Post-treatment Technologies Research Articles

Electrospun porous polyacrylonitrile/polyvinylpyrrolidone nanofiber membrane with ultra-hydrophilic and high moisture-permeability for dust personal protection

The serious dust pollution in coal mine working environment can cause occupational lung diseases and other diseases, affecting the life and health of miners. Therefore, the prospect of developing an air filtration membrane with high filtration performance is of remarkable significance. This study prepared a porous Polyacrylonitrile (PAN) /Polyvinylpyrrolidone (PVP) nanofiber membrane based on Electrospinning and post-treatment technology used for downhole personal protection. The prepared porous nanofiber membrane increased the specific surface area by 133.63 % and the porosity by 391.02 % (compared with the pure PAN nanofiber membrane), and was able to achieve a high filtration efficiency of 98.76 % and a low pressure drop of 165 Pa at an air flow rate of 85 L/min. Meanwhile, this study conducted contact angle and moisture permeability tests on the prepared composite fiber membrane. After 1 second of water droplets falling on the fiber membrane, it had a 14° contact angle (strong hydrophilicity), and the moisture permeability reached 4256.677 cm3/m2·d·Pa, which could discharge the water vapor generated by respiration in time. In addition, given the complex and irregular pore distribution of electrospun nanofibers, the fractal correlation dimension of nanofiber membrane pores was studied through fractal theory, and the relationship between the fractal dimension of fiber pores and respiratory resistance was discussed. Based on this, the nanofiber membrane prepared in this study can be widely used in individual protection in mines.

Fatigue life prediction model for shot-peened laser powder bed fused 304L steel considering residual stress relaxation and defect distribution

Shot peening (SP) is a post-treatment technology that enhances the surface smoothness, mechanical properties, and fatigue performance at the surface layer of metal materials produced through laser powder bed fusion (LPBF). Therefore, accurate life prediction is crucial to effectively design and evaluate the SP process and enhance fatigue life. This study employs a cost-effective and efficient analytical method to investigate relaxation in residual stress (RS). The method calculates the interaction between RS in SP and external loading and combines it with a life prediction model. In addition, a defect-based parameter area is employed to characterize the impact of the effective defect dimensions on the fatigue life of LPBF materials. The effects of compressive residual stress (CRS) introduced by SP and process-induced internal defects on the fatigue life of LPBF material are investigated via a modified Goodman‐Basquin model. The fatigue life of 304L stainless steel (SS) prepared by LPBF after SP is predicted, and good consistency between measurement and prediction is observed.

Surface roughness and microhardness improvement of laser cladding stainless-steel 316 by laser polishing based on multiple remelting

Laser polishing (LP) has emerged as a promising alternative to traditional post-treatment technologies. Nonetheless, the LP process encounters challenges when dealing with surfaces of high roughness, since the excessive thermal input could induce undesirable effects, including the formation of mid-frequency waviness, expansion of heat-affected zone (HAZ), etc. In this study, we investigated the surface roughness and the characters of the remelted layer and HAZ of polishing the laser-cladding 316 stainless steel layer deposited on the surface of a 45# steel cylinder by a 1064 nm hundred-watt pulsed laser and a 1080 nm thousand-watt CW laser respectively. It is observed that the combination of low power density and extended interaction time failed to produce minimum roughness by the pulse laser, contradicting existing LP theories. To address this, we developed a multi-physics model to elucidate the underlying mechanisms and propose an LP scheme based on multiple remelting cycles with the pulsed laser. The Sa roughness is reduced from 20.958 μm to 0.242 μm, decreasing 98.8 %. The processing quality is equivalent to the surface of the high-power CW laser (Sa of 0.283 μm), while the remelted layer and HAZ are significantly smaller. The pulse laser polishing based on multiple remelting increased the surface microhardness by 22 % to 560 HV, while the CW laser remelting reduced it by 33 % to 309 HV. And the HAZ microhardness all decreased in all cases. This study can provide a theoretical basis and solution for the surface finishing of additive manufacturing parts.

