Relaxations in semicrystalline polyethyleneterephthalate using thermally stimulated currents

Relaxation processes at temperatures above 20 °C in semicrystalline polyethylene-terephthalate have been studied using thermally stimulated depolarization currents (TSDC). The discharge curve shows three relaxation peaks (c, c and *) whose positions and intensities depend on the polarization conditions and the crystallinity. Relaxations c and c are heteropolar, while * may be homopolar or heteropolar according to the polarization temperature used. The effect of the crystallinity on these relaxations has been analysed by the thermal steps stimulation (TSS) method applied to an amorphous sample. Results show that c is fundamentally a dipolar relaxation associated with the amorphous interlamellar zone. The relaxation c is associated with the release of a free charge trapped in the amorphous regions, and * is a Maxwell–Wagner–Sillars relaxation associated with crystalline – amorphous interphases. For polarization temperatures above 150 °C, two relaxations are observed only as a consequence of overlapping C and * relaxations. © 1998 Chapman & Hall     

Theory of periodically driven,current-carrying,superconducting filaments. I. Spatially homogeneous states

Starting from the nonequilibrium theory of dirty superconductors in the Ginzburg-Landau regime, spatially homogeneous states with an applied currentI=I ₀+I ₁ cos (t) are considered. Expressions for the linear response (I₁ small) valid up to high frequencies (k _BT_c) are derived and evaluated analytically for the experimentally important case of smallI ₀ and ₀(T). Then the nonlinear response is treated for frequencies with _E1. Interesting new behavior is found for frequencies ₀ 1, where ₀ is essentially the GL relaxation time.     

Study on the α2/γ interfacial structures in a two-phase (α2?+?γ) alloy deformed at elevated temperature

The details of structure modification on ₂/ interface induced by deformation in a hot-deformed Ti-45Al-10Nb alloy were investigated by conventional and high-resolution transmission electron microscopy. A new type of dislocation ledge containing 1/3[111] partials was identified. The Burgers vectors of these dislocation ledges were determined to be 1/2[110] or 1/2101]. The formation mechanism of this new type of dislocation ledge is discussed. Also, two types of hot deformation induced ₂/ interfaces, coherent interfaces with high density of ledges and misoriented semi-coherent ₂/ interfacial boundaries were observed. For the misoriented semi-coherent ₂ interfaces, the density of dislocation ledges in these interfaces increases with the misoriented angle between the (111) and (0001) planes, and 1/3[111] partial dislocations were involved in all the dislocation ledges. The formation mechanism of these deformation-induced ₂/ interfaces were discussed related to the role of ₂/ interfaces adjusting the deformation as a dislocation sink absorbing the slipping dislocations in the phase. Moreover, misoriented semi-coherent ₂ interface related deformation twinning and structure transformation induced by deformation were analyzed and discussed related to the role of ₂/ interfaces as a dislocation source during deformation.     

Oxidation behavior of Mo≤5Si3C≤1 and its composites

The oxidation behavior of Mo₅Si₃C₁ and its composites was studied in air over the temperature range of 500°C–1600°C. Experiments revealed poor oxidation resistance of monolithic Mo₅Si₃C₁ at high temperature. The oxidation was quite rapid at 1200°C and above, resulting in complete oxidation of specimens in a short time. The addition of 2.0 wt% boron was found to produce a Mo₅Si₃C₁ composite with three other phases of MoB, MoSi₂, and SiC, and showed remarkable improvement in oxidation resistance. The mechanism for the improvement was attributed to the viscous sintering of the scale to close the pores formed during the initial oxidation period. Oxidation tests were also conducted on SiC-Mo₅Si₃C₁ composite at 800°C, 1300°C and 1600°C for more than 100 hours. The oxidation resistance of the composite was found to be very good. The results demonstrate that, though oxidation resistance of monolithic Mo₅Si₃C₁ is far insufficient for high-temperature applications, boron-modification and/or composites with SiC are viable methods to improve oxidation resistance to a practically acceptable level.     

