Thermal neutron equivalent dose measurements with nanostructured zirconia

This paper reports the experimental results concerning the thermoluminescent measurements of thermal neutron using nanostructured zirconium oxide (ZrO₂) powder prepared by the sol–gel method. Transmission electron microscopy and X-ray diffraction techniques were used for morphological and structural characterization of the compound. Thermal annealing processes for the precipitates were studied. It was observed that the crystalline structure and the crystallinity of the powders depend on the annealing temperature. For temperatures higher than 1100 °C, the material presents the monoclinic phase with average nanocrystallite sizes ranging from 8–10 nm up to ～40 nm. These zirconium oxide materials developed in our laboratory were used in this investigation. Within the experimental uncertainties, these measurements were compared with those obtained using the well-known gamma rays sensitive lithium fluoride (LiF:Mg,Cu,P), also developed in our laboratory.     

Effect of phase transformation on optical and dielectric properties of zirconium oxide nanoparticles

Zirconium oxide nanoparticle (ZrO₂) is synthesized by the hydrothermal method at different calcination temperatures. The structural analysis is carried out by X-ray diffraction and Raman spectra. The sample prepared at 400 °C and 1100 °C showed the cubic and monoclinic phase, respectively, and the sample calcined at 600 °C and 800 °C showed the mixed phase with co-existence of cubic and monoclinic phases. Furthermore, the morphology and particle size of these samples were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. The band gap estimated from UV–Vis spectra of ZrO₂ (zirconia) nanocrystalline materials calcined at different temperatures from 400 °C to 1100 °C was in the range of 2.6–4.2 eV. The frequency dependence of dielectric constant and dielectric loss was investigated at room temperature. The low frequency region of dielectric constant is attributed to space charge effects.     

Thermoluminescence (TL) of europium-doped ZrO2 obtained by sol–gel method

This article reports the preparation and characterization of europium-doped zirconium oxide (ZrO₂:Eu³⁺) formed by homogeneous precipitation from propoxyde of zirconium [Zr(OC₃H₇)₄]. The alkoxide sol gel process is an efficient method to prepare the zirconium oxide matrix by the hydrolysis of alkoxide precursors followed by condensation to yield a polymeric oxo-bridged ZrO₂ network. All compounds were characterized by thermal analysis and the X-ray diffractometry method. The thermoluminescence (TL) emission properties of ZrO₂:Eu³⁺ under beta radiation effects are studied. The europium-doped sintered zirconia powder presents a TL glow curve with two peaks (Tmax) centered at around 204 and around 292 ^°C, respectively. TL response of ZrO₂:Eu³⁺ as a function of beta-absorbed dose was linear from 2 Gy up to 90 Gy. The europium ion (Eu³⁺)-doped ZrO₂ was found to be more sensitive to beta radiation than undoped ZrO₂ obtained by the same method and presented a little fading of the TL signal compared with undoped zirconium oxide.     

Synthesis and magnetic properties of Cu0.5Ni0.5Fe2O4 nanoparticles produced by glycothermal and hydrothermal processes

Cu_0.5Ni_0.5Fe₂O₄ nanoparticles have been synthesized in ethylene glycol solution and in deionised water. The glycothermal reaction was carried at 200°C under gauge pressure of 100 psi. The hydrothermal treatment was done at 100°C under zero pressure. Complete single-phase cubic spinel structure in the samples made by glycothermal (sample G) and hydrothermal (sample H) processes formed after annealing at 600°C and 900°C respectively. The coercive field of sample H increases from 72 Oe to 133 Oe after sintering at 700°C and then decrease to 11 Oe on sintering at 1000°C. This variation is attributed to surface effects and crossover from single to multidomain behavior due to increasing particle size.     

