Increase In Domain Size Research Articles

Gradient energy parameters for polymer–polymer–solvent systems and their application to spinodal decomposition in true ternary systems

AbstractThe entropic gradient contributions to the free energy of nonuniform polymer–solvent systems and polymer–polymer–solvent systems have been obtained using a mean field approach. The results for a polymer–polymer–solvent system reduce to those of de Gennes for a polymer–polymer system at the appropriate limit. The binary results for a polymer–solvent system predict interfacial tensions that are systematically high but closer to experiment than those predicted by the earlier model of Balsara and Nauman. The ternary results have been applied to spinodal decomposition in polymer–polymer–solvent systems. The linear theory predicts a decrease in the domain size with increasing quench depth. Also, it predicts an increasing domain size with an increase in compatibility between the two polymers for any given quench depth.

Relationship between disordered c(2 × 2) structure and diffracted intensity: The 5-site filling model and the hard-square lattice GAS

The relationship between the size of disordered c(2 × 2) domains on a square lattice, and the associated diffracted intensity, is investigated for two specific models. The hard-square model describes an equilibrium lattice gas with infinitely repulsive nearest-neighbor (NN) interactions. A transition from short-range to long-range c(2 × 2) order occurs at θ c = 0.368 monolayers mimicking Cl/Ag(100) behavior. Here the singular ( 1 2 , 1 2 )-beam diffracted intensity behavior matches that of the average size (number of atoms) and radius of gyration of suitably defined c(2 × 2) domains. In the non-equilibrium 5-site filling model, empty sites fill irreversibly, at random, provided that all four NN sites are empty. A saturation state occurs at θ s = 0.364 monolayers modelling metastable disordered c(2 × 2) O/Fe(001). Here the ( 1 2 , 1 2 )-beam behavior does not match rapid increases in average domain size and radius of gyration near θ s, but correlates better with domain chord length behavior. This difference between equilibrium and non-equilibrium behavior is a general phenomenum.

Percolative c(2 x 2) adlayer structure in nonequilibrium adsorption models.

We consider simple adsorption models describing two systems [${\mathrm{H}}_{2}$O on Fe(001) and ${\mathrm{O}}_{2}$ on Pd(100)] in which c(2\ifmmode\times\else\texttimes\fi{}2) short-range order is formed during chemisorption, and metastable saturation states result. This ordering is characterized using concepts from correlated percolation theory. Rapid increases in average domain size near saturation are associated with ``ghost percolation thresholds'' just above saturation. Generalizing these adsorption models to include an island-forming propensity, \ensuremath{\alpha}, is shown to move the saturation state closer to c(2\ifmmode\times\else\texttimes\fi{}2) percolation. The \ensuremath{\alpha}\ensuremath{\rightarrow}\ensuremath{\infty} behavior is elucidated by analyzing corresponding ``continuum two-phase grain growth models'' using ideas from stochastic geometry, continuum, and random lattice percolation theory.

Nonequilibrium c(2 x 2) island formation during chemisorption: Scaling of spatial correlations and diffracted intensity.

During chemisorption, islands often form in which adspecies have superlattice spacing. Upon meeting, these coalesce if in phase, and form a domain boundary otherwise. Manifestly nonequi- librium island distributions can develop as a result of kinetic limitations, and a metastable saturation state of domain boundaries may, in turn, result. We analyze irreversible cooperative filling models for the formation of c(2\ifmmode\times\else\texttimes\fi{}2) islands, where island structure is kinetically determined, and extensive coalescence near saturation produces a ``percolative'' domain structure. We show that the associated dramatic increase in domain size, and fractal domain structure, are not reflected in the spatial pair-correlation or diffracted-intensity behavior. Consequently, we identify quasi-one-dimensional measures of domain size which better reflect correlation-length behavior. These are then used to develop scaling relations for pair correlations and diffracted intensities. A special case of our model describes metastable c(2\ifmmode\times\else\texttimes\fi{}2)O/Fe(001) formed after exposure of Fe(001) to ${\mathrm{H}}_{2}$O.

