Si-rich Layer Research Articles

Thermodynamic mechanism of the intermixing of multilayered structures in the SiOx/SiO2 superlattices with nanometer thick layers

In this paper, a thermodynamic model of the behavior of superlattices consisting of alternating Si-rich oxide (SiOx) and SiO2 layers, during high temperature annealing, is presented. It is demonstrated that complete layer intermixing and breakdown of superlattice structure are expected in such superlattices at specific relations between the thicknesses of neighboring layers and for definite SiOx stoichiometries. The mechanism of this process is related to the decrease of the Gibbs free energy of intermixed superlattice state as compared to initial one if the higher kinetic efficiency condition of layer intermixing over SiOx phase separation is satisfied. The intermixing behavior of the Si oxide based superlattices is studied as a function of the initial characteristics of superlattice and the annealing temperature. The criteria for the complete layer intermixing are established. The correspondence between theoretical predictions and experimental data is discussed in terms of the borderline character of the SiOx and SiO2 layer interaction during annealing.

A comparison study of boron emitter passivation by silicon oxide and a PECVD silicon nitride stack

Surface recombination of minority charge carriers is a significant loss mechanism in crystalline-Si (c-Si) solar cells. For n+ (phosphorous) doped regions a sufficient surface passivation is achieved by using a silicon nitride (SiNX) film deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD). However, on p+ boron doped regions, SiNX does not passivate the surface. Instead, a stack of layers comprising of a thin silicon dioxide (SiO2), or aluminium oxide (Al2O3), and a SiNX film is commonly used to passivate boron doped regions.In this study we investigated the passivation quality of boron doped emitters by varying the composition of SiO2/SiNX stack layers. For this purpose, n-PERT (passivated emitter, rear totally-diffused) solar cells with boron doped front side emitter and phosphorous doped back-surface-field (BSF), as well as symmetrical boron doped structures, were fabricated on 6-inch n-type wafers.The results show that the optimum passivation is achieved by a stack layer of a thermal SiO2, with a thickness of at least 10 nm, and a SiNX layer with a low refractive index. The chemical composition of SiNX capping layer plays an important role for surface passivation. A more Si-rich SiNX layer show significant degradation in surface passivation of the stack, due to the increase in the density of interface states (Dit) and fixed positive charges (Qtot) at the interface.

Effect of Sn addition on the separation and purification of primary Si from solidification of Al-30Si melt under electromagnetic stirring

In the present work, the effect of Sn addition on the separation and purification of primary Si from solidification of Al-30Si melt under rotating magnetic field (RMF) was investigated. The results revealed that the as-cast solidification microstructure of ternary Al-30Si-Sn alloy is composed of the primary Si phase, eutectic α-Al+Si, and eutectic α-Al+β-Sn structure. The application of RMF can separate the primary Si from solidification of Al-30Si-Sn melt, consequently forming a Si-rich layer on the periphery of the ingot. The atomic fraction of primary Si in Si-rich layer increases with increasing Sn content because the addition of Sn can enlarge the crystallization temperature range of the primary Si phase. The content of non-metallic B in primary Si increases due to the increasing segregation coefficient of B with the increasing Sn content. However, the contents of typical metallic impurities (Fe and Ca) exhibit an opposite trend, which may be attributed to the back-diffusion of impurities suppressed by the addition of Sn.

Effect of combined additions of Si, Mn, Cr and Al to carbon steel on material transfer in a steel/TiN coated tool sliding contact

Material transferred from steel work materials onto the cutting tools largely affects tool life and machining performance. This material transfer is strongly influenced by the steel composition, and different alloying can have very different effects. Crossed cylinders sliding tests can be used to simulate the contact between the chip and the tool in machining. In this work such a test is used to evaluate material transfer and friction characteristics of a TiN coated tool sliding against five model steels. These model steels are especially designed to study the effects from specific combination of alloy elements, i.e. the steels, containing 0.55 mass% C and 1 mass% Si, are alloyed with one or more of 1 mass% Mn, Cr and Al. When using the steels alloyed without Al, Si-rich oxide layers are formed on the coating, resulting in a low friction coefficient. When using the steels alloyed with Al, almost pure Al–O layers are formed, resulting in a higher friction coefficient and rapid coating cracking. Essentially, the most easily oxidized alloy element is most strongly enriched in the oxide and decides the main mechanism of the material transfer and friction behavior.

