In this study, the Ca33Mg9Al13Si45 layer was fabricated on the SiCf/SiC surface by APS to simulate the coexistence of high-velocity impact and molten-state deposition. Subsequently, the corrosion and infiltration behaviors of the molten Ca33Mg9Al13Si45 in air and water-vapor environments (H2O:O-2 = 90:10 vol%) at 1300 degrees C for 300 h were investigated. The results indicated that, during corrosion, the molten Ca33Mg9Al13Si45 infiltrated into the interior of the SiCf/SiC through interconnected pores. Under high-temperature air corrosion, Ca and Mg remained restricted to the upper-part pore-filling region. Compared with high-temperature air corrosion, Ca and Mg infiltrated deeper along the pores into the interior of the SiCf/SiC under high-temperature water-vapor corrosion. Once the molten Ca33Mg9Al13Si45 filled these pores, no obvious elemental diffusion or further infiltration was detected at the interface between the molten Ca33Mg9Al13Si45 and SiCf/SiC, suggesting good interfacial chemical stability. The flexural strength of the original SiCf/SiC was 445 +/- 43 MPa, while the SiCf/SiC with the molten Ca33Mg9Al13Si45 after high-temperature air corrosion and water-vapor corrosion exhibited flexural strengths of 409 +/- 30 MPa and 440 +/- 33 MPa. These results demonstrated that the infiltration behavior of the molten Ca33Mg9Al13Si45 had a relatively minor impact on the mechanical behavior of SiCf/SiC, enabling the materials to retain mechanical performance close to the original level after high-temperature exposure.

This study investigated the optimal La2O3 content for improving the oxidation resistance of SiC bond coats on C/C composites. SiC-La2O3 bond coats were fabricated through pack cementation (PC), followed by the deposition of ZrB2-SiC-Si (ZSS) outer coats using atmospheric plasma spraying (APS). The results indicated that a 5wt.% La2O3 concentration most effectively refined the grain structure, increased the size and thickness of the diffusion zone, and alleviated stress induced during preparation and oxidation. This composition enhanced bonding strength, reduced delamination, and improved the oxidation resistance of the composite coating, which exhibited the lowest weight loss rates in oxidation tests.

The prepared nanofluid demonstrates exceptional interfacial properties and absorption capacity, making it a promising carrier for advanced CCUS.

In order to improve the surface hardness and wear resistance of titanium alloy, titanium carbide (TiC) coatings were obtained by a novel method: in-situ solid-phase diffusion of carbon atoms mediated by the Fe layer. During the carburization process, carbon atoms entered the octahedral interstitial positions of gamma-Fe and diffused to the surface of the titanium alloy under the driving force of the carbon concentration gradient. In this process, a dense TiC ceramic coating was formed with a uniform thickness of about 50 mu m. The V atoms were dissolved in the TiC coating and Al atoms were pushed to the interface between the TiC coating and the titanium alloy. The average microhardness of the coating is up to 3273HV(0.2), which is 8 similar to 9 times higher than the hardness of the substrate. Furthermore, the coating demonstrated excellent wear resistance, with a wear rate as low as 9 x 10(-8) mm(3)/N.m.

PURPOSE:To explore the potential involvement of m6A methylation in the neuroprotective mechanism of H2S against hippocampus neuronal apoptosis in aged rats with POCD. METHODS:Sprague-Dawley rats (18-20 months) were subjected to anesthesia and laparotomy surgery to establish an animal model of POCD. The Open Field, Y-maze, and Novel Object Recognition tests assessed behavioral performance. Protein expression levels were analyzed using Western blot analysis, and neuronal apoptosis was analyzed using TUNEL staining. RESULTS:NaHS (100 μmol/kg) significantly increased the alternation ratio of the Y-maze test and the discrimination index of the NOR test, reduced hippocampal neuronal apoptosis, indicated by decreased TUNEL-positive neurons and modulated the expression of apoptosis-related protein markers (Bcl-2 was upregulated and Bax/Cleaved caspase-3 were downregulated). Furthermore, NaHS restored reduced m6A RNA methylation levels and corrected the disturbed expression of m6A-related enzymes (METTL3, METTL14, YTHDF1, YTHDF3, FTO, ALKBH5) in the hippocampus of aged rats with POCD. CONCLUSION:H2S shows neuroprotective effects by mitigating hippocampal neuronal apoptosis and restoring m6A RNA methylation in the hippocampus of aged rats with POCD. These findings provide preclinical evidence that H2S may serve as a potential therapeutic agent for the prevention of POCD.

This work firstly evaluated the effect of temperature on the preparation of SiC coating using Al2O3 as catalyst by pack cementation (PC) method. SiC/ZrB2-SiC-Si (ZSS) and SiC/ZrB2-SiC-Al2O3 (ZSA) coating were prepared on the surface of C/C composites by PC combined with atmospheric plasma spraying (APS). The objective of this work is to study the influence of Si and Al2O3 additives for ablation performances of ZrB2-SiC coating. The coated samples were subjected to ablation test, and the phase composition and microstructure evolution were investigated. The results indicated that SiC/ZSA coating had better ablation resistance because phase transformation and growth of ZrO2 grain was restrained by Al2O3.

