Including Silicon Carbide Research Articles

(Invited) Improving Interface Trap Analysis in Wide Band Gap MIS Structures

Modern power electronic technologies relevant to high power and fast switching applications are embracing wide bandgap (WBG) materials, including silicon carbide and gallium nitride (GaN), for their characteristically large breakdown electric field strengths and their comparatively high electron saturation velocities. However, WBG-based structures are known to exhibit unmitigated charge trapping due dangling bonds or impurities at or near the dielectric/semiconductor interface. Interface charge traps with energies near the band edge introduce threshold-voltage instabilities in metal-insulator-semiconductor (MIS) devices. Large densities of interface trap states and surface charges are also known to adversely alter the current response and channel transport dynamics in field effect transistor (FET) devices. Minimizing the density of these performance-degrading features, which are inherent to any MIS gate structure, remains a primary obstacle that prevents WBG-based technologies from realizing their theoretical potential in various application spaces.The complicated nuance of the numerous interface trap characterization techniques reported in literature have made comparing and communicating interface trap results in power electronics research a near-impossible task. As an example, the typical techniques used to characterize the density of interface states in silicon-based systems, such as the high-low method or the Terman method, are not suitable for WBG-based devices since they require unconventionally high probing frequencies to account for the fast trap states associated with WBG materials. Despite this readily proven fact, these techniques are still very popular in the WBG-based power electronics community, and an overwhelming majority of reported interface trap values are therefore unable to be thoughtfully discussed for the betterment of WBG-based technologies. Mitigating charge traps requires repeatable and physically accurate characterization techniques that follow a standard analysis protocol to correlate processing methods with device performance and reliability.Over the last decade, Sandia National Laboratories has made substantial contributions to the development of GaN power semiconductor devices and their characterization. In this talk, we will present recent work conducted at Sandia to develop a standardized procedure for determining interface trap state densities using quasi-static capacitance-voltage analysis in WBG-MIS-capacitor structures that produces repeatable and relatable results. Quasi-static methods that do not require frequency-based capacitance measurements, such as the - technique, have been suggested as a viable solution for determining the interface trap state densities in WBG systems. However, the results produced by the - technique are shown to be susceptible to errors in the analysis procedure and these errors were investigated in detail. These sources of error will be discussed, and we will present new strategies to greatly improve the accuracy of interface trap analysis measurements, including novel techniques to (1) calibrate the surface potential/gate voltage relationship and (2) measure the energy-dependence of capture cross sections. This collection of work greatly simplifies the interface trap analysis procedure and offers a solution to the present obstacle of reporting and comparing interface trap distributions in WBG-MIS structures. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Design of an optimized nuclear fuel pellet

Background The design of an improved nuclear fuel pellet for use in the Westinghouse AP1000 reactor that is more powerful than existing pellets, is less expensive to manufacture, and meets Nuclear Regulatory Commission requirements for certification was undertaken to complete a senior design course in the ABET-certified nuclear engineering curriculum of Rensselaer Polytechnic Institute, Troy, NY. Methods The modeling team selected the Monte Carlo N-Particle (MCNP) program for assessing how well the pellet design achieves a k-effective value of 1, designed the base model consisting of a fuel pin inside a boron-water moderator with reflector, and ran MCNP tests on the base pellet. The design team modified the base pellet and tested it at different uranium-235 enrichments, with void spheres of varying volume and silicon carbide inclusions in the void volume. The simulation team selected K-code for testing the fuel pellets. The economics team analyzed the cost of manufacturing the improved pellet from cost of raw material through its tail assay in the form of Separative Work Unit (SWUs). The impacts team researched environmental, societal, governmental, political, and public affairs aspects of nuclear fuel production. Results Multiple configurations of uranium enrichment and silicon carbide volume inclusions in the nuclear fuel pellet achieved a k eff of 1, and the price per pellet, assuming fabrication costs comparable to existing manufacturing processes, was reduced by as much as about 50% when the volume of uranium oxide replaced by silicon carbide is 0.27 cm3. At smaller replacement volumes, the price per pellet is reduced by as little as 5%. Conclusions The goal of designing an optimized fuel pellet was met. Replacing a 0.27 cm3-volume sphere of uranium oxide with silicon carbide from the center of a pellet of 4%, 5%, or 6% uranium-235 enrichment reduced the cost of the pellet by approximately 50%.

