High-Temperature Corrosion Behavior of SiBCN Fibers for Aerospace Applications

Phase-Transformation Nanoparticles Synchronously Boosting Mechanical and Electromagnetic Performance of SiBCN Ceramics

Precursor-derived silicoboron carbonitride ceramic (PDC-SiBCN) has attracted significant attention as an advanced electromagnetic (EM) wave-absorbing material. However, the inherent porous and brittle characteristics limit its application as a structural load component in an EM interference environment. In this study, phase-transformation HfO₂ nanoparticles were incorporated into PDC-SiBCN to reduce volume shrinkage, improve bonding interactions, and control structural defects, simultaneously boosting the plastic deformation and EM performance of brittle ceramics. The obtained HfO₂/SiBCN ceramic showed enhanced flexural strength of up to 430.1% compared with that of the pure SiBCN ceramic. Furthermore, the HfO₂/SiBCN ceramic also demonstrated excellent high-temperature EM absorption. The minimum reflection coefficient (RC_min) could reach -45.26 dB, and the effective absorption bandwidth (EAB) covered 2.80 GHz of the X band at 2.28 mm thickness at room temperature. Furthermore, the RC_min can still reach -44.83 dB, and the EAB can cover 2.4 GHz at 1.58 mm even at 1073 K. This work shows that phase-transformation nanoparticles could simultaneously improve the deformation ability and EM wave absorption properties of SiBCN ceramics. The results could guide the design and preparation of PDCs with strong carrying capacity and excellent EM absorption, even in harsh environments.

Approaches to Preceramic Polymer Fiber Fabrication and On-Demand Applications

The demand for lightweight, high-modulus, and temperature-resistant materials for aerospace and other high-temperature applications has contributed to the development of ceramic fibers that exhibit most of the favorable properties of monolithic ceramics. This review demonstrates preceramic-based polymer fiber spinning and fiber classifications. We discuss different types of fiber spinning and the advantages of each. Tuning the preceramic polymer chemical properties, molar mass, functional chemistry influences, and incorporation with fillers are thoroughly investigated. Further, we present the applications of preceramic-based polymer fibers in different fields including aerospace, biomedical, and sensor applications. This concise review summarizes recent developments in preceramic fiber chemistry and essential applications.

Enhanced Electromagnetic Wave Absorption for Y2O3-Doped SiBCN Ceramics

Polymer-derived SiBCN ceramics (PDCs-SiBCN) are promising ultrahigh-temperature ceramics owing to their excellent high-temperature oxidation resistance and electromagnetic wave (EMW)-absorbing capability. In this paper, the microstructure evolutions, the dielectric properties, and EMW absorption properties of Y₂O₃-doped SiBCN ceramics were investigated. The results reveal that Y₂O₃ acting as a catalyst promotes the formation of SiC, BN(C), and graphite crystalline phases in the SiBCN ceramics, and these crystalline phases are constructed as conduction phases and polarization phases to enhance the EMW-adsorbing properties. The minimum reflection loss (RL_min) reaches -42.22 dB at 15.28 GHz, and the effective absorption bandwidth is 4.72 GHz (13.28-18.00 GHz). In addition, there is only 0.56 wt % mass loss for the Y₂O₃-doped SiBCN ceramics when they are heated from ambient temperature to 1500 °C in air, indicating that the Y₂O₃-doped SiBCN ceramics obtain excellent oxidation resistance at high temperature. We believe that rare metal oxidation is beneficial for the growth of crystalline phases in the PDCs, resulting in high EMW-absorbing properties and oxidation resistance. Thus, the research extends a novel method and design strategy for microstructure regulation and property enhancement of PDCs.

