Strong Oxidation Resistance Research Articles

Oxidation behavior and failure mechanisms of enamel coatings at different temperature

This work studies the prolonged high-temperature oxidation behavior and failure mechanisms of enamel coatings at three distinct temperatures: 600°C, 800°C, and 1000°C. The evolution of the coating’s microstructural morphology was characterized, and the kinematics of porosity, crystal precipitation, and oxide layer thickness were measured. The results indicated that at 600°C and 800°C, the coatings exhibit strong oxidation resistance and retain their mechanical integrity. However, at 1000°C, the coatings rapidly deteriorate due to formation of Cr microcrystalline bands and the diffusion of oxidation layer, leading to volume expansion and element segregation. These factors result in the formation of voids and stress concentrations. The precipitation of crystals further exacerbates localized stress and microcracks, increasing the brittleness and enlarging the stress concentration areas, ultimately causing coating spallation. The effects of cooling rate on the long-term oxidation lifetime of the coatings were also examined. The findings of this work suggest that the temperatures below 800°C are suitable for long-term application of the enamel coatings, while exposure to 1000°C results in their rapid failure.

Effect of cobalt on Microstructure and toughness properties of 9Cr-1.8W-0.4Ni-xCo weld metal

In this research, microstructural characterization and mechanical properties of 9%Cr, 0.4%Ni (including W and Mo) steel weld metal with alloyed cobalt were investigated. Due to their strong creep resistance, oxidation resistance, and low thermal expansion, 9%Cr steels are used in nuclear power plants, petrochemical industries, and fossil fuel-powered power plants that operate in high temperature conditions. In this context, weld metals comprising 0.5 %, 1 % and 1.5 % cobalt and cobalt-free weld metal were produced by SMAW (shielded metal arc welding) technique. Microstructure of the weld metals were characterized with optical microscope (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Also, XRD analysis was performed on the bulk samples and precipitated carbide/nitride phases extracted from the weld metals. In addition, differential scanning calorimetry (DSC) was used to determine the phase transformations. Thermo-Calc modeling study was also performed. Hardness, tensile and Charpy-V impact tests were carried out to determine the mechanical properties. The hardness did not change significantly when cobalt up to 1.5 % in the weld metal. However, with the increase of cobalt, the yield and tensile strength increased without affecting the elongation value too much. In the Charpy impact tests performed at different temperatures (−40 °C, −20 °C, +20 °C, +40 °C, +60 °C), the amount of cobalt increased toughness, especially at +40 and + 60oC temperatures. Ductile brittle transformation temperature (DBTT) of the weld metal with 1.5 % Co decreased from 29 °C to 15 °C compared to cobalt free weld metal. It is thought that this may be caused by the further separation of C, Cr and W from the matrix through forming precipitate by the cobalt effect. Besides the mechanical properties, microstructure was also affected by adding Co with inhibition of delta ferrite formation which decrease the toughness. Curie temperature increased with increasing cobalt content detected by DSC.

Mechanism and kinetics study of vanadium leaching from landfilled metallurgical residues by ultrasonic with ozonation enhancement in a low-acid medium

Landfilled metallurgical residues are valuable raw materials for the recovery of strategic vanadium resources. However, efficient separation of vanadium from these residues is challenging due to its strong oxidation resistance and coating within silicate inclusions. To address this issue, this study proposes an enhanced leaching process utilizing the synergistic effect of O3-catalyzed ultrasonic field in a low concentration sulfuric acid system. Results show that following a 10-minute O3 and ultrasonic treatment, the direct leaching rate of vanadium experienced a remarkable 46.7 % increase. Quenching experiments revealed a hierarchical order of active species within the reaction process:⋅OH >⋅O2−> H+, with⋅OH oxidation exhibiting the most pronounced capacity for disrupting the inclusion structure. Electron Paramagnetic Resonance analysis indicated that the highest⋅OH yield arose from the combined application of ultrasound and ozone. Kinetic investigations demonstrated that the vanadium leaching process is governed by interfacial chemical reactions. The activation energy of vanadium oxidation leaching under ultrasonic-O3 conditions was determined to be 40.41 kJ/mol, representing a 20.19 % reduction compared to ultrasonic conditions alone. Through the integration of analysis, characterization, and comparative evaluations, it was discerned that the synergistic impact of ultrasonic and ozone treatments significantly enhances the breakdown of silicate inclusions by low-concentration HF, particularly in the conversion of SiOSi bonds into SiOH bonds and SiF bonds. In summary, the refined leaching methodology incorporating ozone catalysis in conjunction with ultrasonic treatment provides a new idea for the separation and extraction of refractory residual vanadium.