Green metal matrix composites: a multi-faceted study on Al alloy composites with egg shell powder and silicon carbide as reinforcements

This article is about Green Metal Matrix Composites (GMMCs) produced with aluminum alloys and reinforcements include silicon carbide and eggshell powder. The GMMCs offer a new approach to sustainable materials through the use of ecofriendly reinforcements. A novel class of composites results from a combination of silicon carbide, which has superior mechanical properties, and agricultural waste based eggshell powder. Furthermore, eggshell powder mainly comprised of calcium carbonate lowers its density as well as serves as long-term reinforcement. Silicon carbide enhances their mechanical properties in terms of strength and hardness respectively. This report involves a systematic study using mechanical testing and scanning electron microscopy to explain microstructural evolution and evaluate performance during mechanical loading. Further, wear resistance gives indications on suitability for different industrial applications. Variations in reinforcement contents were done so as to include 3–12% silicon carbide, and 2–8% eggshell powders in the aluminum alloys. Production strictly adhered to guidelines that controlled some variables such as stirring speed and duration which was aimed at achieving exact control. These cast composites were subjected to wear tests, tensile tests, and hardness tests as well as microstructural analysis. EDS-SEM results demonstrate successful incorporation of the reinforcements into the hybrid composites. Unveiling a surprising evenness of distribution of reinforcements throughout the Aluminum matrix through Microstructural examination is amazing. Unique wear behavior trends are presented here. The matrix alloys show mainly adhesive wear while the composites display abrasive wear mediated by reinforcements. This research proposes an eco-friendly method for metal matrix composites, thus advancing sustainable materials and offering hope for strong yet lightweight green materials suitable for aerospace, automotive and other engineering sectors.

An investigation on the mechanical and corrosion characteristics of magnesium-zinc alloy nanocomposites manufactured via ultrasound-assisted stir squeeze casting

Magnesium alloy (Mg-Zn) was strengthened by including silicon carbide nanoparticles at different weight rates (0, 0.5, 1.0, and 1.5 wt%). The fabrication process involved the help of ultrasonication-assisted stir squeeze casting method. We studied the mechanical, microstructural, and corrosion quality of nanocomposites in relation to variations in SiC particle weight percentage and grain size. A comparison was made between the experimental results and the basic alloy. The findings show that nanocomposites’ mechanical characteristics improve as the SiC particle concentration rises and falls as the particle size increases. In accordance with the ASTM standard, immersion and potentiodynamic polarization tests were conducted to validate that the nanocomposites’ resistance to corrosion increased as the reinforcement weight percentage was increased. The optical microscope was used to observe the grain size. Nanoparticles are evenly distributed throughout the Mg matrix, as shown in scanning electron micrographs. XRD confirms that the nanocomposites include SiC. The nanocomposite reinforced with 1.5 wt% SiCP had 44% higher microhardness and 38% higher tensile strength than the base alloy.

Numerical investigation of magnetized nanofluid flow with thermal radiation and homogeneous/heterogeneous reactions over a vertical cylinder

