Electrostatic Spray Technique Research Articles

Cobalt Nanocluster-Doped Carbon Micro-Spheres with Multilevel Porous Structure for High-Performance Lithium-Sulfur Batteries

Lithium-Sulfur batteries (Li-S batteries) have gained great interest in next-generation energy storage systems due to their high energy density and low-cost sulfur cathodes. There is, however, a serious obstacle in the commercial application of Li-S batteries due to the poor kinetics of the redox process at the sulfur cathode and the “shuttle effect” caused by lithium polysulfide (LiPSs). Herein, we report the synthesis of a sulfur cathode host material that can drastically inhibit the “shuttle effect” and catalyze the conversion of LiPSs by a simple electrostatic spray technique, namely, cobalt (Co) nanoclusters doped with N-containing porous carbon spheres (Co/N-PCSs). The results show that Co/N-PCSs has catalytic activity for the transformation of liquid LiPSs to solid Li2S and alleviates the notorious “shuttle effect.” This new sulfur cathode exhibits stable running for 300 cycles accompanied by a capacity of 650 mAh g−1 at a current density of 1 C, a capacity fading rate of 0.051% per cycle, and a Coulombic efficiency maintained at close to 100%. The results demonstrate that Co/N-PCSs offers the possibility of practical applications for high-performance Li-S batteries.

Preparation and release of novel frog egg-like microspheres by coaxial electrostatic spray technique

• novel frog egg-like microspheres were prepared by coaxial electrostatic spray process. • The microspheres have a distinct core-shell structure. • The microspheres showed porous structures on the surface and inside after drying. • The microspheres can prolong the release of ME. Novel frog egg-like microspheres, referred to as SA@Ca 2+ /PCL-ME microspheres, were created by coaxial electrostatic spray technique, applying a gel formed by cross-linking sodium alginate (SA) with calcium ions as the shell material and a mixture of methyl eugenol (ME) and polycaprolactone (PCL) solution as the core material in the current study. Using optical microscopy, a uniform spherical shape was observed in the microspheres along with a distinct core-shell structure, while its porous internal and external features were visible in SEM images after drying. Furthermore, ME was released in microspheres for more than 12 weeks due to the dual sustained release method comprising a calcium alginate gel and PCL. During 8 weeks of trapping tests, ME-loaded microspheres were shown to be consistently effective.

The light absorption enhancement of nanostructured carbon-based coatings fabricated by high-voltage electrostatic spraying technique

The present work aims to achieve excellent light absorption property in the visible light region to near infrared region by fabricating nanostructured and disordered carbon-based coatings. A simple and low-cost technique i.e. high-voltage electrostatic spraying technique was used to fabricate RGO/CNP coating, CMP/CNP coating and CNT/CNP coating, in which reduced graphene oxide (RGO) sheets, carbon microparticles (CMP) and carbon nanotubes (CNT) were used as frameworks, respectively. The structure and light absorption property of coatings were compared to study the influence of different frameworks. Also, CNT/CNP–TiN coating, in which TiN nanoparticles were added as loads, was fabricated to confirm the beneficial effect of TiN addition. Results show that appropriate choice of framework and load is important for the light absorption enhancement of carbon-based coatings fabricated by high-voltage electrostatic spraying technique. CNT/CNP–TiN coating, in which CNT is used as framework, CNP and TiN nanoparticles are used as loads, exhibits excellent light absorption property. The average light absorptance in the wavelength range of 400–1400 nm reaches 97.1%. It is mainly attributed to the formation of honeycomb clusters and the existence of many multi-sized optical cavities. The lights with various wavelengths can be trapped and absorbed easily and effectively by large-sized optical cavities among honeycomb clusters, small-sized optical cavities inside honeycomb clusters and in CNT meshes. Our investigation proves that excellent light absorption property can be achieved by means of the fabrication of nanostructured and disordered carbon-based coatings by using high-voltage electrostatic spraying technique. As highly absorbing coating in the visible light region to near infrared region, CNT/CNP–TiN coating fabricated by high-voltage electrostatic spraying technique is promising in the fields of solar energy collectors, infrared detectors, optical devices and so on.

