Evaluation of Erosion Resistance of Metallic Materials and the Role of Material Properties in Correlations

A study of the correlations between material properties and normalized erosion resistance (inverse of erosion rates) of various materials tested in the rotating disk and the flow venturi at various intensities indicates that different individual properties influence different stages of erosion. At high and low intensities of erosion, energy properties predominate the phenomenon, whereas at intermediate intensities strength and acoustic properties become more significant. However, both strength and energy properties are significant in the correlations for the entire spectrum of erosion when extensive cavitation and liquid impingement data from several laboratories involving different intensities and hydrodynamic conditions are considered. The use of true material properties improved the statistical parameters by 3 to 37%, depending on the intensity of erosion. It is possible to evaluate qualitatively the erosion resistances of materials based on the true stress-true strain curves.

A Bilinear Constitutive Model for Isotropic Bimodulus Materials

Proper formulation of stress-strain relations, particularly in tension-compression situations for isotropic biomodulus materials, is an unresolved problem. Ambartsumyan's model [8] and Jones' weighted compliance matrix model [9] do not satisfy the principle of coordinate invariance. Shapiro's first stress invariant model [10] is too simple a model to describe the behavior of real materials. In fact, Rigbi [13] has raised a question about the compatibility of bimodularity with isotropy in a solid. Medri [2] has opined that linear principal strain-principal stress relations are fictitious, and warned that the bilinear approximation of uniaxial stress-strain behavior leads to ill-working bimodulus material model under combined loading. In the present work, a general bilinear constitutive model has been presented and described in biaxial principal stress plane with zonewise linear principal strain-principal stress relations. Elastic coefficients in the model are characterized based on the signs of (i) principal stresses, (ii) principal strains, and (iii) on the value of strain energy component ratio ER greater than or less than unity. The last criterion is used in tension-compression and compression-tension situations to account for different shear moduli in pure shear stress and pure shear strain states as well as unequal cross compliances.

Comparison of the effect of processing parameters and degradation on the DC and microwave properties of thin films and polycrystalline bulk high-Tc superconducting materials

The sharp increase in microwave power loss (the reverse of what has previously been reported) at the transition temperature in high-Tc superconducting systems such as YBaCu oxide (polycrystalline bulk and thin films obtained by the laser ablation technique) and BiPbSrCaCu oxide is reported. The differences between DC resistivity ( rho ) and the microwave power loss (related to microwave surface resistance) are analysed from the data obtained by a simultaneous measurement set-up. The influence of various parameters, such as preparation conditions, thickness and aging of the sample and the probing frequency (6-18 GHz), on the variation of microwave power loss with temperature is outlined.

Phase diagram of the two-dimensional disordered Hubbard model in the Hartree-Fock approximation

Ground-state properties of the two-dimensional Hubbard model with point-defect disorder are investigated numerically in the Hartree-Fock approximation. The phase diagram in the p(point defect concentration)-delta(deviation from half filling) plane exhibits antiferromagnetic, spin-density-wave, paramagnetic, and spin-glass-like phases. The disorder stabilizes the antiferromagnetic phase relative to the spin-density-wave phase. The presence of U strongly enhances the localization in the antiferromagnetic phase. The spin-density-wave and spin-glass-like phases are weakly localized.

A Feature-Based Solution to Forward Problem in Electrical Capacitance Tomography of Conductive Materials

A new feature-based technique is introduced to solve the nonlinear forward problem (FP) of the electrical capacitance tomography with the target application of monitoring the metal fill profile in the lost foam casting process. The new technique is based on combining a linear solution to the FP and a correction factor (CF). The CF is estimated using an artificial neural network (ANN) trained using key features extracted from the metal distribution. The CF adjusts the linear solution of the FP to account for the nonlinear effects caused by the shielding effects of the metal. This approach shows promising results and avoids the curse of dimensionality through the use of features and not the actual metal distribution to train the ANN. The ANN is trained using nine features extracted from the metal distributions as input. The expected sensors readings are generated using ANSYS software. The performance of the ANN for the training and testing data was satisfactory, with an average root-mean-square error equal to 2.2%.

Self-assembled composite nano-materials exploiting a thermo reversible n-acene fibrillar scaffold and organic-capped ZnO nanoparticles

An organic-inorganic composite material is obtained by self-assembly of 2,3-didecyloxy-anthracene (DDOA), an organogelator of butanol, and organic-capped ZnO nanoparticles (NPs). The ligand 3, 2,3-di(6-oxy-n-hexanoic acid)-anthracene, designed to cap ZnO and interact with the DDOA nanofibers by structural similarity, improves the dispersion of the NPs into the organogel. The composite material displays mechanical properties similar to those of the pristine DDOA organogel, but gelates at a lower critical concentration and emits significantly less, even in the presence of very small amounts of ZnO NPs. The ligand 3 could also act as a relay to promote the photo-induced quenching process.

