Residual Si Research Articles

In-situ observation of the interaction silicon and hematite

The reduction process of the Fe2O3 (α-hematite) by Si was investigated with in-situ transmission electron microscopy (TEM). Hematite and other iron oxides are main component of iron ore and Si is main gangue elements of iron ore. Si reduced hematite and Fe precipitated around 700°C. The electrons due to TEM(=200keV) was not necessary condition of Fe precipitation and grew until run out of Si. The residual Si reacted with precipitated Fe after a certain period of time of electron irradiation. The reaction completed very short time less than one frame of video. One of the reacted material was identified as α-FeSi2. These results indicated that the possibility of new ironmaking without CO2 emission and silicide formation.

How the Crosslinking Agent Influences the Thermal Stability of RTV Phenyl Silicone Rubber.

In this work, a thermal degradation mechanism of room temperature vulcanized (RTV) phenyl silicone rubber that was vulcanized by different crosslinking agents was discussed. Firstly, RTV phenyl silicone rubber samples were prepared by curing hydroxyl-terminated polymethyldiphenylsiloxane via three crosslinking agents, namely, tetraethoxysilane (TEOS), tetrapropoxysilane (TPOS), and polysilazane. Secondly, the ablation properties of RTV phenyl silicone rubber were studied by the muffle roaster test and FT-IR. Thirdly, thermal stability of the three samples was studied by thermogravimetric (TG) analysis. Finally, to explore the thermal degradation mechanism, the RTV phenyl silicone rubber vulcanized by different crosslinking agents were characterized by TG analysis-mass spectrum (TG-MS) and pyrolysis gas chromatogram-mass spectrum (pyGC-MS). Results showed that the thermal stability of RTV phenyl silicone rubber is related to the amount of residual Si–OH groups. The residual Si–OH groups initiated the polysiloxane chain degradation via an ‘unzipping’ mechanism.

Preparation of Si-SiOx nanoparticles from volatile residue produced by refining of silicon

Residual Si was produced on a furnace wall when upgraded metallurgical grade Si was refined by electron beam melting. It was then recycled to prepare Si-SiOx nanoparticles with an average size of 100 nm by planetary ball milling. The obtained Si-SiOx nanoparticles mainly consist of amorphous Si, crystalline Si and amorphous SiOx, which was confirmed by XRD, FTIR, XPS and TEM. SiOx is mainly composed of SiO2 and SiO1.35. Distilled water used as a grinding aid not only enhances milling efficiency, but also plays a key role in obtaining SiOx. During refining of upgraded metallurgical grade Si, the deposition pattern of residual Si on furnace wall agrees with model of three-dimension growth. Growth of Si-SiOx nanoparticles is the mutual effect of distilled water and ball milling. Si-SiOx nanoparticles were doped into phenolic resin pyrolysis carbon as anode materials for lithium ion batteries, and 10% doping was observed to improve the specific capacity. After 500 cycles, specific capacity of delithiation remained around 550 mA h/g. It suggests the residual Si is a value-added by-product, and it can be recycled as anode materials for lithium ion batteries.

Facile and cost-efficient indirect carbonation of blast furnace slag with multiple high value-added products through a completely wet process

Mineral carbonation of blast furnace slag (BFS) has been proposed as a comprehensive method for carbon capture and storage and utilization of the industrial solid waste. However, the challenge for this technology to be applied practically is how to reduce the cost of process. A completely wet process combining a CO2-mineralization cell for CO2 capture and membrane electrolysis for recovery of carbonated mother liquor is proposed to simultaneously fix CO2 and produce multiple value-added products. In this process, Ca, Mg, Al, and Si are extracted from BFS with an NH4HSO4 solution prepared from H2SO4 and (NH4)2SO4 with extraction ratios of 97.3%, 98.8%, 96.4%, and 94.3% under optimized conditions, respectively. The extracted Al and Si are then recovered as NH4Al(SO4)2·12H2O (99.59 wt%) and SiO2 (97.70 wt%) with 93% and 98.1% yield, respectively. The CaSO4-rich leaching residue and MgSO4-rich leachate after complete depletion of the residual Al and Si are successively carbonated with an NH4HCO3 solution obtained from a CO2-mineralization cell with total CO2 capacity up to 361 kg-CO2 per tonne BFS. The preliminary economic evaluation shows that the present carbonation route is a cost-efficient method to comprehensively utilize BFS and reduce CO2 emissions.

What effect does liming have on silicon availability in agricultural soils?

