Multifractal analysis, a method to investigate the morphology of materials

Using the multifractal formalism, we discuss the results obtained to characterized the morphology of polymer alloys and granular discontinuous metallic thin films. In the first case we have found a correlation between the multifractality and the mechanical properties of the alloys. In the second case, we have found that it is possible to measure the differences between the morphology of thin films induced by a growth process on a subtrate and that of percolation clusters of the classical theory of percolation.

Growth and characterization of single crystal cored fibers of organic nonlinear optical materials

The recent development of several organic materials with large nonlinear susceptibilities, high damage threshold and low melting points encouraged researchers to employ these materials in fiber form to efficiently couple diode laser pumps and obtain enhanced second harmonic generation (SHG). In this paper we report the growth of single crystal cored fibers of 4-nitro-4'-methylbenzylidene aniline, ethoxy methoxy chalcone and (-)2-((alpha) -methylbenzylamino)-5- nitropyridine by inverted Bridgman-Stockbarger technique. The fibers were grown in glass capillaries with varying internal diameters and lengths and were characterized using x-ray and polarizing microscope techniques. The propagation loss at 632.8 nm and 1300 nm were measured and SHG was studied using 1064 nm pump.

Mullite-zirconia composites

Mullite-zirconia composite powders were prepared by the combustion of an aqueous heterogeneous redox mixture consisting of Al(NO3)(3), Zr(NO3)(4)/ZrO(NO3)(2), silica fume and urea/diformyl hydrazine at 500 degrees C. X-ray diffraction data showed that a large amount of tetragonal zirconia existed in the composite powders in spite of high temperature calcination. Milled composite powders showed enhanced densification compared to the unmilled powders and the microstructure of the sintered (1600 degrees C) compacts showed the presence of spherical zirconia grains in intergranular positions along with elongated mullite grains.

Synergetic roles of concrete ingredients in strength development

Concrete is basically a heterogeneous material made up of ingredients with distinct physical and mechanical properties. As a result, the presence of interphases is inevitable. In the processing of concrete, fresh and hardened states are the two distinct stages. In the fresh state, the presence of inert constituents in the cement mortar matrix only dilutes the overall potential of concrete to flow. In the hardened state the synergetics play a dominant role in strength development. When the strength of coarse aggregate is far higher than the strength levels for which the matrix or concrete is processed, interphase bonding plays a dominant role on the strength. When the matrix strength is comparable to that of the aggregate strength, in contrast, the concrete strength is affected by the aggregate strength. Besides these aspects, the effects of the size and the surface texture of coarse aggregates have also been analysed. Copyright (C) 1996 Elsevier Science Ltd.

Systematic crystallographic investigation of hydrogen-bonded networks involving monohydrogen tartrate-amine complexes: Potential materials for nonlinear optics

Crystal structures of six binary salts involving aromatic amines as cations and hydrogen tartrates as anions are presented. The materials are 2,6-xylidinium-L-monohydrogen tartrate monohydrate, C12H18O6.5N, P22(1)2(1), a = 7.283(2) Angstrom, b = 17.030(2) Angstrom, c = 22.196(2) Angstrom, Z = 8; 2,6-xylidinium-D-dibenzoyl monohydrogen tartrate, C26H25O8N, P2(1), a = 7.906(1) Angstrom, b = 24.757(1) Angstrom, c = 13.166(1) Angstrom, beta = 105.01(1)degrees, Z = 4; 2,3-xylidinium-D-dibenzoyl monohydrogen tartrate monohydrate, C26H26O8.5N, P2(1), a = 7.837(1) Angstrom, b = 24.488(1) Angstrom, c = 13.763(1) Angstrom, beta = 105.69(1)degrees, Z = 4; 2-toluidinium-D-dibenzoyl monohydrogen tartrate, C25H23O8N, P2(1)2(1)2(1), a = 13.553(2) Angstrom, b = 15.869(3) Angstrom, c = 22.123(2) Angstrom, Z = 8; 3-toluidinium-D-dibenzoyl monohydrogen tartrate (1:1), C25H23O8N, P1, a = 7.916(3) Angstrom, b = 11.467(6) Angstrom, c = 14.203(8) Angstrom, alpha = 96.44(4)degrees, beta = 98.20(5)degrees, = 110.55(5)degrees, Z = 2; 3-toluidinium-D-dibenzoyl tartrate dihydrate (1:2), C32H36O10N, P1, a = 7.828(3) Angstrom, b = 8.233(1) Angstrom, c = 24.888(8) Angstrom, alpha = 93.98 degrees, beta = 94.58(3)degrees, = 89.99(2)degrees, Z = 2. An analysis of the hydrogen-bonding schemes in terms of crystal packing, stoichiometric variations, and substitutional variations in these materials provides insights to design hydrogen-bonded networks directed toward the engineering of crystalline nonlinear optical materials.

