Reduced Oxygen Atmosphere Research Articles

Effect of RE 2BaCuO 5 refinement on the critical current density and trapped field of melt-textured (Gd, Y)–Ba–Cu–O bulk superconductors

We have investigated the superconducting properties of (Gd, Y)–Ba–Cu–O bulk superconductors fabricated from precursors of the Gd123–Y211 with small additions of Pt and CeO 2 in a reduced oxygen atmosphere. The employment of ball-milled ultra-fine Y211 powder as a precursor material was very effective in enhancing critical current density ( J c), since RE211 inclusions in the melt-textured samples could be drastically refined with decreasing the particle size of Y211 starting powder. The maximum J c value reached an extremely high value of 380 kA/cm 2 at 77 K in self-field. However, size reduction of RE211 led to inhomogeneous distribution of RE211 inclusions. The amount of RE211 was extremely small in the vicinity of a seed crystal, when the ultra-fine Y211 powder was employed. The trapped magnetic fields of Ag-added single-grain samples 25 and 33 mm in diameters were 1.5 and 2.0 T at 77 K, respectively.

Effects of Long‐term Storage on Sensory and Nutritional Quality of Rolled Oats

ABSTRACT:Sixteen samples of regular and quick‐cooking rolled oats stored up to 28 y in a reduced oxygen atmosphere in nr 10 cans at ambient temperatures were analyzed for sensory and nutritional quality. A consumer panel evaluated aroma, texture, flavor, aftertaste, and overall acceptability using a 9‐point hedonic scale. Hedonic scores varied from 4.8 to 6.7. Although there was a loss of sensory quality in samples over time, all samples were considered acceptable by at least 3/4 of panelists for use in an emergency. Vitamin B1 amounts ranged from 2.7 to 6.6 μg/g and were highest in some older samples. Vitamin E amounts ranged from 1.3 to 37.8 μg/g and were negatively correlated with headspace hexanal levels. Rolled oats can be included in long‐term food storage regimens because of their sensory and nutritional stability when properly packaged and stored.

Processing of High-Performance (Gd, Y)-Ba-Cu-O Bulk Superconductors With Fine RE211 Pinning Centers

We have investigated the superconducting properties of (Gd, Y)-Ba-Cu-O bulk superconductors fabricated from precursors of Gd123-Y211 in a reduced oxygen atmosphere. The employment of ball-milled ultra-fine Y211 powder as a precursor material was very effective in enhancing critical current density (J/sub c/), since RE211 inclusions in the melt-textured samples could be drastically refined with decreasing the particle size of Y211 starting powder. The maximum J/sub c/ value reached an extremely high value of 380 kA/cm/sup 2/ at 77 K in self-field. However, size reduction of RE211 led to inhomogeneous distribution of RE211 inclusions. The trapped magnetic fields of Ag-added single-grain samples 25 mm and 33 mm in diameters were 1.5 T and 2.0 T at 77 K, respectively.

Piloted ignition times, critical heat fluxes and mass loss rates at reduced oxygen atmospheres

Ignition, pyrolysis and burning of materials in reduced oxygen atmospheres occur when recirculating combustion gases are mixed with the air flowing into an enclosure. Still the incoming air can be sufficient for the complete combustion of the pyrolysis gases. Thus, for the prediction of fires in enclosures it is essential to understand the ignition and burning of materials in a reduced oxygen atmosphere even when plenty of oxidizer is available for complete combustion. Previous work employing gaseous fuels has shown that under these conditions, but before extinction, burning of gaseous fuels issuing from a nozzle is complete but radiation from the flames decreases owing to the reduction of their temperature. Complementary to that work, piloted ignition of solids is investigated here at reduced oxygen concentrations by measuring the ignition times and mass loss rates of the solid at ignition. These results were obtained in a cone calorimeter modified to supply air at reduced oxygen concentrations. Two types of plywood, normal and fire retardant 4 mm thick were examined at three imposed heat fluxes 25, 35 and 50 kW/m 2 and at oxygen concentrations of 21%, 18% and 15% by volume. Because heating at these heat fluxes and material thickness corresponds to intermediate thermal conditions (i.e. neither thin nor thick), novel analytical solutions are developed to analyze the data and extract the thermal and ignition properties of the material. The same novel solutions can be applied to modeling concurrent or countercurrent flame spread. Moreover, a theory for piloted ignition explains why the ignition times and mass pyrolysis rates are weakly dependent on reduced oxygen concentrations.