Controversy surrounds the effects of pH on Si availability in agricultural soils with some workers reporting a negative and others a positive relationship. The factors contributing to this contradiction are examined and discussed. Because soil development typically involves both desilication and decreasing pH, when a group of soils from a region with different ages and weathering rates are compared, there is typically a positive relationship between pH and Si extractability. Raising pH by liming can effect Si availability through a number of mechanisms including weathering. Over the normal range of liming (i.e. pH 4.5 to 6.5) increased pH decreases the solubility of crystalline and amorphous aluminosilicates but above about pH 7 their solubility increases. Specific adsorption of monomeric monosilicic acid (the major form found in soil solution) is at a maximum between pH 9 and 10 (pK1 for silicic acid is 9.8). Thus, increasing pH increases the proportion of Si adsorbed and decreases that present in soil solution leading to a negative relationship between pH and soil solution Si. With time, polymerization of monomeric Si can occur at the surface of metal oxide surfaces and this may hinder desorption reactions. Nonetheless, Si is generally highly mobile in soils and easily leached so that in the longer term, it is conceivable that increased adsorption may be a retention mechanism which effectively increases Si availability. Soils contain a biogenic pool of amorphous silica (mainly of plant phytolith origin) and its solubility has been shown to increase greatly with increasing pH from 2 up to pH 12. Thus, liming would increase Si availability in the short-term by increasing dissolution of biogenic Si but in the longer term it would tend to decrease Si availability through diminution of the biogenic pool of Si. The most common Si fertilizers are slag materials which are both sources of Si and liming materials. Thus when soils with different histories of slag application are compared, there is often a positive relationship between pH and Si extractability. The relationship between pH and Si solubility/availability can therefore be positive or negative depending on the situation and which pool(s) of potentially available Si (lithogenic/pedogenic, biogenic, adsorbed or residual fertilizer Si) is the most important source of soluble and available Si.

Design, synthesis and characterization of polysiloxane and polyetherdiamine based comb-shaped hybrid solid polymer electrolytes for applications in electrochemical devices

In this study, polysiloxane and polyetherdiamine based comb-shaped solid polymer electrolytes (SPEs) are developed by hydrosilylation and sol-gel reactions of polymethylhydrosiloxane, allyltriethoxysilane, bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol and (3-glycidoxypropyl)trimethoxysilane followed by LiClO4 doping. The absence of residual Si‒H functionality in FTIR and 29Si CPMAS NMR spectra confirms the completion of hydrosilylation reaction. The formation of comb-shaped SPEs with silicate backbones is confirmed by 13C and 29Si solid-state NMR spectroscopy. The maximum ionic conductivity value of 5.8 × 10−4 S cm−1 is obtained for the SPE with [O]/[Li] ratio of 16 at 80 °C with electrochemical stability window reaching up to 4.8 V. The fabricated electrochromic device with the hybrid SPE of [O]/[Li] = 16 demonstrates good electrochromic contrast and optical density change values of 49.3% and 0.39, respectively, at wavelength of 550 nm. The results show that the present comb-shaped SPEs have potential to be used in various electrochemical devices.

Conductive stretchable composites properly engineered to develop highly compliant electrodes for dielectric elastomer actuators

Carbon black (CB) particles were used as conductive filler for a high molecular weight polydimethylsiloxane-α,ω-diol (PDMS) to obtain conductive stretchable electrodes suitable for dielectric elastomer actuators. To ensure a perfect compliance between electrodes and the dielectric film, both based on the same PDMS, an original procedure consisting in their co-crosslinking was approached. Some of the Si–OH groups from the electrode solution will condensate with residual Si–OH groups from the surface of the dielectric elastomer (DE) creating chemical bridges. Electrode morphologies were examined by scanning electron microscopy, while their conductivities were evaluated by four-point method. Also, the electrodes influence on mechanical, viscoelastic and actuation properties on the resulted actuators was studied. Good results were obtained consisting in that the chemically bonded electrodes support large deformations (200%) without losing conductivity even after 10 000 cycles with no significant impact on the DE stiffness. The DE transducers exhibit electromechanical actuation of approximately 81% greater than that achieved with the same dielectric but with electrodes consisting of loose CB nanoparticles.

Modeling and interpretation of UV and blue luminescence intensity in β-Ga2O3 by silicon and nitrogen doping

Temperature-dependent cathodoluminescence spectra of (2¯01) Si-doped β-Ga2O3 single crystals and (010) N-doped epitaxial films were comprehensively shown to investigate their electronic structure and defect states. The decrease in the self-trapped exciton (STE) emission at low temperatures in heavily Si-doped crystals implied the Debye-Hückel screening of STEs with the critical charge density larger than 2 × 1018 cm−3. The analysis based on the rate equation model suggested a significant influence of the donor-acceptor-pair recombination involving a SiGa donor on the UV luminescence band in the Si-doped crystals. The blue luminescence band was suppressed for the heavily N-doped epitaxial films with a N concentration of 1 × 1018 cm−3, implying the decrease in the oxygen vacancy (VO) concentration by N doping. The increase in the NO acceptor concentration as well as the decrease in the VO concentration were found to contribute to the compensation of residual Si donors resulting in high resistivity of N-doped epitaxial films.

