Roughness Levels Research Articles

Investigating the Role of Flow Plate Surface Roughness in Polymer Electrolyte Membrane Fuel Cells with the Use of Multiphysics Simulations

This study investigates the influence of surface roughness on the performance of polymer electrolyte membrane fuel cells (PEMFCs) through computational simulations using COMSOL Multiphysics. Two distinct gas flow channel (GFC) models of serpentine and parallel GFC structures were analysed, featuring various surface roughness levels to examine their impact on gas pressure and velocity dynamics. Rough surfaces are modeled using trigonometric functions to replicate machining-induced variations. Finite element simulations were conducted, assessing the time-dependent relationship between gas pressure and velocity while considering different electrode phase potentials as a function of surface roughness. Rough surfaces generally enhance mass transport, water management, and current distribution compared to smooth surfaces. The results indicated that a surface roughness of approximately 1 µm optimizes PEMFC performance by balancing pressure and velocity, enhancing electrochemical reactions, and reducing excessive pressure drops within the cell. Notably, the 0.7 V operating voltage was found to be the most efficient, achieving rapid stabilization of pressure and velocity levels swiftly. The findings underscore the importance of precise control over GFC roughness to enhance PEMFC performance gains in commercial applications, especially when multiple cells are stacked to achieve high power outputs.

Melt Pool characteristics on surface roughness and printability of 316L stainless steel in laser powder bed fusion

Purpose Surface quality and porosity significantly influence the structural and functional properties of the final product. This study aims to establish and explain the underlying relationships among processing parameters, top surface roughness and porosity level in additively manufactured 316L stainless steel. Design/methodology/approach A systematic variation of printing process parameters was conducted to print cubic samples based on laser power, speed and their combinations of energy density. Melt pool morphologies and dimensions, surface roughness quantified by arithmetic mean height (Sa) and porosity levels were characterized via optical confocal microscopy. Findings The study reveals that the laser power required to achieve optimal top surface quality increases with the volumetric energy density (VED) levels. A smooth top surface (Sa < 15 µm) or a rough surface with humps at high VEDs (VED > 133.3 J/mm3) can serve as indicators for fully dense bulk samples, while rough top surfaces resulting from melt pool discontinuity correlate with high porosity levels. Under insufficient VED, melt pool discontinuity dominates the top surface. At high VEDs, surface quality improves with increased power as mitigation of melt pool discontinuity, followed by the deterioration with hump formation. Originality/value This study reveals and summarizes the formation mechanism of dominant features on top surface features and offers a potential method to predict the porosity by observing the top surface features with consideration of processing conditions.

Study of the contact angle and roughness effects on mercury intrusion porosimetry (MIP) analysis in natural/real carbonate rocks using massive pure minerals and synthetic carbonate rocks

Studying pore networks in rocks is critical for understanding reservoir properties, with mercury intrusion porosimetry (MIP) being a key laboratory method. MIP involves capillary intrusion of mercury, with intrusion pressure (P) related to capillary diameter (d) by the Washburn equation, incorporating mercury properties like contact angle (θ) and surface tension (γ). While a constant contact angle of 140° is typically assumed for MIP, it can vary based on rock mineralogy and surface roughness. This study aims to analyze how contact angle variations and surface roughness affect MIP analysis of carbonate rocks. Initially, contact angle data was obtained for calcite, dolomite, and quartz with varying roughness levels. Synthetic rocks were then constructed using these minerals. MIP was performed using the typical 140° contact angle and a calculated contact angle from the Cassie model, which considers surface composition fraction. Natural rock MIP analysis followed, with contact angles varying due to mineral composition and roughness. The study found higher contact angles than the standard 140°, affecting pore size distributions up to 30%. Natural rock pore network curves were adjusted based on synthetic rock data analysis. These findings emphasize the need for accurate contact angle selection in MIP for precise pore distribution analysis and contribute to the further study of carbonate rocks.

