With the advancement of hypersonic vehicles, extreme high temperature environments have imposed increasingly stringent requirements on the performance of thermal protection systems. Consequently, the development of high-performance thermal protection materials capable of withstanding extreme conditions has become a primary focus of current research. Ultra-high temperature ceramics (UHTCs) and their composites, known for their excellent oxidation resistance and ablation performance, are regarded as highly promising non-ablative thermal protection materials. This paper provides a systematic review of recent research progress on UHTC composites in several key areas, including innovations and optimizations in fabrication processes, exploration of toughening strategies and mechanisms, in-depth studies on oxidation and ablation resistance mechanisms, and the development and potential applications of high-entropy ceramics. Furthermore, the paper discusses the practical application prospects of UHTCs and their composites in extreme environments, analyzes the current technical challenges, and proposes future research directions and priorities.

It is of great significance to search oxide thermal/environmental barrier coatings (T/EBCs) with high working temperatures and thermal expansion coefficients (TECs) matching to different substrates. ABO₄-type oxides have been widely studied due to their high working temperatures, adjustable TECs, and low thermal conductivity. In this work, ABO₄-type (A=Ga, In, Cr; B=Nb, Ta) oxides are studied as EBC candidates based on their relatively low TECs. The influences of crystal structures, distortion degree, types of polyhedrons, as well as the A- and B-site ionic radii and atomic weights on TECs are discussed. It is found out that the TECs of ABO₄-type oxides are not depended on one single factor, and reducing A-site ionic radius may be a good way to decrease their TECs. Based on the TECs, AlNbO₄, InNbO₄, and GaTaO₄ are chosen as EBCs for C-, SiC-, and Al₂O₃-based substrates, respectively. The similar TECs between ABO₄-type oxide EBCs and substrates are beneficial for reducing interfacial thermal stress, which is good for their long-term applications. This work shows that the applications of ABO₄-type oxides can be expanded by effectively regulating TECs.

Thermal and environmental barrier coatings play a crucial role in protecting high-temperature structural components in gas turbine engines. As turbine inlet temperatures continue to rise, corrosion challenges posed by dust, volcanic ash, and other particulate matter—collectively known as CMAS—have become increasingly severe. Understanding the reaction mechanisms between CMAS and these coatings, identifying the key factors influencing CMAS corrosion, and developing methods to inhibit CMAS infiltration are essential for advancing high-performance gas turbine engines. This review examines the origins of CMAS corrosion and summarizes recent research on CMAS corrosion mechanisms in thermal and environmental barrier coating materials. Additionally, the role of rare earth elements in CMAS corrosion and various strategies to mitigate CMAS effects are discussed. Finally, the review highlights potential directions for future research.

In order to get a comprehensive understanding of the corrosion behaviour of mild steel (110) with alanine, arginine, cysteine, and tyrosine in gas and aqueous phases, a systematic theoretical study using MC simulation was conducted in the current investigation. Stronger interfacial spontaneous adsorption of amino acid molecules across the Fe (110) surface in the investigated environment is made possible by the more negative adsorption energy values found in the MC simulation. Effectively repelling the corrosive particles from the substrate and delaying their aggregation are the capabilities of four amino acids. The results of the MC simulation also show that, in order to stop corrosion, amino acid molecules replace any other ions or solvent water that had previously been adsorbed on the metal surface. The trend of tyrosine > cysteine > alanine > arginine is shown by the protection capacity derived from the MC simulation. Furthermore, the DFT studies demonstrate that, charge transfer takes place within the molecule based on the calculated E-HOMO and E-LUMO energies. When adsorbed onto a metal surface, heteroatoms like nitrogen, oxygen, and sulphur in an amino acid structure provide the stronger inhibition. The decreased HOMO-LUMO gap, indicating improved electronic contact with the Fe (110) surface. A greater reactivity and potential for electron transfer are suggested by the EHOMO and ELUMO values (EHOMO -19.71 eV for alanine, -16.83 for cysteine, -10.73 for arginine and -16.80 for tyrosine) and (ELUMO EHOMO -10.81 eV for alanine, -9.34 for cysteine, -2.69 for arginine and -9.06 for tyrosine) which are advantageous for adsorption onto the Fe ( 110 ) surface. Current study finds that, alanine, arginine, cysteine and tyrosine were emerging as a novel and effective and sustainable corrosion resistance agent for acid pickling and cleaning procedures. These outcomes may lead to the development of more and large-scale green inhibitors and a better understanding of their mechanisms for eco-friendly industrial processes.