Effect of calcination conditions on lithium conductivity in Li<Subscript>1.3</Subscript>Ti<Subscript>1.7</Subscript>Al<Subscript>0.3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> prepared by sol-gel route

In order to study the influence of powder calcination temperature on lithium ion conductivity, synthesized Li_1.3Ti_1.7Al_0.3(PO₄)₃ (LATP) was calcined at temperatures between 750 and 900 °C. The shape and size of the particles were characterized employing scanning electron microscopy (SEM), and specific surface area of the obtained powder was measured. The crystallinity grade of different heat-treated powders was calculated from XRD spectra. Posteriorly, all powders were sintered at 1100 °C employing field-assisted sintering (SPS), and the electrical properties were correlated to the calcination conditions. The highest ionic conductivity was observed for samples made out of powders calcined at 900 °C.     

Production and Characterization of Zirconia (ZrO2) Ceramic Nanofibers by Using Electrospun Poly(Vinyl Alcohol)/Zirconium Acetate Nanofibers as a Precursor

Zirconia (ZrO₂) inorganic ceramic nanofibers were produced using electrospinning of the poly(vinyl alcohol)/zirconium acetate as a precursor followed by calcinating and sintering to decompose the polymer and turn the metal salt (zirconium acetate) into the metal oxide. Characterization of the nanofibers, including polymer thermal decomposition, chemical and crystal structure, phase transformations, and fiber morphology were investigated by simultaneous thermal analysis (STA), thermomechanical analysis (TMA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). The results showed that the polymer decomposition started at 250°C and zirconia nanofibers with different phases (tetragonal and monoclinic) were obtained by the calcination of the precursor nanofibers at various temperatures between 500°C and 1100°C. The initially crystallized zirconia phase, which formed at 500°C, was tetragonal and with increasing calcination temperature, zirconia nanofibers with increasing amount of monoclinic phase were formed. Consequently, at 1100°C, the tetragonal phase disappeared and was transformed to the monoclinic phase of the zirconia completely. Increasing the calcination temperature caused the fiber average diameter decrease and grain growth took place due to the removal of the polymer and organic groups; neighboring grains sintered to each other and formed fibers with a high aspect ratio. At 1100°C the grains size was about the same as the fiber diameter.     

A comparison of different powder compaction processes adopted for synthesis of lead-free piezoelectric ceramics

Barium zirconium titanate, Ba(Zr_0.15Ti_0.85)O₃ nano-crystalline powders were synthesized using highenergy ball milling. The calcined powders were compacted adopting two different approachesviz. the conventional uniaxial pressing and cold-isostatic pressing (CIP) and the compactswere sintered at 1350 °C. Asingle phase perovskite structure was observed in both cases. BZT ceramics compacted usingCIP technique exhibited enhanced dielectric and ferroelectric properties compared toceramics compacted by uniaxial pressing. The polarization current peaks have been used inthis paper as an experimental evidence to prove the existence of ferroelectricity in theBZT ceramics under study. The peak polarization current was found to be ~700% higher in case of coldiso-statically compacted ceramics. Similarly electric field induces strain showed amaximum strain (S_max) of 0.08% at an electric fieldof 28 kV/cm. The dielectric and ferroelectric properties observed are comparable to singlecrystals of the same material.     

Influence of synthesis conditions on structural,optical and magnetic properties of iron oxide nanoparticles prepared by hydrothermal method

The iron oxide nanoparticles were synthesized by a simple hydrothermal method at different heating temperatures and pH conditions. The synthesized materials were characterized by X-ray diffractometer, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, UV–visible spectrometer and vibrating sample magnetometer. With increment in pH of the synthesized materials were resulted in orthorhombic (goethite) and cubic (magnetite) structures at pH 6 and 12, respectively. The banding nature of synthesized materials was analyzed by infrared spectra. The synthesized powders at 130?°C showed higher percent of nanorods (length = 90–120 nm) in addition to lower percentage of nanoparticles. The material at pH 12 consisted of maximum nanoparticles with size = 10–60 nm with small agglomerations. Band gap energy of synthesized materials was 2.2–2.8 eV. Herein, the reaction conditions tuned the saturation magnetization (M_S). The maximum M_S (59.38 emu/g) was obtained at pH 12 and lower M_S (0.65 emu/g) was observed at pH 6 due to intrinsic property of goethite phase.     

