Oxidation Of Si Research Articles

Facile method for the selective recovery of Gd and Pr from LCD screen wastes using ultrasound-assisted leaching

Rare earth elements (REE) are essential for the production of technological devices. However, their high demand and low availability, together with an increase in electronic waste generation, compel the development of efficient, economic and green methods for recovering these elements from electronic waste. In this work, a facile method for selective recovering of REE from Liquid Crystal Display (LCD) screen wastes, employing ultrasound assisted leaching is presented. The screen wastes were milled and sieved to pass through a − 325 mesh sieve (44 μm). The milled powder was subjected to ultrasound-assisted leaching in an aqueous medium, at room temperature (25 °C) and pH 6 for 60 min. Subsequently, a magnetic separation was applied to the leach residue. Inductively coupled plasma was employed to quantitatively analyze the composition of the LCD powders and determine the effectiveness of the extraction process. Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy allowed qualitative chemical analysis of the solid materials. The results show that the LCD screen wastes are formed, mainly, by amorphous oxides of Si, Fe, In, Sn and REE. The amount of Gadolinium (Gd) and Praseodymium (Pr) in the wastes were 93 and 24 mg kg− 1, respectively, which justifies their recovery. X-ray diffraction analysis of the magnetic portion of the leached residue, confirmed the presence of an amorphous phase together with crystalline metallic iron alloy. The magnetic behavior, obtained by Vibration Sample Magnetometry, helped to understand the nature of the residues. The formation of this metallic alloy is attributed to the effect of high power ultrasonic during the leach. It was confirmed that the magnetic residue concentrates and recovers 87 wt% of Gd and 85 wt% of Pr contained in the original material. Therefore, ultrasound-assisted leaching is a selective and facile method for recovering Gd and Pr from waste LCD.

New insights into fracture of Si in Cu-filled through silicon via during and after thermal annealing

Copper (Cu)-filled through silicon (Si) via (CF-TSV) acts as an electrical conduit between different layers of circuitry in the advanced microelectronic devices. Due to wide difference in the coefficient of thermal expansion between Cu and Si, large thermal stresses get generated in both Si and Cu during the inevitable thermal excursions taking place during fabrication of microelectronic devices and their regular operation. This study examines the fracture of Si wafer in a CF-TSV due to annealing over the temperature range of 250–550 °C and the post-annealing natural ageing. Nucleation of micro-cracks in Si in the vicinity of the Cu pillars were observed, which propagated at a constant velocity during post-annealing room temperature ageing, thereby substantiating delayed fracture in Si. Microstructural examination revealed that the micro-cracks nucleated as a result of formation of a Cu-Si compound during annealing, whereas the crack propagated due to the oxidation of Si at the crack tip. Consistently, the micro-cracks did not propagate when the sample was stored in high vacuum. Furthermore, Raman spectroscopy and finite element method were used to gain insights into stress generation due to Cu-Si reaction, and nucleation and propagation of the crack.

Scale characterisation of an oxidised (Hf,Ti)C-SiC ultra-high temperature ceramic matrix composite

A hybrid carbide ultra-high temperature ceramics matrix [(Hf,Ti)C-SiC] reinforced with BN-coated carbon fibres was fabricated and tested for surface oxidation resistance. The UHTC composite showed an average mass ablation rate of 0.0014 g/s after exposure to a high heat flux (∼17 MW/cm2) oxyacetylene flame test for 30 s above 2500 °C. The cross-sectional profile of the oxides scale formed was characterised and analysed. The scale was multicomponent; consisting of oxides of Hf, Ti and Si, as well as HfTiO4 and HfSiO4, which underwent phase separation and immiscibility. Multiple glassy bubbles formed on the scale surface due to the impediment of escaping gases by the glassy layer on the outer scale. The largest pores in the scale and surface bubbles that resisted rupture were the dominant features of the outermost phase-separated layer. Phase separation in the scale top layer improves the resistance to scale rupture.

