Grade Silicon Carbide Research Articles

Recycling coal overburden waste to fabricate functionally graded SiC foam with gradient microstructure via one step thermo-foaming process

An economical and efficient thermo-foaming method, coupled with an in-situ reaction bonding technique, was employed to produce mullite-bonded functionally graded silicon carbide (SiC) foams with gradient microstructures using coal mine overburden waste (CMW). The foaming process utilized sucrose dehydration with sulphuric acid, allowing for tailored porosity in SiC foams. Mullite bonding material was in situ developed during sintering, facilitated by silica and alumina from CMW, promoting mullite phase formation. Alumina incorporation further enhanced mullitization. The use of CMW as a low-cost precursor for mullite conversion facilitated SiC particle bonding through mullite, reducing sintering temperature and overall production cost. Varied sucrose content and sintering temperature influenced foaming behavior, porosity, microstructural gradient, and mechanical properties. Mullitization process, reaction bonding behavior, and mechanical properties were analyzed based on CMW and alumina content, and sintering temperature. The resulting SiC foams exhibited bulk density and porosity in the range of 0.6–1.2 g/cm3, 60–80 % respectively. This study introduces an eco-friendly approach for repurposing CMW waste and cost reduction in SiC foam manufacturing.

Grinding of silicon carbide for optical surface fabrication. Part II. Subsurface damage.

This paper is the second part of a study of the grinding of three different grades of silicon carbide (SiC) under the same conditions. In this paper, subsurface damage is analyzed using magnetorheological finishing (MRF). The MRF ribbon is brought into contact with the surface and allowed to dwell for different lengths of time to produce dimples or spots at different depths. The roughness parameters are evaluated at the base of the spots. As the spot depth increases the roughness parameters decrease, eventually saturating at a steady-state value. The depth at which saturation occurs is much greater than the initial peak-to-value roughness of the surface and is therefore assumed to be correlated to the depth of subsurface damage in the material. Estimates of the damage depth are comparable to other estimates given in the literature. The validity of this technique is assessed across different grades of SiC under different grinding conditions, and limitations are identified. The study shows that the microstructure of the SiC grade is a major factor that affects the validity of the technique. The technique is suitable for SiC grades that have a more homogeneous microstructure such as chemical vapor deposited or chemical vapor composite grades. The presence of porosity as in the direct sintered grade, or the presence of a secondary phase, for example, silicon in the reaction-bonded and silicon-infiltrated grades, could hinder the technique from providing conclusive results.

High-Yield Deterministic Focused Ion Beam Implantation of Quantum Defects Enabled by In Situ Photoluminescence Feedback.

Focused ion beam implantation is ideally suited for placing defect centers in wide bandgap semiconductors with nanometer spatial resolution. However, the fact that only a few percent of implanted defects can be activated to become efficient single photon emitters prevents this powerful capability to reach its full potential in photonic/electronic integration of quantum defects. Here an industry adaptive scalable technique is demonstrated to deterministically create single defects in commercial grade silicon carbide by performing repeated low ion number implantation and in situ photoluminescence evaluation after each round of implantation. An array of 9 single defects in 13 targeted locations is successfully created-a ≈70% yield which is more than an order of magnitude higher than achieved in a typical single pass ion implantation. The remaining emitters exhibit non-classical photon emission statistics corresponding to the existence of at most two emitters. This approach can be further integrated with other advanced techniques such as in situ annealing and cryogenic operations to extend to other material platforms for various quantum information technologies.

Grinding of silicon carbide for optical surface fabrication, Part 1: surface analysis.

This paper presents a study of the grinding of three different grades of silicon carbide (SiC) under the same conditions. Surface topography is analyzed using coherent scanning interferometry and scanning electron microscopy. The study provides a baseline understanding of the process mechanics and targets effective selection of process parameters for grinding SiC optics with near optical level surface roughness, thus reducing the need for post-polishing. Samples are raster and spiral ground on conventional precision machines with metal and copper-resin bonded wheels under rough, medium, and finish grinding conditions. Material microstructure and grinding conditions affect attainable surface roughness. Local surface roughness of less than 3 nm RMS was attained in both chemical vapor deposition (CVD) and chemical vapor composite (CVC) SiC. The tool footprint is suitable for sub-aperture machining of a large freeform optics possibly without the need for surface finish correction by post-polishing. Subsurface damage will be assessed in Part 2 of this paper series.

