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Aluminium metal matrix composites (AlMMCs) offer several advantages relative to monolithic aluminium alloys such as high stiffness, strength, wear resistance, low thermal expansion coefficient, etc. However, despite considerable improvements in developing AlMMCs, the lack of reliable joining methods restrict their greater application. Fusion welding of AlMMCs has not proved successful because high temperature nature of the process normally causes unfavorable reactions between the reinforcement and the matrix, leading to the formation of a variety of defects. On the other hand, solid-state welding and diffusion bonding may not be suitable due to the presence of chemically stable surface layer of aluminium oxide, which, being insoluble in aluminium, inhibits metal-to-metal contact during diffusion bonding. Furthermore, diffusion bonding requires a very smooth and clean contact surface, which is difficult to obtain in industrial applications. As an alternative, transient liquid phase (TLP) diffusion bonding, which operates at a lower temperature, can be used to circumvent the problems associated with the oxide layer. The formation of liquid phase (eutectic) can assist the disruption of the oxide layer and promote metallic contact. The composite material used in the present study consisted of 6061 alloy containing 15 volume % of SiC particulates of 23 μm diameter. TLP bonding was carried out at 560 C in argon atmosphere using copper as an interlayer with different pressures and holding times. TLP-bonded AlMMCs were characterized by optical and scanning electron microscopy, microhardness survey, and shear tests. The results indicated that adequate bond strength could be achieved with suitable bonding parameters such as holding time and initial pressure. [ABSTRACT FROM AUTHOR]

Abstract: Optical and EPR investigations of chromium and nickel doped zinc phosphate glasses are carried out at room temperature to evaluate crystal field, spin-Hamiltonian and bonding parameters. For Cr3+ ion, the site symmetry is ascribed to a distorted octahedron, whereas the Ni2+ ion is located in a near octahedral site. In addition, the bonding parameters suggest covalent nature for Cr3+ and a moderate covalent nature for Ni2+ in the zinc phosphate glasses. [Copyright &y& Elsevier]

Staining of tissues by dyes is accomplished through various types of bonds, some of which have been poorly defined in traditional biological literature. Here, basic principles of bonding are reviewed to establish uniform terminology and definitions consistent with the field of chemistry. The concept of charge – its presence or absence, magnitude, extent of delocalization and potential for being displaced by outside forces – underlies all bonding phenomena. These same attributes influence solubility and resistance to extraction during dehydration of tissue sections. Covalent bonds involve shared electrons; they are very strong and essentially irreversible under conditions encountered during staining. Polar covalent bonds within dye molecules generate partial atomic charges that create the potential for hydrogen bonding. This is measured by the hydrogen bonding parameter ( h ), the number of groups bearing charges within the ranges -0.15 to -0.50 eV or +0.15 to +0.30 eV. The potential for ionic bonding is indicated by net charge ( Z ), while the strength of such bonds is a function of charge site geometry on both bonding partners. Charge delocalization owing to conjugation, electron influencing groups, and resonance creates soft charge sites in which the ionic charge is spread over a large volume. Poorly delocalized charges or point charges are hard (small in volume). Firm bonds result from hard-hard or soft-soft pairs. Hard-soft combinations are weak, readily displaced in competitive interactions, and disrupted by solvents. Coordinate bonds with certain metals are involved with mordant staining and metal chelation dyes. Three different van der Waals attractions comprise the remainder of bonding types, all involving dipoles: Keesom (dipole-dipole) forces, Debye (dipole-induced dipole) forces and London (induced dipole-induced dipole) forces. Potentials for engaging in any of these is quantified by measures of polarity (dipole moment, d ), polarizability (crudely with π atoms describing the size of the conjugated system, or more directly with α ), hydrophobicity (with the octanol-water partition coefficient, log P or the more convenient Hydrophobic Index, HI ), and the number of halogen atoms ( X ). By using molecular modeling software, quantitative measures of bonding potential (bonding parameters) have been determined for over 400 dyes. [ABSTRACT FROM AUTHOR]

Optical absorption and EPR spectra of Co2+ and Ni2+ doped sodium phosphate glasses have been investigated. Crystal field parameters and g values are determined. For Co2+ doped glass Dq=890, B=700, C=4125 cm-1 and g values of 4.23 and 2.04 at 20 K, for Ni2+ doped glass Dq=890, B=770, C=3700 cm-1 and a g value of 2.28 at room temperature were found. Correlating the optical and electron paramagnetic resonance data suggests the bonding between transition metal ions and ligands as ionic in nature. [Copyright &y& Elsevier]