Statistical distribution of static stress resolved onto geometrically-rough faults

The in-situ stress state within fault zones is technically challenging to characterize, requiring the use of indirect methods to estimate. Most work to date has focused on understanding average properties of resolved stress on faults, but fault non-planarity should induce spatial variations in resolved static stress on a single fault. Assuming a particular stochastic model for fault geometry (band-limited fractal) gives an approximate analytic solution for the probability density function (PDF) on fault stress that depends on the mean fault orientation, mean stress ratio, and roughness level. The mean stress is shown to be equal to the planar fault value, while deviations are described by substituting a second-order polynomial expansion of the stress ratio into the inverse distribution on fault slope. The result is an analytical expression for the PDF of shear-to-normal stress ratio on 2-D rough faults in a uniform background stress field. Two end-member distributions exist, one approximately Gaussian when all points on the fault are well away from failure, and one reverse exponential, which occurs when the mean stress ratio approaches the peak. For the range of roughness values expected to apply to crustal faults, stress deviations due to geometry can reach nearly 100% of the background stress level. Consideration of such a distribution of stress on faults suggests that geometric roughness and the resulting stress deviations may play a key role in controlling earthquake behavior.

Comparative analysis of surface roughness level for bearing coating using VMD of vibration signal

Degradation in surface finish of the material is an important concern in engineering applications. However, most of the conventional techniques available to monitor the surface roughness requires dismantling of the machine element. Though in rotary components like bearing, it is practically not feasible. Therefore, in this work, an on-board technique is proposed to compare the level of surface roughness based on vibration signature. To demonstrate, five different industrial standard coatings (Nickel, Copper, Zinc phosphate (ZnP), Silver, and Black oxide) were carried out on raw five ball bearings (NBC6205). Two sets of coated bearing were prepared, where first set was utilised for experimentation and second for the purpose of measuring surface roughness of bearing surface. These coated bearings were tested at five different RPMs ranging from 300 RPM to 1500 RPM and their vibration signals were recorded. The recorded vibration signals must be having characteristics originated from ball rolling on different level of surface roughness and hence distributed in nature. Further, to target distributed characteristics present in the signal, commonly used statistical parameters for vibration signature analysis (RMS, Crest factor, Variance, Skewness, Kurtosis, Shannon entropy and Log energy) were calculated. Then, correlation of the parameters was checked in relation to the different levels of surface roughness but no relation was found. The signals were then decomposed into six intrinsic mode functions (IMFs) using Variational Mode Decomposition (VMD) method. Again, same statistical parameters were calculated for these decomposed levels, it has been noted that Shannon entropy have shown correlation to surface roughness in at least one decomposed level between 900 to 1500 RPM with minimum value of chain index as 176.65. Moreover, in this RPM range, responsive frequency bands found to be shifted towards higher side i.e. from 567 to 4590 Hz.

Roughness affects the response of human fibroblasts and macrophages to sandblasted abutments

BackgroundA strong seal of soft-tissue around dental implants is essential to block pathogens from entering the peri-implant interface and prevent infections. Therefore, the integration of soft-tissue poses a challenge in implant-prosthetic procedures, prompting a focus on the interface between peri-implant soft-tissues and the transmucosal component. The aim of this study was to analyse the effects of sandblasted roughness levels on in vitro soft-tissue healing around dental implant abutments. In parallel, proteomic techniques were applied to study the interaction of these surfaces with human serum proteins to evaluate their potential to promote soft-tissue regeneration.ResultsGrade-5 machined titanium discs (MC) underwent sandblasting with alumina particles of two sizes (4 and 8 μm), resulting in two different surface types: MC04 and MC08. Surface morphology and roughness were characterised employing scanning electron microscopy and optical profilometry. Cell adhesion and collagen synthesis, as well as immune responses, were assessed using human gingival fibroblasts (hGF) and macrophages (THP-1), respectively. The profiles of protein adsorption to the surfaces were characterised using proteomics; samples were incubated with human serum, and the adsorbed proteins analysed employing nLC–MS/MS. hGFs exposed to MC04 showed decreased cell area compared to MC, while no differences were found for MC08. hGF collagen synthesis increased after 7 days for MC08. THP-1 macrophages cultured on MC04 and MC08 showed a reduced TNF-α and increased IL-4 secretion. Thus, the sandblasted topography led a reduction in the immune/inflammatory response. One hundred seventy-six distinct proteins adsorbed on the surfaces were identified. Differentially adsorbed proteins were associated with immune response, blood coagulation, angiogenesis, fibrinolysis and tissue regeneration.ConclusionsIncreased roughness through MC08 treatment resulted in increased collagen synthesis in hGF and resulted in a reduction in the surface immune response in human macrophages. These results correlate with the changes in protein adsorption on the surfaces observed through proteomics.

