Extraneous Phases Research Articles

The Influence of Diffusion Fluxes on the Detection Limit of the Jalpaite Copper Ion-Selective Electrode

Abstract : It has been suggested that electrode dissolution and the concomitant saturation of the electrode's diffusion layer restricts the detection limit of the jalpaite Cu ion-selective electrode (ISE) to samples with total Cu levels above 10(exp-5) mol dm(exp -3) [1, 2]. This article will use rotating disk electrode (RDE) data for San Diego Bay seawater and Fick's law of diffusion to demonstrate that the static commercial Orion Cu ISE (employing a jalpaite membrane) produces a background level of contamination of (2.0 plus or minus 0.5) x 10(exp -8) mol dm(exp -3) total Cu, and the reduced thickness of the Orion Cu ISE's diffusion layer in the presence of hydrodynamic flow [e.g., at an RDE, or in continuous flow analysis (CFA)] lowers the background contamination of Cu to < 10(exp-9) mol dm(exp -3). Furthermore, the RDE Cu ISE employing an electrode fabricated using jalpaite precipitated in 80% excess Na2S, so as to minimize the presence of occluded and leachable Cu salts and extraneous phases such as silver sulfide [3 - 5], reveals an improvement in the lower limit of detection compared to the commercial Orion Cu ISE.

Phase composition of microspheres for production of heat-insulating corundum ceramics

The phase composition of hollow fused corundum microspheres is investigated. The problem of the presence of extraneous phases and their removal is discussed. The effect of heat treatment on the phase composition of the microspheres is studied.

Application of a near coincidence site lattice theory to the orientations of grains on (001)

Various orientations of grains in polycrystalline films prepared on (001) substrates by the d.c. sputtering method were studied by x-ray diffraction experiments. The relation between the a and b axes of the thin film and the in-plane lattice vectors of the substrate has been directly obtained by an x-ray reflection scan. The orientational relations agree well with the predication of a simplified theory of a near-coincidence site lattice between and . The grains were found to have a high probability of forming low-angle or low- boundaries among themselves. These grain boundaries are of low energy, free from extraneous phases, and exhibit a high connectivity of Mn - O - Mn nets. Therefore, the boundaries can still support the GMR effect.

Water And Hydrocarbon Phase Trapping In Porous Media-Diagnosis, Prevention And Treatment

Abstract The entrapment of extraneous phases within porous media can occur in a number of different situations during drilling, completion, workover and production operations. The introduction of an additional immiscible phase, or an increase in an existing phase saturation within porous media can cause deleterious relative permeability effects which can substantially impact the permeability and relative permeability to oil or gas. This phenomenon is commonly described as aqueous phase trapping or hydrocarbon phase trapping, depending on the situation under consideration. This paper describes specific conditions required for the establishment of aqueous and hydrocarbon phase traps and provides diagnostic equations to evaluate the potential severity of an aqueous phase trap in a given reservoir situation. Specific procedures are recommended for the prevention of aqueous phase traps during drilling, completion and production operations and, in a situation where phase traps are determined to exist in a reservoir, a variety of treatment techniques are presented to attempt to remove or reduce the severity of the aqueous or hydrocarbon phase trapping phenomenon. Introduction Aqueous phase trapping and hydrocarbon phase trapping represent a significant mechanism of impaired productivity in many oil and gas reservoirs in various locations throughout the world. Bennion et al. (1994)(1) have provided a detailed discussion of the basic mechanisms of aqueous and hydrocarbon phase trapping and associated reductions in permeability. Aqueous phase trapping can occur in both oil and gas reservoirs and may be associated with reservoir situations where the reservoir exhibits a sub-irreducible initial water saturation. Specific additional documentation on subirreducible water saturation reservoirs is documented by Katz et al. (1982)(2) and Masters et al. (1984)(3). Hydrocarbon phase traps may be established in gas reservoir applications where extraneous immiscible hydrocarbon phases are introduced into the reservoir, or in retrograde condensate reservoir applications where the reservoir is produced at some pressure below the dewpoint resulting in the accumulation of liquid retrograde condensate within the pore space. This paper discusses various types of phase trapping and provides criteria for the diagnosis of the potential severity of a reservoir to be susceptible to aqueous phase traps. Additional discussion is then presented with respect to the prevention of aqueous and hydrocarbon phase traps in different reservoir operational situations and potential remediation of oil and gas reservoirs where aqueous or hydrocarbon phase traps have already been established. Mechanisms of Aqueous Phase Trapping Figure 1 provides a schematic illustration of the establishment of an aqueous phase trap within a low permeability gas reservoir application. The initial basis for the establishment of an aqueous phase trap is a reservoir which exists at what is classified as a subirreducible saturation, where the initial water saturation in the reservoir is less than what would be typically quantified as the irreducible water saturation which would exist in the porous media under the prevailing capillary conditions. Sub-irreducible saturations are postulated to be established by a combination of dehydration, desiccation, compaction and diagenetic effects which occur over the life of certain reservoirs.

