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•Deposition of AlCrTiVZr high-entropy alloy (HEA) nitride films by HiPIMS.•Films show a continuous change in structure from amorphous to columns with FCC.•Intense bombardment effect ...caused by HiPIMS improves HEA nitride films properties.•The (AlCrTiVZr)N films show a super-hardness of 41.8 GPa and low wear rate.
Super-hard AlCrTiVZr high-entropy alloy (HEA) nitride films were synthesized by high power impulse magnetron sputtering (HiPIMS) without external heating. The effect of N2 gas low rate (FN), ranging from 0 sccm to 20 sccm, on the HiPIMS plasma discharge characterization, element concentration, deposition rate, microstructure, cross-sectional morphology, residual stress, and mechanical properties of films were explored. Results show that increasing FN increases the HiPIMS discharge current, accompanying with the decreased deposition rate. The saturated nitride (AlCrTiVZr)N films were obtained at FN = 8 sccm and higher, which exhibit a simple NaCl-type FCC structure. A continuous variation in the microstructure, from amorphous to columnar crystal structure, has been observed for these nitride films. It is discovered that the moderate FN of 0 sccm to 12 sccm leads to an enhanced bombardment with high-energy particles due to the increased plasma density, while the bombardment effect is weakened because of the decreased plasma energy as the FN is increased further. The nitride films deposited at FN = 12 sccm have super-hardness of 41.8 GPa and low wear rate of 2.3 × 10−7 mm3/Nm. Meanwhile, a change of preferred orientation from (2 0 0) to (1 1 1) is presented as the FN increases from 12 sccm to 20 sccm.
A novel four-arc co-filter cathodic vacuum arc deposition technique which was optimized was introduced to deposit (AlCrMoTiV)Nx high-entropy alloy nitride films that were corrosion-resistant, high ...hardness and adhesion. The effect of nitrogen on the microstructure, corrosion resistance and mechanical properties of films was systematically investigated. As the N2 gas flow rate continues to increase, the phase structure of the (AlCrMoTiV)Nx films transforms from a body-centred cubic structure to an amorphous structure, and then to a nanocomposite structure with nano- crystallites embedded in the amorphous matrix. The hardness of the films is proportional to the ratio of N2:Ar and reaches maximum (34.08 GPa) at a ratio of 7:4. The adhesion of deposited films was higher than 20 N owing to the bombardment of the substrate by energetic ion beams during the deposition of coatings. The enhanced hardness at higher N contents is mainly gives rise to the combined effect of formation of strong metal‑nitrogen bonding, solid solution strengthening, the formation of the nanocomposite structure and ion beam assisted bombardment strengthening. Furthermore, the excellent corrosion resistance can be obtained by the (AlCrMoTiV)Nx films.
•AlCrMoTiV HEA nitride films were prepared by co-filter cathodic vacuum arc deposition.•Effect of gas flow ratio of N2:Ar on structure and properties of film was studied.•The phase structure changes from BCC to amorphous and then to nanocomposite structure.•(AlCrMoTiV)Nx films prepared under N2:Ar = 7:4 show a high-hardness of 35.7 GPa.•AlCrMoTiV HEA nitride films show better corrosion resistance than 304 stainless steel.
Si doped hydrogenated amorphous carbon (a-C:H:Si) films were fabricated in mixed atmosphere of SiH4 and Ar by magnetron sputtering methods, with different SiH4 flow rates. The microstructures and ...tribological performances were measured by Atomic Force Microscopy (AFM), Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy and Tribo-tests. The results showed that the as-fabricated a-C:H:Si films exhibited good tribological performances with low friction and wear. The -OH termination which was deduced by SiO structure inside the a-C:H:Si film reacted with water molecules in atmosphere could passivate the film and counterpart surface, leading to the low friction of a-C:H:Si film. The wear rate increased with the increase of SiH4 gas flow rate, which could be attributed to the formation and increase of SiC phase with high hardness. The SiC phase enhanced the three-body abrasion between the contact surfaces, which increase the wear of the a-C:H:Si film at high SiH4 flow rate.
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•With the Si atoms content as 18.89 %, the DLC films can reach a low friction as 0.05.•The wear rate of the film increases with the increase of the Si atoms content.•The proportion of SiO bond decrease with the increase of silicon atom content.
Super-hard and corrosion-resistant (AlCrMoSiTi)Nx high-entropy nitride coatings were prepared using a novel multi-arc cathodic vacuum magnetic filtration deposition at different N2 gas flow rates ...(RN) of 0, 20, 50 and 70 sccm. The influence of RN on the element composition, phase structure, mechanical, tribological and corrosion properties of the coatings were systematically studied. Higher RN promoted higher N contents in the coatings that resulted in a transformation from an amorphous to face-centered-cubic (FCC) phase. At a high N content of 49 at. % (RN = 70%), the coating exhibits a simple FCC structure, and offers a superior combination of super-hardness, excellent wear and corrosion resistance. The exceptional hardness of the (AlCrMoSiTi)N coating (41.6 GPa) that surpasses most high-entropy ceramics is underlain by the formation of strong metal-nitride phase, the solid-solution strengthening and the fine grain strengthening. Therefore, (AlCrMoSiTi)Nx nitride coating presents a potential application in protective coating owing to its extraordinary mechanical properties and corrosion resistance.