New high-pressure Sr-Ca-Cu-O compounds and their superconducting properties

It is shown for (Sr, Ca)_1–y CuO_2.00+z (nominal composition) superconductors fabricated under a high pressure of 5 GPa and at 930°C that, as z increases, the Meissner fraction increases from a few percent to 20% and then starts to decrease. In the X-ray powder diffraction pattern for the sample with the maximum Meissner fraction, it is obvious that the infinite-layer structure has been decomposed and a new structure becomes the major phase. It appears that the new structure is the 0223 structure which consists of rock-salt and the infinite-layer type blocks. This material is likely to be a new superconducting cuprate.     

Plastic zones in Fe-3Si steel double-cantilever-beam specimens

Plastic zones generated in double-cantilever-beam specimens of an Fe-3Si steel are revealed by etching. Zones corresponding to relative stress intensity levels in the range 0.4 (in.)<K/_Y< 0.8(in.), beam height to length ratios H/W = 0.125 and 0.35, and conditions approaching plane strain are examined. The fürthest extent of the zones, p 0.13 (K/_Y)², is about half that previously observed in plates loaded in tension to comparable K-levels. The results are consistent with previous, measurements by Clark and lend support to Wilson's calculations. At high stress levels, when the zone size to beam height ratio /H 0.09, the zone begins to tilt backwards and undergoes a transition from a crack- to a beam-zone. Implications of this transition with respect to the minimum beam height requirement are examined.

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Zusammenfassung In Doppelkamileverproben aus Fe-3 Si-Stahl gebildete plastische Zonen werden durch Ätzen sichtbar gemacht. Zonen welche einem relativen Spannungsintensitätsniveau im Bereich von 0,4,(in.)<K/_Y< 0,8,(in.) entsprechen, Höhen zu Längen-Verhältnisse H/W = 0,125 und 0,35 sowie Bedingungen, welche sich der planen Verformung annähern, werden untersucht.Die größte Ausbreitung dieser Zonen, 0,13 (K/_Y)² erreicht nur die Hälfte derer die früher in Blechen beobachtet worden waren, welche bei gleichen K-Werten Zugspannungen ausgesetzt wurden. Diese Ergebnisse sind in guter Übereinstimmung mit den schon von Clark durchgeführten Messungen und bekräftigen die Berechnungen von Wilson.Bei hohem Spannungsniveau, wo das Verhältnis /H 0,09 ist, beginnt die Zone sich nach rückwärts zu beugen und sich vom Rissbereich ins Innere des Trägers zu verschieben. Die sich hieraus ergebende Folgerung für die erforderliche minimale Trägerhöhe wird untersucht.

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Résumé Les zones de déformation plastique qui se développent dans des éprouvettes en forme de double poutre cantilever d'acier Fe-3Si ont été mises en évidence par attaque chimique. On envisage les zones correspondant aux conditions suivantes: niveaux relatifs de l'intensité de contraintes compris dans la fourchette: 0,4(in)<K/y<0,8(in) et rapports hauteur/longueur de poutre H/W = 0,125 et 0,350. On examine les conditions voisines de l'état plan de déformation. L'épanouissement le plus large des zones, exprimé par 0,13 (K/_Y)², est la moitié de celui que l'on a observé précédemment dans le cas de tôles sollicitées en traction à des niveaux K comparables.Ces résultats sont compatibles avec les mesures qu'a obtenues Clark, et confirment les calculs de Wilson. Sous contraintes élevées, lorsque le rapport de la dimension de la zone plastifiée à la hauteur de la poutre /H 0,09, cette zone commence à se cambrer vers l'arrière et passe de la fissure au corps même de la poutre.On examine les implications que comporte cette transition sur les hauteurs minimum de poutres à observer.

