High Degree Of Supersaturation Research Articles

Iceberg-hosted nanoparticulate Fe in the Southern Ocean: Mineralogy, origin, dissolution kinetics and source of bioavailable Fe

Sediments from icebergs and glaciers contain nanopartculate Fe(III) oxyhydroxides (including ferrihydrite) which form in aqueous, oxic (micro)environments where Fe(II)-bearing rock minerals oxidise and high degrees of supersaturation are promoted by freezing and thawing. An ascorbic acid extraction dissolves only labile Fe present in fresh (loosely aggregated) ferrihydrite that is directly or indirectly bioavailable. Glacial and iceberg sediments contain ferrihydrite aggregates that provide 0.04 to 0.17% Fe soluble in ascorbic acid, rather larger than the concentrations in a limited suite of atmospheric dusts. The dissolution behaviour of labile Fe from glacial and iceberg sediments by ascorbic acid is controlled by the access of reactant, or removal of solute, through micropores to or from active sites in the interior of ferrihydrite aggregates. A first-order kinetic model is presented to examine the rates at which bioavailable Fe can be supplied by melting icebergs in the Weddell Sea. The model utilizes rate constants from the literature for the processes which solubilise Fe from nanoparticulate ferrihydrite (dissolution, photochemical reduction and grazing) and the processes that remove Fe nanoparticulates (sinking, scavenging and incorporation in faecal material), and render them less reactive (transformation, aging). Model results demonstrate that icebergs can supply bioavailable Fe to the Weddell Sea by the dissolution of nanoparticulate ferrihydrite (despite loss/removal of nanoparticles by sinking, aging, transformation, scavenging and incorporation into faecal pellets) at rates that are comparable to atmospheric dust. Dissolution enhanced by photochemical reduction and grazing provides the most rapid rates of bioavailable Fe production.

Fast and Efficient Numerical-Simulation Method for Supersonic-Gas Processing

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 131239, ’A Fast and Efficient Numerical-Simulation Method for Supersonic-Gas Processing,’ by Dengyu Jiang, Qitai Eri, Changliang Wang, Huoxing Liu, and Yao Yuan, Beijing University of Aeronautics and Astronautics, prepared for the 2010 CPS/SPE International Oil & Gas Conference and Exhibition in China, Beijing, 8-10 June. The paper has not been peer reviewed. Supersonic-swirling-separation technology separates heavy hydrocarbons and water vapor from natural gas. The de Laval nozzle, where condensation occurs, is used to generate supersonic flow and achieve a high degree of supersaturation in a natural-gas dehydration unit. To optimize the structure of the nozzle and achieve higher separation efficiency, numerical simulation was used to accelerate development cycles and reduce the cost of experiment. Rather than use multiphase models and a real-gas model, a quick and efficient method was validated and used to determine the location of the nucleation zone and the droplet-growth zone. Introduction Spontaneous condensation occurs when a supersaturated gas passes through a strong expansion process. As part of the process, latent heat is released to the environment and the latent heat makes the state of the parameters of the flow field (e.g., temperature, pressure, and density) change suddenly, the so-called condensation-jump phenomenon. If the amount of heat released exceeds some critical value, the flow becomes thermally choked and the structure of the flow field changes, even forming a condensation shock. Condensation can be divided into two physical processes: nucleation and droplet growth. Homogeneous nucleation occurs when the condensation nuclei are gas molecules that collect spontaneously rather than because of contact with dust particles. Then, the nuclei grow into droplets because of gas molecules colliding with and adhering to the surface of other gas molecules under chemical reaction. Nonequilibrium condensation occurs if the scale of the change of gas-state parameters is much less than the time scales of gas molecules adhering to and merging with other particles. At that moment, the gas is supersaturated, indicative of a metastable non-equilibrium state of the vapor phase. As these metastable clusters exceed some critical size, the process of droplet growth sets in, leading to the formation of a stable liquid phase. The full-length paper details the numerical-simulation method of condensation. Adapting This Method for a de Laval Nozzle The engineering objective of super-sonic-gas processing is superior dew-point depression and a high-pressure recovery; therefore, research on the interaction between the condensation and the flow condition provides some directive standards. To determine the interaction between condensation and the flow conditions, this method was adapted to model the nonequilibrium-condensation flow field in a de Laval nozzle. Fig. 1 shows the nozzle and structure mesh. By use of precision and efficiency, dramatic-change regions of density in the flow field and the near-wall area were refined, and wall functions were chosen for solving the boundary layer.

