Showing papers on "Phase (matter) published in 1972"

Phase Analysis in Zirconia Systems

Abstract: Linear calibration curves were developed for determining the content of free ZrO2 in partially stabilized zirconia ceramics by X-ray diffraction techniques. Two methods were studied. The matrix method, in which free ZrO2 was considered to be distributed in a matrix (the cubic phase), gave approximately equal mass absorption coefficients for the monoclinic and cubic phases. The polymorph technique, in which the cubic phase was considered to be a polymorph of ZrO2 and in which integrated intensities were used, gave the better results.

Process for the demonstration and determination of reaction components having specific binding affinity for each other

Abstract: The present invention relates to a process for the determination of a component of the reaction between a specific binding protein and the substance being specifically bound by such a protein comprising reacting the component to be determined with its binding partner in an insolubilized form, separating the solid phase of the reaction mixture from the liquid phase, reacting the solid phase with a determined amount of a coupling product of the substance to be determined with an enzyme, and finally determining the enzyme activity of the liquid or solid phase of the reaction mixture obtained.

Phase instabilities during high temperature exposure of 316 austenitic stainless steel

Abstract: Although Type 316 austenitic stainless steel is widely used in steam generating plants and nuclear reactors the knowledge about aging reactions, nature of precipitates, and precipitation kinetics during high temperature exposure is limited. Time-temperature-precipitation (TTP) diagrams were determined between 400° and 900°C for up to 3000 hr as a function of carbon content, solution treatment temperature, and cold work. The nucleation and growth phenomena, morphology, and composition of the various carbide (M23C6, M6C) and intermetallic phases (σ, χ, η were determined. The complex sequence of phase instabilities can be explained on the basis of the carbon content, effect of molybdenum and chromium on the carbon solubility, thermodynamic stability of the phases, and the kinetics of the various precipitation reactions.

Static and Dynamic Pore‐Collapse Relations for Ductile Porous Materials

Abstract: Static and dynamic pore‐collapse relations for ductile porous materials are obtained by analysis of the collapse of a hollow sphere of incompressible elastic‐plastic material, with appropriate pore radius and over‐all porosity. There are three phases of the pore‐collapse process: an initial phase, a transitional elastic‐plastic phase, and a plastic phase. The change in porosity during the first two phases is quite small. In the plastic phase, the static pore‐collapse relation is an exponential law that depends only on the yield strength of the material; the dynamic relation is a nonlinear second‐order ordinary differential equation that involves the yield strength and a material constant (with the physical dimension of time) that depends on the yield strength, the density, the initial porosity, and the pore radius. Comparison of the theoretical predictions with finite‐difference computer‐code calculations for pore collapse of a hollow sphere of compressible material indicates that the effect of elastic co...

Structural Influences on Adsorption Energy. III. CO on Cu(100)

Abstract: The adsorption of CO on Ni(100) has been studied using LEED, Auger, and work function measurements and was found to be completely reversible. The isosteric heat of adsorption was approximately 1.30 eV/molecule independent of coverage up to 0.61 monolayers. Three surface structures were observed: (1) a disordered phase at high temperature and/or low coverage, (2) a c(2× 2) phase at coverages up to and including 0.5 monolayers at sufficiently low temperature, and (3) a compressible hexagonal phase between 0.61 and 0.69 monolayers. Evidence is presented which supports an attractive CO–CO interaction at coverages of less than 0.5 monolayers. A number of two‐dimensional phase transitions were observed and suggest an interesting T—θ phase diagram with a eutecticlike triple point. The importance of scrupulous cleaning procedures in allowing all possible adsorbed phases to be observed has again been demonstrated.

Ceramics based on the Si-Al-O-N and Related Systems

Abstract: TSUGE et al.1 have shown that β -Si3N4 can accommodate up to about 60% by weight Al2O3 in solid solution without major change of crystal structure but with increasing a and c unit-cell dimensions as the Al2O3 concentration increases. The products, obtained by sintering the mixed powders at 1,700 and 1,770° C, are undoubtedly similar to a new phase observed by Oyama and Kamigaito2 in mixtures of Si3N4, Al2O3 and Li2CO3 hot-pressed at 1,750° C. We report here a variety of ceramic materials built up of (Si,Al)(N,O)4 tetrahedra joined by sharing corners just as the silicate structures are built up of SiO4 and (Si,Al)O4 units.

