Raman spectrum of diglycine barium chloride monohydrate

The Raman spectrum of diglycine barium chloride monohydrate in the single crystal form has been recorded using λ 2536·5 excitation. 43 Raman lines (9 lattice and 34 internal) have been recorded. Satisfactory assignments have been given for most of the observed Raman lines. It is concluded from a comparison of the Raman spectrum of this compound with those of glycine and of other addition compounds of glycine, that the glycine unit exists in the zwitterion form in the structure of diglycine barium chloride monohydrate.

Mechanism of low-temperature deformation in quenched aluminium-magnesium alloys

The dislocation mechanisms for plastic flow in quenched AlMg alloys with 0.45, 0.9, 2.7 and 6.4 at. % Mg were investigated using tensile tests and change-in-stress creep experiments in the temperaturhttp://eprints.iisc.ernet.in/cgi/users/home?screen=EPrint::Edit&eprintid=28109&stage=core#te range 87° -473° K. The higher the magnesium content in the alloy, the higher was the temperature dependence of flow stress. The alloys showed no perceptible creep in the vicinity of room temperature, while they crept at lower as well as higher temperatures. The most probable cause of hardening at temperatures below ∼ 200° K was found to be the pinning of dislocations by randomly distributed solute atoms, while athermal locking of dislocations by dynamic strain ageing during creep was responsible for the negligibly small creep rate in the room temperature range.

Room-temperature equal channel angular extrusion of pure magnesium

In this paper, we demonstrate a way to impart severe plastic deformation to magnesium at room temperature to produce ultrafine grain size of similar to 250 nm through equal channel angular extrusion (ECAE). The strategy to deform magnesium at lower temperature or to achieve such grain sizes has been proposed as: (i) to obtain a suitable initial orientation with high Schmid factor for basal slip and low Schmid factor for pyramidal/prismatic slip; (ii) to take advantage of low stacking fault energy of basal and high stacking fault energies of prismatic/pyramidal planes in order to relatively work-harden the basal plane with respect to the pyramidal/prismatic plane; and (iii) to lower the temperature of deformation in steps, leading to continual refinement of grains, resulting in finer grain size. The experimental as well as simulated texture of ECAE-processed samples indicate that the deformation mechanism leading to ultrafine grain size is slip-dominated. The recrystallization mechanism during ECAE has been found to be orientation-dependent. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Aspects of tautomerism. Part II. Reactions of the pseudo-acid chloride of o-benzoylbenzoic acid with nucleophiles

Reactions of fourteen nucleophiles with the pseudo-acid chloride of o-benzoylbenzoic acid in two solvents have been studied. The nucleophiles that react primarily at the tetrahedral carbon atom to give pseudo derivatives, are weaker than those that react at the carbonyl carbon atom causing opening of the lactone ring. An explanation for this phenomenon is advanced.

Stereoselectivity in the addition of hydrogen chloride to cyclohex-1-enecarbonitrile: Possible role of chlorine lone pair-nitrile π-orbital pseudoallylic A1, 3 interaction

The (overall trans) addition of hydrogen chloride to cyclohex-1- enecarbonitrile in anhydrous alcoholic media proceeds to give cis-2-chlorocyclohexanecarboxylate (together with some cis-2- chlorocyclohexanecarboxamide): no corresponding products with the trans-configuration are detectable. In anhydrous ether the addition proceeds to give a single isomer, presumably cis-, of 2-chlorocyclohexanecarbonitrile, indicating that the configuration of the products may not be equilibrium-controlled in alcoholic media. An examination of the steric factors indicates that the transition state for protonation of the presumed intermediate, 2-chlorocyclohexylidenemethylideneimine, leading to cis-product is favoured if interaction between the lateral π-orbital of the C-N double bond and the lone-pairs on the chlorine atom at the 2-position is large. Consideration of interactions in the transition states meets Zimmerman's criticism that invoking A1, 3 interaction existing in ground states to explain product configuration takes insufficient account of the Curtin-Hammett principle.

Electron-metallographic studies of precipitation in an aluminium-zinc-magnesium alloy

The mechanism of sub-microscopic precipitation in an Al-Zn-Mg alloy selected for its maximum response to ageing has been studied by a standardized oxide-replica technique in a 100 kV. Philips Electron Microscope. Contrary to earlier conclusions, examination of the oxide replicas has been shown to reveal details of the precipitation process almost as clearly as the thin-foil transmission technique. The reported formation of spherical Guinier-Preston zones followed by the development of a Widmanstaetten pattern of precipitated platelets has been confirmed. The zones have, however, been shown to grow into the platelets and not to dissolve in the matrix as reported earlier. The precipitation process has been correlated with the Hardness/Ageing Time curve and the structure of the precipitates has also been discussed.

Studies on phosphorus oxychloride and aluminium chloride complex

1. Anhydrous aluminium chloride reacts with phosphorus oxychloride to give a complex with a composition AlCl3.2 POCl3 which can be prepared in the form of a free flowing powder. 2. The phosphorus oxychloride-aluminium chloride complex in nitrobenzene dissociates into AlCl3.POCl3 and POCl3 as indicated by the cryoscopic measurements. 3. The solution of the complex in nitrobenzene has a higher specific conductivity than the corresponding electrical conductivities of individual components. Similar higher electrical conductance is observed when the two components are mixed in nitrobenzene in different proportions. 4.When a solution of anhydrous aluminium chloride in nitrobenzene is titrated conductometrically against a solution of phosphorus oxychloride in nitrobenzene, a limiting value in the conductivity is reached at point corresponding to the molecular composition, the components in the ratio of 1:2 AlCl3: POCl3 in solution. 5. The absorption maxima of the complex in nitrobenzene solution differ from the absorption maximum of the individual components.