Characteristics of HPHT diamond grown at sub-lithosphere conditions (10–20 GPa)

We have conducted high pressure–high temperature (HPHT) diamond synthesis experiments at the conditions of growth of superdeep diamonds (10–20GPa), equivalent to the transition zone, using MgCO3 carbonate (oxidising) and FeNi (reducing) solvent catalysts. High rates of graphite–diamond transformation were observed in these short duration experiments (20min). Transformation rates were higher using the metallic catalyst than in the carbonate system. High degrees of carbon supersaturation at conditions significantly above the graphite–diamond stability line, led to a high nucleation density. This resulted in the growth of aggregated masses of diamond outlined by polygonised diamond networks, resembling carbonado. Where individual crystals are visible, grown diamonds are octahedral in the lower pressure experiments (≤10GPa in MgCO3 and ≤15GPa in FeNi) and, cubo-octahedral at higher pressure. All grown diamonds show a high degree of twinning. The diamonds lack planar deformation features such as laminations or slip planes, which are commonly associated with natural superdeep diamonds.

Cu-Rich Scales in the Reykjanes Geothermal System, Iceland

Seawater-dominated fluids discharge from the subaerial Reykjanes geothermal system, Iceland. There is a sharp pressure decrease in surface pipes at an orifice (throttle point), and Cu-rich scales deposit at this orifice that consist largely of bornite and digenite, along with sphalerite and other sulfides. The bornite and digenite form complex intergrowths with sphalerite and galena, accompanied by high concentrations of gold and silver (up to 590 ppm and 2.3 wt %, respectively). The precipitates form in response to rapid boiling (flashing) of the hydrothermal fluids due to the sharp decrease in pressure (~37–22 bars) at the orifice, downstream of the well-head. The boiling, and concomitant separation of the vapor phase, results in a temperature decrease from 252° to 220°C across this throttle over distances of centimeters. There is a nearly quantitative deposition of metals from solution compared to concentrations in reservoir liquids, resulting in formation of the metastable Cu-FeS solid solution, rich in silver and gold, plus sphalerite and galena. A high degree of supersaturation of metals in the quenched liquid is indicated by the very fine grain size of the sulfides and dendritic textures. Postdepositional cooling likely caused exsolution of bornite and digenite from the high-temperature solid solution; in addition, silver was expelled from the Cu-Fe-S solid solution and remobilized into late fractures in the scales, whereas the gold appears to have remained in solid solution or as submicroscopic inclusions in the bornite and digenite. The observed mineral assemblage at Reykjanes contrasts with that of sea-floor black smokers, despite similar fluid compositions. The sea-floor hydrothermal vents characteristically have Cu-rich linings composed predominantly of chalcopyrite, which is precipitated by a combination of conductive cooling of high-temperature (~350°C) hydrothermal fluids and mixing with seawater. The difference in sulfide mineralogy between the Reykjanes orifice scales, with Cu sulfides dominated by bornite and digenite, and many sea-floor vents may provide an indication of the subsea-floor mineralization where fluids boil before discharging at sea-floor vents.

Titanium Oxide Nanoparticles Precipitated from Low‐Temperature Aqueous Solutions: II. Thin‐Film Formation and Microstructure Developments

We explored effects of the degree of supersaturation, which depends on solution concentration, pH, and temperature, on the development of microstructures of the TiO2 thin films deposited from the controlled hydrolysis of TiCl4 aqueous solutions. It was shown that, with precursor (TiCl4) solution of low degree of supersaturation, a porous flower‐like dendritic structure was synthesized, while a densely packed particulate nanostructure was obtained with that of high degree of supersaturation. The former morphology was attributed to the directional growth of TiO2 crystals from the already‐deposited films, whereas the latter to the bulk precipitated TiO2 nanoparticles nucleated in the solution, followed by their attachment and self organization. By establishing the processing–microstructure relations, this study provided a means of generating a wide spectrum of reproducible TiO2 microstructures using the low‐temperature aqueous solution processing.