A FT-IRAS study of the vibrational properties of CO adsorbed on Cu/Ru(001). II. The dispersion of copper

The dispersion of copper adsorbed on a Ru(001) substrate has been investigated by using Fourier transform-infrared reflection absorption spectroscopy (FT-IRAS) and carbon monoxide as a molecular probe. Copper films evaporated at 85 K show a drastically different CO adsorption behavior compared to annealed films and exhibit a variety of adsorption sites. Characteristic C–O stretching frequencies allow us to identify small copper clusters of 1–4 atoms (2138–2123 cm−1), two-dimensional (2120–2110 cm−1) and three-dimensional (2098 cm−1) copper aggregates. After annealing to 250 K copper films at sub- and monolayer coverages form well-ordered small two- and three-dimensional copper aggregates. Formation of the epitaxial monolayer or islands of copper (2082 cm−1) requires a surprizingly mild annealing temperature of 350 K. Further annealing to 540 K results in increasing domain size of the copper islands or annealing of defect sites of the epitaxial monolayer. Multilayer coverages of copper evaporated at 85 K exhibit C–O stretching frequencies found for high-index copper single crystal surfaces, e.g., (211) and (755). This indicates a large number of surface steps and protruding copper atoms associated with rough films. Annealing to 540 K results in a smooth copper layer with preferential (111) orientation (2075 cm−1). The vibrational data presented here for Cu–Ru(001) agree well with previous reports of CO adsorption on copper single crystals, supported or evaporated films, and matrix-isolated clusters. They further allow us to determine the dispersion of supported Cu–Pt and Cu–Ni catalysts from data in the literature.

Hysteresis in the thermopower of 2H-TaSe2in the charge-density-wave state

The thermopower of 2H-${\mathrm{TaSe}}_{2}$ crystals was studied in the temperature range of 40 to 160 K. There is a sharp change in slope of the thermopower at the charge-density-wave (CDW) transition temperature 122 K. A large defect-dependent hysteresis is observed in the thermopower between 60 and 110 K. The thermopower hysteresis above 85 K is consistent with published CDW structural studies; however, no hysteresis in the CDW structure has been reported between 60 and 85 K. The thermopower hysteresis between 60 and 85 K is correlated with an increase in CDW domain size on cooling observed by electron microscopy and may be related to carrier-scattering effects associated with CDW domain walls. Alternatively, CDW domain orientation or a subtle change in the CDW structure below 85 K could provide an explanation of the thermopower hysteresis.

Ｃｏ‐Ｚｒ‐Ｎｂ／ＳｉＯ２積層膜を用いた単磁極形垂直磁気ヘッドの再生感度

Effects of domain structures of main pole films on reproducing sensitivities are investigated for single pole type perpendicular magnetic recording heads. The reproducing sensitivity of the single pole head made of a Co-Zr-Nb single layer becomes unstable and decreases with the increase of the closure domain size when the track width narrows and the anisotropy field Hk decreases. On the contrary, for a narrow track main pole made of Co-Zr-Nb multilayered amorphous film with 50 A thick SiO2 interlayer, the closure domain cannot be observed clearly. Consequently, the reproducing sensitivity becomes larger than that of the single layer main pole and the reproduced voltage is very stable even for smaller Hk and narrower track.

The effects of domain size and fluid conditions at the boundary, on convection inside an annulus heated from below

We use the theory of self adjoint operators to come to some definite conclusions on the behaviour of the critical Rayleigh number with domain size and rigidity of sides in an annulus. The annulus which has two aspect ratios, provides an interesting connection between a cylinder and rectangular channel. The critical Rayleigh number does not monotonically decay with increase in lateral domain size but increases monotonically as the sides become more rigid and as we proceed from total slip to the no slip condition. The analysis also provides a useful way of obtaining first order effects in an annulus as the domain changes or rigidity changes. Our analysis provides monotonicity results only because of the ability to formulate the equations in the form of operator which are self adjoint in a certain inner product.

Structure‐property relationships in N‐vinyl pyrrolidone grafted onto segmented polyurethanes

AbstractLinear unsaturated segmented polyurethanes have been modified by grafting onto their backbones N‐vinyl pyrrolidone chains. The thermal behaviour of the unmodified and graft copolymers was investigated using TGA and DSC/DTA instruments in a nitrogen atmosphere. Viscosity measurements show that the graft copolymers have relatively lower limiting viscosity numbers compared to the original polyurethane. X‐ray studies show that the copolymers are amorphous while electron microscopy studies show an increase in spherical domain size in the graft copolymers. The modified polymers possess better mechanical properties.

