Eutectic structure from amorphous Al2O3-ZrO2-Y2O3 system by rapid quenching technique for potential hybrid solar cell application

Abstract

Ternary Al₂O₃-ZrO₂-Y₂O₃ samples with a eutectic composition were prepared using the rapid quenching method, with some samples further annealed at 1300°C for 30?min and then slow cooled. The microstructural evolution was observed with XRD, SEM, and TEM. The SEM and TEM observations of the ternary samples agreed with the XRD. The rapid quenched sample was an amorphous phase with a small amount of crystalline phase mixed in. Observations showed that the rapid quenched and annealed sample was completely crystalline with a granular structure and well defined crystals of 40-60?nm in size.     

Synthesis of NdAlO3 with good microwave dielectric properties by stearic acid method

In this study, NdAlO₃ with perovskite structure was synthesized by the stearic acid method at relatively low temperature. The structural characteristics of the as-synthesized product were identified by TG–DSC, XRD, FT–IR, SEM, and TEM techniques. Using the powders as starting materials, NdAlO₃ bulk microwave ceramics were prepared, and the corresponding densification process, microstructural and dielectric properties were studied. The XRD and FI–IR results confirmed that single phase NdAlO₃ could be prepared at low temperature by the stearic acid method. A unique two-dimensional platelike morphology with an unevenly dispersed bubble shape structure was observed in the calcined powder. However, the TEM result revealed that the powder calcined at 800 °C had a good dispersity accompanied with narrow particle size distribution within a range of 20–35 nm. The average particle size of 27.3 nm was in accordance with that calculated from the XRD data. Using the powder calcined at 800 °C as raw materials, the as-obtained NdAlO₃ ceramics sintered at 1500 °C for 4 h possessed the highest density and favorable combined microwave dielectric properties (i.e., ε_r = 23.02, Q × f = 65320 GHz, and τ_f = −32.4 ppm/^°C). The present work developed a fast, energy-efficient approach to synthesize NdAlO₃ powder used as promising raw materials of microwave dielectric ceramics.     

Fabrication and optical properties of transparent LaErZr2O7 ceramic with high excess contents of La and Er

In this study, transparent LaErZr₂O₇ ceramic with high excess La and Er contents (nominally La_1.28Er_1.28Zr₂O_7.84) was successfully prepared by vacuum sintering at 1850?°C for 6?h using nanosized powder. The XRD, SEM, EDX and TEM results reveal that the single pyrochlore phase in the powder sample transforms to the coexistence of La-rich pyrochlore phase and Er-rich defect fluorite phase after high temperature sintering. The high excess amounts of La and Er favor the formation of pyrochlore structure. Despite the coexistence of two phases, the sample with 1?mm thickness shows excellent in-line transmittance in the visible to mid-infrared region (as high as 81% at 1100?nm). The upconversion and infrared emission under 980?nm exciting were measured and discussed as well.     

Effect of Temperature on Structural and Optical Properties of Boehmite Nanostructure

The nanocrystalline boehmite, γ‐AlOOH, was synthesized by the hydrothermal method using AlCl₃·6H₂O and urea as precursors, and the effect of different annealing temperatures resulting in different phases of alumina (Al₂O₃) was obtained. The effects of different temperature on the phase and micrographs of the prepared γ‐AlOOH nanostructures were investigated. The obtained products were characterized by X‐ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy techniques. The XRD results show that with the increasing temperature, the transformation of boehmite into well‐crystallized α‐Al₂O₃ and the morphology from nanoplatelets with spindle‐like edges to vermicular structure take place. The crystallite size and lattice parameters were calculated by Rietveld refinement. The convincing evidence for the crystal phase of the as‐prepared and annealed samples was provided by FTIR spectra. The Raman spectra unveil the change in vibrational modes of the phase transition alumina.     

Visible light induced decomposition of organic compounds on WO3 loaded PtPb co-catalysts

Tungsten oxide (WO₃)-supported ordered intermetallic PtPb nanoparticles (PtPb NPs/WO₃) were prepared through a co-reduction of Pt and Pb precursors with sodium borohydride in anhydrous methanol containing WO₃. The PtPb NPs/WO₃ were characterized based on the crystal structure obtained through powder X-ray diffraction (pXRD) as well as X-ray photoemission spectroscopy (XPS) and transmission electron microscopy (TEM). The formation of an ordered PtPb intermetallic phase on the WO₃ surface was confirmed. The PtPb NPs/WO₃ were more efficient when decomposing acetic acid (AcOH) and acetaldehyde (AcH) with visible light irradiation compared to the same process over WO₃ loaded with Pt nanoparticles (Pt NPs/WO₃).     