Influence of process condition on stretch flange-ability of Al–Mg–Si alloys

Hole expanding limit, λ, measured as an index of stretch flange-ability of 6022 aluminum alloy was severely decreased by slow cooling (forced air: 10 K/s) after solutionizing at 823 K for 15 s, in 0.5% Cu added Al–0.6%Mg–0.9%Si alloy sheet which ingot was homogenized at a high temperature, 823 K. Whereas by fast cooling (water quenching: 500 K/s), 1.5 mm thick sheets of both alloys showed the λ higher than 50%. Influences of homogenizing temperature and cooling rate after solution treatment on the λ were investigated by semi-quantitative metallography. Ingot homogenization at higher temperature decreases amount of Mg–Si precipitates and increases solute concentration. Judging from measured conductivity (IACS%) , almost all of added Cu seems to remain in solid solution. Even after hot rolling, cold rolling, solution treatment and T4 treatment for more than 600 ks at room temperature, IACS% of the T4 sheets was in nearly same order as ingots. The severe decrease of the λ in the Cu added alloy sheets homogenized at 823 K and slowly cooled after solution treatment will be explained by coarse Si precipitates on grain boundaries formed during the slow cooling. The Cu addition and high homogenization temperature will lead to a high degree of solute supersaturation and elevate temperature for precipitation starting. Region of high dislocation density was observed nearby the coarse Si precipitates by transmission electron microscopy after the hole expanding test.

Effects of natural aging and reversion treatments on artificial aging behavior of 6000 series aluminum alloys

Three 6000 series commercial alloys (6061, 6022 and 6 N01) were aged at room temperature, reverted at temperatures above 473 K and finally aged at 448 K. The negative effect of room-temperature pre-aging on age-hardening at 448 K in 6061 and 6022 alloys was not varied by times of pre-aging longer than 10 days. In the 6061 alloy, reversion treatment at 573 K for 30 s resulted in a significant reduction in age hardening at 448 K. It is conjectured that rapid precipitation occurred during the reversion treatment because of the high degree of super saturation caused by its high solute content. Hardening by paint baking at 448 K for 1.2 ks of automotive body panels was largely improved by reversion treatments for 30 s at 523 K in 6061, at 523 K or 548 K in 6022 and at 548 K in 6N01. Concerning with maximum age-hardening at 448 K, improvement by reversion in the negative effect was the same temperature that improved paint bake response the most. The range of reversion temperatures at which the hardening was most improved tended to become narrower with increasing Mg and Si contents.

Titanium Oxide Nanoparticles Precipitated from Low‐Temperature Aqueous Solutions: I. Nucleation, Growth, and Aggregation

Titanium oxide (TiO2) thin films can be prepared by controlled hydrolysis of a titanium tetrachloride (TiCl4) precursor in an aqueous solution at temperatures below 100°C. As part of an effort to understand the formation of such TiO2 films, the kinetics of the nucleation, growth, and aggregation of TiO2 nanoparticles in aqueous solutions of TiCl4 were studied using dynamic light scattering and a transmission electron microscope (TEM). A higher degree of supersaturation, produced by a higher solution temperature, a higher concentration of TiCl4, or a higher pH, results in a shorter nucleation induction time, a faster initial growth/aggregation rate, and a larger aggregate size. The interfacial energy of TiO2 nanoparticles was found to be 0.072 J/m2 from the homogeneous nucleation theory. Further investigations by a high‐resolution scanning electron microscope (SEM) and TEM for the as‐deposited films showed the structure hierarchy organized from nanocrystalline particles precipitated in the supersaturated solution. As a result, the effect of solution conditions on the nucleation, growth, and aggregation of TiO2 nanoparticles can provide useful guidance for tailoring of microstructures of the TiO2 films.