Hydrothermal-microwave synthesis of fine disperse powders of simple and complex zirconium and hafnium oxides

Hydrothermal and hydrothermal-microwave techniques were used to synthesize nanocrystalline (8–20 nm in size) powders of zirconium and hafnium dioxides at 180 and 250°C and fine disperse powders of barium zirconate and hafnate at 150°C (hafnium compounds were first synthesized by the hydrothermal-microwave method). Analysis of physicochemical properties of samples allowed us to reveal the synergetic effect of the hydrothermal treatment and microwave action.     

Temperature-controlled fabrication of SnO<Subscript>2</Subscript> nanoparticles via thermal heating of Sn powders

We report a method by which we have produced nano-sized crystalline tin oxide (SnO₂) particles with a rutile structure. We have employed thermal evaporation of solid Sn powders in ambient air. Samples were characterized by scanning electron microscopy, X-ray powder diffraction, transmission electron microscopy, and photoluminescence (PL) spectroscopy. The size of SnO₂ particles in an agglomerated state was found to decrease on decreasing the synthesis temperature in the range of 700–850 °C. The product synthesized at a low temperature of 700 °C was comprised of a trace amount of tetragonal SnO phase. Photoluminescence spectra showed visible light emission, with its overall intensity being increased on increasing the synthesis temperature. PACS 81.07.Wx; 81.05.Hd; 61.10.Nz; 68.37.Hk; 68.37.Lp     

Hydrothermal synthesis of hierarchical WO3 nanostructures for dye-sensitized solar cells

Hierarchical architectures consisting of one-dimensional (1D) nanostructures are of great interest for potential use in energy and environmental applications in recent years. In this work, hierarchical tungsten oxide (WO₃) has been synthesized via a facile hydrothermal route from ammonium metatungstate hydrate and implemented as photoelectrode for dye-sensitized solar cells. The urchin-like WO₃ micro-patterns are constructed by self-organized nanoscale length 1D building blocks, which are single crystalline in nature, grown along (001) direction and confirm an orthorhombic crystal phase. The obtained powders were investigated by XRD, SEM, TEM and UV–Vis Spectroscopy. The photovoltaic performance of dye-sensitized solar cells based on WO₃ photoanodes was investigated. With increasing the calcination temperature of the prepared nanopowders, the light-electricity conversion efficiency (η) was increased. The results were attributed to increase the crystallinity of the particles and ease of electron movement. The DSSC based on hierarchical WO₃ showed a short-circuit current, an open-circuit voltage, a fill factor, and a conversion efficiency of 4.241 mA/cm², 0.656 V, 66.74, and 1.85 %, respectively.     

Synthesis and characterization of tin oxide (SnO2) nanocrystalline powders by a simple modified sol–gel route

This paper reports the synthesis and characterization of nanocrystalline tin oxide (SnO₂) powders by a simple method using a chitosan–polymer complex solution. To obtain SnO₂ nanocrystalline powders, the precursor was calcined at 500–600 °C in air for 2 h. The phase composition of calcined samples was studied by X-ray diffraction (XRD). The XRD results confirmed the formation of a SnO₂ phase with tetragonal structure. The particle sizes of the powder were found to be 22–23 nm as evaluated by the XRD line broadening method. TEM investigation revealed that the SnO₂ samples consist of crystalline particles of 19–21 nm. The corresponding selected area electron diffraction analysis further confirmed the formation of the tetragonal structure of SnO₂ without any impurity phases. The optical properties of the samples were explored by Fourier transform infrared spectroscopy, optical absorption and Raman studies. The estimated band gaps of the samples were in the range of 3.44–3.73 eV.     