Large negative magnetoresistance and metal-insulator transition observed in MnO/C composite coatings grown on ceramic alumina by metalorganic chemical vapor deposition

MnO/C composite coatings were grown by the metalorganic chemical vapor deposition process on ceramic alumina in argon ambient. Characterization by various techniques confirms that these coatings are homogeneous composites comprising nanometer-sized MnO particles embedded in a matrix of nanometer-sized graphite. Components of the MnO/C composite coating crystalline disordered, but are electrically quite conductive. Resistance vs. temperature measurements show that coating resistance increases exponentially from a few hundred ohms at room temperature to a few megaohms at 30 K. Logarithmic plots of reduced activation energy vs. temperature show that the coating material undergoes a metal-insulator transition. The reduced activation energy exponent for the film under zero magnetic field was 2.1, which is unusually high, implying that conduction is suppressed at much faster rate than the Mott or the Efros-Shklovskii hopping mechanism. Magnetoconductance us. magnetic field plots obtained at various temperatures show a high magnetoconductance (similar to 28.8%) at 100 K, which is unusually large for a disordered system, wherein magnetoresistance is attributed typically to weak localization. A plausible explanation for the unusual behavior observed in the carbonaceous disordered composite material is proposed. (C) 2010 Elsevier Ltd. All rights reserved.

Length-scale-dependent ensemble-averaged conductance of a 1D disordered conductor: Conductance minimum

An exact numerical calculation of ensemble-averaged length-scale-dependent conductance for the one-dimensional Anderson model is shown to support an earlier conjecture for a conductance minimum. The numerical results can be understood in terms of the Thouless expression for the conductance and the Wigner level-spacing statistics.

Chemical Approaches to the Design of Oxide Materials.

Chemical methods of synthesis play a crucial role in designing and discovering new and novel materials and in providing less cumbersome methods for preparing known materials. Chemical methods also enable the synthesis of metastable materials which are otherwise difficult to prepare. In this presentation, the various innovative chemical methods of synthesising oxide materials will be briefly reviewed with emphasis on soft-chemical routes. Electrochemical synthesis, ion-exchange method, alkali-flux method and some of the interaction reactions will be highlighted, besides topochemical aspects of solid state synthesis. Cuprate superconductors as well as intergrowth structures will also be examined.

Combustion synthesis of oxide materials for nuclear waste immobilization

Oxide materials like perovskite, zirconolite, hollandite, pyrochlore, NASICON and sphene which are used for nuclear waste immobilization have been prepared by a solution combustion process. The process involves the combustion of stoichiometric amount of corresponding metal nitrates and carbohydrazide/tetraformyl trisazine/diformyl hydrazide at 450 degrees C. The combustion products have been characterized using powder X-ray diffraction, infrared spectroscopy, and Si-29 MAS-NMR. The fine particle nature of the combustion derived powders has been studied using density, particle size, BET surface area measurements and scanning electron microscopy. Sintering of combustion derived powder yields 85-95% dense ceramics in the temperature range 1000 degrees-1300 degrees C.

Controlled combustion synthesis and properties of fine-particle NASICON materials

Fine-particle NASICON materials, Na1+xZr2P3-xSixO12 (where x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5), have been prepared by controlled combustion of an aqueous solution containing stoicthiometric amounts of sodium nitrate, zirconyl nitrate, ammonium perchlorate, diammonium hydrogen phosphate, fumed silica and carbonohydrazide. Formation of NASICON has been confirmed by powder XRD, Si-29 NMR and IR spectroscopy. These NASICON powders are fine (average agglomerate size 5-12 mum) with a surface area varying from 8 to 30 m2 g-1. NASICON powders pelletized and sintered at 1100-1200-degrees-C for 5 h achieved 90-95% theoretical density and show fine-grain microstructure. The coefficient of thermal expansion of sintered NASICON compact was measured up to 500-degrees-C and changes f rom -3.4 x 10(-6) to 4.1 x 10(-6) K-1. The conductivity of Sintered Na3Zr2PSi2O12 compact at 300-degrees-C is 0.236 OMEGA-1 cm-1.

Shear alignment of a disordered lamellar mesophase

The shear alignment of an initially disordered lamellar phase is examined using lattice Boltzmann simulations of a mesoscopic model based on a free-energy functional for the concentration modulation. For a small shear cell of width 8 lambda, the qualitative features of the alignment process are strongly dependent on the Schmidt number Sc = nu/D (ratio of kinematic viscosity and mass diffusion coefficient). Here, lambda is the wavelength of the concentration modulation. At low Schmidt number, it is found that there is a significant initial increase in the viscosity, coinciding with the alignment of layers along the extensional axis, followed by a decrease at long times due to the alignment along the flow direction. At high Schmidt number, alignment takes place due to the breakage and reformation of layers because diffusion is slow compared to shear deformation; this results in faster alignment. The system size has a strong effect on the alignment process; perfect alignment takes place for a small systems of width 8 lambda and 16 lambda, while a larger system of width 32 lambda does not align completely even at long times. In the larger system, there appears to be a dynamical steady state in which the layers are not perfectly aligned-where there is a balance between the annealing of defects due to shear and the creation due to an instability of the aligned lamellar phase under shear. We observe two types of defect creation mechanisms: the buckling instability under dilation, which was reported earlier, as well as a second mechanism due to layer compression.