An attempt to predict the mechanism of Mo-Ni-O powders electrodeposition from the results of their TEM analysis

The Mo-Ni-O powders were electrodeposited from ammonium sulfate containing electrolytes with different Mo/Ni ion concentration ratios. The phase composition of these powders was investigated using TEM, EDS and XRD analysis. The TEM analysis showed that two types of particles were present in the powders: amorphous and crystalline. For crystalline particles it was found that two phases, MoO₃ and MoNi₄ prevail in all powders, while the NiO phase was detected in the powder electrodeposited at Mo/Ni = 0.3/1. These findings are in good agreement with our previous results where MoO₃, MoNi₄ and NiMoO₄ phases were detected in the recrystallized Mo-Ni-O powders. In this work we discovered that the NiMoO₄ phase was formed by solid state reaction between NiO and MoO₃ at elevated temperature.     

Preparation of hydrophobic polymer particles by radical polymerization and subsequent modification into magnetically doped particles

The application potential of hydrophobic polymer is numerous. Lauryl methacrylate (LMA) having long alkyl chain is a commercially available hydrophobic monomer. In this investigation, poly‐LMA (PLMA) latex particles were prepared by suspension polymerization in aqueous media using 2,2′‐azobis(isobutyronitrile) (AIBN) in presence of poly(vinyl alcohol) (PVA) as steric stabilizer. The preparation kinetics was studied in detail in terms of percentage yield and particle size variation. Low glass transition temperature (～ ?65°C) associated with high flexibility did not allow electron micrographic observation though ¹H‐NMR and particle size measurement confirmed the formation of PLMA latex. To improve the glass transition temperature, aqueous emulsion copolymerization of LMA with methyl methacrylate (MMA) was carried out. The solubility of LMA was improved by adding ethanol to the aqueous phase. Two types of polymeric stabilizers, PVA and poly(vinyl pyrrolidone) (PVP) were used to stabilize the colloidal particles. The nature of the stabilizer affected both morphology and final rate of polymerization. The hydrophobic P(LMA‐MMA) copolymer particles were subsequently modified by nanosized magnetic (Fe₃O₄) particles by two different methods. The in situ formation of Fe₃O₄ particles in presence of P(LMA‐MMA) was found to be suitable for the preparation of magnetic latex particles. Scanning electron microscope (SEM), FTIR, transmission electron microscope (TEM), X‐ray diffraction (XRD) and energy‐dispersive X‐ray spectroscopy (EDX) were used for the characterization of magnetically doped particles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Highly efficient ruthenium and ruthenium–platinum cluster-derived nanocatalysts for hydrogen production via ethanol steam reforming

Alumina-supported Ru and Ru–Pt nanoparticles, obtained by the decarbonylation of organometallic cluster precursors, were found to be highly active and selective catalysts for ethanol steam reforming. These catalysts outperformed a commercial Ru/Al₂O₃ catalyst, as well as catalysts that had been prepared from inorganic salts using the conventional impregnation method. The highly dispersed nanoparticles derived from cluster precursors were much smaller than the salt-derived nanoparticles, as evidenced by TEM and powder XRD studies; this might account for the improved catalytic performance of the cluster-derived catalysts. Finally, EDX studies suggest that Pt played a role in resisting coke formation in both cluster- and salt-derived catalysts.     

Fabrication of biphasic calcium phosphates nanowhiskers by reflux approach

Nanowhiskers of biphasic calcium phosphates composed of monetite/hydroxyapatite were fabricated using a cost-effective reflux hydrothermal approach from calcium nitrate and ammonium hydrogen phosphate precursors in presence of urea. The produced nanowhiskers were characterized using, FT-IR-spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron micrograph (TEM) and BET surface area determination. The major phase in Biphasic was (monetite, CaHPO₄.) and their grown crystals were morphologically formed with irregular sizes of well defined rod or whiskers crystal structure. The specific surface area of these fabricated nanowhiskers was found to be 8.48?m²/g according to BET studies. The N₂ adsorption/desorption isotherm of the as prepared monetite calcium phosphate is of type IV indicating that this material has a mesoporous structure. The produced nanowhiskers had 80% of monetite and 20% is hydroxyapatite. By controlling the parameters of the reflux approach it is possible to manipulate the composition and the size of these produced nanowhiskers.     

Synthesis of Yttria Nanopowders by Two Precipitation Methods and Investigation of Synthesis Conditions

Yttrium oxide nanopowder was successfully synthesized by two precipitation methods, through which Y₂O₃ nanopowder was prepared by ammonium hydroxide and ammonium hydrogen carbonate as precipitants. Hydroxide and carbonate precursors of Y₂O₃ with approximate composition of Y(OH)₃ and Y₂(CO₃)₃, respectively, were synthesized using yttrium nitrate as the starting salt. XRD results show cubic yttrium oxide phase for annealed samples. SEM and TEM images show that samples are composed of agglomerated and nonagglomerated nanoparticles with different shapes and sizes. Optimal conditions for synthesis of nanoparticles were defined as 3‐h aging time, ammonium hydrogen carbonate as precipitant, and calcination temperature of 1000°C.     