Dissolution Rates of Actinolite in Water and Its Modified Mineral Surface Across the Critical State

Dissolution kinetic experiments of actinolite in water were performed using a flow-through reactor at temperatures from 20 to 400 °C and 23.5±0.5 MPa. The results indicate that the steady-state release rates of the different elements of actinolite vary with temperature. Generally, Ca, Mg, Fe, and Al dissolve more quickly than Si at temperatures from 20 °C to near 300 °C, but slower from 300 to 400 °C. The Si release rate increases with temperatures from 20 to 300 °C and then decreases from 300 to 400 °C. Si release rate reaches the maximum at 300 °C. Amorphous Si-rich surface layers occur at temperature 300 °C. Water property variations within the critical region strongly affect the dissolution rates and the modification of surface.

Pore-Scale Geochemical Reactivity Associated with CO2 Storage: New Frontiers at the Fluid-Solid Interface.

The reactivity of carbonate and silicate minerals is at the heart of porosity and pore geometry changes in rocks injected with CO2, which ultimately control the evolution of flow and transport properties of fluids in porous and/or fractured geological reservoirs. Modeling the dynamics of CO2-water-rock interactions is challenging because of the resulting large geochemical disequilibrium, the reservoir heterogeneities, and the large space and time scales involved in the processes. In particular, there is a lack of information about how the macroscopic properties of a reservoir, e.g., the permeability, will evolve as a result of geochemical reactions at the molecular scale. Addressing this point requires a fundamental understanding of how the microstructures influence the macroscopic properties of rocks. The pore scale, which ranges from a few nanometers to centimeters, has stood out as an essential scale of observation of geochemical processes in rocks. Transport or surface reactivity limitations due to the pore space architecture, for instance, are best described at the pore scale itself. It can be also considered as a mesoscale for aggregating and increasing the gain of fundamental understanding of microscopic interfacial processes. Here we focus on the potential application of a combination of physicochemical measurements coupled with nanoscale and microscale imaging techniques during laboratory experiments to improve our understanding of the physicochemical mechanisms that occur at the fluid-solid interface and the dynamics of the coupling between the geochemical reactions and flow and transport modifications at the pore scale. Imaging techniques such as atomic force microscopy, vertical scanning interferometry, focused ion beam transmission electron microscopy, and X-ray microtomography, are ideal for investigating the reactivity dynamics of these complex materials. Minerals and mineral assemblages, i.e., rocks, exhibit heterogeneous and anisotropic reactivity, which challenges the continuum description of porous media and assumptions required for reactive transport modeling at larger scales. The conventional approach, which consists of developing dissolution rate laws normalized to the surface area, should be revisited to account for both the anisotropic crystallographic structure of minerals and the transport of chemical species near the interface, which are responsible for the intrinsic evolution of the mineral dissolution rate as the reaction progresses. In addition, the crystal morphology and the mineral assemblage composition, texture, and structural heterogeneities are crucial in determining whether the permeability and transport properties of the reservoir will be altered drastically or maintain the sealing properties required to ensure the safe sequestration of CO2 for hundreds of years. Investigating the transport properties in nanometer- to micrometer-thick amorphous Si-rich surface layers (ASSLs), which develop at the fluid-mineral interface in silicates, provides future direction, as ASSLs may prevent contact between the dissolving solids and the pore fluid, potentially inhibiting the dissolution/carbonation process. Equally, at a larger scale, the growth of micrometer- to millimeter-thick alteration layers, which result from the difference in reactivity between silicates and carbonates, slows the transport in the vicinity of the fluid-solid interface in polymineralic rocks, thus limiting the global reactivity of the carbonate matrix. In contrast, in pure limestone, the global reactivity of the monomineralic rock decreases because the flow localization promotes the local reactivity within the forming channels, thus enhancing permeability changes compared with more homogeneous dissolution of the rock matrix. These results indicate that the transformation of the rock matrix should control the evolution of the transport properties in reservoirs injected with CO2 to the same extent as the intrinsic chemical reactivity of the minerals and the reservoir hydrodynamics. This process, which is currently not captured by large-scale modeling of reactive transport, should benefit from the increasing capabilities of noninvasive and nondestructive characterization tools for pore-scale processes, ultimately constraining reactive transport modeling and improving the reliability of predictions.