     

Phase transformations and structure characterization of calcium polyphosphate during sintering process

Calcium polyphosphate (CPP) may be a promising bone substitute with controllably degraded ability. In this investigation, the effects of sintering temperatures on CPP's phase transformations and microstructure parameters, such as the distribution of crystallite size and micro-strain, were investigated by X-ray diffraction (XRD). The qualitative phase analysis and quantitative phase analysis based on reference intensity ratio (RIR) method were conducted for the CPP sintered at 585, 600, 650, 700, 750, 800 and 900°C. The distribution of crystallite size and micro-strain were calculated with the Warren-Averbach Fourier Transfer method. The results demonstrated that the transformation of amorphous CPP to semi-crystalline CPP occurred below 585°C, and semi-crystalline CPP to -CPP at temperature of 585–600°C; -CPP to -CPP at 585–700°C. CPP sintered between 600–700°C were composed of both -CPP and -CPP, and the mass fraction of -CPP increased with rising of temperature. Above 700°C, the sintered CPP only contained -CPP. At different ranges of the sintering temperature, the average crystallite size (D) and micro-strain () showed significant difference, for example, D and is about 2.9 nm and 1.68% at 585°C, but D and was 8.0 to 8.7 nm and 0.159 to 0.134% at 600 and 700°C, respectively. The results of the phase transformations and the variations of microstructure parameters in the present study may be able to provide some fundamental data for explaining CPP degradation phenomena.     

Heat transfer of a semitransparent plate under conditions of a regular regime of the second kind

The kinetics of the cooling of a plane semitransparent layer under conditions of a regular regime of the second kind is analyzed.Notation time - T temperature - T_e temperature of the surrounding medium (the ambient temperature) - T° initial temperature of the layer - h_e coefficient of convective heat exchange - x coordinate - coefficient of absorption of the substance - n index of refraction - B(, T) surface density of radiation of a black body - C bulk specific heat - K thermal conductivity - wavelength of the radiation - _t range of wavelengths in which the material is partially transparent - _op range of wavelengths in which the material is opaque - degree of blackness of the surfaces in the range of _op - R() coefficient of reflection from the inner surfaces of the layer - ⁺ intensity of the rays consisting of acute angles with the inner normal to the surface x = 0 - ^– intensity of rays in the opposite direction - q thermal flux - angle measured from the inner normal to the surface x = 0 Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 541–546, September, 1981.     

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.     

Mössbauer studies of α″-Fe16N2 and α′-Fe8N films

Conversion-electron Mössbauer spectra of epitaxial -Fe₁₆N₂ and -Fe₈N films have been studied and their differences are discussed in detail. The Mössbauer spectrum of -Fe₁₆N₂ can be decomposed into three subspectra, which correspond to the 4d, 8h and 4c sites. The Mössbauer spectrum of -Fe₈N can be fitted using four spectra based on a nitrogen-atom-random-distribution model. The average hyperfine field is larger (3%) for -Fe₁₆N₂ than for -Fe₈N, which is approximately consistent with a 4.1% enhancement of the magnetic moments for -Fe₁₆N₂. The iron moments tend to locate in the film plane for -Fe₁₆N₂ and to arrange perpendicularly to the film plane for -Fe₈N.     

Viscoelastic properties of the nucleus pulposus of the intervertebral disk in compression

The viscoelastic properties of the nucleus pulposus were measured in compression for 35 specimens dissected from 9 sheep. Measurements on 19 specimens were made on the day of slaughter; the remaining 16 specimens were stored frozen and thawed before testing. A preload of 0.2 N was applied to each specimen and a cyclic compression of 10 m applied at eight frequencies in the range 0.1–10 Hz at a temperature of 37 °C. Freezing appeared to increase the storage modulus, E , but not the loss modulus, E , or tan =E /E . These parameters, E , E and tan , had values of 64±28 kPa, 24±11 and 0.33 kPa±0.07, respectively. The value of tan passed through a minimum at a loading frequency of 0.9±0.2 Hz. The water content of the specimens was 80±2%. © 2001 Kluwer Academic Publishers     

Distribution of α-AlFeSi and β-AlFeSi particles in surface layer of AA6063 alloy billets after heat treatment

