An Investigation of the Efficient-Precise Continuous Electrochemical Grinding Process of Ti-6Al-4V.

Titanium alloys have many excellent characteristics, and they are widely used in aerospace, biomedicine, and precision engineering. Meanwhile, titanium alloys are difficult to machine and passivate readily. Electrochemical grinding (ECG) is an ideal technology for the efficient-precise machining of titanium alloys. In the ECG process of titanium alloys, the common approach of applying high voltage and active electrolytes to achieve high efficiency of material removal will lead to serious stray corrosion, and the time utilized for the subsequent finishing will be extended greatly. Therefore, the application of ECG in the field of high efficiency and precision machining of titanium alloys is limited. In order to address the aforementioned issues, the present study proposed an efficient-precise continuous ECG (E-P-C-ECG) process for Ti-6Al-4V applying high-pulsed voltage with an optimized duty cycle and low DC voltage in the efficient ECG stage and precise ECG stage, respectively, without changing the grinding wheel. According to the result of the passivation properties tests, the ideal electrolyte was selected. Optimization of the process parameters was implemented experimentally to improve the processing efficiency and precision of ECG of Ti-6Al-4V. Utilizing the process advantages of the proposed process, a thin-walled structure of Ti-6Al-4V was obtained with high efficiency and precision. Compared to the conventional mechanical grinding process, the compressive residual stress of the machined surface and the processing time were reduced by 90.5% and 63.3% respectively, and both the surface roughness and tool wear were obviously improved.

Effect of Bimetal Element Doping on the Low-Temperature Activity of Manganese-Based Catalysts for NH3-SCR.

A series of novel Mn6Zr1-xCox denitrification catalysts were prepared by the co-precipitation method. The effect of co-modification of MnOx catalyst by zirconium and cobalt on the performance of NH3-SCR was studied by doping transition metal cobalt into the Mn6Zr1 catalyst. The ternary oxide catalyst Mn6Zr0.3Co0.7 can reach about 90% of NOx conversion in a reaction temperature range of 100-275°C, and the best NOx conversion can reach up to 99%. In addition, the sulfur resistance and water resistance of the Mn6Zr0.3Co0.7 catalyst were also tested. When the concentration of SO2 is 200ppm, the NOx conversion of catalyst Mn6Zr0.3Co0.7 is still above 90%. 5 Vol% H2O has little effect on catalyst NOx conversion. The results showed that the Mn6Zr0.3Co0.7 catalyst has excellent resistance to sulfur and water. Meanwhile, the catalyst was systematically characterized. The results showed that the addition of zirconium and cobalt changes the surface morphology of the catalyst. The specific surface area, pore size, and volume of the catalyst were increased, and the reduction temperature of the catalyst was decreased. In conclusion, the doping of zirconium and cobalt successfully improves the NH3-SCR activity of the catalyst.

Selective catalytic reduction of NO x by low-temperature NH3 over Mn x Zr1 mixed-oxide catalysts.

Mn x Zr1 series catalysts were prepared by a coprecipitation method. The effect of zirconium doping on the NH3-SCR performance of the MnO x catalyst was studied, and the influence of the calcination temperature on the catalyst activity was explored. The results showed that the Mn6Zr1 catalyst exhibited good NH3-SCR activity when calcined at 400 °C. When the reaction temperature was 125-250 °C, the NO x conversion rate of Mn6Zr1 catalyst reached more than 90%, and the optimal conversion efficiency reached 97%. In addition, the Mn6Zr1 catalyst showed excellent SO2 and H2O resistance at the optimum reaction temperature. Meanwhile, the catalysts were characterized. The results showed that the morphology of the MnO x catalyst was significantly changed, whereby as the proportion of Mn4+ and Oα species increased, the physical properties of the catalyst were improved. In addition, both Lewis acid sites and Brønsted acid sites existed in the Mn6Zr1 catalyst, which reduced the reduction temperature of the catalyst. In summary, zirconium doping successfully improved the NH3-SCR performance of MnO x .

Kinetic Analysis of Laminar Combustion Characteristics of a H2/Cl2 Mixture at CO2/N2 Dilution.

Garbage and biomass contain more chlorine, which reacts with H2 to form HCl gas during combustion or gasification, resulting in corrosion of metal walls. In this paper, based on the chlorine mechanism in Ansys Chemkin-Pro, the laminar combustion characteristics of H2/Cl2 are simulated with different diluents CO2/N2 under an initial temperature of 298 K, equivalence ratio range of 0.6-1.4, and initial pressure of 0.1-0.5 MPa. The results show that the laminar burning velocity of H2/Cl2 decreases significantly with the increase of dilution gas ratio, and the effect of diluent CO2 is more significant than that of N2. Due to the dilution effect, the fuel and oxidation components are reduced. Through sensitivity analysis, reaction R2: Cl + H2 = HCl + H is the main reaction of HCl formation. On improving the initial pressure, the laminar burning velocity is slightly lowered, and the thermal diffusivity of the fuel mixture increases with the increase of the initial pressure. According to the sensitivity analysis of the velocity, reactions R2, R9, and R10 are the main reactions that affect the laminar burning velocity, and the product HCl will be generated with a delay with the increase of the initial pressure.

