High-Performance Nanofluidic Osmotic Power Generation Enabled by Exterior Surface Charges under the Natural Salt Gradient

High-performance osmotic energy conversion (OEC) requires both high ionic selectivity and permeability in nanopores. Here, through systematical explorations of influences from individual charged nanopore surfaces on the performance of OEC, we find that the charged exterior surface on the low-concentration side (surfaceL) is essential to achieve high-performance osmotic power generation, which can significantly improve the ionic selectivity and permeability simultaneously. Detailed investigation of ionic transport indicates that electric double layers near charged surfaces provide high-speed passages for counterions. The charged surfaceL enhances cation diffusion through enlarging the effective diffusive area, and inhibits anion transport by electrostatic repulsion. Different areas of charged exterior surfaces have been considered to mimic membranes with different porosities in practical applications. Through adjusting the width of the charged ring region on the surfaceL, electric power in single nanopores increases from 0.3 to 3.4 pW with a plateau at the width of ~200 nm. The power density increases from 4200 to 4900 W/m2 and then decreases monotonously that reaches the commercial benchmark at the charged width of ~480 nm. While, energy conversion efficiency can be promoted from 4% to 26%. Our results provide useful guide in the design of nanoporous membranes for high-performance osmotic energy harvesting.Comment: 30 pages and 7 figure

Ultrasonic abrasive polishing of additive manufactured parts: An experimental study on the effects of process parameters on polishing performance

The rough surface of metal parts produced by the powder-based layered Additive Manufacturing (AM) technology such as Selective Laser Melting (SLM) is an important problem that needs to be solved. This study introduces obvious improvements in the surface quality of the AM parts by means of ultrasonic abrasive polishing (UAP), which uses cavitation collapse and micro-cut of abrasive particles for finishing surfaces. Experiments were conducted using the orthogonal experimental design method with an L9(34) orthogonal array to investigate the effects of ultrasonic power, machining time, abrasive particle size, and particle concentration on surface roughness Ra and material removal rate (MRR). The wear of the abrasive particles in the slurry was also studied. IN625 nickel-based alloy specimen manufactured by Selective Laser Melting (SLM) was chosen as the target workpiece. The results show that when the ultrasonic output power was too high, both surface quality and machining efficiency were deteriorated. And the surface roughness Ra was not further improved by just increasing the machining time. Severe cavitation erosion occurred in the polishing process and created leftover pits on the workpiece surface, which has a large influence on Ra. The size and amount of the abrasive particles should be within a certain range, which is helpful for material removal and improving the polishing performance. The work is useful for studying the influential process parameters involved in UAP and finding out the appropriate conditions

The dynamics of reinforced particle migration in laser powder bed fusion of Ni-based composite

The dynamics of the reinforced particles' migration remains unclear during the rapid non-equilibrium laser powder bed fusion (LPBF) process. Conducting real-time observations to obtain a comprehensive understanding of the reinforcements' movement is challenging due to the complex physical phenomena that occur during experimentation. The proposed numerical simulation in the present study incorporates a Lagrangian discrete phase model (DPM) to simulate the added submicrometre-sized TiC particles. The simulation results indicate that the migration of TiC particles was primarily induced by the combination of recoil pressure and Marangoni convection force. The TiC particles were also noted to be relatively uniformly distributed in the LPBF-fabricated Hastelloy X-1 wt% TiC composite under a 600 mm/s scanning speed. The present study offers insights into understanding the dynamics of added reinforced phases within the LPBF additive-manufacturing process to further accelerate the development of advanced metal matrix composites processed using the LPBF process

Design of a novel crack-free precipitation-strengthened nickel-based superalloy and composites for laser powder bed fusion

Avoiding cracking defects is crucial to ensuring processability in the laser powder bed fusion (LPBF) of metallic materials. In this study, a crack-free Ni-based superalloy with a high volume fraction of the γ′ phase was designed for the LPBF process using the thermodynamic approach. The results indicate that the designed SD01 Ni-based alloy was crack-free and over 21% of the spherical γ′ phase was uniformly distributed in the matrix after heat treatment. In addition, 1 wt.% TiB2 particles were introduced into the SD01 alloy to further enhance high-temperature mechanical performance. It was found that the morphology of the γ′ phase was altered from spherical to cubic structures, and its volume fraction increased from 21% to 40% after the TiB2 addition. The SD01-TiB2 composite exhibited an excellent combination of tensile strength (437.43 MPa) and elongation (7.71%) at 900 °C compared with the SD01 alloy (252.03 MPa, 3.02%). These findings provide a new metallic material design method for the LPBF of crack-free high-performance Ni-based materials

