The thermal,electrical and mechanical properties of porous α-SiC ceramics bonded with Ti3SiC2 and β-SiC via low temperature in-situ reaction sintering

Porous SiC ceramics have recently attracted wide attention for their applications in the electrically heatable filter. Further improvement of the thermal and electrical conductivity without sacrificing permeability is a critical parameter for such applications. In the present work, porous SiC/Ti₃SiC₂ ceramic composites with Ti₃SiC₂ and micro/nano SiC have been prepared from TiC/Si/α-SiC mixtures at a low sintering temperature (1400 °C). Nano-laminated Ti₃SiC₂ enhanced the electrical conductivity, while the good thermal conductivity was achieved through in-situ formed nano β-SiC and raw coarse α-SiC in the porous ceramics. Along with the increase of initial α-SiC particle size from 0.76 to 16.13 μm, the permeability, thermal and electrical conductivity improved due to the decreased porosity and increased pore size in porous SiC/Ti₃SiC₂ ceramics. The results suggested that the decoupling of the electrical conductivity from the thermal conductivity could be tuned by adjusting the initial α-SiC particle size.     

Electrically conductive and corrosion resistant MAX phases with superior electromagnetic wave shielding performance

MAX phases have emerged as promising corrosion-resistant electromagnetic interference (EMI) shielding materials. Herein, four MAX phases: Ti₃SiC₂, Ti₃AlC₂, V_0.5Cr_1.5AlC, and Nb₄AlC₃, were synthesized via solid–liquid reactions. The electrical conductivities of Ti₃SiC₂, Ti₃AlC₂, V_0.5Cr_1.5AlC, and Nb₄AlC₃ are 14.7 × 10³, 15.5 × 10³, 5.1 × 10³, 8.0 × 10³ S/cm, respectively, and the corresponding average EMI shielding effectiveness values in the frequency of 18–26.5 GHz are 53.9, 69.2, 19.4, and 29.0 dB, respectively. Most importantly, these MAX phases are highly corrosion resistant under acidic conditions. Despite the exposure to the acidic environment and a slight decrease in the electrical conductivity, the corroded MAX phases exhibited excellent EMI shielding properties compared to the pristine MAX phases. Additional analysis showed that reflection was the primary EMI blocking mechanism. The study offers a guide for designing MAX phase ceramics that exhibit high EMI shielding performance in corrosive environments.     

Foam gel-casting preparation of SiC bonded ZrB2 porous ceramics for high-performance thermal insulation

Lightweight SiC-ZrB₂ porous ceramics is of great potential as thermal insulation material used in aerospace, chemical and energy industries. In this work, a series of SiC bonded ZrB₂ (SiC_b-ZrB₂) porous ceramics with porosity high up to 86.9% were prepared by a simple foam gel-casting method. The SiC_b-ZrB₂ porous ceramic prepared at 1573 K exhibited a low thermal conductivity of 0.280 W/(m?K) and a reasonable compressive strength of 0.52 MPa. It could maintain the original geometric shape and microstructure after a secondary heat treatment at 1473 K in inert atmosphere. When heating the samples with thickness of 30 mm for 12 min with an alcohol spray lamp (～1273 K), the temperatures of the cold sides of SiC_b-ZrB₂ ceramics were all lower than 432 K, demonstrating their exceptional insulation capabilities. The present work provides a simple route to produce robust and thermally-insulating non-oxide porous ceramics for use under high temperature.     

Multifunctional nanocomposites integrate electromagnetic shielding,thermal, mechanical,and wear resistance properties

The SiC_nws/SiC nanocomposites were in situ synthesized by using nickel carbon foam as catalyst and skeleton. This technique has a series of advantages including simple operation, low cost, and high efficiency. Due to the excellent microwave absorption and thermal properties of SiC_nws, SiC_nws/SiC nanocomposites possess excellent electromagnetic shielding performance with a high SE_T value of 38.3 dB and good thermal properties with thermal conductivity of 13.77 ± 0.098 wm⁻¹k⁻¹ at room temperature. Meanwhile, the bending strength of the nanocomposites is 110.9 ± 7.7 MPa. The friction coefficient of nanocomposites is about 0.26 with a wear speed of about 67 um³/s. Therefore, the nanocomposites integrate many advantages including lightweight (2.0 g/cm³), excellent electromagnetic shielding, good heat conduction, high strength, and wear resistance.     

