SiC-based Ceramics Research Articles

Wet oxidation behavior of Al-Y synergistic modified liquid phase sintered SiC

The wet oxidation behavior of LPS-SiC ceramics as well as the synergistic modification effect of Al2O3 and Y2O3 as sintering aids are investigated. The results show that SiO2 oxide scale is transformed to aluminosilicate with the addition of Al2O3, which can inhibit the crystallization of oxide layer and formation of cracks. The aluminosilicate oxide layers have low kl value close to zero, which can reduce the consumption of protective oxide layer under water-containing atmosphere. Y2O3 are mainly transformed to Y2Si2O7 to resist the diffusion of oxidative gas. However, with the increase of sintering aids content, the aluminosilicate layer with excessive viscosity limits the emission of gas generated by oxidation and causes many bubbles left in oxide scale which provided rapid channel for oxidative gas. Therefore, LPS-SiC with lower content of sintering aids has better oxidation resistance. This work can provide guidance for the component design of SiC-based ceramics and composites.

Preparation and erosion resistance of SiC-based ceramic-PCM sensible-latent heat composite heat storage materials

Alloy phase change materials (PCM) are key materials in latent heat storage systems for solar thermal power generation, however, their application is limited by the high corrosion and oxidation problems of alloys. To reduce the erosion problem of alloy PCM, SiC-based ceramic encapsulated flake graphite (EG) modified Al-Cu28-Si6 alloy was used to successfully prepare composite PCM with high compatibility and oxidation resistance. Adopting static erosion test method, the composite PCM was subjected to 50 thermal cycles (25–1000 °C holding time of 10 h was recorded as 1 cycle). The results showed that SiC-based ceramics have excellent corrosion resistance to composite PCM with 10 wt% EG added, which due to the excellent reticulation and encapsulation of EG. Based on the Young-Laplace equation and the contact angle, the erosion resistance mechanism of silicon carbide ceramic alloys has been revealed. SiC-based ceramic-PCM sensible heat-latent heat composite heat storage material was expected to be used for high-temperature heat storage in solar thermal power generation.

Spark plasma sintering of SiC-based bulk materials from carbonaceous residue of rice husk thermal processing

Relevance. The search for a useful application of carbonaceous residues of rice husks thermal processing. These residues due to high silicon content in the inorganic part can potentially be used to produce silicon carbide – an important functional material for various fields of science and technology. Useful utilization of this waste will allow not only solving the environmental problem associated with their inefficient application and formal disposal, but also obtaining value-added products in the form of SiC-based ceramics. Aim. To obtain SiC-based bulk products from carbonaceous residues of rice husk thermal processing by spark plasma sintering with a minimum number of additional stages of feedstock processing. Objects. SiC-based bulk products obtained using carbonaceous residues of rice husk thermal processing. The samples were obtained by spark plasma sintering at 1800 °C, pressure of 60 MPa and holding time of 10 minutes. Methods. Spark plasma sintering; X-ray diffractometry (X-ray phase analysis); scanning electron microscopy; vacuumless arc discharge synthesis method. Results. The authors have carried out the experimental studies to assess the possibility of applying carbonaceous residue of rice husk thermal processing as a precursor for the synthesis of silicon carbide in bulk (ceramics) and dispersed (powder) forms. A series of experiments on spark plasma sintering of carbonaceous residue from rice husk thermal processing in the initial and milled form, with SiO2 silica sand additives, as well as with the use of silicon carbide powders synthesized from carbonaceous residue by vacuumless arc discharge method were implemented. The latter is performed within a one-stage fast-flowing process in an air environment and does not require the use of a vacuum system. Preliminary results demonstrated the possibility of obtaining bulk products and dispersed powders based on silicon carbide with a content of at least 50 and 60 wt %, respectively, and indicate the prospects of further increasing phase purity by optimizing spark plasma sintering and vacuumless arc discharge synthesis.

