Infiltrated Silicon Carbide Research Articles

Study of the effect of the impurity composition of silicon on the defectiveness of reaction-bonded silicon carbide samples

Large-sized complex-shaped silicon carbide products can be obtained via liquid silicon infiltration, however, the presence of free silicon in their composition limits the scope of their application. The silicon content can be reduced by forming a fine-grained porous structure of the material and control of the growth rate of the carbide layer on the pore walls during liquid-phase silicification. We present the results of studying the effect of the impurity composition of silicon grade KR00 on the appearance of defects in the structure of fine-grained reaction-bonded silicon infiltrated silicon carbide (The results obtained can be used in the production of tribotechnical parts, valves, etc. on the basis of RGCC.). It is shown that iron contained in industrial silicon KR00 exerted the greatest effect. At a content of Fe below 0.94 %wt., SiSiC samples are almost defect-free with the density not less than 3.00 ± 0.05 g/cm3. At a Fe content of 1.49 %wt., defects in SiSiC samples are observed in the form of under-impregnated regions, which are probably attributed to the increased solubility of carbon in the silicon melt upon impregnation with technical silicon with an increased iron content and, as a consequence, more intensive growth of the silicon carbide layer on the pore walls with their subsequent overlapping. As the melt moves deeper into the carbonized porous sample, it becomes depleted in silicon with an increase in the content of impurities, primarily Fe and Al, and the formation of SiC, Fe3C, and FeSi. The theoretical calculation showed that the relative changes in volume for the reactions of SiC and Fe3C formation upon interaction of 1 mole of carbon with silicon and iron are 134 and 339%, respectively. Moreover, with a significant content of iron in the melt, a significant role in the overlap of capillaries can be played by the volumetric change associated with the formation of Fe3C. The results obtained can be used in the production of SiSiC-based tribotechnical parts, valves, etc.

Fabrication of dense SiSiC ceramics by a hybrid additive manufacturing process

AbstractIn this work, we report the fabrication of Silicon infiltrated Silicon Carbide (SiSiC) components by a hybrid additive manufacturing process. Selective laser sintering of polyamide powders was used to 3D print a polymeric preform with controlled relative density, which allows manufacturing geometrically complex parts with small features. Preceramic polymer infiltration with a silicon carbide precursor followed by pyrolysis (PIP) was used to convert the preform into an amorphous SiC ceramic, and five PIP cycles were performed to increase the relative density of the part. The final densification was achieved via liquid silicon infiltration (LSI) at 1500°C, obtaining a SiSiC ceramic component without change of size and shape distortion. The crystallization of the previously generated SiC phase, with associated volume change, allowed to fully infiltrate the part leading to an almost fully dense material consisting of β‐SiC and Si in the volume fraction of 45% and 55% respectively. The advantage of this approach is the possibility of manufacturing SiSiC ceramics directly from the preceramic precursor, without the need of adding ceramic powder to the infiltrating solution. This can be seen as an alternative AM approach to Binder jetting and direct ink writing for the production of templates to be further processed by silicon infiltration.

High-Performance SiC–Based Solar Receivers for CSP: Component Manufacturing and Joining

Concentrated solar power (CSP) is an important option as a competitive, secure, and sustainable energy system. At the moment, cost-effective solutions are required for a wider-scale deployment of the CSP technology: in particular, the industrial exploitation of CSP has been so far hindered by limitations in the materials used for the central receiver—a key component in the system. In this context, the H2020 NEXTOWER project is focused on next-generation CSP technologies, particularly on advanced materials for high temperatures (e.g., >900 °C) and extreme applications environments (e.g., corrosive). The research activity described in this paper is focused on two industrial solutions for new SiC ceramic receivers for high thermal gradient continued operations: porous SiC and silicon-infiltrated silicon carbide ceramics (SiSiC). The new receivers should be mechanically tough and highly thermally conductive. This paper presents the activity related to the manufacturing of these components, their joining, and characterization.