Crystallization kinetics and growth mechanism of Pb(Zr0.52·Ti0.48)O3 nanopowders

In this study, Pb(Zr_0.52·Ti_0.48)O₃ nanopowders were synthesized via sol–gel process. Particle morphology, crystalline phases and thermal behavior were characterized by scanning electron microscopy, X-ray diffraction and simultaneous thermal analyzer, respectively. The X-ray diffraction pattern showed perovskite phase clearly. The non-isothermal activation energy for the perovskite crystallization in Pb(Zr_0.52·Ti_0.48)O₃ gel powders was 224.91 kJ mol^?1. Both growth morphology parameter (n) and crystallization mechanism index (m) are close to 3.0, indicating that the bulk nucleation is dominant in the perovskite PZT formation. To determine dielectric properties, the calcined Pb(Zr_0.52·Ti_0.48)O₃ nanopowders were pressed using uniaxial press. It was found that the Pb(Zr_0.52·Ti_0.48)O₃ disks, by sintering at 1,200 °C for 2 and 10 h, and at 1 kHz frequency, had 966 and 1,490 of the dielectric constant, respectively.     

Eu-doped B2O3–ZnO–PbO glass phosphor powders with?spherical shape and fine size prepared by spray pyrolysis

Eu-doped B₂O₃–ZnO–PbO glass phosphor powders with spherical shape and fine size were directly prepared by spray pyrolysis. The glass phosphor powders prepared at a temperature of 1100°C had broad XRD peak at around 28°. One glass phosphor powder was formed from one droplet at the preparation temperature range from 900 to 1100°C. The mean size of the glass phosphor powders was 0.75 μm. The glass transition temperature (T _g ) of the glass phosphor powders prepared by spray pyrolysis was 378.5°C. The excitation spectrum of the glass phosphor powders prepared at the optimum preparation temperature of 1100°C had bands at 362, 381, 392, 463, 525, and 532 nm. The glass phosphor powders had emission spectra with bands at 579, 614, and 653 nm. The glass phosphor powders with doping concentration of Eu of 7 wt% had the maximum photoluminescence intensity. The glass phosphor layer formed from the glass phosphor powders had high transparencies above 90%.     

Phase transformation of ZrO2 nanoparticles produced from zircon

This article focuses on the phase transformation of zirconia (ZrO₂) nanoparticles produced from zircon using a bottom-up approach. The influence of mechanical milling and thermal annealing on crystalline phase transformation of ZrO₂ nanoparticles was explored. It was found that the iron oxide, as an inherent impurity present in ZrO₂ nanoparticles, produced from zircon stabilises the cubic phase after calcination at 600°C. The stabilised cubic phase of ZrO₂ nanoparticles was disappeared and transformed into partial tetragonal and monoclinic phases after mechanical milling. The phase transformation occurred on account of the crystal defect induced by high-energy mechanical milling. The destabilisation of cubic phase into monoclinic phase was observed after the thermal annealing of ZrO₂ nanoparticles at 1000°C. The phase transitions observed are correlated to the exclusion of iron oxide from the zirconia crystal structure.     

Processing and characterization of ultra-thin yttria-stabilized zirconia (YSZ) electrolytic films for SOFC

Sub-micron yttria-stabilized zirconia (YSZ) electrolyte layer was prepared by a liquid state deposition method and with an average thickness of 0.5 μm to improve the performance of the anode-supported solid oxide fuel cell (SOFC). The YSZ precursors, containing yttrium and zirconium species and an additive, poly-vinyl-pyrrolidone (PVP), were spin-coated on a Ni/YSZ anode substrate. Several properties, including crystalline phases, microstructures, and current–voltage (I–V) characteristics, were investigated. The thin film of 4 mol% Y₂O₃-doped ZrO₂ (4YSZ) consisted of cubic, tetragonal, and a trace of monoclinic phases, and showed a crack-free layer after sintering at 1300 °C. The anode supported SOFC, which consists of the Ni–YSZ anode, 4YSZ electrolyte, and Pt/Pd cathode, showed power densities of 477 mW/cm² at 600 °C, and 684 mW/cm² at 800 °C. Otherwise, the surface cracks of the other YSZ-coated samples (e.g. 8YSZ) can be repaired by a multi-coating method.     