Preparation of Poly(4′-oxy-4-biphenylcarbonyl) Needlelike Crystals with the Aid of Copolymerization

Preparation of poly(4′-oxy-4-biphenylcarbonyl) (POBP) needlelike crystals was examined by using reaction-induced crystallization of oligomers during copolymerization of 4-(4-acetoxyphenyl)benzoic acid (APBA) and 4-acetoxybenzoic acid (ABA). Polymerizations were carried out in aromatic solvent at various ABA molar ratios in feed (χf). When the χf was 20−10 mol %, starlike aggregates of needlelike crystals and fibrillated slablike crystals were separately formed, exhibiting similar morphology to poly(4-oxybenzoyl) and POPB crystals. 4-(Oxyphenyl)benzoyl (OPB) homo-oligomers and co-oligomers rich in OPB moiety were more rapidly precipitated due to the lower solubility, and the slablike crystals were formed. Afterward, 4-oxybenzoyl (OB) homo-oligomers and the co-oligomers rich in OB moiety were precipitated to form spindlelike crystals. The OPB homo-oligomers and the co-oligomers rich in OPB moiety were continuously crystallized on both crystals due to the high degree of supersaturation, and the spindlelike crystals grew to the needlelike crystals mainly comprised of POBP. Copolymerization of 4-(4-acetoxybenzoyloxy)benzoic acid and APBA at χf of 10 mol % yielded the needlelike crystals without coexisting fibrillated slablike crystals. This result provides a new methodology for morphology control with the aid of copolymerization.

Spherical submicron-size copper powders coagulated from a vapor phase in RF induction thermal plasma

Spherical submicron-sized powder of copper was synthesized through condensation from a vapor phase with a significantly high degree of supersaturation in thermal plasma. The degree of supersaturation was increased by the relatively high feed rate of raw copper powder. A high concentration of metal vapor was attained by using copper powder in Ar–H 2 plasma, and relatively large particles of up to 0.1 μm in diameter were prepared. The powder feed rate, reactor pressure and gas flow rate of hydrogen were varied to examine their effects on the evaporation of the raw powder. Particle size and its distribution in the powder sample were evaluated by image analysis. The total amount of evaporated raw powder depended on the powder feed rate, the reactor pressure and hydrogen flow rate. The copper vapor concentration increased in proportion to the total amount of evaporation. Particle growth subsequently took place through heterogeneous condensation to form submicron-sized particles.

Preparation of Ultrafine Beclomethasone Dipropionate Drug Powder by Antisolvent Precipitation

The purpose of this study was to prepare ultrafine beclomethasone dipropionate (BDP) powder via antisolvent precipitation without any surfactants. Various solvents were screened to determine the suitable system for optimum processing while deionized water was kept as the antisolvent. Methanol was selected as the solvent, because a higher degree of supersaturation could be achieved. Several experimental parameters, such as the volume ratio of solution to antisolvent, the concentration of BDP−methanol solution, the temperature, and the stirring speed and time, were investigated in the methanol−deionized water system. The results showed that the yielded powder had a mean particle length of 850 nm and 85% of the particles were distributed in the range of 0.2−1.2 μm, whereas the raw particle size was 2.13 μm, ranging in size from 0.2 μm to 12 μm. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis indicated no change in chemical group structure and crystal structure during the ...

高周波熱プラズマによる球状銅系サブミクロン粒子の作製

Spherical submicron copper particles were synthesized through evaporation and subsequent condensation of copper powders in Ar-H2 thermal plasma. Copper powders of ∼40μm in size injected into the plasma, evaporated instantly and fine particles were formed through homogeneous nucleation and subsequent heterogeneous condensation. Particle size and the distribution in the synthesized powders were changed depending on the powder feed rate. Formation of submicron size spherical powders attributed to a significantly high degree of supersaturation in a vapor phase. Particle sizes of the as-produced powders range from submicron to several tens of micrometers. A simple sedimentation treatment was successfully applied to separate the as-formed powders with alcohol solvent to give uniform spherical submicron-size particles with monomodal size distributions. Cu-W composite powders were synthesized through the Ar-H2 plasma treatment of Cu-WO3 composite powders. The starting temperature of shrinkage was made significantly higher than pure Cu powders by mixing with several wt% of W.

Atomic ordering in Ni3Mn-Ni3V microcrystalline alloys

Neutron diffraction analysis has been used to determine concentrational dependences of the parameters of long-and short-range atomic order and the sizes of antiphase domains in Ni3Mn-Ni3Al microcrystalline alloys produced by quenching from the melt and in the quenched bulk alloys of the system. The parameters of atomic order were shown to depend on the temperature of the order-disorder transition. The γ′-phase micro-crystals were found to be characterized by high degrees of long-range order. The effect found is explained by the high degree of solid-solution supersaturation with excess vacancies formed upon quenching from the melt and, therefore, by abruptly increasing diffusion mobility of atoms.

