Relationship between single and bulk mechanical properties for zeolite ZSM5 spray-dried particles

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.

Microstructure and luminescent properties of Eu^3+-activated MgGa2O4:Mn^2+ ceramic phosphors

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.