Tribological Performance of Random Sinter Pores vs. Deterministic Laser Surface Textures: An Experimental and Machine Learning Approach

This work critically scrutinizes and compares the tribological performance of randomly distributed surface pores in sintered materials and precisely tailored laser textures produced by different laser surface texturing techniques. The pore distributions and dimensions were modified by changing the sintering parameters, while the topological features of the laser textures were varied by changing the laser sources and structuring parameters. Ball-on-disc tribological experiments were carried out under lubricated combined sliding-rolling conditions. Film thickness was measured in-situ through a specific interferometry technique developed for the study of rough surfaces. Furthermore, a machine learning approach based on the radial basis function method was proposed to predict the frictional behavior of contact interfaces with surface irregularities. The main results show that both sintered and laser textured materials can reduce friction compared to the untextured material under certain operating conditions. Moreover, the machine learning model was shown to predict results with satisfactory accuracy. It was also found that the performance of sintered materials could lead to similar improvements as achieved by textured surfaces, even if surface pores are randomly distributed and not precisely controlled.

Study on a Novel Biodegradable and Antibacterial Fe-Based Alloy Prepared by Microwave Sintering

This research produced a porous Fe-8 wt.% Cu alloy by microwave sintering in order to achieve (i) an increased biodegradation rate, and (ii) an antibacterial function. The Fe-8Cu alloy had higher density, hardness and degradation rate (about 2 times higher) but smaller and fewer surface pores, compared to the pure Fe. The Fe-8Cu alloy had a strong antibacterial function (the antibacterial rates against E. coli were up to 99.9%) and good biocompatibility. This work provides a novel approach of alloy design and processing to develop novel antibacterial Fe-based alloys.

UV-C LED Irradiation Reduces Salmonella on Chicken and Food Contact Surfaces

Ultraviolet (UV-C) light-emitting diode (LED) light at a wavelength of 250–280 nm was used to disinfect skinless chicken breast (CB), stainless steel (SS) and high-density polyethylene (HD) inoculated with Salmonella enterica. Irradiances of 2 mW/cm2 (50%) or 4 mW/cm2 (100%) were used to treat samples at different exposure times. Chicken samples had the lowest Salmonella reduction with 1.02 and 1.78 Log CFU/cm2 (p ≤ 0.05) after 60 and 900 s, respectively at 50% irradiance. Higher reductions on CB were obtained with 100% illumination after 900 s (>3.0 Log CFU/cm2). Salmonella on SS was reduced by 1.97 and 3.48 Log CFU/cm2 after 60 s of treatment with 50% and 100% irradiance, respectively. HD showed a lower decrease of Salmonella, but still statistically significant (p ≤ 0.05), with 1.25 and 1.77 Log CFU/cm2 destruction for 50 and 100% irradiance after 60 s, respectively. Longer exposure times of HD to UV-C yielded up to 99.999% (5.0 Log CFU/cm2) reduction of Salmonella with both irradiance levels. While UV-C LED treatment was found effective to control Salmonella on chicken and food contact surfaces, we propose three mechanisms contributing to reduced efficacy of disinfection: bacterial aggregation, harboring in food and work surface pores and light absorption by fluids associated with CB.

Apatite/Salt Slurry Emission Control of Post Combustion Flue Gas of Lignite and Coal in Fluidized Bed - Double Circulation Microwave Column Adsorber

Heated Ca apatite slimes in microwave radiated salt slurries are one of the most promising technologies for advanced fuel energy storage with favorable economic potential and intrinsic properties. The development of solid pellet technology for molten salt is a key issue in the heat transport processing. The apathite phosphate, slurry salt in the slime-salt bath mixes was investigated under microwave radiation heating to result in insoluble sorbent fines dissolved in porous basket. The insoluble consists of noble metal fission products, such as Pb, Zn, Cu. In this study, there have been very few transport studies of wet steam alkali slurry (metal fines-molten alkali salt mixture). Bath ferrite/apatite particle size changed the heat conductivity to salt bath. A major reason is that the retention time in fixed film processes is longer than in solid–gas processes. This allows more time to the heat absorption for cracking to the desorbed persistent compounds. Furthermore, radiated ferrite by microwave allows a sufficient intimate contact between coal and biomass surface pores and gas atmosphere in the furnace due to more pyrolysis gas desorption. Bubbling slurry of sorbent porosity decreases while temperature decreases. There was a critical porous structure of bubbling sorbent bath which is a factor that determines to a great extent both the sorbent rate and degree of boiling it was found that, a porous slurry bath over 45% was more efficient with radiated a low amount ferrite below weight rate of 15% in microwave column.

Influence of Sodium Hypochlorite Treatment on Pore Size Distribution of Polysulfone/Polyvinylpyrrolidone Membranes

This work was focused on the study of hypochlorite treatment on the pore size distribution of membranes. To this end, ultrafiltration membranes from a polysulfone/polyvinylpyrrolidone blend with a sponge-like structure were fabricated and exposed to hypochlorite solutions with different active chlorine concentrations for 4 h at ambient temperature. Liquid–liquid displacement and scanning electron microscopy were employed to study the limiting and surface pores, respectively. After treatment with 50 ppm hypochlorite solution at pH = 7.2, a five-fold increase in water permeance up to 1400 L/(m2·h·bar) was observed, accompanied by a 40% increase in the limiting pore sizes and almost a three-fold increase in the porosity. After 5000 ppm treatment at pH = 11.5, a 40% rise in the maximum limiting pore size and almost a two-fold increase in the porosity and permeance was observed, whereas the mean pore size was constant. Apparently, changes in the membrane structure at pH = 11.5 were connected with polyvinylpyrrolidone (PVP) degradation and wash-out, whereas at lower pH and despite lower active chlorine concentration, this process was coupled with polysulfone (PSf) destruction and removal.