Post-treatment technologies for high-speed additive manufacturing：Status, challenge and tendency

In the process of high-speed additive manufacturing, machining defects such as low surface accuracy, high surface roughness, residual stresses and micro-cracks have a serious impact on the performance and life of the product. These machining defects need to be removed by post-treatment in order to promote the use of additive manufactured parts in industrial production. This article provides a systematic review of existing post-treatment technologies for additive manufactured parts, divided into surface post-treatment technologies and overall post-treatment technologies. The processing cost expenditure of the most common post-processing methods is analyzed. The core values and key metrics of post-processing are explored. The prospects for post-processing technology for additive manufactured parts in six key development directions are discussed. The present review systematically discusses the process capabilities and research developments of post-processing technologies for high-speed additive manufacturing, taking into account knowledge from both basic and applied research areas.

Environmental regulations implemented by local officials in China: Is there a hometown effect?

The emotional connection of the people-hometown relationship is an informal but important mechanism in environmental regulation. Based on firm-level Pollution Database in China, this study explores the impacts and mechanisms of the emotional connection between local officials and their hometowns in the implementation of environmental regulation. We found that (1) in the implementation of environmental regulation, the presence of native local officials (i.e., those serving in their home province) leads to a significant reduction in the exhaust gas emissions of industrial enterprises within their jurisdiction, which we call the “hometown effect” of local officials in environmental regulation; (2) Mechanism analysis shows that native local officials enforce stricter environmental regulations, manifested in reduced approval for the entry of polluting firms and less land transfer for developing key polluting industries. Simultaneously, firms are observed with remarkable improvements in their environmental protection technologies, with advancements in pre-emission reduction technology, post-treatment technology, and post-treatment efficiency within the jurisdiction of native local officials; (3) The trade-off between local environment quality and economic growth can be explained within the framework of local accountability. Additionally, the study reveals that the “hometown effect” of local officials in pollution control becomes larger in regions with a richer cultural and natural environment.

High-Quality Hybrid Perovskite Thin Films by Post-Treatment Technologies in Photovoltaic Applications.

Incredible progress in photovoltaic devices based on hybrid perovskite materials has been made in the past few decades, and a record-certified power conversion efficiency (PCE) of over 26% has been achieved in single-junction perovskite solar cells (PSCs). In the fabrication of high-efficiency PSCs, the postprocessing procedures toward perovskites are essential for designing high-quality perovskite thin films; developing efficient and reliable post-treatment techniques is very important to promote the progress of PSCs. Here, recent post-treatment technological reforms toward perovskite thin films are summarized, and the principal functions of the post-treatment strategies on the design of high-quality perovskite films have been thoroughly analyzed by dividing into two categories in this review: thermal annealing (TA)-related technique and TA-free technique. The latest research progress of the above two types of post-treatment techniques is summarized and discussed, focusing on the optimization of postprocessing conditions, the regulation of perovskite qualities, and the enhancement of device performance. Finally, an outlook of the prospect trends and future challenges for the fabrication of the perovskite layer and the production of highly efficient PSCs is given.

Review on Laser Shock Peening Effect on Fatigue of Powder Bed Fusion Materials

The ability to manufacture parts with complex geometry by sending a model from CAD directly to the manufacturing machine has attracted much attention in the industry, driving the development of additive manufacturing technology. However, studies have shown that components manufactured using additive manufacturing technology have several problems, namely high tensile residual stresses, cracks, and voids, which are known to have a major impact on material performance (in service). Therefore, various post-treatment methods have been developed to address these drawbacks. Among the post-treatment techniques, laser shock peening (LSP) is currently considered one of the most efficient post-treatment technologies for improving the mechanical properties of materials. In practice, LSP is responsible for eliminating unfavorable tensile residual stresses and generating compressive residual stresses (CRS), which result in higher resistance to crack initiation and propagation, thus increasing component life. However, since CRS depends on many parameters, the optimization of LSP parameters remains a challenge. In this paper, a general overview of AM and LSP technology is first provided. It then describes which parameters have a greater influence during powder bed melting and LSP processing and how they affect the microstructure and mechanical properties of the material. Experimental, numerical, and analytical optimization approaches are also presented, and their results are discussed. Finally, a performance evaluation of the LSP technique in powder bed melting of metallic materials is presented. It is expected that the analysis presented in this review will stimulate further studies on the optimization of parameters via experimental, numerical, and perhaps analytical approaches that have not been well studied so far.