Fireside Corrosion of Ni Base Self-Fluxing Alloy Coatings in WtE Plant: Effect of Flue-Gas and Metal Temperature

Increase in the efficiency of energy recovery facilities is one of the challenges facing waste-to-energy (WtE) operators in the EU. To achieve this target, one option is optimization of the water/steam cycle to increase electrical efficiency. Nevertheless, increase in steam temperature in heat exchanger tubes results in increased fireside corrosion risks, particularly in superheater tubes, where severe corrosion loss of materials, frequent shutdowns for repairs and high operational costs occur. In this study, two heat-treated self-fluxing Cr–Mo–Si–B–Ni base alloys containing, respectively, 15.6 and 16.4 wt.% Cr, were applied to low- and high-temperature pendant superheater tubes (LTSH and HTSH). Detailed analyses for flue-gas and metal temperatures in service at different locations of the pendant tubes (around 850 and 400 °C, respectively) and analyses of deposits collected on both tubes (Na, K, Ca, Si, Zn, Pb, Cl, S) were conducted. Both coatings exhibited a corrosion rate close to ones reported for Inconel 625 in similar conditions. Localized corrosion was found and associated with molten phase-assisted corrosion mechanism damaging Si-rich protective layer. Correlations between corrosion rate and %Cr in the coating, T flue-gas, T metal and amount of molten phase in deposit are presented.

Aluminum to titanium laser welding-brazing in V-shaped groove

Laser assisted joining of AA5754 aluminum alloy to T40 titanium with use of Al-Si filler wires was carried out. Continuous Yb:YAG laser beam was shaped into double spot tandem and defocalized to cover larger interaction zone in V shaped groove. Experimental design method was applied to study the influence of operational parameters on the tensile properties of the joints. Microstructure examination and fractography study were carried out to understand the relation between local phase content and fracture mode.Within defined window of operational parameters, statistically important factors that influenced the strength of T40 to AA5754 joints in V groove configuration were Si content in the filler metal and groove opening angle on T40 side. The best quality joint showed joint coefficient of 90% (or 200MPa of apparent UTS). Tensile strength of the joints was found to be determined by the proportion between well-developed and under-developed reaction zones of T40/melted zone interface. The formation of 2–25μm thick Si-rich interlayers composed by Ti5Si3 and τ2 proved to enhance the strength of brazed interface. The creation of very thin (<0.5μm) Si-rich layers at the bottom of the groove was found not sufficient to establish mechanical continuity of the joint and thus should be avoided.

NanoSIMS isotope studies of rare types of presolar silicon carbide grains from the Murchison meteorite: Implications for supernova models and the role of 14C

We have conducted a NanoSIMS ion imaging survey of about 1800 presolar silicon carbide (SiC) grains from the Murchison meteorite. A total of 21 supernova (SN) X grains, two SN C grains, and two putative nova grains were identified. Six particularly interesting grains, two X and C grains each and the two putative nova grains were subsequently studied in greater detail, namely, for C-, N-, Mg-Al-, Si-, S-, and Ca-Ti-isotopic compositions and for the initial presence of radioactive 26Al (half life 716,000yr), 32Si (half life 153yr), and 44Ti (half life 60yr). Their isotope data along with those of three X grains from the literature were compared with model predictions for 15M⊙ and 25M⊙ Type II supernovae (SNe). The best fits were found for 25M⊙ SN models that consider for the He shell the temperature and density of a 15M⊙ SN and ingestion of H into the He shell before the explosion. In these models a C- and Si-rich zone forms at the bottom of the He burning zone (C/Si zone). The region above the C/Si zone is termed the O/nova zone and exhibits the isotopic fingerprints of explosive H burning. Satisfactory fits of measured C-, N-, and Si-isotopic compositions and of 26Al/27Al ratios require small-scale mixing of matter originating from a region extending over 0.2M⊙ for X and C grains and over 0.4M⊙ for one of the putative nova grains, involving matter from a thin Si-rich layer slightly below the C/Si zone, the C/Si zone, and the O/nova zone. Simultaneous fitting of 14N/15N and 26Al/27Al requires a C-N fractionation of a factor of 50 during SiC condensation. This leads to preferential incorporation of radioactive 14C (half life 5700yr) over directly produced 14N and can account for the 14N/15N along with 26Al/27Al ratios as observed in the SiC grains. The good fit for one of the putative nova grains along with its high 26Al/27Al points towards a SN origin and supports previous suggestions that some grains classified as nova grains might be from SNe. Apparent problems with the small-scale mixing scheme considered here are C/O ratios that are mostly <1 if C-, N-, and Si-isotopic compositions and 26Al/27Al ratios are simultaneously matched, underproduction of 32Si, and overproduction of 44Ti. This confirms the limitations of one-dimensional hydrodynamical models for H ingestion and stresses the need to better study the convective-boundary mixing mechanisms at the bottom of the convective He shell in massive star progenitors. This is crucial to define the effective size of the C/Si zone formed by the SN shock. The comparison between the Si isotope data of the SN grains and the models gives a hint that the predicted 30Si is too high at the bottom of the He burning shell.