Multifunctional “Solvent‐in‐Diluent” High Voltage Electrolyte for Lithium Metal Batteries

AbstractSulfone liquids can be used as solvents for high‐voltage electrolytes and have been extensively studied for their strong oxidation resistance. However, the problem of high viscosity and susceptibility to side reactions with metallic lithium has been the subject of criticism. To solve the issue of incompatibility with lithium, researchers adopted a high‐concentration electrolyte, namely solvent‐in‐salt, which allows the anions in the lithium salt to preferentially contact the surface of the lithium metal and react to form an SEI film to block the reaction between sulfone solvents and lithium. However, the issue of high viscosity is particularly severe. This work proposes a new solvent model called “solvent‐in‐diluent” electrolyte to address both of these issues simultaneously, different from previous models of salt‐in‐solvent, the model not only effectively prevents sulfone contact with lithium metal surfaces, but also maintains a capacity retention rate of 82% after 500 cycles in the voltage range of 2.8–4.6 V, additionally, the temperature range in which the battery can operate using this electrolyte model has been extended (−20–60°C). This work proposes a new solvent model and challenges the minimum concentration of high‐voltage electrolytes (0.04 m), providing a new approach and possibility for studying high‐voltage electrolytes.

Solvent-free one-step green synthesis of MXenes by “gas-phase selective etching”

Two-dimensional transition metal carbides and nitrides (MXenes) have attracted extensive attention due to their unique electronic properties and various applications for energy harvesting. However, the current synthesis procedures involve using fluoride-based aqueous solutions via reacting with Al-containing MAX phases. Besides, fluorine-free, cost-effective, and straightforward synthetic methods are rarely reported and need to be explored. Here, a solvent-free one-step gas-phase dry etching method, named “Gas-Phase Selective Etching”, was first proposed and used to etch different elements A (Al, Si, Sn, etc.) of MAX phases using the strong oxidation ability of halogens and hydrogen halides gases (Cl2, Br2, I2, HCl, HBr, and HI). The gas-phase etching can achieve a pure product of MXenes coupled with specific gas-induced functional groups. Meanwhile, MXenes powder can be directly obtained without the removal processes of etchants and by-products. Furthermore, the multilayer-MXene with -Cl functional groups (Ti3C2Cl2) has strong oxidation resistance and superior rate performance of capacitance. It provides us with an intelligent, cost-effective synthesis strategy that has a high yield and is safe, allowing for the promising mass production of MXenes.

Astaxanthin attenuates UV-irradiation aging process via activating JNK-1/DAF-16 in Caenorhabditis elegans.

Astaxanthin (AST) is a xanthophyll carotenoid with strong oxidation resistance, which can effectively scavenge various free radicals and protect organisms from oxidative damage. AST is also known to have prominent anti-aging effects, but the underlying mechanism of AST in anti-radiation aging is largely unknown. In this work, we applied ultraviolet (UV) irradiation to accelerate the aging of Caenorhabditis elegans (C. elegans) and treated the nematodes with AST to explore whether and how AST could attenuate the radiation-induced aging effect. Our results showed that AST improved the survival rate of C. elegans, reduced the aging biomarkers, and alleviated the mitochondrial dysfunction caused by the irradiation. Based on the transcriptome sequencing analysis, we identified that the key genes regulated by AST were involved in JNK-MAPK and DAF-16 longevity signaling pathways. Furthermore, we employed jnk-1 and daf-16 mutants and verified the role of the JNK-1/DAF-16 signaling pathway in the anti-aging effect. As such, this study has not only demonstrated that AST can resist the aging process caused by UV-irradiation but also revealed the anti-aging mechanism of AST through JNK-1/DAF-16 activation in C. elegans.

Five new flavonoids and their pharmacological activities from Iris tenuifolia Pall.

Five new components including two new isoflavones, 5, 7, 2′, 3′-tetrahydroxy-6-methoxyisoflavone (1), 5, 7, 2′, 3′-tetrahydroxy-8-methoxyisoflavone (2), one flavonol 3, 5, 3′, 4′-tetrahydroxy-7, 2′-dimethoxyflavonol (3), one flavanone (2S)-5, 7, 3′-trihydroxy-2′-methoxyflavanone (4), and one flavanonol (2R, 3R)-3, 5, 3′, 4′-tetrahydroxy-7, 2′-dimethoxyflavanonol (5), along with nine known flavonoids (6–14) were isolated from under ground parts of Iris tenuifolia Pall. Their structures were elucidated by NMR and HRESIMS data and by comparison of CD spectra with compounds having similar structure. The separated compounds were evaluated for in vitro antioxidant activities by DPPH and ABTS. The α-glucosidase inhibitory activity of the compounds were evaluated with the pNPG method, the results indicated flavonoids were potential inhibitors of α-glucosidase. Moreover, in vitro anti-oxidative assay using flow cytometry indicated that compounds 1–5 showed strong oxidation resistance ability on C8D1A cells without affecting the cell viability.

