Nucleation of the Al6(Fe,Mn)-to-α-Al–(Fe,Mn)–Si transformation in 3XXX aluminium alloys. II. Transformation in cast aluminium alloys

The nucleation behaviour of the homogenization-induced Al₆(Fe,?Mn)-to-α-Al–(Fe,?Mn)–Si transformation is investigated in a companion paper to part I (a study with roll-bonded diffusion couples). Diffusion experiments using silicon-coated Al–0.53?wt%?Fe–1.02?wt%?Mn alloy blocks allow control of the thermodynamic driving force for transformation within a microstructure typical of a cast ingot. As expected, this microstructure appears to give ready and yet stochastic nucleation as silicon diffuses into the alloy sections. In addition, transmission electron microscopy is used to analyse partially transformed particles in heat-treated alloy samples of fixed silicon content. This confirms the suggestion made in part I that the transformation preferentially nucleates at matrix grain/cell boundaries. Nucleation theory suggests this results from the ability of the boundaries to relieve volume changes associated with the nucleation event.     

Substrate and elastic recovery effects in hardness measurement of CVD WC-based coatings

Hard coatings are used in a very broad range of applications, for example in the automotive, tooling and gas industries. The apparently simplest way to compare different coatings is to measure their hardness. However, interpreting such measurements is not a trivial problem for thin coatings (10 μm or less); standard micro-indenters (with a typical minimum applied load of 10gf) usually produce a penetration depth such that the substrate influences the measurements, giving a ‘composite’ hardness value of the coating and the substrate. At the same time there might be a more or less evident recovery of the indentation, because of residual elasticity around the sub-indentation plastic zone or because of residual stresses. One possible solution is the use of a nano-indenter. An alternative method for obtaining ‘true’ Vickers hardness values for the coating is described here, using changes in shape of Knoop micro-indentations to characterize the elastic recovery effects, together with use of a composite model for thin film microhardness. Results of hardness testing on thin WC-based coatings, using nano-indentation, Vickers and Knoop indenters, are compared.     

The fission systematics of (15.9 MeV/u) Au ions in polymer CR-39

It has been demonstrated that high-energy heavy ions undergo fission while propagating in dielectric solids. Since these materials act as particle detectors because of their ability to retain primary ionization damage that can be fixed and enlarged with chemical etching, therefore, in principle, a complete kinematical analysis of fission events is possible. The crucial point in this regard is the availability of a well-calibrated range-energy relation, which is necessary for mass identification. We have developed an analytical method to convert the geometrical parameters of fission fragment tracks into physical parameters using an equation that expresses velocity as a polynomial of mass and range. A set of nine different polynomials was used to represent small regions of mass and range in order to improve accuracy. In the case of (15.9 MeV/u) Au ions incident normally on CR-39, we have found about 200 events which could be categorized as in-flight fission of Au ions inside the body of the detector. Mass distributions and cross sections of fission events have been calculated.     

Theoretical study of the reaction of H2 with a Cu2Pt2 cluster

The study of the interaction of a pyramidal tetramer of Cu₂Pt₂ with the H₂ is reported here through ab initio multiconfigurational self-consistent field (MC-SCF) calculations, plus extensive multireference configuration interaction (MR-CI), variational and perturbative calculations. The lowest three electronic states X ¹A′, a ³A′ and a ¹A′ of the bare cluster were considered in order to study this interaction. For the H₂ C_s approaching a Pt vertex, results show that the Cu₂Pt₂ pyramid cluster in its X ¹A′ and a ¹A′ states can spontaneously capture and dissociate the H₂. For the H₂ C_s approaching a Cu vertex, where H₂ is located in the C_s reflecting plane, the Cu₂Pt₂ cluster in its X ¹A′ electronic state shows capture of the hydrogen molecule after surmounting an energy barrier; moreover, in this approach the Cu₂Pt₂ cluster in its a ¹A′ electronic state shows spontaneous capture of the hydrogen molecule. For the H₂ approaching a Cu vertex, where the C_s reflecting plane bisects the H₂ molecule, the Cu₂Pt₂ cluster in its three lowest-lying states is able to capture the hydrogen molecule after surmounting a small barrier. The Cu₂Pt₂+H₂ C_s face-on interactions show a lower H₂ activation than that which was obtained in the equivalent Pt₄+H₂ interactions.     

