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


Journal ArticleDOI
TL;DR: In this article, the content of free ZrO2 in partially stabilized zirconia ceramics by X-ray diffraction techniques was determined by linear calibration curves.
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.

1,302 citations



Journal ArticleDOI
TL;DR: In this paper, time-temperature-precipitation 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.
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.

658 citations


Journal ArticleDOI
TL;DR: In this article, the collapse of a hollow sphere of incompressible elastic-plastic material, with appropriate pore radius and over-all porosity, has been analyzed.
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...

556 citations


Journal ArticleDOI
TL;DR: In this paper, the adsorption of CO on Ni(100) has been studied using LEED, Auger, and work function measurements and was found to be completely reversible.
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.

435 citations


Journal ArticleDOI
10 Jul 1972-Nature
TL;DR: In this article, a variety of ceramic materials built up of (Si,Al)(N,O)4 tetrahedra joined by sharing corners are reported. But the results are limited to 1,700 and 1,770° C.
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.

351 citations


Journal ArticleDOI
W. L. McMillan1
TL;DR: In this paper, 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.
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.

302 citations


Journal ArticleDOI
TL;DR: In this article, a theory is developed to describe the vertical percolation of water in isothermal snow, based on the general theory of Darcian flow, and 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.
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.

245 citations


Journal ArticleDOI
TL;DR: Ritsema et al. as mentioned in this paper presented a phase diagram for the MgSiO3-FeSiO4-SiO2 system at 800 and 1,000°C.

221 citations


Journal ArticleDOI
TL;DR: 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 as mentioned in this paper.
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].

212 citations


Journal ArticleDOI
TL;DR: The dependence of the enthalpies of the cooperative transitions of aqueous dispersions of synthetic dimyristoyl and dipalmitoyl l-α-lecithin on the cholesterol content has been determined in an adiabatic differential scanning calorimeter.

Journal ArticleDOI
TL;DR: In this article, the orientational structures and phase transitions of solid CD4 are investigated by coherent neutron scattering from powder samples as well as from single crystals, and it is found that CD4 crystallizes within the space group Fm3m with four molecules per unit cell and a lattice constant a0=5.96 A at 77°K.
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.

Journal ArticleDOI
TL;DR: In this article, the lattice parameter and density results have been obtained for alloys in the β-NiAl and 6-Ni2Al3 phase fields of the nickel-aluminium system.
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.

Journal ArticleDOI
TL;DR: In this article, a simple nearly free electron model for the electrical resistivity of liquid noble and transition metals and their alloys is presented, where the scattering is described in terms of the phase shifts of muffin tin potentials constructed for the liquids.
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.

Journal ArticleDOI
S.L. Blank1, J.W. Nielsen1
TL;DR: In this article, phase relationships in the PbO-B 2 O 3 -garnet systems and their relationship to high quality -low defect epitaxial films are discussed and the effects of growth temperature, lattice mismatch and growth rate on the magnetic properties of multiple-doped rare earth iron garnets are shown.

Journal ArticleDOI
TL;DR: In this article, 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.
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.

Journal ArticleDOI
TL;DR: The time-dependent mechanical properties of amorphous Pd-20 at.% Si, i.e., fracture-strain rate effect, load relaxation, creep and elastic after effect characteristics, were determined as a function of both stress and temperature as discussed by the authors.


Journal ArticleDOI
TL;DR: In this paper, 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.
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.

Journal ArticleDOI
TL;DR: In this paper, the authors used backscattering of MeV He ions to investigate the composition and growth kinetics of metal silicides formed from thin films of Pd, Ti, Cr, and Mo evaporated onto Si.
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.

Journal ArticleDOI
S.L. Sass1
TL;DR: In this paper, the authors reviewed the literature concerning the decomposition of Zr and Ti alloys with particular emphasis on the b.c. phase transformation and the structure of the b-c.c structure relative to a 2 3 longitudinal displacement wave.
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.