The corrosion behavior of CVI SiC matrix in SiCf/SiC composites under molten fluoride salt environment

High temperature corrosion behavior and microstructural evolution of designed chemical-vapor-infiltrated SiC matrix in SiC fiber reinforced SiC ceramic matrix composites in 46.5LiF-11.5NaF-42.0KF (mol. %) eutectic salt at 800 °C for various corrosion time was studied. Worse damage was observed as extending the exposure time, with the mass loss ratio increasing from 0.716 wt. % for 50 h to 5.914 wt. % for 500 h. The mass loss rate showed a trend of first decrease and then increase with the extended corrosion exposure. Compared with the near-stoichiometric SiC matrix layers, the O-contained boundaries between deposited matrix layers and the designed Si-rich SiC matrix layers were much less corrosion resistant and preferentially corroded. Liner relationship between the mass loss ratio and the corrosion time obtained from 50 h to 300 h indicated that the corrosion action was reaction-control process. Further corrosion would lead to matrix layer exfoliation and higher mass loss ratio.

Effect of Temperature on Microstructure and Formability of Al-10 mass% Si Coatings

AbstractThe type-1 aluminized (Al-10 mass% Si) coating on hot stamped steel is used in commercial applications. The effect of temperature on microstructure and formability of the Al-10 mass% Si coating was investigated. Hot-dip aluminized 22MnB5 steel was heated at 870, 900, 930, and 1050 °C for 5 min. After heat treatment at different temperatures, the microstructure of Al-10 mass% Si was characterized by field-emission scanning electron microscopy and energy-dispersive spectroscopy. The results show that when the Al-10 mass% Si coating was heated at 870 °C for 5 min, three types of intermetallic phases were formed: two ternary Fe-Si-Al phases (Fe2 SiAl7 + Fe2 Si2 Al5, and Fe2 SiAl2 + Fe2Si2Al5) and one binary Fe-Al phase (FeAl3). The phases in the coating became Fe2SiAl2 + Fe2Si2 Al5 and FeAl3, the binary Fe-Al phase near the interface became Fe2Al5 and the Si-rich layers were decreased with the increase of heating temperature. When the heat treatment was 1050 °C for 5 min, the Si-rich layer disappeared, the coating consisted of FeAl and Fe3Al, and the Kirkendall voids were formed. When the heating temperature was increased through 870, 900, and 930 °C, the coating hardness was reduced and cracks were formed in the coating after hot stamping. The formability of the coating with temperature change was confirmed by a hot stamping test. When heated at 1050 °C, the coating was formable but continuous Kirkendall voids were observed.

Mineralogical evolution of Fe–Si-rich layers at the olivine-water interface during carbonation reactions

Recent studies investigating carbonation of iron-bearing silicates have shown that the rates of these reactions, although formally not depending on oxygen fugacity, are strongly different at different redox states of the system (Saldi et al. 2013; Sissmann et al. 2013). Here we provide a micro- and nanostructural characterization of the olivine/water interface during the carbonation of forsteritic olivine at 150 °C and p CO 2 = 100 bar. When the reaction starts under oxic conditions, the observed temporal sequence of interfacial layers consists of: a hematite/SiO 2(am) assemblage, Fe-rich phyllosilicates with mixed Fe valence and a non-passivating Fe-free amorphous SiO 2 layer, which allows the formation of ferroan magnesite. In contrast, starting at micro-oxic conditions, carbonation rates are much faster, with no real evidence of interfacial layers. Separate deposits of goethite/lepidocrocite in the early stages of the reaction and then formation of magnetite are observed at these conditions, while precipitation of siderite/magnesite proceeds unhindered. The evolution of the redox conditions during the reaction progress controls the sequence of the observed reaction products and the passivating properties of Fe–Si-rich interfacial layers. These findings have important implications for modeling the carbonation of ultramafic rocks under different oxygen fugacity conditions as well as for understanding the technological implications of adding accessory gases to CO 2 in carbon capture and storage mineralization processes involving ultrabasic rocks.