Superior oxidation resistance of a Y-Hf co-doped Al18Co30Cr10Fe10Ni32 eutectic high-entropy alloy at 1100–1300 °C

We report a study on the oxidation behavior of Al18Co30Cr10Fe10Ni32 eutectic high-entropy alloy co-doped with reactive elements (RE) Y and Hf at 1100–1300 °C. The highly stable eutectic microstructure of γ’/β phases within this alloy contributes to a low coefficient of thermal expansion, thus a low residual stress in the Al2O3 scale. The spinel with a low thickness is formed at the top of Al2O3 scale at 1100 °C due to the low Al diffusion coefficient of γ’-phase and low aspect ratio of β-phase in maze-like eutectic region. As the oxidation temperature increases, the oxidation products transition to exclusive Al2O3 at 1200 °C and 1300 °C, facilitated by the increased Al diffusion coefficient. The Al2O3 scale exhibits a dominated columnar grain microstructure at 1100–1300 °C, suggesting that the inward O diffusion plays more critical role than Al diffusion and thus leads to the low oxidation rate. Besides, the segregation of S to scale/metal interface is inhibited by the uniform RE distribution in the alloy resulting from the fine eutectic microstructure in the alloy. Overall, this alloy exhibits low residual stress in the oxide scale, slow oxidation rate, and the lack of interfacial sulfur segregation, thus contributing to its superior oxidation resistance. The strong oxidation resistance of Y-Hf co-doped Al18Co30Cr10Fe10Ni32 eutectic high-entropy alloy makes it a potential candidate for advanced oxidation-resistant alloy or coating applications.

Simultaneous ultrasound and microwave application in myosin-chlorogenic acid conjugation: Unlocking enhanced emulsion stability

This study investigated the grafting chlorogenic acid (CA) onto myosin, utilizing various techniques including conventional method, ultrasound, microwave, and combination of ultrasound and microwave (UM). The grafting efficiency was as follows: conventional method < microwave < ultrasound < UM. The UM technique manifested the highest CA-binding capacity (80.26 μmol/g myosin) through covalent bonding, and a much shorter time was required for conjugation than conventional method. The conjugation of polyphenol significantly increased the solubility of myosin with reduced aggregation behavior, which was accompanied by structural alterations from ordered structures (α-helix and β-sheet) to disordered forms. The emulsion stabilized by UM-myosin-CA conjugate exhibited the most homogeneous microstructure with favorable creaming stability. Moreover, the resulting emulsion presented strong oxidation resistance and storage stability. These results illustrate the promising potential of employing CA-grafted myosin, especially when processed using the UM technique, in the development of highly efficient emulsifiers.

One-step generating protect film resisting ozone and strong acid on conductive silicone adhesive with atmospheric pressure plasma-assisted

Enhancing the oxidation resistance of conductive silicone adhesive is crucial for long-term stability in rich oxygen and high-temperature environments. Coating thin film featuring low oxygen permeability on the adhesive has been considered a reliable solution. However, the current processes of coating film require extra precursor materials and post-treatment. Here we demonstrated a simple process with atmospheric pressure plasma-assisted to coat SiOxCy thin film on the conductive silicone adhesive within minutes. Our results indicated that the coated thin film has strong oxidation resistance that protects the conductive silicone adhesive from oxidation by 0.1 M HCl solution within 7 days and exposure to ozone for 20 min. The film presented a strong hydrophobic property with a contact angle of 120°. The film’s chemical structure was detected mainly with Si3+: –[Si(R)(-O-)-O–]– and Si4+: [Si(-O-)2–O–]–. The coating process is simple, requires no precursor material, and does not change the original conductivity of the conductive adhesive.

