Synthesis and characterisation of rare earth oxysulphide phosphors. I. Studies on the preparation of Gd2O2S:Tb phosphor by the flux method

Terbium activated gadolinium oxysulphide phosphor (Gd₂O₂S:Tb) shows bright green luminescence and high efficiency under X-ray excitation. Phosphor utilisation depends on powder characteristics and luminescence properties that are regulated during the synthesis stage. The paper presents some of our new results on the synthesis of Gd₂O₂S:Tb phosphor by solid-state reaction route from oxide precursors. Efficient luminescent powders utilisable in the manufacture of X-ray intensifying screens for medical diagnosis were prepared from optimised synthesis mixtures containing oxide precursors, alkaline carbonate based flux, alkaline phosphate based mineralising additives and sulphur suppliers.     

Mechanochemical synthesis of hybrid electrolytes from the Li2S–P2S5 glasses and polyethers

Novel hybrid solid electrolytes were prepared by mechanochemistry using the Li⁺ conductive Li₂S–P₂S₅ glasses and –OH terminated oligomers. The P–O–C bonds were observed in FT-IR spectra for the obtained electrolytes, suggesting that the molecular level hybrid materials were synthesized. The addition of small amounts of oligomers into the glass successfully enhanced the conductivity of hybrid electrolytes by lowering glass transition temperature. The hybrid electrolyte with 2 mol% of 1,4-butanediol exhibited the ambient temperature conductivity of 9.7 × 10⁻⁵ S cm⁻¹, which is 1.5 times as large as the conductivity of the pristine glass. The hybrid with a polyether showed lower conductivity than the hybrid with 1,4-butanediol. Incorporating oligomer blocks into glass network is a new approach to enhance the conductivity of glass-based solid electrolytes.     

New conjugated materials containing cyano substituents for light-emitting diodes

New electroluminescent cyano-substituted phenylenevinylene (PV) monomeric and oligomeric chromophores, 1–3, were synthesized by Knoevenagel condensation and investigated in terms of their photoluminescence (PL) and electroluminescence (EL) behavior. All show PL emission maxima between 463 and 471 nm in solution with quantum efficiencies of 0.65, 0.46 and 0.68, respectively. EL maxima in an LED configuration ITO/PEDOT–PSS/1–3/Ca–Al were 507, 518 and 551 nm with luminance efficiencies 0.01, 0.05 and 0.02 cd/A, respectively.     

Hydrodynamic and mass transfer study in a rectangular three-phase air-lift loop reactor

This study concerns a three-phase rectangular air-lift reactor. The first part deals with the reactor’s gas–liquid two-phase flow hydrodynamics. Parameters, such as the gas hold-up, the liquid velocity, the mixing parameters, and the solid hold-up, were quantified in the presence of two different plastic solids—a regular shape solid called P1, and an heterogeneous shape solid, P4. No fundamental influence of the solids on the studied parameters was noticed, except for the gas hold-up. Indeed, a bubble coalescence phenomenon was highlighted for high solid concentrations (ε_s > 16%). Moreover, a comparison of these two materials led to the conclusion that P4 exhibited better hydrodynamic performances. In a second set of experiments, the oxygen mass transfer was characterised in three-phase flow, with both kinds of plastic materials. The k_La coefficient was deduced from a mass balance on the gas phase. It was found to be weakly influenced by the presence, the nature or the quantity of solid.     

Preparation of PZT suspensions for direct ink jet printing

The present paper contains an experimental study of two different kinds of PZT suspensions for direct ink jet printing at 25 and 120 °C, respectively. The effect of processing parameters such as mixing time, the amount of dispersant, solid loading and milling method was investigated for the optimisation of viscosity for feasible jetting. The viscosity of PZT suspensions was within 5–15 mPa·s range for room temperature suspensions with MEK/EtOH medium and 10–20 mPa·s for high temperature suspensions with wax medium. FTIR analysis is also presented to explain the rheological behaviour of PZT suspensions. Finally, a demonstration of room temperature jetting of PZT suspension is shown.     

Grain refinement with increasing magnetron discharge power in sputter deposition of nanostructured titanium aluminium nitride coatings

Nanostructured titanium aluminium nitride coatings were produced via magnetron co-sputtering. The results showed the significant effect of magnetron discharge power on structural refinement of the coatings. As the aluminium magnetron power increased from 1.5 to 6.0 W/cm², the average grain diameter of the coatings was reduced from ∼210 to ∼90 nm.     