Partial Oxidation of Methane to Syngas over Calcined Ni–Mg/Al Layered Double Hydroxides

The catalytic partial oxidation of CH₄ to syngas was carried out over an Ni–Mg/Al mixed-oxide catalyst prepared from layered double hydroxide-type precursors. The catalysts were characterized by XRD, TPR, UV-DRS, XRF, BET and CHNS analysis. The effects of the catalyst composition and the calcination temperature on the catalytic performance and the extent of catalyst deactivation were investigated. Ni–Mg/Al oxide catalysts converted CH₄ into syngas efficiently with high selectivity. The catalyst performance was strongly related to the Ni particle size and the calcination temperature. The catalysts that were calcined at higher temperature exhibited a better catalytic performance. In conclusion, the NiAl₂O₄ spinel phase had a positive effect on the stability of the catalyst.     

Molten salt synthesis of SrTiO3 nanocrystals using nanocrystalline TiO2 as a precursor

A molten salt method was proposed to synthesize SrTiO₃ nanocrystals in the eutectic NaCl–KCl at 700 °C for 6 h, by using the homemade TiO₂ nanocrystals and commercial Sr(NO₃)₂ powder as raw materials. Besides, a control experiment with the commercial TiO₂ submicron-sized crystallites as a precursor was also conducted. The structure and composition of the obtained products were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The results from XRD and XPS revealed the preparation of pure cubic phase SrTiO₃ powders. The TEM observation demonstrated that the nanocrystalline TiO₂ precursor played an important role in the current molten salt synthesis of SrTiO₃ nanocrystals, which were likely formed by the template formation mechanism.     

Aqueous ammonia route to Cu1.8S with triangular and rod-like shapes

Digenite crystalline Cu_1.8S was synthesized through solvothermal reaction of CuCl₂·2H₂O and sulfur powder at low temperature in aqueous ammonia. X-ray powder diffraction (XRD) pattern indicates Cu_1.8S is cubic phase. Transmission electron microscope (TEM) shows Cu_1.8S obtained at 160 °C is triangular and Cu_1.8S formed at 140 °C is rod-like. X-ray photoelectron spectrum (XPS) was used to determine the composition of as prepared products. The influence of solvent and reaction temperature was investigated. Raman spectrum of Cu_1.8S was recorded.     

Synthesis and magnetic properties of nano-sized Cu0.5Ni0.5Fe2O4 via citrate and aloe vera: A comparative study

In this report, Cu_0.5Ni_0.5Fe₂O₄ nanoparticles were synthesized by solgel using eco-friendly aloe vera extract and citric acid separately and their properties were discussed. Structural, Functional, morphological, magnetic properties of the samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Transmission electron microscopy (TEM), Vibrating sample magnetometer (VSM). XRD exhibited the samples have single phase cubic spinel with average size of 46.4?nm and 35.45?nm. Two characteristics bands of ferrite were confirmed by FTIR. TEM indicated different morphology of the samples with some regularity. VSM data showed that higher coercivity for the sample prepared by aloe vera extract.     

Crystallization behaviour and microstructural development in ZrSiO4 and V-ZrSiO4 solid solutions from colloidal gels

Zircon and vanadium-doped zircon blue pigments were prepared by heat treatment of gel precursors. Gels with nominal compositions V_x-ZrSiO₄ with x=0.0, 0.002, 0.004, 0.02 and 0.2 were prepared by formation of a silica coating on zirconia colloidal particles previously obtained. The crystallization behavior and microstructural evolution were studied using X-ray powder diffraction (XRD), energy dispersive X-rays microanalysis (EDX), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results indicated that the vanadia loading in the precursor gels speeds up the crystallization of the vanadium-containing tetragonal zirconia solid solutions and their transformation to the monoclinic form. The overall conversion rate of gel precursors to pigmenting powders increased when the vanadia content was higher. Microstructural data revealed that the used procedure for the preparation of vanadium-zircon pigments allowed high-purity and non-agglomerated powders with controlled particle size to be obtained.     

