Anisotropy in the hardness and friction of calcium fluoride crystals

Anisotropy in the Knoop indentation hardness and the friction of diamond cones on calcium fluoride crystals has been investigated at experimental temperatures from 20 to 300° C. It is shown that the directions of minimum and maximum indentation hardness, on the (001) plane, are 110 and 100 respectively whilst the 1¯10 are harder than the 11¯2 directions on the (111) plane. Also, the sliding friction in the (001) plane is greatest in the 110 directions and least in the 100 and, on the (111) cleavage plane, [¯1¯12] sliding leads to higher friction than [11¯2]. The nature of anisotropy, for both hardness and friction measurements, does not change over the experimental temperature range covered in this work. Observations on the resultant deformation are made and these anisotropic properties are explained in terms of the effective resolved shear stresses developed on the {100} 011 primary slip systems at all experimental temperatures.     

On the formation of thermally sprayed alumina coatings

A model for the fomation of thermally sprayed alumina coatings is proposed. The spreading and crystallization of liquid droplets on impact with the substrate are analysed and the thermal history of individual particles related to the kinetics of nucleation of -Al₂O₃ to other forms. The results suggest that under the usual spraying conditions undercooling of the liquid droplets is such that -Al₂O₃ nucleates in preference to -Al₂O₃ and the cooling rate after solidification is sufficiently rapid to prevent transformation to -Al₂O₃ or -Al₂O₃. Transformation of initially formed -Al₂O₃ to -Al₂O₃ appears to be possible only if the lamellae formed on impact are thicker than about 10 m if the substrate is heated to about 1000° C, or if the thickness is greater than about 20 m on an unheated substrate. The -Al₂O₃ generally observed in thermally sprayed coatings is the result of crystallization from pre-existing nuclei arising from incomplete melting of the feed material.     

Nonlinear behavior of some hydrostatically stressed isotropic elastomeric foams

Summary We calculate the stress-strain relation for elastomeric foam from anab initio theory, which shows that the plateau and densification regions should be described by a hyperbola. The theory seems to agree reasonably well with experiment.     

Paramagnetic resonance in a “dirty” spin-glass

For a spin-glass with nonmagnetic defects (n _m ^1/3l 1, where n _m is the magnetic impurity concentration and l is the mean free path) an absorption function () is derived. Three ranges of temperature and external magnetic field are considered. In the vicinity of the transition the value of () d is estimated as a function of temperature and field.     

Phase equilibria and thermodynamic properties in the system Ni-Mo-O

Coexisting phases in the Ni-Mo-O ternary system at 1373 K have been identified by X-ray diffraction, optical microscopy and scanning electron microscopy. The samples were equilibrated in evacuated quartz capsules. Only one ternary phase, NiMoO₄, was found to exist in the system. The reversible e.m.f. values of the following solid-state galvanic cells were measured in the temperature range 900 to 1500 K: (I) Pt, Ni + NiO/(CaO) ZrO₂/NiO + MoO₂ + NiMoO₄, Pt; (II) Pt, Mo + MoO₂/(CaO) ZrO₂/O₂, Pt; and (III) Pt, Mo + MoO₂/(CaO) ZrO₂/Ni-Mo + MoO₂, Pt. The Gibbs energies of formation of NiMoO₄ and MoO₂ and activities in Ni-Mo alloys were derived from the e.m.f. data. For the reaction NiO + MoO₂ + 2(02) NiMoO₄ we obtain G _r ⁰ = -201 195 + 69.70T (±400) J mol^–1; for Mo + (02) MoO₂ we obtain G _f ⁰ = –578880 + 168.5T (+500) J mol^–1. Based on the information from phase identification studies and thermodynamic stabilities, the isothermal section and oxygen potential diagram for the Ni-Mo-O system at 1373 K have been developed.     