Maximum Achievable N Content in Atom-by-Atom Growth of Amorphous Si-B-C-N Materials

Amorphous Si-B-C-N alloys can combine exceptional oxidation resistance up to 1500 °C with high-temperature stability of superior functional properties. Because some of these characteristics require as high N content as possible, the maximum achievable N content in amorphous Si-B-C-N is examined by combining extensive ab initio molecular dynamics simulations with experimental data. The N content is limited by the formation of unbonded N2 molecules, which depends on the composition (most intensive in C rich materials, medium in B rich materials, least intensive in Si-rich materials) and on the density (increasing N2 formation with decreasing packing factor when the latter is below 0.28, at a higher slope of this increase at lower B content). The maximum content of N bonded in amorphous Si-B-C-N networks of lowest-energy densities is in the range from 34% to 57% (materials which can be grown without unbonded N2) or at most from 42% to 57% (at a cost of affecting materials characteristics by unbonded N2). The results are important for understanding the experimentally reported nitrogen contents, design of stable amorphous nitrides with optimized properties and pathways for their preparation, and identification of what is or is not possible to achieve in this field.

High-Temperature Properties and Applications of Si-Based Polymer-Derived Ceramics: A Review

Ceramics derived from organic polymer precursors, which have exceptional mechanical and chemical properties that are stable up to temperatures slightly below 2000 °C, are referred to as polymer-derived ceramics (PDCs). These molecularly designed amorphous ceramics have the same high mechanical and chemical properties as conventional powder-based ceramics, but they also demonstrate improved oxidation resistance and creep resistance and low pyrolysis temperature. Since the early 1970s, PDCs have attracted widespread attention due to their unique microstructures, and the benefits of polymeric precursors for advanced manufacturing techniques. Depending on various doping elements, molecular configurations, and microstructures, PDCs may also be beneficial for electrochemical applications at elevated temperatures that exceed the applicability of other materials. However, the microstructural evolution, or the conversion, segregation, and decomposition of amorphous nanodomain structures, decreases the reliability of PDC products at temperatures above 1400 °C. This review investigates structure-related properties of PDC products at elevated temperatures close to or higher than 1000 °C, including manufacturing production, and challenges of high-temperature PDCs. Analysis and future outlook of high-temperature structural and electrical applications, such as fibers, ceramic matrix composites (CMCs), microelectromechanical systems (MEMSs), and sensors, within high-temperature regimes are also discussed.

SiBCN ceramic precursor modified phthalonitrile resin with high thermal resistance

In order to expand the application of phenolic-type phthalonitrile resin in high-temperature fields, a series of organic–inorganic hybrid materials have been prepared via conventional blending and doping method. The chemical transformations were monitored by various measurements, while the curing behavior was evaluated by differential scanning calorimetry (DSC), and these new blends could be also cured under auto-catalytic process. The onset polymerization exothermic temperature shifted to lower temperatures (195.3°C). Later, the compatibility within the cured products was analyzed by using energy dispersive spectrometer (EDS) and scanning electron microscope (SEM), where no phase separation occurred between the ceramic domain and the phthalonitrile polymer. Upon curing, the thermal properties of the polymers were characterized by dynamic thermomechanical analysis (DMA) and thermogravimetric analysis (TGA), where enhanced heat resistance and thermal stability were discovered, The blends residual weight (Cy) value was 57.6% with 15 wt.% SiBCN at 1000°C. And when blended with SiBCN precursor, no peak or onset point could be observed in the temperature range (50 to 500°C), which indicated the glass transition temperature greater than 500°C. Additionally, the dielectric properties were evaluated. And when the content was 5 wt.%, the blends dielectric loss was 0.0043 and the permittivity was 4.31. The above results indicated that the introduction of ceramic precursors could enhance the thermal performance of phthalonitrile polymers, consequently the hybrid materials shown great potential in the application of higher temperature fields.