An X-ray Study of the Heusler-type Ordering in AuAgZn<SUB>2</SUB> Alloy

The kinetic behavior of the Heusler(L21)-type ordering in the stoichiometric AuAgZn2 alloy quenched from the CsCl(B2)-type ordered region was studied by X-ray diffraction. The degrees of the B2-type order (S1) and the L21-type order (SH) and the domain size of the L21-type superstructure were measured as a function of annealing time during the isothermal ordering process at 366, 386 and 406 K. The isothermal change of SH was analyzed by the standard rate equation and the activation energy of the L21-type ordering was found to be 46 kJ/mol. The increase of the L21-type domain size was proportional to the three-tenth power of the annealing time. The temperature dependence of S1 and SH were also studied. S1 showed a minimum whereas SH decreased to zero at the critical temperature of the L21-type order on heating.

Effect of Binder Domain Size on Transverse-Rupture Strength of TiC-Mo2C-Ni Alloy

The transverse-rupture strength of TiC-Mo2C-Ni cermets free from large residual pores was studied at room temperature and at 1000°C as a function of their domain (grain) size of the binder phase.It was found that the effect of the binder domain size of cermets on the strength was similar to that of WC-Co cemented carbides, that is, the strength decreased with increasing domain size at room temperature, whereas at 1000°C it increased. However, it was demonstrated that in the case of cermets, the effect was not so marked; the dependence of the size of fracture source on the binder domain size was rather slight. The fracture of cermets was not always initiated from the domain boundaries of the binder in contrast to the case of cemented carbide.

ＷＣ‐Ｃｏ超硬合金のクリープ破壊強度に及ぼすＷＣ粒度および結合相粒度の影響

Bending creep-rupture strength of WC-(6-20)%Co high carbon alloys was investigated at 700-900°C for the rupture time up to 2 hr in relation to the carbide grain size (1.3-3.8 μm) and domain size of binder phase (60-500 gm).The results obtained were as follows; (1) As the test temperature increased, the creep-rupture strength of each alloy having a given domain size tended to show a maximum with increasing carbide grain size. On the other hand, the strength of the alloys having a given carbide grain size increased with increasing domain size. (2) In each alloy, it was generally observed that microcracks were first formed at WC/WC interfaces and then connected each other to yield a main stable crack. The growth rate of main stable crack, therefore, appeared to correlate with the formation rate of microcracks. (3) The high temperature creeprupture strength of WC-Co cemented carbides would be controlled by the WC/WC interfaces.

ＷＣ‐（ＴａＣ，ＴｉＣ）‐Ｃｏ超硬合金の短時間曲げクリープ破壊強度

The effect of tantalum carbide or titanium carbide addition on the short-time creep-rupture strength of WC-Co alloy was studied at 700-900°C in relation to the carbon content, carbide grain size and the domain (or grain) size of binder phase of the alloy.The results are as follows. At temperatures above about 800°C, the creep-rupture strength of tantalum carbide and/or titanium carbide contained alloys increased with increasing amount of those carbides. The observed increase in the creep-rupture strength of tantalum carbide contained alloy was found to be mainly due to the increased domain size, and that of titanium carbide contained alloy, due to the effect of increased strength of carbide skelton in addition to the increased domain size.

Structure and properties of bubble domains in cholesteric-nematic mixtures

Textural laser diffraction and light-scattering studies on homeotropically aligned nematic material (MBBA) doped with cholesteryl nonanoate (CN) has been carried out with and without an applied ac (50 Hz) electric field. In the narrow range of the ratio of the pitch p to the thickness l of the cell, 1.2<p/l<2, one observes uniformly densely packed bubble domains which grow in size on application of an electric field. In the range p/l≳2, the bubble domains become visible only at certain applied electric fields which increase with a decrease in the CN concentration. These bubble domains constitute a cholesteric phase with the spiral axis perpendicular to the substrate in a matrix of homeotropically aligned nematic material. The increase in the bubble domain size on application of electric field constitutes a nematic → cholesteric transformation. Light-scattering experiments indicate an optimum doping in relation to the threshold potential, contrast ratio, etc.