In-Plane Fourfold Symmetry of the Upper Critical Field Observed in La(Sr)214 Single Crystals

In order to establish the existence of in-plane anisotropy of the upper critical field H _c2 (), the out-of-plane resistivity _c measurements were performed on La(Sr)214 single crystals with rectangular and cylindrical shape under rotating magnetic field applied within the ab-plane. Although observed _c shows non-sinusoidal twofold symmetry, clear fourfold symmetry was obtained after subtracting twofold sinusoidal component in _c which is due to the unavoidable misalignment of the magnetic field with respect to ab-plane. H _c2 () is estimated from the extracted fourfold component of _c with the flux flow theory. Angular dependence of H _c2 () was well fitted by cos(4). Since the fourfold component of H _c2 () was largest at = n/2, which corresponds to the a-axis direction, the present results strongly suggest the type symmetry in La(Sr)214. In addition, the difference in fourfold component of H _c2 at = n/2 and n/2+/4 was found to increase with decreasing temperature.     

Structure and Magnetism of the Composite Crystal Ca0.824CuO2

We have studied the magnetic state from a viewpoint of crystallographic features of the 1-D chain compound Ca_0.824CuO₂. A possible spin-hole arrangement in the magnetically coexisting state was determined by analyzing the local structural distortion in the CuO₂ chain by means of a modulated-crystal-structure analysis. The essential periodic sequence expected is (: up- and down-spin, : hole), which can be regarded as a kind of spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain.     

Analysis of the effect of the decomposition of char-forming heat-insulating materials on the free discharge of a gas mixture

The article presents results of a numerical solution of a nonsteady problem on the free discharge of a mixture of gases from a hemispherical volume with allowance for thermal decomposition of heat-insulating materials.Notation V volume - S area - t - P p - T - u v - Q q, dimensional and dimensionless time, pressure, temperature, TIM decomposition rate, and heat flux - adiabatic exponent - R gas constant - density - H specific enthalpy - c specific heat - thermal conductivity - , , _s dimensionless complexes - coefficient expressing the radiative properties of the gas medium and the heat-transfer surface - Stefan-Boltzmann constant Indices 0 initial state and scale factors - s surface - coke - M TIM material - P pyrolysis front - A ablation front - v volatile degradation products - adiabatic conditions - c completion of discharge Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 5, pp. 787–793, May, 1988.     

Response of a spinning liquid column to pitch excitation

Summary The response of a solidly rotating liquid bridge consisting of inviscid liquid is determined for pitch excitation about its undisturbed center of mass. Free liquid surface displacement and velocity distribution has been determined in the elliptic (>2₀) and hyperbolic (<2₀) excitation frequency range.List of symbols a radius of liquid column - h length of column - I ₁ modified Besselfunction of first kind and first order - J ₁ Besselfunction of first kind and first order - r, ,z cylindrical coordinates - t time - u, v, w velocity distribution in radial-, circumferential-and axial direction resp. - mass density of liquid - free surface displacement - velocity potential - ₀ rotational excitation angle - ₀ velocity of spin - forcing frequency - _1n natural frequency - surface tension - acceleration potential - for elliptic range >2₀ - for hyperbolic range >2₀     

Multi-length scale modeling of CVD of diamond Part II A combined atomic-scale/grain-scale analysis

Chemical vapor deposition of polycrystalline diamond films is studied by combining an atomic-scale kinetic Monte Carlo model with two one three-dimensional and one two-dimensional grain-scale models. The atomic-scale model is used to determine the growth rates of 111- and 100-oriented surface facets, the surface morphology of the facets and the extent of incorporation of the crystal defects. Using the atomic-scale modeling predicted growth rates for the 111- and 100-oriented facets, grain-scale modelling is carried out to determine the evolution of grain structure, surface morphology and crystallographic texture in the polycrystalline diamond films. It is found that depending on the relative growth rates of the 111- and 100-oriented facets, which can be controlled by selecting the CVD processing conditions, one can obtain either 110-textured films with a relatively smooth faceted surface or 100-textured films with a highly pronounced deep facets. In both cases, however, the film surface is composed entirely of the 111 facets. This findings are found to be fully consistent with the available experimental results.     

