Cobalt(II), nickel(II) and copper(II) complexes of bidentate bibenzimidazoles

Complexes of cobalt(II), nickel(II) and copper(II) with novel bidentate bibenzimidazoles, [M(L-L)Cl2], where L-L are methylenebis(1, 1prime-benzimidazole), methylenebis(2, 2prime-benzimidazole) and dimethylenebis(2, 2prime-benzimidazole) are described and characterized by different physical measurements. The four coordinate complexes have distorted tetrahedral or square coplanar structures. The bridging entity between the two donor groups apparently influences the ligand field strength and the ligands occupy a higher position than that of benzimidazole in the spectrochemical series.

A computer study of the miscibility limits of Pd-Cu-Si

Metallic glasses are of interest because of their mechanical properties. They are ductile as well as brittle. This is true of Pd77.5Cu6Si16.5, a ternary glassy alloy. Actually, the most stable metallic glasses are those which are alloys of noble or transition metals A general formula is postulated as T70–80G30-20where T stands for one or several 3d transition elements, and includes the metalloid glass formers. Another general formula is A3B to A5B where B is a metalloid. A computer method utilising the MIGAP computer program of Kaufman is used to calculate the miscibility gap over a range of temperatures. The precipitation of a secondary crystalline phase is postulated around 1500K. This could produce a dispersed phase composite with interesting high temperature-strength properties.

Recent studies on the behaviour of interference fit pins in composite plates

Composites are finding increasing application in many advanced engineering fields like aerospace, marine engineering, hightech sports equipment, etc., due to their high specific strength and/or specific stiffness values. The use of composite components in complex situations like airplane wing root or locations of concentrated load transfer is limited due to the lack of complete understanding of their behaviour in the region of joints. Joints are unavoidable in the design and manufacture of complex structures. Pin joints are one of the most commonly used methods of connection. In regions of high stresses like airplane wing root joints interference fit pins are used to increase its fatigue life and thereby increase the reliability of the whole structure. The present contribution is a study on the behaviour of the interference fit pin in a composite plate subjected to both pull and push type of loads. The interference fit pin exhibits partial contact/separation under the loads and the contact region is a non-linear function of the load magnitude. This non-linear behaviour is studied by adopting the inverse technique and some new results are presented in this paper.

Varistor property of n‐BaTiO3 based current limiters

Highly stable varistor (voltage-limiting) property is observed for ceramics based on donor doped (Ba1-xSrx)Ti1-yZryO3 (x < 0.35, y < 0.05), when the ambient temperature (T(a)) is above the Curie point (T(c)). If T(a) < T(c), the same ceramics showed stable current-limiting behavior. The leakage current and the breakdown voltage as well as the nonlinearity coefficient (alpha = 30-50) could be varied with the T(c)-shifting components, the grain boundary layer modifiers and the post-sintering annealing. Analyses of the current-voltage relations show that grain boundary layer conduction at T(a) < T(c) corresponds to tunneling across asymmetric barriers formed under steady-state joule heating. At T(a) > T(c), trap-related conduction gives way to tunneling across symmetric barriers as the field strength increases.

Can equipartition fields produce the tilts of bipolar magnetic regions?

The effect of turbulence on the nonaxisymmetric flux rings of equipartition field strength in bipolar magnetic regions is studied on the basis of the small-scale momentum exchange mechanism and the giant cell drag combined with the Kelvin-Helmholtz drag mechanism. It is shown that the giant cell drag and small-scale momentum exchange mechanism can make equipartition flux loops emerge at low latitudes, in addition to making them exhibit the observed tilts. However, the sizes of the flux tubes have to be restricted to a couple of hundred kilometers. An ad hoc constraint on the footpoints of the flux loops is introduced by not letting them move in the phi direction, and it is found that equipartition fields of any size can be made to emerge at sunspot latitudes with the observed tilts by suitably adjusting the footpoint separations.

Swellability properties of polyelectrolyte complexes of polyaniline

Polyelectrolyte complexes of polyaniline with both strong and weak anionic polyelectrolytes have been prepared. It has been found that the swellability of the complexes depends on the charge content of polyaniline, i.e., on the intercrosslinking between polyaniline (which is a polyacation) and polyanions. It has also been observed that polyaniline in the polyaniline-polystresulfonic acid complex exists in the conducting state when equilibrated with basic pH in aqueous media of moderately high ionic strength.