Crack healing in the SiC–SiC ceramic matrix composites fabricated with different process

In this study, crack healing in a SiC–SiC ceramic matrix composite (CMC) was investigated. As a gas turbine often operates at a high temperature above 1350 °C and is frequently cooled to room temperature, small cracks that form in the interior of a hot gas component propagate to the surface of the component. Owing to a mechanical constraint condition and dynamic vibrations, stress concentration occurs at the cracks, which grow and eventually reduce the service life of the turbine component. Self-healing technology has been used to solve this problem. We studied the crack-healing behavior of plate-type SiC–SiC CMC samples prepared by liquid melt infiltration (LMI) and cylindrical SiC–SiC CMC samples produced by chemical vapor infiltration (CVI) in an experiment. First, a crack was deliberately formed on the surface of the samples through indentation. Subsequently, the sample was subjected to heat treatment, in which the crack-healing temperature and the healing time were controlled. The crack-healing regions on the surface of the samples were observed using a scanning electron microscope, and the composition of the crack-healing region was analyzed by energy-dispersive spectrometry. While the cracks in the SiC–SiC CMC samples prepared by CVI were healed at 1500 °C, those in the SiC–SiC CMC samples produced by LMI were healed at a lower temperature, 1400 °C, because of the oxidation of residual Si. The four-point bending test was performed at room temperature and a high temperature (1200 °C) on the SiC–SiC CMC samples prepared by LMI, and it confirmed the healing in the samples.

Effect of oxygen content on the reaction course and radiation performance of Si/MTV system

Large numbers of studies show that silicon (Si) will not be oxidized into silicon fluoride (SiF4) and silicon oxide (SiO2) in the MSiTV (Magnesium Silicon Teflon Viton) system, which causes a waste of energy. The limited efforts in this paper focused on adding the oxidant barium nitrate (Ba(NO3)2) to the MSiTV pyrotechnics to study the oxidation reaction course and the effect of oxygen content on the radiation combustion performance. The infrared radiation of the agent during the combustion process is tested with a Spectraline SC7000 imaging spectrometer, and the combustion performance such as the burning area and radiation temperature is tested by the SC7000 thermal imager. The solid combustion products of the medicament are collected in a vacuum box combustion experiment and tested by infrared spectroscopy for their combustion products. Assumed that the amount of oxygen in the air participating in the reaction is constant. Then the oxygen difference theory (The calculation method is listed at the end of 3.1) can be used to calculate the hypoxia degree of the pyrotechnics and simply predict the oxidation reaction history. The experimental results show that the oxidation sequence of MSiTV compositions can be divided into 3 steps with the increase of oxidant content. The first step is to oxidize the incompletely reacted Magnesium (mg) to Magnesium Oxide (MgO). The radiation performance changes little during this process for the reaction release a lot energy and make up for the mass loss of MTV. The second step is the carbon ash oxidized to generate CO which greatly reduce the emissivity of the agent. The near-infrared radiation (NIR) spectral energies was reduced by up to 33% from 724.2 J/g*sr to 484.8 J/g*sr and the mid-infrared radiation (MIR) spectral energies reduced by up to 27% from 298.0 to 218.6 J/g*sr. The third step is the simultaneous oxidation of Si to SiO2 and Carbon monoxide (CO) to (carbon dioxide) CO2 by excess oxygen. The NIR intensity gradually decreases from 484.8 J/g*sr to 232.3 J/g*sr and the MIR spectral energies decreases from 218.6 J/g*sr to 122.3 J/g*sr for the reduction of MTV content even though the oxidation of Si released much heat. The far-infrared radiation (FIR) spectral energies of the pyrotechnics increased from 29.2 W/Sr to 59.9 W/Sr, an increase of 105% owing to the strong emissivity of Si in FIR. At this moment, the near-middle-far infrared ratio changed from 2.4: 1: 0.15 of MTV to 1.9: 1: 0.5.

Scalable Synthesis of Hollow β-SiC/Si Anodes via Selective Thermal Oxidation for Lithium-Ion Batteries.

