Structure and properties of nanocomposites prepared from ball milled 6061aluminium alloy with ZrO2 nanoparticles

Ball milling of 6061 aluminum alloy and nanocrystalline ZrO₂ powder allowed to obtain homogeneous mixture of nanocrystalline aluminum solid solution of grain size near 50 nm and ZrO₂ particles. The ZrO₂ particles are partially transformed after milling from tetragonal to the monoclinic crystal structure. After hot pressing in vacuum at temperature of 380 °C bulk nanocomposites were obtained of porosity below 1% consisting of aluminum solid solution of the average grain size near 80 nm and nano‐size ZrO₂ particles. Partial recrystallization occurred after hot pressing particularly near particles boundaries, where elongated recrystallized grains free from ZrO₂ nanoparticles of thickness near 1 μm and length of a few μm were identified. Estimated fraction of recrystallized grains was below 10%. The compression strength approaching 1000 MPa was obtained in composites containing 20% ZrO₂ nanoparticles, what is more than reported for ultra and nano‐grain 6XXX aluminum alloys. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of compounds LixMn1+xFe2–2xO4 with spinel structure in the quasiternary system “LiO0,5 – MnOx – FeOx“

The thermal decomposition of freeze‐dried Li‐Mn(II)‐Fe(III)‐formate precursors was investigated by means of DTA, TG and mass spectroscopy. By the thermal treatment of the prefired precursors between 400 and 1000°C, single phase solid solutions Li_xMn_1+xFe_2–2xO₄ (0 ≤ x ≤ 1) with cubic spinel structure were obtained. To get single phase spinels, special conditions concerning the temperature T and the oxygen partial pressure p(O₂) during the synthesis are required. Because of the high reactivity of the freeze‐dried precursors, in comparison with the conventional solid state reaction, the reaction temperature can be lowered by 200°C. The cation distribution and the properties of the Li‐Mn‐ferrites were studied by chemical analysis, X‐ray powder diffraction and magnetization measurements. It was found that for high substitution rates, almost all lithium occupies the tetrahedral coordinated A‐sites of the spinel lattice AB₂O₄, while at small x‐values, lithium ions are distributed over the tetrahedral and octahedral sites. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X‐ray powder diffraction structural characterization of Ba1‐xEuxTiO3 ternary oxides

The single‐phase Ba_1‐xEu_xTiO₃ (0.1≤x≤0.4) samples have been synthesized by solid state reaction under high pressure and ‐temperature. X‐ray powder diffraction data was determined by MS Modeling using Reflex Powder Indexing technique. The Ba_1‐xEu_xTiO₃ series exhibited an interesting orthorhombic‐tetragonal‐cubic structural transformation as Eu composition increases, the distinct change of the X‐ray diffraction peak profile in the vicinity of 45.5º is characteristic of structural transformation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ultra-high thermal expansion glass–ceramics in the system MgO/Al2O3/TiO2/ZrO2/SiO2 by volume crystallization of cristobalite

Glasses in the system MgO/Al₂O₃/TiO₂/ZrO₂/SiO₂ with and without the addition of As₂O₃ and Sb₂O₃ were thermally treated. Up to a temperature of 950 °C, this resulted in the formation of ZrTiO₄, sapphirine and high quartz solid solution. Annealing at higher temperatures led to the formation of low quartz solid solutions, ZrTiO₄ and sapphirine. This resulted in a continuous increase of density, hardness, fracture toughness and thermal expansivity. In the glass doped with As₂O₅ and Sb₂O₅ annealing temperatures >1000 °C resulted in the formation of cristobalite instead of quartz. Then the density, hardness and strength decreased again, while the fracture toughness (up to 2.8 MPa m^1/2) and the thermal expansion coefficient increased strongly. In the dilatometric curves, a steep increase in expansion is observed in the temperature range from 100 to 200 °C, which is attributed to the transformation of low cristobalite to high cristobalite. The mean linear thermal expansion coefficient (25–200 °C) is 20 × 10^?6 K^?1 and the largest up to now reported in the literature for alkali-free silicate glass–ceramics.     