Geochemical characteristics of gold bearing boninites and banded iron formations from Shimoga greenstone belt, India: Implications for gold genesis and hydrothermal processes in diverse tectonic settings

This paper is the first documentation of boninites from the Kudrekonda Formation of Shimoga greenstone belt (SGB) in western Dharwar Craton (WDC), India and the occurrence of native gold in the associated quartz veins. We also investigate the gold mineralization hosted in the banded iron formations (BIFs) of Ganajur, Karajgi and Palavanahalli areas of the SBG. The Kudrekonda metavolcanic rocks are composed of clinopyroxene, orthopyroxene and plagioclase with secondary amphibole. The geochemical attributes of these rocks, based on MgO, TiO2 Ni, Cr and Co contents, Al2O3/TiO2, (Gd/Yb)N and (La/Sm)N ratios, classify them as boninites and their relative LILE-HFSE abundance suggests magma generation in an intraoceanic arc setting. The Gd/Yb and Dy/Yb ratios suggest parent magma origin through partial melting of a spinel lherzolite mantle source. Geochemical signatures of the boninites suggest high temperature, shallow level melting of refractory mantle wedge metasomatized by fluids derived through dehydration of oceanic slab during subduction initiation. Quartz veins present in the Kudrekonda boninites contain gold grains showing affinity towards quartz-carbonate vein type greenstone hosted occurrences. EPMA data record 88.5–90.3wt.% Au content with 7.7–8.4wt.% Fe, 0.05–2.1wt.% S and negligible Ag. The Au is hosted in Fe-oxides. Bulk chemical analyses show 4.1–684.4ppb Au and 139.4–2186.4ppb Ag in the studied samples. The gold mineralization of Kudrekonda boninites is syngenetic, mesothermal, convergent margin orogenic type. Decarbonation, desulphidization and metamorphism of subducted oceanic lithosphere and devolatilization of metasomatized enriched mantle wedge in intraoceanic arc setting are the viable processes that contributed to gold genesis in the Kudrekonda boninites. Devolatilization during prograde metamorphism, hydrothermal fluid generation, syntectonic gold remobilization and migration of gold enriched fluids through shear zones account for Au transportation and precipitation in quartz veins emplaced within the boninites. The BIFs of Ganajur, Karajgi and Palavanahalli areas of Shimoga greenstone belt dominantly comprise alternating Si-rich layers of quartz and Fe-rich hematite and magnetite layers. Geochemical characteristics of the BIF samples including their depleted ƩREE, positive Eu anomalies, negative to negligible Ce anomalies, and superchondritic Y/Ho ratios suggest that the BIFs were (i) derived by chemical sedimentation from paleo-ocean enriched in dissolved iron and silica with marked contributions from hydrothermal fluids of volcanic origin, and (ii) deposited in an off-shelf marine environment proximal to a mid-oceanic spreading centre where hydrothermal activity induced release of Eu and Y enriched hydrothermal solutions under low oxygen fugacity conditions. Native gold occurs in banded strata-bound disseminated sulphide lenses compositionally characterized as pyrite, arsenopyrite, chalcopyrite and galena. Mineral chemical analyses reveal 73–100% Au content with variable concentrations of Ag (0.02–15.2wt.%). Geochemical compositions of BIFs are characterized by pronounced enrichment in Au (706–15,831ppb) and Ag (630–2435ppb). Gold mineralization in Shimoga BIFs is epigenetic, epithermal type akin to Homestake type iron-formation hosted vein and disseminated lode gold deposit. Gold genesis in these BIFs is attributed to migration of oxygen depleted, reducing, sulphidic–auriferous fluids of hydrothermal origin to the site of BIF deposition that served as chemical traps for the auriferous fluids. The Kudrekonda boninites represent accretion and preservation of a slice of older oceanic crust onto a relatively younger, active continental margin through arc–continent collision during Neoarchean time.

