Phase Homogeneity Research Articles

Ordering and segregation reactions in f.c.c. binary alloys

Within the Bragg-Williams-Gorsky approximation the most stable atomic configurations of f.c.c. solid solutions are determined in dependence on two energy parameters W (1) and W (2), the interchange energies between first and second nearest neighbours. The most stable atomic configurations of homogeneous solid solutions (configuration diagrams) are presented for a representative set of values out of the whole range of W (1) and W (2) Therefrom the most stable states without the constraint of homogeneity (phase diagrams) are derived.

Mqrphotropic phase boundary in the Pb(ZrxTi1-x)O3system

Abstract A current version of the Pb(ZrxTi1-x) phase diagram is shown in Figure 1. According to earlier studies there is a morphotropic phase bountary at x = 0.54. For this composition there is found to be an equal proportion of rhombohedral and tetragonal phases and the coexistence region extends over 6 atomic percent. We have recently evolved a sol-gel technique for PZT synthesis which is superior to the conventional technique in the degree of phase homogeneity. For such materials it is noted that there is no evidence of coexisting phases but a sharp boundary not larger than one atomic percent and located at x = 0.51.

Systematics of crack controlled mechanical properties for a suite of Conway granites from the White Mountains, New Hampshire

The Conway granite of New Hampshire is a highly radioactive intrusive into which a 1-km deep borehole was drilled and continuously cored. The formation is composed of two major granitic units, the Osceola and the Conway; and it is cut by three lamprophyre dikes. The suite of rocks used in this paper contained eight granitic and two lamprophyre samples on which acoustic and strain measurements were performed over the pressure range of 1 atm. to 0.4 GPa. The V p data were subjected to cluster analyses to determine what, if any, similarities in pressure-dependence existed among the samples. Three distinct similarity groupings were found: the lamprophyre dike rocks and two groups each of which contains samples from both granitic units. These groupings by V p behavior were also found to correlate exactly with sample similarity groupings formed by dynamic and static moduli data, crack spectra, and rock texture. Such sample similarities in the functional forms of the pressure-dependence were found not to correlate with mineral modes nor with original in situ depth, but rather with grain size and the degree to which the mineral phases were homogeneously mixed. A consideration of the results suggests that for these rocks, grain size and mineral phase homogeneity exerted a dominant influence on crack population formation. Further, it appears that the exhumation and coring of these samples may have intensified the amount of cracking over that in situ but it did not necessarily introduce any individual distinct crack populations.

The terbium-antimony alloy system

A phase diagram is proposed for the Tb-Sb system on the basis of differential thermal, X-ray, chemical and microscopy analyses. A peritectic reaction develops as a result of antimony additions and the transformation temperature of terbium is lowered by 25 °C. Eutectic reactions occur at 14 at.% Sb and 1130 °C and at greater than 99.0 at.% Sb and 623 °C. There are four compounds in the system: Tb 5Sb 3 and Tb 4Sb 3 result from peritectic reactions at 1650 and 1770 °C while TbSb melts congruently at 2160 °C. The overall phase homogeneity range is no more than 1 at.%. Results for the formation of TbSb 2 at normal pressures are reported. Tb 4Sb 3 and TbSb were observed to exhibit polymorphic transformations.

The growth of single crystal lithium-aluminum, 7LiAl

Single crystal lithium-aluminum has been prepared as chemically and isotopically pure 7LiAl. Growth has been by the Stockbarger technique in a low-pressure bomb. Pyrolytic boron nitride crucibles have proven to be nonreactive and noncontaminating containers for pyrometallurgial synthesis and for crystal growth from the melt. The chemical and physical quality of the monocrystalline boules have been documented. The lattice constant varies with composition across the β-phase and can be used as a probe to evaluate stoichiometry and phase homogeneity.

The Characteristics of Standard Cells with a Low Temperature Coefficient

Through a series of precise measurements of electromotive force (EMF) of standard cells with a temperature range of 0-40°C, this paper proposes the following quartic equations for the cells with Cd-Pb, Cd-Sn, and Cd-Sn-Pb amalgam electrodes, respectively: Et = E20 - [17.36(t - 20) + 0.728(t - 20)2 - 0.0089(t - 20)3 + 0.000 03(t - 20)4] × 10-6(V) Et = E20 - [15.57(t - 20) + 0.624(t - 20)2 - 0.0107(t - 20)3 + 0.000 04(t - 20)4] × 10-6(V) Et = E20 + [23.57(t - 20) - 0.130(t - 20)2 + 0.0104(t - 20)3 - 0.000 08(t - 20)4] × 10-6(V) At the same time it has been found that the characteristics of these cells are almost similar to those of the normal Weston cells. The "criteria of hysteresis voltage" and the "criteria of standard cells of high quality" cannot be used as criteria for our cells. The quality of cells with Hg2SO4 prepared by the electrolytic method is better than that by the chemical method. The compositions of multimetal amalgams and the homogeneity of metal phases have a significant effect on the characteristics of these cells.

Phase diagram and homogeneity gap in microemulsions

Microemulsions are investigated for a wide range of concentrations and temperatures. After a direct observation of the samples, light scattering and viscosity measurements are performed. Structural transitions are clearly indicated. In addition, a homogeneity gap is found, in which the sample separates into two phases. Each of these consists of a micro-emulsion but they have different structures.