Process optimization for 123 and Bi-based superconductors

Abstract The development of pure phase 123 and Bi-based 2223 superconductors has been optimized. The pre-heat processing appears to be a very important parameter in achieving this objective. In addition, the synthesis of pure phases in the Bi-based system involves effects due to oxygen partial pressure, time and temperature. The optimization of this processing is a key step towards the successful continuation of the superconducting materials development, i.e. in substitutions, c-axis orientation, melt-sintering processes, and in synthesizing single crystals. An example of optimized bulk substitution is the 70% limit of Sr for Ba substitution in the yttrium-based 123 superconductor. In a nominal composition containing no barium, a majority 123 phase has also been observed, though this phase is apparently not superconducting. In the Bi-based system, substitution of Sb and Pb for Bi has been obtained in the 2223 phase. The Sb substitution into the pure phase has no apparent advantage over the parent Bi compound or the Pb-substituted phase. Orientation/melt-sintering effects include the extreme c-axis orientation of yttrium 123 and of the bisumuth 2223, 2212 and 2201 phases. Surface orientation of all three Bi-based phases can be obtained from one sample of a specific nominal bulk composition. The surface orientation for both series of samples is dependent upon a number of factors including pre- heat processing, exact composition and/or extraneous phases present, heat rates, temperatures, and times. A procedure for establishing Sr substitution for Ba into 123 single crystals has been determined. Systematic substitution of up to 30% Sr for Ba in the structure has been successful. This procedure as well as those above will be described and discussed.

Interface between gold and superconducting YBa2Cu3O7−x

Gold (Au) and silver (Ag) are known to be important contact metals on YBa2Cu3O7−x (YBCO). Both metals have been used as additives in fabricating tapes of YBCO and Bi2Sr2CaCu2O8 (BSCCO) materials, and have favorable results in improving not only the flexibility but also the weighted critical currents of the resulting composites. Previous results on superconductor/normal metal/superconductor junctions made using YBCO/Au/YBCO and YBCO/Au/Nb demonstrated that a supercurrent can be induced in the normal metal layers through the proximity effect. Our transmission electron microscopy study of the Au/YBCO interfaces shows a well-bonded interface with no extraneous phases present. Lattice fringes of the (001) plane in YBCO terminated at the interface abruptly. This observation supports previous results of contact resistance of x-ray photoelectron spectroscopy (XPS). Both (001) integral steps and multiples of 1/3 (001) steps were observed at the Au/YBCO interface. When the top gold layer was absent locally, surface degradation was observed as the (001) lattice fringes stopped short from the surface by 10 nm. Our results support that Au is a desirable contact metal and a dependable surface passivation material for YBCO.

