Luminescence of Eu3+ and Eu2+ in the new BaLnB9O16 borates (Ln = rare earth)

The luminescence of Eu³⁺ in the borates BaLnB₉O₁₆ (Ln = La, Gd and Y) has been investigated. Under UV excitation the Eu³⁺-activated lanthanum and gadolinium compounds show a bright red luminescence at room temperature, whereas the Eu³⁺-activated yttrium borate is characterized by a red-orange luminescence which indicates a change in the symmetry of the rare earth ion sites. As a consequence of the high energy of the charge transfer band the Eu³⁺ emission has a high efficiency under 253.7 nm excitation, a characteristic favorable for lighting applications. The sensitization of the Eu³⁺ emission by Bi³⁺ has been examined. Energy transfer from Bi³⁺ to Eu³⁺ is observed, but in presence of bismuth the efficiency of excitation through the Eu³⁺ charge transfer band is reduced. The luminescence of Eu²⁺ has also been studied. Eu²⁺-activated BaGdB₉O₁₆ shows an intense blue emission band under UV excitation.     

Hydroxyl groups of the non-framework aluminium species in dealuminated Y zeolites

By comparing dealuminated Y zeolites with and without non-framework aluminium species it is shown that the bands at 3693 and 3606 cm⁻¹ in the i.r. spectrum and the line at 2.6 ppm in the ¹H MAS n.m.r. spectrum represent hydroxyl groups associated with non-framework aluminium.     

Bending of thin laminated plates

Rectangular thin composite plates are analysed by the finite-element displacement method for linear bending deformation. Transverse displacement and surface strain measurements from experiments on multi-layered symmetrical laminates consisting of carbon fibres embedded in an epoxy resin (T300/code 69) are compared with finite-element solutions. It is shown that the numerical technique predicts accurately the bending up to a central transverse displacement equal to about the plate thickness, providing certain modelling conditions are used.     

The influence of oxygen and water vapour on the friction and wear of an aluminium alloy under fretting conditions

An investigation was conducted to determine the effect of oxygen and water vapour on the friction and wear behaviour of an Al-Zn-Mg alloy under fretting conditions. Fretting wear experiments were carried out in wet air, dry air and in dry argon. In this case the peak-to-peak relative slip amplitude was varied from 20 to 260 μm to determine the critical slip amplitude of fretting wear in these environments.The experimental results indicated that the wear rates in dry air and in dry argon under macroslip conditions were almost the same and quite lower than the wear rate in wet air. This revealed that the effect of oxygen on fretting wear was not large but that water vapour accelerated the fretting wear of the aluminium alloy. The cyclically softened material due to overaging was observed below the contact surface during fretting in wet air. The mechanism involved rapid fretting wear in wet air which caused the removal of a heavily work-hardened layer as it was formed but the softened material below it was not removed.     

Electronic-structure calculation of point defects in silicon

Density-functional theory allows studies of ground-state properties of a many-electron system from first principles. Using Green-function technique and the local density (or local spin-density) approximation, it is possible to calculate charge (ion) states, total energies, donor- and acceptor levels, and spin-densities of point defects in semiconductors. Focussing on existing open questions and controversies, we present results of recent theoretical studies of single substitutional and interstitial chalcogens and 3d transition-metal impurities in silicon. For the chalcogen point defects S, Se and Te we identify their positions in the silicon lattice as the substitutional site. For 3d impurities in silicon we obtain spin-multiplicities and donor and acceptor levels in good agreement with available experimental data. The early 3d interstitial and the late 3d substitutional ions are predicted to have low-spin ground-states which is in conflict with the generally accepted model of Ludwig and Woodbury (LW). A large number of predictions will be offered to be tested by future experimental studies.     

The influence of copper upon the atmospheric corrosion of iron

The atmospheric corrosion of pure iron and the binary alloy Fe-0.5Cu has been analyzed by a simultaneous measurement of the anodic current density of the metal dissolution and the cathodic current density of the O₂ reduction reaction during several wet/dry cycles using a magnetic and a gas volumetric technique, respectively. The results show three typical stages of the atmospheric corrosion: stage 1 (wetting of a dry surface): rapid corrosion with rust reduction as cathodic process; stage 2 (wet surface): slow corrosion with O₂ reduction as cathodic process; and stage 3 (drying out of the surface): very rapid corrosion with O₂ reduction as the cathodic process during critical wetting of the surface. The effect of copper is restricted to stage 3, where the corrosion rate is much smaller for the Fe-0.5Cu alloy than for pure iron. Two models are discussed to explain these results.     

Electrolyte solutions in liquid ammonia—IX. Electrodeposition and electrodissolution of metals from their salts

Anodic dissolution and cathodic deposition of 20 transition metals in acidic solutions in liquid ammonia has been surveyed. The early transition metal elements Ti, Zr, V Nb, Mo and W form high oxidation-state insoluble amido complexes during anodic oxidation. Soluble ammines of normal metal oxidation states are produced with Cr(III), Mn(II), Fe(II), Co(III), Ni(II), Cu(II), Ag(I), Zn(II), Cd(II) and Hg(II) (Mn dissolves spontaneously). The metals Ru, Pd, Pt and Au only dissolve slightly after prolonged electrolysis. Anodic enrichment of Au in its alloys is unlike that in aqueous solution; in ammonia both Cu and Ag can be simultaneously depleted from a 9 carat gold alloy. Cathodic reduction of metal-bearing solutions follows wide variations of behaviour. Fe and Ru ammines reduce to amido-complexes with concomittant hydrogen evolution, but Cr is not reduced. Solutions of Mn, Co, Ni, Pd, Pt, Ag, Au, Zn, Cd and Hg give metallic cathode deposits under differing conditions. Electrodeposition is potential dependent for Ni, Cu and Ag; metal plate at low potentials, and powders at high potentials. The two different products are the result of reduction of species with different degrees of solvation.     

Optical properties of electropolymerized orthoaminophenol

The optical properties of a surface polymer formed by electropolymerization of ortoaminophenol (OAP) are studied by ellipsometry and in situ visible spectrophotometry. The polymer is opaque in the oxidized state and transparent in the reduced one. The complex refractive index of the oxidized and the reduced states were measured as a function of wavelength. At λ = 546.1 nm n̄_r = 1.704 − i 0.02 and n̄_ox = 1.699 − i0.175.