Synthesis, characterizations and kinetics of MOF‐5 as herbicide vehicle and its controlled release in PVA/ST biodegradable composite membranes

AbstractPolyvinyl alcohol/starch based composite membranes containing herbicide‐loaded metal‐organic‐framework (MOF‐5) was successfully synthesized by electrostatic spraying technique. Several main parameters affecting the adsorption of MOF‐5 were studied, including the initial concentration of the herbicide solution, adsorption time, and temperature. Under optimal conditions, herbicide‐loaded MOF‐5 was successfully synthesized and the main properties were characterized by Scanning Electron Microscopy (SEM), X‐Ray Diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR), Thermogravimetric Analysis (TG), and Brunauer‐Emmett‐Teller (BET), respectively. The results showed that the adsorption capacity of MOF‐5 at optimal conditions was 60.12wt%±0.61 % for atrazine. The sustained release effect of the AT@MOF‐5/PVA/ST composite membranes was reliable, and the cumulative release rate was about 50 % for 15 h. The release behaviour of AT from AT@MOF‐5/PVA/ST composite membranes was first dominated by the mechanism of Fickian diffusion and then by the mechanism of matrix erosion. The main advantages of agricultural herbicide film can be attributed to the eco‐friendly, biodegradable, and persistence of herbicide.

Morphology and Mechanical Properties of a Composite Coating by Electrostatic Dry Spray Method

Powder spray coating was used for many applications such as paint decoration and protection against corrosive environments. The electrostatic spray method is used to lower the manufacturing cost and the environmental effect during the production process. It is done by electrostatic device and spray gun to create a layer on the substrate to play a protective role. Different dry powders were mixed to form a composite mixture consisted of Al2O3 and SiC or ZrSiO4 with Al powder as a binder. The powders mixture was deposited by electrostatic spray technique with a high voltage of 15 kV on a low carbon steel substrate of (40 x 10 x 4) mm in dimensions. Two groups of mixtures were used to form the coating layers. Powders of Al2O3 with (20 and 40) weight percent (wt%) of SiC as the first group and (20 and 40) wt% of ZrSiO4 as the second group were used. 5 wt% of Al powder was added as a binder, and the samples were heat treated at 900 C° for 2 hours. A detailed characterization of the composite coating layers was performed using XRD, SEM, and EDX, as well as, micro-hardness measurements. The obtained surface composite layers were smooth and having good particle distribution which leads to enhance roughness values (Ra). Furthermore, the hardness increased with increasing the amount of carbide and zirconia, and the obtained layers show no presence of defects or cracks.

Durable and washable carbon nanotube-based fibers toward wearable thermoelectric generators application

Fiber-based flexible thermoelectric (TE) materials are very promising for wearable electronics. Carbon nanotubes (CNTs) have shown considerable promise as thermoelectric materials, however, integrating CNTs into a fiber always lowers the performance, which limits the application of CNT-based fibers (CNTFs). This work proposes a low-cost and simple manufacturing process based on electrostatic spray technique to prepare high-performance CNTFs, whose TE and mechanical properties can be optimized by tuning spray voltage and time. With the aid of the optimized electrostatic field, the prepared CNTFs possess excellent durability and the electrical conductivity showing almost no degradation after being washed and deformed repeatedly. In addition, the CNTFs are proved to be easily converted into n-type via polyethyleneimine (PEI) doping process. Based on the prepared p- and n-type CNTFs, this work fabricates a π-type thermoelectric generator (TEG), of which the CNTFs show the ability to optimize thermal design to compensate negative effect of the intrinsic high thermal conductivity of CNTs on the output performance of the device. As a result, a maximum power of 26.2 nW with output voltage of 6.46 mV is achieved at a temperature difference of 33.4 K. This method provides a new way for preparing high-performance fiber-based TE materials.