Experimental and numerical analysis of the complex permittivity of open-cell ceramic foams

Open-cell ceramic foams are promising materials in the field of microwave heating. They can be manufactured from susceptor materials and can, therefore, be used as selective heating elements. In this study, the complex permittivities of ceramic foam materials, including silicon-infiltrated silicon carbide (SiSiC), pressureless sintered silicon carbide (SSiC), silicate-bonded silicon carbide (SBSiC), and cordierite were determined. The dielectric properties of the foams were determined by the cavity perturbation technique using a TE104 WR340 waveguide resonator at 2.45 GHz. Samples were preheated in a tubular furnace, enabling temperature-dependent permittivity measurements up to 200 °C. The effective dielectric constant and effective loss factor were found to depend on the porosity and material composition of the foam. The SiSiC material had a higher effective dielectric constant than the SSiC and SBSiC ceramics. The effective dielectric constant of the foams showed a trend of gradual increase with increasing temperature. Some selected dielectric mixing relations were then applied to describe the effective permittivity of the foams and compare them with predictions from finite element simulations performed using the CST Studio Suite. The foam morphologies and simple block inclusions were used in the simulations.

Silicon infiltrated silicon carbide from extruded thermoplastic wood polymer composites

AbstractSilicon‐infiltrated silicon carbide (SiSiC) is an important technical ceramic material for several demanding applications such as heat exchangers, nozzles or mechanical seals. However, shaping and machining tools are quickly worn down, due to the application of hard abrasive silicon carbide (SiC) particles as part of the conventional starting compounds for monolithic SiSiC ceramics. Within this work, an alternative route fabricating SiSiC without primary SiC particles and with low residual carbon contents derived from thermoplastic wood polymer composites (WPC) is described. By varying the proportions of the raw materials, the phase compositions of the SiC ceramic could be modified. A reduction in the average wood particle size from 120 to 60 µm led to a homogenous SiSiC with high SiC content. SiSiC with flexural strengths up to 230 MPa and a Weibull modulus of 16 were developed. The residual carbon content could be reduced below 1 wt%.

Testing and Modeling of Creep Behavior of Different Fiber Content and Type Single-Tow CVI-SiC <sub>f</sub>/SiC Minicomposites

The understanding of creep deformation in high-temperature SiCf /SiC composites is essential in order to better predict stress-redistribution and life-limiting scenarios under high temperature and stress conditions. One area that warrants further investigation is the effect of constituent content and type on creep behavior. Therefore, this study evaluated the tensile creep behavior of different fiber volume fraction pristine and precracked Hi-Nicalon, Hi-Nicalon Type S, and Tyranno ZMI SiC fiber reinforced minicomposites with boron nitride (BN) interphase and chemical vapor infiltrated silicon carbide (CVI-SiC) matrix. Creep tests were performed in air at 1200°C for pristine minicomposites and some minicomposites that were pre-cracked. Precracking stresses were determined from room temperature monotonic tensile tests with acoustic emission monitoring. A single fiber tow minicomposite can be considered the basic architectural feature of woven and laminate ceramic matrix composites (CMCs). The minicomposite creep damage behavior represents the creep behavior of 0° fiber tows in the axial loading direction of a macrocomposite or component. A bottom-up creep damage characterization and modeling approach was applied where creep parameters of the different minicomposite constituents were obtained separately at 1200° C. Next, a theoretical model based on the rule of mixtures was derived to model the fibers and matrix creep-time-dependent stress redistribution and fiber volume fraction effect on load transfer. Fiber and matrix creep parameters, load transfer model results, and developed numerical model methodology were used to construct a creep strain model to predict creep damage evolution of the different fiber type and content minicomposites, which was used to model the creep behavior of Hi-Nicalon and Hi-Nicalon Type S SiC fiber-reinforced minicomposites. This study demonstrates a testing methodology and modeling approaches for use in screening, developing, and improving new generation ceramic matrix composites.

Corrosion resistance of silicon-infiltrated silicon carbide (SiSiC)

Silicon carbide ceramics have found widespread use due to their high corrosion stability. Both solid state-sintered silicon carbide, which has an extremely high corrosion resistance, and silicon-infiltrated silicon carbide are used for various applications. The latter material contains SiC as well as free silicon, which is less stable. Hence, in the present work, the corrosion behavior of silicon-infiltrated silicon carbide ceramics was investigated in NaOH solutions. Long-term corrosion experiments were conducted, and a method for analyzing the corrosion behavior in short-term experiments was developed. The short-term method is based on the accurate measurement of the corrosion depth by laser scanning microscopy on polished surfaces. The results of both methods were in good agreement. The advantage of the short-term method is that it provides information on changes in corrosion mechanisms and corrosion rates in the initial period and as a function of the impurities present. Preferential corrosion of Si at the interface to SiC was observed. TEM investigations revealed that this enhanced corrosion was caused by the segregation of impurities.