Effects of fault roughness on estimating critical slip-weakening distance from fault slip history: A laboratory study

Earthquakes are the dynamic rupture of faults governed by fault weakening processes. Critical slip-weakening distance (Dc) is a crucial source parameter of earthquakes, and the determination of Dc is of great concern to semiologists. However, determining Dc for natural earthquakes is challenging due to the trade-off in inversed source models. To solve this problem, Fukuyama and his coworkers proposed a simple method (denoted as the F&M method) to estimate Dc directly from slip-velocity functions. According to the F&M method, the fault slip at the peak slip velocity (Dc') can be used as an approximation of Dc. However, the feasibility of this method has not been completely resolved. Here, we performed laboratory earthquake rupture experiments to examine the validity of the F&M method. Experiments were conducted on faults with different roughness and stress level. We studied the effect of fault roughness on the validity of the F&M method. Our results show that the increase in fault roughness could complicate the fault weakening process, producing repeated weakening and strengthening phase, which leads to a prominent deviation between Dc' and Dc. Furthermore, we also observed a correlation between the critical slip-weakening distance Dc and the final fault slip D. Such correlation implies the scale-dependent nature of Dc, which is consistent with seismic observations in the field.

Comparative Evaluation of Surface Roughness and Color Stability Between Single-Shade Composite and Multi-Shade Composite: An In Vitro Study.

Introduction Composite resin materials are a popular choice for direct tooth-colored restorative purposes due to their excellent aesthetic qualities and versatility. The key determinants that impact the visual aspect of the restoration are gloss, surface roughness, and color stability. Research indicates that there is a direct correlation between the level of roughness on a composite resin surface and the likelihood of discoloration. The aim of this study was to compare and evaluate the surface roughness and color stability of a single-shade and multi-shade composite resin after subjecting it to toothbrush simulation and immersion in coffee and an aerated drink. Materials and methods Ten single-shade composite resinsand 10 multi-shade composite resins were packed into a Teflon mold and light cured. Pre-operative surface roughness values were evaluated using a surface profilometer. Toothbrush abrasion was simulated using a toothbrushing simulator. All these resin molds were then evaluated for initial color using a spectrophotometer machine (Konica Minolta, Japan). Five resin molds were then immersed in a beaker containing coffee for seven days and five resin molds were immersed into a beaker containing an aerated drink for seven days. Following this, the resin molds were re-evaluated for color stability using a spectrophotometer machine. Results The results of this study show that single-shade composite showed increased discoloration when compared with multi-shade composite resin. Also, there is a statistical difference between the single-shade composite and multi-shade composite when it comes to surface roughness and discoloration. Conclusion With the limitations of the present study, it can be concluded that single-shade composite resins have more discoloration potential in beverages than multi-shade composite resins.

Optimization of CNC milling parameters using the response surface method for aluminum 6061

The manufacturing sector is constantly seeking ways to optimize the machining process, specifically for 3-axis CNC machines. This study aims to identify the optimal parameter values that result in the lowest roughness and the highest process capability in 3-axis CNC milling. The roughness level (Ra) of the product is primarily influenced by factors such as feed rate, spindle speed, and depth of cut. Additionally, the reliability of the machining process was analyzed to evaluate its ability to consistently achieve low roughness values and to validate the process capability of the VH850L3 series 3-axis CNC milling machine. The suggested approach for this analysis was the RSM central composite design method, which involved conducting experiments under various input conditions. The results indicated that the feed rate had the most significant impact on roughness, followed by the spindle speed, while the depth of cut had no effect. The parameters that resulted in the lowest roughness response were a spindle speed of 2589.76 rpm, a depth of cut of 0.159 mm, and a feed rate of 247.731 mm/min. These parameter values were tested on a 3-axis CNC machine, and the resulting data exhibited variations. Data processing revealed that the machine still performed optimally in the machining process, as indicated by the value of . However, the milling process deviates from the standard target, as the response value shows significant variation with a Cpk value 1.

In Vitro Evaluation of Color and Surface Roughness Changes of Polyetheretherketone, Monolithic Zirconia, and Resin Nanoceramics Exposed to Staining Liquids.

This study aims to investigate color stability and surface roughness of polyetheretherketone (PEEK), zirconia, and hybrid ceramics while stored in different liquids. A total of 240 specimens were prepared from monolithic zirconia, PEEK, and hybrid ceramics. All specimens were polished using rubber sets with different grain sizes. Color parameters (L*, a*, b*) were measured three times using a dental spectrophotometer in standard D65 lightning. Each group was divided into eight different groups to be kept in eight different solutions as distilled water, cola, red wine, tea, coffee, heptane, citric acid, and 50% ethanol. Specimens were held in solutions at 37°C for 12 days. Color measurements were repeated, and color change (ΔE) was calculated using the CIE Lab formula. The color difference of PEEK specimens was found above the clinically acceptable limit; however, color differences for monolithic zirconia produced by coffee were found within the clinically acceptable limits. ZR and HC specimens' color change values were found between threshold values (1<ΔE < 3.3). The differences observed in surface roughness levels amongst the ZR specimens could be caused by the polishing instrument and procedure. The color change of the materials was within acceptable limits, whereas the surface roughness increased more than 0.2 µm. Especially cola, heptane, and red wine significantly increased the mean surface roughness.

