Dissociation pressure and Gibbs energy of formation of Y3Fe5O12 and YFeO3

Compounds in the ternary system Y  Fe  O are of significant interest due to their magnetic properties. Electrochemical solid state galvanic cell techniques have been employed to study their thermodynamic properties in the temperature range from 900 to 1250 °C. The following oxygen dissociation pressures were obtained: log P_O2$\text{[}\text{Pa}\text{] = ?}\text{26365}\text{T}\text{+ 17.13}$ for yttrium iron garnet, Y₃Fe₅O₁₂, in the entire temperature range, log P_O2$\text{[}\text{Pa}\text{] = ?}\text{29345}\text{T}\text{+ 13.00}$ for perovskite, YFeO₃, below 1080 °C and log P_O2$\text{[}\text{Pa}\text{] = ?}\text{39375}\text{T}\text{+ 20.43}$ for YFeO₃ above 1080 °C. The standard Gibbs energies of formation from metallic iron, yttria (Y₂O₃) and oxygen were determined to be $\text{2}\text{G}{}^{\mathrm{o}}\text{= ? 2078.2 + 0.5850·}\text{T kJ}\text{/}\text{mol}$ for the formation of Y₃Fe₅O₁₂ and $\text{2}\text{G}{}^{\mathrm{o}}\text{= ? 421.3 + 0.1148·}\text{T kJ}\text{/}\text{mol}$ for the formation of YFeO₃. The standard enthalpies and entropies of formation are ? 2078.2 kJ/mol and ? 585.0 J/mol·K for Y₃Fe₅O₁₂ and ? 421.3 kJ/mol and ? 114.8 J/mol·K for YFeO₃, respectively.     

Fatigue crack growth in polyurethane foam

The growth of fatigue cracks in compact tension specimens of rigid polyurethane foam has been studied at room temperature under conditions of constant load-amplitude cycling. The growth of the cracks at the frequencies employed (0.2 Hz) is found to be reasonably reproducible and the growth rate can be related to the cyclic stress intensity range in the conventional way. The rate of growth of the cracks is also found to depend on the mean stress level and an attempt has been made to separate out the effects of stress-intensity range, K, and the maximum stress intensity in each cycle, K _max, by combining the data obtained under a variety of loading conditions.     

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An analysis of reaction diffusion in metal-non-metal systems

The formation of a single M _x N _y intermediate phase in a metal-non-metal system is governed by two parabolic growth regions if the metal side of the couple is finite in extent and initially unsaturated with non-metal. The first parabolic region is described by semi-infinite conditions on the metal side of the couple, while the second is according to saturated conditions. The intermediate phase reaction layer grows non-parabolically when conditions are such that the concentration profile cannot be described by either semi-infinite or saturated conditions on the metal side of the couple. Expressions have been obtained relating the growth constants to diffusion coefficients and information from an equilibrium phase diagram. The mathematical formulation of the problem was tested by application to the titanium-carbon system. The diffusion coefficient of carbon in titanium carbide was found to be in close agreement with values reported elsewhere in the literature.     

Mechanical properties in the initial stage of sintering

Silicon nitride-based ceramics with different compositions were sintered in the 60%–90% range of theoretical density. Linear correlations between the apparent density and the modulus of elasticity, the three- and four-point bend strengths or the Vickers hardness, were observed. The slopes of the straight lines were nearly the same for all compositions. Furthermore, the modulus of elasticity, hardness, fracture toughness and strength were calculated as functions of density by modelling the structure as a random arrangement of spheres as suggested by Fischmeister and Arzt. The relationships obtained have been compared with the measured ones.Nomenclature a average contact area - a _c increase of the area of a crack - A area of the reference plane - b size of the critical defect - c constant in Equation 4 - D density - D ₀ density before shrinkage - D _T theoretical density - e direction of macroscopic strain - E modulus of elasticity - E ₀ modulus of elasticity of the dense material - f force loading a contact - f() projection of force f to e - F force loading the reference plane - g geometry parameter in the Griffiths relationship - H hardness - K _IC fracture toughness - N number of particles in unit volume - N() the fraction of N in a given spherical angle - n() number of particles in the volume around the reference plane - P porosity - R initial particle radius - R particle radius after fictitious growth - R particle radius after redistribution of material - R _SQ shared correlation coefficient - S surface energy of the defect - vector connecting the centres of neighbouring particles - W work necessary for increase the area of a crack - Z average coordination number - Z ₀ initial coordination number - strain - _T strain at theoretical strength - strength - _T theoretical strength (limit of elasticity) - angle between v and e     

J. H. Kulick, J. M. Jarem, R. G. Lindquist, S. T. Kowel, and M. W. Friends are with the Department of Electrical and Computer Engineering, University of Alabama in Huntsville, Huntsville, Alabama 35899

The development and modeling of a liquid-crystal phase grating for real-time diffractive three-dimensional displays are discussed. The system being developed, which is called the ICVision system, utilizes a number of ideas that will result in a rugged, low-power three-dimensional display offering both vertical and horizontal parallax and eventually full color. Fringing fields created between interdigitated electrodes formed on top of VLSI die will induce a diffraction pattern in a thin layer of liquid crystal that will cover the die. A detailed electrostatic and diffraction analysis of liquid-crystal phase-grating regions that will make up the final display is given here. The electrostatic analysis is developed by use of the method of moments. The diffraction analysis is developed by use of rigorous coupled-wave diffraction theory. The numerical results obtrained from the mathematical model are compared with experimental diffraction results from preliminary LCD cells that have been assembled as prototype ICVision devices.