Analysis of electromagnetic field due to a buried coated PEMC circular cylinder

An analytical solution for the scattering of an electromagnetic plane wave from a coated perfect electromagnetic conducting (PEMC) circular cylinder, buried in the dielectric half space, is presented. Scattering characteristics of a buried PEMC cylinder when coated by double-positive (DPS) or double-negative (DNG) materials is investigated. The cylinder as well as coating layer is of infinite length (2-D problem). Plane wave spectral representations of the fields have been used to solve the problem. Saddle point method is used to solve the integral arising in the analysis. All the multiple interactions between the buried geometry and the dielectric interface separating the two half spaces have been considered in the analysis. The derivation includes both TM and TE polarization cases. It is observed that the response of the coated PEMC cylinder can be used to detect the underground pipes and other buried objects having a cylindrical shape.     

Study of projectile fragmentation in the reaction (158 A GeV) Pb + Pb using CR-39

The fragmentation of Pb ions at 158 A GeV energy produced in the interaction with Pb target has been studied using a CR-39 track detector. A stack comprising of 64 detectors was prepared such that a target of 1 cm thickness was sandwiched between the sheets of CR-39. The purpose of this exposure geometry was to calibrate CR-39 with respect to relativistic heavy ions as well as to study the fragmentation of Pb ions at 158 A GeV energy. The exposure was carried out at the SPS beam facility of CERN at normal incidence with a fluence of . Two detectors from the exposed stack have been selected for this study: one before and the other after the target material. After etching, the detectors were scanned using an optical microscope and the etched track lengths and the diameters of the track openings were measured manually. Considering that the lengths of tracks provide the best charge resolution for Z>65, we have measured track lengths for a sufficiently large number of fragments to identify individual charge states for 65<Z<83. The total charge-changing cross section has also been determined.     

Simultaneous determination of potassium clavulanate and cefixime in synthetic mixtures by high-performance liquid chromatography

A simple, precise, and sensitive high-performance liquid chromatographic method was developed and validated for the simultaneous determination of potassium clavulanate and cefixime in synthetic mixture form. The analytes were separated on a C18 column by using 0.03 M disodium hydrogen phosphate buffer (pH 6.5)-methanol (84 + 16, v/v) as the mobile phase with detection at 220 nm. The method exhibited high sensitivity and good linearity in the concentration ranges of 12.5-62.5 and 20-100 microg/mL for potassium clavulanate and cefixime, respectively. The total run time for the 2 components was <8 min, and the average recovery was >101.5% with a relative standard deviation of <1.0%. The proposed method was validated according to guidelines of the International Conference on Harmonization by evaluation of linearity, recovery, selectivity, robustness, limits of detection and quantitation, and within- and between-day precision. The results obtained for the synthetic mixture show that the method is highly precise and accurate for the simultaneous determination of potassium clavulanate and cefixime.     

High throughput synthesis of diverse 2,5-disubstituted indoles using titanium carbenoids bearing boronate functionality

A titanium benzylidene complex bearing a boronate group converted resin-bound esters into enol ethers. Suzuki cross-coupling with aryl iodides followed by cleavage with acid completed the solid-phase synthesis of 2,5-disubstituted N-Boc-indoles. Also reported is the use of tert-butyllithium and 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane to convert an aryl bromide into an arylboronate in the presence of a dithiane, with simultaneous reduction of an aryl azide to an amine.     

Some aromatic polyimides based on diamines containing hydrazo group and ether linkages

Three new hydrazo-bridged diamines, 4,4′-bis [4-(4-aminophenyloxy) phenylhydrazyl] biphenyl (BPD-2), 4,4′-bis [4-(4-aminophenyloxy) phenylhydrazyl] biphenyl ether (SPD-2) and 4,4-bis [4-(4-aminophenyloxy) phenyl] hydrazine (APD-2), were synthesized by the reduction of three azo-diols, 4,4′-bis (4-azo-1-hydroxyphenyl) biphenyl (BPD), 4,4′-bis (4-azo-1-hydroxyphenyl) biphenyl ether (SPD) and azo-4-hydroxybenzene (APD), and polymerized with pyromellitic dianhydride (PM), 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BP) and 3,4,9,10-perylenetetracarboxylic acid dianhydride (PR) either by one-step solution polymerization or by two-step procedure which includes ring-opening polyaddition to give poly(amic acid) followed by cyclic dehydration to polyimide. The monomers and polyimides were characterized by their elemental analyses, FTIR and ¹H NMR spectroscopy. Glass transition temperatures of the polymers are quite high (175-310 °C), characteristic of polyimides. The decomposition temperatures for 10% weight loss fall in the range of 280-575 °C in nitrogen. Activation energies of pyrolysis for each of the polymers calculated from Horowitz and Metzger's method are also high (52.54-95.28 kJ mol⁻¹). The inherent viscosities of the polyimides at a concentration of 0.5 g/dl in DMF range from 0.94 to 1.93 dl/g.