Atomic ordering in Ni3Mn-Ni3Ti microcrystalline alloys

Neutron diffraction is used to determine the concentration dependences of the long-and short-range order parameters and the antiphase-domain size in Ni3Mn-Ni3Ti microcrystalline alloys produced by melt quenching and the initial bulk alloys quenched from 1433 K. The dependences of the order parameters on the order-disorder transition temperatures are determined. Microcrystals of the γ’ phase are found to have a high long-range order parameter as compared to this parameter in the bulk alloys. This fact is explained by the high degree of supersaturation of a solid solution with excess vacancies formed during melt quenching and, hence, a sharp increase in the atomic diffusion mobility.

Calcium phosphate nucleation on cellulose fabrics

Nonwoven cellulose (regenerated, oxidized) fabrics were coated with hydroxy carbonated apatite (HCA) using a procedure based on a biomimetic method. Simulated body fluid (SBF) with a high degree of supersaturation (5xSBF) was applied to accelerate the biomimetic formation of bonelike apatite on the cellulose fabrics. After creating calcium phosphate nuclei on the cellulose fibers in a first 5xSBF with high Mg2+ and HCO3− concentrations, the cellulose fabrics were additionally soaked in a second 5xSBF which was optimized with respect to accelerated crystal growth by reduced Mg2+ and HCO3− concentrations. The hydroxy carbonated apatite (HCA) layer thickness increased from 6 μm after 4 h of soaking in the latter solution to 20 μm after 48 h. The amount of CO32− substituting PO43− in the hydroxyapatite (HA) lattice of the precipitates can be varied by changing the soaking time.

Abnormal behavior of the atomic order parameter during quenching of the Ni3(Mn,V) alloys from the liquid state

An abnormal phenomenon of increasing long-range order in the Ni3(Mn1−xVx) alloys following the L12 pattern after quenching from the melt with a rate of 106 deg/s is revealed by the neutron diffraction method. It is demonstrated that the established effect can be explained by a high degree of supersaturation (by 4–5 orders of magnitude) with excess quenching vacancies and, as a consequence, by a sharp increase in the diffusion mobility of atoms in the solid solution.

Geology and metamorphic zonation of the Ryoke Metamorphic Belt on Kasado-jima Island, SW Japan

The Cretaceous low-pressure/high-temperature Ryoke Metamorphic Belt contains abundant Ryoke and San-yo Granitoids that intruded to various crustal depths during or after formation of the belt. To clarify the tectono-metamorphic history of the belt, it is necessary to evaluate the thermal effects of the intrusion of the different types of granitoids. The geology of Kasado-jima Island, SW Japan, consists of metasedimentary rocks, massive biotite granite, and migmatitic biotite tonalite. The granite and tonalite occur in the central and southern areas of the island, respectively. Within the central area, granite intrudes metasedimentary rocks and cuts across bedding-parallel schistosity within the metapelites; this indicates that intrusion of the granite postdates Ryoke metamorphism. In contrast, tonalite in the southern area was emplaced parallel to the schistosity. On the basis of the field occurrences and petrographic characteristics of these granitoids, we correlate the biotite tonalite and biotite granite with the Older Ryoke and San-yo Granitoids, respectively. Based on the paragenesis of schistosity-forming minerals within metapelites, we identify two mineral zones in the island: the biotite and cordierite zones. The biotite zone is characterized by a mineral assemblage of muscovite + biotite ± garnet, and the cordierite zone is characterized by the assemblage muscovite + biotite + K-feldspar + cordierite or garnet. On the basis of mineral chemistry, we estimate peak metamorphic conditions for the biotite and cordierite zones to be ∼ 470 °C (reference pressure: 200 MPa) and ∼ 550 °C at 250 MPa, respectively. In the central part of the island, a contact aureole adjacent to the biotite granite is identified by the occurrence of randomly oriented muscovite and very large dendritic cordierite porphyroblasts. These randomly oriented porphyroblasts may have formed under a high degree of supersaturation associated with the thermal perturbation of the shallow intrusion of the biotite granite into cooler crust. In the southern area, most metamorphic minerals are of similar size, and their long axes are aligned to form a schistosity; this indicates a small degree of thermal perturbation and/or a high strain rate. These observations indicate that the biotite tonalite on Kasado-jima Island, as a deep-seated granitoid, was related to regional low-pressure/high-temperature metamorphism.