Tribological and mechanical characterization of epoxy/graphite composite coatings: Effects of particles’ size and oxidation

The present study investigates the mechanical and tribological properties of an epoxy matrix filled with different graphitic particles deposited on an aluminum substrate by the electrostatic spray technique. Three different particles added to the epoxy matrix were the received graphite, the crushed graphite obtained by crushing the natural flake graphite particles using a ball mill, and graphite oxide obtained by oxidation treatment. Nanoindentation tests were conducted on the different coatings in order to evaluate the surface hardness and the contact elastic modulus. The effect of the oxidation treatment and the loading content on the tribological behavior of the above composites were also evaluated under dry-friction conditions. As expected, the smaller the particle size, the greater the reduction in the dynamic friction. The experimental findings showed that adding 5 wt % of crushed graphite (10 µm) provided a similar dynamic friction as the addition of 10 wt % of received graphite (20 µm). The epoxy filled with received graphite showed a lower wear rate than that filled with graphite oxide and crushed graphite. Moreover, both hardness and elastic modulus increased in the case of the epoxy filled with graphite oxide and crushed graphite.

Analysis of electrostatic solid lubricant spray process parameters during turning Ti-6Al-4V alloy

Titanium alloys are considered as hard-to-cut material due to its relatively high resistance to corrosion, low thermal conductivity and high chemical reactivity. Effective penetration of sufficient amount of lubricant in the metalworking process is of utmost importance to (a) reduce frictional resistance at the high-temperature tool–workpiece interface and (b) avert the formation of built-up edge in machining process. Traditionally, the lubricant forms a thin fluid film to reduce the friction. In order to reduce or eliminate coolant usage and to apply lubri-coolant efficiently at tool–chip–workpiece interface, a novel near-dry machining technique called electrostatic charged solid lubricant spray system has been developed. In electrostatic charged solid lubricant spray technique, the aerosolized micro-droplet particles were sprayed from the nozzle tip which uses a phenomenon called contact-charge electrification principle. The quick penetration and wettability of charged atomized droplet particles are impinged with high velocity at the tool–chip interface. The focus of the present experimental research is to analyse the optimum lubrication process parameters of the experimental set-up in terms of effectively applying cutting fluid in the machining zone. The study shows that the desired atomization and machining performance of the electrostatic charged solid lubricant spray technique can be obtained by governing different spray parameters (lubricant flow rate, air pressure, spray nozzle position, nozzle distance, electrostatic voltage). The results revealed that when the charged lubricants are applied with high velocity and large number of droplets, it will have significant influence on surface roughness and cutting force. The fabricated electrostatic charged solid lubricant spray technique provides us with an efficient and economic machining solution by applying solid lubricants effectively at tool–material interface during turning of Ti-6Al-4V alloy material. The present approach and the obtained results will help in better understanding of the machinability of hard-to-cut materials in manufacturing industries.

The preservation performance of chitosan coating with different molecular weight on strawberry using electrostatic spraying technique

In this study, chitosan (CH) coating with different number-average molecular weight (MW, ca. 5, 19 and 61 kDa) was electrostatic sprayed on strawberry. The effects of MW on strawberry quality changes were evaluated during 15 days of storage at 4 °C. The qualities of strawberry included mold growth, weight loss, firmness, total soluble solids (TSS), pH, flavonoids content, superoxide dismutase (SOD) activity and malondialdehyde (MDA) content. Results showed that CH coating could significantly maintain the strawberry qualities during storage compared to uncoated treatment. CH coating with 61 kDa was more effective in retarding the increases of pH and MDA, and could better maintain flavonoids content. However, MW had no significant impact on mold growth, weight loss, firmness, SOD activity of coated strawberry. According to evaluation criteria, CH coating with 61 kDa had better performance on strawberry preservation with the highest synthetic value (6.93), and could be used to maintain quality and prolong the shelf life of strawberry during cold storage.

Effect of molecular weight on the properties of chitosan films prepared using electrostatic spraying technique

Chitosan (CH) films were prepared with different number-average molecular weight (MW, ca. 6.55, 12.93 and 47.70 kDa) and concentration (0.5, 0.75, and 1.0%) using electrostatic spraying (ES) technique. The effects of MW on film-forming solution properties, ES-atomization performances, and film characteristics were investigated. With increase of MW, conductivity, viscosity, surface tension, and contact angle of CH film-forming solution was raised due to the increases of proportions of amine-groups and degrees of CH chain entanglements. Spray cone angle was generally higher at 12.93 kDa, while the average median diameters of film-forming solution droplets were in the range of 6.3–12.0 μm, indicating well atomization effect. Water barrier property and tensile strength of CH films were improved along with increased MW, which was in accordance with the more completed, rougher and more crystalline microstructures implying by SEM, AFM and XRD. However, film antibacterial capacities against E.coli and L. innocua were descended with increased MW. Considering the overall properties, CH film prepared by 47.70 kDa at 0.5% possessed the best performances.