Strong and thermostable hydrothermal carbon coated 3D needled carbon fiber reinforced silicon-boron carbonitride composites with broadband and tunable high-performance microwave absorption

Excellent electromagnetic wave (EMW) absorbing materials with high-temperature stable and superior mechanical properties are among the most promising candidates for practical application. Here, novel hydrothermal carbon coated three-dimensional (3D) needled carbon fiber reinforced silicon-boron carbonitride (HC-CF/SiBCN) composites with a hierarchical A (CF)/B (HC)/C (SiBCN) structure were constructed and prepared for the first time by combining hydrothermal transformation and precursor infiltration and pyrolysis (PIP) process. The thickness of the HC coating controlled by the glucose concentration played a crucial role in tailoring the EMW capacity of the composite. The incorporation of SiBCN could not only effectively improve the oxidation resistance but also actively enhance the mechanical properties of the HC coated CF structure. Compared to the weak high-temperature oxidation resistance and mechanical properties of pristine 3D needled CF felt, the composites after the introduction of HC and SiBCN were thermostable in air atmosphere beyond 1000 °C to about above 70% weight retention, and the maximum flexural and compression strength of the composites could reach to 23.51 ± 1.37 and 12.22 ± 1.12 MPa, respectively. A substantial enhancement of EMW absorption ability was achieved through incorporation of HC and SiBCN, which could be attributed to the matched characteristic impedance and enhanced loss ability, whose optimization EMW absorption performance was the minimum reflection loss (RL_min) of -52.08 dB and effective absorption bandwidth (EAB) of 7.64 GHz for the composite obtained by two PIP cycles with 24 wt% glucose solution, demonstrating that the HC-CF/SiBCN composites with high-temperature stable, excellent mechanical and superior EMW absorption properties could be considered as a promising candidate for the applications in harsh environments.

Three new coordination polymers based on bis(4-(4H-1,2,4-triazol-4-yl)phenyl)methane: syntheses, structures, multiresponsive luminescent sensitive detection for antibiotics and pesticides, and antitumor activities

Three novel coordination polymers (CPs), namely, {[Ag2(L)2(Mo4O13)·(CH3CN)]} n (1), {[Zn(L)(1,4-bdc)2·2(1,4-H2bdc)]} n (2), {[Cd(L)(1,4-bdc)0.5]} n (3) have been synthesized under solvothermal conditions by the reaction of bis(4-(4H-1,2,4-triazol-4-yl)phenyl)methane (L) and varied metal salts. Their structures are determined by single X-ray crystal diffraction, and further characterized by elemental analysis, IR, TGA and PXRD. CP 1 with ammonium molybdate as a secondary ligand displays a 2D network with (2,3,3,3,4)-connected net topology and the point symbol of {4·82}6{4·84·10}2{8}, CP 2 and CP 3 with 1,4-H2bdc as a secondary ligand demonstrate 3D structures with different topologies. CP 2 exhibits high sensibility and low detection limit in the recognition of antibiotics (NZF, NFT and FZD) and pesticide (DCN) identification. CP 1 demonstrates good anti-tumor activity toward the tested glioma cells. The possible luminescent sensitivity and anti-tumor mechanisms are also discussed.

Nanochannel Diffusion-Controlled Nitridation of Polycarbosilanes for Diversified SiCN Fibers with Interfacial Gradient-SiC xN y Phase and Enhanced High-Temperature Stability

Diversified SiCN fibers with gradient-SiC _xN _y phase in the interfacial regions between the major phases of carbon-rich SiC phase and Si₃N₄ phase were prepared via nanochannel diffusion-controlled nitridation of polycarbosilane fibers under different NH₃ flow rates. The obtained fibers with excellent mechanical properties showed a different nanostructure and improved high-temperature behavior compared with polysilazane- and polysilylcarbodiimide-derived SiCN ceramics. The enhanced high-temperature properties could be contributed to the inhibition of carbothermal reduction of the Si₃N₄ phase by the gradient-SiC _xN _y phase in the interfacial region between the Si₃N₄ phase and carbon-rich SiC phase. Meanwhile, a suitable amount of interfacial SiC _xN _y phase as well as the fine distributed microstructure can be helpful to inhibit the high-temperature crystallization of both the SiC phase and Si₃N₄ phase. Additionally, a nanostructural model has been proposed to understand the effect of interfacial gradient-SiC _xN _y phase and compositional-dependent high-temperature behavior of obtained SiCN fibers. Our findings provide a novel strategy to prepare SiCN-based ceramic materials with excellent high-temperature stabilities, which we expect to possess great potential in structural and (multi)functional applications at high temperatures and under harsh environments.