On the strong coupling effects in superfluid 3He. II

Introducing a generalized model for the momentum dependence of the normal-state effective quasiparticle vertex function , we have calculated the strong coupling effects in superfluid ³He as well as the transport coefficients in the normal liquid ³He. Using those values of that account for the observed values of the normal-state transport coefficients, we have predicted the possible ranges for the values of the jump in specific heat at T _c in the BW, ABM, and A₁ states of superfluid ³He. We have also found that, compared to the normal-state transport properties, the strong coupling effects in superfluid ³He are much more sensitive to the forms of .rk supported in part by grant No. A4630 of the National Research Council of Canada.     

Dielectric relaxation in polychlorotrifluoroethylene

The effect of increasing lamellar thickness in bulk polychlorotrifluoroethylene (PCTFE) by various methods (annealing and increasing time and temperature of crystallisation) on the parameters of the and relaxations has been studied.For the a relaxation consistent increase in temperature of maximum loss and activation energy with increasing lamellar thickness confirms the strong suggestion of earlier work [6] on oriented specimens and shows that the relaxation arises mainly in the interior of the lamellae with little contribution from the chain folds.No systematic changes in these parameters with increasing lamellar thickness was found for the relaxation and this is explained by the presence of _c and _a components in crystalline and amorphous regions respectively. The component _a (as well as the _c one) shows a marked anisotropy in magnitude with respect to the draw direction in oriented specimens relative to the direction of the applied electric field. This implies a lining up of the chain molecules parallel to one another in amorphous regions.The non-existence of analogous short chain compounds and experimental scatter prevented detailed checking of the consistency of the data for the relaxation with the theory for the _c-C _c model [5].     

Structural studies of nylon 13,13

A structural study of nylon 13,13 has been carried out by means of X-rays and electron microscopy. Both X-ray and electron diffraction data, obtained from oriented films as well as from lamellar crystals prepared in solution, evidenced that nylon 13,13 adopts a structure in a monoclinic lattice of parameters a _o=0.488 nm, b _o=0.473 nm, c _o=3.40 nm, ==90°, =121°. As expected from the constitution of the nylon, no trace of structure with chains in fully extended conformation (-form) was observed throughout this study.     

γ ? α2 Phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%)

The ₂ phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%) alloy has been studied by analytical electron microscopy. ₂ and phases were found at grain boundaries. ₂ layers that suspended in layers and interfacial ledge higher than 2d ₍₁₁₁₎ at /₂ interfaces were observed in the lamellar grains. These facts indicated that ₂ phase transformation and dynamic recrystallization have occurred during high temperature stress rupture deformation. It can be concluded that deformation induced ₂ phase transformation and dynamic recrystallization resulted in the presence of particles at grain boundaries. A structural and compositional transition area between deformation-induced ₂(or ) and its adjacently original (or ₂) phases was found by HREM and EDS and is suggested as a way to transform between and ₂ phase during high temperature stress rupture deformation. The transition area was formed by slide of partial dislocations on close-packed planes and diffusion of atoms.     

A high-resolution-electron-microscopy study of a γ/γ′-α directionally solidified eutectic alloy

The microstructure of a /- directionally solidified (DS) eutectic alloy with a nominal composition of Ni-30.26Mo-6.08Al-1.43V (wt%) was investigated by means of high-resolution electron microscopy (HREM) and analytical electron microscopy. The -fibres exhibited a typical morphology with a rectangular cross-section and they displayed the Bain orientation relationship (OR) with the / matrix; that is, [001][001] and (110)(010). Misfit dislocations and lattice strain fields existed at the / interface for different habit planes; that is, (110)(010) and (100)(110) were analysed. EDAX (Energy dispersive X-ray) analysis showed that the composition of the -phase was approximately Ni₄(Mo, Al, V); it contained 90° rotational domains of Ni₃(Mo, Al, V) with a DO₂₂ structure and Ni₂(Mo, Al, V) with a Pt₂Mo structure.     

Polymorphism in Sr3Fe2O7−x

The compound Sr₃Fe₂O_7–x , with variable iron valence, was investigated by X-ray powder techniques, both at room and at high temperatures. If the material is examined in massive form, a single phase called -Sr₃Fe₂O_7–x appears as previously reported in the literature. This -phase is tetragonal and exhibits the lattice parameters: a=3.874 and c=40.314 Å. Two other phases, called and -Sr₃Fe₂O_7–x , respectively, can be obtained on heating the finely powdered material when laid on a flat platinum support. The form is stable up to 1275° C, while the form is revealed only above 1275° C and changes always into -Sr₃Fe₂O_7–x when quenched. Both and phases are tetragonal, with a=4.001 and c= 58.251 for the form and a=4.013, c=57.092 Å for the form. The transition involves a true phase equilibrium, while the transformation is possible only by means of a suitable mechanical treatment of the material.     