Determination of impurity distribution in IG-11/110 nuclear graphite using TOF-SIMS

Graphite serves as moderator and structural material in various type of graphite-based reactors. The presence of impurities within the graphite matrix can lead to adverse consequences, including diminished fuel efficiency, heightened radionuclide production, and catalytic oxidation. High-purity graphite materials also find essential applications in diverse industries, such as semiconductor manufacturing and chemical analysis. In this study, we conducted an investigation into IG-11 graphite, which has an ash content of 347 ppm, and its purified version, IG-110 nuclear grade graphite, which has an ash content of 12.7 ppm, to understand the purification mechanism of polycrystalline graphite. The analysis of Time-of-flight secondary ion mass spectrometry spectra revealed that metallic impurities in IG-11 were primarily segregated within graphite porosities or appeared as discrete point inclusions, rather than uniformly distributed throughout the graphite matrix. IG-110 demonstrated a significant reduction in impurities such as Na, K, Ca, and Al compared to IG-11, but Ti was still present within its porosity. Notably, impurities residing on the walls of these porosities can accelerate graphite oxidation. The establishment of the theory on impurity segregation in porosities help to develop innovative graphite purification techniques that produce graphite with even greater purity and stronger oxidation resistance.

Repairing vacancy defects for stabilization of high surface area hexagonal boron nitride under harsh conditions

Hexagonal boron nitride (h-BN) with high specific surface area (SSA) is a desirable material for many applications, including heterogeneous catalytic reactions as a catalyst itself or support in high-temperature oxidation. However, stabilizing h-BN with high SSA and under harsh conditions has proven to be a challenge due to the presence of inevitable vacancy defects (h-BN-V). In this study, we propose an efficient method for stabilizing h-BN-V by repairing the vacancy defects with metal ions. Our results demonstrate that repairing the vacancy defects in h-BN with metal ions, such as Ni, can significantly improve the antioxidant stability of the material under oxidizing environments at high temperatures (e.g., 550 °C). Compared to unrepaired h-BN-V, the Ni-repaired h-BN-V (Ni-h-BN-V) was capable of maintaining a few-layer structure under harsh conditions by forming less NOx or boron oxide on the surface, resulting in high SSA (521 vs 54 m2/g). Our density functional theory (DFT) calculations suggest that Ni ions are thermodynamically favorable for trapping by the B-vacancy (Ni-B-vacancy), which contributes to the strong antioxidant stability due to the weak oxygen affinity of Ni-h-BN-V. The high SSA and strong oxidation resistance of Ni-h-BN-V make it an excellent platform for fundamental studies and applications, either as a catalyst or as a support under harsh reaction conditions.

Effect of Mn content on the high-temperature oxidation behaviors of Mn-substituted-for-Ni alumina-forming austenitic stainless steel

We studied high Mn-substituted-for-Ni AFA steel (Fe-14Cr-(6–12) Mn-10Ni-2.5Al-3Cu-Nb-C AFA steel) oxidation behaviors at 800 °C in air. (6–12) Mn AFA steel formed a three-layered scale: the outer layer is (Mn, Fe)-rich oxide, such as (Mn0·983Fe0.017)2O3, the intermediate is Cr-rich oxide, and the inner layer is Al2O3. (6–8) Mn-AFA steels formed a protective Al2O3 layer with stronger oxidation resistance than (10–12) Mn-AFA steels. The oxidation rate constants of 6Mn- and 8Mn-AFA steels are 1.7 × 10−3 and 2.4 × 10−3 mg2/(cm4·h), respectively, approximately 10 times higher oxidation resistance than that of 10Mn- and 12Mn-AFA steels. (10–12) Mn-AFA steels cannot form a continuous Al2O3 layer. The discontinuous Al2O3 layer allows the elements to diffuse outward, eventually forming Mn-Fe-Nb-rich oxide nodules on the surface of the steel. Mn concentrations with the potential to form protective alumina at 800 °C were identified.

Copper-ceria catalysts with improved water and sulfur resistance: Computational design and structural optimization