Determination of neutron irradiation temperatures of SiC using electrical resistivity method

The irradiation temperature of silicon carbide (SiC) was determined post-irradiation by examination of the recovery of the electrical resistivity due to thermal annealing in a rapid heating/cooling optical furnace. High-purity, high-resistivity grade SiC is routinely used as a passive temperature monitor in neutron irradiation studies at the High Flux Isotope Reactor (HFIR), and this paper presents an alternative automated technique for determination of the irradiation temperature the SiC experienced. Neutron collisions with the atoms results in displaced lattice atoms (interstitials) that act as electron donors yielding a significant decrease in electrical resistivity. The irradiation defects become thermodynamically unstable and start to recombine, when annealed above the irradiation temperature, resulting in a recovery of the electrical resistivity. The resistivity is measured at a fixed elevated temperature above ambient, which is below the target irradiation temperature. When the resistivity is plotted as a function of annealing temperatures, a clear increase is observed due to the recovery of irradiation defects. We have demonstrated that this electrical resistivity measurement of SiC is effective to determine irradiation temperature of SiC. Energy levels of various defects in SiC were calculated from Arrhenius plots of electrical conductivity versus inverse temperature.

Crystal structures and the electronic properties of silicon-rich silicon carbide materials by first principle calculations

Silicon carbide has been used in a variety of applications including solar cells due to its high stability. The high bandgap of pristine SiC, necessitates nonstoichiometric silicon carbide materials to be considered to tune the band gap for efficient solar light absorptions. In this regards, thermodynamically stable Si-rich SixC1-x materials can be used in solar cell applications without requiring the expensive pure grade silicon or pure grade silicon carbide. In this work, we have used density functional theory (DFT) to examine the stability of various polymorphs of silicon carbide such as 2H–SiC, 4H–SiC, 6H–SiC, 8H–SiC, 10H–SiC, wurtzite, naquite, and diamond structures to produce stable structures of Si-rich SixC1-x. We have systematically replaced the carbon atoms by silicon to lower the band gap and found that the configurations of these excess silicon atoms play a significant role in the stability of Si-rich SixC1-x. Hence, we have investigated different configurations of silicon and carbon atoms in these silicon carbide structures to obtain suitable SixC1-x materials with tailored band gaps. The results indicate that 6H-SixC1-x is thermodynamically the most favorable structure within the scope of this study. In addition, Si substitution for C sites in 6H–SiC enhances the solar absorption, as well as shifts the absorption spectra toward the lower photon energy region. In addition, in the visible range the absorption coefficients are much higher than the pristine SiC.

Design and synthesis of foam glasses from recycled materials

AbstractRecycling has emerged as an environmental key point due to the diminishing of natural resources and the generation of ever‐increasing amounts of industrial solid wastes. Glass wastes are among the materials that attract great interest in the recycling concept. This work presents the results of foams production from four series of compositions. The first series comprises powders of a sodium‐calcium‐silicate sheet glass cullet as the main component, an alkali‐earth aluminosilicate glass as an additive, and a reagent grade silicon carbide (SiC) powder as gassing agent. In the second series, the glass cullet was used in combination with fly ashes (FLA) as main components, while SiC waste from abrasive paper served as foaming agent. In the third and fourth series, carbonates (calcite and dolomite) were used for foaming powder mixtures composed of sheet glass cullet and FLA, and powdered cathode ray tube panel glasses, respectively. All the processing parameters, including the main components, the nature and content of foaming agents are shown to play a crucial role on the foaming ability and final properties of the glass foams.

Impact of short-term aging temperatures of asphalt binder and aggregate roughness levels on bond strength