Dual-function yttrium-silicate-modified SiC ceramics with prominent antioxidant performance

The oxidation of dense yttrium-silicate-modified and unmodified SiC-based ceramic (YPS-SiC and RMI-SiC) at 1200, 1300, and 1400 °C was studied. Oxide scale formed on the surface protects internal ceramics from further oxidation. Y2Si2O7 promoted the rapid crystallisation of cristobalite and no large catastrophic bubbles were observed. The high-crystallinity oxide scale of YPS-SiC slowed down the diffusion of the oxidant. The results showed the better oxidation resistance of the YPS–SiC ceramic with a thinner oxide scale than RMI-SiC. Based on oxidation thermodynamics and kinetics analysis, oxidation models were established to reveal the oxidation resistance mechanism of yttrium-silicate-modified SiC-based ceramics.

Fabrication of Layered SiC/C/Si/MeSi2/Me Ceramic-Metal Composites via Liquid Silicon Infiltration of Metal-Carbon Matrices.

The growing demand for composite materials capable of enduring prolonged loads in high-temperature and aggressive environments presents pressing challenges for materials scientists. Ceramic materials composed of silicon carbide largely possess high mechanical strength at a relatively low density, even at elevated temperatures. However, they are inherently brittle in nature, leading to concerns about their ability to fracture. The primary objective of this study was to develop a novel technique for fabricating layered composite materials by incorporating SiC-based ceramics, refractory metals, and their silicides as integral constituents. These layered composites were produced through the liquid-phase siliconization method applied to metal-carbon blanks. Analysis of the microstructure of the resultant materials revealed that when a metal element interacts with molten silicon, it leads to the formation of a layer of metal silicide on the metal's surface. Furthermore, three-point bending tests exhibited an enhancement in the bending strength of the layered composite in comparison to the base silicon carbide ceramics. Additionally, the samples demonstrated a quasi-plastic nature during the process of destruction.

Tuning the electrical, thermal, and mechanical properties of porous SiC ceramics using metal carbides

The effect of addition of various metal carbides on the electrical, thermal, and mechanical properties of porous SiC ceramics was investigated. The results showed a decrease in the electrical resistivity from 1.2 × 102 to 1.3 × 10-3 Ω‧cm and thermal conductivity from 14.2 to 3.6W.m-1K-1 whereas the compressive strength increased from 12.7 to 21.1–81.1MPa at ~60.2% porosity. The decrease in electrical resistivity and thermal conductivity was caused by the introduction of conductive carbides and multiple heterophase interfaces, respectively, in the porous ceramics. The electrical and thermal conductivities and compressive strength of porous SiC-based ceramics, processed with a SiC-B4C-VC-ZrC-NbC composition, were 8.0 × 102 Ω-1‧cm-1, 3.6W‧m-1K-1, and 58.0MPa, respectively. Therefore, it is proven that the electrical, thermal, and mechanical properties of porous SiC ceramics can be tuned over a wide range by adding a suitable combination of metal carbides.

Microstructure and mechanical properties of SiC-GNPS-SiCW ceramics by oscillatory pressure sintering

The preparation of SiC-based ceramics with high densification, high strength and exceptional toughness is still a severe challenge. In the present work, an advanced sintering technique namely oscillatory pressure sintering (OPS) was applied to prepare SiC ceramics with one-dimensional silicon carbide whiskers (SiCw) and two-dimensional graphene nanoplatelets (GNPs) as reinforcing phases, and the microstructure and mechanical properties were comprehensively investigated. When the contents of GNPs and SiCw were 1 wt% and 5 wt% respectively, the relative density of SiC-based ceramics reached 99.86%, while the Vickers hardness, flexure strength and fracture toughness were 31.55 GPa, 742 MPa and 7.32 MPa m1/2, respectively. The interface was strengthened, meanwhile the grain size was decreased, both of which enhanced the flexural strength of the composites. Results also proved that crack deflection and bridging as well as the bridging of GNPs and SiCw toughened SiC-based ceramics. Furthermore, the coherent interfaces of SiC/GNPS and SiC/SiCw with good match were observed, leading to an enhancement of mechanical properties of such ceramics.