Microstructure and mechanical properties of rapidly quenched L20 and L20+L12 alloys in Ni-Al-Fe and Ni-Al-Co systems

Ductile L2₀-type wires and+L1₂-type duplex wires with high strengths and large elongation in the Ni-Al-Fe and Ni-Al-Co ternary systems have been manufactured directly from the liquid state by an in-rotating-water spinning method. The wire diameter was in the range 80 to 180m and the average grain size was 2 to 4m for the wires and 0.2 to 1.0m for the+ wires. _y, _f and _p of the wires were found to be about 360 to 760 MPa, 560 to 960 MPa, and 0.2 to 5.5%, respectively, for the Ni-Al-Fe system, those of the+ wires were about 395 to 660 MPa, 670 to 1285 MPa, and 3.5 to 17%, respectively, for the Ni-Al-Fe system, and about 260 to 365 MPa, 600 to 870 MPa, and 4.0 to 7.0%, respectively, for the Ni-Al-Co system. Cold-drawing caused a significant increase in _y and _f and the values attained were about 1850 and 2500 MPa, respectively, for Ni-20Al-30Fe and Ni-25Al-30Co wires drawn to about 90% reduction in area. The high strengths, large elongation and good cold-workability of the melt-quenched and+ compound wires have been inferred to be due to the structural change into a low-degree ordered state containing a high density of phase boundaries, suppression of grain-boundary segregation and refinement of grain size.     

Interaction between a dislocation and an impurity in KCl: Mg2+ single crystals

The interaction between a dislocation and the impurity in KCl: Mg²⁺ (0.035 mol% in the melt) was investigated at 77–178 K with respect to the two models: one is the Fleischer's model and the other the Fleischer's model taking account of the Friedel relation. The latter is termed the F-F. The dependence of strain-rate sensitivity due to the impurities on temperature for the specimen was appropriate to the Fleischer's model than the F-F. Furthermore, the activation enthalpy, H, for the Fleischer's model appeared to be nearly proportional to the temperature in comparison with the F-F. The Friedel relation between effective stress and average length of the dislocation segments is exact for most weak obstacles to dislocation motion. However, above-mentioned results mean that the Friedel relation is not suitable for the interaction between a dislocation and the impurity in the specimen. Then, the value of H(T _c) at the Fleischer's model was found to be 0.61 eV. H(T _c) corresponds to the activation enthalpy for overcoming of the strain field around the impurity by a dislocation at 0 K. In addition, the Gibbs free energy, G ₀, concerning the dislocation motion was determined to be between 0.42 and 0.48 eV on the basis of the following equation ln / = G ₀/(kT_p0)1 – (T/T _c)^{1/2 –1}(T/T _c)^1/2 + ln ₀/where k is the Boltzmann's constant, T the temperature, T _c the critical temperature at which the effective stress due to the impurities is zero, _p0 the effective shear stress without thermal activation, and ₀ the frequency factor.     

Determination of In-Plane Anisotropy from Magnetoresistivity Measurements on YBa2Cu3O7−δ

The magnetoresistance of six untwinned YBa ₂ Cu ₃ O _7– crystals has been measured above T _c for IBc. Fluctuation theories allowing for an in-plane coherence length anisotropy ( _{a b} ) were used in the analyses. The results suggest that the anisotropy, = _b / _a , is considerably lower than that expected from the resistivity ratio, i.e., . Some magnetoresistive measurements with the field in the ab-plane are also presented.     

Oxidation of an Al2O3-γAlON ceramic composite

The oxidation of dispersed aluminium oxynitride particles in an alumina matrix has been studied. The kinetics law of this reaction is linear and the activation energy is 420±40 kJ mol^–1 (100±10 kcal mo^–1). A-alumina layer is formed and leads to-alumina above 1200° C. The-alumina formation produces surface compressive stresses, and thus the mechanical properties ( _f, HV) are improved. We have proved that the formation of-alumina in the Al₂O₃-AION composite can lead to the best properties for this ceramic. A-alumina layer has a very interesting effect on the wear resistance of this material.     