A copper-doped LiRbB4O7 crystal was grown by the Czochralski technique. Powder X-ray, EPR and optical absorption studies were carried out. The results and discussion of the copper doped LiRbB4O7 crystal indicate that the copper ions enter the host lattice by replacing Li ions. The Cu(II) ion spectrum is characteristic of a tetragonally elongated octahedral site. Lattice and spin-Hamiltonian parameters were evaluated. The bonding parameters indicate that the bonding between copper and the ligands is partly covalent. [Copyright &y& Elsevier]

Vanadium and copper doped sodium phosphate glasses are prepared. EPR and optical absorption investigations are carried out. The results and analysis of the copper doped glass indicate that the copper ions enter the glass matrix as Cu2+ ions. The Cu2+ ion spectra are characteristic of tetragonally elongated octahedral site. The spectra of vanadium doped glass are characteristic of VO2+ and because of the short V&z.dbnd6;O band the distortion appears to be a tetragonally compressed one. Crystal field and spin-Hamiltonian parameters are evaluated. The bonding parameters indicate that bonding between the metal ions and ligands is partially covalent. [Copyright &y& Elsevier]

In this paper, the static and dynamic torque capacities of the cocured joints were observed with respect to several bonding parameters such as surface roughness, bonding length and stacking angle and compared with those of conventional adhesively bonded joints. In order to analyze the stresses of the cocured joint, finite element analysis was performed incorporating the nonlinear shear behavior of epoxy resin. The dependence of the static torque capacities on the bonding parameters was investigated numerically. [ABSTRACT FROM PUBLISHER]

Single crystal EPR spectra of a natural mineral, apophyllite, containing VO(II) ion as an impurity have been investigated. The EPR spectra of the mineral, as obtained, was complex in nature, but was simplified by annealing the crystals at 490 K. The EPR parameters of the VO(II) species in the annealed crystal, g = 1.924 (2); g = 1.983 (2); A = 18.35 (5); and A = 7.24 (5)mT, are very close to a typical VO(II) impurity. Theoretically calculated line positions, using second-order hyperfine terms in the spin Hamiltonian with an axially symmetric g and A tensor values, agreed very well with the experimental ones. The EPR analysis of the annealed crystal has further revealed that the most preferred location of the VO(II) impurity is a substitutional Ca(II) site. The calculated bonding parameters and admixture coefficients indicate a fair amount of covalent bonding in the complex. [ABSTRACT FROM AUTHOR]

ESR and optical absorption studies are described for a number of copper(II) single and mixed ligand complexes formed with substituted salicylic acids and acetylacetone. ESR spectra of all these complexes give well-resolved spectra in DMF both at room and liquid nitrogen temperatures. The molecular orbital coefficients are estimated assuming an axial symmetry. A partial covalency is observed in all the single ligand complexes while the in-plane π-bonding is as strong as the σ-bonding in all the mixed ligand complexes. No regular trend is observed in the value of χ (which is proportional to hyperfine constants) with the change in the overall electron withdrawing capacity of the substituent on salicylic acid, either in single ligand or in mixed ligand complexes. However, the χ values for all the complexes (except in the case of bis(acetylsalicylato)copper(II) and (acetylacetonato)-(3,5-dinitrosalicylato)copper(II)) are in agreement with the computed value of χ = −3.61 for single crystals of copper-acetylacetonate possessing the same environment of four oxygens around copper(II). [ABSTRACT FROM AUTHOR]

Abstract: Using the decay curve analysis frequency upconversion under continuous wave NIR laser radiation (∼890nm) following the non-resonant excitation at higher energies than 1G4 level has been reported. The decay curve of the antistokes emission (3P0 → 3H4) shows similar behavior as that of the stokes emission (3P0 → 3H4) and does not show any rise time attributing to the excited state antistokes absorption assisted by phonon emission. The covalency, bonding parameters and nephalauxetic effect for the present system has also been determined. [Copyright &y& Elsevier]

Cu(II) ion-doped NaCaAlPO(4)F(3) phosphor has been synthesized using a solid state reaction method. The prepared sample is characterized by powder X-ray diffraction, scanning electron microscope, optical absorption, electron paramagnetic resonance photoluminescence and Fourier transform infrared spectroscopy techniques. The crystallite size evaluated from x-ray diffraction data is in nanometers. Scanning electron microscopy micrographs showed the presence of several irregular shaped particles. From optical absorption and electron paramagnetic resonance spectral data the doped Cu(II) ions are ascribed to distorted octahedral site symmetry. The synthesized phosphor exhibits emission bands in ultraviolet, blue and green regions under the excitation wavelength of 335 nm. The CIE chromaticity coordinates (x = 0.159, y = 0.204) also calculated for the prepared sample from the emission spectrum. The Fourier transform infrared spectroscopy spectrum revealed the characteristic vibrational bands of the prepared phosphor material., (Copyright © 2014 John Wiley & Sons, Ltd.)