Study of the effect of the morphology of initial powders on the structural and dimensional characteristics of SiC-based porous ceramic materials

The realization of the necessary energy-efficient technological solutions for the production of highly porous SiC-ceramic materials requires appropriate research. The results of developing energy-efficient one-step methods for the synthesis of porous SiC-based ceramics and studying the characteristics of the obtained ceramics are presented. The effect of the morphology of initial powders on the synthesized product is considered. Ultrafine silicon carbide powders of two types, identical in characteristic particle size, but quite different in the surface morphology, were used as fillers in the synthesis of experimental samples of porous ceramics. The first one was obtained by the traditional furnace method (SiCf), the second one was synthesized by the technology of self-propagating high-temperature synthesis (SiCshs). It is shown that the particle morphology of initial powder components determines the structural parameters and characteristics of synthesized porous ceramics. The pore space parameters (average pore size, specific surface area, equivalent hydraulic diameter, permeability, etc.) can vary significantly. Porous ceramic materials synthesized on the basis of SiCf have an open porosity of 47%, high liquid permeability (up to 2 mDarcy), overwhelming dominance of α-SiC phase, and a narrow pore distribution with an average pore size of about 1 μm. High open porosity (more than 58 %), highly developed nanostructured pore space surface with an area of more than 12 m2/g, and wider pore size distribution (average pore size — 140 nm) are observed in porous ceramic materials based on SiCshs. The obtained results can be used to improve energy-efficient synthesis technologies and methods for predicting the properties of highly porous SiC-based ceramic materials. This will make it possible to create highly porous SiC ceramics within a priory predicted limits of effective applicability for the processes of ultrafiltration or catalysis.

Screening and manipulation by segregation of dopants in grain boundary of Silicon carbide: First-principles calculations

The effect of segregation behavior of non-metallic dopants (H/He/O) and metallic dopants (Be/Al/Mg/Y) on the performance of grain boundary (GB) in SiC has been systematically investigated by first-principles calculations. Firstly, the GB energy and excess volume of different GBs have been studied to evaluate the stability of GB and the capacity to accommodate dopant atoms. The solution energies of dopant atoms greatly reduce in the GB region compared with those in the bulk, which makes the dopant atoms inside the grain tend to segregate and aggregate near the GB. The driving force of GB on dopant segregation generally decreases with the increase of distance from GB plane, and the preferential site of dopant is closely correlated with the atomic size of dopant. In addition, H and Y atom possesses the lowest segregation energy at the interstitial and substitutional site near the GB, respectively. Next, the segregation of single dopant induced the changes in the strength and stability of GB have been explored. It is found that non-metallic dopants have the significant embrittlement effects on GB strength. However, the segregation of most metallic dopants could strengthen the GB and Mg atom has the most significant strengthening effect on the GB. The stability of GB can be greatly improved by segregation of Al and Y dopants. Besides, the aggregation of H atoms has the obvious embrittlement effect on the GB. Furthermore, the co-segregation behavior of different dopants has also been explored. Be and Mg dopants have the most significant inhibition effect on the segregation of detrimental impurities H/He/O due to the repulsive interaction between dopant atoms. The present results provide a new insight into the effect of dopant segregation on GB properties and are expected to be a useful guidance for screening the chemical composition and manipulating the performance of SiC-based ceramics.

Ultra-low thermal conductivity and excellent high temperature resistance against calcium-magnesium-alumina-silicate of a novel β-type pyrosilicates

The materials which have low thermal conductivity, a good match of coefficient of thermal expansion with SiC-based ceramics matrix composites (CMCs) and excellent resistance against calcium-magnesium-alumina-silicate (CMAS) are suitable candidates for thermal/environmental barrier coating. To fulfil the above requirements we developed a new multicomponent rare earth (Y0.2Dy0.2Er0.2Yb0.2Ho0.2)2Si2O7 or (5RE0.2)2Si2O7 high entropy ceramics pyrosilicate by a single step solid solution method. The x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis revealed that the as-fabricated bulk composite (5RE0.2)2Si2O7 has a single phase β-type structure match well with single rare earth ytterbium disilicate (Yb2Si2O7) and the different rare earth oxides mixed well with each other. The excellent coefficient of thermal expansion (4 × 10−6-5 × 10−6 °C−1) and ultra-low thermal conductivity (0.7–1.6 W/m C) was observed as compared to other single and multicomponent high entropy ceramics composites. The (5RE0.2)2Si2O7 ceramics pyrosilicate show an excellent CMAS resistance at various temperatures (1300, 1400, and 1500) °C for 4 h compared with single principle RE disilicates. The above all mentioned results identify that this material is a suitable candidate for coating on the SiC-based ceramics composite for thermal/environmental barrier coating.

