Capture Of Impurities Research Articles

Dislocation-mediated interfacial re-equilibration of pyrite: An alternative model to interface-coupled dissolution-reprecipitation and gold remobilisation

Minerals and/or their compositions (substituted minor elements) can become metastable in changing conditions or if formed outside of equilibrium. Unstable minerals undergo chemical and/or structural modifications at rates determined by re-equilibration processes, such as diffusion, coupled dissolution-reprecipitation and recrystallization. However, re-equilibrated domains with sharp contacts that lack porosity or deformation microstructures are difficult to reconcile with previously documented processes. In this study, we investigate the mechanism by which Au-rich pyrite re-equilibrates to Au-poor pyrite. Gold and As-rich {100} oscillatory bands are truncated by Au-As-poor pyrite along {100} re-equilibration interfaces. At the nanoscale, dislocations oriented consistently along <100>, are enriched in Ni, As, Cu, Sb, Pb, and Au. Dislocations are located at the re-equilibration interfaces between the Au-As-rich and Au-As-poor pyrite. Quantitative crystallographic orientation maps do not show the presence of deformation-related boundaries along the re-equilibration interfaces, indicating that the dislocations are not deformation-related but are misfit dislocations to accommodate for lattice stain between As-rich and As-poor pyrite. The co-location of steps along the re-equilibration interfaces and dislocations suggests that pyrite can re-equilibrate by the migration of dislocations. The process is likely driven by lattice strain minimisation induced by As impurities. Element transport is achieved by a two step process with (1) capture of impurities by dislocation-impurity pair diffusion during the migration of dislocations and (2) pipe diffusion along the dislocation network towards the exterior of the crystal. We propose that re-equilibration of Au-rich arsenian pyrite, and the resulting remobilisation of Au, can operate through a dislocation-mediated interfacial re-equilibration (DMIR) process. This new mechanism may be active in a range of mineral reactions, particularly in metamorphic settings where limited fluid availability precludes interface-coupled dissolution-reprecipitation processes.

Dynamics of passive admixture in surface and subsurface external deformation field above an ocean guyot

Within the framework of a three-layer quasi-geostrophic model in the f-plane approximation, a numerical study of the effect of an isolated submarine obstacle on the movement of surface and subsurface patches of a neutral admixture transfered by a vertically homogeneous zonal current was carried out. The possibility of partial capture of impurities by quasi-stationary topographic eddy in the vicinity of the submarine obstacle is shown. The role of the initial location (both horizontally and vertically) on the resulting pollution distribution pattern is revealed.

Pristine Multi-walled carbon nanotubes for a rapid and efficient plasmid DNA clarification

Therapeutic approaches based on nucleic acids to modulate cell activity have recently gained attention. These molecules arise from complex biotechnological processes, requiring effective manufacturing strategies, high purity, and precise quality control to be used as biopharmaceuticals. One of the most critical and time-consuming steps for nucleic acids-based biotherapeutics manufacturing is their purification, mainly due to the complexity of the extracts. In this study, a simple, efficient, and reliable method to isolate and clarify plasmid DNA (pDNA) from complex samples is described. The method is based on the selective capture of RNA and other impurities, using pristine carbon nanotubes (CNTs). Multi-walled CNTs (MWCNTs) with different diameters were studied to determine their adsorption capacity and to address their ability to interact and distinguish between nucleic acids. The results revealed that MWCNTs preferentially interact with RNA and that smaller MWCNTs present a higher adsorption capacity, as expected by the higher specific surface area. Overall, this study showed that MWCNTs significantly reduce the levels of impurities, namely RNA, gDNA, and proteins, by approximately 83.6 % compared to their initial level, enabling the recovery of clarified pDNA in solution while maintaining its stability throughout the recovery process. This method facilitates the pre-purification of pDNA for therapeutic applications.

Nonequilibrium capture of impurities that completely block kinks during crystal growth

Some impurities cannot integrate into isolated kinks because they completely block the growth of the kinks to which they adsorb. For this class of impurity, we derive an equation for the amount that incorporates into a crystal during growth of the elementary step by assuming that such an impurity incorporates if and only if it gets captured between a kink and an antikink. We show that the impurity concentration in the crystal increases monotonically with the impurity concentration in the mother phase, but that it can vary non-monotonically with both the supersaturation of the mother phase and the kink density of the step. In contrast to other capture mechanisms, we find that weakly adsorbed impurities incorporate to an extent that is independent of the supersaturation when the supersaturation is high. Irrespective of the growth conditions, the amount of impurity that can incorporate into a crystal is limited by an upper bound determined by the kink density.