Effect of hot isostatic pressing on the mechanical and corrosive properties of Ti–Ni alloy fabricated by selective laser melting

Hot isostatic pressing (HIP) is capable of mitigating the internal defects of materials, such as pores and cracks, resulting in improved mechanical properties and corrosion resistance, so it is particularly suitable as a post-treatment technology for the Ti–Ni alloys fabricated by selective laser melting (SLM), which display a broad application prospect in the biomedical field. Herein, the effect of HIP treatment on the mechanical and corrosion-resistant properties of SLM Ti–Ni alloys was systematically investigated. It was demonstrated that HIP treatment did not substantially affect the phase transformation behavior of the SLM Ti–Ni alloy, only showing a slight decrease in the values of As and Ms. However, HIP treatment improved the ultimate tensile strength and the elongation to fracture of the SLM Ti–Ni alloy by 67.3% and 23.2%, respectively. Meanwhile, the corrosion current density was reduced by two orders of magnitude after HIP treatment, indicating the significantly increased corrosion resistance. The enhanced mechanical properties and corrosion resistance of SLM Ti–Ni alloy were credited with the elevated temperature and pressure applied during the HIP process, which significantly eliminated the porosity defects and made the microstructure more uniform. These findings highlight the importance of performing HIP to enhance the comprehensive properties of SLM Ti–Ni alloys, which can expand the application prospects of SLM Ti–Ni alloys in the biomedical field.

Treatment of diluted palm oil mill effluent (POME) synchronous with electricity production in a persulfate oxidant-promoted photocatalytic fuel cell.

Attributable to the prosperous production growth of palm oil in Malaysia, the generated palm oil mill effluent (POME) poses a high threat owing to its highly polluted characteristic. Urged by the escalating concern of environmental conservation, POME pollution abatement and potential energy recovery from the effluent are flagged up as a research topic of interest. In this study, a cutting-edge photocatalytic fuel cell (PFC) system with employment of ZnO/Zn nanorod array (NRA) photoanode, CuO/Cu cathode, and persulfate (PS) oxidant was successfully designed to improve the treatment of POME and simultaneous energy production. The photoelectrodes were fabricated and characterized by field emission scanning electron microscopy with energy (FESEM), X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and Brunauer, Emmett, and Teller analysis (BET). Owing to the properties of strong oxidant of PS, the proposed PFC/PS system has exhibited exceptional performance, attaining chemical oxygen demand (COD) removal efficiency of 96.2%, open circuit voltage (Voc) of 740.0mV, short circuit current density (Jsc) of 146.7 μA cm-2, and power density (Pmax) of 35.6μWcm-2. The pre-eminent PFC/PS system performance was yielded under optimal conditions of 2.5mM of persulfate oxidant, POME dilution factor of 1:20, and natural solution pH of 8.51. Subsequently, the postulated photoelectrocatalytic POME treatment mechanism was elucidated by the radical scavenging study and Mott-Schottky (M-S) analysis. The following recycling test affirmed the stability and durability of the photoanode after four continuous repetition usages while the assessed electrical energy efficiency revealed the economic viability of PFC system serving as a post-treatment for abatement of POME. These findings contributed toward enhancing the sustainability criteria and economic viability of palm oil by adopting sustainable and efficient POME post-treatment technology.

Gradient microstructure and prominent performance of wire-arc directed energy deposited magnesium alloy via laser shock peening