Elastic anisotropy and the grain size dependence of ceramic fracture energies

A literature review of fracture energy ()-grain size (G) trends of cubic ceramics, and an analysis based on adaptation of a model for thermal expansion anisotropy effects are made to evaluate effects of elastic anisotropy (EA) on . Although the model does not give the specific, typically limited, —G dependences suggested by experimental data, it does predict the level of the maxima indicated at intermediateG in some materials, and the lower values at large against smallG. Further, both of these deviations from constant are shown to be dependent on crack size and hence consistent with their being more frequently and extensively seen with notch beam (NB) as against most other measuring methods.     

IN-713C characteristic properties optimized through different heat treatments

The strength of a nickel-based superalloy hardened through precipitation is related to the volume fraction, particle size and distribution of the precipitated phase, . These parameters may vary as a result of heat treatment, or high-temperatures service. The information obtained, describing the influence of time and temperature on the precipitated phase, , is of special importance owing to its technological application at high temperatures. Dissolution or precipitation kinetics are such that the volume-fraction balance of the phase is quickly established at an ageing temperature given by successive changes due only to the particle growth. The results of the present study describe heat-treatment effects on size and distribution of the phase, and precipitated carbides ageing of a nickel-based superalloy (IN-713C). These on ageing studies at a certain temperature show that the kinetic growth of particles by controlled diffusion follows that r t ^1/3 law.     

Microstructure of laser melted/rapidly solidified γ/Cr3Si metal silicide “in situ” composites

In order to improve the ductility of Cr₃Si metal silicide alloys, rapidly solidified /Cr₃Si metal silicide in situ composites were fabricated by laser melting/rapid solidification technology using Cr-Si-Ni alloy powders. Microstructure of the /Cr₃Si in situ composites was characterized by OM, SEM, XRD and EDS. The effect of Ni content in the alloy powder on microstructure and hardness of the /Cr₃Si composites was investigated. The /Cr₃Si metal silicide in situ composites have high hardness and rapidly solidified fine microstructure consisting of primary Cr₃Si dendrites and the interdendritic /Cr₃Si eutectics. The volume fraction of the Cr₃Si primary dendrites in the laser melted/rapidly solidified /Cr₃Si metal silicide in situ composites decreases with the increasing nickel content. Because of the presence of the ductile nickel-base solid solution and the rapidly solidified fine microstructure, the /Cr₃Si metal silicide in situ composites are expected to have adequate combination of strength and toughness. The results demonstrate that laser melting/rapid solidification for /Cr₃Si metal silicide in situ composites is a promising toughening method for improving the ductility of Cr₃Si metal silicide alloys.     

Study of the paramagnetic-antiferromagnetic transition and the γ → ε martensitic transformation in Fe-Mn alloys

The paramagnetic-antiferromagnetic transition and the martensitic transformation of Fe-Mn (Mn 15–32 wt%) alloys have been investigated by resistivity, dilatometry and X-ray diffraction (XRD). The results show that paramagnetic-antiferromagnetic transition increases the resistivity and the volume of alloys, whereas the martensitic transformation reduces the resistivity and volume of alloys. The A _f that was determined by the dilatometric method is not the temperature that martensites in the Fe-Mn alloys have reverse transformed to austenites completely. Mn additions reduce M _s, increase T _N and the lattice parameter of austenite in the Fe-Mn alloys. Both the antiferromagnetic transition and the martensitic transformation lead to an increase in the lattice parameter of austenite. The lattice parameters both above T _N and below T _N decrease linearly with temperature. The lattice parameter below M _s increases first and then decreases. Moreover, the (110) and (002) atomic planes in the Fe-15Mn-0.15C alloy are separated into two peaks: 2 for (002) is 44.16°, 2 for (110) is 44.47°.     

Knudsen molecular flow in a channel with a small temperature difference at its ends

The thermomolecular pressure difference (TPD) of helium, argon, and krypton is measured in a packet of glass capillaries for temperatures 273 and 293 K at their ends in a 10–100 range of Knudsen numbers.Notation exponent of the thermomolecular pressure difference effect - Kn Knudsen number - rarefaction parameter - Q_T reduced thermal creep flux - Q_P reduced Poiseuille flux - C(_t) Cercignani-Lampis scattering kernel - R specular scattering kernel - (1 – ) fraction of specular reflection - _t accommodation coefficient of the tangential momentum - P_c, P_h gas pressure in the cold and hot volumes, respectively - coefficient of dynamic viscosity - m mass of gas molecules - k Boltzmann constant - D, L the capillary diameter and length, respectively Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 5, pp. 719–724, May, 1988.     