Comparative investigation of microstructure, mechanical properties and strengthening mechanisms of Al-12Si/TiB2 fabricated by selective laser melting and hot pressing

Near-fully dense Al-12Si matrix composites reinforced with TiB2 ceramic particles (2 wt%) were successfully fabricated by selective laser melting (SLM) and hot pressing (HP) of powder mixtures. TiB2 ceramic particles are homogeneously distributed in the Al-12Si matrix at the micrometer-scale owing to a very good wetting between molten Al-12Si alloy and TiB2 ceramic. The microstructural analysis of the as-fabricated SLM samples show the formation of a supersaturated α-Al phase and the decrease of free residual Si with respect to the hot-pressed ones. Both composites exhibit a fine microstructure with a grain size of ~ 5.1 µm and ~ 5.8 µm for SLM- and HP-fabricated samples with addition of TiB2 ceramic particles. The SLM Al-12Si/TiB2 composite exhibits significantly improved microhardness (~ 142 ± 6.0 HV0.05) and yield strength (~247 ± 4.0 MPa) compared to the corresponding HP one. Fine cell morphology and nanostructured dispersion strengthening are responsible for the improved mechanical strength of the Al-12Si/TiB2 composite processed by SLM.

Microstructure and properties of plain-weave carbon fabric reinforced ceramic composites containing Cu-Si alloy

Abstract Aiming to improve the physical properties, the soft Cu3Si phase was successfully introduced into C/C-SiC composites to partially replace SiC and residual Si via a simultaneously infiltration of Si and Cu. The microstructure and physical properties of the as-prepared C/C-SiC-Cu3Si composites (CSCS) were investigated in comparison to the C/C-SiC composites with same fiber architecture. The results indicated that the thermal diffusivity of CSCS is improved from 8.32 to 11.02 mm2/s, while both SiC and Si content in CSCS composites were obviously reduced to 23.2 wt% and 10.8 wt%, respectively. Moreover, compared to the C/C-SiC, the flexural strength which is fiber-dependent is significantly enhanced, while the compressive strength which is matrix-dependent is slight decreased in CSCS. The microstructural investigations revealed that fibers with less aggressiveness by liquid silicon and lower capacity to uniformly deformation of matrix in CSCS are main reasons for higher flexural strength and lower compressive strength, respectively.

Precipitation kinetics and hardening mechanism in Al-Si solid solutions processed by high pressure solution treatment

A dense uniform distribution of nanoscale Si precipitates in Al-Si binary alloys were achieved using high pressure solution treatment and aging treatment. Precipitation kinetics, hardening effect as well as supersaturation-growth-hardening relationships during aging treatment were quantitatively investigated. The results reveal that there exists a critical supersaturation value (0.026) during precipitation process, which divides the size versus time curve into two stages corresponding to different slopes. The sudden variation in the curve around the critical point indicates a great change in the growth rate of second phase, which is assumed to be related to the inconstancy of diffusion coefficient over a wide supersaturation range. The dense nanoscale precipitates could lead to extraordinarily high precipitation strengthening, which is combined with solid solution hardening caused by residual Si solute atoms in Al matrix, resulting in much more complicated age hardening response than that in low solubility alloys. Ultra-high hardness (~ 130 HV) is achieved in Al-7Si alloy with optimized microstructure. This work provides a promising approach for achieving high performance alloys with nanoscale secondary phase as well as insights into the underlying mechanism of microstructure evolution during aging process.

Process optimization and mechanical property evolution of AlSiMg0.75 by selective laser melting

A central composite design of experiment has been carried out to investigate the effect of selective laser melting (SLM) process parameters on the relative density of AlSiMg0.75 alloy and obtain samples with relative density of 99.0624%. Square samples and flat tensile samples were manufactured with optimized process parameters to study the evolution of microstructure, microhardness and tensile property. The microstructure of as-built samples shows fine grains and coarse grains with Al-rich cellular structure and Si-segregated network structure in top view. However, a large number of dendrite grains with very small space are observed in side view. After heat treatment, the cellular and dendrite structure broke into particles of different sizes with microhardness reduction and Si phase appearance by XRD and DSC. The heat treated samples show lower tensile strength and yield strength with the reduction of residual stress and Si solubility, and the destruction of small structures. But the elongation is higher than the as-built ones. The fracture morphology of as-built samples shows cleavages with small and shallow dimples, which indicates a mixture of brittle and ductile fracture. The fracture morphology of heat treated samples shows big and deep dimples, which indicates a ductile fracture.