Wire-arc directed energy deposition (DED) has attracted significant interest for the fabrication of large-sized, lightweight Mg-alloy components. However, these components generally exhibit poor mechanical properties and limited corrosion resistance owing to their inherent residual stress and non-equilibrium microstructures. Herein, laser shock peening (LSP) was adopted to successfully modify the stress state and microstructure of AZ31 Mg-alloy fabricated using wire-arc DED. The influence of LSP on the residual stress, mechanical properties, electrochemical behaviour, and microstructural evolution was systematically investigated. The experimental results indicate that, compared with the as-built specimen, the performance of the LSP-treated specimen was notable, with a ≈63.8% decrease in the corrosion current density and ≈30% and ≈13% decreases in the yield strength (YS) and ultimate tensile strength, respectively. The enhanced corrosion resistance can be attributed to the LSP-induced compressive residual stress, nanograins, and nanoparticles. Nanocrystallisation, particle refinement, dense mechanical twins (MTs), and planar dislocation arrays (PDAs) jointly contributed to the enhancement of the YS. The LSP-induced nanocrystallisation was rationalized by the accumulation of PDAs, the intersection of multiple nano-MTs, and the transformation of nano-MTs blocks into sub-grains and then into nanograins owing to continuous dynamic recrystallisation. The particle refinement mechanism involved dislocation proliferation and the development of dislocation slip bands, which eventually led to fragmentation and separation. Therefore, this study introduces a LSP post-treatment technology for the residual stress regulation, microstructural modification, and performance enhancement of Mg alloys fabricated using wire-arc DED. Based on the ability of LSP to tailor the microstructure and performance of Mg alloys, a novel method of wire-arc DED with online LSP treatment is proposed. This method can achieve in-situ surface strengthening and the integrated formation of large-sized components with complex geometries.

Laser Powder Bed Fusion of 316L Stainless Steel: Effect of Laser Polishing on the Surface Morphology and Corrosion Behavior

Recently, laser polishing, as an effective post-treatment technology for metal parts fabricated by laser powder bed fusion (LPBF), has received much attention. In this paper, LPBF-ed 316L stainless steel samples were polished by three different types of lasers. The effect of laser pulse width on surface morphology and corrosion resistance was investigated. The experimental results show that, compared to the nanosecond (NS) and femtosecond (FS) lasers, the surface material’s sufficient remelting realized by the continuous wave (CW) laser results in a significant improvement in roughness. The surface hardness is increased and the corrosion resistance is the best. The microcracks on the NS laser-polished surface lead to a decrease in the microhardness and corrosion resistance. The FS laser does not significantly improve surface roughness. The ultrafast laser-induced micro-nanostructures increase the contact area of the electrochemical reaction, resulting in a decrease in corrosion resistance.

One-step synthesis of hierarchical ZSM-5 zeolites with low defect density as long-lived MTH catalysts

The combination of introducing mesopores and minimizing framework defects in zeolite catalysts has been proved to be highly effective in improving their catalytic lifetime in the MTH reaction. However, there is currently a lack of simple method to realize these two purposes at the same time. In this work, we report a simple one-step approach which not only completed the introduction of abundant mesopores into zeolite catalyst but also simultaneously realized the reduction of framework defects. Secondary template, fluoride media and post-treatment technology were not used during the synthetic process. As an example, a hierarchical ZSM-5 zeolite catalyst with low defect density was successfully synthesized. In the MTH reaction, the synergy effect of the hierarchical pore structure and the less framework defects endowed the prepared zeolite catalyst with a very long lifetime, which is 7.1 times that of the reference catalyst.

Removal of Contaminants of Emerging Concern from Wastewater Using an Integrated Column System Containing Zero Valent Iron Nanoparticles

Non-steroidal anti-inflammatory drugs (NSAIDs) and endocrine disruptors (EDCs) are among the most important categories of contaminants of emerging concern (CECs), and many advanced technologies have been developed for their elimination from water and wastewater, including nano-zero valent iron (nZVI). This study investigates the performance of nZVI synthesized from green tea extracts and incorporated into a cationic resin (R-nFe) in the removal of four selected NSAIDs, namely ibuprofen (IBU), naproxen (NPX), diclofenac (DCF), and ketoprofen (KFN), and an EDC, namely bisphenol A (BPA). Column experiments were conducted to evaluate the effect of various operating parameters, including initial CECs concentration, contact time, pH, addition, and dose of sodium persulfate (PS). To the authors’ knowledge, this is the first time that environmentally friendly produced nZVI has been combined with PS in column experiments for the removal of CECs from wastewater. With a contact time of 2.2 min, PS = 1 mM, and influent pH = 3.5, 27–72% of IBU, 70–99% of NPX, 70–95% of DCF, 28–50% of KFN, and 61–91% of BPA were removed during a 12-day operation of the system, while the initial concentration of each substance was 5 μg/L. Therefore, it is anticipated that the proposed system could be a promising post-treatment technology for the removal of CECs from wastewater.