Measuring mineral dissolution kinetics using on-line flow-through time resolved analysis (FT-TRA): an exploratory study with forsterite

We explore the applicability of on-line flow-through time-resolved analysis (FT-TRA) to measure mineral dissolution rates, determine dissolution rate parameters, and monitor dissolution stoichiometry under both constant and transient eluent conditions. A custom-built automated flow-through system is used to subject mineral samples to controlled eluent flows of constant or varying composition, and the dissolution products are measured on-line with a quadrupole ICP–MS. Because forsterite dissolution has been extensively studied, this mineral provides an ideal benchmark to test the approach.FT-TRA has several advantages compared to the mixed-flow reactors conventionally used to measure mineral dissolution. The mineral dissolution regime (surface vs transport-controlled) can be readily established prior to conducting dissolution experiments, which is important if the goal of the experiment is to determine dissolution rate parameters. Because of the small volume (25μL) of the flow-through reactor, the time to reach steady state concentration in the effluent is shorter and is limited by the intrinsic properties of the mineral, instead of the residence time of the effluent in the reactor. For minerals reaching steady-state dissolution rapidly, dissolution rate parameters (rate constant(s) and reaction order(s)) are established in a few hours, allowing for replications, statistical analysis of the results, and investigation of the underlying causes of variability. The experimental set-up can be adapted for minerals that require longer periods of time to reach steady-state dissolution. In addition, FT-TRA lends itself particularly well for detailed monitoring of dissolution rates and dissolution stoichiometry under transient conditions. For forsterite dissolution under acidic conditions, preferential release of Mg when pH transits to lower values, and preferential release of Si when pH transits to higher values is clearly documented and can be interpreted as indicating changes in the mean depth of the Si-rich surface layer in response to changes in eluent acidity. Episodes of exfoliation of the Si-rich surface layer can also be identified, providing a means to study one of the potential rate limiting steps for CO2 sequestration by carbonation of olivine. The results presented here indicate that FT-TRA with online ICP–MS analysis could be a useful and multifaceted addition to the toolbox available to study mineral dissolution.

Effect of traveling magnetic field on separation and purification of Si from Al–Si melt during solidification

Separation and purification of the Si crystal during solidification process of hypereutectic Al–30Si melt under traveling magnetic field (TMF) were investigated in the present study. The results showed that under a proper condition the Si-rich layer can be formed in the periphery of the ingot while the inner microstructure is mainly the Al–Si eutectic structure. The intense melt flow carries the bulk liquid with higher Si content to promote the growth of the primary Si phase which is first precipitated close to the inner wall of the crucible with a relatively lower temperature, which resulting in the remarkable segregation of the primary Si phase. The impurity contents of the refined Si can be reduced to a very low level. The typical metallic impurities have removal fraction higher than 99.5%. In addition, there is a significant difference in the P contents between the primary and eutectic Si phases, which might be ascribed to the formation of AlP phase that acts as the heterogeneous nucleation sites. Furthermore, a considerable amount of Fe-containing particles with a size about 100–300nm is found inside the eutectic Si phase, indicating an unintended entrapment of Fe in Si.

Influences of alloyed Si on the corrosion resistance of Co–Cr–Mo alloy to molten Al by iso-thermal oxidation in air

The corrosion resistance of Co–Cr–Mo alloys with various Si concentrations after oxidation to molten Al was investigated. Si was helpful in forming a more homogeneous, compact Cr2O3 film after oxidation. Correspondingly, the Cr2O3-dominant film was more effective in enhancing the corrosion resistance than the duplex film of CoO and Cr2O3 of alloy with low Si concentration. In addition, local defects such as the cracks acted as initiation sites of failure in oxide film. Ascribed to its higher stability, Si-rich layer beneath the oxide film delayed the reaction between Al and matrix even after the failure of oxide film.

Investigation of micro-arc oxidation coating growth patterns of aluminum alloy by two-step oxidation method

The micro-arc oxidation (MAO) process of 2A70 aluminum alloy in different electrolytes containing silicate or phosphate by two-step oxidation was investigated. The growth rate, surface roughness and element distributions of the micro-arc oxidation coatings were characterized. The results show that the coating growth patterns are different in Si and P electrolytes although they both grow inward. The discharge channels formed in Si-electrolyte and P-electrolyte are trumpet-shaped and dumbbell-shaped, respectively. The trumpet-shaped channel is conducive to gather heat and extend the reaction area inward, which leads to a layer growth pattern in P-electrolyte. The dumbbell-shaped channel limits the reactive area but introduces more electrolytes during the cooling process, which results in an island growth pattern in Si-electrolyte. Therefore, a newly formed P-rich layer can be observed between substrate and initially formed Si-rich layer after the second-step oxidation in P-electrolyte, but only localized Si-rich areas could be found when the second-step oxidation was performed in Si-electrolyte.

