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Methods of recycling unplasticized polyvinyl chloride (uPVC) window frame waste were investigated. The quality of untreated granular waste was compared to that of waste treated by a range of contaminant removal processes including melt filtration and dissolution. Processability of each recyclate was evaluated by using a highly instrumented single screw extruder that enabled melt viscosity and process variation to be monitored in real time. Product quality measurements such as mechanical properties and surface defects were made on extruded strip, and the nature of the stabilizers present was determined. The mechanical properties of recyclates were found to be comparable to or better than those of virgin material in all cases and conformed to industry standards for window profile. Contaminant removal stages significantly reduced the amount of large surface defects detected in extrudate. Processability was comparable to that of virgin compounds, but melt viscosity varied among different batches of recyclate, depending on the source and composition of the original PVC formulation. J. VINYL ADDIT. TECHNOL., 11:119–126, 2005. © 2005 Society of Plastics Engineers

Injection moulding studies are reported, during which in process measurements have been used to monitor batch to batch variation of several production grade polymers. Three materials were studied: a polyamide 6, a polyacetal, and a flexible poly(vinyl chloride), all of which were commercial injection moulding polymers supplied by industrial collaborators. Instrumented high precision electric and servohydraulic moulding machines were used to mould parts in house from a number of different material batches. Moulding conditions were kept constant throughout and several process variables were monitored during injection, including melt pressure, melt temperature, and viscosity index –a specific pressure integral calculated from primary injection. Part weights were measured to provide an indication of part quality. Results showed that in each case, variations between batches produced a measurable effect on part quality. These variations were detected by in process measurements, particularly by viscosit...

In-process and off-line rheometry studies are reported for compounds based on Mg(OH)2 filled low density polyethylene, some of which were first subjected to a range of strain histories in typical compounding operations. In the study reported here, the compounds were processed using an instrumented, computer monitored single screw extruder in the IRC laboratories, fitted with in line rheometers (ILR). In initial experiments a four sensor ILR slit die was used for the in-process shear rheometry, and a Rosand RH7 twin bore capillary rheometer for off-line shear and entry pressure measurements. Off line and in-line results are compared, showing good agreement for shear. Estimates have been obtained for the sensitivity to filler loading of the off line rheometer (shear flow and entry pressure measurements), and the 4 sensor ILR (shear flow measurements), which indicate that the ILR offers similar resolution of filler level to the off line rheometer at the higher loadings, although the ILR appears to have much lower sensitivity at higher shear rates at lower loadings, an effect which appears to be related to processing effects on the rheology of the compound rather than the measurement ability of the ILR. The ILR was also able to discriminate between samples with differing processing histories. Results from a six-sensor ILR die have shown good agreement in shear flow measurements, and have added the ability to measure entry pressures, which are compared with off-line measurements.

A highly sensitive multichannel SQUID gradiometer, optimized uniquely for spatial resolution, was used to map in two dimensions the magnetic field perturbations from circular holes and thin slots in conducting plates and strips, respectively. Holes as small as 0.75 mm radius in electrically conducting plates were measured directly using a single channel. Edge slots as short as 0.5 mm long in conducting strips were detected, using a multiple-channel measurement method which eliminated the effects from the edge of the strip and the current leads. Clear magnetic signatures from these simulated cracks were measured using low current densities. Numerical computations of the theoretical field distributions are presented which confirm the experimental results. Calculations indicate that much smaller defects should be detectable with an optimization of test parameters.

Microfilamentary composites of continuous Nb fibers in Cu matrices were tested for superconducting transport properties after heat treatments at 200–900 °C. The critical current density at applied magnetic field was reduced dramatically as the heat treatment temperature was increased. The scaling relations describing the critical current as a function of applied field shifted from conventional (1−h)2 scaling to higher‐order relations as the heat treatment history was varied. Critical temperature transitions were abnormally broad in the fine‐filament composites examined. The upper critical fields and transition temperatures approached bulk values after severe heat treatment.

A systematic study of the effects of cold work and precipitation on the critical current density of an Nb-27at.%Zr alloy is reported. Heavy cold working, leading to a reduction of more than 99% in the area by swaging and wire drawing increases Jc in a transverse magnetic field of 4 T by a factor of about 13 relative to Jc for the recrystallized alloy. Precipitation of β-Zr, in combination with cold work, further enhances Jc. The highest level of Jc results when the precipitation heat treatment is given at an intermediate stage of working. Such a process in this study gives a value of Jc at H = 4 T, that is more than five times higher than Jc in the most heavily cold-worked specimen. Optical metallographic examination reveals that deformation twinning takes place in this alloy and that precipitation of β-Zr occurs preferentially at deformation twin boundaries.