The volume change at the superconducting transition of lead and aluminum

The volume change at the magnetic field-induced transition from the super-conducting to the normal state has been measured on single crystals of lead and aluminum between 0.3 K andT _c. From these data we have deduced the pressure dependence of the critical fieldH _c, of the critical temperatureT _c, and of the electronic specific heat coefficient . In lead, the results are in good agreement with theoretical calculations by Carbotte, where strong coupling effects are taken into account. We find ln / lnV=3.1±0.8, whereV is the volume. The measurements on aluminum giving ln / lnV=3±4 are consistent with results derived from thermal expansion experiments.This work was in part financially supported by the Schweizerischer Nationalfonds.     

The surface chemical properties of cobalt-modified γ-Fe2-O3 magnetic particles

The surface chemical properties of cobalt-modified -Fe₂O₃ (Co--Fe₂O₃) magnetic particles were studied by adsorption isotherms, FT-i.r. spectroscopy and microcalorimetry. The monolayer-adsorption amount of water on Co--Fe₂O₃ surfaces is 4.8 molecules per square nanometre, and the surface is considered to be covered with a thin water film in its normal environment. The surface hydrophilicity of Co--Fe₂O₃ is comparable to that of TiO₂. The acidic carboxyl group shows the strongest interaction with Co--Fe₂O₃, and a portion of this group chemically interacts. The basic amino group indicates stronger interaction with Co--Fe₂O₃ than the neutral hydroxyl group. It is concluded that the Co--Fe₂O₃ surface possesses a basic rather than an acidic character. This is interpreted in terms of the inherent nature of the adsorption site of Co--Fe₂O₃. Furthermore, the Co--Fe₂O₃ adsorption site appears to be energetically heterogeneous.     

Electronic specific heat of La2−xSrxCu1−yMyO4(M=Ga,Zn): Impurity effects on a D-wave superconductor

The electronic specific heat C_el was studied in Ga- and Zn-doped La_2–xSr_xCuO₄ (0.16x0.22) at T10K. Partial substitution of Ga or Zn for Cu suppresses T_c and revives the T-linear electronic specific heat, T, markedly. The (y)/n vs T_c/T_c0 relation for Zn-doped samples with x0.2 is in good agreement with the theoretical one for resonant impurity scattering in a d-wave superconductor, while those for Ga-doped samples and for Zn-doped samples with x 0.2 deviate slightly from the theoretical curve. The deviation will be discussed in relation to changes in the magnetic properties of 3d electrons.     

Calculation of radiative fluxes in flame power units

An engineering procedure is suggested for calculation of radiation properties of gas-dust media. It is based on using factors (attenuation, scattering factors, etc.) tabulated for discrete spectral ranges and averaged on particle size fractions. Application of the procedure is demonstrated using the example of a coal dust flame and the furnace working volume with account of ash and triatomic gases.Notation C_i mass fraction of the i-th component - _j mass fraction of the j-th particle fraction - n(r) calculated function of the particle size distribution - r particle radius - radiation wave length - diffraction parameter - m complex refraction index of the particle material - k_s attenuation, scattering, and scattering anisotropy factors for individual particles - K_s attenuation, scattering, and scattering anisotropy factors for the whole dust - averaged scattering anisotropy cosine - a_a, b_n Mie coefficients - , , volumetric attenuation, scattering, absorption factors for a dust flow - single-scattering albedo - emissivity All-Union Research and Design Institute of Metallurgical Heat Power Engineering, Nonferrous Metallurgy, and Refractory Materials, Ekaterinburg, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 3, pp. 287–291, March, 1993.     

The mechanism of adhesion of moist powders to solid surfaces in the presence of a temperature field

An examination is made of the basic factors which influence the creation of forces causing powders to adhere to solid surfaces in the presence of a temperature field. An experimental investigation has been conducted on an apatite concentrate.Notation p_c capillary pressure - density of fluid - g acceleration due to gravity - h_cap, h limiting and actual height of capillary rise - surface tension - r radius of equivalent capillary - q specific suction force - k_w water saturation coefficient - V_w volume of water in pores - V_pore volume of pores - Wg humidity by weight - R particle radius - polar angle - _c area of contact - N total adhesive force - _m, _w specific weight of powder and water