Solvothermal synthesis of micron-sized spherical particles in TiO2–ZrO2 binary system

We prepared TiO₂–ZrO₂ binary oxide particles with various Ti/(Zr+Ti) mole ratios (x) from the solutions containing Ti(OC₃H₇ⁱ)₄, Zr(OC₃H₇ⁿ)₄ and acetylacetone (acac). The spherical particles of 1–5 μm in diameter were obtained via solvothermal treatment at 150 °C. The spheres were anatase at x=1 and amorphous at x=0–0.8. The spheres were thought to be formed through the moderate hydrolysis and nucleation provided by the chelation of the alkoxides by acac. Crystalline TiO₂–ZrO₂ particles were obtained by the heat treatment of the as-precipitated spheres, and the crystalline phase changed with the Ti/(Zr+Ti) mole ratios. Pure ZrO₂ and TiO₂, ZrO₂ doped with Ti⁴⁺, TiO₂ doped with Zr⁴⁺ and ZrTiO₄ phases were produced, and the spherical shape remained after the heat treatment at 500–750 °C.     

TiO2 nanoparticles synthesis for application in proton exchange membranes

In the present paper, suitable TiO₂ nanoparticles are successfully synthesized by sol‐gel method, in order to utilize the freshly prepared TiO₂ nanoparticles for proton exchange membrane (PEM) preparation. Titanium tetrachloride (TiCl₄) is used as precursor and ethanol as a solvent. The optimum and suitable TiO₂ nanoparticles were obtained by varying gelatinisation time (4–120 h), concentration of precursor (TiCl₄) in ethanol (2–15 vol%), and reaction temperature (15–35 °C). The morphology, size and purity of the nanoparticles are investigated by transmission electron microscope (TEM), dynamic light scattering (DLS) and X‐ray diffraction (XRD). Optimum results were found at 4 h of gelatinisation time, 10% precursor concentration and 25 °C temperature for preparation of TiO₂ nanoparticles. Thus prepared nanoparticles are found to be suitable for preparation of nanocomposite PEM, and consequently the prepared PEM indicates enhanced properties, such as, higher thermal stability (high glass transition temperature of 184.1 °C), excellent proton conductivity (0.0822 S cm⁻¹ at room temperature) and low methanol permeability (1.11 × 10⁻⁹ cm2 s⁻¹).     

Structural investigation and electronic band transitions of nanostructured TiO2 thin films

Titanium dioxide (TiO₂) thin film was deposited on n‐Si (100) substrate by reactive DC magnetron sputtering system at 250 °C temperature. The deposited film was thermally treated for 3 h in the range of 400‐1000 °C by conventional thermal annealing (CTA) in air atmosphere. The effects of the annealing temperature on the structural and morphological properties of the films were investigated by X‐ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD measurements show that the rutile phase is the dominant crystalline phase for the film annealed at 800 °C. According to AFM results, the increased grain sizes indicate that the annealing improves the crystalline quality of the TiO₂ film. In addition, the formation of the interfacial SiO₂ layer between TiO₂ film and Si substrate was evaluated by the transmittance spectra obtained with FTIR spectrometer. The electronic band transitions of as‐deposited and annealed films were also studied by using photoluminescence (PL) spectroscopy at room temperature. The results show that the dislocation density and microstrain in the film were decreased by increasing annealing temperature for both anatase and rutile phases. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology and crystal structure of A1-doped TiO2 nanoparticles synthesized by vapor phase oxidation of titanium tetrachloride

Al-doped titanium dioxide nanoparticles with precisely controlled characteristics were synthesized in an aerosol reactor between 900 °C and 1500 °C by vapor-phase oxidation of titanium tetrachloride. The effect of process variables (reactor temperature, initial TiCl₄ concentration, residence time and feeding temperature of oxygen) on particle morphology and phase characteristics was investigated using TEM, XRD, EDS, ICP and XPS, etc. The average particle size increased with decreasing oxygen feeding temperature and increasing reaction temperature, residence time and TiCl₄ concentration. The presence of aluminum during gas phase reaction increased the rate of phase transformation from anatase to rutile and altered the particle morphology from polyhedral to irregular crystals. TiO₂ and Al₂O₃ co-precipitated during particle formation which lead to the aluminum solid solution in titania. α-Al₂O₃ and Al₂TiO₅ were observed at AlCl₃/TiCl₄ ratios higher than 1.1 and reactor temperatures in excess of 1400 °C. The rutile content, which increased with increasing Al/Ti ratio and residence time, was at a maximum at about 1200 °C and decreased at both lower and higher reactor temperatures.     

