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In this study, Si3N4−Si2N2O composite ceramics were prepared through a two‐step combination of the direct nitriding method and spark plasma sintering method with diamond‐wire saw silicon waste in the photovoltaic industry as raw material. The whole holding time at the constant temperature of the preparing process only lasts 35 min, in which the nitriding time only takes 30 min and the sintering time only takes 5 min. The effects of the Fe2O3 additive on the nitriding and sintering process were investigated in detail. The results show that the Fe2O3 additive accelerates the nitriding process by promoting the formation and diffusion of the gas phase and reducing the apparent activation energy of the reaction between the gas phase containing silicon and N2. Meanwhile, the Fe2O3 additive also promotes the sintering process by lowering the eutectic temperature of the SiO2−Al2O3 and the SiO2−Y2O3 binary system. The optimal technical parameters follow the nitriding temperature of 1400°C, the nitriding time of 30 min, the sintering temperature of 1800°C, and the sintering time of 5 min. The Si3N4−Si2N2O composite ceramic prepared under the above conditions exhibits good performance with an apparent porosity of 2.7%, Vickers hardness of 16.54 GPa, and fracture toughness of 4.1 MPa·m1/2. [ABSTRACT FROM AUTHOR]

In this work, first-principles methods were performed to simulate interactions between hydrogen and common alloying elements of high strength low alloy (HSLA) steel. The world has been convinced that hydrogen could be one of the future clean energy sources. HSLA steel with a balance of strength, toughness, and hydrogen embrittlement susceptibility is expected for application in large-scale hydrogen storage and transportation. To evaluate the property deterioration under a hydrogen atmosphere, hydrogen embrittlement (HE) of HSLA steel attracts attention. However, due to the small size of hydrogen atoms, the mechanism of HE is challenging to observe directly by current experimental methods. To understand the HE mechanism at an atomic level, DFT methods were applied to simulate the effects of alloying elements doping in bcc-Fe bulk structure and grain boundary structure. Furthermore, the potential application of DFT to provide theoretical advice for HSLA steel design is discussed. [ABSTRACT FROM AUTHOR]

We investigate the effect of Cr-doping on the properties of α-Fe2O3(001) thin films with Fe termination using the local density approximation plus a Hubbard U correction. We find that both the doping site and concentration of Cr atoms dramatically affect the electronic structure and work function (WF) of α-Fe2O3 films. The results demonstrate that it is most energetically favorable for Cr atoms to substitute the Fe atoms in the sub-surface of α-Fe2O3 thin films. The doping of Cr atoms in the sub-surface not only lowers the band gap of the film but also greatly enhances the work function by 0.9 eV with respect to the pure α-Fe2O3 film. The increase of WF correlates with the reduction of occupied O px/py states at the top valence band which leads to a decrease of the Fermi energy. As the Cr concentration changes from 4.2% to 16.7%, the WF firstly increases, and then drops. The WF reaches a maximum of 6.61 eV for the Cr concentration of 8.3%. These results suggest that doping Cr atoms in a α-Fe2O3(001) thin film can increase the corrosion potential and benefits the protection of steel from corrosion. [ABSTRACT FROM AUTHOR]

We investigate the effect of Cr-doping on the properties of α-Fe 2 O 3 (001) thin films with Fe termination using the local density approximation plus a Hubbard U correction. We find that both the doping site and concentration of Cr atoms dramatically affect the electronic structure and work function (W F ) of α-Fe 2 O 3 films. The results demonstrate that it is most energetically favorable for Cr atoms to substitute the Fe atoms in the sub-surface of α-Fe 2 O 3 thin films. The doping of Cr atoms in the sub-surface not only lowers the band gap of the film but also greatly enhances the work function by 0.9 eV with respect to the pure α-Fe 2 O 3 film. The increase of W F correlates with the reduction of occupied O p x /p y states at the top valence band which leads to a decrease of the Fermi energy. As the Cr concentration changes from 4.2% to 16.7%, the W F firstly increases, and then drops. The W F reaches a maximum of 6.61 eV for the Cr concentration of 8.3%. These results suggest that doping Cr atoms in a α-Fe 2 O 3 (001) thin film can increase the corrosion potential and benefits the protection of steel from corrosion.