Preparation and properties of nanocrystal SmBO3 by nitrate-citrate sol-gel combustion method

Nanocrystal SmBO3 powders were synthesized by nitrate-citrate sol-gel combustion method. The phase evolution, morphologies and absorbency of the synthesized powders were characterized by X-ray diffraction (XRD), Field emission scanning electronic microscope (FESEM), Fourier transform infrared spectroscopy (FTIR) and UV-3101PC spectrophotometer (UVPC), respectively. XRD and FESEM re-sults showed that pure SmBO3 phase was obtained at 750 ℃, with an average original particle size of about 100 nm. FTIR showed that there were apparently concentrated absorbent peaks between 500 and 1400 cm-1. Moreover, the reflectivity of the powders apparently decreased at the wavelength between 1.05 and 1.15 μm. Therefore, SmBO3 might be a kind of absorbent material for infrared laser.     

Optical property of SmAlO3 applied as 1.06μm laser absorbing material

SmAlO3 powders were successfully synthesized through the citrate sol-gel combustion method. The phase evolution of the prepared powders were characterized using thermal gravimetric （TG） analysis, differential scanning calorimetry （DSC） analysis and Fourier transform infrared spectroscopy （FTIR）. X-ray diffraction （XRD） was applied to examine the purity of the powders. The re-flective properties of SmAlO3 with changing temperatures were investigated by ultraviolet-visible near-infrared spectrophotometer （UVPC） specular reflection spectrum. The results displayed that pure SmAlO3 phase with preferable reflectivity at 1.06μm could be obtained at 900 oC for 2 h. Furthermore, the reflectivity of SmAlO3 at various temperatures from-40 to 500 oC transformed within ±0.1%, and all maintained below 1%at 1.06μm. The absorbance of SmAlO3 in the resin solution was 2.134 and the moral absorption coefficient was about 384.8 in the work. The study indicated that SmAlO3 powders may be a promising kind of heat resistant absorb-ing material for 1.06μm laser defense, which could be further applied to laser absorbing coatings with a wide range of temperatures.     

Synthesis of <Emphasis Type="Italic">α</Emphasis>- and <Emphasis Type="Italic">β</Emphasis>-Rhombohedral Boron Powders<Emphasis Type="Italic"> via</Emphasis> Gas Phase Thermal Dissociation of Boron Trichloride by Hydrogen

The α-rhombohedral and β-rhombohedral crystal structures of pure elemental boron powders have been synthesized via gas phase thermal dissociation of BCl₃ by H₂ on a quartz substrate. The parameters affecting the crystal structures of the final products and the process efficiency, such as BCl₃/H₂ molar ratio (1/2 and 1/4) and reaction temperature (1173 K to 1373 K [900 °C to 1100 °C]), have been examined. The experimental apparatus of original design has enabled boron powders to be obtained at temperatures lower than those in the literature. The surface/powder separation problem encountered previously with different substrate materials has been avoided. Boron powders have been synthesized with a minimum purity of 99.99 pct after repeated HF leaching. The qualitative analysis of exhaust gases has been conducted using a Fourier transform infrared spectroscope (FTIR). The synthesized powders have been characterized using an X-ray powder diffractometer (XRD) and scanning electron microscope (SEM) techniques. The results of the reactions have been compared with equilibrium predictions performed using the FactSage 6.2 (Center for Research in Computational Thermochemistry, Montreal, Canada) thermochemical software.     

Luminescence properties of YAl3（BO3）4 phosphors doped with Eu^3＋ ions

YAl3 （BO3）4： Eu^3＋ phosphors were prepared by the conventional solid state reaction. The phase structure and morphology were investigated by X-ray diffraction （XRD） and scanning electron microscope （SEM）. Doping YAl3（BO3）4： Eu^3＋ phosphors with concentration of Eu^3＋ ions of 0, 2, 5, 8 and 10 mol% were studied and their luminescent properties at room temperature were discussed. The excitation spectrum of Y0.95Eu0.05Al3（BO3）4 was composed of a broad band centered at about 252 nm and a group of lines in the longer wavelength region. In the emission spectra, the peak wavelength was about 614 nm under a 252 nm UV excitation. The optimal doping concentration of Eu^3＋ ions in YAl3（BO3）4： Eu^3＋ phosphors was 8 mol%.     