The evolution of structure induced by intensive milling in the system 2Bi2O3 · 3TiO2

Concurrent mechanochemical treatment of either a stoichiometric 2Bi₂O₃ · 3TiO₂ powder mixture or (pulverized) Bi₄Ti₃O₁₂ compound was performed in a planetary ball mill. Relevant structural parameters: crystallite size, amount of amorphous phase and the transformed fraction (as a result of chemical reaction between Bi₂O₃ and TiO₂) of the powders milled for various milling times and intensities were derived from X-ray powder diffraction data. The obtained structural parameters were used to follow the kinetics of the reduction of crystallite size, amorphous phase formation and chemical reaction. In the powder mixture, during the early stage of mechanochemical treatment the Bi₂(CO₃)O₂ phase was found as an intermediate product which transformed into the highly amorphized Bi₄Ti₃O₁₂ phase as the milling progressed. On the other hand, mechanochemical treatment of Bi₄Ti₃O₁₂ powder induced a gradual deformation of the crystal lattice and destruction of the perovskite-type structure. However, in both cases, after a certain milling time, a very disordered, amorphous/nanocrystalline structure was obtained. It was demonstrated that in the steady state, the amorphous/nanocrystalline phase ratio depends on the milling conditions. Higher milling intensities induce ‘nanocrystallization’ of the amorphous phase, i.e., precipitation of crystallites with an average size below 20 nm. A kinetic model involving a nanocrystalline ↔ amorphous reaction, in which the forward and reverse reaction were first-order was postulated and used to analyze the formation of an amorphous phase.     

Preparation of nanocrystalline lithium niobate powders at low temperature

A facile route to prepare lithium niobate (LiNbO₃) powders was proposed by an alternative solid‐state method. Stoichiometric Li₂C₂O₄ and ammonium niobium oxalate were mixed with small amounts of water and then dried at room temperature. It was demonstrated that Li[NbO(C₂O₄)₂]·n H₂O intermediate was produced by an ion‐exchange reaction. Pure LiNbO₃ powders were successfully synthesized by heating the intermediate at 500, 600 and 700 °C for 3 h. X‐ray diffraction (XRD), scanning electron microscopy (SEM), Fourier‐transform infrared (FTIR) spectroscopy, UV‐Vis diffuse reflectance (UV‐Vis) spectroscopy and thermogravimetric (TG) analysis were used to characterize the precursor compound and as‐prepared samples. XRD results reveal that all the products are identified as hexagonal structure with high relative crystallinity (>87%). The particle size is found to be about 40 nm for the mixture calcined at 500 °C according to XRD data, which is in good agreement with SEM data. The as‐prepared LiNbO₃ powders by this method are high quality according to FTIR spectra. (Li_0.996Nb_0.005)Nb_0.999O₃ phase was formed when the calcination temperature was raised to 800 °C. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of annealing temperatures on properties of sol‐gel grown ZnO‐ZrO2 films

Mixed ZnO‐ZrO₂ films have been obtained by sol‐gel technology. By using spin coating method, the films were deposited on Si and glass substrates. The influence of thermal annealings (the temperatures vary from 400 °C to 750 °C) on their structural properties has been studied. The structural behavior has been investigated by the means of XRD and FTIR techniques. The results revealed no presence of mixed oxide phases, the detected crystal phases were related to the hexagonal ZnO and to crystalline ZrO₂. The sol‐gel ZnO‐ZrO₂ films showed polycrystalline structure with a certain degree of an amorphous fraction. The optical transmittance reached 91% and it diminished with increasing the annealing temperatures. The optical properties of the sol‐gel ZnO‐ZrO₂ films, deposited on glass substrates are excellent with high transparency and better then those of pure ZrO₂ films, obtained at similar technological conditions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and optical properties of AgGaS2 nanofilms