The Effect of Post Annealing in Reduced Oxygen Atmosphere on Critical Current Density of (Bi, Pb)2Sr2Ca2Cu3Oy Long Bulks

Sinter forging has been employed to improve critical current density of Bi-2223 bulks. After that, optimal post annealing is also very important to get good performance. Different annealing schedules have been used to produce Bi-2223 sinter-forged bulks in different atmospheres. In this paper, Bi-2223 long bulks were prepared by a combination of cold isostatic pressing (CIP) and sinter-forging techniques. The samples were undergone deformation rates from 50 to 90% totally. The effect of post annealing in atmosphere of 7.5% O2/N2 on critical current density Jc for such (Bi, Pb)2Sr2Ca2Cu3Oy long bulks was investigated. Their microstructure features and phase changes were also studied.

Synthesis and luminescence properties of novel ZnO nanostructures: micro and nanospheres, polyhedral cages, tetra-pods, needles, tipped nanorods, nanowires and other “microphone–shaped” structures

ABSTRACTNovel ZnO nanostructures such as hollow nanospheres, nano-cages, nanoneedles, tetra-pods, nanowires, aligned nanorods and nanotubes are synthesized via thermal evaporation of ZnO and graphite powder mixtures in reduced oxygen atmosphere in the presence of argon and nitrogen flows. The ZnO nanostructures, especially nanospheres, have a unique shape and are hollow inside with walls densely decorated with aligned nanowires. Photoluminescence of synthesized ZnO structures measured at 300 K exhibits a strong near band edge peak at ∼380 nm and deep level green band centered at ∼550 nm. Fabricated ZnO structures can be studied for various applications in optoelectronics and sensors.

Mechanism of Cutting Edge Chipping and Its Suppression in Diamond Turning of Copper

This paper investigates the mechanism of cutting edge chipping in diamond turning of copper in terms of the change in Hertzian strength of diamond specimens subjected to thermal histories. The study suggests that the strength of diamond decreases as the result of the propagation of existing surface micro cracks caused by the thermo-chemical erosion of oxygen at the crack tips. The catalytic reaction involving copper is also shown to accelerate the crack propagation. Then, a cutting technique of reduced oxygen atmosphere is proposed to suppress the cutting edge chipping in diamond turning of copper over an extended cutting time.

Synthesis and transport properties of oxygen controlled melt growth textured(MixedRE)Ba2Cu3Oy (RE = Nd,Sm, Gd, Eu)

((RE)0.33Eu0.33Gd0.33)Ba2Cu3Oy bulksuperconductors (RE = Sm, Nd) were textured by the top seeded melt textured growth method in a reducedoxygen atmosphere, so-called oxygen controlled melt growth (OCMG). Largesingle domains of diameter 16 mm were successfully grown. Their microstructureand their magnetic and transport properties were investigated and compared.The resistive transition was found around 88 K, which is not the optimalTc of 95 K that could be obtained on a small re-oxygenated sample cutout from the bulk. Transport measurements were also performed onthese samples at various temperature from 77 to 88 K. In the case ofNd0.33Eu0.33Gd0.33Ba2Cu3Oy (NEG) composition, the angular dependence of the critical current densities along the(a,b) planes as a function of magnetic field was also measured.Transport critical current densities higher than50 000 A cm−2 arereached at 77 K and up to 2 T, corresponding to the nominal critical currents of 90 A injected through sectionsless than 0.25 mm2 reproducibly. This confirms the high quality of the single domain obtained with a wellcontrolled process, evidencing that mixing of rare earth is a very promising composition fortransport and high-field applications.

Effects of annealing treatments on the superconducting properties of melt-processed YBCOdoped with Ni

To optimize the superconducting properties of Ni-doped YBCO by selective substitution of Nidopants on Cu(2) plane sites, the effects of annealing treatments in reduced oxygen atmospherehave been studied. The results indicate that the superconducting transition temperature,Tc, of the Ni-doped samples with optimal oxygen content further decreases afterheat treatment in reduced oxygen atmosphere. This suggests that substitutedNi at the Cu(1) sites moves to the Cu(2) sites. However, the flux pinningcapabilities of the sample optimally doped with Ni after heat treatment in reducedO2 atmosphere are weaker compared to melt-processed YBCO doped with Li or Zn.

Quality at Time of Purchase of Dried Milk Products Commercially Packaged in Reduced Oxygen Atmosphere

Nonfat dry milk (NDM) and powdered whey beverages are available at the retail level, packaged in No. 10 cans in a reduced oxygen atmosphere to prolong shelf life. The objective of this research was to determine the sensory and nutritional quality of these dried milk products at the time of purchase. In the 10 brands tested, wide variation existed in headspace oxygen, can seam quality, sensory quality, and vitamin A (with 6 of 10 brands entirely lacking the vitamin). Manufacturers of dried milk products packaged in cans for long-term storage need to give careful attention to can seam quality, product labeling, and vitamin fortification. Consumers would be well advised to evaluate several brands of dried milk products prior to large quantity purchases.