Synthesis of monodisperse erbium aluminum garnet （EAG） nanoparticles via a microwave method

Uniform Er3Al5O12 spheres are of great value for fabricating optical ceramics. The highly monodisperse and size-controllable erbium aluminum garnet (EAG) precursors for transparent ceramics were successfully synthesized through a new microwave process. The precursors constituted of ultrafine particles joining together by a hydroxyls formed compact network structure in the absence of SO42-, however, the morphologies of the precursors exhibited spheres with trace amount of SO42-. With manipulated programming of microwave irradiation parameters, narrow distributed particles of 40-50 nm were finally obtained by a separation of nucleation and nanocrystal growth. The mechanism behind the influence of microwave irradiation parameters on the growth of EAG precursors was preliminarily analysed. Easily dispersible and pure phase EAG were obtained at 950 ℃. The as-prepared EAG powders were used to fabricate transparent ceramics and transparent polycrystalline EAG ceramics were obtained under hydrogen furnace at 1750 ℃ for 8 h.     

Fabrication and luminescent properties of red phosphor M3BO6:Eu3+(M=La,Y)

A series of red phosphors M₃BO₆:Eu³⁺ (M=La, Y) were synthesized at 1150 °C by conventional solid state reaction method and their luminescent properties were investigated. Structural characterization of the luminescent materials was carried out with X-ray powder diffraction (XRD) analysis. Photoluminescence measurements indicated that the La₃BO₆:Eu³⁺ phosphor exhibited bright red emission centered at about 612 nm 626 nm under UV excited. La₃BO₆:Eu³⁺ phosphor had better luminescent intensity than Y₃BO₆:Eu³⁺ phosphors under the same excitation and measuring conditions. It was shown that the 0.08 mol.% Eu³⁺ ions in La₃BO₆:Eu³⁺ phosphors was optimal. The color parameter indicated that La₃BO₆:Eu³⁺ phosphor was a preferable red phosphor for white LED.     

Multistage sintering approach to prepare Ni3Al/α-Al2O3 composites

The nickel aluminide intermetallic matrix composites (IMC), Ni₇₆Al₂₄B_0.1 with either 5 or 10 vol pct α-Al₂O₃, were synthesized through a multistage sintering approach from the elemental powders of Ni, Al, and oxide of α-Al₂O₃. An electroless nickel-boron (Ni-B) plating process was adopted to improve the contacted interface between the reinforced oxide ceramics and the metal matrix, as well as to supply the atomic scale boron in the metallic matrix of the IMCs. The entire process comprises steps involving preparing a powdery starting material, sealing it within a metal sheath or can, compacting or cold deforming it, preliminarily heating the compacted material at a relatively low temperature, executing a pore-eliminating (mechanical deforming) process to eliminate the pores resulting from the preceding heating step, and sintering the material at a relatively high temperature to develop a transient liquid phase to heal or to eliminate any microcracks, crazes, or collapsed pores from the previous steps. Most of all, it is important that contact with a heat absorbent material, such as a metal sheath, produces the Ni₂Al₃ phase during preliminary heating. This new phase is a brittle and crispy material with a low melting point (1135 °C). It has been found to play an important role in preventing any significant cracks during the pore-eliminating process and in developing a transient liquid phase in the following 1200 °C sintering step. This multistage sintering with a heat absorbent process is beneficial for producing a product that has large dimensions, a desirable shape, good density, and excellent mechanical properties. The resulting elongation of tensile tests in air reaches 14.6 and 8.9 pct for the present 5 and 10 vol pct powder metallurgy IMCs, respectively.     