Nanoscale removal mechanisms in abrasive machining of brittle solids

Brittle solids with dominant covalent-ionic bonding, including single crystals, polycrystals, and optical glass, are core materials for modern microelectronic and optoelectronic devices that are widely used in energy, communication, transportation, and medicine sectors. In high performance device applications, those brittle materials must be machined into parts that often have an extremely smooth surface and a damage-free subsurface with sub-micron precision. Optimisation of an abrasive machining process for the brittle solids can significantly enhance production efficiency and reduce manufacturing cost, as well as prolong device life. The development of high efficiency and low damage ultraprecision shaping technologies for this class of solids requires an in-depth understanding of their deformation and removal mechanisms at nanoscale. In this work, the fundamental mechanisms of deformation and removal of brittle materials involved in individual or cumulative contacts with blunt and sharp grits are analysed, using the scratch-related micromechanics as the theoretical basis. Essentials of brittle-to-ductile transitions in abrasive machining are outlined. Influence of the diversity in material microstructures in determining local deformation and subsequent removal is highlighted. Practical requirements are suggested for further advancing ultraprecision abrasive machining of those brittle solids

An Experimental Study to Enhance the Cutting Performance in Abrasive Waterjet Machining

An experimental study to enhance the cutting performance in abrasive waterjet (AWJ) machining is presented. The study uses the techniques of jet forward impact angles and multipass operations both individually and concurrently when cutting an alumina ceramic and a polymer matrix composite. A brief report on the effect of jet impact angle in single pass cutting is made first, which shows that the optimum jet impact angle for both the ceramics and polymer matrix composite is about 80o. It is found that the multipass cutting technique can increase the cutting capability and application domain of AWJ cutting. It can also improve the major cutting performance such as the depth of cut as compared to single pass cutting within the same total cutting time. The benefit of using multipass cutting operations is further enhanced when it is combined with a jet forward angle of 80o in cutting alumina ceramics

Friction and Wear Characteristics of Aqueous ZrO2/GO Hybrid Nanolubricants

Aqueous nanolubricants containing ZrO2 nanoparticles, graphene oxide (GO) nanosheets, or hybrid nanoparticles of ZrO2 and GO were formulated using a cost-effective ultrasonication de-agglomeration method. The friction and wear characteristics of these water-based nanolubricants were systematically investigated using a block-on-ring testing configuration with a stainless- and alloy steel contact pair. The concentrations and mass ratios of nanoadditives were varied from 0.02 to 0.10 wt.% and 1:5 to 5:1, respectively, to obtain optimal lubrication performance. The application of a 0.06 wt.% 1:1 ZrO2/GO hybrid nanolubricant resulted in a 57% reduction in COF and a 77% decrease in wear volume compared to water. The optimised ZrO2/GO hybrid nanolubricant was found to perform better than pure ZrO2 and GO nanolubricant in terms of tribological performance due to its synergistic lubrication effect, which showed up to 54% and 41% reductions in friction as well as 42% and 20% decreases in wear compared with 0.06 wt.% ZrO2 and 0.06 wt.% GO nanolubricants. The analysis of wear scars revealed that using such a ZrO2/GO hybrid nanolubricant yielded a smooth worn surface, with 87%, 45%, and 33% reductions in Sa compared to water and 0.06 wt.% ZrO2 and 0.06 wt.% GO nanolubricants. The superior tribological performance can be ascribed to the combination of the rolling effect of ZrO2 nanoparticles and the slipping effect of GO nanosheets

Modelling the Depth of Jet Penetration in Abrasive Waterjet Contouring of Alumina Ceramics

Predictive mathematical models for the depth of jet penetration are presented for both straight-slit cutting and contouring by an abrasive waterjet (AWJ). The plausibility and predictive capability of the models are assessed and verified by an experimental investigation when cutting an 87% alumina ceramic. It shows that the predictions of the models are in good agreement with the experimental data

Optimization of Flocculation Settling Parameters of Whole Tailings Based on Spatial Difference Algorithm

In order to obtain the optimum parameters of total tailings flocculation settling, an optimization method of total tailings flocculation settling parameters based on the spatial difference algorithm was proposed. Firstly, the input and output factors of the whole tailings flocculation settling parameters are effectively analyzed, and the relevant factors affecting the flocculation settling parameters are obtained. Secondly, the flocculation settling velocity of the whole tailings is optimized by combining the spatial difference algorithm with the mathematical symmetry algorithm, and the optimal value of the flocculation settling velocity of the whole tailings is obtained. The experimental results show that anionic flocculation has the best flocculation settling effect on the whole tailings. The optimal settlement velocity is close to the actual settlement velocity, and the error of settlement velocity is less than 3.5%. The results show that compared with the traditional method, this method is an effective method to optimize the flocculation and settlement parameters of the whole tailings