Effect of plasticizers on magnesium-poly(ethyleneoxide) polymer electrolyte

Solid polymer electrolytes (SPEs) of poly(ethyleneoxide) and magnesium triflate, which are plasticized with propylene carbonate (PC), ethylene carbonate (EC) and a mixture of PC and EC, are studied for their conductivity, ac impedance of the Mg I SPE interface, cyclic voltammetry, infrared spectroscopy and differential scanning calorimetry. in the presence of plasticizers, the ionic conductivity (a) increases from a value of 1 x 10(-8) S cm(-1) to about 1 x 10(-4) S cm(-1) at ambient temperature. The a is found to follow a VTF relationship with temperature. The values of the activation energy, pre-exponential factor and equilibrium glass transition temperature are shown to depend on the concentration of plasticizer. Ac impedance studies indicate lower interfacial impedance of Mg/plasticized SPE than stainless steel/plasticized SPE. The impedance spectra are analyzed using a non-linear least square curve fitting technique and the interfacial resistance of Mg/plasticized SPE is evaluated. The cyclic voltammetric results suggest a quasireversible type of Mg/Mg2+ couple in plasticized SPE. (C) 2000 Elsevier Science B.V. All rights reserved.

Role of aluminum-magnesium alloys in humid aging of composite solid propellants

The humid aging of composite propellants containing a terpolymer of polybutadiene, acrylic acid, and acrylonitrile (PBAN) as a binder has been studied as a function of aging temperature, relative humidity, and aging time. Three composite types - AP-PBAN, AP-Al-PBAN, and AP-(Al-Mg) alloy- PBAN - have been studied. The burning rates of all three propellant types were unaffected by aging. The calorimetric values of composites containing aluminum-magnesium alloy decreased on aging, and the lattice parameter of the alloy decreased to a value close to that of aluminum. Water absorption in all of the samples increased with increases in the temperature, relative humidity, and aging time. The compression strength of the nonmetalized and aluminized samples decreased on aging, whereas that of the composites containing the alloy increased. The latter effect has been traced to reaction of residual carboxyl groups on the polymer chains with magnesium, leading to cross-linking. The reaction between the -COOH groups and magnesium has been proved using infrared spectroscopy. (Author)

An alpha-aminomethyl carbanion equivalent via a novel Barbier reaction: (1H-naphtho[1,8-de]-1,2,3-triazin-2-yl)methyl anion

A novel sonication-promoted Barbier reaction putatively generated the titled species from the corresponding naphthotriazinylmethyl chloride and magnesium in THF: its formal addition to a variety of carbonyl compounds in situ occurred in excellent yields. Subsequent catalytic hydrogenolysis of the triazine moiety demasked the amine, thus defining a route to various phenylethylamines (including the alkaloid 'mescaline'), or ethanolamines (in two cases), in excellent overall yields. (C) 2000 Elsevier Science Ltd. All rights reserved.

Creep Behaviour of AE42 Magnesium Alloy and Its Composites Using Impression Creep Technique

The creep behaviour of a creep-resistant AE42 magnesium alloy has been examined in the temperature range of 150 to 240 degrees C at the stress levels ranging from 40 to 120 MPa using impression creep technique. A normal creep behaviour, i.e., strain rate decreasing with strain and then reaching a steady state, is observed at all the temperatures and stresses employed The stress exponent varies from 5.1 to 5.7 and the apparent activation energy varies from 130 to 140 kJ/mol, which suggests the high temperature climb of dislocation controlled by lattice self-diffusion being the dominant creep mechanism in the stress and temperature range employed The creep behaviour of the AE42 alloy has also been compared with its composites reinforced with Saffil short fibres and SiC particles in four combinations. All the composites exhibited a lower creep rate than the monolithic AE42 alloy tested at the same temperature and stress levels and the decrease in creep rate was greater in the longitudinal direction than in the transverse direction, as expected. All the hybrid composites, i.e., the composites reinforced with a combination of Saffil short fibres and SiC particles, exhibited creep rates comparable to the composite reinforced with 20% Saffil short fibres alone at all the temperature and stress levels employed, which is beneficial from the commercial point of view.

Laser Surface Alloying of a Creep Resistant Magnesium Alloy MRI 230D with Al and Al2O3

A creep resistant permanent mould cast Mg alloy MRI 230D was laser surface alloyed with Al and a mixture of Al and Al2O3 using pulsed Nd:YAG laser irradiation at four different scan speeds in order to improve the corrosion and wear resistance. The microstructure, corrosion and wear behavior of the laser surface alloyed material is reported in this manuscript. The coating comprised of a featureless microstructure with cellular-dendritic microstructure near the interface and exhibited good interfacial bonding. A few solidification cracks reaching down to substrate were also observed. The two step coating with Al followed by a mixture of Al and Al2O3 exhibited a slightly better corrosion resistance than the single step coating with Al. In the long run, however, corrosion resistance of both the coatings became comparable to the as-cast alloy. The corroded surface of the laser surface alloyed specimens revealed a highly localized corrosion. The laser surface alloyed specimens exhibited an improvement in wear resistance. The laser scan speed did not exhibit a monotonic trend either in corrosion or wear resistance.

REACTION OF THIOPHOSPHORYL FLUORIDE AND THIOPHOSPHORYL CHLORIDE WITH DIMETHYL SULPHOXIDE

Solid complexes of thiophosphoryl fluoride and thiophosphoryl chloride with dimethyl sulphoxide (DMSO) have been prepared and characterized.