Silicon for anodes in lithium-ion batteries has received much attention owing to its superior specific capacity. There has been a rapid increase of research related to void engineering to address the silicon failure mechanism stemming from the massive volume change during (dis)charging in the past decade. Nevertheless, conventional synthetic methods require complex synthetic procedures and toxic reagents to form a void space, so they have an obvious limitation to reach practical application. Here, we introduce SiCx consisting of nanocrystallite Si embedded in the inactive matrix of β-SiC to fabricate various types of void structures using thermal etching with a scalable one-pot CVD method. The structural features of SiCx make the carbonaceous template possible to be etched selectively without Si oxidation at high temperature with an air atmosphere. Furthermore, bottom-up gas phase synthesis of SiCx ensures atomically identical structural features (e.g., homogeneously distributed Si and β-SiC) regardless of different types of sacrificial templates. For these reasons, various types of SiCx hollow structures having shells, tubes, and sheets can be synthesized by simply employing different morphologies of the carbon template. As a result, the morphological effect of different hollow structures can be deeply investigated as well as the free volume effect originating from void engineering from both a electrochemical and computational point of view. In terms of selective thermal oxidation, the SiCx hollow shell achieves a much higher initial Coulombic efficiency (>89%) than that of the Si hollow shell (65%) because of its nonoxidative property originating from structural characteristics of SiCx during thermal etching. Moreover, the findings based on the clearly observed different electrochemical features between half-cell and full-cell configuration give insight into further Si anode research.

Design and formation of SiC (0001)/SiO2 interfaces via Si deposition followed by low-temperature oxidation and high-temperature nitridation

We report an effective approach to reduce defects at a SiC/SiO2 interface. Since oxidation of SiC may inevitably lead to defect creation, the idea is to form the interface without oxidizing SiC. Our method consists of four steps: (i) H2 etching of SiC, (ii) Si deposition, (iii) low-temperature (∼750 °C) oxidation of Si to form SiO2, and (iv) high-temperature (∼1600 °C) N2 annealing to introduce nitrogen atoms. The interface state density estimated by a high (1 MHz)–low method is in the order of 1010 cm−2 eV−1, two orders of magnitude lower than that of an interface formed by SiC oxidation.

Enhancement of surface properties of austenitic stainless steel by nickel based alloy cladding developed using microwave energy technique

In the present work, microwave cladding was carried out as a processing method for enhancement of surface properties of Chromium-austenitic stainless-steel (SS-321). Cladding of Nickel based alloy powder of approximately 0.2 mm thickness was developed on SS-321 substrate. Microstructural characterization was done on the developed clad cross sections using Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Spectroscope (EDS) and X-Ray Diffraction (XRD) analysis. It revealed good metallurgical bonding of clad layer and substrate by inter diffusion of the constituent elements. From microhardness testing, it was found average microhardness of the clad region as 458 HV and 234 HV in substrate region. Sliding wear test revealed significant wear resistance of clad surfaces compared to unclad surfaces. From cyclic oxidation test, it was observed that the oxide growth in clad samples was less and stable compared to unclad surfaces by thermogravimetric studies. Cladding of substrate surfaces lead to formation of a compound containing chromium, cobalt and silicon due to which formation of transient Ni oxides was inhibited and protective Cr, Co and Si oxides were formed. These oxides avoided diffusion of oxygen into inner layers of clad region and keeping it away from deterioration due to oxidation at 750 °C.