Journal ArticleDOI
18 Dec 1972-Nature
TL;DR: In this article, a two-stage chain extended crystallization is shown to proceed by a two stage mechanism. Crystal thickening at the triple point may be kinetically controlled, but it is not shown in this paper.
Abstract: Chain extended crystallization is shown to proceed by a two-stage mechanism. Crystal thickening at the triple point may be kinetically controlled.


Journal ArticleDOI
TL;DR: In this paper, the inverse power potential φ (r)=e ( σ / r)nn was used to model the behavior of the soft metals and showed that the same three phase behavior occurs for the models provided that the interparticle repulsion is sufficiently soft (n ≤ 7).
Abstract: Most of the softer metals exhibit a low‐temperature close‐packed phase, an intermediate‐temperature body‐centered phase, and a high‐temperature fluid phase. Here we relate this behavior to that of theoretical model systems in which particles interact with the inverse power potential φ (r)=e ( σ / r)n. We show that the same three‐phase behavior occurs for the models provided that the interparticle repulsion is sufficiently soft (n ≤ 7). For the model systems the phase boundary between the close‐packed and the body‐centered phases is located using lattice dynamics. The fluid—solid melting line is deduced from Monte Carlo computer experiments.

Journal ArticleDOI
TL;DR: In this article, the crystal chemistry of Li3PO4, Li3VO4 and Li3AsO4 is compared and the occurrence of high, low, and of distorted high and low phases is correlated with the temperature of preparation and rate of cooling.


Journal ArticleDOI
TL;DR: The phase equilibria of the system CaO-Al2O3-CaF2 have been studied by quenching in sealed platinum capsules followed by microscopic and X-ray examination of quenched products as mentioned in this paper.
Abstract: The phase equilibria of the system CaO-Al2O3-CaF2 have been studied by quenching in sealed platinum capsules followed by microscopic and X-ray examination of quenched products. The established phase diagram contains five ternary eutectics, two ternary peritectics and two invariant points of four-phase monotectic transformations. The system Al2O3-CaF2 has been established to be the stable diagonal of the reversible reciprocal system Al2O3 + 3CaF2 = 3CaO + 2AlF3. In the high-fluoride region a wide zone of liquid immiscibility has been found. The system also shows such rarely noticed but theoretically possible phenomena as the transformation of peritecticals into eutecticals and occurrence of three different primary fields under single continuous zone of liquid immiscibility.

Journal ArticleDOI
Francis Birch1
TL;DR: In this article, the authors present speculative projections on the temperature-volume plane of the phases of iron, assuming that the melting curves for each phase are assumed to be straight lines in this representation.
Abstract: Summary Thermodynamic data on the phases of iron are assembled in the form of speculative projections on the temperature-volume plane. Following a proposal by Kraut and Kennedy, the melting curves, for each phase, are assumed to be straight lines in this representation. As the position of the triple point, gamma-epsilon-liquid, is unknown, two hypothetical locations are considered: (1) at about 4Mb, (2) at about 1 Mb. In the former case, the gamma phase is in equilibrium with the liquid at core pressures, in the latter, the epsilon phase. Nothing is known directly about the slopes of these melting curves, but the gamma melting temperatures are estimated to lie some 700" above the projection given by Higgins and Kennedy, with epsilon melting temperatures still higher. The relation of the isentropes of the liquid to these melting curves is also unknown, but ' conventional ' isentropes, originating on the melting curve, may be found which lie in the liquid field at the pressures of the outer core. Application to the Earth is complicated by the requirement for a light alloying element in the outer core; if the alloying element is silicon, a proportion of about 15 per cent by weight accounts satisfactorily for the density-velocity relation. The phase relations may be considerably modified by the presence of so much silicon: it is conjectured that the gamma phase is suppressed or confined to low pressures, that the epsilon phase will be the stable solid phase at core pressures, and that the isentrope originating at the melting temperature of the inner core-outer core boundary lies entirely in the liquid phase.