In the field, roughness of aggregates varies during production process due to abrasion, stripping and ravelling, which influences its bonding potential with asphalt binder. However, no study relating aggregate roughness levels and bond strength of aggregate-binder system was conducted. In addition, change in short-term aging temperature of asphalt binder during production processes may affect aggregate-binder bond. Therefore, present study evaluates effects of aggregate roughness and short-term aging temperature of binder on bond strength based on surface free energy (SFE) and asphalt bond strength (ABS) test approaches. For the purpose of the study, basalt aggregate was polished using 220, 400, 600 and 800 grade silicon carbide (SiC) powders and their roughness values were measured using zeta-profiler. Also, AC30 binder was short-term aged using rolling thin-film oven (RTFO) at temperatures 143 °C, 163 °C and 173 °C. Bond strength was evaluated using energy ratio (ER) and bond strength ratio (BSR) parameters, obtained from SFE and ABS approaches, respectively. Bond strength of aggregates having different roughness values was evaluated with standard short-term aged binder (163 °C for 85 min) whereas, bond strength of binder aged at different temperatures were evaluated with 220SiC polished aggregate. The present study also validates use of 280SiC polished aggregates as recommended by AASHTO T-361, by examining relationship between aggregate roughness and BSR. Results showed that bond strength increases with increase in aggregate roughness and short-term aging temperature of binder. Further, one-way ANOVA and Post-Hoc test showed significant effect of aggregate roughness and binder aging levels on aggregate-binder bond strength. Markedly, linear correlation was observed between ER and BSR with aggregate roughness and binder short-term aging conditions.

Stability and Electronic Properties of Silicon-Rich Silicon Carbide Structures

The high stability of silicon carbide make it an attractive materials to be used in different applications such as solar cells. Silicon-rich silicon carbide (Si-rich SiC) materials are necessary to tune the band gap for efficient solar light absorptions. Si-rich SiC materials which are thermodynamically stable can be used in solar cell applications without requiring the expensive pure grade silicon or pure grade silicon carbide. Density functional theory (DFT) calculations were used in order to examine different phases of Si-rich SiC to predict stable structures. Since the configurations play a significant role in getting stable results, different configurations of silicon and carbon atoms in Si-rich SiC were considered. The electronic structures were studied, and the total energies were calculated as well as the formation energies. We will present that higher-order hexagonal-phases are more favorable structures than other Si-rich SiC structures due to their more covalent nature of bonding compared to the cubic counterpart.

C-ring testing of nuclear grade silicon carbide composites at temperatures up to 1900 °C

Silicon carbide matrix reinforced with silicon carbide fiber (SiC-SiC) composite is an advantageous material for many high temperature applications due to retention of room temperature strength above 1100 °C, which is the current operational limit for many high temperature metals. For the nuclear industry, this property, along with excellent radiation tolerance, has made SiC-SiC an attractive cladding material for the accident tolerant fuel program. The mechanical strength at high temperatures of these composites needs to be evaluated to address improvements in the third generation of Nicalon fibers, fabrication processes, as well as tested in a form-factor relevant to fuel cladding. In this work, mechanical strength of SiGA™ composite tubes, a SiC-SiC composite fabricated at General Atomics using the current generation of Hi-Nicalon Type S SiC fiber and chemical vapor infiltration processing (CVI) of the matrix, was evaluated at temperatures up to 1100 °C in ambient air and ∼1900 °C in an inert gas environment with nominal 30–60 min dwell time. The results of this study show full retention of room temperature strength at both test regimes. Some degradation of material toughness was observed at temperatures above ∼1760 °C. During this study, effects of interphase, fiber, and matrix morphological changes as a function of temperature were investigated.

Strength of SiCf-SiCm composite tube under uniaxial and multiaxial loading

The authors report mechanical strength of nuclear grade silicon carbide fiber reinforced silicon carbide matrix composite (SiCf-SiCm) tubing under several different stress states. The composite tubing was fabricated via a Chemical Vapor Infiltration (CVI) process, and is being evaluated for accident tolerant nuclear fuel cladding. Several experimental techniques were applied including uniaxial tension, elastomer insert burst test, open and closed end hydraulic bladder burst test, and torsion test. These tests provided critical stress and strain values at proportional limit and at ultimate failure points. Full field strain measurements using digital image correlation (DIC) were obtained in order to acquire quantitative information on localized deformation during application of stress. Based on the test results, a failure map was constructed for the SiCf-SiCm composites.

Dimensional stability and anisotropy of SiC and SiC-based composites in transition swelling regime

Swelling, or volumetric expansion, is an inevitable consequence of the atomic displacement damage in crystalline silicon carbide (SiC) caused by energetic neutron irradiation. Because of its steep temperature and dose dependence, understanding swelling is essential for designing SiC-based components for nuclear applications. In this study, swelling behaviors of monolithic CVD SiC and nuclear grade SiC fiber – SiC matrix (SiC/SiC) composites were accurately determined, supported by the irradiation temperature determination for individual samples, following neutron irradiation within the lower transition swelling temperature regime. Slightly anisotropic swelling behaviors were found for the SiC/SiC samples and attributed primarily to the combined effects of the pre-existing microcracking, fiber architecture, and specimen dimension. A semi-empirical model of SiC swelling was calibrated and presented. Finally, implications of the refined model to selected swelling-related issues for SiC-based nuclar reactor components are discussed.