In this paper, AgGaS₂ nanofilms have been prepared by a two‐step process involving the successive ionic layer absorption and reaction (SILAR) and annealing method. Using AgNO₃, GaCl₃ and Na₂S₂O₃ as reaction sources, the mixture films were firstly deposited on quartz glass substrates at room temperature, and then annealed in Ar environment at 200–500 °C for 4 h, respectively. The effects of annealing temperature on structural and optical properties were investigated by XRD, UV‐Vis, EDS and photoluminescence (PL) spectra. It was revealed in XRD results that α‐Ag₉GaS₆ was contained in the samples annealed at 200 °C, and this phase was decreased with increase of the annealing temperatures. When the sample was annealed at above 400 °C, the chalcopyrite AgGaS₂ nanofilm was obtained. The preferred orientation was exhibited along the (112) plane. It was shown in atomic force microscopy (AFM) results that the grain sizes in AgGaS₂ nanofilms were 18‐24 nm and the thin films were smooth and strongly adherent to the substrates. When the annealing temperature was higher than 400 °C, it is an optimum condition to improve the structural and optical properties of the AgGaS₂ thin films. The room temperature PL spectra of AgGaS₂ nanofilms showed prominent band edge emission at 2.72 eV. Based on all results mentioned above, it can be concluded that the SILAR‐annealing method is preferable to preparing high‐quality AgGaS₂ nanofilms. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tribological properties of WSe2 nanorods as additives

This work demonstrats a convenient and effective approach to synthesize WSe₂ nanorods at only 600 °C in argon atmosphere after ball milling. The friction and wear properties of WSe₂ nanorods as additives in two kinds of base oil, GyT130 oil and 60N oil were systematically investigated. Compared to base oil, the friction coefficient of the base oil containing WSe₂ nanorods was obviously reduced and the wear behaviour was improved. The nanorods in the 60N base oil showed better tribological properties than that in the GYT130 oil. The friction‐and‐wear mechanism of the WSe₂ nanorods as lubrication additive was discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical and magnetotransport properties of La0.7Sr0.3MnO3/TiO2 composites

The composite samples with nominal compositions of (1‐x) La_0.7Sr_0.3MnO₃ + x TiO₂ (x = 0, 0.05, 0.10, 0.15 and 0.20) were synthesized via solid state reaction process. The X‐ray diffraction and scanning electronic microscopy observations reveal no reaction between La_0.7Sr_0.3MnO₃ (LSMO) and TiO₂ phases. Temperature dependence resistivity measurements show that TiO₂ phase shifts the metal‐insulator transition temperature (T_p) towards lower temperature and increases the resistivity. Moreover, the magnetization of the composite samples decreases with TiO₂ content. An enhancement in magnetoresistance is observed in the composite samples with x = 0.05 and x = 0.10 at low magnetic fields, which is encouraging for potential application of magnetoresistive materials at low field. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,structural and optical properties of well dispersed anatase TiO2 nanoparticles by non‐hydrothermal method

The formation of nanocrystalline TiO₂ particles has been investigated via a surfactant‐free synthetic non‐hydrothermal method. Titanium isopropoxide and toluene were used as the starting materials. At a low temperature of 250 °C for 6 h, the reaction mixture turned in to a white precipitate (TiO₂) as a result of the thermal decomposition of metal alkoxide. The obtained product was found to crystallize purely in the anatase phase with well defined morphology. The powder XRD study confirms that the average size of the particle is close to ∼15 nm. The TEM analysis indicates the sizes of the primary and secondary particles in the range between 8‐10 nm and 15‐20 nm respectively. The quantum size confinement of the crystallites is evident from the blue shift of the absorption edge in the UV‐Visible absorption spectrum. The luminescence property of the TiO₂ nanoparticles studied by the emission spectrum confirms the presence of defect levels caused by the oxygen vacancies. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth of zirconium‐doped KTiOPO4 crystals in the K2O‐P2O5‐TiO2‐ZrF4 system

Zirconium‐doped KTiOPO₄ (KTP) crystals were grown using a high temperature flux method in the K₂O‐P₂O₅‐TiO₂‐ZrF₄ system. The dopant content in the single crystals with general composition KTi_1‐xZr_xOPO₄ (where x = 0 – 0.026) strongly depends on zirconium concentration in the homogeneous melts. AES‐ICP method and X‐ray fluorescence analysis were used to determine the composition of the obtained crystals. Phase analyses of the products were performed using the powder XRD. The structures of KTiOPO₄ containing different quantities of Zr were refined on the basis of single crystal XRD data. Applying ZrF₄ precursor for zirconium injection into the flux allowed growing the zirconium‐doped KTP crystals at 930–750°C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Glass-ceramics in the system BaO/TiO2(ZrO2)/Al2O3/B2O3 and their thermal expansion