A comparison of the structures of low and high pigeonite

These listings are available in microfiche. Order from the American Geophysical Union, 1707 L Street, N.W., Washington, D.C. 20036. Document J72-006; $1.00. Payment must accompany order. The crystal structure of high pigeonite has been determined from single-crystal intensity data taken on a pigeonite crystal (Wo9En39Fs52) from the Isle of Mull, Scotland, at 960°C (∼30°C above the low- to high-pigeonite transition for this composition). Anisotropic refinement in space group C2/c using 183 nonequivalent reflections resulted in an unweighted R of 0.035. Refinement in space group P21/c yielded positional and thermal parameters not significantly different from those consistent with C2/c symmetry. A difference Fourier calculated with the final coordinates of the C2/c refinement showed no anomalies indicative of a lower symmetry. (C2 or Cc). Analysis of the relative atomic displacements and the apparent rms thermal displacements provides evidence that the high-temperature polymorph is truly C-centered and not a space-average artefact. The structure of low pigeonite was anisotropically refined to an unweighted R factor of 0.057 using 1126 nonequivalent intensities collected at 24°C with the same crystal prior to the high-temperature experiment. Comparison of the low and high structures reveals two major structural changes: (1) extension of the B silicate chain with increasing temperature until it becomes crystallographically equivalent to the A chain at the transition (O3-O3′-O3” = 173.4°) and (2) a concomitant change in the primary coordination sphere of the M2 cation. The average bond length expansions of the SiO4 tetrahedron, the M1O6 octahedron, and the M2O8 polyhedron during the 24°–960°C temperature increase are 0.06, 1.2, and 1.4%, respectively; the average polyhedral volume expansions are 0.2, 3.5, and 5.9%, respectively. The apparent anisotropic rms atomic displacements at 960°C are approximately double those at 24°C. Refinement of Fe/Mg distributions in both the 24° and 960°C refinements resulted in KD values of 0.045 and 0.134, respectively. The temperature at which the Fe/Mg distribution equilibrated is roughly estimated to be ∼520°C. The fact that heat treament of Mull pigeonite at 940°C for 50 hours resulted in a decrease in class b peak diffusiveness relative to class a peaks suggests an increase in domain size.

An X-Ray Investigation of Fatigue Behavior of Cold Worked Aluminum

AbstractDouble bending fatigue tests were performed on cold worked 1100 aluminum, with a maximum bending stress varying from 100 to 50% of the yield stress. Variation of residual macrostress from the cold worked state during the fatigue tests was measured by the photographic x-ray diffraction method. A general decrease of this macrostress was observed. Line profile analysis was used to study the change in the mean effective domain size and microstrain. A rate dependence of the increase in the effective domain size with respect to the maximum bending stress was observed. Microhardness and tensile tests were also made on the specimens during the fatigue testing and the results are correlated with the x-ray Parameters.

Messung von spannungen in vanadiumkarbid und ihre bedeutung

Lattice deformations have been determined by an X-ray-method on specimens of VC which were ball milled and on the other hand compacted under different pressures. The mean strain was determined by an X-ray impulse-method and the peaks were separated by a least square method under assumption of Lorentz profiles. The strain determined on the pressed (50 kbar) and on the ball milled specimens were of the same order. From X-ray line broadening and from electron microscope examinations, maximum dislocation densities of about 10 10 cm −2 were approached. These dislocation densities are comparable with those measured for severely deformed metals. The recovery of the deformed VC began at about 750 °C with increase in domain size and decrease in strain. Vanadium monocarbide therefore exhibits a behaviour such as is familiar with metals, and it is hence to be assumed that here also the initial stage of the sintering, the recrystallisation, and resulting further sintering, are influenced in a similar manner by induced dislocations as is well known in the case of metals.

Electrical Analog of the Eddy-Current-Limited Domain-Boundary Motion in Ferromagnetics

The observed losses in a ferromagnetic core are always greater than those calculated on the basis of a homogeneous permeability. In a magnetization process by domain-boundary displacements the permeability is certainly not homogeneous, but attains extreme values in the domain walls. As a result of this concentration of the changes in magnetic flux the dispersion curves of the initial permeability as a function of frequency show a shift of the dispersion region towards lower frequencies with increasing domain size. This is the well-known eddy-current anomaly encountered in laminated cores. An electric-circuit model was utilized to determine the eddy-current distribution and domain-boundary motion in a number of idealized cases.