Microstructure and mechanical properties of Al-12Si produced by selective laser melting

Al–12Si specimens are produced by selective laser melting (SLM) from gas atomized powders. Installation for the production of powder is original. All specimens were prepared using the EOSINT M 280 device. A fine cellular structure is observed with residual free Si along the cellular boundaries. Room temperature tensile tests reveal remarkable mechanical behavior: the samples show yield and tensile strengths of about 102 MPa and 425 MPa, respectively, along with fracture strain of 12%. The study of crack surface morphology was shown by the example of a sample. Except the spherical pores, the interface of the molten pool also appears on the fracture surface, which indicates a mixture of fragile and ductile fracture. Additionally, the agglomerated silicon group appears also on the fracture surface.

Fabrication of practically pure Si2N2O ceramic with high performance from amorphous BN surface modified nano-sized Si3N4 powders

In this study, amorphous nano-sized Si3N4 powders were surface modified by BN. Then a stable and dense Si2N2O ceramic was fabricated using the BN surface modified powders, rather than Si2N2O-Si3N4 composites usually prepared from nano-sized Si3N4 powders without surface modification. The effect of BN surface modification on phase transformation, microstructure and mechanical properties were also investigated. Si2N2O ceramics obtained by means of the present method have no residual Si, crystal SiO2 and other oxide additives, which are usually produced by other methods and may seriously influence high-temperature structural and functional applications of Si2N2O ceramics.

Facile synthesis of SiOx spheres or dumbbell-shaped β-SiC whiskers on expanded graphite by silicon vapor deposition

A facile method was developed to synthesize SiOx spheres or dumbbell-shaped β-SiC whiskers on expanded graphite (SiOx/EG or β-SiC/EG) by silicon vapor deposition without catalyst. With the carbon black atmosphere, the above hybrids were synthesized above 1100 °C in a graphite crucible where silicon powder was placed under the expanded graphite (EG). The growth of SiOx spheres is controlled by vapor-solid mechanism at 1100 °C and 1200 °C. Namely, the active carbon atoms absorbed SiO (g) and Si (g) to form SiC nuclei. Then, the SiO2, residual SiO (g) and Si (g) deposited on SiC nuclei to form SiOx spheres. At 1300 °C and 1400 °C, the same SiOx spheres formed on EG as well as many dumbbell-shaped β-SiC whiskers. The growth of dumbbell-shaped β-SiC whiskers is controlled by vapor-vapor and vapor-solid mechanism successively. In a word, firstly, the β-SiC whiskers with defects formed via the reaction between Si (g) and CO (g). After that, the SiO2, residual SiO (g) and residual Si (g) preferentially deposited on defects, then deposited on other parts of β-SiC whiskers to form dumbbell-shaped SiC whiskers.

A MMSE-based Beamforming Algorithm for MIMO Point-to-Point Full-Duplex Communication Systems

In this paper, we focus on the precoding design for sum rate maximization while considering the effects of residual SI for point – to-point multiple input/multiple output (MIMO) Full-Duplex systems. The MMSE-based beamforming algorithm was proposed to cancel the SI. The results shown that, the self-interference cancellation is done by matrix precoding at the transmitter if the total number of transmitting antenna of two nodes is greater than the number of receiving antenna of one node. The Bit Error Rate (BER) was also evaluated in the simulation.

Inorganic characteristics of cake layer in A/O MBR for anaerobically digested leachate from municipal solid waste incineration plant with MAP pretreatment

Inorganic characteristics of cake layer in an anoxic/oxic membrane bioreactor (A/O MBR) for anaerobically digested leachate from a municipal solid waste incineration plant with MAP (magnesium ammonium phosphate precipitation) pretreatment was reported. During 90days of operation, the A/O-MBR had formed a thick cake layer, causing severe fouling. BCR (European Community Bureau of Reference) results showed that Fe, Al, Ca, Mg, Si were the dominant inorganic components (especially residual Si and Al) in the cake layer. X-ray diffraction (XRD) analysis further presented that the cake layer contained complex inorganic substances with FeSiO3, CaAl2O3, Ca5(PO4)3OH, CaCO3, CaPO3OH, Mg2(PO4)OH, etc., while Si-Al crystal was the major inorganic component in the cake layer. Additionally, SEM-EDX showed a consistent distribution of inorganics along the front cross-section of the cake layer, indicating that the stable particles and metal ions led to the steady inorganic accumulation onto the membrane surface. However, it was revealed that high suction pressure aggravated the inorganic particle accumulation, especially for the Si-Al crystals, at the end of the cake layer.