Hydrothermal synthesis of dy-doped BaTiO3 powders

Submicron-sized (∼200 nm), monodisperse, and spherical powders of pure and dysprosium (Dy)-doped (0.8 at. pct) BaTiO₃ have been prepared by “hydrothermal synthesis” at 90 °C in an air atmosphere. The powder preparation procedure developed in this work did not necessitate the use of strict and expensive processes, which were commonly required for the removal of free CO₂ present in the atmosphere. The prepared powders were found to be crystalline, pure, and contained no BaCO₃ as an impurity phase. Pure and Dy-doped BaTiO₃ powders synthesized at 90 °C had the pseudocubic (space group: Pm-3m) crystal structure. Grain growth characteristics of pure and Dy-doped BaTiO₃ pellets were compared during sintering in air over the temperature range from 1200 °C to 1500 °C. The Dy doping was found to be significantly effective in inhibiting the anomalous grain growth in BaTiO₃ samples heated at or above 1200 °C.     

Preparation and Characterization Upconversion Luminescence Material of Yttrium Aluminate Doped with Rare Earth

Low phonon energy yttrium aluminate was adopted as matrix and the upconversion materials yttrium aluminate co-doped with Yb³⁺ and Er³⁺ was synthesized by solid-state reaction method. The X-ray diffraction spectra and the upconversion emission spectra of various samples were measured and the effect of Er³⁺ concentration, sensitization, fluxing agent and calcining temperature on the luminescence properties was studied. Research results showed that the sample could emit green light at 543 and 570 nm when excited 980 nm laser; the optimum concentration of Er³⁺ should be 1.0%; sensitization of Yb³⁺ could enhance luminescent effects of Er³⁺ obviously; the optimum content of F₃BO₃ fluxing agent should be 8% and the optimum calcining temperature should be 1500 °C.     

Preparation and morphology of nano-size ceria by a stripping precipitation using oxalic acid as a precipitating agent

The precursors organic cerium deposits were obtained by a stripping precipitation method from cerium-loaded P507 organic phase using oxalic acid as a precipitating agent and nano-sized ceria particles were prepared by calcining the precursors at 500 °C. The morpholo-gies, phase structure of the precursors and ceria particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TG-DSC) and infrared spectroscopy analysis (FTIR). The results indicated that the concentration of oxalic acid had a little impact on the morphology of the precursors, which was blocky-shape Ce2(C2O4)3·10H2O with a monoclinic lattice structure. With the volume ratio of organic phase and oxalic acid aqueous solution (aqueous phase) varied from 1:3 to 1:6, the morphologies of the precursors Ce2(C2O4)3·10H2O precipitates gradually changed from inhomogeneous blocky-shape to uniform spherical particles. The precursors could be turned to CeO2 crystal particles with a fluorite structure by calcining, and the products ceria particles were similar in the size and morphology to the precursors.     

Understanding the Magnesiothermic Reduction Mechanism of TiO<Subscript>2</Subscript> to Produce Ti

Titanium dioxide (TiO₂) powders in the mineral form of rutile were reduced to metallic and an intermediate phase via a magnesiothermic reaction in molten Mg at temperatures between 973 K and 1173 K (700 °C and 900 °C) under high-purity Ar atmosphere. The reaction behavior and pathway indicated intermediate phase formation during the magnesiothermic reduction of TiO₂ using XRD (X-ray diffraction), SEM (scanning electron microscope), and TEM (transmission electron microscope). Mg/TiO₂ = 2 resulted in various intermediate phases of oxygen containing titanium, including Ti₆O, Ti₃O, and Ti₂O, with metallic Ti present. MgTi₂O₄ ternary intermediate phases could also be observed, but they were dependent on the excess Mg present in the sample. Nevertheless, even with excessive amounts of Mg at Mg/TiO₂ = 10, complete reduction to metallic Ti could not be obtained and some Ti₆O intermediate phases were present. Although thermodynamics do not predict the formation of the MgTi₂O₄ spinel phase, detailed phase identification through XRD, SEM, and TEM showed significant amounts of this intermediate ternary phase even at excess Mg additions. Considering the stepwise reduction of TiO₂ by Mg and the pronounced amounts of MgTi₂O₄ phase observed, the rate-limiting reaction is likely the reduction of MgTi₂O₄ to the Ti_tO phase. Thus, an additional reduction step beyond thermodynamic predictions was developed.     