Multi‐scale damping of graphene foam‐based polyurethane composites synthesized by electrostatic spraying

An electrostatic spraying technique was used to synthesize 3D graphene foam (GrF)‐reinforced polyurethane (PU) composites. Glass transition temperature (Tg) of PU increased from 120 to 148 °C after 3.3 vol% GrF addition. Strong interfacial bonding accounts for the improvement in Tg of PU‐GrF composites. Energy dissipation behavior is probed at multiple load scales to examine the intrinsic and structural damping characteristic. Micro‐scale damping at 1 mN and 1,000 Hz exhibited loss tangent value (tan δ), which is 200% higher and 3 times faster than PU. Nano dynamic mechanical analysis of PU‐3.3 vol% GrF composite demonstrated up to 383% tan δ improvement than of PU at 5 μN dynamic load. Physical mechanisms including rippling effect and weak van der Waals forces in graphene account for the high energy dissipation of PU‐GrF composite. This study suggests that PU‐GrF nanocomposites have the potential to serve as a good damping material in vibrating systems. POLYM. COMPOS., 40:E1862–E1870, 2019. © 2018 Society of Plastics Engineers

Tribological Performance of UHMWPE/GNPs Nanocomposite Coatings for Solid Lubrication in Bearing Applications

Ultra-high molecular weight polyethylene (UHMWPE)/ graphene nanoplatelets (GNPs) nanocomposite coatings were developed to reduce friction and wear in the absence of liquid lubrication. UHMWPE nanocomposite powders with different loadings (0.25, 1, and 2 wt.%) of GNPs were prepared and electrostatic spraying technique was then used to deposit the nanocomposite powders on aluminum alloy to form a thin coating. Friction and wear tests were conducted on the coatings against a flat-end pin, made of hardened tool steel to determine the best loading of GNPs. That was further tested to investigate the effect of sliding speed and contact pressure on its tribological properties and to establish coating operating limits. Results showed that UHMWPE nanocomposite coating reinforced with 1 wt.% GNPs showed the best tribological performance. It reduced wear rate by about 51% as compared to the pristine UHMWPE coating. The coating sustained a maximum sliding speed of 1 m/s at a contact pressure of 4 MPa equivalent to a pressure and velocity (PV) value of 4 MPa.m/s.

Effect of deacetylation degree on properties of Chitosan films using electrostatic spraying technique

Chitosan (CH) films at 4.4 kDa with different deacetylation degree (DD, 81.0, 88.1 and 95.2%) and concentration (0.9, 1.2 and 1.5%) were prepared using electrostatic spraying (ES) system. The effects of DD and concentration on film-forming solution properties, ES-atomization effects, and film performances were investigated. Results indicated that surface tension and viscosity of CH solution declined with the increase of DD, while solution conductivity displayed the opposite trend. The spray angles of film-forming solution during ES were in the range of 10.6–14.2°, and the average median diameters of droplet sizes were all ranged from 6.4 to 13.9 μm. The spray angle and droplet size generally reduced with increasing DD, and thus more complete, rougher and more crystalline microstructures of CH films were observed by SEM, AFM and XRD. CH films at 88.1 and 95.2% DD had better water barrier property and tensile strength. In addition, antibacterial capacities of CH films against L.innocua and E. coli were enhanced with DD. The results could provide guidance on the application of ES technology to improve the commercial food safety such as, fruits, vegetables, poultry, meat, and seafood.