Upcycling of Fe-bearing sludge: preparation of erdite-bearing particles for treating pharmaceutical manufacture wastewater

Groundwater treatment sludge is a type of solid waste with 9.0–28.9% wt.% Fe content and is precipitated in large quantity from backwash wastewater in groundwater treatment. The sludge is mainly composed of fine particles containing Fe, Si and Al oxides, such as ferrihydrite, quartz and boehmite. The Fe oxides mostly originate from the oxidation of ferrous Fe in groundwater, whilst the silicate/aluminium compounds mainly originate from the broken quartz sand filter in the backwash step. In general, the sludge is firstly coagulated, dewatered by filter pressing and finally undergoes harmless solidification before it is sent to landfills. However, this process is costly (approximately US$66.1/t) and complicated. In this study, groundwater treatment sludge was effectively recycled to prepare novel erdite-bearing particles via a one-step hydrothermal method by adding only Na2S·9H2O. After hydrothermal treatment, the quartz and boehmite of the sludge were dissolved and recrystallised to sodalite, whilst ferrihydrite was converted to an erdite nanorod at 160 °C and a hematite at 240 °C. SP160 was prepared as fine nanorod particles with 200 nm diameter and 2–5 μm length at a hydrothermal temperature of 160 °C. Nearly 100% OTC and its derivatives in pharmaceutical manufacture wastewater were removed by adding 0.1 g SP160. The major mechanism for the removal was the spontaneous hydrolysis of erdite in SP160 to generate Fe oxyhydroxide and use many hydroxyl groups for coordinating OTC and its derivatives. This study presents a novel method for the resource reutilisation of waste groundwater treatment sludge and reports efficient erdite-bearing particles for pharmaceutical manufacture wastewater treatment.

Reactive molecular dynamics on the oxidation of passivated H-terminated Si (111) surface: 1-Alkynes vs 1-Alkenes

In this paper, we employed a series of ReaxFF molecular dynamics simulations to study the oxidation of different passivated Si (111) surface, which terminated by 1-Alkynes and 1-Alkenes. Research suggests that the Si substrate was oxidized by the peroxy-like structures (H2O2) during the process. We found that the organic monolayers on the Si surface will make the surface more passivated than the full H-Si surface. In addition, There is higher oxygen consumption in alkenes than the alkynes system. The alkynes system retained more Si-H bonds than alkenes system. And we found more SiOSi and SiOH bonds in the alkenes system rather than the alkynes system. Moreover, simulation results indicate that the O2 molecule is more difficult to pass through the alkynes than alkenes monolayers, which is why better passivation could be reached in alkynes system rather than the alkenes system. This study present atomistic insight into the oxidation of different passivated H-terminated Si (111) Surface, which is helpful to optimize the manufacturing process of the semiconductor devices.

Porous SiO composite tailored by scalable mechanochemical oxidation of Si for Li-ion anodes

In this study, we propose a simple strategy for the mass-production of a porous SiO material as an anode material for rechargeable Li-ion batteries. The porous SiO composite was prepared by mechanochemically oxidizing inexpensive Si powder while simultaneously reducing ZnO powder using a high-energy ball milling process. The resulting Zn of the SiO/Zn composite was chemically removed by acid-aided etching. Both micro- and nano-sized Si powders were used as a starting material to compare their final microstructure and electrochemical properties. X-ray diffraction and X-ray photoelectron spectroscopy were employed to confirm the mechanochemical synthesis of the SiO materials. Electron microscopy analyses with elemental mapping demonstrated that the SiO composite had a Si nanocrystallite embedding microstructure in an amorphous silicon suboxide matrix with highly abundant inside mesopores. The porous SiO composite electrode exhibited improved electrochemical properties over a commercially available SiO electrode because of its microstructure modification. Also, the effects of the starting Si powder's particle size on the resulting microstructure and electrochemical properties were thoroughly investigated with the abovementioned material and electrochemical characterization tools.

Two-dimensional, P-doped Si/SiOx alternating veneer-like microparticles for high-capacity lithium-ion battery composite

Si is a promising candidate for next-generation anode materials in lithium rechargeable batteries as it has a high theoretical specific capacity. However, mechanical damage due to volume changes during electrochemical cycling and low electrical conductivity are critical limitations for practical anode applications. Herein, a novel microscale 2D active material with alternating layers of Si and silicon oxide is developed, and its energy storage properties are investigated by fabricating a composite anode with conventional graphite. The composite anode shows improved specific capacity by the introduction of veneer-shaped Si microparticles and 88% capacity retention after 200 charge–discharge cycles. The adequate thickness of the layers and the repeating buffering layer existence in the high aspect-ratio microscale particles that mimic a 2D nanostructure minimized the volume changes of the Si-based electrode during cycling while achieving high electrical conductivity. This strategy can provide fundamental breakthroughs in overcoming the existing limitations of Si-based materials for the development of high-energy-density active materials for Li batteries.