Seebeck Coefficient in Bulk and Quantum Wells of Non-Parabolic Kane-Type Materials

We present a simplified and quantitative analysis of the Seebeck coefficient in degenerate bulk and quantum well materials whose conduction band electrons obey Kane's non-parabolic energy dispersion relation. We use k.p formalism to include the effect of the overlap function due to the band non-parabolicity in the Seebeck coefficient. We also address the key issues and the conditions in which the Seebeck coefficient in quantum wells should exhibit oscillatory dependency with the film thickness under the acoustic phonon and ionized impurity scattering. The effect of screening length in degenerate bulk and quantum wells has also been generalized for the determination of ionization scattering. The well-known expressions of the Seebeck coefficient in non-degenerate wide band gap materials for both bulk and quantum wells has been obtained as a special case and this provides an indirect proof of our generalized theoretical analysis.

Hydrogen-Bond-Directed Nonlinear-Optical Organic Materials - Evidence For The Control Of 2nd-Harmonic Generation Activities From The X-Ray Crystal-Structures Of The Complexes Of L-Tartaric Acid With M-Anisidine and P-Toluidine

Several substituted anilines were converted to binary salts with L-tartaric acid. Second harmonic generation (SHG) activities of these salts were determined. The crystal packing in two structures, (i) m-anisidinium-L-tartrate monohydrate (i) and (ii) p-toluidinium-L-tartrate (2), studied using X-ray diffraction demonstrates that extensive hydrogen bonding steers the components into a framework which has a direct bearing on the SHG activity

Nanoscale Ag–Pd and Cu–Pd alloys

Nanoparticles of Ag-Pd and Gu-Pd alloys with diameters in the 5-40 nm range have been prepared over the entire range of compositions, by employing the heterogeneous reaction of dry methanol or ethanol with intimate mixtures of AgNO3+PdOx and CuOx+PdOx, respectively. The nanoscale alloys have been characterized by energy-dispersive Xray (EDX) analysis, transmission electron microscopy (TEM) and X-ray diffraction (XRD). All the alloy particles possess the fee structure and can be obtained in bulk quantities.

Novel materials synthesis by mechanical alloying/milling

An account is given of the research that has been carried out on mechanical alloying/milling (MA/MM) during the past 25 years. Mechanical alloying, a high energy ball milling process, has established itself as a viable solid state processing route for the synthesis of a variety of equilibrium and non-equilibrium phases and phase mixtures. The process was initially invented for the production of oxide dispersion strengthened (ODS) Ni-base superalloys and later extended to other ODS alloys. The success of MA in producing ODS alloys with better high temperature capabilities in comparison with other processing routes is highlighted. Mechanical alloying has also been successfully used for extending terminal solid solubilities in many commercially important metallic systems. Many high melting intermetallics that are difficult to prepare by conventional processing techniques could be easily synthesised with homogeneous structure and composition by MA. It has also, over the years, proved itself to be superior to rapid solidification processing as a non-equilibrium processing tool. The considerable literature on the synthesis of amorphous, quasicrystalline, and nanocrystalline materials by MA is critically reviewed. The possibility of achieving solid solubility in liquid immiscible systems has made MA a unique process. Reactive milling has opened new avenues for the solid state metallothermic reduction and for the synthesis of nanocrystalline intermetallics and intermetallic matrix composites. Despite numerous efforts, understanding of the process of MA, being far from equilibrium, is far from complete, leaving large scope for further research in this exciting field.