Mechanical property degradation of high crystalline SiC fiber–reinforced SiC matrix composite neutron irradiated to ∼100 displacements per atom

For the development of silicon carbide (SiC) materials for next-generation nuclear structural applications, degradation of material properties under intense neutron irradiation is a critical feasibility issue. This study evaluated the mechanical properties and microstructure of a chemical vapor infiltrated SiC matrix composite, reinforced with a multi-layer SiC/pyrolytic carbon–coated Hi-NicalonTM Type S SiC fiber, following neutron irradiation at 319 and 629 °C to ∼100 displacements per atom. Both the proportional limit stress and ultimate flexural strength were significantly degraded as a result of irradiation at both temperatures. After irradiation at 319 °C, the quasi-ductile fracture behavior of the nonirradiated composite became brittle, a result that was explained by a loss of functionality of the fiber/matrix interface associated with the disappearance of the interphase due to irradiation. The specimens irradiated at 629 °C showed increased apparent failure strain because the fiber/matrix interphase was weakened by irradiation-induced partial debonding.

Identification and Characterization of New Materials for Construction of Heating Plates for High-Temperature Guarded Hot Plates

The selection of a material for making the hot and cold plates of high-temperature guarded hot plates (HTGHPs) working up to \(800\,{^\circ }\hbox {C}\) is still an issue. The material must be machinable, have a high mechanical stability to keep the high level of flatness of the plates and have a high thermal conductivity and a high resistance to oxidation when used in air. Nickel 201 alloy has been used in several instruments, but has shown, sometimes, problems of mechanical stability. The total hemispherical emissivity of the plates must be higher than 0.8 as recommended by the standards. Three ceramic materials, a silicon infiltrated silicon carbide (SiSiC), a machinable aluminum nitride and a sintered aluminum nitride (AlN) with high thermal conductivity claimed at ambient temperature, were selected for tests in thermal conductivity and opacity to thermal radiation. Three paints withstanding high temperatures were tested in total hemispherical emissivity and durability at high temperature. Above \(600\,{^\circ }\hbox {C}\), Nickel 201 alloy has a higher thermal conductivity than the three ceramics. Below \(600\, \,{^\circ }\hbox {C}\), the SiSiC and the sintered AlN have a thermal conductivity significantly higher than Nickel 201, but the sintered AlN shows a wide transparency spectral band at short wavelengths (below \(6.5\,\upmu \hbox {m}\)). Above \(300\,{^\circ }\hbox {C}\), the three paints have a total hemispherical emissivity above 0.8. One of the paints has polluted the specimens of an insulation material tested in thermal conductivity up to \(650\,{^\circ }\hbox {C}\). The other two can be recommended to coat the hot and cold plates of HTGHPs used up to \(800\,{^\circ }\hbox {C}\).

Experiments and Modeling of Methane Autothermal Reforming over Structured Ni–Rh-Based Si-SiC Foam Catalysts

Novel silicon-infiltrated silicon carbide (Si-SiC) foams coated with a 10–0.3 wt % Ni–Rh/MgAl2O4 catalyst were studied for the autothermal reforming of model biogas for the production of fuel cell hydrogen. Kinetic studies were performed by varying the inlet concentration of methane, water, and carbon dioxide as well as the temperature. Despite the very good heat conductivity of the SiC structured support, it was not possible to operate the reactor at isothermal conditions because of the succession of fast reactions that were, first, strongly exothermic and, second, strongly endothermic. The experimental data were compared to a reactor model taking explicitly the heat balance in the gas and solid phases into account. The reforming kinetics were based on the methane steam reforming model by Xu and Froment [Xu, J.; Froment, G.F. AIChE J., 1989, 35, 88–96] complemented by a simple equation for methane oxidation. The kinetics were adapted by introducing an oxygen adsorption term to describe the consecutive co...

Radial two-phase thermal conductivity of ceramic sponges up to high temperatures – experimental results and correlation

The experimental determination of the radial two-phase thermal conductivity with forced convection (often also called effective thermal conductivity) at high temperatures up to 1100 K for different ceramic sponges (variation of material, porosity and cell size) is presented. The experimental results are shown and dependencies are clarified. The sponges investigated were made of alumina, mullite, oxidic-bonded silicon carbide (OBSiC) and silicon infiltrated silicon carbide (SiSiC). They have porosities between 75% and 88% and cell densities in the range of 10 ppi to 30 ppi. Due to the high temperature domain, the thermal radiation is significant and cannot be neglected. The radial two-phase thermal conductivity under forced convection conditions is highly dependent on the superficial air velocity, the temperature, the porosity and the cell size of the sponge sample. Furthermore, for future prediction of the radial two-phase thermal conductivity of sponges, a correlation based on an approach summing up the different underlying heat transfer mechanisms is developed.