Copper species dispersed on ceria have emerged as promising catalysts for various energy and environmental applications. However, the presence of water vapor in the actual application environment can significantly hinder the catalyst activity. Flame-synthesized catalysts have been found to possess good water resistance as well as strong mercury oxidation and sulfur resistance. In this study, two types of copper-cerium binary structures were compared: Cu/CeO2 and CuO/CeO2, which represent highly dispersed copper on the CeO2 lattice surface (the main structure of the flame-synthesized catalyst) and CuO clusters supporting on the CeO2 lattice (the main structure of catalyst synthesized by impregnation methods), respectively. The adsorption energies of SO2, H2O, and Hg0 over these structures were studied by density functional theory calculations. The results revealed that Cu-O2/CeO2 (Cu/CeO2 with absorbed O2) had the highest Hg0 adsorption energy (−81.4 kJ/mol), followed by CuO/CeO2 (−13.1 kJ/mol) and CeO2 (−4.4 kJ/mol). Both Cu-O2/CeO2 and CuO/CeO2 showed improved sulfur resistance compared to CeO2, because SO2 was preferentially absorbed on copper sites, protecting the active sites on the CeO2 surface·H2O was absorbed and hydrolyzed into hydroxyl groups on the surfaces of all structures. The hydrolysis process consumed active oxygen on the CeO2 surface for CeO2 and CuO/CeO2, but consumed oxygen absorbed from the surrounding air for Cu-O2/CeO, leading to its best water resistance among the three. This finding opens up possibilities for the development of highly efficient and water-resistant catalysts.

Activated carbon modified by Mo-doped CQDs: An efficient method to reduce the thermal hazard in toluene adsorption

Activated carbon (AC) is one of the typical adsorbents for industrial treatment of VOCs, but AC itself has a high calorific value. When the heat generated by low-temperature oxidation cannot be released, it is easy to store heat and oxidize spontaneously, resulting in immeasurable harm. Therefore, it is important to study and improve the thermal stability of AC. In this study, Mo-doped carbon quantum dots (CQDs) was synthesized to enhance the safety of AC usage. The structure of AC before and after modification was characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffractometer (XRD). On the modified Mo-doped CQDs/AC, there are more crystalline structures formed by Mo oxides on the surface, which makes the intermolecular force on the surface of AC increase. At the same time, Mo oxide has strong oxidation resistance, which can inhibit the thermal decomposition process of AC, and has stronger stability. The spontaneous combustion tendency and thermal hazard of AC before and after modification were greatly improved. The heat released in the toluene adsorption by the modified AC at different temperatures was significantly lower than the heat released by the unmodified AC. According to the Langmuir adsorption isotherm, the adsorption performance of Mo-doped CQDs (2.5 wt%) was 1.6 times higher than that of AC when the system was 25 °C. The results showed that Na2MoO4 CQDs modified AC could effectively improve the thermal stability and greatly reduce the spontaneous combustion tendency. A relative fire safety performance evaluation model was also established to comprehensively evaluate the fire risk of VOCs treatment by AC.

Study of Thermal Conductivity of Fluorinated Graphene

With the rapid development of technology and the advent of the 5G era in recent years, the heat dissipation of electronic devices has received great attention. However, the high intrinsic conductivity of ordinary graphene materials limits their potential applications in electronic packaging materials because of their poor thermal management. The results show that fluorinated graphene has excellent heat resistance, corrosion resistance, and strong wear resistance. It can also play a role in lubrication and is commonly used in high-temperature coatings, wear-resistant lubrication coatings and corrosion-resistant coatings because it does not react easily with other substances. Due to the strong electronegativity of fluorine, fluorinated graphene has strong stability and oxidation resistance at high temperatures. Therefore, in this paper, a fluorinated graphene with high compressibility, high thermal conductivity, and high electrical insulation was developed by hydrothermal method assisted by hydrofluoric acid, and the effect on the thermal conductivity of fluorinated graphene was investigated by changing the fluorine-to-carbon ratio (F/C) by adjusting the hydrofluoric acid content. The structure of fluorinated graphene was characterized by SEM and XRD, which proved to be porous and a customized interconnected graphene network with adjustable fluorine coverage. The prepared fluorinated graphene has good insulating properties with a minimum conductivity of 4×10-7 S cm-1 and a thermal conductivity of 1.254 W m-1 K-1, which has been confirmed by the electrical conductivity test results. Meanwhile, because of the porous structure of graphene fluoride, we prepared epoxy resin/fluorinated graphene nanocomposites by vacuum-assisted infiltration process using epoxy resin as the filler material. This material and fluorinated graphene showed outstanding thermal performance during the typical cooling process. The conclusion shows that graphene fluoride and epoxy resin/fluorinated graphene nanocomposites are promising for electronic packaging.