Processing of Al2O3–SiCw–TiC ceramic composite by powder mixed electric discharge grinding

Abstract Background The machining of conductive alumina ceramic was successful by the electric discharge grinding (EDG). Therefore, the aim of the present work is to increase the material removal rate (MRR) during EDG of conductive alumina ceramic by addition of ceramic powder with dielectric. Methods To achieve the objective through experimental investigation is carried out and the influence of input process parameters (powder concentration, duty ratio, pulse on time, table speed and wheel speed) on surface roughness (SR), MRR and surface integrity has been studied. The fine grade silicon carbide powder of #1000 mesh sizes was mixed in dielectric medium with varying concentration to understand the influence of the powder concentration and its interaction with other process parameters during powder mixed electric discharge grinding (PMEDG). The central composite rotatable design (CCRD) has been used to plan the experiments. Optimization of the obtained statistical models of MRR and SR has been done to obtain highest MRR and lowest SR. Result It was observed that the MRR achieved by PMEDG was 3 – 10 times higher than EDG. It was found that all the process factors and interactions show significant contribution on SR. The SR obtained by PMEDG was 2 – 4 times higher than EDG. Conclusions It has been established that the PMEDG process is a better option for processing of Al2O3–SiCw–TiC ceramic material as preliminary operation before EDG to achieve high MRR. In the present work the surface and subsurface damages were also assessed and characterized by the scanning electron microscope (SEM).

Erosion Resistance and Interface Properties of Epoxy Composite Filled with Graded Silicon Carbide

In the present study, the effect of graded aggregate on the erosion resistance and interface performance of SiC/EP (epoxy resin) composite was investigated. The graded aggregate (84% 550μm and 16% 110 μm) SiC particles was designed by the modified coarse aggregate void filling approach from the theory of concrete. The erosion mechanism of obtained composite was discussed through the microstructure analysis. Obtained results from different erosion tests showed the graded structure contributed to increasing the hard spots and density, which significantly reduced erosion rate. The mechanical properties and wear fraction indicated that the preferred interface could be obtained using migration with KH-550.

Experimental study of thermo-mechanical behavior of SiC composite tubing under high temperature gradient using solid surrogate

Nuclear grade silicon carbide fiber (SiCf) reinforced silicon carbide matrix (SiCm) composite is a promising candidate material for accident tolerance fuel (ATF) cladding. A major challenge is ensuring the mechanical robustness of the ceramic cladding under accident conditions. In this work the high temperature mechanical response of a SiCf–SiCm composite tubing is studied using a novel thermo-mechanical test method. A solid surrogate tube is placed within and bonded to the SiCf–SiCm sample tube using a ceramic adhesive. The bonded tube pair is heated from the center using a ceramic glower. During testing, the outer surface temperature of the SiC sample tube rises up to 1274 K, and a steep temperature gradient develops through the thickness of the tube pair. Due to CTE mismatch and the temperature gradient, the solid surrogate tube induces high tensile stress in the SiC sample. During testing, 3D digital image correlation (DIC) method is used to map the strains on the outer surface of the SiC-composite, and acoustic emissions (AE) are monitored to detect the onset and progress of material damage. The thermo-mechanical behavior of SiC-composite sample is compared with that of monolithic SiC samples. Finite element models are developed to estimate stress–strain distribution within the tube assembly. Model predicted surface strain matches the measured surface strain using the DIC method. AE activities indicated a progressive damage process for SiCf–SiCm composite samples. For the composites tested in this study, the threshold mechanical hoop strain for matrix micro-cracking to initiate in SiCf–SiCm sample is found to be ∼300 microstrain.

Brominated Chemistry for Chemical Vapor Deposition of Electronic Grade SiC

Chlorinated chemical vapor deposition (CVD) chemistry for growth of homoepitaxial layers of silicon carbide (SiC) has paved the way for very thick epitaxial layers in short deposition time as well as novel crystal growth processes for SiC. Here, we explore the possibility to use a brominated chemistry for SiC CVD by using HBr as additive to the standard SiC CVD precursors. We find that brominated chemistry leads to the same high material quality and control of material properties during deposition as chlorinated chemistry and that the growth rate is on average 10% higher for a brominated chemistry compared to chlorinated chemistry. Brominated and chlorinated SiC CVD also show very similar gas-phase chemistries in thermochemical modeling. This study thus argues that brominated chemistry is a strong alternative for SiC CVD because the deposition rate can be increased with preserved material quality. The thermochemical modeling also suggest that the currently used chemical mechanism for halogenated SiC CVD m...