Effect of Indium Addition on the Low-Temperature Selective Catalytic Reduction of NO x by NH3 over MnCeO x Catalysts: The Promotion Effect and Mechanism.

A MnCeInO x catalyst was prepared by a coprecipitation method for denitrification of NH3-SCR (selective catalytic reduction). The catalysts were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry, scanning electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis, H2 temperature-programmed reduction, and NH3 temperature-programmed desorption. The NH3-SCR activity and H2O and SO2 resistance of the catalysts were evaluated. The test results showed that the SCR and water resistance and sulfur resistance were good in the range of 125-225 °C. The calcination temperature of the Mn6Ce0.3In0.7O x catalyst preparation was studied. The crystallization of the Mn6Ce0.3In0.7O x catalyst was poor when calcined at 300 °C; however, the crystallization is excessive at a 500 °C calcination temperature. The influence of space velocity on the performance of the catalyst is great at 100-225 °C. FTIR test results showed that indium distribution on the surface of the catalyst reduced the content of sulfate on the surface, protected the acidic site of MnCe, and improved the sulfur resistance of the catalyst. The excellent performance of the Mn6Ce0.3In0.7O x catalyst may be due to its high content of Mn4+, surface adsorbed oxygen species, high specific surface area, redox sites and acid sites on the surface, high turnover frequency, and low apparent activation energy.

Numerical Simulation of the Effect of CH4/CO Concentration on Combustion Characteristics of Low Calorific Value Syngas.

The composition of low calorific value synthesis gas varies greatly depending on the raw material and processing technology, which makes the combustion extremely complicated. The three mechanisms of the GRI-Mech 3.0, Li-Model, and FFCM-Mech are used to numerically simulate CH4/CO/H2/N2 air premixed combustion by using ANSYS CHEMKIN-PRO. The numerical simulation is the calculation of laminar flame velocity and adiabatic flame temperature at an initial temperature of 298 K, an equivalence ratio of 0.6-1.4, and an initial pressure of 0.1-0.5 MPa, discussing through thermodynamics and chemical kinetics. The formation of NO X , H, and OH radicals by fuel composition was analyzed. The result shows that the concentrations of H, O, and OH radicals have a positive effect on laminar flame velocity. The combustion reaction of H2 is higher than that of CH4 and CO; with the increase of N2 content, the priority is higher. The thermal diffusivity of flame under different equivalence ratios is affected by inert gas, which affects adiabatic combustion temperature and laminar combustion velocity. In thermal kinetics and chemical kinetics, CH4 has more influence on combustion temperature than CO, while laminar flame velocity is relatively low. Under the change of initial pressure, the laminar combustion flux increases to the initial pressure and the laminar combustion velocity decreases to the increase in pressure. Reactions H + O2 = O + OH, HO2 + H = 2OH, and CH3 + HO2 = OH + CH3O are mainly due to change in the concentration of O, H, and OH radicals.

Plasma-Assisted Controllable Doping of Nitrogen into MoS2 Nanosheets as Efficient Nanozymes with Enhanced Peroxidase-Like Catalysis Activity.

Heteroatom doping is one of the effective ways to improve the catalytic performances of nanozymes. In the present work, the plasma-assisted controllable doping of nitrogen (N) into MoS2 nanosheets has been initially proposed, resulting in efficient nanozymes. The so-obtained nanozymes were characterized separately by TEM, XRD, XPS, and FTIR. It was discovered that the resulting N-doped MoS2 nanosheets could present dramatically enhanced peroxidase-like catalytic activities depending on the plasma treatment time. Particularly, that with the 2-min treatment could display the highest catalytic activity, which is over 3-fold higher than that of pristine MoS2, that was also demonstrated by the kinetics studies. Herein, the N2 plasma treatment could facilitate the N elements to be doped covalently into MoS2 nanosheets to achieve the increased surface wettability and affinity of nanozymes for the improved access of the electrons and substrates of catalytic reactions. More importantly, the covalent doping of N elements into MoS2 nanosheets with a lower Fermi level, as evidenced by the DFT analysis, could facilitate the promoted electron transferring, resulting in the enhanced catalysis of N-doped MoS2 nanozymes, in addition to the high catalytic stability in water. Such a controllable plasma treatment strategy may open a new door toward the large-scale applications for doping heteroatoms into various nanozymes with improved catalysis performances.

Synergetic Ag2S and ZnS quantum dots as the sensitizer and recognition probe: A visible light-driven photoelectrochemical sensor for the "signal-on" analysis of mercury (II).