Nanofluid flow has gained attention due to its promising applications in numerous industries. Nanofluids exhibit a significant advantage over conventional fluids due to their superior heat transfer capability, attributed to the presence of nanoparticles that enhance thermal conductivity, resulting in improved heat dissipation and efficiency. Current research aims to numerically investigate the impact of homogeneity and heterogeneity on the mixed convection flow of incompressible viscous nanofluids through a vertically permeable cylinder under suction/injection circumstances. The study also considers thermal radiation and heat source/sink phenomena. Ethylene glycol is utilized as base fluid, while nanoparticles include silicon carbide SiC and Titanium dioxide TiO2. The mathematical flow model, based on nonlinear partial differential equations (PDEs), is converted into ordinary differential equations (ODEs) by using suitable similarity transformations that pronounced nonlinear system of ODEs. To deal with this nonlinear system, the bvp4c and shooting methods are used in the commercial software MATLAB to solve these ODEs numerically. The impacts of flow parameters on various quantities of interest are elaborated graphically. From obtained results it is analyzed that velocity field boosts up versus higher values of nanoaprticle volume fraction. The velocity field is decreases with increasing the amount of magnetic field. An increase in the thermal field is observe with a rise in the thermal radiation parameter. The good agreement between current results and published work is noted.

SiC modified self‐healing ytterbium disilicate materials for potential environmental barrier coating application

AbstractEnvironmental barrier coatings (EBCs) are crucial to the reliability and durability of SiCf/SiC composite components seeking applications in hot sections of next‐generation advanced aero‐engines. The cracks initiated and developed in EBCs owing to various reasons during service greatly undermine their lifespans. To address this problem, in this work, silicon carbide (SiC) in the forms of particles and whiskers with various amounts have been introduced to ytterbium disilicate (Yb2Si2O7), the mainstream EBC topcoat materials, so as to gain some self‐healing potential. The results reveal that, the SiC inclusions in Yb2Si2O7 in the presence of ytterbium monosilicate (Yb2SiO5) can trigger the following reactions. Specifically, SiC self‐healing agents are oxidized to form viscous SiO2, which actively reacts with Yb2SiO5 upon encountering it, forming Yb2Si2O7. This has brought twofold beneficial effects including ① silicon supplementation of disilicate topcoat, whose silicon element tends to be “dragged out” by water vapor, leading to the deterioration of thermal mismatch; as well as ② crack self‐healing resulting from the volume expansion induced by the above reactions. Then the two aspects of self‐healing agents, namely the “promptness” and “sustainability,” have been discussed in detail. The former is unveiled to be more pertinent to the repairing of large cracks, whilst the latter is more relevant to the self‐healing of tiny cracks at initiation or early stage of propagation. The current work sheds some lights on the design and development of more durable and robust EBCs with self‐healing capability.

Non‐linear electrical conductivity of ethylene‐propylene‐diene monomer‐based composite dielectrics by tuning inorganic fillers

AbstractIn this study, three kinds of inorganic fillers are chosen and filled into ethylene‐propylene‐diene monomer (EPDM) matrix, including silicon carbide, copper calcium titanate (CCTO), and vanadium dioxide (VO2). The electrical properties of the three modified composites at different temperatures have been systematically studied. The intrinsic conductance behaviours of different inorganic fillers on the direct current conductance and electric breakdown strength of the composite dielectrics are also analysed, and the possible mechanism for non‐linear conductivity is revealed. The electrical conductivity increases with the increase of fillers content, where 30 wt.% CCTO/EPDM composite dielectric has a high non‐linear coefficient of 5.71. The increase in temperature can further increase the conductivity of the composites, accompanying a lower breakdown strength. When the temperature rises to 70°C, the VO2/EPDM composite has a higher conductivity, but the electric breakdown strength degrades seriously. The simulation results show that the composites with non‐linear electrical conductivity characteristics can effectively uniform the electric field and solve the problem of electric field concentration at the root of the stress cone, which is beneficial to improving the safe operation of the cable accessories.