Enhanced Low Cycle Fatigue Properties of Ti-6Al-4V Alloy by Post-treatment Technology of Pulse High-Intensity Magnetic Field

Enhanced Low Cycle Fatigue Properties of Ti-6Al-4V Alloy by Post-treatment Technology of Pulse High-Intensity Magnetic Field

Feasibility of rapid gravity filtration and membrane ultrafiltration for the removal of microplastics and microlitter in sewage and wastewater from plastic industry

Wastewater treatment plants (WWTPs) act as barriers in reducing uncontrolled microplastic and microlitter (MP-ML) emissions from both urban and industrial wastewaters. Despite removing most of the MP-ML, large quantities of this waste still enter the environment through WWTP effluents, which means further post-treatment technologies are needed. This study contains a technical evaluation of MP-ML removal from urban wastewater (UWW) and from the wastewater from the recycling plastic industry (PIWW) using two different pilot-scale post-treatment systems: rapid gravity filtration (RGF) and ultrafiltration (UF) membranes. The MP-ML mass concentrations contained in UWW and PIWW were measured by a simplified method adapted for the long-term monitoring of WWTP operations. The method was validated on standard samples. Despite the RGF system consumed less energy than UF treating UWW (0.097 kWh·m−3 and 0.156 kWh·m−3, respectively), RGF was not efficient enough to properly decrease the risk of MP-ML emissions (39.5 ± 34.6 % of MP-ML removal). With respect to PIWW, the energy consumption of the UF plant decreased up to 0.059 kWh·m−3. The combination of RGF and UF technologies was expected to reduce membrane fouling but it did not show significant differences in the mid-term operation.

A pilot-scale study of a down-flow hanging sponge reactor as a post-treatment for domestic wastewater treatment system at short hydraulic retention times

This study proposes a down-flow hanging sponge (DHS) reactor as a post-treatment process for sewage treatment systems. A pilot-scale DHS reactor was operated over 1000 days under relatively short hydraulic retention times (HRT) of 1–3 h to evaluate its effectiveness as a post-treatment technology. The DHS reactor consistently achieved superior effluent water quality with total suspended solid <10 mg/L, biochemical oxygen demand < 10 mg/L, and ammonium nitrogen < 5 mg/L. The effective removals (> 2-log10 reduction) of Escherichia coli, a fecal contaminant indicator, and Arcobacter spp., a potentially pathogenic bacterial group, were achieved. The treatment performance was compared with the previous operation treating raw domestic wastewater under long HRTs of 4 and 5 h. As a result, the DHS reactor under short HRT conditions showed advantages for biological oxidation and fecal contaminant removal. These results indicate that the DHS reactor could be a compact post-treatment technology.

Evaluation and prediction of pore effects on single-crystal mechanical and damage properties of selective laser melted Inconel-718

Pore defects inescapably occur during the selective laser melting (SLM) process of metallic materials, which are difficult to be eliminated even by advanced process optimizing and post-treatment technologies. Properties of SLM-fabricated materials depend on the influence of pores, while the effect mechanism is not clearly understood. To clarify the pore effects and achieve reliable forecasting, a statistical-theory-based grain-scale simulation work was performed. Taking Inconel-718 as the example, actual pore defects were detected and classified into three types i.e., gas pore, keyhole pore and lack-of-fusion (LOF) pore, which were then fitted by single or multiple ellipsoids. The volume, shape and posture of pores were characterized by independent parameters, and single-pore-included single-crystal simulations were carried out. Furthermore, overall pore effects were divided into single-ellipsoidal effects, sub-pore quantity effects and sub-pore intersection effects, and the influence mechanisms of pore characteristics on the mean tensile strength and the maximum damage driving force were clarified through partial correlation analysis. Eventually, single-crystal mechanical and damage property prediction models for the grain with an internal pore defect were developed and verified, which show good accuracy with 8–22% relative deviation for damage resistance predictions, and show excellent accuracy with lower than 0.3% relative deviation for strength property predictions.