Microstructures and mechanical properties of spray-formed and squeeze-cast Al–25Si–0.89Cu–1.0Ni–0.84Mg alloys in solutionized and aged conditions

The microstructures and mechanical properties of spray-formed and squeeze-cast Al–25Si–0.89Cu–1.0Ni–0.84Mg alloys in solutionized and aged conditions were compared. DSC analysis was used to study the degree of supersaturation between the spray-formed and squeeze-cast alloys, and the tensile properties of extruded spray-formed alloy in various heat treatment conditions were investigated. The as-spray-formed alloy exhibits more uniform and finer microstructures than the as-squeeze-cast alloy. The Al 2Cu was the main phase involved in the solutionizing and aging heat treatment. DSC analysis showed the spray-formed alloy had higher degree of supersaturation than the squeeze-cast alloy. For the same heat treatment condition, the matrix microhardness of spray-formed alloy is higher than that of squeeze-cast alloy. The aging hardening curves reveal two peaks and the time to peaks for the spray-formed alloy is shorter than that for the squeeze-cast alloy. The peak-aged spray-formed alloy exhibits an ultimate strength of 366.0 MPa, a yield strength of 235.3 MPa and an elongation of about 3.4%.

Mixing and separation characteristics of isobutane with refrigeration oil

This paper discusses the transient mixing and separation characteristics of isobutane with/from refrigeration oil. The mixing/separation processes are observed and investigated experimentally in a glass cylindrical vessel. Since liquid isobutane is less dense than refrigeration oil, the mixing process proceeds one dimensionally by diffusion from the interface between isobutane gas and refrigeration oil. The progress of mixing, therefore, is very slow compared with a combination of halocarbon refrigerant and refrigeration oil having convection flow during the mixing process. The diffusion process can be analyzed using a one-dimensional diffusion model with an appropriate diffusion coefficient, which increases linearly with temperature. The separation of isobutane from the oil–refrigerant mixture occurs at the interface and the denser oil from which isobutane is separated causes a convective flow. Bubble generation under the depressurized conditions is unstable, but in the most cases, it tends to start when a high super saturation degree is reached. The temperature change during the separation process is estimated using latent heat as the separation heat of refrigerant.

Cave air control on dripwater geochemistry, Obir Caves (Austria): Implications for speleothem deposition in dynamically ventilated caves

There are very few process studies that demonstrate the annual variation in cave environments depositing speleothems. Accordingly, we initiated a monitoring program at the Obir Caves, an Austrian dripstone cave system characterized by a seasonally changing air flow that results in a predictable pattern of high pCO 2 during summer and low pCO 2 in winter. Although similar seasonal changes in soil pCO 2 occur, they are not directly connected with the changes in the subsurface since the dripwaters are fed from a well-mixed source showing little seasonal variation. Cold season flushing by relatively CO 2-poor air enhances degassing of CO 2 in the cave and leads to a high degree of supersaturation of dripwater with regard to calcite. Forced calcite deposition during the cold season also gives rise to a pronounced pattern of synchronous seasonal variations in electrical conductivity, alkalinity, pH, Ca and δ 13C DIC which parallel variations recorded in δ 13C cave air. Chemical components unaffected by calcite precipitation (e.g., δD, δ 18O, SiO 2, SO 4) lack a seasonal signal attesting to a long residence in the karst aquifer. Modeling shows that degassing of CO 2 from seepage waters results in kinetically-enhanced C isotopic fractionation, which contrasts with the equilibrium degassing shown from the Soreq cave in Israel. The Obir Caves may serve as a case example of a dripstone cave whose seepage waters (and speleothems) show intra-annual geochemical variability that is primarily due to chemical modification of the groundwater by a dynamic, bidirectional subsurface air circulation.