We developed the EPMA mapping method of small -AlFeSi(Al_8.3Fe₂Si) and -AlFeSi(Al_8.9Fe₂Si₂) particles in the billets of Al-Mg-Si alloys such as AA6063 alloys. To discriminate between -AlFeSi and -AlFeSi particles we used the relative X-ray intensities of Fe/Si ratio, the I _Fe/I _Si ratio, instead of the Fe/Si mass ratio. To obtain the I _Fe/I _Si ratio, we used a Monte Carlo method. In this study, using this method the mapping of -AlFeSi and -AlFeSi particles in the surface layer of AA6063 billets after the heat treatment (for 2 h at 580°C) was done. Namely, the distribution of -AlFeSi and -AlFeSi particles of zones from the billet surface to a depth of 800 m was measured. Results showed the zone from the surface to a depth of 200 m was occupied mainly by -AlFeSi particles and the zone from a depth of 200 m toward the center was occupied mainly by -AlFeSi particles. From these results, it was found that if we remove zones from the surface to a depth of 200 m, we can remove the majority of the -AlFeSi particles, and thus improve the quality of anodizing performance of Al-Mg-Si alloys extrusions.     

The influence of ageing on the stability of β-γ/γ′ derived microstructures in Ni-Al-Cr-(Co) alloys

Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with (B2)- (A1)/(L1₂), - or - microstructures can exhibit significant room-temperature tensile ductility. In the case of Ni-Al-Cr-based alloys, microstructural development is complicated by the precipitation of -Cr, which can supplant the -phase during ageing of three-phase -/ microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from -/ is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L1₀ type martensite and interdendritic /. Extensive intra- and interdendritic -Cr precipitation was also observed. The stability during ageing of the interdendritic / microstructure is also considered and transformation of the L1₀ martensite is examined.     

Breakup of an anomolously viscous liquid film in a centrifugal force field

An equation is obtained for the breakup radius with consideration of tipping moments and Laplacian pressure forces acting on the liquid ridge at the critical point.Notation K, n rhenological constants - density - surface tension - r current cup radius - R maximum cup radius - r_c critical radius for film breakup - ¯r=¯r=r/R dimensionless current radius - ¯r_c=r_c/R dimensionless critical radius - ₀, _c actual and critical film thicknesses - current thickness - R_r ridge radius - h₀ ridge height - h current ridge height - ₀ limiting wetting angle - current angle of tangent to ridge surface - angle between axis of rotation and tangent to cup surface - angular velocity of rotation - q volume liquid flow rate - v₁ and v meridional and tangential velocities - =4vv _lm/r,=4v_m/r dimensionless velocities - M moments of surface and centrifugal forces - M_v moment from velocity head - p_r pressure within ridge - P_vm pressure from velocity head - p_m, p_pm pressures from centrifugal force components tangent and normal to cup surface - deviation range of breakup radius from calculated value - ¯r_max, ¯r_min limiting deviations of breakup radius - _c angle of tangent to curve _c/°₀=f(¯r) at critical point - t random oscillation of ratio _c/_c Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 1, pp. 51–56, July, 1980.     

High-frequency dielectric properties of Mg-Al-Si,Ca-Al-Si and Y-Al-Si oxynitride glasses

Recently developed coaxial line techniques [1] have been used to determine, at room temperature, the values of the real () and imaginary (') parts of the dielectric constants for some Mg-Al-Si, Ca-Al-Si and Y-Al-Si oxynitride glasses over the frequency range 500 MHz to 5 GHz. The frequency dependencies of and ' are consistent with the universal law of dielectric response in that (-_t8)^(n–1) and '^(n–1) for all glass compositions; the high experimental value of the exponent (n=1.0±0.1) suggests the limiting form of lattice loss [2] situation. In this frequency range, as previously reported [3] at longer wavelengths, the addition of nitrogen increases the dielectric constant, (); in both the oxide and oxynitride glasses is also influenced by the cation, being increased with cation type in the order magnesium, yttrium, calcium as at lower frequencies.     