Effect of heat treatment on the microstructure and magnetic properties of polycrystalline MnZn ferrites

The effect of heat treatment of commercially available polycrystalline MnZn ferrite slabs was studied for temperatures near typical recording head glassing temperatures. Toroid-shaped specimens were heated in atmospheres of varying levels of oxygen and the deterioration in magnetic properties was measured. The surfaces of the exposed specimens were inspected by means of optical and electron microscopy and the occurrence of ferrite instabilities such as grain growth, segregation of secondary phases etc. were observed. The degradation also appeared to be surface-driven. To investigate this further, some samples were heat treated in highly oxidizing and reducing atmospheres to induce gross ferrite instabilities. The near surface regions of these samples were then characterized by x-ray diffraction, x-ray photoelectron spectroscopy (XPS) and conversion electron and conversion x-ray Mossbauer spectroscopy (CEMS and CXMS). In addition to grain growth and other structural changes, the precipitation of extraneous phases appears to be a major mode of ferrite failure during such annealing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Study of intrinsic defects in vacuum/air annealed CuInSe 2

This paper describes the influence of vacuum/air annealing and the Cu: In ratio on defects produced in chemically prepared CuInSe 2 thin films/powders. Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques were used for analysis. Two isotropic EPR signals A (g = 2.0030) and B (g = 2.1642) obtained in both air and vacuum annealed samples have been ascribed to In Cu donors and V Cu acceptors, respectively. On annealing CuInSe 2 in air, the concentration of In Cu donors decreases, V Cu acceptor concentration increases, increase in p-type nature and resistivity decreases. However, on increasing the Cu: In ratio, the concentration of both types of defects decrases but p-type nature increases with decreasing resistivity. Air annealing of the samples also induces the formation of extraneous phases like Cu 2Se, SeO 2 and In 2O 3. The near-stoichiometric and Cu-rich samples have been found to be chalcopyrite, whereas Cu-poor samples have the tendency to be sphalerite. All the results obtained can be understood in terms of In Cu donor-oxygen interaction and the formation of V Cu acceptors.

Development of high-T/sub c/ superconductor wires for magnet applications

Bi-2212/Ag phi 1-mm round untextured wires have been produced with critical current densities of 1200 A/cm/sup 2/ at 77 K, 0 T and up to about 2.0*10/sup 4/ A/cm/sup 2/ at 4.2 K in magnetic fields beyond 20 T. In order to achieve this, a two-step annealing procedure is necessary with a partial melting of the wire core, the melt having a composition near Bi/sub 2/(Sr,Ca)/sub 2/Cu/sub 1/O/sub 6+x/. On cooling, the Bi/sub 2/(Sr,Ca)/sub 2/Cu/sub 1/O/sub 6+x/ phase appears at 880 degrees C, as revealed by in situ XRD (X-ray diffraction) measurements. Long-term annealing at 840 degrees C leads to the transformation of this phase into the Bi/sub 2/Sr/sub 2/Ca/sub 1/ Cu/sub 2/O/sub 8+x/ phase. The alkaline earth cuprate (Sr,Ca) /sub 14/Cu/sub 24/O/sub approximately=40/ and CuO occur as major extraneous phases. Helically shaped samples yield a lower j/sub c/ between 3*10/sup 3/ and maximum 1.0*10/sup 4/ A/cm/sup 2/ at 4.2 K, 10 T. Cracks due to thermal expansion mismatch with the sample holder and remaining inhomogeneities along the wire are responsible for these lower values. From I-V curves measured at 4.2 K, n-values were determined to be 20 to 25 in the interesting very-high-field region beyond 20 T. Bi-2223/Ag highly textured thin tapes yield an appreciably higher j/sub c/ of 2.6*10/sup 4/ A/cm/sup 2/ at 77 K, 0 T. Temperature-dependent measurements of j/sub c/ as a function of magnetic field B yielded onset of significant flux creep above 20 K, limiting the range of application in magnet technology to the temperature range up to 20 K unless an additional more effective pinning mechanism is introduced.