电子气体中金属杂质的捕集及分析方法综述

电子气体中金属杂质的捕集及分析方法综述

Cost and performance of some carbon capture technology options for producing different quality CO2 product streams

A techno-economic assessment of power plants with CO2 capture technologies with a focus on process scenarios that deliver different grades of CO2 product purity is presented. The three leading CO2 capture technologies are considered, namely; oxyfuel combustion, pre-combustion and post-combustion capture. The study uses a combination of process simulation of flue gas cleaning processes, modelling with a power plant cost and performance calculator and literature values of key performance criteria in order to evaluate the performance, cost and CO2 product purity of the considered CO2 capture options. For oxyfuel combustion capture plants, three raw CO2 flue gas processing strategies of compression and dehydration only, double flash system purification and distillation purification are considered. Analysis of pre-combustion capture options is based on integrated gasification combined cycle plants using physical solvent systems for capturing CO2 and sulfur species via three routes; co-capture of sulfur impurities with the CO2 stream using Selexol™ solvent, separate capture of CO2 and sulfur impurities using Selexol™, and Rectisol® solvent systems for separate capture of sulfur impurities and CO2. Analysis of post-combustion capture plants was made with and without some conventional pollution control devices. The results highlight the wide variation in CO2 product purity for different oxyfuel combustion capture scenarios and the wide cost variation for the pre-combustion capture scenarios. The post-combustion capture plant with conventional pollution control devices offers high CO2 purity (99.99mol%) for average cost of considered technologies. The calculations performed will be of use in further analyses of whole chain CCS for the safe and economic capture, transport and storage of CO2.

Formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet grown by horizontal directed crystallization method

It is shown that the formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet (YAG) grown by the method of HDC is caused by local accumulation of impurities, disturbance of morphological stability of the crystallization front and capture of inclusions and impurities in the nodal region of the melt two‐vortex convection. Studied is the influence of thermal and geometrical parameters of the melt and the shape of the crystallization front on the conditions of the formation of the capture of inclusions.

High Efficiency and Low Cost of Electricity Generation from Fossil Fuels While Eliminating Atmospheric Emissions, Including Carbon Dioxide

NET Power has developed a novel, oxy-fuel thermodynamic power cycle [1] that uses hydrocarbon fuels, captures 100% of atmospheric emissions, including all carbon dioxide, and has a cost of electricity that is highly competitive with the best current systems that do not have CO2 capture. The proprietary system achieves these results through a closed-loop, high-pressure, low-pressure-ratio recuperated Brayton cycle that uses supercritical CO2 as the working fluid. The cycle exploits the special thermodynamic properties of carbon dioxide as a working fluid by eliminating the energy losses that steam-based cycles encounter due to the heat of vaporization and condensation. The compelling economics of the system are driven by high target efficiencies – 59% net LHV for natural gas and 51% net LHV for coal – and low projected capital and O&M costs, which are the result of utilizing only a single turbine, having a smaller plant footprint, and requiring fewer, smaller components than comparable fossil-fuel systems.NET Power, Toshiba Corporation, Exelon Corporation, and the Shaw Power Group are partnering to commercialize this system by developing a 50MWt facility that is scheduled to begin testing in 2014. This facility will generate electricity from natural gas and capture 100% of emissions, including all CO2. The initial design for a commercial system with an electrical output in the range of 200MWt to 500MWt is also under development. The turbine for the 50MWt plant is being designed at the 500MWt level and then scaled down for the demonstration plant to facilitate rapid development of the large-scale turbine in the future. The demonstration plant will test all components and control systems and the operability of the cycle, including 100% capture of carbon dioxide and other impurities, using a range of fuel gas compositions.The NET Power cycle will have an important impact on the power industry's ability to control and limit greenhouse gas emissions. Driven by its competitive cost when compared to state-of-the-art technologies without CO2 capture, the authors believe the NET Power cycle will remove economic barriers to the deployment of 100%-carbon-capture, fossil-fuel-based electricity generation technology. This will enable both the developed and developing world to produce cheap electricity that does not contribute to CO2-based climate change.