Cr₂AlC, as a ternary layered MAX phase ceramic with excellent oxidation resistance and ablation resistance, has great potential in thermal protection materials. To further tap its potential as a recyclable thermal protection material in extreme environment, the cyclic ablation performance of Cr₂AlC under nitrogen plasma flame at 1600^° C was systematically studied in this paper. During the cycles (each lasting three minutes) of ablation, Cr₂AlC maintained structural integrity and exhibited low linear and mass ablation rates. After three cycles of ablation, the linear ablation rate and mass ablation rate were 0.050μ" " m/s and 0.048mg/s, respectively. The analysis of surface and near-surface components shows that Al_8 Cr_5 produced by the decomposition of Cr₂AlC is the origin of the excellent ablation performance of Cr₂AlC ceramics. However, as the cycle time and total ablation time increase, Cr₂AlC and Al_8 Cr_5 near the surface will be depleted under high-temperature oxidation, leading to material failure. This study presents the excellent cycling and long-term ablation properties of Cr₂AlC ceramics, revealing their enormous application prospects in reproducible thermal protection materials.

This study explored the prevention of mild steel (MS) corrosion in sulfuric acid through deployment of N, N-dibutylaniline (NNDBA) as an organic inhibitor. The inhibition efficacy was meticulously scrutinized using a blend of qualitative and quantitative methodologies. The gravimetric method was executed across a spectrum of NNDBA concentrations (10^-1 M -10^-7 M ) and temperatures, 298 K-328 K (with 10 K increments), facilitating an intricate kinetic and thermodynamic exploration of the inhibition mechanism. Adsorption isotherm analyses affirmed NNDBA's adherence to Langmuir's model, signifying a monolayer adsorption paradigm. The adsorption process was found to be spontaneous and thermodynamically favorable, predominantly governed by physisorption. Empirical data delineated an inverse relationship between temperature and inhibition efficiency, whereas an augmentation in NNDBA concentration bolstered corrosion resistance. Potentiodynamic Polarisation (PDP) confirmed that NNDBA is a mixed-type inhibitor with a maximum efficiency of 92.4%. Electrochemical Impedance Spectroscopy (EIS) measurements revealed a marked decrement in the double-layer capacitance at the Fe/H₂SO₄ interface, corroborating inhibitor adsorption. Notably, the lower value of the phase shift exponent n for NNDBA suggests increased surface heterogeneity due to inhibitor film formation. Scanning Electron Microscopy (SEM-2D) and Atomic Force Microscopy (AFM-3D) unveiled distinct morphological alterations indicative of surface passivation. Density functional theory (DFT) calculations provided insights into the electronic structure of NNDBA, revealing a highly negative E_HOMO, low E_LUMO, and a small ΔE(5.24eV), all suggesting strong reactivity and the formation of a stable metal-inhibitor complex. The mechanistic pathway and spatial orientation of the interaction between the NNDBA molecule and MS surface were explored through molecular dynamics simulation to gain insights into its inhibitory behavior. Thus, the theoretical insights harmonize with experimental findings, substantiating its efficacy as a potent corrosion mitigant.