Active Junction Temperature Control for SiC MOSFETs Based on a Resistor-Less Gate Driver

Junction temperature fluctuation is the main cause of failure of power devices including silicon carbide (SiC) MOSFETs, and active junction temperature control is an effective way to improve their reliability. Most existing methods of active junction temperature control rarely consider the system efficiency and the complexity of hardware implementation, which limits their applications. This article proposes an active junction temperature control method for SiC MOSFETs based on a resistor-less gate driver, which consists of two auxiliary MOSFETs with adjustable gate–source voltages. Hence, the switching loss of the SiC MOSFET can be continuously and accurately adjusted to mitigate the efficiency suffer with the junction temperature control. The power loss model of SiC MOSFETs with the proposed gate driver was established. The design principle of the junction temperature controller is introduced. The experimental results show that the junction temperature fluctuation is reduced by 24.1%, and that the lifetime of the SiC MOSFET is prolonged by 3.92 times via using the proposed junction temperature control method. The energy loss of the prototypical inverter is decreased by 4.15% over the whole testing period. The experiment was conducted with SiC MOSFETs, and the proposed method is also suitable for other Si-based semiconductor devices.

Reluctance Synchronous and Flux-Modulation Machines Designs: Recent Progress

Electric machines provide the conversion of mechanical energy to electrical energy (in the generating mode) and vice versa (in the motoring mode), via magnetic energy storage in their airgap (mainly) and in their permanent magnets (PMs) (if any). They are crucial in electric energy conversion and processing and for motion (torque, speed, and position) control in all industries, for better productivity, energy savings, and less harm to environment. Traveling field electric machines are still standard as synchronous and induction machines. The former (synchronous) need dc rotor excitation, or PMs or magnetically salient rotor to create a-fixed-to-rotor traveling field while the latter (induction) implies a cage (or wound) rotor winding. The average torque is nonzero as stator and rotor traveling fields are at standstill with each other. In an effort to take advantage of the variable reluctance concept in producing nonzero magnetic co-energy (and torque) in the machine versus variation of rotor position, better reluctance synchronous machines (RSMs) (line-start or inverter-fed) in terms of efficiency <inline-formula> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> power factor, torque density, and costs without and with assisting PMs have been introduced lately. High magnetic saliency is implicit and requires a high ratio of pole pitch to airgap and a distributed ac stator winding, in the hope to meet the IEC 4, 5 standards of efficiency. On the other hand, better magnetic materials (with lower core losses) and higher fundamental frequency provided by pulsewidth modulation (PWM) static power converter (including silicon carbide (SiC) arrival) up to 1 kHz, in general, and the high price (and scarcity) of high energy PMs have triggered formidable Research and Development worldwide efforts to investigate many machine topologies without and with PMs (mainly ferrites or bonded NdFeB of lower cost), with mainly concentrated ac windings based on the principle of &#x201C;flux-modulation (F-M)&#x201D; provided by variable reluctance (magnetic anisotropy) concept. This article aims to summarize recent progress in reluctance electric machines, without and with PM assistance of synchronous and &#x201C;F-M&#x201D; types in terms of topologies, modeling, design, control, and merits and demerits based on comprehensive-technical and economic performance indexes.

A comprehensive review on wire EDM performance evaluation

Wire electric discharge machining (WEDM) technique is a fast-growing, advanced manufacturing process which is used for machining of hard materials including various alloys of steel, nickel, tungsten, cubic boron nitride, metal matrix composites (MMC's), superalloys, and ceramic materials. Moreover, it is employed for machining complex profiles and micromachining of hardened materials which are not feasible by various conventional machining processes. Generally, this process is employed to machine electrically conductive materials but during this scenario, it is also being used for machining of electrically low conducting and non-conducting ceramics including silicon carbide, aluminium oxide, silicon nitrate, and zirconium oxide ceramics by modifying the WEDM method with assisted electrode technique or forming composite of conductive and non-conductive materials. This paper presents a comprehensive review on the influence of several WEDM control factors including pulse-on time, pulse-off time, wire feed rate, peak current, wire tension, type of wire (tool) materials, types of base materials and types of powder mixed dielectric fluids on the output responses such as surface roughness (Ra), material removal rate (MRR), width of cut (kerf), wire wear ratio (WWR), wire breakage, microstructural defects, recast layer thickness, and thermal deformation. Moreover, various simulation methods, post processing methods and optimization of WEDM parameters using various techniques were discussed and at last this paper shapes the important recommendations and upcoming developments in WEDM.