The objective of this work is to design environmental barrier coatings with new structure to improve the thermal shock and oxidation resistance. A novel tri-layer SiC nanowires+Si/Yb2Si2O7-Si/Yb2Si2O7 coating was designed and fabricated on the surface of C/SiC composites by chemical vapor reaction route and combination of the method of atmospheric plasma spraying. All coated samples were subjected to thermal shock test at 1300 celcius. Results indicated that the interfacial bond among the layers in the coating system and C/SiC composites was still intact without delamination crack. The Si in the Yb2Si2O7-Si layer consumed the oxygen diffused into coating and then reacted with Yb2SiO5 to form Yb2Si2O7, which could decrease the release of tensile stress caused by thermal mismatch. The study also investigates the Yb2Si2O7 formation in the Yb2SiO5-Si system, and finds that the Yb2Si2O7 formation was controlled by the diffusion of Yb3+ and Si4+ ions through the Yb2Si2O7 layer.

SiC coatings reinforced with SiC nanowires were prepared on carbon/silicon carbide (C/SiC) composites through chemical vapor reaction route and chemical vapor deposition (CVD). The SiC nanowires were introduced to mainly improve the interface bonding properties of the coating and C/SiC composites. The microstructure, phase composition, thermal cycling, and bonding strength of the SiCnws-SiC coating were investigated. After nine thermal cycles, the weight loss of the SiCnws-SiC-coated C/SiC composites was only 4.6 wt.%. Tensile test results show that the tensile strength of the SiCnws-SiC-coated C/SiC composites was more than 4.5-4.6 MPa. The introduction of SiC nanowires effectively improved interface bonding strength, thus enhancing the thermal cycling and mechanical properties of the coating.

Ultra-high temperature ceramic (UHTC) has been developed to protect C/C composites exposed to hightemperature oxidizing environment. In this study, the effect of additive for the ablation behavior of ZrB2based coating was investigated. The SiC-La2O3 bond coat was firstly prepared on the C/C composites by the method of pack cementation (PC). ZrB2-SiC-Si (ZSS) and ZrB2-SiC-Al2O3 (ZSA) coatings with dense microstructure and excellent interfacial bonding then were prepared on the surface of C/C composites coated with SiC-La2O3 layer by the method of atmospheric plasma spraying (APS). The ablation experiments of all coated samples were conducted under oxyacetylene torch with a heat flux of 4.18 MW/m2. The microstructure, phase compositions, interfacial bonding, ablation and oxidation behaviors of coating were investigated. After ablation test, the ZrO2 sketon with prorous structure was formed in the central region of ZSS coating. However, denser structure still can be observed at ZSA coating due to the formation of liquid phase. The SiC-La2O3-C/C interface are still without cracks. Furthermore, the diffusion of La element into ZSS and ZSA coatings from the SiC-La2O3 layer was beneficial for the improvement of ablation resistance. The result indicated that SiC-La2O3/ZSA could effectively provide protection for C/C composites.

To reduce Si layer delamination or spallation caused by volume change of the layer during thermal cycle and improve the oxidation resistance of Si layer, the SiC-nanowire-reinforced Si layer (SiCnws-Si layer) was prepared in situ on carbon/silicon carbide (C/SiC) composites though the chemical vapor reaction route and atmospheric plasma spray (APS). The SiC nanowires was conducive to fabricate a dense and homogeneous layer. The SiC nanowires was introduced to improve the bonding strength between Si layer and C/SiC composites, enhance the toughness of Si layer and relieve the thermal stress caused by volume change. Therefore, the results of thermal cycling and the tensile strength tests showed that the weight loss of the SiCnws-Si-coated C/SiC composites was 8.3%-60.9% lower than that of Si layer after suffering 12 times thermal cycles between room temperature and 1673 K. Moreover, due to the bridging effect of SiC nanowires on the interface, the tensile strength of the SiCnws-Si-coated C/SiC composites was higher than 3.9 MPa.

The root structure was introduced to mainly improve the oxidation resistance and bonding strength of chemical vapor deposition (CVD) SiC coating on C/SiC composites. The microstructure, phase composition, bonding strength, and thermal cycling performance of SiC coatings with root structure were investigated. The results indicated that the designed and prepared root structure, consisting of pores and SiC nanowires, improved the bonding strength between the matrix and SiC coating. The tensile strength of the coating increased to over 4.67 MPa. The root structure reduced coating cracking or spalling by relieving thermal stress, inhibiting the propagation of cracks, and improving bonding strength. The oxidation resistance of coating could be effectively increased. After 9 thermal cycles between 1873 K and room temperature, the weight loss was only 0.48 wt%.