Glasses in the system BaO/TiO₂(ZrO₂)/Al₂O₃/B₂O₃ were melted from the raw materials with and without the addition of platinum. They were crystallized in two steps at 720 and 780 °C. TiO₂ does not act as nucleating agent in this system, but widely prevents crystallization. Samples additionally doped with platinum show the crystallization of BaAl₂B₂O₇. However, samples containing equimolar quantities of TiO₂ and ZrO₂ showed the crystallization of this phase without the addition of platinum. The thermal expansion coefficients of samples with TiO₂-concentration ⩽7 mol% or TiO₂/ZrO₂-concentrations ⩽5 mol% exhibit zero or even slightly negative thermal expansion coefficients.     

The crystal structure of α‐SrGaBO4

A new compound α‐SrGaBO₄ has been synthesized by solid state reaction at high temperatures, and its structure has been solved by direct methods from powder X‐ray diffraction. α‐SrGaBO₄ has an orthorhombic system, Pccn space group, with lattice parameters a = 15.3154(7) Å, b = 8.9186(4) Å, c = 5.8130(3) Å, and Z = 8. The structure consists of infinite chains run parallel to the c axis and built up of GaO₄ tetrahedral and BO₃ triangles. The basic unit of these chains is a six ‐ membered Ga₂BO₈ ring formed by two GaO₄ tetrahedra and one BO₃ triangles. The Sr atom is bonded to eight oxygen atoms. The strontium atoms serve to hold the chains together through co‐ordination with oxygen atoms. DTA curve of noncrystalline glassy SrGaBO₄ was discussed. The XRD results show no phase transition occurs between ‐173 °C and 127 °C. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure and thermal behaviour of (Rb,Cs)BSi2O6 solid solutions

The crystal chemistry of Rb‐Cs boroleucites has been studied by means of X‐ray powder diffraction at room and elevated temperatures. The cubic I‐43d → cubic Ia3d phase transition was investigated using a series of samples prepared by solid‐state reaction along the pseudobinary system RbBSi₂O₆ ‐ CsBSi₂O₆. The Rietveld refinement of the structures of Rb_1‐xCs_xBSi₂O₆ solid solutions (x = 0.2, 0.4, 0.6, 0.8) demonstrates that the solutions with a high Rb content crystallise in the cubic I‐43d space group, and the boroleucites with a considerable Cs content have Ia3d symmetry. Rb can substitute Cs in a wide range of compositions. Within a narrow range of x = 0.5 ‐ 0.6 immiscibility was revealed. Under Rb‐Cs substitution the cubic lattice parameter, the (Rb,Cs)‐O distances, and the angles between tetrahedra of the I‐43d phase change clearly, while those of the Ia3d phase change slightly. The HTXRD data shows that the I‐43d phase transforms into a Ia3d phase on heating analogously to a change of the composition. As the Cs content increases the transition temperature decreases. The low temperature I‐43d phase shows a higher thermal expansion than the high temperature Ia3d phase. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Intermediates and transport phenomena in two‐temperature synthesis of ZnGeP2

High quality semiconducting ternary compound ZnGeP₂ was synthesized by a modified two‐temperature technique using high purity elemental zinc, germanium and phosphorus as the starting materials. Transport phenomena of zinc and phosphorus vapors and the major reaction intermediates, taking place in ZnGeP₂ formation, were studied by interrupting the synthesis process using quenching technique as well as by adjusting the temperatures of cold and hot zones. The powder X‐ray diffraction analysis showed that the major reaction intermediates were ZnP₂, Zn₃P₂, and GeP, which proportions were changed at the different temperature stages. ZnP₂ was formed in the temperature gradient region and ZnGeP₂ was formed in the hot zone when the temperature of the hot zone was higher than 900 °C. The 520‐1040 °C temperature profile was chosen for the ZnGeP₂ synthesis and charge amount per run reached 200 g. The powder X‐ray diffraction pattern of the synthesized ZnGeP₂ compound was in agreement with the standard pattern of ZnGeP₂. These results demonstrated that the synthesized ZnGeP₂ compound was a single phase. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)