Calculation of crystal orientations using laue patterns

Confocal Raman microscopy in the lattice phonon region has been used to study the polymorphism of the organic semiconductor 5,6,11,12-tetraphenyl-tetracene (rubrene). Following literature guidelines, crystals of rubrene have been prepared using a number of solution growth and vapour deposition methods, obtaining samples of different morphologies which could be related to the various polymorphs of this compound. The technique has enabled us an easy and non invasive identification of the three known polymorphs and of their phase homogeneity with a lateral spatial resolution below 1 μm.

Études sur le carbure de bore iii. domaine d'existence de la phase carbure de bore

We have studied the boron carbide phase homogeneity range in the boron-carbon system. The samples have been electron beam melted and characterised by electron microprobe analysis, metallographic techniques, X-ray diffraction and Knoop microhardness measurements. Metallographic investigations, together with the electron microprobe phase analysis, show that the boron carbide phase exists in the homogeneity range 9–10 and 20 at.%C. Boron carbide melts congruently and forms a eutectic between carbon rich compounds and graphite. For the boron-rich compounds we assume the existence of a peritectic transformation with a solid solution of carbon in the β-rhombohedral boron structure. When the carbon content increases, within the homogeneity range of boron carbide, X-ray data and Knoop microhardness measurements show that the crystal lattice dimensions decrease and the microhardness increases regularly with an extreme value of HK 200g of 2840 ± 60 kg mm −2 for 20 at.%C (after electrolytic etching).

Crystal chemistry of lithium in octahedrally coordinated structures. I. Synthesis of Ba 8(Me 6Li 2)O 24 (Me = Nb or Ta) and Ba 10(W 6Li 4)O 30. II. The tetragonal bronze phase in the system BaONb 2O 5Li 2O

The preparation, single crystal growth, and crystallographic properties of a close-packed, eight-layer, hexagonal ( a = 5.803 Å, c = 19.076 Å) modification having the stoichiometry Ba 8Nb 6Li 2O 24 and of a close-packed, ten-layer, hexagonal ( a = 5.760 Å, c = 23.742 Å) phase with Ba 10W 6Li 4O 30 stoichiometry are discussed. The isostructural Ba 8Ta 6Li 4O 24 form of the eight-layer phase was also prepared ( a = 5.802 Å, c = 19.085 Å). Proposed crystal structures involve the pairing of lithium and metal (Nb, Ta, or W) octahedra to yield face-sharing units. The relationship of this phenomenon to other known close-packed phases containing Li is demonstrated. An investigation of the Ba 8Nb 6Li 2O 24Ba 10W 6Li 4O 30 system is reported. A tetragonal bronze phase homogeneity region was delimited at 1200°C in the BaONb 2O 5Li 2O system. A new orthorhombic phase ( a = 10.197 Å, b = 14.882 Å, c = 7.942 Å) was prepared with the stoichiometry Ba 4Li 2Nb 10O 30.

Effects of Phase Homogeneity on the Chemical Consequences of (n, γ) Reactions in Binary Organic Systems Containing Bromine

Article Effects of Phase Homogeneity on the Chemical Consequences of (n, γ) Reactions in Binary Organic Systems Containing Bromine was published on November 1, 1968 in the journal Radiochimica Acta (volume 10, issue 1-2).

Effects of phase homogeneity on the chemical consequences of nuclear reactions

Effects of phase homogeneity on the chemical consequences of nuclear reactions

Molecular weight fractionation and the self-suppression of complex coacervation.

AbstractA marked molecular weight fractionation accompanies the demixing or phase separation resulting from the complex coacervation of mixtures of aqueous solutions of salt‐free isoionic unfractionated gelatins with pI's of 5 and 9. Viscosity studies show that the fractionation is such that the concentrated phase tends to maintain constant, homogeneous composition. A second feature, seen in phase volume and concentration measurements, is a marked self‐suppression of coacervation intensity with increasing mixing concentration. These data were interpreted in terms of a dilute‐phase aggregate model which assumes nearly equal electrostatic free energies of mixing in dilute aggregate and concentrated random phase. The driving force for phase separation is the entropy increase upon formation of the random phase but demixing also depends upon the polymer‐solvent interaction parameter χ, in the same fashion as in simple coacervation. The dilute‐phase aggregate model indicates that the sharp molecular weight selection takes place in the aggregate formation step and explains the self‐suppression. Phase equilibria studies utilizing fractionated, paucidisperse high molecular weight gelatins, emphasize the requirement for concentrated phase homogeneity and indicate that aggregates of different molecular weight may act as different components, so that χP1Q1,PkQk > 0, bringing about a separation of the system into three or more coexisting phases. The formation of several coexisting phases from a homologous polyelectrolyte system and the very marked requirement for phase homogeneity suggest that the phenomenon of complex coacervation is a very good model for some of the essential steps in the pre‐biologic organization of polymeric polyions.

A study of the sintering of chromium-nickel steel powders

1. An investigation was made of the phase composition and homogeneity ofreduced powders of stainless steels Kh30, Kh17N2, Kh23N18, 1Kh18N9T, and OKh18N9. The surface layers of chromium-nickel steel powders contain oxides, including spinel type phases. 2. The effect of temperature on the shrinkage, strength, structure, electrical resistivity, interparticle contact size, and phase composition of sintered specimens was studied. It was shown that the sintering of ferritic steel powders is much more intensive than that of austenitic steel powders. 3. A study was made of the activated sintering of stainless steels 1Kh18N9T and Kh17N2, based on the use of packing materials containing halides and TiH2 or on alloying with phosphorus, copper, and boron. For porous materials, it is advantageous to employ sintering in packing materials with titanium hydride.