Radiation of internal waves during vertical motion of a body through a nonuniform liquid

Energy losses to radiation of internal waves during the vertical motion of a point dipole in two-dimensional and three-dimensional cases are computed.Notation _o(z), p_o(z) density and pressure of the ground state - z vertical coordinate - v, p, perturbed velocity, pressure, and density - H(d 1n _o/dz)^–1 characteristic length scale for stratification - N=(gH^–1–g²c _o ^–2 )^1/2 Weisel-Brent frequency - g acceleration of gravity - c_o speed of sound - vertical component of the perturbed velocity - V vector operator - k wave vector - frequency - d vector surface element - W magnitude of the energy losses - (t), (r) (x)(y)(z) Dirac functions - v_o velocity of motion of the source of perturbations - d dipole moment of the doublet - _o,l length dimension parameters - _o intensity of the source Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 619–623, October, 1980.     

The Interplay of Electronic and Nuclear Magnetism in PtFe x at Milli-, Micro-, and Nanokelvin Temperatures

We have measured ac susceptibility, nuclear magnetic resonance, and nuclear heat capacity of two PtFe _x samples with concentrations of magnetic impurities x = 11 ppm and 41 ppm at magnetic fields (0 ± 0.05) mTB248 mT. The susceptibility data have been measured at temperatures of 0.3 KT100 mK, no hint for nuclear magnetic ordering could be detected to a temperature of 0.3 K. The nuclear heat capacity data taken at 1.4 KT10 mK show enhanced values which scale with x at low polarization. This effect is described by a model assuming an internal magnetic field caused by the impurities. No indication for nuclear magnetic ordering could be detected to 1.4 K. The nuclear magnetic resonance experiments have been performed on these samples at 0.8 KT0.5 mK and 2.5 mTB22.8 mT as well as on three other samples with x = 5, 10, 31 ppm in a different setup at 40 KT0.5 mK and at 5.4 mTB200 mT. Spin-lattice and effective spin-spin relaxation times ₁and ₂ ^* of ¹⁹⁵ Pt strongly depend on x and on the external magnetic field. No temperature dependence of ₁and ₂ ^* could be detected and the NMR data, too, give no hint for nuclear magnetic ordering to 0.8 K.     

Relationship between the structure and mechanical properties in ß III titanium alloy

The ageing reactions that take place during the heat-treatment of solution-treated III titanium (11.5 wt% Mo, 6 wt% Zr, 4.5 wt% Sn, balance Ti) were followed by detailed structure characterization using electron microscopy. The variations in mechanical properties with heat treatment were also followed systematically. The electron microscopy investigations indicated that the omega phase formed on quenching. The size and volume fraction of the omega phase increased on subsequent ageing,, and phases were found to co-exist at ageing temperatures between 800 and 900° F (427 and 482° C) for short ageing times. From the observations of interfacial dislocations at the/ interface and the precipitation of fine alpha near the omega particles, with a morphology that is characteristic of the prior morphology, it is suggested that the-phase forms directly from the omega phase. The observed increase in yield strength over the solution-treated condition, due to the precipitation of phase, was found to agree well with that predicted by the Orowan hardening mechanism. Since the precipitation of fine ellipsoidal-phase was found to increase the yield strength of the alloy with reasonable ductility, it is suggested that the optimum heat treatment to produce high strength with good ductility in III titanium is to age at 900° F (482° C) for 10 to 25 h.     

One Method of Determination of the Effective Absorption Coefficient in Pulsed Laser Irradiation of Metals

An experimentaltheoretical method of determination of the absorption coefficients in laser treatment of metals has been proposed based on the solution of the boundaryvalue axisymmetric problem of heat conduction for a halfspace and metallographic measurements of the dimensions of the thermalhardening zone.     

Dielectric Dispersion in Yttrium and Erbium Formate Dihydrate Crystals

The dielectric properties of Y(HCOO)₃ · 2H₂O and Er(HCOO)₃ · 2H₂O are studied. The frequency dependences (0.01 Hz to 20 kHz) of the real () and imaginary () parts of dielectric permittivity ( = – i) are shown to follow a fractal scaling law for the dielectric response of solids. In the tan versus temperature curves, a number of maxima are revealed in a narrow temperature range. The experimental data are used to evaluate the activation energies of relaxation processes. The observed anomalies are assumed to be associated with changes in the dynamics of protons in hydrogen bonds.