The natural chemical modifications of messenger RNA (mRNA) in living organisms have shown essential roles in both physiology and pathology. The mapping of mRNA modifications is critical for interpreting their biological functions. In another dimension, the synthesized nucleoside analogs can enable chemical labeling of cellular mRNA through a metabolic pathway, which facilitates the study of RNA dynamics in a pulse-chase manner. In this regard, the sequencing tools for mapping both natural modifications and nucleoside tags on mRNA at single base resolution are highly necessary. In this work, we review the progress of chemical sequencing technology for determining both a variety of naturally occurring base modifications mainly on mRNA and a few on transfer RNA and metabolically incorporated artificial base analogs on mRNA, and further discuss the problems and prospects in the field.
The surface of steel substrate was pretreated by nickel plating and Aluminum/nickel-plated steel bimetal was prepared by compound casting. After liquid aluminum was casted on the surface of the nickel-plated steel, it was placed in a heat preservation device and temperature set at 760 °C. In the compound casting process of molten aluminum and nickel-plated steel, good metallurgical bonding is formed between aluminum and steel by means of diffusion. Subsequently, the microstructure of the aluminum/nickel-plated steel bimetal was examined using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) techniques. The phase composition of the intermediate layer was analyzed by x-ray diffraction (XRD). Further, the bonding properties and fracture mechanism of the intermediate layer were analyzed by measuring the corresponding Vickers microhardness and shear strength. The results show that the intermediate layer is divided into two layers. In addition, intermetallic compounds appear in the intermediate layer; Al5Fe2, near the steel side, and Al8Fe2Si, near the aluminum side. The main phases in the intermediate layer are α-Al, α-Fe, Al5Fe2, Al5FeSi and Al8Fe2Si. The microhardness of the intermediate layer of the aluminum/steel bimetal is higher than that of both the aluminum matrix and steel matrix. It is observed that the thickness of the intermediate layer of the aluminum/nickel-plated steel bimetal increases with the increase of the holding time. When the holding time was 15 min, the intermediate layer of the aluminum/nickel-plated steel bimetal exhibits the highest shear strength, i.e. 13.4 MPa. The fracture of the aluminum/steel bimetal is a brittle fracture, and starts from the intermediate layer. The results show that nickel plating on steel substrate can obviously improve the casting properties of an aluminum/steel bimetal.
The research focuses on the high temperature oxidation resistance of martensitic heat-resistant steel. A new type of martensitic heat-resistant steel was developed with the addition of Al and Cu, and the oxidation behavior of the new martensitic heat-resistant steel at 650 °C and 700 °C was analyzed. The high temperature oxidation kinetics curves of new martensitic heat-resistant steel at 650 °C and 700 °C were determined and plotted by cyclic oxidation experiment and discontinuous weighing method. XRD technique was applied to qualitatively analyze the surface oxide of the material after oxidation. The surface and cross-section morphology of the material were observed by field emission scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), and the oxidation mechanism at high temperature was analyzed. The results show that the oxide film can be divided into two layers after oxidation at 650 ºC for 200 h. The outer oxide film is mainly composed of Fe and Cu oxides, and the inner oxide film is mainly composed of Al2O3, SiO2 and Cr2O3. After oxidation at 700 ºC for 200 h, the outer layer is mainly composed of Fe, Cu, Mn oxides, and the inner layer is mainly composed of Cr, Al and Si oxides. The addition of a small amount of Cu promotes the diffusion of Al and Si elements, facilitates the formation of Al2O3 and SiO2, and improves the high-temperature oxidation resistance of martensitic heat-resistant steel.
A new type of hot working die steel was designed by using JMatPro, and high-temperature oxidation tests were carried out in the ambient atmosphere at 600 ℃ and 700 ℃. The heat treatment process and oxidation mechanism of the designed 4Cr4Mo2NiMnSiV steel were studied in detail. XRD, SEM and EDS were used to analyze the crystallographic phases, surface and cross-section morphologies of the oxide films. The results show that the main phases in the 4Cr4Mo2NiMnSiV steel were γ and α + δ. During the high-temperature oxidation, oxidation of the Fe outer layer and Cr inner layer occurred. After oxidation at 600℃, the surface oxidation layer comprised a monolayer with an uneven morphology. The surface oxide film had two layers after oxidation at 700℃. The outer oxide layer mainly contained Fe2O3 and Fe3O4, while the inner oxide layer mainly contained Cr2O3. The microstructure was relatively regular and had a significant effect on the protection of the metallic matrix. When oxidized, the 4Cr4Mo2NiMnSiV alloy steel easily formed protective layers, such as Cr2O3 and SiO2, so that the test steel had excellent oxidation resistance at high temperatures.
In this paper, the Titanium carbide/Molybdenum (TiC/Mo) alloy was prepared by spark plasma sintering (SPS). The oxidation process of the TiC/Mo alloy at different oxidation temperatures was studied, and the oxidation mechanism was discussed in depth. The focus is on the influence of the introduction of TiC particles on the high-temperature oxidation properties of Mo alloys. The phase composition and morphology of the oxide film were analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results showed that, after oxidation, the surface oxide film is mainly composed of Titanium dioxide (TiO2), Molybdenum dioxide (MoO2), Molybdenum trioxide (MoO3) and Molybdenum oxide hydrate (MoO3(H2O)2) phases. As the oxidation temperature increases, the surface of the oxide film will warp, and thereby increase porosity. The dense MoO2 will form a protective inner oxide layer and inhibit further progress of the TiC/Mo alloy. Oxygen will undergo violent oxidation through the pores and the inside of the matrix, and the protective MoO2 internal oxide film will disappear. TiC particles dispersed in the matrix will be oxidized to form TiO2, which will be gradually deposited on the surface of the oxide film, hindering the diffusion of oxygen to the matrix. The quantity loss during the entire oxidation process is significantly reduced. Therefore, the introduction of TiC can greatly improve the oxidation resistance of Mo alloys.
In this paper, with reference to the composition and properties of widely used H13 hot working die steel, and the amount of alloying elements in the steel is reasonably improved, and a new steel grade of 4Cr4Mo2NiMnSiV die steel is designed. A new process was designed and the wear properties of 4Cr4Mo2NiMnSiV die steel were studied. SEM, EDS and XRD were utilized to observe the microstructure of the worn surface, and the wear products were analyzed to discuss the wear mechanism. Conclusion illustrates the coefficient of friction of cast steel 4Cr4Mo2NiMnSiV gradually increases with increasing temperature. Wear of the 4Cr4Mo2NiMnSiV die steel is mainly caused by spalling and high-temperature oxidation. The surface oxidation products of high temperature wear samples are Fe2O3 and Fe3O4, and spalling debris caused by fatigue cracks is blocky and a small amount of long flake oxide. The oxide film generated during the high temperature wear process effectively reduces the wear of the material. Through comparison experiments, it is found that the 4Cr4Mo2NiMnSiV die steel of martensite and bainite structure has the best wear resistance, followed by martensitic alloy steel, and the wear resistance of H13 steel which is involved in comparison is lower than that of alloy steel.
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