Effect of Cu3P addition on sintering behaviour of elemental powders in the composition of 465 stainless steel

Abstract

The addition of Cu₃P for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated were sintering temperature, sintering time and wt-%Cu₃P. In vacuum sintering, effective sintering took place between 1300 and 1350°C. The maximum sintered density of 7·44 g cm^?3 was achieved at 1350°C for 60 min with 4–6 wt-%Cu₃P. More than 6 wt-%Cu₃P content and temperature >1350°C caused slumping of the specimens. The sintered specimens were heat treated and a maximum ultimate tensile strength (UTS) of 767 MPa was achieved with 4 wt-%Cu₃P content. The maximum hardness of 45·5 HRC was achieved in heat treated condition with 4 wt-%Cu₃P content. Above 4 wt-%Cu₃P content increase in density was observed whereas the response to heat treatment decreased. Fracture morphologies of the sintered specimens were also reported. A comparison of sintering behaviour and mechanical properties of elemental powders with prealloyed powders was also given in the present study.     

Phase Transformation and Microstructure of Zn2Ti3O8 Nanocrystallite Powders Prepared Using the Hydrothermal Process

This paper examines the phase transformation and microstructure of Zn₂Ti₃O₈ nanocrystallite powders prepared using the hydrothermal process that includes TiCl₄ and Zn(NO₃)₂·6H₂O as the initial materials. Differential thermal analysis, X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction, nanobeam electron diffraction, and high resolution TEM were utilized to characterize the transition behavior of zinc titanate precursor powders after calcination. Nanocrystalline Zn₂Ti₃O₈ powders with a size range of about 5.0 to 8.0 nm were obtained when the precursor powders were calcined at 773 K (500 °C) for 1 hour. When the zinc titanate precursor powders were calcined at 1073 K (800 °C) for 1 hour, the cubic crystal of Zn₂Ti₃O₈ with a _o = 0.8399 ± 0.0003 nm still remained the predominant crystalline phase and the crystallite size increased to 20.0 nm. In addition, ZnTiO₃ phase first appeared because of the 13.8 pct of Zn₂Ti₃O₈ decomposition when the zinc titanate precursor powders were calcined at 1073 K (800 °C) for 1 hour. When the zinc titanate precursor powders were calcined at 1073 K (800 °C) for 9 hours, the Zn₂Ti₃O₈ crystallites grew continuously to 80.0 nm and enhanced the crystallinity. When the precursor powders were calcined at 1273 K (1000 °C) for 1 hour, Zn₂TiO₄ crystallites with a _o = 0.8461 ± 0.0002 nm were the predominant crystalline phase.     

Preparation and properties of some ODS Fe-Cr-Al alloys

Several alloys based on Fe-25Cr-6Al and Fe-25Cr-11Al (wt pct) with additions of yttrium, Al₂O₃, and Y₂O₃ have been prepared by mechanical alloying of elemental, master alloy and oxide powders. The powders were consolidated by extrusion at 1000°C with a reduction ratio of 36:1. The resulting oxide contents were all approximately either 3 vol pct or 8 vol pct of mixed Al₂O₃-Y₂O₃ oxides or of Al₂O₃. The alloys exhibited substantial ductility at 600°C: an alloy containing 3 vol pct oxide could be readily warm worked to sheet without intermediate annealing; an 8 vol pct alloy required intermediate annealing at 1100°C. The 3 vol pct alloys could be recrystallized to produce large elongated grains by isothermal annealing of as-extruded material at 1450°C, but the high temperature strength properties were not improved. However, these alloys, together with some of the 8 vol pct materials, could be more readily recrystallized after rod (or sheet) rolling; sub-stantially improved tensile and stress rupture properties were obtained following 9 pct rod rolling at 620°C and isothermal annealing for 2 h at 1350°C. In this condition, the rup-ture strengths of selected alloys at 1000 and 1100°C were superior to those of competitive nickel-and cobalt-base superalloys. The oxidation resistance of all the alloys was ex-cellent. F. G. WILSON and C. D. DESFORGES, formerly with Fulmer Re-search Institute     