The Influence of Reinforcement Purity on Corrosion Resistance of AM50/SiC Composites

The microstructure and corrosion behaviour of AM50/SiC magnesium matrix composites reinforced with SiC particles were investigated. Composites containing 10 wt. % of SiC were fabricated by means of gravity casting. Technical grade silicon carbide used for the composites fabrication was subjected to a purification procedure leading to the removal of iron containing impurities from its surface. The corrosion resistance of the composite with purified SiC particles was compared to the corrosion resistance of the one containing crude technical grade silicon carbide as well as to the corrosion resistance of the matrix alloy. Voltammetry and an electrochemical noise technique as well as hydrogen evolution rate measurements were utilized for that purpose. Corrosion tests were performed in 0.5 mol dm3 NaCl saturated with Mg (OH)2. It has been demonstrated that the composite containing purified SiC was less susceptible to corrosion than the one containing crude SiC particles. Both composites were less resistant to corrosion than their matrix itself. Regardless of a purity level of SiC which was used for the composites fabrication, the same constituents were revealed in their microstructure, namely: α-phase (a solid solution of aluminium in magnesium), fully divorced eutectic α + γ (where γ-phase is Al12Mg17), intermetallic compound Al8Mn5 and SiC particles uniformly distributed in the whole volume of the matrix.

Ceramic Composite Material Based on Silicon Carbide and Corundum with a Corundum Matrix

Results are provided for studying preparation and some properties of an abrasive composite material of the SiC–Al2O3 system with a corundum matrix. The material is prepared by adding molten aluminum to a charge used in existing manufacturing technology for commercial grade silicon carbide.

Mechanical and abrasive wear behavior of glass and basalt fabric‐reinforced epoxy composites

AbstractMultipass two‐body abrasive wear behavior of basalt and glass fabric‐reinforced epoxy composites have been carried out by using a pin‐on‐disc machine. Basalt and glass fabric‐reinforced epoxy composites have been fabricated by hand layup technique. The mechanical properties of basalt and glass fabric reinforced epoxy composites were evaluated. Abrasive wear performance was evaluated at ambient temperature using 400 grade Silicon Carbide paper as a counter face. The elemental compositions of fabricated composites were quantitatively analyzed by using energy dispersive X‐ray spectroscopy. The abrading wear mechanisms have also been studied by worn surface analysis using scanning electron microscopy. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Improved bonding of zirconia substructures to resin using a “glaze-on” technique

ObjectiveTo investigate the influence of applying thin intermediary coatings of acid-etchable glasses on the shear bond strength between a methacrylate resin based cement and an yttria-stabilized zirconia dental ceramic substrate. MethodsThe upper and lower surfaces of 110 sintered yttria-stabilised tetragonal zirconia polycrystalline disc-shaped specimens were polished using sequential grades of Silicon Carbide, then air-abraded with 25μm diameter alumina particles. Specimens were randomly allocated to 11 groups (A–K) (n=10), group A acting as control. The upper surface of Group A specimens was subjected to a tribochemical coating regime (CoJet, 3M ESPE). Five glazing ceramics were applied and fired according to the manufacturer's recommended firing regime. The glaze was etched with 10% HF acid and all specimens coated with a silane primer. Two differing storage regimes were employed (wet storage vs thermocycling). Shear bond strength testing specimens were created by cementing resin-based composite cylinders to the centre of the prepared ceramic surface using Rely-X Unicem (3M ESPE) resin based cement. Shear bond strength testing was performed and load at failure recorded. ResultsA factorial analysis of variance at a 95% significance level demonstrated that all glazing techniques resulted in a significant increase in the shear bond strength compared with using the resin based cement alone (P<0.01), with the different glazing ceramics resulting in significant differences in mean shear bond strength (P=0.008). The differences were a function of the storage state (wet storage vs thermocycling (P=0.013)). ConclusionThe glazing techniques used in the current investigation resulted in a significantly enhanced shear bond stress to the resin based cement when compared with the current ‘gold standard’ – tribochemical coating.