Erratum to “Reparametrization-Invariant Reaction–Diffusion Equation as the Model of the Thermal Oxidation of Si” [J. Phys. Soc. Jpn. 89, 064601 (2020)

Erratum to “Reparametrization-Invariant Reaction–Diffusion Equation as the Model of the Thermal Oxidation of Si” [J. Phys. Soc. Jpn. 89, 064601 (2020)

An initial screening of commercial phosphorus ligands on the recovery of metal ions from red mud

Abstract The manufacturing of alumina from bauxite through the Bayer process generates a large amount of highly alkaline waste called bauxite residue or “Red mud”. The annual generation of bauxite residue throughout the world is around 120 million tons and 2.7 billion tons of it has already been stockpiled. Methods for large scale remediation of red mud are an active area of interest around the world. One of the prime challenges to overcome is to ensure that the remediation process is economically feasible. Red mud is a potential source for various metal oxides (oxides of Al, Fe, Ti, Si, Ca, Na and Mg) and many valuable metal ions (including rare earth and transition metals). Out of the mixture of metal ions rare earth (RE) elements are the most economically and strategically important component. The remediation process can be made economical if the rare earth portion of the mixture can be effectively separated into a product. An economically viable process was developed by the authors for the recovery of scandium as Sc2O3 from Jamaican red mud. Even though the developed process was profitable, since the amount of scandium is too low in the red mud the process couldn’t resolve the remediation in terms of large volume waste management. Herein we are reporting an initial study conducted to develop a solvent extraction method for the selective recovery of the large volume elements as well as the critically important rare earth elements by using commercially available phosphorus ligands from simulated waste liquor.

Low thermal budget high-k/metal surface gate for buried donor-based devices

Atomic precision advanced manufacturing (APAM) offers creation of donor devices in an atomically thin layer doped beyond the solid solubility limit, enabling unique device physics. This presents an opportunity to use APAM as a pathfinding platform to investigate digital electronics at the atomic limit. Scaling to smaller transistors is increasingly difficult and expensive, necessitating the investigation of alternative fabrication paths that extend to the atomic scale. APAM donor devices can be created using a scanning tunneling microscope (STM). However, these devices are not currently compatible with industry standard fabrication processes. There exists a tradeoff between low thermal budget (LT) processes to limit dopant diffusion and high thermal budget (HT) processes to grow defect-free layers of epitaxial Si and gate oxide. To this end, we have developed an LT epitaxial Si cap and LT deposited Al2O3 gate oxide integrated with an atomically precise single-electron transistor (SET) that we use as an electrometer to characterize the quality of the gate stack. The surface-gated SET exhibits the expected Coulomb blockade behavior. However, the gate’s leverage over the SET is limited by defects in the layers above the SET, including interfaces between the Si and oxide, and structural and chemical defects in the Si cap. We propose a more sophisticated gate stack and process flow that is predicted to improve performance in future atomic precision devices.

Reparametrization-Invariant Reaction–Diffusion Equation as the Model of the Thermal Oxidation of Si

The thermal oxidation of Si with a planar interface in the dry oxidation condition is studied by constructing a continuum model based on a reparametrization-invariant reaction–diffusion equation. B...

