Poorly graphitized carbon as a new cosmothermometer for primitive extraterrestrial materials

The presence of carbon in primitive extraterrestrial materials has long been considered a useful indicator of prevailing geochemical conditions early in the formation of the Solar System. A recent addition to the suite of primitive materials available for study by cosmochemists includes particles collected from the stratosphere called chondritic porous (CP) aggregates1. Carbon-rich CP aggregates are less abundant in stratospheric collections and contain many low-temperature phases (such as layer silicates) as minor components2,3. We describe here the nature of the most abundant carbon phase in a carbon-rich CP aggregate (sample no. W7029* A) collected from the stratosphere as part of the Johnson Space Center (JSC) Cosmic Dust Program4. By comparison with experimental and terrestrial studies of poorly graphitized carbon (PGC), we show that the graphitization temperature, or the degree of ordering in the PGC, may provide a useful cosmothermometer for primitive extraterrestrial materials.

Civil Procedure : Commentary and Materials (5th ed.)

This book provides a comprehensive analysis of the practical and theoretical issues encountered in Australian civil procedure, including alternative dispute resolution. Each chapter features in-depth questions and notes together with lists of further reading to aid understanding of the issue. It also examines and discusses each substantive and procedural step in the trial process. Topics include jurisdiction of a court to consider a matter, alternative dispute resolution. limitations of actions, commencing proceedings, pleading, gathering evidence, trial and appeal, costs and practice directions. Each of the state, territory and federal procedures is covered.

The effect of Yb addition in bi2sr2ca 1-xybxcu2oy partial melted thick films

To study the phase relations in the Bi-2212 and Yb2O3 system, Bi2Sr2Ca1-xYbxCu 2Oy thick films are prepared by partial melt processing via an intermediate reaction between Bi-2212 and Yb2O3. When Bi-2212 and Yb2O3 are partially melted and then slowly cooled, solid solutions of Bi2Sr2Ca 1-xYbxCu2Oy, form by reactions between liquid and solid phases which contain Yb. Following these reactions, Ca is partially replaced in Bi-2212 matrix and participates in the formation of secondary phases, such as Bi-free, (Ca, Sr)Ox and CaO. Variation of the Bi-2212-Yb2O3 ratios and processing parameters changes the balance between the phases and leads to different Yb:Ca ratios in the Bi-2212 matrix of processed thick films. When the partial melting process is optimized for each sample to minimize the growth of secondary phases, x = 0.42-0.46 for the samples prepared at pO2 = 0.01 atm, x = 0.24-0.29 for the samples prepared at pO2 = 0.21 atm, x = 0.18-0.23 for the samples prepared at pO2 = 0.99 atm are obtained regardless to the starting compositions. It is found that superconducting properties of Bi 2Sr2Ca1-xYbxCu2O y thick films strongly depend on the processing conditions, because the conditions result in different Yb content in the Bi-2212 matrix and the volume fraction of the secondary phases. The highest Tc(0) of 77, 90 and 91 K were obtained for the samples processed at 0.01, 0.21 and 0.99 atm of O2, respectively.

Nutrient removal from wastewaters using high performance materials

Return side streams from anaerobic digesters and dewatering facilities at wastewater treatment plants (WWTPs) contribute a significant proportion of the total nitrogen load on a mainstream process. Similarly, significant phosphate loads are also recirculated in biological nutrient removal (BNR) wastewater treatment plants. Ion exchange using a new material, known by the name MesoLite, shows strong potential for the removal of ammonia from these side streams and an opportunity to concurrently reduce phosphate levels. A pilot plant was designed and operated for several months on an ammonia rich centrate from a dewatering centrifuge at the Oxley Creek WWTP, Brisbane, Australia. The system operated with a detention time in the order of one hour and was operated for between 12 and 24 hours prior to regeneration with a sodium rich solution. The same pilot plant was used to demonstrate removal of phosphate from an abattoir wastewater stream at similar flow rates. Using MesoLite materials, >90% reduction of ammonia was achieved in the centrate side stream. A full-scale process would reduce the total nitrogen load at the Oxley Creek WWTP by at least 18%. This reduction in nitrogen load consequently improves the TKN/COD ratio of the influent and enhances the nitrogen removal performance of the biological nutrient removal process.