Laboratory Factors Influencing Slim Tube Test Results

Abstract The equipment and operating procedure for slim tube testing of hydrocarbon solvent-reservoir oil interactions within a porous medium has now been developed to the point where comprehensive checking of results is practical. Such tests have revealed laboratory factors which can lead to difficulties in interpretation of a solvent test program result. The discussion addresses the impact on test results of reservoir fluid sample quality, processing rate and the slim tube packing material. If these factors are not considered, either apparent inconsistencies in laboratory results or misinterpretation of displacement process effects can result. Suggestions for avoidance and/or adjustment procedures to delete the extraneous effects will be included. Introduction The primary object in solvent design is to identify an injection fluid which effectively removes available oil from the pore space; maintains its integrity as a moving fluid zone in the reservoir; and is cost-effective. The petroleum industry has been working since the early 19505 to find test procedures to identify competent, practical solvents and injection processes for effective, commercial miscible floods. Reservoir Criteria Relative permeability effects dictate that any injected solvent must be single phase at reservoir conditions to prevent the formation of high gas saturation zones. Such zones, in turn, could preferentially divert solvent from contacting the remaining oil saturation, reducing volumetric sweep efficiency. Alternate injection of water with the solvent can suppress such problems, but can offset only minor free gas content in the pore space. The design objective is, therefore, to find an injection fluid in which the light and intermediate hydrocarbons will progress through the reservoir at the same rate. Extraneous phases which have low interfacial tension with the reservoir oil do not pose a problem, since they should move as a weak emulsion in the porespace. Standard Testing Development of the slim tube test has allowed solvent/oil interactions to be observed and compared in a standardized, controlled experimental environment. The results of several tests can then be compared on a Rutherford plot(1) to define the "minimum miscible concentration" (MMC) and the minimum concentration required for the attainment of effective first contact miscibility (JFCM). The design solvent analysis can then be selected in relation to these limits, balancing the risk associated with too lean a solvent composition against extra cost for unnecessary richness. The concept of design "safety" is thus implicit in the selection process. The above description implies the need to test interactions between solvent and reservoir oil in a porous medium which resembles the reservoir as closely as possible with respect to temperature, pressure, hydrocarbon fluids in place and pore space configuration. The equipment and procedures often cannot be so precise, leading to the need for adjustment and interpretation methods to ensure valid conclusions from the comparison of results for several tests. Practical Operation The inherent instability in natural gas liquids (NGL) supplies has led to the development of solvent design correlations, which permit the injection plant operators to react on an hour-by-hour basis if required.

Microstructure of YBa2Cu3O7−x thin films grown on single-crystal SrTiO3

YBa2Cu3O7−x thin films on (001) and (014) SrTiO3 were prepared by coevaporation of Y, BaF2, and Cu, and annealing in oxygen at 850 °C. Cross-sectional samples prepared by cutting films and substrates along the SrTiO3 (100) plane were studied with transmission electron microscopy. The growth of YBa2Cu3O7−x in as-deposited films is extremely anisotropic with the [001] being the slow direction and the (001) plane being the fast growth plane. When the (001) planes of YBa2Cu3O7−x grains are parallel to the film plane, as on (001) SrTiO3, there is a dominance of this orientation over the whole film. Three types of YBa2Cu3O7−x grains, 90° misoriented from each other, are observed to grow on both (001) and (014) surfaces of single-crystal SrTiO3 substrates with their c directions aligned with one of the three 〈100〉 directions of cubic SrTiO3. This ambiguity creates a threefold degenerate epitaxy of YBa2Cu3O7−x on SrTiO3, which results in 90° grain boundaries in the final YBa2Cu3O7−x thin films. These boundaries are free of any second phase and decorations. While some extraneous phases were observed in these films, they were located away from the crystallographically special, 90° boundaries. Therefore, the presence of extraneous phases elsewhere in the films was not damaging to the superconducting transport.

Structure and magnetism of the RTiFe/sub 11/ compounds (R=Gd, Tb, Dy, Ho and Er)

Ternary alloys of the composition RTiFe/sub 11/ (R=Gd, Tb, Dy, Ho and Er) were prepared and investigated. The samples were found to be nearly single-phase materials, with small amounts of extraneous phases appearing primarily along the grain boundaries. The Curie temperatures were observed to be in the range 502 to 603 K and to vary with the R component according to the square root of the de Gennes function, reflecting the R-Fe exchange interaction. All of the compounds studied, except TbTiFe/sub 11/, possess uniaxial anisotropy at room temperature. The results obtained indicate that the R and Fe sublattices couple in an antiparallel manner, as is normally the case in heavy rare-earth-transition-metal compounds. A first-order magnetization process (FOMP) was observed in the Dy and Ho compounds, but not in their Gd and Er analogs. In the case of the Tb compound, there were some indications of the FOMP, but it was not nearly as pronounced as in the case of the Dy- and Ho-based compounds. The M versus T curves provide strong evidence of spin reorientations in the systems containing Tb, Dy, and Ho. AC susceptibility studies suggest the presence of a spin reorientation in the Er compound.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magnetic and structural properties of SmTiFe 11 -xCo x alloys