X-Ray Scattering from Liquid Crystals. I. Cholesteryl Nonanoate and Myristate

Abstract: X-ray scattering intensities from unoriented samples of cholesteryl nonanoate and myristate are reported for several temperatures in the smectic $A$, cholesteric, and isotropic liquid phases. The measured Bragg-scattering intensities from the smectic planes are used to test a recent theoretical model of the smectic $A$ phase. Strong pretransition scattering (short-range-order or order-parameter fluctuations) are observed in the cholesteric phase and a Landau theory is constructed to describe this effect.

A Theory of Water Percolation in Snow

Abstract: A theory is developed to describe the vertical percolation of water in isothermal snow. The general theory of Darcian flow is reviewed to establish a reasonable physical basis for the construction of a model. It is shown that in simple gravity drainage, capillarity is negligible compared with gravity since values of water saturation are generally in the “mid-range”. It is postulated that the permeability to the water phase increases as a certain function of the water saturation, and porosity is assumed to decrease linearly with depth. Ice layers and other inhomogeneities are treated in the theory by considering the permeability of the snow with the inhomogeneities included. A method by which this value of permeability can be calculated is presented using the method of characteristics. The theory is applied to the Seward Glacier firn where Sharp measured water fluxes at various depths. A periodic surface flux is assumed and the particular solution for water flux at any depth is given. From this solution the wave forms passing each depth are constructed and compared with the measured ones. Although the experimental data are affected by the presence of ice layers, the comparison between theory and experiment is favorable and the theory is thought to be essentially correct.

Destruction of Long-range Order in One-dimensional and Two-dimensional Systems Possessing a Continuous Symmetry Group. II. Quantum Systems.

Abstract: The asymptotic behavior of the correlations in the low-temperature phase are found for the following two-dimensional quantum systems: a two-dimensional lattice of plane rotators, two-dimensional magnetic substances having an easy plane of magnetization, a two-dimensional Bose liquid (Sec. 1), and a two-dimensional isotropic Heisenberg ferromagnet (Sec. 2). The nature of the change of the asymptotic behavior with increasing temperature is investigated for the systems considered in Sec. 1. The nature of the change of the asymptotic behavior with increasing temperature is investigated for the systems considered in Sec. 1. The nature of the low-temperature phase consists in the superfluidity of a twodimensional Bose liquid; the corresponding property can also be formulated in terms of magnetic substances.

Phase transition in diamond-structure crystals during hardness measurements

Abstract: The mechanism of microhardness print forming in diamond-structure crystals is considered to be the result of a local phase transition under the indenter with the formation of a metallic phase due to the high hydrostatic pressure generated in this case. It is shown that at the temperature T < 0.3 to 0.4 Tml, where the microhardness Hv is weakly temperature-dependent, one has Hv ≈ Pc(Pc transition pressure). In GaAs crystals, where Hv ≪ Pc, the athermal part in the hardness-temperature curve was not observed. It is shown as well that at the moment when the indenter entering the crystal is stopped there is a thin layer around it which still contains the metallic phase with high electrical conduction. The estimated thickness of the layer is ≈ 0.05 μm. The plastic deformation is supposed not to proceed at this moment because of the friction forces which oppose the squeezing-out of the metallic layer. [Russian text ignored].

Chemically joined phase separated thermoplastic graft copolymers

Abstract: The present invention relates to thermoplastic graft copolymers comprised of copolymeric backbones containing a plurality of uninterrupted repeating units of the backbone polymer and at least one integrally copolymerized moiety per backbone polymer chain having chemically bonded thereto a substantially linear polymer which forms a copolymerized sidechain to the backbone, wherein each of the polymeric sidechains has substantially the same molecular weight and each polymeric sidechain is chemically bonded to only one backbone polymer.