Electrical and optical properties of CdHgTe films grown by molecular-beam epitaxy on silicon substrates

The electrical and optical properties of epitaxial CdHgTe films grown on silicon substrates by molecular-beam epitaxy have been studied. The results of photoluminescence measurements are indicative of the high structural perfection of the films, and Hall data combined with low-energy ion treatment point to a low concentration of residual donors (∼5 × 1014 cm−3). Acceptor states supposedly related to the capture of impurities at structural defects typical of strongly lattice-mismatched heteroepitaxial structures are found in the films.

Transmission electron microscopic observations of nanobubbles and their capture of impurities in wastewater

Unique properties of micro- and nanobubbles (MNBs), such as a high adsorption of impurities on their surface, are difficult to verify because MNBs are too small to observe directly. We thus used a transmission electron microscope (TEM) with the freeze-fractured replica method to observe oxygen (O2) MNBs in solutions. MNBs in pure water and in 1% NaCl solutions were spherical or oval. Their size distribution estimated from TEM images close to that of the original solution is measured by light-scattered methods. When we applied this technique to the observation of O2 MNBs formed in the wastewater of a sewage plant, we found the characteristic features of spherical MNBs that adsorbed surrounding impurity particles on their surface.PACS: 68.03.-g, 81.07.-b, 92.40.qc

Investigations of impurity striations in potassium bichromate crystals

AbstractImpurity striations in potassium bichromate crystals (KBC, lopezite) formed during crystal growth from aqueous solution were revealed by chemical etching and analyzed. Striations were revealed as etch grooves, as rows of dislocation etch pits and as rows of flat‐bottomed etch pits. Various types and groups of striations have been visualized. Some striations were due to lateral segregation of impurities caused by convection flow of the mother solution, other were formed during growth stoppages whereas induced striations were generated by changes in hydrodynamical conditions. Growth rates changes resulted in zonal distribution of impurities, formation of planar lattice strain, rows of clusters of point defects and rows of dislocations. Generation of striations with different intensities in various sectors is a proof of the selective capture of impurities. Ratios of growth rates of various faces of KBC crystals growing in forced and free convection regimes were determined by induced striations. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Adsorption mechanisms of the nonequilibrium incorporation of admixtures in a growing crystal

The nonequilibrium partition of components between a crystal and solution is mainly controlled by impurity adsorption on the surface of the growing crystal. The specificity of adsorption on the faces of various simple forms leads to the sectorial zoning of crystals. This effect was studied experimentally for several crystallizing systems with different impurities, including isomorphous, 2d-isomorphous, and nonisomorphous, readily adsorbed impurities. In all systems, the sectorial selectivity of impurity incorporation into host crystals has been detected with partition coefficients many times higher than in the case of equilibrium partition. Specific capture of impurities by certain faces is accompanied by inhibition of their growth and modification of habit. The decrease in nonequilibrium partition coefficients with degree of oversaturation provides entrapment of impurities in the growing crystals. Thereby, the adsorption mechanism works in much the same mode for impurities of quite different nature. The behavior of partition coefficient differs drastically from impurity capturing by diffusion mechanism.

X-ray multiple diffraction in synthesized diamond with a multi-layered structure

Structural investigations of synthesized crystals of diamond have been carried out by means of multiple coplanar diffraction. The x-ray divergent-beam technique and the method of numerical solution of Takagi's equations have been used. It has been shown that diamond crystals synthesized in the Ni–Mn–C system contain laminated segregations in the form of growth regions due to the inhomogeneous capture of nitrogen or boron impurities during the crystal growth and the quasiperiodic strain fields generated.

Efficiency of cavity gettering in single and in multicrystalline silicon wafers

Multicrystalline silicon wafers are submitted to He ion implantations at various energy levels and fluences in the ranges 40–120 keV and 1016–1017 cm−2, respectively. Cavities are formed after annealing at 900°C for 1 h to 4 h in argon flow and induce a segregation gettering. For comparison the wafers experience a Al–Si gettering after the deposition of a backside 1 μm thick Al wafer and annealing at 900°C for 4 h in argon. Some wafers are voluntarily contaminated by nickel atoms and diffusion lengths of minority carriers are determined by SPV technique and measured before and after gettering. Float zone single crystalline wafers were also investigated for comparison. It is found that gettering by cavities works well provided the fluence is 1017 cm−2, although the capture of impurities by the cavities is limited by the saturation of their internal surface. Al–Si alloying appears more efficient. This is most likely due to the high solubility of metal atoms in the liquid Al–Si alloy formed during the annealing. The two gettering techniques can protect the wafers during processing steps.