Carbon-based composites are widely utilized in aerospace engines, thermal protection systems of hypersonic vehicles, and ultrahigh-temperature structural components, due to their lightweight nature, high strength, excellent mechanical properties, and thermal stability. However, the inherent susceptibility of carbon-based composites to high-temperature oxidation significantly limits their service life, highlighting the urgent need for the development of efficient oxidation-resistant barriers to enhance the long-term operational stability. In recent years, ultra-high temperature ceramic (UHTC) coatings have attracted considerable attention owing to their outstanding oxidation resistance. Nevertheless, such protective coatings still face critical challenges to hinder practical applications, including crack propagation, dynamic consumption instability of oxidation glass films, generation of oxidation holes and interfacial damage, which remain prevalent. In this work, a comprehensive overview of the research progress in UHTC coatings for carbon-based composites is provided, with particular emphasis on examining the influence of hierarchical structural design on oxidation resistance. Specifically, the role of advanced manufacturing techniques in optimizing microstructural stability and interfacial bonding strength is thoroughly discussed. Furthermore, the high-temperature oxidation protection mechanisms of UHTC coatings are examined, including strategies to optimize the composition of the oxidation glass film, stabilize the self-generated glass phase, and enhance densification of coating. In addition, various characterization methods are discussed for evaluating the oxidation resistance of the coatings, along with a systematic evaluation of stability under different service conditions. Finally, analysis of current technical challenges and unresolved issues, especially challenges and technical prospects regarding the field of oxidation-resistant coatings for carbon-based composites are discussed, while offering perspectives on future developments.

Flexible piezoelectric composite (FPC) materials with strong designability are increasingly utilized in vibration control and structural health monitoring. The sensing and actuating performances of FPCs are directly affected by the several parameters, such as ceramic fiber volume fraction, flexible interdigitated electrode width, electrode spacing, and component thicknesses. These parameters should be optimized in order to make the tradeoff between the sensingactuation performance and the compliance. This study systematically explored the relationships between material properties (such as electrostrain coefficients, dielectric coupling coefficients, and compliance matrix) and component parameters. A representative volume element (RVE) model at the microscale was employed to investigate the electric field distribution and sensing/actuation effects of FPCs with varying parameter configurations under voltage excitation. This analysis identified optimal component parameter ratios for FPCs, providing a theoretical foundation for their design and fabrication. The study concluded that an FPC with a ceramic fiber volume fraction of 75%, electrode spacing of 0.1 mm, and electrode width of 0.01 mm achieves optimal sensing and actuation performance while maintaining good compliance. This research offers valuable insights for the development of flexible piezoelectric composites with tailored properties for advanced applications.

High-entropy ceramics (HECs) have attracted growing research attention since 2015, when the pioneering work on entropy-stabilized oxides was first reported. Derived from the definition of high-entropy alloys, HECs initially referred to disordered ceramic solid solutions comprising five or more principal elements in equimolar ratios occupying the same Wyckoff sites. The concept has rapidly evolved to encompass more complex systems with tunable element distributions across multiple crystallographic positions. Distinct from conventional ceramics, HECs are characterized by their unique chemical diversity and high configurational entropy, which contribute to enhanced structural stability and promising functional properties. Given the remarkable progress of HECs, this review systematically summarizes advancements over the past five years, including oxides (both simple and complex) and non-oxides (carbides, borides, and related compounds). Specifically, we focus on theoretical design principles for stability prediction and property optimization. We then examine the expanding compositional and structural space of emerging compounds and also discuss structure-property correlations and innovative processing methods. Furthermore, we provide a comprehensive overview of the most extensively investigated properties, including mechanical, thermal, electrical, catalytic, magnetic and dielectric characteristics. Looking forward, HECs hold great promise for various applications, and this review may provide some fundamental insights and practical design strategies for realizing their full potential.

As a new member of two-dimensional (2D) materials family, 2D transition metal borides (MBenes) have attracted rising attention owing to the remarkable thermodynamic stability, electrical and mechanical properties. Over the past several years, the study of MBenes has been extended from theoretical simulations to experimental applications, stimulated by the increasing synthesis methods of MBenes. However, the recent experimental applications about MBenes have not been comprehensively introduced. This review concentrates on a comprehensive overview of MBenes which have accordion-like structures derived from multilayer MAB phases and their relevant experimental progress. First, the concept of MBenes, development progress, structural, basic properties are introduced. Then synthetic routes for the production of MBens, including alkaline/acid solution, dealloying, molten salt-assisted etching methods are surveyed. Subsequently, the introduction and analysis of the latest applications such as metal-ion batteries, metal-air batteries, photocatalysis, electrochemical catalysis, sensors, environmental technology, magnetism, lubrication are summarized. Finally, perspectives and challenges for MBenes in synthesis and applications are briefly presented.