Electromagnetic shielding properties of carbon‐rich chemical vapor infiltration‐prone silicon carbide matrix composites

This study focuses on the electromagnetic interference shielding effectiveness (EMI SE) of SiC nanowire/SiC ceramic composites (SiC_nw/SiC) manufactured by chemical vapor infiltration of SiC_nw aerogels with carbon‐rich SiC. The total EMI SE of a 1.0 mm thick ceramic composite specimen with density of only 2.68 g/cm³, was found to be 43‐44 dB, which indicates an excellent EM shielding capability of the ceramic composite corresponding to blocking of 99.99% of the incident EM signal. It was found that the carbon‐rich CVI‐SiC matrix possess excellent EM shielding properties, therefore, the CVI‐SiC CMCs themselves possess an excellent EM shielding property as a result of the carbon‐rich SiC matrix.     

Ti3C2Tx-coated diatom frustules-derived porous SiO2 composites with high EMI shielding and mechanical properties

Effective electromagnetic interference (EMI) shielding materials have garnered substantial interest for their efficacy in attenuating electromagnetic wave energy, ensuring data confidentiality, ensuring the operational stability of fragile electronic systems. To begin, artificially cultured diatom frustules (DF)-derived porous silica (DFPS) skeletons were constructed as templates in this study. Porous ceramics hot-pressed at 800 °C displayed a high compressive strength with a high specific surface area due to their three-dimensional (3D) multilayered and porous structures. Then, mechanically robust Ti₃C₂T_x/DFPS composites with exceptional EMI shielding performance were fabricated by immersing porous DF-based ceramics into Ti₃C₂T_x solutions and annealing in an argon environment to increase the materials’ shielding efficiency (SE). The EMI SE of composites hot-pressed at 800 °C achieved the maximum EMI SE of 43.2 dB in the X-band and a compressive strength of 67.5 MPa, establishing a hitherto unreported balance of mechanical characteristics and shielding performance. Prolonged transmission paths, multiple dissipation, scattering and reflection of electromagnetic energy were achieved using a well-maintained hierarchical porous silica framework decorated with MXene, with adsorption caused by surface MXene serving as the primary shielding mechanism for the composites. Due to their superior overall performance, MXene/DFPS EMI shielding composites have a bright future in the aircraft sector as delicate electronic device components.     

Mechanical Behavior and Electromagnetic Interference Shielding Properties of C/SiC–Ti3Si(Al)C2

In this paper, a low‐temperature densification process of Al–Si alloy infiltration was developed to fabricate C/SiC–Ti₃Si(Al)C₂, and then the microstructure, mechanical, and electromagnetic interference (EMI) shielding properties were studied compared with those of C/SiC–Ti₃SiC₂ and C/SiC–Si. The interbundle matrix of C/SiC–Ti₃Si(Al)C₂ is mainly composed of Ti₃Si(Al)C₂, which can bring various microdeformation mechanisms, high damage tolerance, and electrical conductivity, leading to the high effective volume fraction of loading fibers and electrical conductivity of C/SiC–Ti₃Si(Al)C₂. Therefore, C/SiC–Ti₃Si(Al)C₂ shows excellent bending strength of 556 MPa, fracture toughness 21.6 MPa·m^1/2, and EMI shielding effectiveness of 43.9 dB over the frequency of 8.2–12.4 GHz. Compared with C/SiC–Si and C/SiC–Ti₃SiC₂, both the improvement of mechanical properties and EMI shielding effectiveness can be obtained by the introduction of Ti₃Si(Al)C₂ into C/SiC, revealing great potential as structural and functional materials.     

Effect of thermal stability of Mn+1AXn phases on microstructure and mechanical properties of Mn+1AXn/ZA27 composites