Tribological Evaluation of a UHMWPE Hybrid Nanocomposite Coating Reinforced With Nanoclay and Carbon Nanotubes Under Dry Conditions

A novel hybrid polymer nanocomposite coating of ultrahigh molecular weight polyethylene (UHMWPE) reinforced with nanoclay (C15A) and carbon nanotubes (CNTs) has been developed to protect metallic mating surfaces in tribological applications. The hybrid nanocomposite coatings were deposited on aluminum substrates using an electrostatic spraying technique. Ball-on-disk wear tests using a 440C stainless steel ball as the counterface were conducted on the coatings under dry conditions to determine the optimum amount of the loadings of the nanofillers and evaluate their tribological performance at different normal loads and linear velocities. Micro-indentation, raman spectroscopy, scanning electron microscopy (SEM), and optical profilometry techniques were used to characterize the coatings in terms of hardness, dispersion of the nanofillers, morphology, and wear mechanisms, respectively. Results showed that the UHMWPE hybrid nanocomposite coating reinforced with 1.5 wt % of C15A nanoclay and 1.5 wt % of CNTs did not fail even until 100,000 cycles at a normal load of 12 N and a linear speed of 0.1 m/s showing a significant improvement in wear resistance as compared to all other coatings evaluated in this study.

UHMWPE hybrid nanocomposite coating reinforced with nanoclay and carbon nanotubes for tribological applications under water with/without abrasives

Abstract The tribological performance of a novel ultra-high molecular polyethylene (UHMWPE) based hybrid nanocomposite coating under aqueous environment is evaluated in this study by using ball-on-disk configuration and scratch testing. A combination of two nanofillers such as carbon nanotubes (CNTs) and nanoclay (C15A) is used as reinforcement to improve the load bearing capacity of the coating and to improve the resistance to water absorption respectively. The coatings are deposited on aluminum substrates using an electrostatic spraying technique. UHMWPE hybrid nanocomposite coating reinforced with 1.5 wt% of CNTs and 1.5 wt% of C15A nanoclay showed excellent scratch resistance and improved tribological performance under water (with/without abrasives).

Microstructure and corrosion resistance of micro arc oxidation plus electrostatic powder spraying composite coating on magnesium alloy

Based on the morphological characteristics of the microporous micro arc oxidation (MAO) ceramic coating, a double layer composite coating system was applied on the surface of AZ31 magnesium alloy by MAO plus electrostatic powder spraying (EPS) technique. The Mg sample coated with MAO plus EPS (MAO + EPS) was compared with Mg sample coated by MAO coating or EPS monolayer. The results indicated that the corrosion resistance of AZ31 Mg alloy was significantly improved by MAO + EPS composite coating with the exellent binding force. Furthermore, the corrosion mechanism of three coated Mg alloy was discussed.

A novel organoclay reinforced UHMWPE nanocomposite coating for tribological applications

Abstract In the past few decades, there has been a growing demand for inert, wear-resistant, cost efficient, environmental friendly and low friction coatings. Polymer coatings are one of the best candidates to fulfill these demands due to their low density, anticorrosion properties, self-lubricity, low cost and ease of processing. However, some limiting factors such as low load bearing capacity restrict their applications. By keeping in view this limitation, polymer based nanocomposite coatings were developed in the present study by reinforcing ultra-high molecular polyethylene (UHMWPE) with different loadings of C15A nanoclay (0.5, 1.5 and 3 wt%) to improve the tribological performance of the polymer coating. A novel electrostatic powder spraying technique was used to deposit the coatings on an aluminum substrate. Tribological performance of pristine and C15A/UHMWPE nanocomposite coatings, with different loadings of C15A, was evaluated by using a ball-on-disk configuration with a counterface of 440C hardened stainless steel ball at room temperature under dry conditions. After the optimization of nanoclay loading, effect of linear sliding speed (such as 0.1, 0.2, and 0.3 m/s) on the tribological performance of the coating was also evaluated. X-ray diffraction, scanning electron microscopy and optical profilometry techniques were used to characterize the morphology and dispersion of nanoclay in the polymer matrix, evaluate the thickness and understand the wear mechanisms, respectively. It is observed from the results that 1.5 wt% C15A/UHMWPE nanocomposite coating did not fail even until ∼100,000 cycles (sliding distance = 1.3 km) at a normal load of 9 N and a linear sliding speed of 0.1 m/s as compared to the pristine UHMWPE coating which failed early under same conditions. The improvement in the performance of 1.5 wt% C15A/UHMWPE nanocomposite coating is attributed to the resulting exfoliated morphology of the clay platelets in the polymer matrix due to its uniform dispersion that provides an efficient bridging effect, holding the polymer chains together and resisting their easy pull-out.

