Synthesis of Green-Emitting Gd2O2S:Pr3+ Phosphor Nanoparticles and Fabrication of Translucent Gd2O2S:Pr3+ Scintillation Ceramics

A translucent Gd2O2S:Pr ceramic scintillator with an in-line transmittance of ~31% at 512 nm was successfully fabricated by argon-controlled sintering. The starting precipitation precursor was obtained by a chemical precipitation route at 80 °C using ammonia solution as the precipitate, followed by reduction at 1000 °C under flowing hydrogen to produce a sphere-like Gd2O2S:Pr powder with an average particle size of ~95 nm. The Gd2O2S:Pr phosphor particle exhibits the characteristic green emission from 3P0,1→3H4 transitions of Pr3+ at 512 nm upon UV excitation into a broad excitation band at 285–335 nm arising from 4f2→4f5d transition of Pr3+. Increasing Pr3+ concentrations induce two redshifts for the two band centers of 4f2→4f5d transition and lattice absorption on photoluminescence excitation spectra. The optimum concentration of Pr3+ is 0.5 at.%, and the luminescence quenching type is dominated by exchange interaction. The X-ray excited luminescence spectrum of the Gd2O2S:Pr ceramic is similar to the photoluminescence behavior of its particle. The phosphor powder and the ceramic scintillator have similar lifetimes of 2.93–2.99 μs, while the bulk material has rather higher external quantum efficiency (~37.8%) than the powder form (~27.2%).

Direct ultrasound synthesis of vanadyl pyrophosphate catalyst for partial oxidation of n-butane to maleic anhydride

Three VPO catalyst were prepared via direct ultrasound technique using organic, sesquihydrate and dihydrate routes, denoted as VPOuo, VPOus and VPOud respectively. These catalysts were synthesised solely on direct ultrasound technique and calcined in n-butane/air mixture. All catalysts exhibited well-crystallised (VO)2P2O7 phase. VPOus and VPOud showed αII-VOPO4, which led to an increase in average oxidation state of vanadium. All catalysts were showing O1s approx. 530 eV, similar P2p value and V2p3/2 at approx. 517 eV, giving vanadium oxidation state of approx. 4.0 – 4.2. FE-SEM micrographs showed the secondary structure consisting of thin plate-like crystals in different sizes agglomerate to each other due to cavitation effect. HR-TEM demonstrated the existence of polycrystalline phase. The nature of the oxidants was investigated by TPR in H2. VPOus showed highest amount of total removal of oxygen species suggesting that it had highest activity compared to VPOuo and VPOud. The XANES measurement of these catalysts showed the occurrence of vanadium oxide reductions in flowing hydrogen gas, which indicates the presence of V4+ and V5+ species. Catalytic tests demonstrated that the activity and selectivity to maleic anhydride increased with direct ultrasound technique. This study showed that catalyst synthesis time can be reduced to only 2 hours and giving polycrystalline particles compared to conventional method.

UTILIZAÇÃO DO PÓ DE ACIARIA ELÉTRICA MODIFICADO TERMICAMENTE EM REAÇÕES PARA REDUÇÃO DO NITROBENZENO À ANILINA

Nitroaromatic compounds appear as important agents in environmental contamination, with the highlight, its high resistance to microbial degradation. The reductive processes using metallic iron have been studied by several researchers with the purpose of formation of substrates that are less recalcitrant compounds. In this study the flue dust electric iron rich residue was thermally reduced under flowing hydrogen gas to obtain a composite phase reduced iron. This composite was used as reducing agent in transformation reaction of nitrobenzene to aniline. The results show that heat treatment of the residue promoted the formation of phases of reduced iron as FeO and Fe This material has high efficiency in reduction reaction of nitrobenzene to aniline, where the concentration of this contaminant was reduced ca. 86%.

Spectral Monitoring CH/C2Ratio of Methane Plasma for Growing Single-Layer Graphene on Cu

Single-layer graphene was grown on copper at a low temperature of 600°C by plasma-assisted thermal chemical vapor deposition. Its growth mechanism was discussed with reference to the emission spectra of the plasma. The methane plasma produces the active species (Hx, CHx, and Cx) without the addition of flowing hydrogen, and the amounts of hydrogen-containing species can be controlled by varying the plasma power. The effective distance was found between the plasma initial stage and the deposition stage for the single-layer graphene synthesis. The results reveal that high-quality graphene can be synthesized using methane plasma at a suitable plasma power.

Phase Development in Carbothermal Reduction and Nitridation of Ilmenite Concentrates

The phase development in the course of carbothermal reduction and nitridation of ilmentie concentrates and synthetic rutile was studied in temperature programmed reduction (623–1873 K) and isothermal reduction experiments. Ilmenites and synthetic rutile were reduced in a tube reactor with continuously flowing hydrogen-nitrogen mixture or pure nitrogen. The rate and extent of reduction were monitored by online off-gas analysis. Samples reduced to different extent were subjected to XRD and SEM/BSE analyses. Pseudorutile and ilmenite were the main phases in ilmenite concentrates; rutile was the main phase in synthetic rutile. Pseudorutile was first converted to ilmenite and titania which occurred at temperatures below 623 K; iron oxides in ilmenite were quickly reduced to metallic iron. Titania was reduced to titanium suboxides and further to titanium oxycarbonitride. Reduction of ilmenites and synthetic rutile in hydrogen-nitrogen mixture was much faster than in pure nitrogen. The rate of conversion of titanium oxides to oxycarbonitride was affected by iron content in the ilmenites. The rate of reduction increased with increasing iron content in ilmenite (decreasing grade) when ilmenites were reduced in the hydrogen-nitrogen gas mixture, but decreased with decreasing ilmenite grade in reduction experiments in nitrogen; reduction in nitrogen was the fastest for synthetic rutile. The difference in the reduction behaviour was attributed to different chemical compositions and morphologies of ilmenites of different grades.

The Influence of the Milling Environment on the Structure of a W-Cu Composite

This work reports an investigation about the influence of the environment of milling on the characteristics of the powders and on the structure and density of sintered samples made of these powders. Mixtures of composition W-30wt%Cu were milled for 51 hours in a high energy planetary mill in dry and wet (cyclohexane) conditions. The milled powders have composite particles. The powders were pressed and sintered at 1050º, 1150º and 1200°C under flowing hydrogen. The isothermal times were 0 minutes for the first two temperatures and 60 minutes for the latter. The samples reached around 95% of relative density. The powders were characterized by means of XRD and SEM. The sintered samples were characterized by means of SEM, optical microscopy and density measurement.