Innovative procedure for 3D printing of hybrid silicon carbide/carbon fiber nanocomposites

AbstractA novel route to fabricating hybrid ceramic matrix composites has been developed. The fabrication is based on the unique combination of additive manufacturing (AM), a preceramic polymer, and a chopped carbon fiber precursor. After introducing the photoinitiator to the preceramic polymer formulation, a photosensitive resin was introduced. The resulting resin was loaded with distinct weight percentages of stabilized polyacrylonitrile nanofiber—the carbon fiber precursor. These formulations were 3D printed, cured, and converted to ceramic phases using a pyrolysis cycle. The end objective of the pyrolysis cycle is the conversion of the polycarbosilane resin into a silicon carbide matrix and the transformation of the PAN polymer into reinforcing carbon nanofibers within one cycle. The results of this work showed that ceramic matrix composite components can be successfully fabricated using a suitable combination of 3D printing, resin formulation, and processing cycle. The pyrolyzed ceramic hybrid composite was fully dense with nearly linear shrinkage and a shiny, smooth surface. Approximately 60% retained weight after pyrolysis to 1350°C was confirmed by thermogravimetric analysis. In terms of crystallography, the ceramic matrix composite displayed three coexisting phases including silicon carbide, silicon oxycarbide, and turbostratic carbon. The results showed this combination of material and processes has a high potential for fabricating hybrid composites with high‐temperature performance and improved mechanical properties combined with complex geometries.

An investigation on wear behavior of UHMWPE/carbide composites at elevated temperatures

AbstractUltra‐high molecular weight polyethylene (UHMWPE) is extensively used in frictional applications due to its advanced wear resistance. This advanced polymer is reinforced with hard particulate fillers for further developments against wear conditions. Since elevated temperatures prevail in the service conditions, wear behavior of UHMWPE composites is an important issue for the engineering applications. In the present work, UHMWPE‐based composites including silicon carbide (SiC) fillers were fabricated in a compression molding chamber. In the specimen preparation stage, molding pressure, filler amount, and filler particle size were varied to investigate the influence of these variables. Upon deciding the optimum parameters from the wear tests conducted at room temperature, the wear experiments were repeated for the optimum specimen at elevated temperatures, such as 40 and 60°C. According to the results, the wear behavior of the SiC/UHMWPE composites is heavily changed by the effect of elevated temperature. Adhesive effect is pronounced at elevated temperatures while the wear characteristics possess the abrasive effect in the sliding path. In addition, the composites exhibit an accelerated material loss as temperature increases during the frictional system.

Research on dynamic thermal performance of high-power ThinGaN vertical light-emitting diodes with different submounts

Investigation of dynamic thermal performance is a key to improve the heat management of high-power (HP) vertical light-emitting diodes (VLEDs). Specifically, the thermal time constant is a crucial parameter for optimizing the design and reliability of HP LEDs. Herein, the dynamic thermal behavior of seven HP ThinGaN VLEDs with different constructions was demonstrated. The LEDs’ thermal parameters were measured through the thermal transient tester system by a forward voltage technique. A three-stage of multiexponential function model was applied to divide the transient response curve into three regions with different thermal properties. This study focused on analyzing the first region that involved the chip region (epitaxial layer, wafer bonding layer, and submount) and chip bonding layer. The submounts of the LEDs under consideration include silicon carbide (SiC), silicon (Si), sapphire (Al2O3), and germanium (Ge). The results revealed that with a qualified wafer bonding layer, the LED packages with SiC, Si, and Al2O3 submount presented the optimum thermal time constant, which was 85, 69, 75, and 81 ms, respectively.