Re-melting of Bi-2212/Ag laminated tapes by partial melting process

Bi-2212 tapes are prepared by a combination of dip-coating and partial melt processing. We investigate the effect of re-melting of those tapes by partial melting followed by slow cooling on the structure and superconducting properties. Microstructural studies of re-melted samples show that they have the same overall composition as partially melted tapes. However, the fractional volumes of the secondary phases differ and the amounts and distribution of the secondary phases have a significant effect on the critical current. Critical current of Bi-2212/Ag tapes strongly depends on the maximum processing temperature. Initial J(c)'s of the tapes, which are partially melted, then slowly solidified at optimum conditions and finally post-annealed in an inert atmosphere, are up to 10.4 x 10(3) A/cm(2). It is found that the maximum processing temperature at initial partial melting has an influence on the optimum re-heat treatment conditions for the tapes. Re-melted tapes processed at optimum conditions recover superconducting properties after post-annealing in an inert atmosphere: the J(c) values of the tapes are about 80-110% of initial J(c)'s of those tapes.

Melt textured Y123 bulk and thick film

YBa2Cu3O7-δ - 25mol%Y2BaCuO5 bars and thick films have been melt textured using a stationary furnace with a temperature gradient of 3 or 6°C/cm. Samples are heated above the peritectic reaction temperature and quenched to just above the solidification temperature and then slowly cooled below the solidification temperature. All bar shaped samples consist of 2-5 mm grains though the grain orientations strongly depend on the heat treatment conditions. The bar shows the maximum Jc of above 3,000 A/cm2, whereas the maximum Jc of 200 A/cm2 and Tczero of 88K are obtained for the thick film on (100) LaAlO3 single crystal.

Bi-2212/Ag laminated tapes: Bending and joining effects

Superconducting composite Bi-2212/Ag tapes and their joints are fabricated by a combination of dip-coating and partial melt processing. The heat treated tapes have a critical current (Ic) between 8 and 26A, depending on tape thickness and the number of Bi-2212 layers. Current transmissions between 80% and 100% have been achieved through the joints of tapes. Different types of HTS joints of Bi-2212/Ag laminated tapes are made and their transport properties during winding operations are investigated. Irreversible strain values (ε irrev) for laminated tapes and their joints are determined and it is found that the degradation of Ic during tape bending depends on the type of joint.

Bi-2212/Ag tapes and laminates : effects of bending

Superconducting Bi-2212 tapes and laminates are fabricated by a combination of dip-coating and partial melt processing. The heat treated tapes have critical current densities (Jc) up to 11 kAcm -2. We investigate the degradation of critical current (Ic) during bending experiments for both single tapes and tapes with laminate structure. Although degradation of Ic is observed in both forms, the characteristics of the degradation differ. It is determined that laminated tapes perform better than single tapes when critical current is measured against bending radius, and laminated tapes tolerate a higher strain for a given reduction in critical current. It is found that increasing the number of Bi-2212 layers increases the total Ic of the laminated tape, but degradation of critical current is more pronounced during bending because of the increased total thickness of the laminate structure. It is also found that addition of silver to the Bi-2212 layers reduces critical current degradation during bending for both tapes and laminates.

Binder effect on microstructure and properties of YBa2Cu3O7-x extruded wires

YBa2Cu3O7-x wires have been extruded with 2 and 5 wt.% of hydroxy propyl methylcellulose (HPMC) as binder. Both sets of wires sintered below 930°C have equiaxed grains while the wires sintered above this temperature have elongated grains. In the temperature range which gives equiaxed grains, the wires extruded with 5 wt.% HPMC have higher grain size and density. Cracks along the grain boundaries are often observed in the wires having elongated grains. Critical current density, Jc, increases initially, reaches a peak and then decreases with the sintering temperature. The sintering temperature giving a peak in Jc strongly depends on the heat treatment scheme for the wires extruded with 5 wt.% HPMC. TEM studies show that defective layers are formed along grain boundaries for the wires extruded with 5 wt.% HPMC after 5 h oxygenation. After 55 h oxygenation, the defective layers become more localised and grain boundaries adopt an overall cleaner appearance. Densification with equiaxed grains and clean grain boundaries produces the highest Jc's for polycrystalline YBa2Cu3O7 wires.