SiC-based ceramics with remarkable electrical conductivity prepared by ultrafast high-temperature sintering

SiC-based ceramics with high electrical conductivity are applied widely as electrode materials and semiconductor materials. In this study, a SiC-based ceramic with relative density of 96% was prepared by ultrafast high-temperature sintering (UHS) at 2000 ℃ (with a heating rate of 1000 ℃/min) for 40 s. The resistivity of as UHS-ed SiC-based ceramic was 1/15 of that prepared by the pressureless sintering. We found that the components of as-sintered body (SiC, Si and Y3Si5) by UHS were different from those (SiC and YAG) prepared by the pressureless sintering. The reason for the remarkable increase of the electrical conductivity of UHS-ed body was that the Si with higher electrical conductivity than SiC had emerged. Besides, the reaction mechanism was proposed and the unusual composition of the SiC-based ceramic sintered by UHS may also provide new reference for the application of SiC in specific fields.

Fabrication and characterization of SiC–TiB2 composite ceramics used as infrared source material

SiC–TiB2 composite ceramics were fabricated by pressureless sintering at 2200 °C using B4C and C as sintering additives. The effects of TiB2 content on the microstructure, electrical properties, infrared radiation properties and mechanical properties of the composites have been systematically studied. The prepared composites have high relative density (>98%) and good mechanical properties. The existence of Schottky barrier at the SiC–SiC grain boundary makes SiC-based ceramics showing high resistivity and nonlinear electrical feature. The introduction of TiB2 forms the SiC–TiB2 grain boundary with lower barrier height, which allows electrons to pass through more easily. Therefore, the nonlinear coefficient and the resistivity of SiC–TiB2 composite ceramics both gradually decrease with the increase of TiB2 content. When the TiB2 content reaches 15 vol%, the electrical percolation property is obtained, and the bulk resistivity drops to 0.87 Ω cm. The infrared emissivity of the composites shows a decreasing tendency, which is not conducive to practical application. According to the results of electrical and infrared radiation properties, the addition amount of 15 vol%TiB2 is a better formula.

Low-temperature reactive spark plasma sintering of dense SiC-Ti3SiC2 ceramics

SiC-based ceramics are of great interest for various advanced applications. However, its fabrication requires high-temperature treatment at ∼2000 – 2100 °С. In this study, we developed an approach based on low-temperature reactive spark plasma sintering to produce dense SiC-based ceramics with superior mechanical properties. It was found that an SPS temperature of 1600 °C and introduction of 10 – 15 wt% of mechanically activated non-oxide Ti–Si–C additive is required to manufacture ceramics with a theoretical density of higher than 90%. Nonetheless, employing 5 – 15 wt% of the additive mixture and an SPS temperature of 1700 °C, the maximum density of ∼ 98% was achieved. The controlled formation and decomposition of the in-situ Ti3SiC2 MAX phase enables the fabrication of the engineering ceramics with enhanced compressive strength (550 MPa), elastic modulus (485 GPa), and microhardness (32 GPa), which are comparable to the best-reported SiC ceramics. The study has a significant potential for practical application in the production of advanced SiC-based ceramics for various purposes and could be used for further understanding and development of the high-temperature sintering methods.

High-temperature oxidation performance of novel environmental barrier coating 50HfO2-50SiO2/YxYb(2−x)Si2O7 at 1475 °C

Environmental barrier coating systems (EBCs) have been developed to protect SiC-based ceramics exposed to harsh environments. A series of novel EBCs containing 50HfO2-50SiO2 (molar ratio, 50HS) bond coat and YxYb(2−x)Si2O7 (x = 0.3, 0.5, 0.8, and 1.0) topcoat layers were deposited on SiC substrate using atmospheric plasma spraying in this work. Cyclic oxidation of EBCs was performed between room temperature and 1475 °C under dry air and 90%H2O-10%O2 conditions, respectively. Monosilicate (Y/Yb)2SiO5 formed during the YxYb(2−x)Si2O7 deposition. The Re2O3-stabilized HfO2 solid solution with a high coefficient of thermal expansion formed at the YxYb(2−x)Si2O7/50HS interface due to the reaction between monosilicate (Y/Yb)2SiO5 and HfO2 originating from the 50HS bond coat, which was detrimental to EBCs. Furthermore, the thermally grown oxide layer was found at the bond coat/SiC interface, and its formation mechanism has been studied. The results showed that the novel 50HS/YxYb(2−x)Si2O7 EBCs could effectively protect the SiC substrate at 1475 °C.