Field and model constraints on silicic melt segregation by compaction/hindered settling: The role of water and its effect on latent heat release

To investigate how large volumes of silicic melts segregate to form granitic plutons, we conducted a case study of a zoned pluton, in which SiO 2 increases from intermediate (69 wt%) to highly silicic compositions (74 wt%) toward the contact with metasedimentary wallrock in the outer 25 m of the pluton. All other major, minor, and trace elements vary systematically with SiO 2 and indicate that outward increasing SiO 2 is due to a decrease in mafic elements and minerals. Whole-rock oxygen isotopes and elemental variation diagrams do not support mixing with wallrock as an explanation for the Si-rich boundary layer. Instead, mafic enclaves, which are common in the pluton, also decrease in abundance in the outer 25 m of the pluton, suggesting a mechanical origin for the Si-rich boundary layer. The coupling of mechanical and geochemical boundary layers, combined with geochemical modeling, indicate that the silica-rich, enclave-poor boundary layer formed by hindered settling or compaction of a crystal-rich (crystal fractions >60%) magmatic mush. Segregation of melts at high crystal fraction is known to be a slow process. However, petrography and Zr-based thermometry indicate that the residual Si-rich liquids were water-saturated. Water decreases melt viscosity, which helps expulsion, but equally importantly, water also delays much of the latent heat release to late in the thermal and crystallization history of a cooling magma. We show that the higher the water content, the longer the time interval over which a magma chamber resides at the stage when water-saturated, high-silica liquids form, allowing sufficient time for exfiltration of silicic liquids before the magma body freezes.

Structural, compositional and electrical characterization of Si-rich SiOx layers suitable for application in light sensors

Metal-Oxide-Silicon (MOS) structures containing silicon nanoparticles (SiNPs) in three different gate dielectrics, single SiOx layer (c-Si/SiNPs-SiOx), two-region (c-Si/thermal SiOx/SiNPs-SiOx) or three-region (c-Si/thermal SiO2/SiNPs-SiOx/SiO2) oxides, were prepared on n-type (100) c-Si wafers. The silicon nanoparticles were grown by a high temperature furnace annealing of sub-stoichiometric SiOx films (x=1.15) prepared by thermal vacuum evaporation technique. Annealing in N2 at 700 or 1000°C leads to formation of amorphous or crystalline SiNPs in a SiOx amorphous matrix with x=1.8 or 2.0, respectively. The three-region gate dielectric (thermal SiO2/SiNPs-SiO2/SiO2) was prepared by a two-step annealing of c-Si/thermal SiO2/SiOx structures at 1000°C . The first annealing step was carried out in an oxidizing atmosphere while the second one was performed in N2. Cross-sectional Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy have proven both the nanoparticle growth and the formation of a three region gate dielectric. Annealed MOS structures with semitransparent aluminum top electrodes were characterized electrically by current/capacitance–voltage measurements in dark and under light illumination. A strong variation of the current at negative gate voltages on the light intensity has been observed in the control and annealed at 700°C c-Si/SiNPs-SiOx/Al structures. The obtained results indicate that MOS structures with SiO1.15 gate dielectric have potential for application in light sensors in the NIR–Visible Light–UV range.

Si Purity Control and Separation from Solidification of Al–30Si Melt under Pulse Electromagnetic Field

Purification of metallurgical-grade silicon (MG–Si) by a combination of Al-Si solidification refining and electromagnetic oscillating separation and acid leaching collection has been studied. The primary Si crystals and Al-Si alloy in hypereutectic Al-30%Si melt were separated during solidification under the pulse electromagnetic field (PEF). The results show that the Si content in Si-rich layer increases with increasing discharging frequency. The typical metallic impurities (Fe, Ti, and Ca) have removal fraction higher than 99.5%. The removal fractions of the impurities B and P which are more difficult to remove are over 90% and 85%, respectively.