On the dispersion of gases under the action of the medium

Some general regularities of dispersion of a gas emerging from a nozzle submerged in a liquid are considered. A condition for establishment of the so-called maximum dispersion state is formulated.Notation ₀ coefficient of surface tension at the liquidgas boundary - contact angle of wetting of the nozzle material surface by the liquid - p_at atmospheric pressure - p air pressure - density of the liquid - g gravitational acceleration - h height of the liquid column - ₁, and _g dynamic viscosity coefficients of the liquid and gas, respectively - R and r radii of the bubble and nozzle, respectively - Q and F dimensionless criteria - , , , , and undetermined coefficients - ratio of the circumference of a circle to its diameter     

Internally Consistent Thermodynamic Description of Three-Component Liquid-Metal Systems at High Temperatures in the Entire Region of Concentration Triangle

A method is suggested for the investigation of the thermodynamic properties of ternary liquid-metal alloys at high temperatures in the entire region of concentration triangle. The method is demonstrated for a Na–K–Cs ternary system. Data are obtained for the enthalpy and Gibbs energy of formation of alloy in the temperature range of 200 T 1200 K and concentration range of 0 x _{i (j, k)} 1. The results reveal a very fine effect associated with the temperature rise, namely, the inversion of excess partial Gibbs energy G¯ _i ^*= RTln _i ( _i is the activity coefficient of the liquid component) and the change of sign of deviation of partial pressure, as well as of total pressure, from the respective values in accordance with Raoult's law. The obtained results may be used to interpret the available literature data on independent measurements of the saturation pressure.     

Oriented mosaic model analysis of anisotropic thermoelectric properties of heterogeneous materials

Thermoelectric properties of heterogeneous materials are discussed in terms of a randomly oriented rectangular plate-like mosaic of anisotropic crystalline grains embedded in a homogeneous host material. Anisotropies in effective thermoelectric parameters and the values of thermoelectric parameters can be related to the mean orientation of the plate-like grains which, in turn, can be related to the orientation factor of Lotgering. They are also functions of various parameters such as dimension ratios , and of electrical resistivities, thermal conductivities, and the Seebeck coefficient, respectively, of grains to those of host medium. Use of f-dependent anisotropies in conjunction with relative magnitudes of electrical and thermal conductivities as well as of the Seebeck coefficient, allows , and to be estimated, which characterize the intergranular medium.     

Synthesis, crystal structure and X-ray powder diffraction data of the phosphor matrix 4SrO·7Al2O3

The white phosphor matrix 4SrO·7Al₂O₃ has been synthesized by firing the appropriate mixture of SrCO₃, Al(OH)₃ and H₃BO₃ in the molar ratios 1:3.5:0.135 at 1300°C for 4–7 h. The crystal structure of 4SrO·7Al₂O₃ has been determined as a orthorhombic Pmma space group with a=24.7451(2)Å, b=8.4735(6)Å, c=4.8808(1)Å, V=1023.41(3)ų, Z=2, and D=3.66 g cm^–3 by the Rietveld analysis. The refinement figures of merit are R_p=8.26, R_wp=11.60, R_bragg=4.44 and s=2.61 for 844 reflections with 2<119.94°. And the corresponding X-ray powder diffraction data are presented for search/match analysis.     

Studying the effect of the temperature factor on the transition from a laminar to a turbulent regime of flow in a boundary layer

Based on the generalization of experimental data, we propose a formula for the calculation of the effect of the temperature factor and the transition from a laminar flow regime to one that is turbulent in the boundary layer of a plate; this formula has been confirmed by experiments performed in the following range of parameter variation: 0.5 2.6; 0.2 M 3.6; 0.1 9%.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 16, No. 2, pp.218–224, February, 1969.     