High-temperature filtration demonstration applying Fe-Al intermetallic membrane for a 410 t/h scale coal-fired power plants

High-temperature filtration in coal units is a promising approach for the clean and efficient utilization of coal power. In this paper, a high-temperature precipitator was applied in a 5000 Nm3/h pilot scale platform and especially a full scale 410 t/h pulverized coal boiler, where the precipitator was installed in front of the denitrification unit. The 410 t/h pulverized coal boiler was tested before and after the installation of high-temperature precipitator. The results showed that the particulate matter concentrations at the outlet of the high-temperature precipitator are both less than 8 mg/m3 at nominal 70% and 90% loads. Meanwhile, the outlet concentration increases with the boiler load. The pressure drop for a high-temperature precipitator applying Fe-Al intermetallic membrane is only 500 ± 50 Pa under 90% loads, which is much less than that of conventional fabric filter. Furthermore, gaseous ammonia injection and ammonia escape in the SCR reactor are both decreased under the same denitrification efficiency compared with the typical flue gas pollution post-treatment technologies. The air preheater blockage is potentially the biggest issue for coal-fired power plant and has attracted extensive attention. As expected, the application of the high-temperature precipitator greatly alleviated the negative effects of high fly ash concentrations and reduced the pressure drop for the air preheater during the test. The pressure drops benefit brought by the high-temperature precipitator for the module including high-temperature precipitator, SCR unit, air preheater approaches 1500 ± 50 Pa. Taking a 1000 MWe coal-fired unit and a typical bituminous coal for example, a 1000 MWe coal-fired unit applying the high-temperature precipitator is expected to achieve 30% relevant energy consumption benefit. Furthermore, a total of 4.48 million tons CO2 emission reduction per year could be achievable if 70% of the Chinese national thermal power market employed them by 2060.

Review of the Effect of Surface Coating Modification on Magnesium Alloy Biocompatibility

Magnesium alloy, as an absorbable and implantable biomaterial, has been greatly developed in the application field of biomaterials in recent years due to its excellent biocompatibility and biomechanics. However, due to the poor corrosion resistance of magnesium alloy in the physiological environment, the degradation rate will be unbalanced, which seriously affects the clinical use. There are two main ways to improve the corrosion resistance of magnesium alloy: one is by adding alloying elements, the other is by surface modification technology. Compared with adding alloy elements, the surface coating modification has the following advantages: (1) The surface coating modification is carried out without changing the matrix elements of magnesium alloy, avoiding the introduction of other elements; (2) The corrosion resistance of magnesium alloy can be improved by relatively simple physical, chemical, or electrochemical improvement. From the perspective of corrosion resistance and biocompatibility of biomedical magnesium alloy materials, this paper summarizes the application and characteristics of six different surface coating modifications in the biomedical magnesium alloy field, including chemical conversion method, micro-arc oxidation method, sol-gel method, electrophoretic deposition, hydrothermal method, and thermal spraying method. In the last section, it looks forward to the development prospect of surface coating modification and points out that preparing modified coatings on the implant surface combined with various modification post-treatment technologies is the main direction to improve biocompatibility and realize clinical functionalization.

Performance and kinetics of a fluidized bed anaerobic reactor treating distillery effluent

Abstract The kinetic analysis of an anaerobic fluidized bed bioreactor treating distillery effluent was carried out. Natural zeolite was used as biomass carrier at various organic loading rates and hydraulic retention times (HRT). The degradation followed first order kinetics and fitted Michaelis–Menten kinetic model for substrate utilization. The kinetic analysis showed that 9% of the TOC was nonbiodegradable which corresponds to about 14% COD. The non-biodegradable component was responsible for the dark-brown color of the distillery effluent and therefore there was a need for employing a post-treatment technology for their removal. Biomass yield was found to be 0.4658 g/g while endogenic microorganisms decay coefficient was 0.0293, which suggested that there was a need to install a sludge handling unit prior to post-treatment. The maximum micro-organisms’ growth rate was found to be 0.136 d−1 while the specific growth rate of the micro-organisms reduced with an increase in HRT at constant feed concentration. The specific substrate utilization rate was found to increase linearly with an increase in the ration of food to micro-organisms and the mean cell residence time was found to be at least 2.5 times the HRT due to application of zeolite as microbial support in the reactor.