Optical properties and Judd–Ofelt analysis of Nd2O3 nanocrystals embedded in polymethyl methacrylate

PMMA matrices were doped with nano-crystalline neodymium oxides synthesized by thermal decomposition process. X-ray diffraction and high-resolution transmission electron microscopy measurements were carried out to investigate the structure, phase, and the morphology of the Nd_2O_3 nanocrystals and those embedded in the PMMA matrix. The average grain sizes were estimated 35 ± 6 nm and 46 ± 4 nm for non-annealed and annealed Nd_2O_3 particles, respectively. The grain size distributions(GSD) were calculated from the diffraction peaks of the annealed and non-annealed Nd_2O_3 powders and doped PMMA samples. The mass density, refractive index. UV-Visible absorption spectra were measured and the data were analyzed using the Judd-Ofelt approach to determine the oscillator strengths, the spontaneous emission probabilities and the branching ratios as a function of the nano-crystalline Nd_2O_3 content in the range of 0.1 wt.%-20 wt.% of MMA. Luminescence spectra upon 808 nm diode laser excitation were carried out in the wavelength range of 850-1550 nm at room temperature. The photoluminescence study has shown that the reasonably sharp emission peaks were observed upon heat treatment at 800 ℃ for 24 h for all concentrations of Nd_2O_3 nanopowders in PMMA. The infrared laser transition of Nd~(3+) ions at about 1.06 μm due to the ~4F_(3/2)→~4I_(11/2) transition was analyzed and discussed in Nd_2O_3 system for their possible applications in the photonic technology.     

Rapid synthesis of ternary carbide Ti3SiC2 through pulse-discharge sintering technique from Ti/Si/TiC powders

Ti/Si/TiC powders with molar ratios of 1:1:2 (M1) and 2:2:3 (M2) were prepared for the synthesis of a ternary carbide Ti₃SiC₂ by using the mixture method for 24 hours in an Ar atmosphere. The synthesis process was conducted at 1200 °C to 1400 °C under a pressure of 50 MPa, using the pulse-discharge sintering (PDS) technique. After sintering, the phase constituents and microstructures of the samples were analyzed by X-ray diffraction (XRD) technique and observed by optical microscopy and scanning electron microscopy. The results showed that the phases in all the samples consisted of Ti₃SiC₂ and small amounts of TiC, and the optimum sintering temperature was found to be in the relatively low range of 1250 °C to 1300 °C. By the standard additive method, the relative content of Ti₃SiC₂ was calculated. For the M1 samples, the lowest TiC content can be only decreased to about 3 to 4 wt pct, whereas the content of Ti₃SiC₂ in the M2 samples is always lower than that in the M1 samples. When the M2 powder was sintered at 1300 °C for 8 to 240 minutes, the TiC peaks were found to show a very low intensity, and the corresponding content of Ti₃SiC₂ was calculated to be higher than 99 wt pct. The grain size of Ti₃SiC₂ increased from 5 to 10 μm to 80 to 100 μm in the entire applied sintering temperature range. The relative density of the M2 samples was measured to be higher than 99 pct at sintering temperatures above 1275 °C. It indicates that the PDS technique can rapidly synthesize high-content Ti₃SiC₂ from the Ti/Si/TiC powders in a relatively low temperature range.     