Influence of stabilizers on Na-β′′-Al2O3 phase formation in Li2O(MgO)-Na2O-Al2O3 ternary systems

The influences of stabilizers on - and -Al2O3 phase formations in Li2O(MgO)-Na2O-Al2O3 systems were investigated. When stabilized with 4MgCO3Mg(OH)25H2O, most of the -Al2O3 phase formed below 1200°C and further - to -Al2O3 transformation with an increase of temperature was not observed. On the other hand, when stabilized with Li2CO3,-Al2O3 formation occurred by two steps. First, -Al2O3 was partly formed below 1200°C, and, second, noticeable transformation from -Al2O3 to -Al2O3 occurred at higher temperature ranges. It was shown that transient eutectic liquid in the Li2O-Na2O-Al2O3 system promoted the - to -Al2O3 transformation at higher temperatures. Uniform distribution of both Mg2+ and Li+ stabilizing ions enhanced -Al2O3 formation at low temperatures. In the Li-stabilized systems, however, homogeneous distribution of Li+ ions hindered both the formation of transient eutectic liquid and the second - to -Al2O3 phase transformation at high temperatures.     

Amplifier based on a field-effect triode with negative current feedback

Conclusions A field-effect triode amplifier with series negative current feedback allows a voltage gain of the order of 200–300 to be obtained for a load resistance R_s1 M. The coefficient K_u begins to decrease noticeably only for a feedback resistance above 500 .The current gain reaches (8–10)·10³. Increasing the resistances R_s and R_L to hundreds of ohms has practically no effect on K_i. For a further increase of R_s and R_L the coefficient K_i decreases.The power gain reaches its maximum value (of the order of 10⁴ or more) for R_s100 and R_L=10–100 k. An increase in R_s leads to a reduction of K_pmax and to a shift of the extremum of the function K_p=f(R_L) into the range of higher values of R_L.A large input resistance of the amplifier (tens of megohms and higher) is obtained when R_s increases to 10–100 M. The maximum input resistance is obtained for R_L and R_s and may exceed values of from hundreds of megohms to several gigaohms. The minimum input resistance is hundreds of kilohms for R_L and R_s0.The minimum input resistance (5–10 k or less) is ensured for R_g and R_L0. An increase of the output resistance to hundreds of megohms or higher occurs for R_g and R_s.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 67–70, September, 1971.     

Tilted and Crossing Vortex Chains in Layered Superconductors

No Heading In presence of the Josephson vortex lattice in layered superconductors, small c-axis magnetic field penetrates in the form of vortex chains. In general, structure of a single chain is determined by the ratio of the London [] and Josephson [_J] lengths, = /_J. The chain is composed of tilted vortices at large s (tilted chain) and at small s it consists of crossing array of Josephson vortices and pancake-vortex stacks (crossing chain). We study chain structures at the intermediate s and found two types of phase transitions. For 0.6 the ground state is given by the crossing chain in a wide range of pancake separations a [2–3]_J. However, due to attractive coupling between deformed pancake stacks, the equilibrium separation can not exceed some maximum value depending on the in-plane field and . The first phase transition takes place with decreasing pancake-stack separation a at a = [1 – 2]_J, and rather wide range of the ratio , 0.4 0.65. With decreasing a, the crossing chain goes through intermediate strongly-deformed configurations and smoothly transforms into the tilted chain via the second-order phase transition. Another phase transition occurs at very small densities of pancake vortices, a [20 – 30]_J, and only when exceeds a certain critical value 0.5. In this case small c-axis field penetrates in the form of kinks. However, at very small concentration of kinks, the kinked chains are replaced with strongly deformed crossing chains via the first-order phase transition. This transition is accompanied by a very large jump in the pancake density.PACS numbers: 74.25.Qt, 74.25.Op, 74.20.De     

Theory of quasi-two-dimensional quantum solids. II. An anisotropic reaction-matrix approach

A self-consistent theory is proposed for anisotropic quantum solids such as dense helium monolayers adsorbed onto graphite, based upon the reactionmatrix formalism. The effect of the excitations normal to the adsorption plane is fully included in the ground-state as well as in the vibrational properties. Dispersion relations are derived both for the in-plane and out-of-plane vibrational modes, and the coupling of the two modes is studied as well.     

Energy‐Environmental Analysis of Combustion of Fuel Gases in Heating Furnaces of Metallurgical and Engineering Plants

Results of an energyenvironmental analysis of the expediency of purifying artificial fuel gases are given. Experimental investigations have been carried out in industrial furnaces of modern structure where various kinds of high and lowcalorific gaseous fuels are used.