Special layered structure endows ternary M_n+1AX_n phase ceramics with good electrical and thermal conductivity, excellent abrasive resistance, and perfect thermal shock resistance. In this work, three kinds of M_n+1AX_n phase ceramics (Ti₃SiC₂, Ti₃AlC₂, and Ti₂SnC) were chosen to reinforce the ZA27 alloys, respectively. By employing “two-step sintering” technology which is pressureless sintered at 870°C for 1 h firstly and then hot pressed at 500°C for 1 h, M_n+1AX_n/ZA27 composites were successfully fabricated. The effects of thermal stability of the above M_n+1AX_n on microstructure, mechanical properties, and friction performance of the three M_n+1AX_n/ZA27 composites were investigated. The different reaction degrees between the three M_n+1AX_n reinforcements and the ZA27 matrix were ascribed to the differences of chemical bond energy. The results demonstrated that at the sintering temperature of 870°C, Ti₂SnC was completely reacted in Ti₂SnC/ZA27 composite, and Ti₃AlC₂ partially reacted in ZA27 matrix, while no reaction happened between Ti₃SiC₂ and ZA27 matrix. Hence, the order of thermal stability for the three M_n+1AX_n phases in ZA27 matrix is Ti₃SiC₂ > Ti₃AlC₂ > Ti₂SnC. Besides, Ti₃AlC₂/ZA27 composites possess the best mechanical properties and wear resistance, which was attributed to interfacial reaction improved the boding between matrix and reinforcement.     

Flexible and stretchable Ti3SiC2-based composite films for efficient electromagnetic wave absorption

Ti₃SiC₂, as ternary layered ceramic with good electrical and thermal conductivity, has great application potential in the field of absorbing materials. Absorbing materials are also increasingly required to be lightweight, ultrathin, and flexible. Herein, Ti₃SiC₂/poly (TEP, DOP and PVB) composite film was biomimetically designed and fabricated by type casting process. As-fabricated composite film with 38% content of Ti₃SiC₂ was only 1.62 mm in thickness but exhibited excellent absorbing performance. The maximum reflection loss value of Ti₃SiC₂-based films was as high as −38.41dB and absorption bandwidth below −10 dB was 2.480 GHz. Polymer matrix wrapped around Ti₃SiC₂ not only enhanced the flexibility of the film, but also regulated its impedance matching and complex dielectric constant compared with pure Ti₃SiC₂. Superior wave absorption and flexibility imply excellent potential of this Ti₃SiC₂-based composite film for eliminating electromagnetic interference.     

Processing and thermal properties of SrTiO3 /Ti3AlC2 ceramic nanocomposites

Modulating the thermal conductivity has been a pragmatic approach for the development of high-performance thermoelectric material and thereby a step forward towards commercialization. Despite some efforts, the reduction in thermal conductivity of SrTiO₃ ceramic has not been fully realized. In this work, Ti₃AlC₂ in 3, and 7 vol% were uniformly incorporated in SrTiO₃ through nanostructured powder processing. The pristine SrTiO₃ and composites powders were consolidated by the spark plasma sintering at 1200 °C under uniaxial pressure of 50 MPa. Thermal properties of the bulk samples were evaluated from room temperature to 750 K through laser flash analysis. The thermal conductivity of SrTiO₃ based composites decreases substantially with the addition of nanostructured Ti₃AlC₂ from the pristine SrTiO₃ bulk sample. The reduction in thermal conductivity of 7 vol% composites is more than 30% at room temperature and even higher at elevated temperatures from the SrTiO₃. The interface thermal resistance was estimated which indicates a dominant role in diminishing the thermal conductivities of the composites. The results suggest that the addition of Ti₃AlC₂ as a second phase and nanostructuring through ball milling has significantly altered the phonon scattering mechanisms through multiple factors and thereby contributed to reducing effective thermal conductivities of the composites. This, work provide a scalable and economical route for the development of high-performance thermoelectric material.     

Si-rich pressureless sintering of the gelcasted Ti3SiC2 bulk ceramic

The Si-rich pressureless sintering was used to fabricate the Ti₃SiC₂ bulk ceramic. The results show that the optimized Ti₃SiC₂ suspension could be prepared at the absolute value of zeta potential, pH level, PAA-NH₄ dosage, and solid loading of 62.1 mV, 11, 2.0 wt%, and 50 vol%, respectively. The channels existing in the Si-free sintered body facilitated the reactants and products to diffuse to the interior and out of the Ti₃SiC₂ matrix, thereby forming the porous reaction layer of TiC-Ti₃SiC₂. The co-effects of the channels and the reaction layer of TiC-Ti₃SiC₂ severely lowered mechanical properties of the Si-free sintered Ti₃SiC₂ ceramic. On the contrary, the Si-rich sintering method isolated the volatile carbon and established a closed Si-rich atmosphere to sinter the green Ti₃SiC₂ cylinder. The porosity, density, fracture toughness, hardness, and flexural strength of the Si-rich sintered Ti₃SiC₂ ceramic reached 0.74 vol%, 4.36 g/cm³, 5.49 MPa·m^1/2, 4.03 GPa, and 383 MPa, respectively.     