SmTiFe 11 -x Co x (0⩽ x⩽11) alloys were synthesized and studied by X-ray, SEM, EDXS and magnetometry at fields up to 90 kOe in the temperature range of 4.2–1100 K. It is established that almost single-phase materials exhibiting a ThMn 12 type structure can be formed only for x<2. The results of SEM and EDXS analyses indicate the presence of extraneous phases of Th 2Zn 17 type structure and Fe-Co-Ti ternary at higher Co concentrations ( x⩾2). The Co/Fe ratio is found to be the same in both the 1:12 and 2:17 phases and increases with increasing Co content. The SmTiFe 11 -x Co x alloys exhibit high saturation magnetization (120–145 emu/g) in the temperature range 4.2–295 K. A characteristic maximum in composition dependence of saturation magnetization is found for x≈2. The SmTiFe 11 compound possesses high anisotropy fields (≈102 kOe at 295 K) which is decreased in the presence of Co, and the material is magnetically soft at higher Co concentrations. The SmTiFe 11 -x Co x alloys exhibit a first-order magnetization process, which is quite evident in SmTiFe 9Co 2 at 77 and 4.2 K. The Curie temperatures are significantly increased by Co substitution, especially at low Co concentration. The direction of easy magnetization in these alloys appears to change from axial to cone to planar with increasing Co content.

TEM sample preparation of superconducting oxides

The preparation and observation of high Tc superconducting TEM samples deserves a great deal of care since, as when characterizing any new material, mistreatment can bring about extrinsic features leading to erroneous conclusions. In dealing with materials such as these, where the structural origins of the electromagnetic properties are tantamount, this is especially true. The three most common practices of sample preparation are suspending crushed powder, ultramicrotomy, and ion-beam milling. The illustrations will be made with YBa2Cu3O7-x samples.The powder suspension technique requires grinding the material with a suitable mortar and pestle (e g., agate) to a size which will allow electron transparency. Dispersing the particles in a suitable solvent such as water or acetone prevents aggregation. If the sample has large amounts of extraneous phases, the choice of medium is crucial as reactions will occur. Ni or Ti grids (50 to 75 mesh) with carbon films are used to fish out the suspended particles.

Characterization of intergranular cuprous oxide in polycrystalline YBa2Cu3O7-x

The identification of extraneous phases is important in understanding of high Tc superconducting oxides. The spectroscopic techniques commonly used in determining the origin of superconductivity (such as RAMAN, XPS, AES, and EXAFS) are surface-sensitive. Hence a grain boundary phase several nanometers thick could produce irrelevant spectroscopic results and cause erroneous conclusions. The intergranular phases present a major technological consideration for practical applications. In this communication we report the identification of a Cu2O grain boundary phase which forms during the sintering of YBa2Cu3O7-x (1:2:3 compound).Samples are prepared using a mixture of Y2O3. CuO, and BaO2 powders dispersed in ethanol for complete mixing. The pellets pressed at 20,000 psi are heated to 950°C at a rate of 5°C per min, held for 1 hr, and cooled at 1°C per min to room temperature. The samples show a Tc of 91K with a transition width of 2K. In order to prevent damage, a low temperature stage is used in milling to prepare thin foils which are then observed, using a liquid nitrogen holder, in a Philips 430T at 300 kV.