Structure and Phase Transitions of Solid Heavy Methane (CD4)

Abstract: The orientational structures and the phase transitions (27.0 and 22.1°K) of solid CD4 are investigated by coherent neutron scattering from powder samples as well as from single crystals. In its high temperature phase, CD4 is found to crystallize within the space group Fm3m with four molecules per unit cell and a lattice constant a0=5.96 A at 77°K. The molecular orientations are completely disordered at 35°K, while an indication of partial order was detected at 77°K. The transition to phase II is accompanied by critical fluctuations with a correlation length of about 24 A (at 27.7°K) and appears to be of second order (critical exponent β =0.4± 0.1. In phase II six of eight molecules order with a local symmetry 42m, while the remaining two are orientationally disordered. The space group is cubic Fm3c with 32 molecules per unit cell and a0=11.64 A at 24.5°K. The transition to phase III is predominantly of first order. With the present data the structure of phase III cannot be determined unambiguously. Superlattice reflections can be indexed cubic primitive. The number of molecules per unit cell remains 32, with a0=11.61 A at 17.5°K. The data suggest, that the low temperature structure is to be understood by an ordering within the sublattices of molecules disordered in phase II together with slight distortions of the other sublattices. The structures of phases I and II agree with the ones predicted by James and Keenan under the assumption of octupole—octupole interaction between nearest neighbour molecules. For phase III the model of James and Keenan, as well as other predictions, hitherto published, must be ruled out.

Further studies on the nickel–aluminium system. I. β‐NiAl and δ‐Ni2Al3 phase fields

Abstract: New lattice parameter and density results have been obtained for alloys in the β-NiAl and 6-Ni2Al3 phase fields of the nickel–aluminium system. The lattice parameter of the β-NiAl phase (CsCl-type) falls linearly from 2.8870 A at 50 at.% Ni to 2.8618 A at 66. at.% Ni, with 2.00 atoms per unit cell. On the other hand, the lattice parameter on the Al-rich side of NiAl falls linearly from 2.8870 A to 2.8652 A, while the number of atoms per unit cell falls from 2.00 to 1.817 by the creation of vacancies in normally nickel sites. The trigonal 6-Ni2Al3 phase-structure, which is essentially an extension of cubic β-NiAl, but with every third plane of nickel atoms perpendicular to the trigonal axis missing, shows a minimum in the a and c spacings at stoichiometric Ni2Al3. Density measurements indicate that the vacancies formed by the missing planes are progressively filled as nickel is added to Ni2Al3, but that a substitutional solid solution is formed on the aluminium-rich side of stoichiometric Ni2Al3 with aluminium replacing nickel atom by atom. In the NiAl phase, the number of valence electrons increases from 2.28 per unit cell at 61.9 at.% Ni to 3.00 at stoichiometric NiAl, and remains constant at 3.00 as the vacancies form until Ni2Al3 is reached, at which stage the number of vacancies will have reached a maximum when there are only 1.67 atoms per pseudo-cubic cell. The number of electrons per pseudo-cubic unit cell then begins to rise and reaches the phase boundary value of 3.12 at 37.6 at.% Ni.

A simple muffin tin model for the electrical resistivity of liquid noble and transition metals and their alloys

Abstract: A simple nearly free electron model for the electrical resistivity of liquid noble and transition metals and their alloys is presented. The scattering is described in terms of the phase shifts of muffin tin potentials constructed for the liquids.

Diffusion and Reaction Studies in the System Al2O3‐SiO2

Abstract: High-temperature diffusion kinetics and phase relations between couples of fused SiO2 or cristobalite and sapphire or mullite were investigated in air and in helium. Subsolidus liquid formation between sapphire and cristobalite indicates the existence of a metastable system without mullite. A liquid phase is considered to be essential for the nucleation of mullite. The growth rate of mullite exceeded its dissolution rate in semi-infinite fused-SiO2-sapphire couples above 1634°C. The inter-facial liquid compositions provided data for a minor revision of the mullite liquidus curve. Diffusion coefficients calculated from the Al profiles vary greatly with concentration and temperature, resulting in a large range of values for apparent activation energy, which decreases with increasing Al2O3 content (∼310 to ∼60 kcal/mol for ∼4 to ∼22 wt% Al2O3). The diffusion process in the liquid is considered to be cooperative movement of oxygen-containing Al and Si complexes whose nature changes with composition and temperature; this change in the diffusing species contributes to the range in the values of experimental apparent activation energies.

