Mn2+and the trivalent europium(Eu3+)-doped MgGa2O4 ceramics are characterized using a multi-experimental approach.The formation of spinel-structured ceramics is ascertained from X-ray diffraction(XRD)analysis.Morpholo...Mn2+and the trivalent europium(Eu3+)-doped MgGa2O4 ceramics are characterized using a multi-experimental approach.The formation of spinel-structured ceramics is ascertained from X-ray diffraction(XRD)analysis.Morphology investigations with transmission electron microscopy(TEM)show irregularly shaped grains and grain boundaries with a homogeneous distribution of Eu3+ions.The inability of Eu activator to penetrate the bulk of ceramic grains is inferred from positron annihilation lifetime spectroscopy data.The Eu doping is shown to enhance the positron trapping rate due to the occupancy of vacancy-type defects at ceramic grains by Eu3+ions.Both Mn2+and Eu3+doped samples show a broad multi-color luminescence in 350–650 nm range under 240 nm and 270–300 nm excitations.Blue emission is concluded to originate from host defects,whereas green emission and narrow lines in the red region of the spectrum are attributed to Mn2+and Eu3+ions,respectively.High asymmetry around Eu3+ions can be concluded from the photoluminescence and positron annihilation lifetime spectra analysis.展开更多
In this work typical mechanical properties for a catalyst support material, ZSM5 （a spray-dried granular zeolite）, have been measured in order to relate the bulk behaviour of the powder material to the single partic...In this work typical mechanical properties for a catalyst support material, ZSM5 （a spray-dried granular zeolite）, have been measured in order to relate the bulk behaviour of the powder material to the single particle mechanical properties. Particle shape and size distribution of the powders, determined by laser diffraction and scanning electron microscopy （SEM）, confirmed the spherical shape of the spray-dried particles. The excellent flowability of the material was assessed by typical methods such as the Hausner ratio and the Cart index, This was confirmed by bulk measurements of the particle-particle internal friction parameter and flow function using a Schulze shear cell, which also illustrated the low compressibility of the material. Single particle compression was used to characterize single particle mechanical properties such as reduced elastic modulus and strength from Hertz contact mechanics theory. Comparison with surface properties obtained from nanoindentation suggests heterogeneity, the surface being harder than the core. In order to evaluate the relationship between single particle mechanical properties and bulk compression behaviour, uniaxial confined compression was carried out. It was determined that the Adams model was suitable for describing the bulk compression and furthermore that the Adams model parameter, apparent strength of single particles, was in good agreement with the single particle strength determined from single particle compression test.展开更多
基金This study is supported by the Ministry of Education and Science of Ukraine under the Young Scientists Program(0117U007189)R.GOLOVCHAK acknowledges the U.S.National Science Foundation(Grant No.DMR-1725188)for the acquisition of PAL spectrometerJ.CEBULSKI acknowledges support from the SAIA for partial support of this research within the National Scholarship Program of the Slovak Republic.
文摘Mn2+and the trivalent europium(Eu3+)-doped MgGa2O4 ceramics are characterized using a multi-experimental approach.The formation of spinel-structured ceramics is ascertained from X-ray diffraction(XRD)analysis.Morphology investigations with transmission electron microscopy(TEM)show irregularly shaped grains and grain boundaries with a homogeneous distribution of Eu3+ions.The inability of Eu activator to penetrate the bulk of ceramic grains is inferred from positron annihilation lifetime spectroscopy data.The Eu doping is shown to enhance the positron trapping rate due to the occupancy of vacancy-type defects at ceramic grains by Eu3+ions.Both Mn2+and Eu3+doped samples show a broad multi-color luminescence in 350–650 nm range under 240 nm and 270–300 nm excitations.Blue emission is concluded to originate from host defects,whereas green emission and narrow lines in the red region of the spectrum are attributed to Mn2+and Eu3+ions,respectively.High asymmetry around Eu3+ions can be concluded from the photoluminescence and positron annihilation lifetime spectra analysis.
基金the EU for financial support through the Framework 6 Marie Curie Action "NEWGROWTH", contract number MEST-CT-2005-020724Johnson Matthey Plc and Birmingham Science City for funding and supporting this research
文摘In this work typical mechanical properties for a catalyst support material, ZSM5 （a spray-dried granular zeolite）, have been measured in order to relate the bulk behaviour of the powder material to the single particle mechanical properties. Particle shape and size distribution of the powders, determined by laser diffraction and scanning electron microscopy （SEM）, confirmed the spherical shape of the spray-dried particles. The excellent flowability of the material was assessed by typical methods such as the Hausner ratio and the Cart index, This was confirmed by bulk measurements of the particle-particle internal friction parameter and flow function using a Schulze shear cell, which also illustrated the low compressibility of the material. Single particle compression was used to characterize single particle mechanical properties such as reduced elastic modulus and strength from Hertz contact mechanics theory. Comparison with surface properties obtained from nanoindentation suggests heterogeneity, the surface being harder than the core. In order to evaluate the relationship between single particle mechanical properties and bulk compression behaviour, uniaxial confined compression was carried out. It was determined that the Adams model was suitable for describing the bulk compression and furthermore that the Adams model parameter, apparent strength of single particles, was in good agreement with the single particle strength determined from single particle compression test.