Durability Analysis and Experimental Validation of Environmental Barrier Coating (EBC) Performance Using Combined Digital Image Correlation and NDE

To understand the failure mechanism or to predict the spallation life of environmental barrier coatings (EBC) on fiber reinforced ceramic matrix composites, the fracture strength of EBC and the process of the crack growth in EBC layers need to be experimentally determined under standard or simulated engine operating conditions. The current work considers a multi layered barium strontium aluminum silicate (BSAS)-based EBC-coated, melt infiltrated silicon carbide fiber reinforced silicon carbide matrix composite (MI SiC/SiC) specimen that was tensile tested at room temperature. Numerous tests were performed under tensile loading conditions, and the specimen was loaded until failure under pre-determined stress levels. The specimen was examined with optical microscopy, scanning electron microscopy (SEM), computed tomography (CT) scan, and digital image correlation (DIC) camera. Observation from the computed tomography scanning, the SEM, and the optical microscopy did not offer conclusive information concerning the cracks that spawned during the tests. However, inspection with the DIC camera offered some indication that cracks had developed and allowed their detection and the location of their initiation site. Thus, this study provides detailed discussion of the results obtained from the experimental investigation and the nondestructive evaluation (NDE), and it also includes assessment of the stress response predicted by analytical modeling and their impact on EBC durability and crack growth formation under complex loading settings.

A study of pressure drop in reticulated ceramic sponges using direct pore level simulation

New values for the viscous and inertial coefficients of the Ergun equation to calculate the pressure drop within open cell ceramic sponges made of alumina and silicon infiltrated silicon carbide (SiSiC) are provided based on the direct pore level simulations (DPLS) results. The fluid flow through ceramic structures of different cell densities and porosities are simulated using standard Navier–Stokes equation without any simplification. The computational grid data are reconstructed from three-dimensional computer tomography scans of different reticulated porous media. Influence of tortuosity on the pressure drop is included in a Ergun equation based pressure drop correlation. The new correlation is dependent on the sponge properties such as, cell diameter, specific surface area and flow tortuosity.

Flow Regime Transition in Open-Cell Solid Foam Packed Reactors: Adaption of the Relative Permeability Concept and Experimental Validation

The trickle-to-pulse flow regime transition in silicon-infiltrated silicon carbide (SiSiC) foam packed fixed bed reactors has been investigated. Based on the film stability concepts of Grosser et al. [AIChE J. 1988, 34, 1850. DOI: 10.1002/aic.690341111] as well as Attou and Ferschneider [Chem. Eng. Sci. 2000, 55, 491. DOI: 10.1016/S0009-2509(99)00344-9], two predictive models have been adapted to foams’ specific geometric parameters. To account for the different nature of solid foams and their interactions with various fluids, the fixed bed characteristics (specific surface area and bed porosity) and fluid specific parameters (gas and liquid density, liquid viscosity, surface tension) have been incorporated in the model. Ergun parameters and static liquid holdup which are required for the modeling of the prevailing tractive forces were determined experimentally. The modeling results were compared to regime transition measurements performed for SiSiC solid foams with different linear pore densities (20, 30...

Development of a Silicon-Infiltrated Silicon Carbide (SiSiC) Friction Layer by the Doctor-Blade Technique Using a Computer-Optimized Calculation for the Packing Density

This paper focuses on an iterative algorithm for setting and attaining particle packing densities by means of different concentrations of a matrix material. The mechanical properties of a product, such as fracture toughness, bending strength and thermal conductivity are directly dependent on the amount of matrix material present. A tape cast friction layer was developed, in order to investigate the dependence of the parameters of the RRSB distribution on concentration of matrix material. The results verify the calculation method of a solid mixture and show a linear dependence of the RRSB particle-parameternon the concentration of matrix material (SiC-content).

Picosecond laser machining of deep holes in silicon infiltrated silicon carbide ceramics

Silicon infiltrated silicon carbide (Si-SiC) ceramics, as high hardness materials, are difficult to machine, especially drilling micro-holes. In this study, the interaction of picosecond laser pulses (1 ps at 1 030 nm) with Si-SiC ceramics was investigated. Variations of the diameter and depth of circular holes with the growth of the laser energy density were obtained. The results indicate that the increase of machining depth follows a nonlinear relation with the increasing of laser energy density, while the diameter has little change with that. Moreover, it is found that some debris and particles are deposited around and inside the holes and waviness is in the entrance and at walls of the holes after laser processing.