Microstructure of laser cladded carbide reinforced Inconel 625 alloy for turbine blade application

Inconel 625 - WC metal matrix composite is a very promising material for high temperature applications. In this study, microstructure investigation and phase composition of a mixture between Inconel 625 and fine tungsten carbide (φ≈0.64 µm) was performed by means of XRD, SEM with EDS and TEM with EDS. Two powder mixtures were prepared: 20 wt% of WC and 30 wt% of WC and deposited on Inconel 625 substrate by laser cladding obtaining a crack and pore free material. The high temperature of the process resulted in partial dissolution of WC in Inconel 625 matrix. In sample containing 30 wt% of WC appearance of topologically close-packed (TCP) phases was observed at grain boundaries. WC, W2C, NbC, W₆C_2.54 and (W,Cr,Ni)₂₃C₆ were detected by XRD. Angular residual carbides and spherical oxide precipitates were visible in both types of samples. Processes occurring during laser action were explained.     

Combustion synthesis and characterisation of lanthanum hexa-aluminate

Abstract

Lanthanum hexa-aluminate (LHA) is considered a promising material for thermal barrier coatings for gas turbine applications as well as oxidation resistant coatings for fibres in oxide based ceramic composites. Combustion synthesis has attractive advantages such as simple experimental setup, low cost, short reaction time, energy savings due to exothermic reaction, better control of stoichiometry and fine powder size. The present study involves combustion synthesis of LHA using lanthanum and aluminium nitrates as oxidising precursors, and urea as fuel. The precursor salts were dissolved in a minimum amount of deionised water and the solution was heated in a mantle heater to temperatures of around 300–350°C, at which combustion takes place with rapid evolution of gas. The LHA powder was also prepared by a precipitation route for comparative study. The as synthesised powders were calcined at up to 1450°C and subjected to X-ray diffraction for phase evolution studies. Product powders were then characterised. The influence of the lanthanum/aluminium molar ratio in the starting composition and the effect of temperature on the formation sequences of lanthanum monoaluminate (LMA) and LHA and on the conversion of LMA to LHA are discussed.     

Synthesis of yttrium aluminum garnet (YAG) powder by homogeneous precipitation combined with supercritical carbon dioxide or ethanol fluid drying

YAG precursors were synthesized by the urea method in aqueous solution using supercritical carbon dioxide and ethanol fluid drying technique, respectively. The composition of the precursors, the phase formation process and the properties of the calcined powders were investigated by means of XRD, IR, TG/DSC, BET, TEM and SEM. Compared with the classically prepared powders at room temperature in air, the amorphous precursor dried by supercritical CO₂ fluid was loosely agglomerated and directly converted to pure YAG at about 900 °C. The resultant YAG powders showed good dispersity with an average crystallite size about 20 nm and specific surface area of 52 m² g⁻¹. However, the precursor dried by supercritical ethanol fluid was crystalline. Extensive phase segregation occurred during the drying process and resulted in the formation of separate phases such as monoclinic Y(OH)₃ and pseudoboehmite. YAM and YAP phases appeared in the calcination process and phase pure were not detected until 1200 °C.     

A meltable precursor for zirconium carbide ceramics and C/C-ZrC composites

For process simplification and rapid densification of ceramic composites, a meltable single-source ZrC precursor was prepared by condensing zirconium acetylacetonate (Zr(acac)₄) at 190?°C for 40–150?min. The preparation of ZrC precursor and the conversion from precursor to ceramics were investigated by using FTIR and NMR spectroscopies, GPC, DSC-TGA, XRD, SEM, EDS and TEM. The precursor had low viscosity (~ 10?mPa?s) and proper processing window (60?min) for precursor infiltration and pyrolysis (PIP). The ceramic yield at 1650?°C was 29.6%, and EDS revealed that the composition was (ZrC)_0.337(HfC)_0.0025(ZrO₂)_0.044C_0.1865. The ceramics were composed of 0.2–0.5?µm grains which aggregated to form a stacked structure surrounded by amorphous carbon. The preparation processes were designed, and C/C-ZrC composites with the density of 2.45?g/cm³ were successfully fabricated through 11 cycles of PIP with Zr(acac)₄. In conclusion, the synthetic method provides a simple and cheap route for precursors, and allows combined composite preparation with high efficiency.     

Preparation of γ-alumina powder from kaolin derived aluminium sulphate solution and its stability by BaO addition

Abstract

The synthesis of γ-alumina powder from kaolin derived aluminium sulphate solution is described and results are reported on the effect of BaO additions made by two different methods, precipitation mixing and mechanical mixing of BaCl₂ .2H₂O, on the thermal stability of γ-alumina powder at high temperatures. The powders were characterised by XRD, SEM, TEM, and measurements of surface area by the BET method. It was found that powder prepared by precipitation mixing was more thermally stable at high temperatures than powder prepared by mechanical mixing, indicating that the precipitation mixing was more effective in retarding the γ-to α-alumina phase transformation at high temperature.