The Determination of the Surface Tensions of Liquid-Iron, Nickel and Iron-Nickel Alloys using the electromagnetic Oscillating Droplet Technique

An oscillating droplet method combined with electromagnetic levitation has been applied to determine the surface tensions of liquid pure iron, nickel and iron-nickel alloys as a function of the temperature. The natural frequency of the oscillating droplet is evaluated using a Fourier analyser. The theoretical background of this method and the experimental set-up were described, and the influence of magnetic field strength was also discussed. The experimental results were compared with those of other investigators and interpreted using theoretical models (Butler's equation, subregular and perfect solution model for the surface phase).

The Determination of the Surface Tensions of Nickel Sulfur Alloys using the Electromagnetic Oscillating Droplet Technique

An oscillating droplet method combined with electromagnetic levitation technique has been applied to determine the surface tensions of liquid nickel sulphur alloys as a function of the temperature and composition. The natural frequency of the oscillating droplet is evaluated using a Fourier analyser, and the influence of magnetic field strength on the surface tension was considered. Furthermore, the applicability of Butler's equation and subregular solution model for the surface was shown to predict the surface tension of the systems containing the surface active elements.

Low-temperature magnetoresistance of ?-phase FexNi80-xCr20 alloys near the critical composition for ferromagnetism

We present a comprehensive study of magnetoresistance (MR) of the crystalline pseudobinary ?-phase Fe alloy series FexNi80-xCr20 (50?x?66). This alloy series shows exotic magnetic phases as the composition (x) is varied. It has a critical composition for ferromagnetism at x=xc?59�60. MR was measured in the temperature range 1.7�110 K and up to a field of 7 T. The observed MR was small and the change was ?1%. The temperature dependence of MR was found to contain a positive and a negative contribution. The positive term was found to be ?H2 and it dominates at high field and high temperatures. We explain this as a manifestation of Kohler�s rule. The negative MR was found to have a quadratic dependence on magnetization M. The magnitude of the negative MR reaches a maximum as x?xc.

Oxidative addition of tetrachloro-1,2-benzoquinone to lambda(3)-cyclotriphosphazanes. An unusual ring contraction-rearrangement

The lambda(3)-cyclotriphosphazanes, [EtNP(OR)](3) [R = 2,6-Me2C6H3 (1), 4-BrC6H4 (2), or CH2CF3(3)], on treatment with tetrachloro-1,2-benzoquinone (TCB) give the lambda(5)-cyclodiphosphazanes, [EtNP(O2C6Cl4)(OR)][EtNP(O2C6Cl4){N(Et)P(OR)(2)}] (5-7) by an unusual ring contraction-rearrangement. The reaction of the mixed substituent lambda(3)-cyclotriphosphazane, [(EtN)(3)P-3(OR)(2)(OR')] [R = 2,6-Me2C6H3, R' = 4-BrC6H4] (4), with TCB gives the lambda(5)-cyclodiphosphazane, [EtNP(O2C6Cl4)(OR')][EtNP(O2C6Cl4){N(Et)P(OR)(2)}] (8), in which 4-bromophenoxide resides on one of the ring phosphorus atoms. The lambda(3)-bicyclic tetraphosphapentazane, (EtN)(5)P-4(OPh)(2), on treatment with TCB undergoes a double ring contraction-rearrangement to give the lambda(5)-cyclodiphosphazane, (EtN)[(EtN)(2)P-2(O2C6Cl4)(2)(OPh)](2) (9). Variable-temperature and high-field P-31 NMR studies indicate the presence of more than one isomer in solution for the rearranged products 5-9. The solid state structure of 8 reveals a trans arrangement of the substituents with respect to the P2N2 ring in contrast to the gauche arrangement observed for 5.

Organometallic chemistry of chiral diphosphazane ligands: Synthesis and structural characterisation

The diphosphazane ligands of the type, (C20H12O2)PN(R)P(E)Y2 (R = CHMe2 or (S)-*CHMePh; E = lone pair or S; Y2 = O2C20H12 or Y = OC6H5 or OC6H4Me-4 or OC6H4OMe-4 or OC6H4But-4 or C6H5) bearing axially chiral 1,1'-binaphthyl-2,2′-dioxy moiety have been synthesised. The structure and absolute configuration of a diastereomeric palladium complex, [PdCl2{ηsu2}-((O2C20H12)PN((S)-*CHMePh)PPh2] has been determined by X-ray crystallography. The reactions of [CpRu(PPh3)2Cl] with various symmetrical and unsymmetrical diphosphazanes of the type, X2PN(R)PYY′ (R = CHMe2 or (S)-*CHMePh; X = C6H5 or X2 = O2C20H12; Y=Y′= C6H5 or Y = C6H5, Y′ = OC6H4Me-4 or OC6H3Me2-3,5 or N2C3HMe2-3,5) yield several diastereomeric neutral or cationic half-sandwich ruthenium complexes which contain a stereogenic metal center. In one case, the absolute configuration of a trichiral ruthenium complex, viz. [Cp*Ruη2-Ph2PN((S)-*CHMePh)*PPh (N2C3HMe2-3,5)Cl] is established by X-ray diffraction. The reactions of Ru3(CO)12 with the diphosphazanes (C20H12O2)PN(R)PY2 (R = CHMe2orMe; Y2=O2C20H12or Y= OC6H5 or OC6H4Me-4 or OC6H4OMe-4 or OC6H4But-4 or C6H5) yield the triruthenium clusters [Ru3(CO)10{η-(O2C20H12)PN(R)PY2}], in which the diphosphazane ligand bridges two metal centres. Palladium allyl chemistry of some of these chiral ligands has been investigated. The structures of isomeric η3-allyl palladium complexes, [Pd(η3-l,3-R′2-C3H3){η2-(rac)-(02C20H12)PN(CHMe2)PY2}](PF6) (R′ = Me or Ph; Y = C6H5 or OC6H5) have been elucidated by high field two-dimensional NMR spectroscopic and X-ray crystallographic studies.