Limiting Factors of Backside External Gettering by Nanocavities and Aluminum-Silicon Alloying in Silicon Wafers

AbstractFloat zone silicon single crystalline wafers are submitted to He ion implantations at various energy levels and fluences in the ranges 40 to 120 keV and 1016 to 1017 cm−2, respectively. Cavities are formed after annealing at 900°C for 1 h in argon. Al-Si gettering results from the deposition of a backside 1 µm thick Al wafer and annealing at 900'C for 4 h in argon. The wafers are voluntarily contaminated by 1014 to 1017 cm−3nickel atoms and diffusion length of minority carriers is determined by SPV technique and measured before and after gettering.It is found that gettering by cavities works fairly well provided the fluence is 1017 cm−2. The gettering efficiency decreases in heavily contaminated samples suggesting that the capture of impurities by the cavities is limited by the saturation of their internal surface. Al-Si alloying appears more efficient at higher contamination levels. This is most likely due to the high solubility of metal atoms in the liquid Al-Si alloy formed during the annealing.

Polyhedral instability — skeletal and dendritic growth

The stability of flat facets is a fundamental problem in crystal growth. Simultaneously, it is also a prerequisite for producing high-quality homogeneous crystals, so essential for the high-tech applications. The preservation of the crystal shape during crystal growth, however, is a complex problem It involves a specific interplay between: mass/and heat transfer to/from the crystal surface, and the kinetics of the elementary incorporation, i.e. between the two major successive steps in the growth process. Rapid growth, and hence diffusion mechanism limitations, can result in various imperfections; such as solvent inclusions, the capture of impurities, the incorporation of veils and the formation of cavities in the facets. Skeletal and dendritic patterns are the following stages. The importance of these crystal forms can be illustrated with ice and snow crystals, and in connection with their role in the nature. The review includes also discussion of skeletal crystal shapes, very familiar to the snow-flakes and dendrites of ice. The problem for the polyhedral instability concerns also the mineralogy, etc.

Colour cathodoluminescence from Bi4[GeO4]3crystals

Abstract The regions of homogeneous and heterogeneous capture of impurities, point and linear defects, affected the luminescence from the undoped Bi4[GeO4]3 (BGO) and doped BGO:V, BGO:Yb, BGO:Cr3+, BGO:Fe as grown single crystals, were studied. A rapid cathodoluminescence (CL) spectral analysis, based on the panchromatic CL-images in scanning electron microscopy (SEM), was used. Depending on the doped impurities and dislocation configuration, changes in the intensity and wavelength of CL from BGO were found.

Lateral Diffusion and Capture of Iron in P-Type Silicon

AbstractThe lateral motion of iron impurities was observed and studied in ptype iron contaminated silicon. The lateral diffusion was induced by and then measured using Schottky diodes with a special interdigitated fingers design. Capture of the impurities was done by diffusing to laterally placed dislocation loops formed by a self aligned ion implantation. Lateral changes in Fe concentration were determined using capacitance-voltage and deep level transient spectroscopy.

Color cathodoluminescence of BGO crystals

AbstractThe color cathodoluminescence (CL) mode in scanning electron microscopy (SEM) is promising in the study of a variety of defects in single crystals pulled from the melt by the Czochralski method. The regions of homogeneous and heterogeneous capture of impurities and of point and linear defects, which affect the luminescence in the undoped Bi4Ge3O12 (BGO) and doped BGO:V, BGO:Yb, BGO:Cr3+, and BGO:Fe as grown single crystals, were observed. Depending on the doped impurities and dislocation configuration, a change was found in both the intensity and wavelength of CL.

Study of the growth mechanism in the ADP‐type anion‐doped crystals

AbstractA simultaneous simulation of the growth process in the A(K)DP‐type anion‐doped crystal and growing of this crystal from aqueous solution under controlled conditions has made it possible to analyse the mechanism of impurity influence on the growth rate of various crystal faces. The anisotropy of the face growth rate and the capture coefficient of various impurities by the faces have been determined by the difference in dissolution heats and in sizes of replacing ions. The increase in energy change, when the ion in a solution enters a crystal, causes an increase in the growth rate and the capture of impurities by the face with the largest change. Breaking of one of the joined faces and increased growth of another one resulted in forming of the new faces, i.e. in changing crystal morphology.