Low sintering shrinkage porous mullite ceramics with high strength and low thermal conductivity via foam-gelcasting

Excessive sintering shrinkage leads to severe deformation and cracking, affecting the microstructure and properties of porous ceramics. Therefore, reducing sintering shrinkage and achieving near-net-size forming is one of the effective ways to prepare high-performance porous ceramics. Herein, low-shrinkage porous mullite ceramics were prepared by foam-gelcasting using kyanite as raw material and aluminum fluoride (AlF₃) as additive, through volume expansion from phase transition and gas generated from the reaction. The effects of AlF₃ content on the shrinkage, porosity, compressive strength, and thermal conductivity of mullite-based porous ceramics were investigated. The results showed that with the increase of content, the sintering shrinkage decreased, the porosity increased, and mullite whiskers were produced. Porous mullite ceramics with 30 wt% AlF₃ content exhibited a whisker structure with the lowest shrinkage of 3.5%, porosity of 85.2%, compressive strength of 3.06 ± 0.51 MPa, and thermal conductivity of 0.23 W/(m·K) at room temperature. The temperature difference between the front and back sides of the sample reached 710°C under high temperature fire resistance test. The low sintering shrinkage preparation process effectively reduces the subsequent processing cost, which is significant for the preparation of high-performance porous ceramics.     

Effect of mullite phase formed in situ on pore structure and properties of high-purity mullite fibrous ceramics

Porous mullite ceramics are potential advanced thermal insulating materials. Pore structure and purity are the main factors that affect properties of these ceramics. In this study, high performance porous mullite ceramics were prepared via aqueous gel-casting using mullite fibers and kaolin as the raw materials and ρ-Al₂O₃ as the gelling agent. Effects of addition of mullite fibers on the pore structure and properties were examined. The results indicated that mullite phase in situ formed by kaolin, and ρ-Al₂O₃ ensured the purity of mullite samples and mullite fibers bonded together to form a nest-like structure, greatly improving the properties of ceramic samples. In particular, the apparent porosity of mullite samples reached 73.6%. In the presence of 75% of mullite fibers, the thermal conductivity was only 0.289 W/m K at room temperature. Moreover, the mullite samples possessed relatively high cold compressive strength in the range of 4.9–9.6 MPa. Therefore, porous mullite ceramics prepared via aqueous gel-casting could be used for wide applications in thermal insulation materials, attributing to the excellent properties such as high cold compressive strength and low thermal conductivity.     

Precipitation induced crack healing in a Ti2SnC ceramic in vacuum

Self-healing ceramics are able to heal cracks through an oxidative healing mechanism at high temperature in oxidizing environments with the recovery of original performance and functionality. However, the oxidation induced repair may be impossible when the ceramics are used in vacuum or inert atmospheres with low oxygen partial pressures. So far little work has been done on crack healing in vacuum or inert atmospheres. Here we report on the crack healing of a Ti₂SnC ceramic in vacuum by a precipitation induced repair mechanism. Cracks induced by thermal shock in Ti₂SnC are completely filled by only metallic Sn at temperatures above 800 °C for only 1 h in vacuum. The electrical conductivity of healed materials is fully recovered, and it even exceeds the initial conductivity. This work might bring a new wave of research on crack healing behavior of ceramics in low oxygen partial pressure environments.     

Comparative investigation of ultrafast thermal shock of Ti3AlC2 ceramic in water and air

In this work, ultrafast thermal shock of Ti₃AlC₂ ceramic was evaluated in water and air by utilizing the induction heating method. First, the annealed samples were heated to the set temperature in tens of seconds and dropped into the cooling water within 0.1 s which is rather short not to degrade the sample temperature. Compared to the traditional thermal shock method when quenching in water, the abnormal thermal shock phenomenon did not occur, which is owing to that no dense oxide layers were formed on the samples’ surface to act as the thermal barrier. The continuous decrease in residual flexural strength when quenched in water is associated with water infiltration, chemical reaction, and large surface tensile stress. The residual strength has 27.25 MPa upon 1250°C. Second, at the same testing temperature, the residual flexural strength when quenched in air maintains a high value of 388 MPa up to 1400°C. Dense oxide scales existed on the quenched surface of Ti₃AlC₂ samples. The results exhibit that Ti₃AlC₂ ceramic possesses excellent thermal shock resistance in water and air, suitable to be applied in extreme environments.     