Enhanced luminescence efficiency and thermal stability via introduction of non-rare earth Bi3+ in Gd5Si2BO13:Eu3+

A series of Gd₅Si₂BO₁₃:Eu³⁺ and non-rare earth Bi³⁺ ions doped Gd₅Si₂BO₁₃:Eu³⁺ phosphors was successfully synthesized via high-temperature solid-state method,and the as-obtained phosphors were studied on their phase structures,luminescence characteristics,thermal stability and luminescence lifetime.Transient fluorescence spectroscopy data show that the addition of Bi³⁺ can obviously enha...     

Preparation and Properties of Ba6-3xEu8+2xTi18O54 Ceramics via Ethylenediaminetetraacetic Acid Precursor

Ba_6-3xEu_8+2xTi₁₈O₅₄ (x=2/3) (BET) ceramic powders were synthesized by the Pechini method using ethyl-enediaminetetraacetic acid (EDTA) as a chelating agent. A milk-white, molecular-level, homogeneously mixed gel was prepared, and transferred into a porous resin intermediate through charring. Single-phase and well-crystallized BET ceramic powders were prepared by sintering and smashing ceramics samples, without the formation of any intermediate phases. Meanwhile, the crystal structure, which was determined by X-ray diffraction, had important effect on the microwave dielectric properties of BET. The BET ceramics had good microwave dielectric characteristics: ɛ_r = 72.13, Q_f = 7111 GHz, τ_f = −36.53 × 10⁻⁶/°C.     

Eu3+-doped BaLiZn3(BO3)3: A novel red-emitting phosphor for blue chips excited white LEDs

A series of novel red-emitting BaLiZn₃(BO₃)₃:Eu³⁺ phosphors were synthesized through the high temperature solid state reaction method. The phase composition, crystal structure, morphology and photoluminescence property of the BaLiZn₃(BO₃)₃:Eu³⁺ samples were systematically investigated. The phosphor can be efficiently excited by the near ultraviolet light (NUV) of 396 nm and blue light of 466 nm, and give out red light emission at 618 nm corresponding to the electric dipole transition (⁵D₀→⁷F₂). The optimal doping concentration of Eu³⁺ ions in BaLiZn₃(BO₃)₃ is determined to be about 3 mol%, and the concentration-quenching phenomenon arise from the electric dipole–dipole interaction. The temperature dependent luminescence behavior of BaLiZn₃(BO₃)₃:0.03Eu³⁺ phosphor exhibits its good thermal stability, and the activation energy for thermal quenching characteristics is calculated to be 0.1844 eV. The decay lifetime of the BaLiZn₃(BO₃)₃:0.03Eu³⁺ is measured to be 1.88 ms. These results suggest that the BaLiZn₃(BO₃)₃:Eu³⁺ phosphors have the potential application as a red component in white light emitting diodes (WLEDs) with NUV or blue chips.     

Hydrothermal synthesis,structure study and luminescent properties of YbPO4:Tb3+ nanoparticles

YbPO₄:Tb³⁺ were synthesized by mild hydrothermal method. The luminescent properties, morphologies and structure of the obtained powders were characterized by photoluminescence (PL) spectra, FESEM, X-ray diffractometer (XRD) and FTIR. The results showed that the prepared YbPO₄:Tb³⁺ nanoparticles were pure tetragonal phase and the average grain size varied with increasing of Tb³⁺ concentration. Hydrothermal temperature was revealed to be the key factor to enhance the emission intensity of YbPO₄:Tb³⁺ phosphors. The spherical nanoparticles could be effectively excited by near UV (369 nm) light and exhibited green performance at 543 nm (⁵D₄→⁷F₅), 489 nm (⁵D₄→⁷F₆) and 586 nm (⁵D₄→⁷F₄). The CIE chromaticity was calculated to be x=0.298, y=0.560. The YbPO₄:Tb³⁺ nanoparticles exhibited potential to act as UV absorber for solar cells to enhance the conversion efficiency.