Two-Step Dopamine-to-Polydopamine Modification of Polyethersulfone Ultrafiltration Membrane for Enhancing Anti-Fouling and Ultraviolet Resistant Properties

Polydopamine has been widely used as an additive to enhance membrane fouling resistance. This study reports the effects of two-step dopamine-to-polydopamine modification on the permeation, antifouling, and potential anti-UV properties of polyethersulfone (PES)-based ultrafiltration membranes. The modification was performed through a two-step mechanism: adding the dopamine additive followed by immersion into Tris-HCl solution to allow polymerization of dopamine into polydopamine (PDA). The results reveal that the step of treatment, the concentration of dopamine in the first step, and the duration of dipping in the Tris solution in the second step affect the properties of the resulting membranes. Higher dopamine loadings improve the pure water flux (PWF) by more than threefold (15 vs. 50 L/m2·h). The extended dipping period in the Tris alkaline buffer leads to an overgrowth of the PDA layer that partly covers the surface pores which lowers the PWF. The presence of dopamine or polydopamine enhances the hydrophilicity due to the enrichment of hydrophilic catechol moieties which leads to better anti-fouling. Moreover, the polydopamine film also improves the membrane resistance to UV irradiation by minimizing photodegradation’s occurrence.

Effect of graphene on the interfacial and mechanical properties of hybrid glass/Kevlar fiber metal laminates

The remarkable resurgence of fiber metal laminates (FMLs) is certainly attributed to the hybrid properties inherent to light metals and fibers reinforced polymer (FRP). There are few reports on the role of nano-size reinforcements in these composites. In this study, the effect of graphene nanoplatelets (GNPs) on the flexural and Charpy impact properties of FMLs of aluminum (Al) 2024 reinforced with hybrid glass/Kevlar fibers-epoxy was investigated. Different wt.% of GNPs (0.0, 0.1, 0.25 and 0.5) and hand lay-up method were used to fabricate nano-FMLs followed by evaluating them in three-point bend and Charpy impact tests. Before making the FMLs, the surfaces of Al sheets were modified to generate surface pores/nano-pores in order to improve the interfacial bonding within the FMLs layers. The FMLs containing 0.1 wt.% GNPs exhibited 10%, 9% and 11% improvement in flexural strength and modulus and impact strength, respectively, compared to the FMLs containing 0.0 wt.% GNPs. Increase of the GNPs to 0.25 wt.% caused a reduction of the flexural strength and modulus and impact strength values; 13.7%, 3% and 25.5% compared to the samples without GNPs. Also increase of the GNPs to 0.5 wt.% decreased these properties to 31.3%, 8.8% and 29.5%. Scanning electron microscopy (SEM) observations of their fracture surfaces showed better adhesion at both polymer/fibers (within the FRP) and Al/FRP interfaces. However, at higher wt.% of GNPs, the FMLs became weaker and more brittle. Agglomerated GNPs at the Al/FRP interface penetrated/filled the surface pores/nano-pores on the Al surfaces. Therefore prevent the polymer penetration in pores, resulting in weak interfacial bond and thus overall weaker and less ductile FMLs. As a result, the Charpy impact values for the 0.25 and 0.5 wt.% GNPs samples were respectively 33 and 37 percent smaller than that for the 0.1 wt.% GNPs sample.

Friction and Lubrication Behavior of a Selective Laser Melted Hydraulic Spool Valve Under Contaminated Conditions

Selective laser melting (SLM) technology has a great potential to reduce size and weight of hydraulic valves. However, the tribological performance of an SLMed valve has not been studied which is crucial for the performance and reliability of the valve, especially under contaminated conditions. In this study, the friction and lubrication behavior between an SLMed valve body and a traditional spool were studied using a scaled reciprocating test rig under various contaminated conditions (frequency at 5 Hz and 25 Hz; particle concentration at 0.4 mg/ml and 4 mg/ml; particle size at 1.6 µm and 15 µm). Three types of SLMed samples were fabricated using different exposure times: one has many large surface pores (pores area > 1000 µm2 accounts for 7.167% of the sample surface); one has a few small surface pores (pores area between 100 µm2 and 1000 µm2 accounts for 0.574% of the sample surface); and one only has micropores (pores area < 300 µm2 accounts for 0.168% of the sample surface). The density, hardness, microstructures, and pore characterization of the SLMed samples were investigated. The results indicated that the frequency greatly influenced friction and lubrication behaviors by determining lubrication regimes. The influence of surface pores on the lubrication and friction depends on contact conditions: pores which served as particle containers to reduce friction are prominent under 5 Hz frequency and high particle concentration; extra lubrication by the surface pores is observed under 25 Hz frequency and low particle concentration.