•AlCrMoSiTi nitride coating prepared by multi-arc cathodic vacuum magnetic filtration.•Effect of N2 flow rate on structure and properties of coating was studied.•AlCrMoSiTi nitride coatings show a phase structure change from amorphous to FCC.•The AlCrMoSiTi nitride coatings show a super-hard of 41.6 GPa and low wear rate.•Super-hard nitride coating has a low corrosion current density of 2.2 × 10−8 A cm−2.
Owing to its importance in extraction of natural gas from underground gas storage as well as its crucial role in determination of final gas mixture in the production facilities of gas/oil industry, ...the dry content of wet gas mixture needs to be calculated precisely. The present study explores the potential of different soft-computing techniques in estimation of the dry gas flow rate (kg/h) (output variable) of wet gas mixture based on two input variables of wet gas flow rate (kg/h) and absolute gas humidity (g/m3). Decision tree-based methods (M5P tree, random forest (RF), random tree (RT), and reduced error pruning tree (REPT) models), kernel function-based approaches (Gaussian process regression (GPR) and support vector machines (SVM)), and non-parametric regression-based technique (multivariate adaptive regression splines (MARS)) were implemented for the first time to estimate the dry gas flow rate, and their respective prediction performances were analyzed statistically. Coefficient of correlation (CC), Nash–Sutcliffe efficiency (NSE), root mean square error (RMSE), mean absolute error (MAE), Legates and McCabe's index (LMI), and Willmott's Index (WI) were used as the statistical indicators for validating the performance of each soft-computing model. While M5P model (MAE = 122.2382 kg/h, RMSE = 580.5626 kg/h, CC = 0.9875 for the testing data set) was better than other tree-based models (MAE = 363.2802–542.6119 kg/h, RMSE = 871.9363–1025.3444 kg/h, CC = 0.9587–0.9706 for the testing data set) and MARS model (MAE = 128.0083 kg/h, RMSE = 622.9515 kg/h, CC = 0.9852 for the testing data set), the statistical indicators approved the superiority of the radial basis kernel function-based GPR model (GPR-RBKF) model (MAE = 163.3266 kg/h, RMSE = 483.1359 kg/h, CC = 0.9915 for the testing data set) over other implemented models in predicting the dry gas flow rate. The findings highlighted the potential of soft-computing methodologies in precise estimation of dry gas flow rate in wet gas mixture, particularly, in situations where the measurement of such parameters with traditional deterministic models is practically not possible.
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•Soft-computing methods for estimation of dry content of wet gas mixture.•Performance evaluation of M5P, RF, RT, REPT, GPR, SVM, and MARS.•Superiority of GPR-RBKF over other models in terms of accuracy.•Superiority of M5P over other tree decision tree models in terms of error.•Higher precision of Gaussian processing with kernel-based regression vector.
In this study, the effects of dead volume and sweep gas flow rate on photocatalytic hydrogen production over Pt/TiO2 were examined to determine their possible impact on hydrogen production rates. ...Five different dead volumes (15, 45, 75, 190, 425 ml) under constant reaction solution and interfacial area experimented by using custom made reactors. It was found that higher dead volumes in the gas phase inversely affect the measured hydrogen production. The difference between highest and lowest H2 production rates (at steady state) among five dead volumes is found as 30 μmol/h gcat which is 24% of the highest rate. On the other hand, the difference due to sweep gas flow rates (15, 30, 45 ml/min Ar) was not as significant. It was concluded from these results that measured hydrogen production rate in photocatalytic systems depend strongly on the reactor size through gas phase dead volume and operational factors like sweep gas flowrate. The difference between highest and lowest hydrogen production rates for different dead volumes or sweep gas flow rates is too great to ignore when the average photocatalytic hydrogen production levels (∼500 μmol/h gcat) in the literature are considered. Uncertainties associated with these factors together with well-known difficulties in measurement (or reporting) of the amount of energy and the characteristics of light absorbed by the reaction solution make the comparison of results from different studies impossible. The results of this study confirm the need for standard protocols of measurement and testing in the photocatalysis field in general, and photocatalytic hydrogen production particularly.
•Transport bottlenecks during photocatalytic hydrogen production are reported.•Mass transfer between the gas and liquid phases depend on sweep gas flow rate.•Dead volume above liquid affects gas holdup & G-L interface concentration gradient.•Position of light source strongly influences incident light flux at reactive zone.•Data must be reported with gas volume, liquid volume, sweep rate & light flux.