In Ukrainian

The contact wetting is one of the effective methods of studying the adsorption capacity of sorbents. The purpose of the work was to compare the experimentally obtained data on the adsorption capacity of shungite, obtained by the sessile drop method, and the results of modeling the behavior of liquid droplets on heterogeneous surfaces using the Boltzmann lattice method, and to show the suitability of the simplified version of the LBM method that we applied within the framework of a two-dimensional model for modeling complex cases of contact interaction between liquids and sorbent, when it cannot be carried out by the method of contact wetting. The adsorption properties of shungite with regard to the extraction of various impurities from water-alcohol solutions and the capability of the sorbent to recover were investigated by the method of contact wetting and analyzed by involving the data obtained by the methods of nitrogen adsorption, thermogravimetry and IR spectroscopy. It is shown that the adsorption properties of shungite are due to the presence on its surface of hydroxyl functional groups attached to carbon atoms in phenol or enol form, which give the surface hydrophilic characteristics. These groups play a key role in the adsorption of components from the liquid (aqueous) phase due to the formation of a hydrogen bond during the sorption of components from the liquid phase, and are restored after heating in the temperature range of 80–180 °C with the formation of carbon-containing gases and water. It has been found that silanol groups present in shungite do not participate in sorption. Compared to the original shungite sample, the sample after five cycles of adsorption is characterized by a noticeable effect of mass loss (1.8 %) in the temperature range of 80–180 °С. At the same time, the loss of mass is not significant at temperatures below 100 °С. This suggests that the sorbed substances are in the pores and not on the surface of shungite, and they begin to be removed only after heating above 100 °C. The LBM method was used to study fast-moving processes at the meso-level. A comparative analysis of the experimental data obtained by the method of contact wetting with the results of simulation by the Boltzmann lattice method within the framework of the two-dimensional model was carried out. 2D modeling by the LBM method turned out to be an effective means of studying capillary condensation in mesopores, anticipatory wetting of the solid phase, liquid penetration into a porous medium with different topologies, and the formation of anisotropic droplets and anisotropic bridges. The role of mesopores in the sorption process was analyzed by modeling the behavior of liquid droplets on heterogeneous surfaces and using data on the course of adsorption and capillary processes on the surface of a solid phase with different levels of porosity, roughness, and functional composition.

Kinematics and coordination of moth flies walking on smooth and rough surfaces.

The moth fly, Clogmia albipunctata, is a common synanthropic insect with a worldwide range that lives in nearly any area with moist, decaying organic matter. These habitats comprise both smooth, slippery substrates (e.g., bathroom drains) and heterogeneous, bumpy ground (e.g., soil in plant pots). By using terrain of varying levels of roughness, we focus specifically on how substrate roughness at the approximate size scale of the organism affects kinematics and coordination in adult moth flies. Finally, we compare and contrast our characterizations of locomotion in C. albipunctata with previous work of insect walking in naturalistic environments.

Виявлення впливу шорсткості та радіального зазору на характеристику осьового багатоступеневого компресора

The operation of gas turbine engines inevitably increases the blade roughness and tip clearance in multistage axial compressors. The result is an increase in its thermogasodynamic parameters. The reason for the increase in the roughness of the blades and the tip clearance can be various factors: clogging of the flow part of the compressor (adhesion and deposition of dust on the surface of the blades), erosion due to the arrival of hard sand grains in the flow part, etc. The subject of this study is thermogasodynamic processes in the flow part of a multistage axial compressor, based on the presence of flow part removal. The goal is to develop a methodology for forecasting and researching the influence of the blade surface roughness and increased tip clearance on the overall characteristics of a multistage axial compressor. A twelve-stage axial compressor was used as the research object. The guiding vanes of the first four stages and the inlet guiding vanes depend on the rotation frequency. As a result, it was not possible to investigate the influence of the surface roughness of the blades and the increased tip clearance on the overall characteristics of the multistage axial compressor. The calculation of the characteristics of an axial multistage compressor with simulation of different levels of roughness and increased tip clearance in comparison with its initial values and obtained several indicators of changes in thermogasodynamic parameters and characteristics of the compressor with changes in roughness (ks = 3 μm, ks = 20 μm, ks = 40 μm) was performed. and tip clearance (Δr=1%, Δr=2%, Δr=5%). The scientific and practical novelty of the obtained results arises from the following: the method of calculating the thermogasdynamic parameters and characteristics of an axial multistage compressor has been improved, which makes it possible to evaluate the effect of the roughness of the surfaces of the blades and the increased tip clearance; new data were obtained regarding the change in the compressor characteristics at different levels of roughness and the size of the tip clearance.