Evaluation of friction and wear characteristics of electrostatic solid lubricant at different sliding conditions

In modern industry, mechanical parts are subjected to friction and wear, leading to heat generation, which affects the reliability, life, and power consumption of machinery. Effective cooling and lubrication in the machining zone are essential to improve friction and temperatures by efficient heat dissipation which increases tool life and surface quality. Solid lubricant additives have demonstrated better tribological performance in terms of reducing friction and sliding zone temperature without polluting the environment. With an appropriate application of solid lubricant additives in the sliding interface, the friction reduction and wear resistance properties of the lubricant have been successfully improved. Therefore, an attempt has been made in this research work with an investigation of using molybdenum disulphide suspension to reduce the friction at machining zone. To achieve this, in the present work, novel electrostatic charged solid lubricant spray technique (ECSL) has been envisaged for effective supply of solid lubricant mixture at an extreme low flow rate to the sliding interface of WC pin and Ti–6Al–4V alloy as disc materials. Excessive tribological measurements with SAE 40 oil concentrated with 20wt% of MoS2 with micron size particles results in lower friction coefficient and wear because of the fact that particles with small size were more likely to interact with the sliding surfaces of the friction pairs to form a surface protection film, which increases anti-wear ability of sliding surface. The results indicate that the solid lubricants applied effectively with the developed experimental set-up and improve the tribological properties of the sliding surface.

Fabrication of perovskite films using an electrostatic assisted spray technique: the effect of the electric field on morphology, crystallinity and solar cell performance.

An electric field assisted spray deposition method is employed for improving the perovskite film morphology, crystallinity, and surface coverage, and for further fabricating an efficient solar cell. By applying different voltages ranging from 0.5 to 2.0 kV during spray deposition, we observed a large variation in the film morphology and surface coverage compared to those fabricated without an electric field, which is due to improved atomization from the Coulomb fission process. The optimized applied voltage of 1.5 kV during spraying led to completion of the reaction between CH3NH3I and PbI2 on a hot substrate for pure phase CH3NH3PbI3 thin film formation with improved grain growth and surface coverage. The cells fabricated using perovskite films showed clear applied voltage dependence in the energy conversion process and alleviation in J-V hysteresis; with 1.5 kV applied voltage the average cell efficiency of 8.9% was obtained compared to films fabricated without applying voltage providing only 6.5%. The best efficiencies are 10.9% and 7.37% for applied voltages of 1.5 kV and 0 kV, respectively. The enhancement in efficiency with applied voltage is due to the formation of more uniform and dense films with large perovskite crystals, which resulted in efficient electron transportation (enhanced photocurrent and modified series and shunt resistances) by minimizing the charge carrier recombination at grain boundaries (resulting in enhanced open circuit voltage). With further optimization of the perovskite film thickness by adjusting the CH3NH3I spray volume, the average cell efficiency of ∼11.0% was obtained.

Preparation and performance of desiccant coating with modified ion exchange resin on finned tube heat exchanger

In this paper, a desiccant coating with lithium and magnesium modified ion exchange resin (MIER) on finned tube heat exchanger was prepared by impregnation method and electrostatic spraying process, respectively. Impregnation condition and spraying process, which would badly affect the adsorption performance of MEIR desiccant coating, were investigated in detail. Also the morphology, structure, composition and thermal performance of desiccant coating were characterized by X-ray diffractometer (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) and temperature programmed desorption (TPD), respectively. Besides, its cycle stability was also taken into consideration. The results manifested that electrostatic spraying technique and impregnation method can be employed to prepare a thick and uniform desiccant coating (120 µm) with modified ion exchange resin on finned tube heat exchanger successfully, which had an excellent cycle stability. The results of TPD analysis showed, for the enhanced interaction between the modified ions and water molecules, desorption activation energy of the modified resin can be raised slightly. And the static and dynamic adsorption curves of modified desiccant coating indicated that, whether in high or low humidity environment, the adsorption performance could be significantly improved after modification.