Mechanical and tribological properties of SiC-GNPs composites prepared by oscillatory pressure sintering

SiC-based ceramics, as structural parts and wear-resistant parts, are required to possess outstanding mechanical properties and wear resistant. Herein, to prepare SiC-based ceramics with desirable properties, the effects of graphene nanoplatlets (GNPs) content on the densification, microstructure, mechanical and tribological properties of SiC-GNPs composites by using an oscillatory pressure sintering (OPS) process were investigated. The addition of GNPs could inhibit the growth of SiC grains, and the resultant mechanisms such as crack bridging, deflection, and GNPs pull-out also promoted the strengthening and toughening of such composites. The flexural strength and fracture toughness of the SiC-1.0 wt% GNPs composites attained the maximum values of 515 MPa (∼27% increase) and 7.11 MPa·m1/2 (∼26% increase), respectively. In addition, the friction behavior of SiC-GNPs composites was analyzed by selecting GCr15 steel ball as friction side under drying friction conditions. Compared with pure SiC ceramics, the friction coefficient and wear rate of SiC-1.0 wt% GNPs ceramics were as low as 0.65 (reduced by ∼25%) and 5.17 × 10−7 mm3·N−1·m−1 (reduced by ∼41%), respectively. This phenomenon can mainly be attributed to the lubricating film formed by GNPs during sliding and excellent mechanical properties.

Synergetic enhancement of electrical conductivity and infrared emissivity of SiC-MoSi2 ceramics via N doping

N-doped SiC-MoSi2 ceramics were successfully fabricated by hot pressing in N2 using Y(NO3)3.6 H2O as both sintering aids and additional N sources. The impact of Y(NO3)3.6 H2O content on the densification, electrical properties, and infrared emission performance of the resulting ceramics were investigated. The distribution of Y-based sintering aid is improved by melting of Y(NO3)3.6 H2O during slurry drying, enabling the relative density to increase up to 97.4%. Y(NO3)3.6 H2O subsequently decomposes during sintering and allows the substitution of atomic N for the C sites in SiC lattice and production of the N-derived donor level. A larger amount of N dopant elevates the carrier density up to 1.90 × 1016 cm-3. Remarkably, The SiC − 10 wt% MoSi2 ceramics sintered with 16.9 wt% Y(NO3)3.6 H2O exhibits the lowest electrical resistivity (0.791 Ω·cm at room temperature) and highest infrared emissivity (0.913 at 800 ℃), the latter of which may also be attributed to lattice distortion induced by N doping. This work demonstrates N doping as a prospective strategy for synergistically optimizing the electrical conduction and infrared emission performance of SiC-based ceramics for infrared source applications.

Dense SiC ceramics prepared by using amorphous sintering additives

Spark plasma sintered SiC-based ceramics with amorphous Y2O3–Al2O3–SiO2 and CaO–Al2O3 sintering additives prepared by melt-quench approach, were compared with those with the direct addition of raw Y2O3–Al2O3–SiO2 and CaO–Al2O3 mixture. The relative densities of SiC-based with raw Y2O3–Al2O3–SiO2 and CaO–Al2O3 were 95.3% and 94.3%, respectively. In spite of the same composition of sintering additive, the relative densities of SiC-based ceramics reached the values of 98.9% and 99.5% by using the glassy additives of Y2O3–Al2O3–SiO2 and CaO–Al2O3, respectively, and the hardness of SiC-based ceramics was improved by about 22.2% and 17.2%, respectively. The amorphous sintering additive effectively improved the densification and hardness of SiC ceramics.

