glycine nitrate procedure (MGNP) or self-propagating reaction at room temperature (SPRT). As the dopants to CeO2, trivalent rare earth oxides such as Nd2O3, Sm2O3, Gd2O3, Dy2O3 and Y2O3 were used, with the total molar fraction of 20%. The pressed powder pellets were subjected to the densification by sintering at 1500 degrees C, in an air atmosphere. A single-phase crystalline form was evidenced by X-ray diffractometry for both sintered materials. By means of complex impedance measurements, the conductivity of the sintered samples was determined as a function of temperature. At 700 degrees C, the conductivity amounted to 2.19 x 10(-2) and 1.40 x 10(-2) ohm(-1) cm(-1) for the SPRT and for the MGNP sample, respectively. The corresponding values of activation energies of conductivity amounted to 0.72 (MGNP) and 0.59 (SPRT) eV in the temperature range 550-700 degrees C. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Nanometric ceria powders with fluorite-type structure were obtained by applying self-propagating room temperature method. The obtained powders were subsequently thermally treated (calcined) at different temperatures for different times. Powder properties such as specific surface area, crystallite size, particle size and lattice parameter have been studied. Roentgen diffraction analysis (XRD), BET and Raman scattering measurements were used to characterize the as-obtained (uncalcined) powder as well as powders calcined at different temperatures. It was found that the average diameter of the as-obtained crystallites is in the range of 3-5 nm whereas the specific surface area is about 70 m(2)/g. The subsequent, 15 min long, calcination of as-obtained powder at different temperatures gradually increased crystallite size up to similar to 60 nm and reduced specific surface down to 6 m(2)/g. Raman spectra of synthesized CeO2-y depicts a strong red shift of active triply degenerate F-2 (g) mode as well as additional peak at 600 cm(-1). The frequency of F-2 g mode increased while its line width decreased with an increase in calcination temperature. Such a behavior is considered to be the result of particle size increase and agglomeration during the calcination. After the heat treatment at 800 degrees C crystallite size reached value larger than 50 nm. Second order Raman mode, which originates from intrinsic oxygen vacancies, disappeared after calcination. (c) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The new porous carbon materials were obtained by templating procedure using mesoporous silica (SBA-15) as template. The ordered mesoporous silica materials were synthesized by using Pluronic P123 (non-ionic triblock copolymer, EO20PO70O20). SBA-15/cryogel carbon composites were obtained by sol gel polycondenzation of resorcinol and formaldehyde in the presence of different amount of SBA-15. The polycondenzation was followed by freeze drying and subsequent pyrolysis. One set of SBA-15/sucrose carbon composites was prepared by using sucrose as carbon source. The silica template was eliminated by dissolving in hydrofluoric acid (HF) to recover the carbon material. The obtained carbon replicas were characterized by nitrogen adsorption-desorption measurements, X-ray diffraction and scanning electron microscopy (SEM). It was revealed that the samples have high specific surface (533-771 m(2) g(-1)), developed meso- and micro-porosity and amorphous structure. Porous structure of carbon replicas was found to be a function of the carbon source, properties of SBA-15 and silica/carbon ratio. Room temperature adsorption of nitrogen and adsorption of phenol from aqueous solutions were investigated. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Ceria ceramics was obtained from multi-doped nanosized ceria powders prepared by both modified glycine nitrate procedure (MGNP) and self-propagating reaction at room temperature (SPRT). Rare earth elements such as Nd, Sm, Gdr, Dy, Y, Yb were used as dopants. The overall mole fraction of dopants was 0.2. One-hour long sintering of powder compacts was performed at 1500 degrees C in oxygen atmosphere. Phase composition, microstructure and ionic conductivity of sintered samples were analysed. Single-phase ceria was detected in all samples. In general, the increase in the number of dopants improved the ionic conductivity. The samples doped simultaneously with five dopants had the highest ionic conductivity, as evidenced by the impedance measurements. At 450 degrees C, the conductivity of sample obtained by MGNP was 3.94 x 10(-3) Omega(-1) cm(-1) whereas the conductivity of sample obtained by SPRT was 2.61 x 10(-3) Omega(-1) cm(-1). The conductivity activation energy for MGNP and SPRT samples was measured to be 0.348 and 0.385 eV, respectively. Finally, the conductivity decreased as the number of dopants increased to six. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The synthesis, crystal structure and magnetic properties of Ca1-xGdxMnO3 (x = 0.05; 0.1; 0.15; 0.2) perovskite has been investigated. Powders with nominal compositions Ca0.95Gd0.05MnO3, Ca0.9Gd0.9MnO3, Ca0.85Gd0.15MnO3 and Ca0.8Gd0.2MnO3 were prepared using a modified glycine nitrate procedure. Obtained powders were calcinated in the temperature interval from 850 degrees C to 950 degrees C for 10 min. All samples where characterized by DTA, XRD and SQUID magnetometry. The possibility of incorporation of Gd ions in the positions A of the perovskite structure was investigated by X-ray methods. Influence of Gd on unit cell volume of the perovskite compounds, occupation numbers and distances between atoms were analyzed by Rietveld refinement. Microstructure size strain analysis was performed, as well. The results revealed that Gd entered positions A in the structure. Magnetic measurements showed that a Gd3+ substituted Ca2+ ions changes antiferromagnetic properties of CaMnO3 by introduction of ferromagnetic interaction due to a double exchange between Mn3+ and Mn4+ ions. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Sphene (CaTiSiO5), a calcium titanosilicate ceramic has been prepared from a powder mixture of CaCO3, TiO2 and SiO2 using vibromilling for homogenization and activation of precursors. The mechanochemical process initially yielded amorphous powders, which on further calcination, crystallized to yield sphene ceramic. The evolution of the phase composition with thermal treatment was investigated by X-ray powder diffraction (XRPD). Powder morphology and particle size distribution were analyzed by scanning electron microscopy (SEM) and laser diffraction, respectively. Rietveld refinement was employed to get the structural information of the synthesized powder. Densification and microstructure evolution was determined by means of density and scanning electron microscopy (SEM). The most favorable conditions for mechanical activation and synthesis of sphene based ceramic material are reported. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.