Silica-undersaturated reaction zones at a crust–mantle interface in the Highland Complex, Sri Lanka: Mass transfer and melt infiltration during high-temperature metasomatism

Sri Lanka is a crucial Gondwana fragment mostly composed of granulitic rocks in the Highland Complex surrounded by rocks with granulite to amphibolite grade in the Vijayan and Wanni Complex that were structurally juxtaposed during Pan-African orogeny. Fluids associated with granulite-facies metamorphism are thought to have controlled various lower crustal processes such as dehydration/hydration reactions, partial melting, and high-temperature metasomatism. Chemical disequilibrium in the hybrid contact zone between a near peak post-tectonic ultramafic enclave and siliceous granulitic gneiss at Rupaha within the Highland Complex produced metasomatic reaction zones under the presence of melt. Different reaction zones observed in the contact zone show the mineral assemblages phlogopite+spinel+sapphirine (zone A), spinel+sapphirine+corundum (zone B), corundum (~30%)+biotite+plagioclase zone (zone C) and plagioclase+biotite+corundum (~5%) zone (zone D). Chemical potential diagrams and mass balance reveal that the addition of Mg from ultramafic rocks and removal of Si from siliceous granulitic gneiss gave rise to residual enrichment of Al in the metasomatized mineral assemblages. We propose that contact metasomatism between the two units, promoted by melt influx, caused steady state diffusional transport across the profile. Corundum growth was promoted by the strong residual Al enrichment and Si depletion in reaction zone whereas sapphirine may have been formed under high Mg activity near the ultramafic rocks. Modelling also indicated that metasomatic alteration occurred at ca. 850°C at 9kbar, which is consistent with post-peak metamorphic conditions reached during the initial stage of exhumation in the lower crust and with temperature calculations based on conventional geothermometry.

Electrical properties of Ni/n-GaN Schottky diodes on freestanding m-plane GaN substrates

The electrical properties of m-plane Ni/n-GaN Schottky diodes grown via metalorganic chemical vapor deposition were investigated. Under growth at 1,120 °C with a V/III ratio of 1,000 (growth rate of 100 nm/min), the residual Si, O, and C impurity concentrations in the m-plane GaN layer were below the secondary-ion mass spectroscopy detection limit. The surface of the Si-doped n-GaN epitaxial layer on the 5°-off m-plane GaN substrate consisted of steps and terraces. A linear correlation between the carrier concentration and the Si atomic concentration was clearly observed from 1 × 1017 to 5 × 1015 cm−3. The reverse current–voltage curves were fitted using the thermionic field-emission model at the measured carrier concentration and qϕB. The leakage current of the diodes under a reverse bias was effectively suppressed at a low carrier concentration of 4.6 × 1015 cm−3.

Silicon fractionation in Mollic Fluvisols along the Central Elbe River, Germany

Quantification of Si in its different forms in soil is a prerequisite to understand the geochemical distribution and fate of Si along with their driving biogeochemical processes. However, different Si fractions in floodplain soils have not been quantified yet, and little is known about the biogeochemical processes driving Si fractionation in these soils. Therefore, we applied for the first time a sequential Si extraction scheme to three floodplain soils (Mollic Fluvisols) to separate six Si fractions: mobile Si, adsorbed Si, Si bound to organic matter, Si included in pedogenic oxides and hydroxides, biogenic as well as minerogenic amorphous silica. Residual Si was calculated. The highest Si proportion apart from the residual fraction (Si bound in primary and secondary silicates) was found in minerogenic amorphous silica (up to 5.6% of total Si), followed by Si occluded in pedogenic oxides and hydroxides (up to 0.7% of total Si). Silicon from biogenic amorphous silica amounted to 0.02–0.6% of total Si. The smallest proportion of Si was found in the mobile Si fraction and made up about 0.01% of the total Si. The results of this study demonstrate the importance of the soil water budget (here periodic flooding with prolonged water saturation) on the accumulation of easy-to-mobilise Si, Si occluded in pedogenic oxides and hydroxides and amorphous minerogenic as well as biogenic silica. Reductive dissolution of Fe and Mn oxides may induce Si release into the soil solution, subsequent oxidizing conditions may induce Si accumulation by adsorption, co-precipitation and occlusion of Si on/with newly formed Fe and Mn oxides. These processes are more pronounced in floodplain than in terrestrial soils, thus implying different distributions of Si among soil fractions.