Recent developments in hybrid aluminium metal matrix composites: A review

This work is done by reviewing the experiments and studies done by various researchers, organizations and institutions on development and mechanical characterization of the hybrid Aluminium metal matrix composites. Metal Matrix Composites or (MMCs) has developed an ever growing interest in recent times for future applications in the aerospace as well as the automotive industries due to their superior strength to weight ratio and higher temperature resistance. MMCs are created by adding a reinforcement material into a metal matrix. Aluminium based metal matrix composites are widely considered one of the best engineering structural elements because of the fact that the possess high strength, high stiffness, high thermal stability, wear resistance and many benefits fitting to its purpose and also varies with the nature and amount of reinforcements used. The work is carried out referring various research papers, publications and educational articles by various authors. The various reinforced aluminium metal matrix composites (AMMCs) reviewed and the development techniques, mechanical property enhancements are put to the analysis. Major reinforcements include silicon carbide, boron carbide, fly ash, tungsten etc while several researches focused on the development of sustainable products by non-conventional and hybrid reinforcements.

Identification and modelling of applicable wear conditions for stir cast Al-composite

A comprehensive study of the tribological performance of the Al-Zn-Mg-Cu/Al2O3 composite and its matrix alloy is presented in this paper, with a specific emphasis to identify and model the applicable wear conditions where the composite provides a minimum of 50% reduction in wear rate and 25% lowering of the friction coefficient. Two-body abrasion experiments following Taguchi L27 orthogonal design have been performed separately on alloy and composite materials, both prepared by the stir casting method. The influence of crucial control factors including silicon carbide (SiC) abrasive size, load, sliding distance, and velocity on the percentage variations of wear rates and friction coefficients between alloy and composite have been studied using the analysis of variance technique and full quadratic regression method. The dominant control factors are identified as abrasive size, load, and the interaction between abrasive size and load. This has been verified by establishing the influence of abrasive size and load on variations of wear mechanisms like microcutting, microploughing, and delamination, identified by means of in-depth characterization of worn surfaces and generated debris for both alloy and composite. The selection of applicable tribological condition for the composite has been accomplished by adopting the multi-response optimization technique based on combined desirability approach to obtain concurrent optimization of the percentage variations of wear rates and friction coefficients. Predictive models correlating the superiority of tribological performance of composite with abrasion conditions have been developed, and these are found to be accurate (errors <10%), as determined by confirmatory experiment.

Improving ultraviolet light photocatalytic activity of polyaniline/silicon carbide composites by Fe‐doping

ABSTRACTIt was aimed to prepare polyaniline (Pani) composites, including silicon carbide (SiC) nanofibers doped with iron (Fe) ions. The Fe‐doping of SiC was performed to enhance the photocatalytic activity of the composites through the separation of photoexcited mobile charge carriers. For comparison purposes, Pani composites were also prepared with undoped SiC nanofibers. The composite samples were characterized by FTIR, XRD, SEM, EDX, and UV–Vis spectroscopies. Experiments on photocatalytic degradation of methylene blue under ultraviolet light irradiation revealed that Pani/SiC‐Fe composites exhibited higher photocatalytic activity when compared with Pani/SiC composites. Almost 22% dye removal was obtained within 300 min with the Pani composite, containing 15 wt.% SiC‐Fe. FTIR, XRD, SEM, EDX, and UV–Vis spectroscopies demonstrated that SiC nanofibers were successfully doped with iron ions and incorporated into the polyaniline matrix. The original aspect of this study was to research the photocatalytic activity of polyaniline composites containing Fe‐doped SiC nanofibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48524.