The Ba(Sr)Mn 2Fe 16O 27 w-type hexagonal ferrites as permanent magnets

The BaMn 2Fe 16O 27 and SrMn 2Fe 16O 27 W-type hexagonal ferrites were prepared; these two compounds are ferrimagnetic ( T c = 424°C, 430°C) with a room temperature magnetization σ ≈ 75 emu/g. The influence of the milling and annealing treatments on the powder samples is studied: in the (700–1200°C) annealing temperature range, the decomposition of the W-phase occurs, leading to the presence of the M-phase and α-Fe 2O 3. Green compacts with or without extraneous phases were prepared by pressing the milled powders under a magnetic field. We give the variations of the density, the remanence and the coercive force as a function of the sintering temperature; the best values are obtained with the presence of the extraneous phases: d ≈ 5 g/cm 3, B r ≈ 2500 G and H J c ≈ 3000 Oe.

Magnetic characterization of antiferromagnetic Ba2Fe6O11

The magnetic properties of the metastable compound Ba2Fe6O11 present in the phase subsystem BaFe2O4 - BaFe12O19 have been analyzed by means of Mossbauer and magnetic measurements. The obtained data indicate that Ba2Fe6O11 is a complex antiferromagnet with Neel temperature TN = 488 K. The overall features of the Mossbauer spectra and the population of the observed iron sublattices suggest for Ba2Fe6O11 a crystalline structure related to that of perovskite like compounds, which are often present in the chemical reactions that lead to the formation of hexaferrites. The extraneous phases present in the obtained samples, one of which turned out to be barium hexaferrite, have also been characterized.

The microstructure of electric discharge machined WC-Co

The electrical discharge machined surfaces of several sintered WCCo alloys were examined at room temperature by x-ray diffraction and optical and electron microscopy. In addition to the hexagonal WC, both W 2C and the face-centered-cubic modification of WC were found. The relative amounts of W 2C and WC(FCC) vary inversely with capacitance. Upon annealing, both phases disappear and are replaced by the η-phase (W 3Co 3C). Certain features of the microstructure are tentatively associated with the extraneous phases, but further interpretation of the x-ray and metallographic results requires a more specific study of the. respective roles of cobalt and carbon in the surface reactions.

Rates and Mechanisms in Formation of Dolomite: ABSTRACT

Dolomite is forming in Deep Springs Lake, California, and marine-associated Coorong lakes of South Australia. Dolomite forms via a surface-layer precursor, which is commonly calcium-rich in comparison End_Page 631------------------------------ with the main body of the crystal, and which yields a calcium-rich dolomite by solid-state diffusion. This can be demonstrated to be true of most dolomite which forms in the absence of extraneous phases of calcite and magnesian calcite, from both the marine-associated Coorong lakes and Deep Springs Lake, by employing the following methods: (1) progressive leachings, with attendant chemical analyses; (2) X-ray diffraction; and (3) electron microscopy. X-ray diffraction data show that it is also true of dolomite forming in the presence of such extraneous phases. Dolomite also forms in the presence of magnesite or calcian magnesite, in certain of the marine-associated Coorong lakes; such dolomite is slightly magnesium rich. This dolomite probably forms via a magnesium-rich precursor, dep sited as a layer on the individual crystals of dolomite, in much the same manner as the calcium-rich layer on the calcium-rich dolomite. Carbon-14 dates of the calcium-rich dolomite from Deep Springs Lake yield growth rates of 500-900 angstroms/103 years. End_of_Article - Last_Page 632------------

Precipitation of Impurities in Large Single Crystals of CdS

Optical microscopy has been used to examine large single crystals of CdS with and without intentionally added impurities. Inclusions of excess cadmium have been observed in high conductivity, n‐type crystals of pure CdS. It has also been demonstrated that extraneous phases precipitate when copper, silver, or gold impurities are present in concentrations as low as . This is also a probable upper limit to the solubility of copper in these crystals. Copper and silver sulfides are distributed as discrete needles or rods at low concentrations, but at higher concentrations, copper forms large disks. These disks may be a more complex phase than a simple sulfide. Gold segregates as hexagonal platelets identified as elemental gold, together with a phase. These precipitates each have a particular orientation with respect to the c‐axis. Dislocations and boundaries have been revealed in many of the crystals by means of decoration effects from the impurities. These results show that caution is required in evaluating properties of cadmium sulfide single crystals which may not be one‐phase systems when usual acceptor elements are present.