As an additive, Al2O3 nano-powder can significantly improve the preparation of SiC coating by the pack cementation process. The three-dimensional morphology of the SiC coating and the interface between coating and substrate were analyzed by synchrotron radiation X-ray computed tomography (SR-CT). Combined SR-CT and other analysis results, an unpredicted effect mechanism of Al2O3 was analyzed in this work, which is obviously different from previous studies. The holes left by the chemical reaction between the Al2O3 and SiC can be the penetrating channels for the liquid Si into the C/C composites, which could obviously increase the thickness of SiC coating. At the same time, the density of SiC coating is also improved by adding the Al2O3 nano powder.

4H-SiC crystals containing polytype defects are investigated by optical microscopy, atomic force microscopy, and Raman scattering, aiming at understanding the mechanism of polytype transformation during growth processes. It is observed that the crystal surfaces around the facet are uneven and contain many macroscopic triangular domains, consisting of wide triangular terraces and giant macrosteps. Nucleation and growth on the wide terraces are demonstrated to be responsible for the polytype transformation. A possible polytype transformation mechanism is put forward, which can explain the stabilizing effect of nitrogen on 4H-SiC growth.

Here, we report a commonly occurring defect related to nitrogen doping in silicon carbide crystals grown by physical vapor transport method while its formation mechanism has remained unclear. It is often mislabeled as planar hexagonal void defect (PHVD) owing to their similar in shape and size on wafer surface. Our results indicate that this is a new type of defect and differs from PHVD with respect to their nitrogen concentrations, void shapes and the connections to micropipe. We found that the carbon-rich vapor during the crystal growth is responsible for the formation of this type of defect. A possible three-stage defect developing mechanism and measures to avoid the defects are proposed.

A MoSi2/SiC multilayer anti-oxidation coating for C/C composites was prepared by pack cementation with a later hydrothermal electrophoretic deposition. The phase compositions, morphologies and anti-oxidation properties of the prepared coatings were analyzed by XRD, SEM and isothermal oxidation test. The influence of hydrothermal temperature on the phase composition, microstructure and oxidation resistance of the coating was investigated. And the oxidation behavior of the as prepared coated samples at 1 500 degrees C and 1 630 degrees C was particularly analyzed. Results show that the outer coatings are mainly composed of MoSi(2)phase with a little MoO3 crystalline phase. The thickness, density and anti-oxidation properties of the MoSi2 coating improve with the increase of the hydrothermal temperature. The MoSi2/SiC coatings exhibit excellent oxidation resistance and thermal shock resistance, which can effectively protect C/C composites from oxidation in air at 1 500 degrees C for 320 h and 17 thermal cycles between 1 500 degrees C and room temperature with a weight loss of 1.07%. The weight loss is 2.17% after oxidation in air for 88 h at 1 630 degrees C. The failure of the coating at 1 630 degrees C is due to the generation of cross-holes in the coating during the thermal shock, which can not be self-cured by the SiO2 glass layer after long time of oxidation.

采用水热电泳沉积法在SiC-C/C复合材料表面制备了纳米碳化硅和二硅化钼的复相(SiCn-MoSi2)抗氧化涂层.采用X射线衍射和扫描电子显微镜等对制备涂层的晶相组成、表面及断面微观结构进行了表征.研究了水热温度对制备涂层的结构及高温抗氧化性能的影响,分析了涂层在1600℃静态氧化行为及失效机理.结果表明:外涂层主要由MoSi2和β-SiC晶相组成.复相外涂层的致密程度、厚度及抗氧化性能随着水热温度的升高而提高.SiCn-MoSi2/SiC复合涂层具有较好的抗氧化和抗热震能力,在1600℃氧化80h后氧化质量损失为3.6×10-3g/cm2.复合涂层在1600℃的氧化失效主要是由于经过长时间氧化后SiO2玻璃膜层不能及时有效填补涂层中的缺陷,涂层中出现贯穿性的裂纹和孔洞导致的.

To protect carbon/carbon (C/C) composites from oxidation at high temperature, a nano SiC–MoSi 2 (SiC n –MoSi 2 ) coating on SiC pre-coated C/C composites was prepared by hydrothermal electrophoretic deposition. The phase composition, surface and cross-section microstructures of the prepared SiC n –MoSi 2 coating deposited with different MoSi 2 /SiC n mass ratio were characterized by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The influence of MoSi 2 content in the hydrothermal electrophoretic deposition suspension on the phase composition, microstructure and high-temperature oxidation resistance of the multi-layer coatings were investigated. Results showed that the content of MoSi 2 phase in the prepared coating increases with the increase of MoSi 2 content in the suspension. The density and oxidation resistance of the SiC n -MoSi 2 coating improve with the increase of MoSi 2 mass content from 20 to 60 wt% in the deposition suspension. However, micro-cracks and micro-holes in the coating are found when deposited with 80 wt% MoSi 2 , and a decrease in oxidation resistance was also detected. The multi-layer coatings deposited with suspension of 60 wt% MoSi 2 exhibited the best anti-oxidation ability, which can effectively protect C/C composites from oxidation in air at 1,873 K for 90 h with weight loss of 2.08%.