Deformation behaviour of commercially pure titanium at extreme strain rates

The evolution of microstructure and texture during room temperature compression of commercially pure Ti with four different initial orientations were studied under quasi-static and dynamic loading conditions. At a low strain rate (epsilon)over dot = 3 x 10(-4) s(-1) the different initial textures yielded the same end texture, despite different microstructural evolution in terms of twin boundaries. High strain rate deformation at (epsilon)over dot = 1.5 x 10(3) s(-1) was characterized by extensive twinning and evolution of a texture that was similar to that at low strain rate with minor differences. However, there was a significant difference in the strength of the texture for different orientations that was absent for low strain rate deformed samples at high strain rate. A viscoplastic self-consistent model with a secant approach was used to corroborate the experimental results by simulation. (C) 2011 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

ChemInform Abstract: Chemical Design of Solid Inorganic Materials

Newer strategies for the synthesis of inorganic solids have made a great impact on present-day materials chemistry. In this article, typical case studies of synthesis involving new methods and soft chemical routes are discussed besides recent results from nebulized spray pyrolysis and synthesis of nanoscale metal and alloy particles.

Oxidation of aqueous sulphur dioxide catalysed by poly-4-vinylpyridine-Cu(II) complex .2. Combined homogeneous and heterogeneous phase oxidation

Aqueous phase oxidation of sulphur dioxide at low concentrations catalysed by a PVP-Cu complex in the solid phase and dissolved Cu(II) in the liquid phase is studied in a rotating catalyst basket reactor (RCBR). The equilibrium adsorption of Cu(II) and S(VI) on PVP particles is found to be of the Langmuir-type. The diffusional effects of S(IV) species in PVP-Cu resin are found to be insignificant whereas that of product S(VI) are found to be significant. The intraparticle diffusivity of S(VI) is obtained from independent tracer experiments. In the oxidation reaction HSO3- is the reactive species. Both the S(IV) species in the solution, namely SO2(aq) and HSO3- get adsorbed onto the active PVP-Cu sites of the catalyst, but only HSO3- undergoes oxidation. A kinetic mechanism is proposed based on this feature which shows that SO2(aq) has a deactivating effect on the catalyst. A rate model is developed for the three-phase reaction system incorporating these factors along with the effect of concentration of H2SO4 on the solubility of SO2 in the dilute aqueous solutions of Cu(II). Transient oxidation experiments are conducted at different conditions of concentration of SO2 and O-2 in the gas phase and catalyst concentration, and the rate parameters are estimated from the data. The observed and calculated profiles are in very good agreement. This confirms the deactivating effect of nonreactive SO2(aq) on the heterogeneous catalysis.

Redistribution Mechanisms for Assignment of Heterogeneous Objects

There are p heterogeneous objects to be assigned to n competing agents (n > p) each with unit demand. It is required to design a Groves mechanism for this assignment problem satisfying weak budget balance, individual rationality, and minimizing the budget imbalance. This calls for designing an appropriate rebate function. When the objects are identical, this problem has been solved which we refer as WCO mechanism. We measure the performance of such mechanisms by the redistribution index. We first prove an impossibility theorem which rules out linear rebate functions with non-zero redistribution index in heterogeneous object assignment. Motivated by this theorem,we explore two approaches to get around this impossibility. In the first approach, we show that linear rebate functions with non-zero redistribution index are possible when the valuations for the objects have a certain type of relationship and we design a mechanism with linear rebate function that is worst case optimal. In the second approach, we show that rebate functions with non-zero efficiency are possible if linearity is relaxed. We extend the rebate functions of the WCO mechanism to heterogeneous objects assignment and conjecture them to be worst case optimal.