Preparation of Antioxidative MXene by Deep Eutectic Solvent-Assisted Electrochemical Ultrasonic Composite Exfoliation and Its Application in Flexible Solid-State Supercapacitors

In this work, we achieved a novel preparation of Ti3C2 MXene (MXene–DES) with few layers and a high degree of hydroxylation by a deep eutectic solvent (DES)-assisted electrochemical ultrasonic composite exfoliation method which is easy to scale up. The electrochemical process used a mixture of low-cost DES (choline chloride–urea) and water as the electrolyte, in which DES acts as a triple role of intercalation, interlayer expansion, and anti-oxidation. DES attached to the surface and interlayer of layered Ti3C2 formed an antioxidative protective cover, resulting in the layered Ti3C2 being grafted with hydroxyl functional groups instead of forming TiO2 in water during the entire exfoliation process. The prepared MXene–DES exhibits fewer layers, larger interlayer spacing, higher degree of hydroxylation, and stronger oxidation resistance than the MXene prepared by traditional ultrasound in a nitrogen atmosphere (MXene–N2). The symmetric flexible solid-state supercapacitor based on an activated carbon electrode and the composite gel polymer electrolyte composed of MXene–DES, DES, and polyvinyl alcohol exhibits good mechanical properties, a wide voltage window of 2.3 V, and a high specific capacitance of 133.7 F·g–1 (0.1 A·g–1). Our strategy paved a simple, low-cost, and relatively environmentally friendly way to the scalable preparation and application of antioxidative high-quality MXene.

Microstructural analysis of tristructural isotropic particles in high-temperature steam mixed gas atmospheres

High-temperature gas-cooled reactors (HTGRs) use tristructural isotropic (TRISO) particles embedded in a graphitic matrix material to form the integral fuel element. Potential off-normal reactor conditions for HTGRs include steam ingress with temperatures above 1,000 °C. Fuel element exposure to steam can cause the graphitic matrix material to evolve, forming an atmosphere composed of oxidants and oxidation products and potentially exposing the TRISO particles to these conditions. Investigating the oxidation response of TRISO particles exposed to a mixed gas atmosphere will provide insight into the stability under off-normal conditions. In this study, surrogate TRISO particles were exposed to high temperatures (T = 1,200 °C) in flowing steam (3% < pH2O < 21%) and CO (pCO < 1%) to determine the oxidation behavior of the SiC layer when exposed to various mixed gas atmospheres. Scanning electron microscopy, x-ray diffraction, and focused ion beam milling was used to determine the impact of CO and steam on the oxidation behavior of the SiC layer. The data presented demonstrates how the SiC layer showed strong oxidation resistance due to limited SiO2 growth and maintained its structural integrity under these off-normal conditions.

Preparation and Properties of MAX Phase High-Temperature Antioxidant Coatings on C/C Composite Surfaces by Ultra-High Speed Laser Cladding

Prefabricated MAX (Ti3SiC2, Ti3AlC2) phase coating materials with coefficient of thermal expansion Si and SiC as transition layers and excellent high-temperature antioxidant properties were used for ultra-high-speed laser melting on the surface of carbon/carbon composites, so that the produced coatings have good interfacial bonding and high-temperature antioxidant properties. In this study, we characterised and analysed the microscopic morphology and composition of the sample coatings using X-ray diffraction and scanning electron microscopy, investigated their interfacial bonding properties by scratch tests and studied the high temperature oxidation resistance of the samples at 1773 K for 1 h. The results show that the bonding strength between the coating and the substrate is good, the surface is flat without flaking, the coating thickness can be controlled below 60 μm, the microstructure is dense, and there is no obvious deformation or failure of the substrate, and the dense coating formed by laser melting has strong oxidation resistance, so that the substrate carbon/carbon composite is well protected at high temperature.

Oxidation Behaviors of ZrB2–SiC Ceramics with Different Porosity

ZrB2–SiC ceramics have great application potential in thermal protection system of hypersonic aircraft, due to their excellent oxidation resistance and mechanical properties. Porosity is one of the main factors which will obviously affect the oxidation behaviors of ZrB2–SiC ceramics. Herein, ZrB2–SiC ceramics with three different porosity are sintered by spark plasma sintering at different temperatures. Then, a series of oxidation tests of the ceramics with different porosity are carried out at different temperatures and with different time. Morphologies and microstructures of the oxidation surface and cross section, as well as the oxide layer thickness and weight change are discussed in detail. Results show that the porosity of ZrB2–SiC ceramics has great influence on the oxidation behaviors of ceramics. The oxide layer thickness and weight change gradually increase with the increase of oxidation temperature and oxidation time for ZrB2–SiC ceramics with different porosity. As the porosity of ZrB2–SiC ceramics decreases, the oxide layer thickness and weight change generally decrease, which shows that the ceramics with lower porosity have stronger oxidation resistance. This work provides a relative systematic analysis of the effects of porosity on the oxidation behaviors of ZrB2–SiC ceramics.