Controlling the composition and the magnetic properties of hexagonal Co2Z ferrite powders synthesized using two different methods

Polycrystalline Co₂Z hexaferrite (Ba₃Co₂Fe₂₄O₄₁) powders have been prepared via two wet chemical routes: sol gel auto-combustion (SGA) and co-precipitation (CP) methods. The effects of synthesis conditions on the crystal structure, crystallite size, morphology, and magnetic properties were systematically studied. The results revealed that single Co₂Z hexaferrite phase was obtained at relatively low temperature 1250 ^°C for 5 h via the SGA method whereas it was formed at 1300 ^°C for 6 h using the CP pathway. The microstructures of the pure powders appeared as a hexagonal platelet-like structure. The particle size of the pure Co₂Z powders by CP method was higher than as obtained by the SGA method. The soft characteristic loops were obtained for single Co₂Z hexaferrite phase synthesized using both routes. High saturation magnetization (M _s =53.7 emu/g) was achieved for the Co₂Z powder synthesized via the CP method compared with the formed single phase synthesized via the SGA method (M _s =47.0 emu/g). Good dielectric and dynamic magnetic properties were obtained for the Co₂Z powder synthesized via the SGA method in comparison with the sample synthesized via CP method. The results obtained are discussed on the basis of electromagnetic theory.     

Spherical shape BaO-ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass powders prepared by spray pyrolysis

Fine-sized BaO-ZnO-B₂O₃-SiO₂ (BZBS) glass powders were directly prepared by high temperature spray pyrolysis. The hollow glass powders prepared at low preparation temperature of 1000 °C had a low density of 2.65 g/cm³. However, the densities of the BZBS powders obtained at preparation temperatures of 1200 and 1400 °C were each 3.92 and 4.13 g/cm³. The mean size of the BZBS glass powders prepared by spray pyrolysis at preparation temperature of 1400 °C was 0.98 μm. The glass transition temperature (T_g) of the prepared BZBS glass powders was 518.9 °C. The dielectric layers formed from the prepared BZBS glass powders with a dense structure had a clean surface and a dense inner structure without voids at the firing temperature of 580 °C. The transparencies of the dielectric layers formed from the prepared BZBS glass powders were higher than 90% within the visible range. PACS 42.70.Ce; 85.60.Pg; 71.55.Jv     

Mössbauer effect studies on the formation of iron oxide phases synthesized via microwave–hydrothermal route

Microwave–hydrothermal (MH) route was employed to synthesize various iron oxide phases in ultra-fine crystalline powders by using ferrous sulphate and sodium hydroxide as starting chemicals. All chemical reactions were carried out under identical MH conditions, namely, at 190°C, 154 psi, 30 min, by varying the molar ratio (MR) of FeSO₄/NaOH in the aqueous solutions. The variation of MR has a dramatic effect on the crystallization behavior of various phases of iron oxides under MH processing conditions. For example, spherical agglomerates of Fe₃O₄ powder were obtained if MR equal to 0.133 (pH?>?10 sample A). On the other hand non-stoichiometric Fe₃O₄ powders (Sample B) were obtained for all higher MR of FeSO₄/NaOH between 0.133 and 4.00 (6.6?2O₃ powders (sample C) were produced. Fe⁵⁷ Mössbauer spectra were recorded for all the three sets of samples at room temperature. In the case of sample B, temperature dependent Mössbauer spectra were recorded in the range of 77–300 K to understand the non-stoichiometric nature of Fe₃O₄ powders. All these results are discussed in the present paper.     

Mossbauer investigations of corrosion environment influence on Fe valence states in oxide films of zirconium alloys

Mössbauer investigations about iron atom redistribution in oxide films of zirconium alloys subjected to corrosion at 500°C in pure oxygen and water pair have been analysed. The alloys were also subjected to autoclave conditions at a pressure of 10.0 MPa and autoclave conditions at 350°C and at a pressure of 16.8 MPa, using distilled water and water with additives of lithium and fluorine. It is shown that, depending on the corrosion environment, various compounds of iron, such as α-Fe₂O₃, Fe₃O₄, and FeO, as solid solutions of iron in ZrO₂ are formed in oxide films.