A visible-light-driven photoelectrochemical (PEC) sensor has been developed for the "signal-on" analysis of Hg2+ by the synergetic combination of low-bandgap Ag2S and wide-bandgap ZnS quantum dots (QDs). Ag2S QDs were synthesized with bead-chain-like structure by the self-assembly route and further covalently bound with ZnS QDs to be coated onto the indium tin oxide (ITO) electrodes. It was discovered that the ZnS@Ag2S-modified electrodes could display the visible-light-driven PEC behavior, of which Ag2S and ZnS QDs could act as the PEC sensitizer and Hg2+-recognition probe, respectively. More importantly, the photocurrent responses of the developed electrodes could be specifically turned on in the presence of Hg2+ under the visible-light irradiation, presumably due to that Hg2+ might conduct a Zn-to-Hg exchange on ZnS QDs to trigger the formation of HgS/ZnS@Ag2S heterojunction towards the enhanced electron-hole separation. The as-prepared PEC sensor could facilitate the detection of Hg2+ with concentrations ranging from 0.010-1000 nM, with a detection limit of about 1.0 pM. Besides, the feasibility of practical applications of the developed PEC analysis strategy was verified by probing Hg2+ in environmental water samples. Such a visible-light-driven PEC detection platform with the unique "turn-on" signal output may promise for the extensive applications for Hg2+ evaluation.

InVO4/ß-AgVO3 Nanocomposite as a Direct Z-Scheme Photocatalyst toward Efficient and Selective Visible-Light-Driven CO2 Reduction.

Photocatalytic CO2 reduction to solar fuel is a promising route to alleviate the ever-growing energy crisis and global warming. Herein, to enhance photoconversion efficiency of CO2 reduction, a series of direct Z-scheme composites consisting of ß-AgVO3 nanoribbons and InVO4 nanoparticles (InVO4/ß-AgVO3) are prepared via a facile hydrothermal method and subsequent in situ growth process. The prepared InVO4/ß-AgVO3 composites exhibit enhanced photocatalytic activity for reduction of CO2 to CO under visible-light illumination. A CO evolution rate of 12.61 µmol·g-1·h-1 is achieved over the optimized 20% In-Ag without any cocatalyst or sacrificial agent, which is 11 times larger than that yielded by pure InVO4 (1.12 µmol·g-1·h-1). Moreover, the CO selectivity is more than 93% over H2 production from the side reaction of H2O reduction. Significantly, based on the results of electron spin resonance (ESR) and in situ irradiated XPS tests, it is proposed that the synthesized InVO4/ß-AgVO3 catalysts comply with the direct Z-scheme transfer mechanism. Significantly improved photocatalytic activities for selective CO2 reduction could be primarily ascribed to effective separation of photoinduced electron-hole pairs and enhanced reducibility of photoelectrons at the conduction band of InVO4. This work provides a new insight for constructing highly efficient photocatalytic CO2 reduction systems toward solar fuel generation.

Facile synthesis of ternary Ag/AgBr-Ag(2)CO(3) hybrids with enhanced photocatalytic removal of elemental mercury driven by visible light.

A novel technique for photocatalytic removal of elemental mercury (Hg(0)) using visible-light-driven Ag/AgBr-Ag2CO3 hybrids was proposed. The ternary Ag/AgBr-Ag2CO3 hybrids were synthesized by a simple modified co-precipitation method and characterized by N2 adsorption-desorption, scanning electron microscope (SEM), X-ray diffraction (XRD), UV-vis diffused reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) techniques. The effects of AgBr content, fluorescent lamp (FSL) irradiation, solution temperature, SO2 and NO on Hg(0) removal were investigated in detail. Furthermore, a possible reaction mechanism for higher Hg(0) removal was proposed, and the simultaneous removal of Hg(0), SO2 and NO was studied. The results showed that a high efficiency of Hg(0) removal was obtained by using Ag/AgBr-Ag2CO3 hybrids under fluorescent lamp irradiation. The AgBr content, FSL irradiation, solution temperature, and SO2 all exhibited significant effects on Hg(0) removal, while NO had slight effect on Hg(0) removal. The addition of Ca(OH)2 demonstrated a little impact on Hg(0) removal and could significantly improve the SO2-resistance performance of Ag/AgBr(0.7)-Ag2CO3 hybrid. The characterization results exhibited that hydroxyl radical (OH), superoxide radical (O2(-)), hole (h(+)), and Br(0), were reactive species responsible for removing Hg(0), and the h(+) played a key role in Hg(0) removal.

Fe3-xCuxO4 as highly active heterogeneous Fenton-like catalysts toward elemental mercury removal.

A series of novel spinel Fe3-xCuxO4 (0

Structural evolution of maize stalk/char particles during pyrolysis.

The structural evolution characteristics of maize stalk/char particles during pyrolysis were investigated. The char was prepared by pyrolyzing at temperatures ranging from 200 to 900 degrees C. Maize stalk and chars were characterized by thermogravimetric analysis, ultimate analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), helium density measurement and N(2) adsorption/desorption method. The char yield decreased rapidly with increasing temperature until 400 degrees C. As temperature increased, the char became progressively more aromatic and carbonaceous. The hydroxyl, aliphatic C-H, carbonyl and olefinic C=C groups were lost at high temperatures. Below 500 degrees C, the removal of volatile matter made pore opening. High temperatures led to the occurrence of softening, melting, fusing and carbon structural ordering. The aromatization process started at approximately 350 degrees C and continued to higher temperatures. The shrinkage of carbon structure occurred above 500 degrees C, which was concurrent with the aromatization process.