Microfilamentary superconducting composites of Nb fibers in Cu matrices prepared by the stack and draw method were tested for tensile critical‐current performance at 4.2 K. The superconducting critical‐current densities increased exponentially under the influence of an applied mechanical strain until the onset of Nb fiber plastic deformation. In the elastic range, the critical‐current densities conformed to log10 Jc =m (strain)+b. In several tests the critical current was increased by more than an order of magnitude by the applied strain. This behavior is consistent with an increase in the upper critical field of the Nb fibers by the applied stress.

Microfilamentary composites of continuous Nb fibers in Cu matrices prepared by the stack‐and‐draw method were tested for normal‐state electrical conductivity, residual stress state, and tensile properties. Composite wires having nominal filament diameters of about 0.1 μm were characterized by elevated matrix annealing temperatures, large Nb residual strains, and high tensile strengths. In the fine‐filament regime, finer wire sizes result in larger matrix resistivities, higher residual fiber strains, and higher tensile strengths with little effect on matrix annealing temperatures.

Quantitative control of surface pinning in the case of In–2% Bi foils was achieved by pressing diffraction gratings into the foil surfaces. The resulting grooves were effective pinners when they were 8.4ξ or wider and ineffective when 4ξ or narrower; the critical Lorentz force for flux flow was consistent with simple static calculations based on the groove geometry. No pinning occurred for flux flow along the grooves. Near Hc2, the strength of pinning decreased linearly with H, and was essentially constant at lower fields. The Jc(H) peak effect was found to depend on pinner spacing.

Niobium‐thorium eutectic alloys having fine acicular microstructures were produced by fast cooling from a vacuum melt. Although the solidified material was normal, continuity between the superconducting niobium‐rich phase, which was essentially pure niobium, was attained by plastic deformation at room temperature. The resulting wire was tested for critical current at 4.2°K, in transverse magnetic fields up to 82.5 kG; at the highest field, critical current densities of slightly more than 104 A per square centimeter were observed. The critical current density was independent of applied field from 20 kG to the highest field used; the level of critical current density depended on diameter in a manner which suggested dependence on cold work. It was concluded that the cold work had reduced the thickness of the needles of niobium below the superconducting penetration depth, and had brought them sufficiently close together to allow the superconducting correlation to interconnect the niobium, in the manner sugges...

Resistive measurements of the critical current density Jc in transverse magnetic fields were made on single crystals of niobium, which had been subjected to systematic thermal, mechanical, and chemical treatments in order to produce a wide range of substructural densities, and variations in the oxygen content. The introduction of plastic deformation into niobium crystals produced a peak in Jc at applied magnetic fields of strength Hc2, the upper critical field. The peaks in Jc were removed by annealing the crystals in the recovery range. The critical current density was increased both below and above Hc2 by producing a dislocation substructure in the crystals. Small additions of oxygen also caused Jc to increase above and below Hc2. The upper critical field, however, was relatively insensitive to structure, varying only through the structure sensitivity of the bulk GLAG parameters.

The magnetic behavior of composites of very fine (less than 1000 A) niobium wires in copper matrices has been measured at temperatures below 10°K. Three Meissner effects were observed, two of which were apparently due to strong proximity effects in the copper. The temperature dependence of the magnetization curve and measurements of the real and imaginary components of zero‐field ac susceptibility agree. The geometry and properties of the composite, which are known in some detail, are used together with current models for proximity effects to develop an adequate explanation of the data.

Nb‐oxide‐In tunneling junctions were constructed on the as‐grown surfaces of Nb single crystals at controlled orientations. The energy gap was observed to be anisotropic for crystals with resistivity ratios of 178 or greater. The lowest gap, 2.84 mV, was observed for the 〈100〉 direction. Local gap maxima were observed at the 〈311〉 and 〈111〉 directions, where the gap was about 3.19 mV. No anisotropy was observed in crystals having resistivity ratios of 65, presumably due to impurity scattering. Some coincidence of the energy gap anisotropy with main features of the proposed group V transition metal Fermi surface is noted.