Microstructure and properties of bilayered B4C-based ceramics

Bilayered B₄C-based ceramics were obtained by hot-pressing. Microstructure, mechanical and ballistic properties of the bilayered ceramics were investigated. One layer was obtained upon addition of Ti and C to the hard B₄C matrix, the newly formed TiB₂ phase uniformly distributed in the matrix. The other layer included variable amounts of Ti₃SiC₂, equal to 10, 20, 30, 40 wt%, and the B₄C-SiC matrix in a fixed weight ratio of 7:3. The amount of TiB₂ and SiC phases, deriving from Ti₃SiC₂ decomposition upon sintering, increased with increasing the Ti₃SiC₂ content. The flexural strength and fracture toughness of bilayered ceramics both increased with increasing the Ti₃SiC₂ content from 10 to 40 wt%. Ballistic testing showed that the B₄C-based ceramic target containing 30 wt% Ti₃SiC₂ broken into pieces upon being impacted by a 12.7 mm armor-piercing incendiary (API) projectile, and effectively consumed the bullet energy and protected the backing plate from serious damage.     

Improved mechanical properties of reaction-bonded SiC through in-situ formation of Ti3SiC2

Reaction-bonded SiC is a ceramic with excellent thermal properties, good corrosion resistance and the characteristic of near-net-shape manufacturing. However, the poor fracture toughness of free Si limits the applications of reaction-bonded SiC. In this study, TiC was added to reaction-bonded SiC and reacted with free Si to form Ti₃SiC₂. The effects of TiC and carbon black on the mechanical properties of reaction-bonded SiC were investigated. The results demonstrated that the in-situ formation of Ti₃SiC₂ and decrease in the content and size of free Si improved the mechanical properties of reaction-bonded SiC ceramics. The mechanical properties of TiC-added reaction-bonded SiC with 17.5 wt% carbon black were superior to those of TiC-added reaction-bonded SiC with 15 wt% carbon black. Moreover, increasing the TiC content of reaction-bonded SiC with 17.5 wt% carbon black from 0 to 7.5 wt% caused an increase in its bending strength from 183.92 to 424.43 MPa and an increase in fracture toughness from 3.7 to 5.24 MPa m^1/2.     

Carbothermal reduction synthesis of high porosity and low thermal conductivity ZrC-SiC ceramics via an one-step sintering technique

In this work, porous ZrC-SiC ceramics with high porosity and low thermal conductivity were successfully prepared using zircon (ZrSiO₄) and carbon black as material precursors via a facile one-step sintering approach combining in-situ carbothermal reduction reaction (at 1600 °C for 2 h) and partial hot-pressing sintering technique (at 1900 °C for 1 h). Carbon black not only served as a reducing agent, but also performed as a pore-foaming agent for synthesizing porous ZrC-SiC ceramics. The prepared porous ZrC-SiC ceramics with homogeneous microstructure (with grain size in the 50–1000 nm range and pore size in the 0.2–4 µm range) possessed high porosity of 61.37–70.78%, relatively high compressive strength of 1.31–7.48 MPa, and low room temperature thermal conductivity of 1.48–4.90 W·m^?1K^?1. The fabricated porous ZrC-SiC ceramics with higher strength and lower thermal conductivity can be used as a promising light-weight thermal insulation material.     

A new Al2O3 porous ceramic prepared by addition of hollow spheres

A method for making porous ceramic prepared by adding hollow spheres was developed, and the resulting porous ceramic was named as hollow spheres ceramic. Water soluble epoxy resin was used as a gel former in the gelcasting process of the Al₂O₃ hollow sphere and Al₂O₃ powder, the porous ceramic porosity varies from 22.3 to 60.1 %. The influence of amount of Al₂O₃ hollow sphere and sintering temperature on the microstructure, compressive strength and thermal conductivity were investigated. With an increasing amount of hollow sphere in the matrix, the porosity increases, which leads to decreased bulk density, compressive strength and thermal conductivity. The compressive strength of the porous ceramics has a power law relation with the porosity, and the calculated power law index is 4.5. The equations of the relationship between porosity and thermal conductivity of porous ceramics are proposed. The thermal conductivity of samples with 60.1 % porosity is as low as 2.1 W/m k at room temperature.