Melt-textured YBa2Cu3O7-x wires having plate-like grains

YBCO wires which consist of well oriented plate-like fine grains are fabricated using a moving furnace to achieve higher mechanical strength. Melt-texturing experiments have been undertaken on YBCO wires with two different compositions: YBa1.5Cu2.9O7-x, and YBa1.8Cu3.0O7-x. Wires are extruded from a mixture of precursor powders (formed by a coprecipitation process) then textured by firing in a moving furnace. Size of secondary phases such as barium cuprate and copper oxide, and overall composition of the sample affect the orientation of the fine grains. At zero magnetic field, the YBa1.5Cu2.9O7-x wire shows the highest critical current density of 1,450 Acm-2 and 8,770 Acm-2 at 77K and 4.2K, respectively. At 1 T, critical current densities of 30 Acm-2 and 200 Acm-2, respectively, are obtained at 77K and 4.2K. Magnetisation curves are also obtained for one sample to evaluate critical current density using the Bean model. Analysis of the microstructure indicates that the starting composition of the green body significantly affects the achievement of grain alignment via melt-texturing processes.

Microstructural characterization of quenched melt-textured YBa2Cu3O7-δ materials

The microstructure of YBa2Cu3O7-δ (YBCO) materials, melt-textured in air and quenched from the temperature range 900-990°C, has been characterized using a combination of x-ray diffractometry, optical microscopy, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectrometry. BaCu2O2 and BaCuO2 were found to coexist in samples quenched from the temperature range 920-960°C. The formation of BaCu2O2 preceded the formation of YBCO. Once the YBCO had formed, BaCu2O2 was present at the solidification front filling the space between nearly parallel platelets of YBCO. Large Y2BaCuO5 particles at the solidification front appeared divided into smaller ones as a result of their dissolution in the liquid that quenched as BaCu2O2.

Bulk manufacture of YBCO powders by coprecipitation

This work presents an assessment of the coprecipitation technique for the reliable production of high-temperature superconducting (HTS) copper-oxide powders in quantities scaled up to 1 kg. This process affords precise control of cation stoichiometry (< 4% relative), occurs rapidly (almost instantaneously) and can be suitably developed for large-scale (e.g. tonne) manufacture of HTS materials. The process is based upon a simple control of the chemistry of the cation solution and precipitation with oxalic acid. This coprecipitation method is applicable to all copper-oxides and has been demonstrated in this work using over thirty separate experiments for the following compositions: YBa2Cu3O7-δ, Y2BaCuO5 and YBa2Cu4O8. The precursor powders formed via this coprecipitation process are fine-grained (∼ 5-10 nm), chemically homogeneous at the nanometer scale and reactive, Conversion to phase-pure HTS powders can therefore occur in minutes at appropriate firing temperatures. © 1995.

Magnetic flux analysis in superconducting Fault Current Limiters under short-circuit conditions

In order to obtain a more compact Superconducting Fault Current limiter (SFCL), a special geometry of core and AC coil is required. This results in a unique magnetic flux pattern which differs from those associated with conventional round core arrangements. In this paper the magnetic flux density within a Fault Current Limiter (FCL) is described. Both experimental and analytical approaches are considered. A small scale prototype of an FCL was constructed in order to conduct the experiments. This prototype comprises a single phase. The analysis covers both the steady state and the short-circuit condition. Simulation results were obtained using commercial software based on the Finite Element Method (FEM). The magnetic flux saturating the cores, leakage magnetic flux giving rise to electromagnetic forces and leakage magnetic flux flowing in the enclosing tank are computed.

Civil procedure : Commentary and materials

This book provides a comprehensive analysis of the practical and theoretical issues encountered in Australian civil procedure. Each chapter features in-depth questions and notes together with lists of further reading to aid understanding of the issue. It also examines and discusses each substantive and procedural step in the trial process. Topics include jurisdiction of a court to consider a matter, limitations of actions, commencing proceedings, service, interlocutory proceedings, pleading, gathering evidence, trial and appeal, costs and practice directions. Each of the state, territory and federal procedures is covered.