Study on Lapping Paste of 6H–SiC Single-Crystal Substrate in Tribochemical Mechanical Lapping

To improve the efficiency and surface quality in tribochemical mechanical lapping of 6H–SiC single-crystal substrate, the effects of oxidant type, content and abrasive size on the material removal rate (MRR) and surface roughness were studied in this paper. The results show that different oxidants have their maximum of material removal rate at their respective optimum content, namely 1768 nm/min for 10% wt sodium hydroxide, 1382 nm/min for 5% wt potassium permanganate and 1271 nm/min for 5% wt dichromium trioxide, respectively. However, the types and contents of oxidants have little effect on the surface roughness of SiC after lapping. Therefore, 10% wt NaOH was chosen as the oxidant of tribochemical mechanical lapping paste for lapping 6H–SiC single-crystal substrate. The abrasive size had a great influence on the material removal rate in lapping 6H–SiC single-crystal substrate. When the abrasive size is 28 µm in diameter, the material removal rate reaches the maximum value, but the surface roughness also is the maximum value after lapping. Then, the composition of optimized lapping paste was obtained. Research results show that the larger the abrasive using in lapping paste is, the larger the MRR and surface roughness are in certain range. The tribochemical reactions on the surface of SiC will occur and oxides of SiO2 or Si(OH)4 or Na2SiO3 or the compound of SiO2, Na2SiO3 and Si(OH)4 produced on the surface of SiC will be removed by the abrasives.

Robust hydrogen generation over layered crystalline silicon materials via integrated H2 evolution routes

Hydrogen generation is the initial challenge in utilization of hydrogen energy. In this work, robust hydrogen generation with a high yield of 53,930 μmol g−1 is demonstrated over layered crystalline silicon material derived from topochemical reaction from CaSi2. The physicochemical properties of the resultant layered crystalline Si material before and after H2 generation are investigated in detail to illustrate the H2 generation mechanism. Integrated H2 evolution routes, including destruction of Si–H bonds, oxidation of Si–Si bonds (hydrolysis of Si) and photocatalytic splitting water, are revealed to be responsible for the robust H2 generation. This work delivers a facile route to synthesize layered crystalline Si material with promising H2 generation performance and gives a deeply insight into the H2 evolution mechanisms of Si-based materials.

Effect of different reduction rates on the near-interfacial structure of pressed 304/Q235 composite plate

The 304 stainless steel/Q235 composite plate was pressed at 1200 °C using a 500-ton hydraulic testing machine at a reduction rate of 25%, 30%, 35%, and 40% respectively. The microstructure of the composite plate was analyzed by means of scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results showed that the black matter at the interface was the oxide of Mn and Si, and during the compression deformation process, the partial oxide film and the linear inclusions were crushed and extruded into fine particles. Small grains of different sizes appeared on the composite interface, and this deformation made the Q235 carbon steel and the 304 stainless steel on both sides of the composite interface show a coordinated deformation tendency when the reduction rate reached 35%. The whole process showed that the deformed carbon steel was first deformed, and the hard-to-deform stainless steel began to be deformed at a certain point, and then they were both further deformed together.

Synchrotron radiation photoelectron spectroscopy study on oxides formed at Ge(100)2 × 1 surface in atmosphere

Synchrotron radiation photoelectron spectroscopy was applied to conduct chemical analysis of Ge oxides formed at the Ge(100)2 × 1 surface in atmosphere at room temperature. High energy-resolution Ge 3d core-level spectra showed that the ambient-exposed Ge(100) surface has oxidation states with 4+ charge state at maximum, which is in strong contrast to in situ studies on pressure-controlled Ge oxidation in vacuum using pure O2 gas. Adsorbed oxygen amount is considerably lower than that observed for the O2-pressure controlled oxidation of Si(111)7 × 7 surface at saturation. The oxidation of Ge(100) surface proceeds slowly even in atmosphere, indicating that reactivity of Ge surface seems to be low against oxidation in the air. The O 1s spectra after keeping in the air exhibit the (−OH) (hydroxyl group) component, deducing that the water molecule from the ambient humidity likely promotes the oxidation, where oxides may have different chemical configurations from that formed by using O2 gas in vacuum. Our findings will contribute to the basic understanding of oxidation mechanisms and stability of oxides at Ge(100)2 × 1 surface in the air.