Electrochemical corrosion of silicon-infiltrated silicon carbide ceramics in aqueous solutions

Silicon carbide ceramics have found widespread use due to their high corrosion stability. Nevertheless, under certain conditions electrochemical corrosion is observed. Hence, in the present work a SiSiC ceramic and a composite material containing SiC as well as free carbon and Si were investigated in terms of microstructure and electrochemical corrosion behaviour. The SiC grains in the SiSiC exhibited a core-rim structure. The core and rim were formed from primary and secondary SiC, respectively, and had different corrosion stabilities due to the higher electrical conductivity of the rim. In contrast to the behaviour observed with pure chemical corrosion, under electrochemical conditions the Si showed a higher stability than the SiC in NaOH. Also, thicker protective SiO2 layers were formed in H2SO4 on the SiC grains than on the Si grains.

Electrical Discharge Milling of Silicon Carbide with Different Electrical Conductivity

Silicon Carbide is a ceramic material with extraordinary properties. Not only does it excel in mechanical properties, such as very high hardness and flexural strength, but also shows excellent thermal properties with a low thermal expansion and operating temperatures above 1000°C. These properties predestine silicon carbide for applications in harsh environments. Structuring silicon carbide in the sintered state with conventional methods is not feasible due to its hardness. A non-conventional process to structure materials independent of their mechanical properties is electrical discharge machining (EDM). A certain conductivity is however required for this process. To fulfill this requirement, the method of an assisting electrode (AE) is used. During the process, an intrinsic AE is generated from the cracked dielectric oil and deposited on the ceramic surface. The process can therefore continue even after the applied AE has been penetrated. For a deeper understanding of the present removal mechanism EDM of non-conducting ceramics, especially in the area of micro EDM, an investigation of the influence of conductivity is necessary. Therefore three silicon carbide ceramics with different electrical conductivity (S-SiC: 1 10-7S/cm; LR-SiC: 10 S/cm; HO-SiC: 5 10-9S/cm) have been microstructured and analysed. It is found that the conductivity of the silicon carbide materials has no influence on the machinability, all samples can be microstructured. The microsections of the machined samples show that the near-surface structure of the SiC materials is not negatively influenced by the EDM process. The analysis of the surface revealed indications that for S-SiC and for HO-SiC, thermal spalling is the present removal mechanism. The LR-SiC surface shows melting structures. The material removal rate of LR-SiC is 8 × 10-3mm3/min, whereas the material removal rate of the S-SiC and the HO-SiC ranges at 3 × 10-3mm3/min. The high MRR of the LR-SiC indicates a removal mechanism analog to Silicon infiltrated Silicon carbide (SiSiC), with removal of a conductive phase.

Determination of All 21 Independent Elastic Coefficients of Generally Anisotropic Solids by Resonant Ultrasound Spectroscopy: Benchmark Examples

We present an experimental methodology for determination of all 21 elastic constants of materials with general (triclinic) anisotropy. This methodology is based on contactless resonant ultrasound spectroscopy complemented by pulse-echo measurements and enables full characterization of elastic anisotropy of such materials from measurements on a single small specimen of a parallelogram shape. The methodology is applied to two benchmark examples: a material with generally rotated cubic anisotropy (single crystal of silicon) and an isotropic material (silicon-infiltrated silicon carbide ceramics). In both the proposed approach is able to provide a full triclinic tensor with relatively low experimental errors and to identify indubitably the anisotropy class of the material; for the cubic material also the orientations of the principal axes and the cubic elastic coefficients are reliably determined.

High Temperature Applications of SiSiC Cellular Ceramics

AbstractSilicon infiltrated Silicon carbide ceramics are commonly employed because of their excellent chemical, oxidation, and thermal shock resistance. SiSiC cellular ceramics with porosity >80% and pore size from 40 to 10 PPI are exploited industrially in applications with high thermal loads, high temperatures, and harsh environments, including porous burners, catalyst supports, heat exchangers, structural ceramic sandwiches, concentrated solar radiation absorbers, and electric heaters. This work attempts to present the components in which SiSiC foams are currently applied because of their superior thermo‐mechanical properties.