Superconductivity of composite of fine niobium wire in copper, measuring critical temperature, transverse magnetic field, current density, etc

The effects of heat treatment and composition on the superconducting transition temperature of Nb3Al were studied in conjunction with an X-ray diffraction investigation of ordering and other structural effects. It was determined that an ordering anneal of 750°C for at least 48 hr achieved a maximum midtransitionT c of 18.5 K in arc-melted samples of Nb3Al. The changes in lattice parameter and order parameter during heat treatment indicate that theβ-tungsten crystal structure becomes more ordered as the maximumT c is approached. Further, theT c of 18.5 K could not be reached in Nb3Al material having nonstoichiometric composition. In such material, there was a direct correlation between increasing percentage of second-phase Nb2Al present and decreasingT c after the maximumT c had been obtained. The information obtained during this investigation led to the development of a simple empirical model to explain the change in theT c of Nb3Al. Also based on this work, a method was evolved for producing conductor material based on the highT c Nb3Al alloy (Appendix I).

Very dilute doping of granular Al films with Ag, Cu, or Au alters the superconducting tunneling behavior of such films in a manner consistent with the appearance of resonant phonon modes.

The transverse and longitudinal resistive critical fields of niobium (columbium) wires with drawing strains up to eleven were measured. The magnitude and anisotropy of the resistive critical field can both be much greater than the bulk Ginzburg-Landau parameters indicate, even if “internal surface” nucleation of superconductivity is assumed. It is suggested that these effects are due to superconductivity in the dislocation cell walls created by drawing or swaging. A simple model for this effect is offered, and various experiments which test this model are discussed.

To investigate the mechanism for the development of large anisotropic resistive critical fields in deformed niobium, the dependence of the parallel critical fieldH∥ on stress σ was measured in both compression and tension, for severely deformed niobium composites. the magnitude of ∂H∥/∂ σ increased with strain up to a value of 27 times that of annealed niobium. Also, both tension and compression increasedH∥. Both of these discrepancies from the thermodynamic predictions can be ascribed to the presence of double-ended dislocation pileups in the cell walls.

Ion implantation was used to introduce 20 at.% Si into an A‐15 Nb3Al0.9Si0.1 substrate. The surface was depleted of Al by a diffusion anneal. The Al deficiency was replaced with Si by successive implantations. The surface structures were determined from reflection electron diffraction photographs. After depletion and implantation, the sample surfaces had a disordered bcc structure. A subsequent 800 °C anneal transformed these surfaces into A‐15 Nb3Al0.2Si0.8 by epitaxial recrystallization.

X‐ray pole figures were determined for the bcc and A15 layers in surface‐diffusion‐processed V3Ga superconducting tapes. Both layers were strongly textured, the A15 layer appearing similar (but not identical) to the bcc layer, which was (112)[110]+(100)[011]. An orientation relationship based on (001)bcc∥ (001)A15, [120]bcc∥[110]A15 is suggested.

The feasibility of vacuum dielectrophoresis as a method for particulate materials separation in a microgravity environment was investigated. Particle separations were performed in a specially constructed miniature drop-tower with a residence time of about 0.3 sec. Particle motion in such a system is independent of size and based only on density and dielectric constant, for a given electric field. The observed separations and deflections exceeded the theoretical predictions, probably due to multiparticle effects. In any case, this approach should work well in microgravity for many classes of materials, with relatively simple apparatus and low weight and power requirements.

A Mo0.75Re0.25 alloy endplate was tested on a Nb TE011 mode microwave cavity resonant at 11.2 GHz. An upper bound for the surface resistance of 2.8 μΩ and a lower bound of 102 G for the microwave magnetic breakdown field were established for the alloy plate. Comparison of these results to current requirements for a superconducting linear accelerator demonstrated the potential feasibility of this alloy as a practical alternative to Nb and Pb for accelerator applications. This is the first alloy shown to be a potential alternative to Nb and Pb and arguments are presented which indicate possible practical advantages of Mo0.75Re0.25 over Nb and Pb.

The resistive critical field of severely drawn Nb increases far beyond the predictions of the GLAG theory for a homogeneous type‐II superconductor and becomes anisotropic. Although no model fits the situation exactly, nucleation of superconductivity at dislocation cell walls is a possible explanation.

The dependence of the anisotropy of the resistive critical field of severely deformed Nb on plastic strain and temperature, the anomalously large stress dependence, and the existence of resistive transitions in fields up to 48 kG all confirm the role of the dislocation cell wall in giving rise to critical‐field enhancement in this material.

The critical currents and ductilities of alloys containing 25 at. % Zr; 2, 5, or 10 at.% Ta; and the balance of Nb are determined. The effects of processing variables (such as cold-swaging) on the superconducting properties are noted. Specimens containing 5 at.% Ta are found to have critical currents greater than 10 amp and critical current densities greater than 10/sup 4/ amp/cm/ sup 2/ for magnetic fields in excess of 90 kOe. (T.F.H.)