Design and Ballistic Penetration of “SiC/Ti6Al4V/UHMWPE” Composite Armor

The penetration resistance of “SiC/Ti6Al4V/UHMWPE” composite armor, which involves four different constructions at the same area density, has been designed and presented against 12.7 mm armor piercing (AP) projectiles experimentally. Three armor materials, including silicon carbide (SiC), Ti6Al4V, and ultra-high molecular weight polyethylene (UHMWPE) fiber composite, were prepared together with the investigation on their mechanical properties. Subsequently the composite armors were manufactured by adhesive technology. The ballistic test results show that the target of SiC/UHMWPE and Ti6Al4V/UHMWPE exhibits better penetration resistance against 12.7 mm AP. The study on the protective mechanism indicates that the thicker ceramic front layer can prolong the interaction time with the projectile, causing more energy dissipation by blunting, eroding, and breaking the projectile efficiently and then the thicker UHMWPE backing layer can fully utilize the tensile deformation of fibers to absorb the remaining energy of the projectile. The enlarged loading area of UHMWPE backing plate caused by the deviation of projectile and the petalling fracture of Ti6Al4V can help to fully develop the tensile deformation of fibers, resulting in more energy absorption. For the target of SiC/Ti6Al4V/UHMWPE, Ti6Al4V interlayer contributes to enhancing the ballistic penetration resistance of composite armors by supporting the front ceramic layer and enlarging the loading area of UHMWPE backplate. However, the insertion of Ti6Al4V partly reduces the thickness of SiC layer and UHMWPE composite layer at the equal areal density of the system, leading to the poorer ballistic penetration resistance of the target of SiC/Ti6Al4V/UHMWPE than that of SiC/UHMWPE and Ti6Al4V/UHMWPE.

Screening microwave susceptors for microwave-assisted pyrolysis of lignin: Comparison of product yield and chemical profile

Lignin was pyrolyzed with microwave heating in the presence of different microwave susceptors including silicon carbide (SiC), activated carbon (AC), and biochar (BC). The heating profiles of microwave heating with different susceptors were characterized. With SiC as the susceptor, three distinct heating stages were observed, which were believed to correspond to the three main stages of lignin decomposition. The effects of temperature, susceptor loading weight, and susceptor type on product yield and composition were investigated. Higher pyrolysis temperatures favored char reduction, demethoxylation and alkylation of phenols, and H2 formation. Higher SiC loading weight promoted the formation of alkyl phenols and syngas (CO and H2). Compared with SiC, both AC and BC enhanced the production of syngas, accounting for 74.5% and 70.1% in volume percentage, respectively. AC contributed to the highest bio-oil and gas production while BC showed highest selectivity to phenol and alkyl phenols, up to 58.2% and 37.7%, respectively.

Biofouling in seawater reverse osmosis (SWRO): Impact of module geometry and mitigation with ultrafiltration

Since no pretreatment method is foolproof for the removal of foulants in reverse osmosis (RO) systems, the aim is to keep the production process efficiency as high as possible. In the vast majority of RO desalination plants, biofouling of membranes is considered as one of the most common operational problems. In this study, a full-scale seawater reverse osmosis (SWRO) desalination plant which was subject to severe biofouling was investigated. Autopsy showed higher biofilm concentrations near the inlet of the module likely due to the abundancy of nutrients. CFD simulation was also used to realize how the geometry of the module inlet could impact the flow within the membrane leaves and thus biofouling. A pilot-scale system including silicon carbide ultrafiltration (SiC-UF) membranes was established in order to filter biological matters. According to the results of this study, SiC-UF membranes appeared to be a reliable pretreatment method for removing almost 100% of all micro-organisms.

Chemical equilibrium analysis of silicon carbide oxidation in oxygen and air

AbstractDue to their refractory nature and oxidation resistance, Ultra‐High Temperature Ceramic materials, including silicon carbide, are of interest in hypersonic aerospace applications. To analyze the thermodynamic behavior of silicon carbide during transition between passive and active oxidation states, chemical equilibrium calculations are performed. The predicted oxygen pressures for passive‐to‐active transition show improved agreement up to an order of magnitude with experimental transition data in the literature, compared with Wagner's model. Both oxygen and air environments are examined, and a 3% difference in transition temperature is observed. Material response analysis demonstrates that a surface temperature jump occurs during thermal oxidation of silicon carbide, corresponding to passive‐to‐active transition.