Polarization switching studies in ferroelectric glycine phosphite single crystals

Glycine Phosphite [NH3CH2COOH3PO3], abbreviated as GPI, undergoes a para-ferroelectric phase transition from the monoclinic symmetry P2(1)/a to P2(1) at 224.7 K. We report here a systematic study of the polarization switching process in this crystal. Growth of these crystals from aqueous solution has been undertaken employing both solvent evaporation and slow cooling methods. Hysteresis loop measurements along the polar b-axis yielded a spontaneous polarization value of 0.5 muC/cm(2) and a coercive field of 2.5 kV/cm. Conventional Merz technique was employed for polarization switching studies, wherein bipolar square pulses were applied to the sample to induce domain reversal. The transient switching pulse that flows through the sample on application of the field was recorded. The maximum switching time required for domain switching was measured both as a function of electric field and temperature. The experimentally observed switching curves were fitted with the model based on the Pulvari-Kuebler theory of nucleation and growth of domains. From the experimental data, the values of mobility and activation field were obtained. It was observed that switching process in this crystal is predominantly governed by the forward growth of domain walls in the high field region. However, switching process in GPI crystal was found to be slower than that found in other glycine based ferroelectric crystals.

The thickness dependence of the electrical and dielectric properties in the laser ablated SrBi2Nb2O9 thin films

he thickness dependence of the electrical properties in the thin films of uniaxial SrBi2Nb2O9 has been studied in this report. According to many published literatures, it could be an effective way to identify the basic conduction process. The laser ablation was chosen as the deposition technique to ensure an oriented growth and a proper stoichiometric deposition. The structural, dielectric and conduction properties were studied as a function of thickness. The films showed good ferroelectric properties, an ordered growth, and a space-charge controlled conduction process, which was double checked by reversing the polarity of the applied voltage, and also by examining the high field current response of the sample varying in thickness.

Effect of neodymium (Nd) doping on the dielectric and ferroelectric characteristics of sol-gel derived lead zirconate titanate (53/47) thin films

The results of the studies on the effect of rare earth Nd doping on the phase formation behavior and electrical properties of sol-gel derived Pb-1.05(Zr0.53Ti0.47)O-3 (PZT) thin films are presented. The perovskite phase is obtained up to 5 at. % doping and beyond that pyrochlore phase was found to coexist with the perovskite phase in all the films. The transition temperature of undoped lead zirconate titanate (PZT) film was found to be reduced with Nd doping. The Nd doped films also exhibited typical relaxor-type behavior and a diffuse phase transition, similar to that observed in relaxor materials. The introduction of Nd into the PZT lattice probably introduces disorder in the B site of ABO(3) lattice, which causes the observed dielectric relaxation. Efforts were made to isolate the irreversible component contributions in low field dielectric and high field polarization switching behavior. (C) 2001 American Institute of Physics.

Temperature deformation behaviour of a Mg-0.8Al alloy

There is considerable interest currently in developing magnesium based alloys as replacements for aluminum alloys in automobile applications, due to their high specific strength as compared to aluminum alloys. However, the poor formability of magnesium alloys has restricted their applications; superplasticity can be utilized to form components with complex shapes. In the present study, the compressive deformation characteristics of a Mg-0.8 wt% Al alloy with an initial grain size of 19 +/- 1.0 mum have been studied in the temperature range of 623-673 K and at strain rates ranging from 10(-7) to 10(-3) s(-1). The stress exponent was observed to decrease with a decrease in stress. The results are analyzed in terms of the existing theoretical models for high temperature deformation. Furthermore, the potential for superplasticity in this alloy is explored, based on the mechanical and microstructural characteristics of the alloy.