Comparative analysis of electro-optic properties in bismuth silicate grown by the Czochralski, Bridgman–Stockbarger, and hydrothermal techniques

The relationship between growth conditions and electro-optic properties was investigated in a comparative analysis of BSO grown by the Czochralski, Bridgman–Stockbarger, and hydrothermal methods. Hydrothermal material was confirmed to be near intrinsic. Due to a higher defect concentration, Czochralski material exhibited higher absorption and photoconductivity near the band-edge as well as a stronger photochromic response than the Bridgman material. No photochromic response was observed in samples that were grown in a sealed ampoule. Subsequent experiments revealed that high temperature annealing in the presence of a limited oxygen supply removed the photochromic response in BSO. Photoconductivity and photorefractivity measurements showed fundamental changes in carrier lifetime as a result of high temperature annealing in a reduced oxygen atmosphere. Growth and processing conditions were seen to have a significant effect on defect incorporation and the resultant electro-optical properties in BSO.

Phase formation and evolution of (Bi,Pb)2223 inside Ag tapes in air and reduced oxygen partial pressure using synchrotron X-rays

Abstract The phase formation of (Bi,Pb)2223 inside a silver sheath was investigated using high-energy X-ray photons (λ=0.5 A), in air at 840 °C and in reduced oxygen atmosphere, 7%O2 + 93%N2, at 832 °C. The data was analysed using the non-overlapping peaks method as well as the full pattern Rietveld refinement method. We identified seven crystalline phases, Bi2201, Bi2212, Bi2223, Bi3221, Ca2PbO4, (Sr,Ca)2CuO4 and CuO, plus silver. There is a significant difference in phase evolution under the two different heat treatment conditions. The heat treatment in reduced oxygen atmosphere at 832 °C favours the formation of Bi2223 with a reduced amount of Bi2201, Bi3221, Ca2PbO4 and (Sr,Ca)2CuO4 whilst a clearly noticeable amount of Bi2201 phase exists throughout the process for samples heat treated in air at 840 °C.

Superconducting properties of textured (LRE I0.33Eu 0.33Gd 0.33)Ba 2Cu 3O y (LRE I=Nd, Sm) processed by OCMG

((LRE) 0.33Eu 0.33Gd 0.33)Ba 2Cu 3O y bulk superconductor (LRE=Sm, Nd) were textured by the top seeded melt textured growth method in a reduced oxygen atmosphere. Their physical properties and their microstructure were studied. (Sm 0.33Eu 0.33Gd 0.33)Ba 2Cu 3O y textured material exhibited a critical temperature of 94 K and critical current densities at 77 K of 50 000 A cm −2 under self field and 20 000 A cm −2 under 2 T. In the case of (Nd 0.33Eu 0.33Gd 0.33)Ba 2Cu 3O y , an optimal critical temperature of 95 K is reached. Moreover, high critical current density under self field of 60 000 A cm −2 is obtained. This last result has been confirmed by transport measurements. Indeed, critical current densities at 77 K higher than 50 000 A cm −2 have been measured when the applied field was below 2 T.

Single domain, c-axis oriented (Nd–Eu–Gd)–Ba–Cu–O bulk superconductors

We prepared c-axis aligned (Nd–Eu–Gd)–Ba–Cu–O bulk superconductors using the melt-processing technique in a reduced oxygen atmosphere, and measured the field-trapping capability. The highest value of the trapped flux density on the surface of these samples was 1.38 T, which was recorded with a 38 mm diameter sample that was prepared with the addition of 40 mol% of (Nd0.33Eu0.33Gd0.33)2BaCuO5 and 15 wt% Ag2O. The critical current density was found to vary with the location in the sample, which can be attributed to the difference in the density of 211 particles, the distribution of which is inhomogeneous in melt-processed bulk samples.

Reviews Of Acoustical Patents

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Field trapping capability of melt-processed (Nd–Eu–Gd)–Ba–Cu–O bulk superconductors

We prepared c-axis oriented (Nd–Eu–Gd)–Ba–Cu–O bulk superconductors by the melt-processing technique in a reduced oxygen atmosphere. Samples with various amounts of excess nominal (Nd 0.33Eu 0.33Gd 0.33) 2BaCuO 5 phase powders were successfully grown, and the highest trapped field at liquid nitrogen temperature of 30 mm diameter samples was 1.18 T. We also studied the effect of changing the molar ratio of Nd, Eu and Gd of the secondary phase, and revealed the trapped field to enhance to 1.38 T with a 40 mol% nominal (Nd 0.5Eu 0.5) 2BaCuO 5 added sample.