Preparation and corrosion resistance of high-entropy disilicate (Y0.25Yb0.25Er0.25Sc0.25)2Si2O7 ceramics

With the increasing demand for high thrust-weight ratio aero-engines, the development of environmental barrier coatings (EBCs) for SiC-based ceramics is an enormous challenge, which requires both high temperature stability and resistance to molten calcium-magnesium-aluminosilicate (CMAS) corrosion. In this work, a novel high-entropy disilicate (Y0.25Yb0.25Er0.25Sc0.25)2Si2O7 ((4RE0.25)2Si2O7) EBC materials was prepared by a two-step process. The high-entropy disilicate powder was synthesized by sol-gel method, and then Y-Si-Al-O silicate glass was used as sintering aids to facilitate densification of the (4RE0.25)2Si2O7 ceramic by liquid sintering. The results of XRD, SEM and EDS showed that as-synthesized powders were pure high-entropy disilicate (4RE0.25)2Si2O7, and bulk (4RE0.25)2Si2O7 ceramic exhibited a dense structure, in which (4RE0.25)2Si2O7 grains were uniformly distributed into Y-Si-Al-O glass. Compared with single disilicate RE2Si2O7 (RE = Y and Er) ceramics, the high entropy (4RE0.25)2Si2O7 ceramic showed a good phase stability and almost no change in grain size during sintering at 1600 °C for in the holding time range of 5–15 h, suggesting a good high temperature stability. During molten CMAS corrosion, Ca2+ ions can diffuse into the Y-Si-Al-O glass phase wrapped on the surface of (4RE0.25)2Si2O7 grains, and then corrode (4RE0.25)2Si2O7 grains, thereby forming the corrosion zone consisting of reaction layer and diffusion layer. The Y-Si-Al-O glass can play a blocking layer role to suppress Ca2+ diffusion and mitigate molten CMAS corrosion, so that as-prepared (4RE0.25)2Si2O7 ceramic showed a relatively good ability for resisting molten CMAS corrosion. After molten CMAS corrosion at 1500 °C for 48 h, thickness of the reaction layer was only 73 µm. The results will be a solid foundation for the application of environmental barrier coating materials in long-period high temperature molten silicate environment.

Single-source-precursor synthesis of porous W-containing SiC-based nanocomposites as hydrogen evolution reaction electrocatalysts

In this paper, W-containing SiC-based ceramic nanocomposites were successfully prepared by a polymer-derived ceramic approach using allylhydridopolycarbosilane (AHPCS) as a SiC source, WCl6 as a tungsten source, polystyrene (PS) as a pore forming agent as well as divinyl benzene (DVB) as a carbon rich source. High-temperature phase behavior of the W-containing SiC-based ceramics after heat treatment was studied, showing that excessive DVB content in the feed will inhibit the crystallinity of W-containing nanoparticles in the final ceramic nanocomposites. The high specific surface area (SSA) of 169.4–276.9 m2/g can be maintained even at high temperature in the range of 1400–1500 °C, due to the carbothermal reaction which usually occurs between 1300 and 1400 °C. All prepared W-containing SiC-based nanocomposites reveal electrocatalytic activity for the hydrogen evolution reaction (HER). In detail, compared with reversible hydrogen electrode (RHE), the ceramic sample PWA-2-1300 after heat treatment at 1300 °C has the smallest overpotential of 286 mV when the current density is 10 mA·cm−2 in acid medium, indicating the promising perspective in the water splitting field.

Multiple thermal resistance induced extremely low thermal conductivity in porous SiC-SiO2 ceramics with hierarchical porosity

Maximizing interfaces for blocking heat conduction in porous ceramic structures is an efficient approach for achieving maximum thermal resistance. Here, we adopted three strategies simultaneously for maximizing thermal resistance in porous SiC-based ceramics: (1) addition of nano-sized silica into nano-sized SiC powder for generating SiC/SiO2 interfaces, (2) addition of nano-sized carbon into nano-sized SiC powder as the template, and (3) sintering in air, which leads to the partial oxidation of the nano-sized SiC particles and burn-out of nano-sized carbon, giving rise to the generation of the SiC-core/SiO2-shell structure and formation of micro-, meso-, and macro-sized pores. The thermal conductivity, compressive strength, porosity, and specific compressive strength of porous SiC-SiO2 ceramics processed at 600 °C with the above strategies were 0.066 Wm−1 K−1, 2.7 MPa, ∼72 %, and 3.9 MPa·cm3/g, respectively.