Ferroelectric and optical properties of Pb5Ge3O11 and its isomorphous compound Pb5Ge2SiO11

Abstract: The temperature characteristics of dielectric constants, spontaneous polarization, thermal‐expansion coefficients, indices of refraction, and optical rotatory power of Pb5Ge3O11 single crystals have been investigated in detail from room temperature up to above the Curie temperature, 177°C. From the results of these measurements, the following constants were obtained: linear thermal‐expansion coefficients (αa)F=7.75×10−6/deg°C and (αc)F=7.79×10−6/deg°C (ferroelectric phase), (αa)P=13.8×10−6/deg°C and (αc)P=13.4×10−6/deg°C (paraelectric phase); quadratic electro‐optic constants g33T=0.47×108 cm4 /C2, g13T=0.37×108 cm4 /C2; and electrogyration coefficient γ33 =8.7 cm2/C. An isomorphous compound Pb5(Ge2O7)(SiO4) was synthesized and was found to be ferroelectric with T c=60°C and Ps=1.7 μC/cm2 at room temperature. Ferroelectric properties and electrogyration coefficient were studied in the solid‐solution system Pb5(Ge2O7)(GeO4)1−x (SiO4)x.

Growth Kinetics Observed in the Formation of Metal Silicides on Silicon

Abstract: Backscattering of MeV He ions has been used to investigate the composition and growth kinetics of metal silicides formed from thin films of Pd, Ti, Cr, and Mo evaporated onto Si. In each system studied, one silicide phase predominated (Pd2Si, TiSi2, CrSi2, and MoSi2). The thickness of the phase increased with (time)0.5 for Pd2Si and TiSi2, and linearly in time for CrSi2 and MoSi2. It was found that these two time dependencies correlate directly with the reaction sensitivity to a thin oxide interface (<100 A) and to the extent of the silicide formation in the neighborhood of a typical device contact region.

The structure and decomposition of Zr and Ti b.c.c. solid solutions

Abstract: The literature concerning the decomposition of Zr and Ti alloys is reviewed with particular emphasis on the b.c.c. ( β )→athermal omega ( ω ) transformation and the structure of Zr and Ti b.c.c. solid solutions. Illustrative examples are taken principally from the ZrNb and TiNb systems. High resolution dark-field electron microscopy, diffraction, and ultrasonic techniques have been used to follow the β → ω phase transformation in Zr and Ti alloys. The ω morphology was shown to consist of 10–15 A diameter particles arranged in 〈111〉 rows. As well, clusters of rows were presented in low solute content alloys and the cluster size decreased with increasing solute content. The observed morphology can explain the presence of {111} planes of diffuse intensity in reciprocal space and the change in appearance of the ω reflections with increasing solute content. The mechanism of the transformation is discussed in terms of instability or metastability of the b.c.c. structure relative to a 2 3 〈111〉 longitudinal displacement wave. This mechanism can be thought of as involving the 〈111〉 displacement of 2 neighboring close-packed rows of atoms relative to each other. Single crystal elastic constant measurements on ZrNb alloys show that C 44 decreases in the vicinity of the β → ω transformation. This is attributed to a softening of the b.c.c. structure which is a precursor to the actual transformation. Alloys that are known to be well above the M s temperature for the β → ω transformation, and hence must be single phase b.c.c. solid solutions, exhibit diffuse ω reflections. It is suggested that the diffuse intensity is due to the presence of a 〈111〉 linear fault (or disorder) in the b.c.c. phase. The atom movements associated with this fault are similar to the displacements required for the β → ω transformation.

New High-pressure Phase in Chain-extended Crystallization of Polythene

Abstract: Chain extended crystallization is shown to proceed by a two-stage mechanism. Crystal thickening at the triple point may be kinetically controlled.

Thermally fixed holograms in linbo3

Abstract: Normally recorded phase holograms in undoped LiNbO3 can be made optically stable, i.e. fixed, by heating the crystal to roughly 100°C. A detailed study of the temperature dependence of this process, coupled with conductivity measurements, suggests a model in which the fixed holograms are associated with ionic charge patterns formed by drift of thermally activated ions in the electric field pattern of the original hologram. These ions would have an activation energy of ∼ 1.1 eV and a concentration in excess of 2 × 1013 cm-3 in fair agreement with previous measurements of ionic conductivity. The room temperature conductivity of the LiNbO3 used in our experiments is concluded to be less than 10-17 Ω cm)-1.