Ni-substituted sites and the effect on Cu electron spin dynamics ofYBa2Cu3−xNixO7−δ

We report Cu nuclear quadrupole resonance experiment on magnetic impurity Ni-substituted YBa$_2$Cu$_{3-x}$Ni$_x$O$_{7-\delta}$. The distribution of Ni-substituted sites and its effect on the Cu electron spin dynamics are investigated. Two samples with the same Ni concentration $x$=0.10 and nearly the same oxygen content but different $T_c$'s were prepared: One is an as-synthesized sample (7-$\delta$=6.93) in air ($T_c$$\approx 80 K$), and the other is a quenched one (7-$\delta$=6.92) in a reduced oxygen atmosphere ($T_c$$\approx 70 K$). The plane-site $^{63}$Cu(2) nuclear spin-lattice relaxation for the quenched sample was faster than that for the as-synthesized sample, in contrast to the $^{63}$Cu(1) relaxation that was faster for the as-synthesized sample. This indicates that the density of plane-site Ni(2) is higher in the quenched sample, contrary to the chain-site Ni(1) density which is lower in the quenched sample. From the analysis in terms of the Ni-induced nuclear spin-lattice relaxation, we suggest that the primary origin of suppression of $T_c$ is associated with nonmagnetic depairing effect of the plane-site Ni(2).

YBCO bulk material processed in an oxygen controlled melt-growth process

YBCO pellets have been submitted to the top-seeding melt-textured growth process under a reduced oxygen atmosphere (1% O2 in Ar). Ce and (Ce, Sn) doping have been investigated. In the Ce-doped sample, a fishtail has been observed when the thermal cycle maximal temperature of 1020 °C is used. However, the microstructure exhibits large Y211 particles under these processing conditions. When the maximal temperature is 1000 °C, the size of Y211 decreases and the critical current density (Jc) is enhanced. The effect observed under a field is a shoulder in the Jc curve. The same effect is observed in the (Ce, Sn)-doped sample. The Ce-doped and (Ce, Sn)-doped samples exhibit Jc under a self-field of 90 000 A cm−2 and 84 000 A cm−2, respectively. Moreover, when the pre-sintering step is suppressed, the values of Jc are improved and the samples present a Jc of 100 000 A cm−2 under a self-field.

Variations in a Boehmite Gel and Oleic Acid Emulsion under Calcination

In this paper, we describe variations in a boehmite (AlOOH) and oleic acid emulsion during the process of forming superfine α‐Al2O3 crystallites from the mixture of oleic acid and a boehmite gel precursor. We also propose that the oleic acid decomposes under calcination, generating carbon, which can effectively prevent agglomeration of Al2O3 particles. Calcination for the present study was conducted under a reduced oxygen atmosphere, in the temperature range 25°–1100°C. Phase variations of the mixture under calcination were identified by Fourier transform infrared spectrometry (FTIR), X‐ray diffractometry (XRD), and transmission electron microscopy (TEM). The FTIR spectra were used when the mixed emulsion of oleic acid and boehmite gel was heated, to investigate the adsorption reaction of the aluminum oleate; the C—O—C cross‐linking structure of oxygenation, which aided in carbon formation; and the ability of the carbon generated with α‐Al2O3 during phase transformation to prevent agglomeration (vermicularity). The products were analyzed by XRD at different temperatures, and TEM was used to examine the individual diameters of the α‐Al2O3 crystallites.

Sm–Ba–Cu–O bulk superconductors melt-processed in air

Recent development shows that melt-processed YBaCuO (Y123) and light rare-earth (LRE) BaCuO superconductors have a high J c at 77 K and high magnetic field. Solidification processes for producing RE123 superconductors are effective for obtaining high J c and are very promising for high field application as a superconducting permanent magnet with the liquid nitrogen refrigeration. LRE BaCuO bulk superconductors melt-processed in a reduced oxygen atmosphere, named oxygen-controlled-melt-growth process, have a high T c and J c. However, processing in air is preferable for practical applications. In this study, we discuss Sm123 bulks melt-processed in air, and their characteristic superconducting properties. Isothermal undercooling growth in air with oxygen annealing and Nd123/MgO thin film cold seeding technique were applied in Sm 1.8Ba 2.4Cu 3.4O y /Ag system to seek the high efficiency of process, homogeneity of composition, and feasibility of batch production. Single-domain growth was achieved using this technique. The result implies that melt-processed in air applying isothermal method and thin film seeding in Sm system is fit for producing larger bulks in large scale applications.