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Modulation of water activation is crucial to water-involved chemical reactions in heterogeneous catalysis. Organic sulfur (COS and CS2) hydrolysis is such a typical reaction involving water (H2O) molecule as a reactant. However, limited by the strong O-H bond in H2O, satisfactory CS2 hydrolysis performance is attained at high temperature above 310 °C, which is at the sacrifice of the Claus conversion, strongly hindering sulfur recovery efficiency improvement and pollution emissions control of the Claus process. Herein, we report a facile oxygen vacancy (VO) engineering on titanium-based perovskite to motivate H2O activation for enhanced COS and CS2 hydrolysis at lower temperature. Increased amount of VO contributed to improved degree of H2O dissociation to generate more active -OH, due to lower energy barrier for H2O dissociation over surface rich in VO, particularly VO clusters. Besides, low-coordinated Ti ions adjacent to VO were active sites for H2O activation. Consequently, complete conversion of COS and CS2 was achieved over SrTiO3 after H2 reduction treatment at 225 °C, a favorable temperature for the Claus conversion, at which both satisfying COS and CS2 hydrolysis performance and improved sulfur recovery efficiency can be obtained simultaneously. Additionally, the origin of enhanced hydrolysis activity from boosted H2O activation by VO was revealed via in-depth mechanism study. This provides more explicit direction for further design of efficacious catalysts for H2O-involved reactions. [ABSTRACT FROM AUTHOR]

Electrochemical machining has the advantage of being free of cathode loss, thermal stress, and residual stress, and is suitable for high precision machining of metal structures. Localization of anodic dissolution can be significantly improved by the side-wall insulation of the cathode. However, for shaped-hole machining, the removal of electrolytic products in the machining gap becomes problematic with the increase of machining depth, which may hinder the machining process. The application of vibration to the cathode in an electrochemical machining is considered an effective approach because the frontal gap is periodically changed by the vibration; therefore, the removal of electrolytic products and the refreshment of electrolyte are facilitated. This study is aimed at finding a suitable method for diamond-shaped hole fabrication using electrochemical machining. The influence of vibrating feed, cathode with and without side-wall insulation on the machining stability and accuracy were studied based on the machining system developed in this study. The experimental results reveal that the machining accuracy of the diamond-shaped hole can be improved remarkably by reducing the width of the tool edge. Meanwhile, the machining stability can be improved significantly with a reasonable vibrating feed mode. [ABSTRACT FROM AUTHOR]

Deep narrow metal grooves have wide application prospects in the field of aeronautics and astronautics. Electrochemical machining (ECM) has a unique advantage in the fabrication of deep narrow grooves due to its advantages of no cutting heat, no cutting force, and high machining efficiency. But, there is significant stray current corrosion in the side wall of the deep narrow groove, which restricts the enhancement of the processing accuracy. In the interest of improving the processing accuracy of the deep narrow groove, the effects of compound feed and matching of pulse and oscillation (MOPAO) on the average current density distribution of the deep narrow groove side wall were studied based on finite element analysis (FEA) of the electrostatic field. The finite element simulation results show that the homogeneity of the deep narrow groove could be significantly improved with the increment of the oscillation amplitude, and the processing accuracy could be improved by prolonging the pulse turn-off time. Moreover, contrast experiments on the deep narrow groove ECM were carried out based on a self-developed ECM system. The experimental results indicate that the matching of pulse and oscillation can remarkably improve the processing accuracy, and smaller average groove width and better groove width uniformity can be obtained in comparison with the compound feed. Moreover, the maximum groove width is 2.78 mm, the minimum groove width is 2.73 mm, the length-width ratio reaches 11:1, and the depth-width ratio reaches 9:1 using the machining mode of MOPAO. [ABSTRACT FROM AUTHOR]

Narrow slits are widely used in aerospace, instrument and meter, and heat-transfer equipment. Electrochemical machining (ECM) has the advantage of being free of tool wear, heat-affected zone, and machining deformation, and is suitable for high-precision machining of narrow slits. However, conventional cathodic continuous linear feeding causes serious stray removal at the narrow slit side wall and results in poor forming precision. This paper presents a new compound feeding method with vibration superimposed on a continuous linear feeding method and investigates the electrochemical machining of a narrow slit using this method. Its influence on narrow slit formation based on the numerical analysis of an electric field is studied as well. The results indicate that compound feeding is superior to linear feeding in terms of less stray removal and a smaller slit width. Comparative experiments of the compound and linear feeding with voltage pulses are also conducted based on a self-developed ECM system, with vibration frequencies from 0 to 50 Hz and vibration amplitudes from 0 to 2 mm. The results demonstrate that not only the average slit width and side-wall slope are smaller, but also the localization of the narrow slit electrochemical machining can be significantly enhanced by compound feeding. [ABSTRACT FROM AUTHOR]