Effect of phase transformation of zirconia on the fracture behavior of electrolyte-supported solid oxide fuel cells

Zirconia solid electrolyte provides the functions of mechanical support, electronic insulation and oxygen ions conductivity for electrolyte-supported solid oxide fuel cell. Ferritic stainless steel is used as current collector to study the structural stability of the two cells during the cooling process. The sample using fully-stabilized zirconia is cracked after the cooling process, while the partially-stabilized zirconia sample has no obvious changes. Thermal expansion coefficient of the two samples is similar, which exhibits that TEC is not the main factor to result in the fracture. In-situ X-ray diffraction results indicated that the conflict between the compression state in cell due to TEC and the volume expansion of the fully-stabilized zirconia sample due to phase transformation can cause cracking. Partially-stabilized zirconia sample can be transformed from tetragonal to cubic phase during the temperature rising, while can be recovered to its initial state during cooling. Even much more cubic phase can be transformed to the tetragonal phase induced by pressure stress during cooling, which plays an important role on the anti-cracking performance.     

Carbon particles modified macroporous Si/Ni composite as an advanced anode material for lithium ion batteries

Carbon particles modified macroporous Si/Ni composite (MP-Si/Ni/C) is easily obtained via a facile fabrication of porous Si/Ni precursor by dealloying SiNiAl alloy followed by a surface growth of carbon nanoparticles. MP-Si/Ni/C composite possesses the multiply conductivity modification that are built through mixing Ni dispersoid and growing one layer of carbon particles. Coupled with the structural advantages of interconnected network backbone, rich voids, and the coated carbon particles, MP-Si/Ni/C exhibits dramatically enhanced lithium storage performances with excellent reversible capacity, enhanced rate performance, as well as outstanding cycling stability compared with pure MP-Si and MP-Si/Ni. Especially, the reversible capacity remains up to 1113.1 and 708.8 mA h g⁻¹ at the current densities of 200 and 1000 mA g⁻¹ after 120 cycles, respectively. Besides, it shows excellent rate capability even when continuously cycled at high current density of 3000 mA g⁻¹. With the advantages of unique structure, excellent performances, and facile preparation, the as-made MP-Si/Ni/C composite shows promising application potential as an alternative anode for lithium ion batteries.     

Structure and hydrogen permeability of V–15Ni alloy

The structure of the V–15Ni at.% alloy before and after hydrogen permeability tests was investigated by means of XRD and SEM with EDS analysis. We have found that decomposition of supersaturated V-based solid solution with variable Ni content occurred during testing. The volume fraction of the solid solution decreased and the fraction of V₃Ni phase increased during permeability testing, thus bringing the alloy to nearly equilibrium. The membrane without Pd coating showed satisfactory hydrogen fluxes with a significant impact of the surface dissociation rate of hydrogen. The shape of hydrogen permeation curves at the downstream side of the membrane at various temperatures was unusual. We attribute it to the high concentration of dissolved hydrogen in the metal lattice and its effect on the hydrogen diffusivity and solubility. In addition, the multiphase structure with non-uniform distribution of nickel both between the phases and within the BCC solid solution (and, consequently, different hydrogen concentrations) may cause dilatation or compressing effect on neighbouring micro-volumes of the alloy.     

Performance and long-term durability of direct-methane flat-tube solid oxide fuel cells with symmetric double-sided cathodes

In this work, we investigated the performance and stability of a large flat-tube SOFC with symmetric double-sided cathodes (DSC), which was directly fueled with methane. The effect of steam/carbon (S/C) ratio, temperature, and current density on the performance, and long-term stability of the DSC as well as the catalytic behavior of the anode was investigated in details. The thick anode support and inner channels of the DSC formed an efficient microreactor for steam-reforming of methane, resulting in high conversion rate of methane and CO selectivity. In particular, when the S/C was 2, the conversion of CH₄ at 750 °C achieved 100% in the DSC and no carbon deposition was observed. Moreover, the voltage of DSC with was stable throughout 190 h under a discharge current density of 0.257 A cm⁻².