•Rarefied gas flow through linearly diverging and converging channels has been computationally studied.•The direct simulation Monte Carlo method has been applied.•The mass flow rate and the flow ...field have been computed in a wide range of gas rarefaction.
Using the direct simulation Monte Carlo direct method, rarefied gas flow into a vacuum through linearly diverging and сonverging сhannels has been studied. The problem has been solved in the complete geometrical setup, namely with including certain pre- and post-channel regions in the geometry under consideration. In a wide range of gas rarefaction, a mass flow rate through the channel, the gas flow diodicity, and flow field both inside the channel and in the regions upstream and downstream have been computed. Computation results are compared to corresponding data for the channel with a constant cross-section. A strong effect of channel geometry and gas rarefaction has been stated. In particular, in the dependence of the mass flow rate on the gas rarefaction, a so-called Knudsen minimum has been revealed; while in the flow field, one-dimensional distribution of gas density in the channel has been found.
•A computational framework incorporating the CFD-DEM numerical model and the electromagnetic heating model was proposed.•The relationship between the nozzle design parameters and the powder flow ...behaviors was established.•The relationship between the powder flow behaviors and the laser energy distribution was established.
The spatial distribution of the flying powder particles was simulated by the established integrated model, in which computational fluid dynamics and discrete element methods were combined. In addition to the finite element model of heat transfer, the influences of the defocused amount, gas flow rate, and nozzle diameter on the DED-AM process were studied. Comparison with experimental observations can validate the proposed models. The results indicate that the negative defocused amount is benefit for powder particles to fly on the melt pool center and higher laser energy can be applied to the deposition layer. The powder particle speeds can be accelerated by increasing both the carrier gas and shield gas flow rates. As a result, the laser energy attenuation and the average temperature rise of powder particles decrease. However, the shield gas can lead to scattering of the powders, which causes the higher average temperature rise. When the carrier gas velocity remains constant, an excessively high or low nozzle diameter can lead to an increase in the divergence angle. The divergence angle can be minimized by the optimal selection of nozzle diameter.
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A stable argon plasma at atmospheric pressure can be generated easily with irradiation of a low power of microwave (MW) to promotors like granules of activated carbon, biomass char, electrically ...conductive media, etc. It is well-known that plasma can contribute to significant activity of reactions. The reforming reaction of methane with carbon dioxide was studied in MW plasma at atmospheric pressure. Low power MW plasma converted methane and carbon dioxide into C2 hydrocarbons like ethylene and acetylene, carbon monoxide, and hydrogen. The effects of power supply, CH4/CO2 ratios, and total flow rate were studied on reforming of CH4 and CO2 in MW plasma at low power conditions. The results showed that increasing power facilitates the decomposition of CH4 and CO2, thereby enlarges the yield of each product. However, high power supply has a negative impact on the selectivity of C2. Higher CH4/CO2 ratio can effectively increase C2 selectivity, although it will reduce CH4 conversion. Longer the reaction time or lower gas flow rate reduces the selectivity of C2, while the high flow rate effectively avoids the re-decomposition of C2 products in the plasma region. Furthermore, it was recognized that an existence of CO2 contributes to activation of methane decomposition in MW plasma as well as the plasma contributes to significantly greater synthesis of C2 hydrocarbons than the yield predicted from the composition in the thermodynamic equilibrium.
Polycyclic aromatic hydrocarbons (PAHs) not only present a risk to human health when released into the air, but also can be precursors to form particulate matter (PM) during sewage sludge pyrolysis. ...In this study, 16 EPA PAHs in PM (ΣPAHPM) during sewage sludge pyrolysis were investigated with increasing temperature (200oC–1000 °C) and holding time under different operation conditions inert gas flow rate (IGFR) (200–800 mL/min) and heating rate (5–20 °C/min). ΣPAHPM varied with temperature, IGFR, and heating rate, and ranged from 597 (±41) μg/g to 3240 (±868) μg/g. ΣPAHPM decreased with increasing IGFR but increased with rapid heating rate. Among PAHs species in PM, naphthalene (Nap) was commonly detected at low temperature ranges in all tested conditions. Chrysene (CHR), benzobfluoranthene (BbF), benzokfluoranthene (BkF), benzoapyrene (BaP), indeno1,2,3-cd pyrene (IND), and benzog,h,iperylene (BghiP) in PM became abundant at high temperature with a low IGFR. At high temperature ranges with high volatile conditions (rapid heating rate and low IGFR), PAH formation and growth reactions were considerable, resulting in the formation of heavy PAHs in PM.
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•PAHs formation depends on the operating conditions of pyrolysis.•High inert gas flow rate lowered PAHs in PM.•Rapid heating rates enhanced PAHs formation in PM.•High temperature enhanced PAH formation and growth in PM.
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