RANS study of surface roughness effects on ship resistance

Abstract In marine engineering, optimizing the performance of vessels is a key issue, particularly in increasing fuel efficiency, reducing operating costs, and minimizing environmental impact. One of the most critical determinants of vessel efficiency is hull resistance, which directly affects fuel consumption, power requirements, and cruising speed. We aim to investigate how surface roughness affects hull flow resistance, to quantify the drag variation at different surface roughness levels using special wall functions that reproduce boundary layer dynamics. This approach involves the complex interaction between the intricate complexity of roughness and the nonlinear pressure drag effects on the hull. The KVLCC2 ship model is used as a representative prototype in the CFD analysis based on the RANS equations and the k-omega SST model to independently evaluate the roughness effects on individual ship sections. The comparative analysis with empirical data reveals the complex relationship between surface roughness and ship resistance and provides insights for ship design and operational improvement. The study investigates the interaction between drag coefficient and vessel performance to improve hydrodynamic efficiency.

Modeling stochastic elastic wave diffraction by the tips of randomly rough defects

Elastic wave scattering from a randomly rough surface of a finite length includes surface reflections and diffractions from the tips. Previous research has focused upon reflection waves with applications in ultrasonic defect detection, seismic wave exploration and phonon boundary transport. However, waves diffracted from the tips/edges have been largely neglected so far for rough defects, despite their importance in engineering applications including ultrasonic defect sizing and imaging for assessment of structural integrity. Currently understanding the statistical nature of elastic wave tip diffraction and the role of roughness is limited due to the lack of theoretical studies. In this article, we develop a statistical geometrical tip diffraction (SGTD) theory to rapidly predict the stochastic properties of tip diffraction amplitude as a function of surface roughness and incident angle. By applying a small slope perturbation to the model, a simplified analytical solution of tip diffraction is obtained. It is found that for defects with small to medium roughness, the diffraction amplitude explicitly follows a Gamma distribution, and its mean and the standard deviation are both proportional to the square of the rms slope. High-fidelity Monte Carlo finite element simulations are then run to evaluate the accuracy of the theoretical model. The range of validity of the analytical solution with respect to the level of roughness and the incident angle is obtained. The SGTD method is accurate when the correlation length is approximately equivalent or larger than one wavelength, for a wide range of angles. It is also applicable for a correlation length as short as half wavelength, but only for small rms values and when the beam angle is larger than 45∘. In addition, at large angles, the tip diffraction is almost not affected by roughness, being very similar to that from a smooth crack. This is explained by the significant dependence on the beam angle factor explicitly shown in the theoretical solution.

Numerical investigation on dynamic characteristics of the droplet impacting on a random rough surface

Water management is a significant problem affecting the reliability and stability of proton exchange membrane fuel cells (PEMFC), in which droplet wall collision is the critical factor affecting the liquid water transmission in the gas channel. The surface roughness directly affects the spreading deformation of the droplet after impacting. This study's influence of surface roughness on the dynamic process of a single droplet of micrometer level impacting random rough surfaces was numerically investigated. Based on the Weierstrass–Manderlbrot (W-M) fractal theory, three-dimensional random rough surfaces with five roughness levels were established, and the dynamic process of droplet impact on the random rough surface was captured. The contour features of the droplet were analyzed, and the results showed that rough peaks hinder the spreading and retracted process of droplets, resulting in a thicker liquid film deposited on the rough surface, which is not conducive to liquid water discharge. The higher roughness level makes it difficult for droplets to gather into liquid film after hitting the wall and further hinders the discharge of liquid water from the flow channel. Therefore, when micrometer-sized droplets collide with a wall velocity of about 10 m/s, the roughness Ra should be controlled below 0.4 μm, which is conducive to the formation of thin liquid film after droplet impact and the effective discharge of water, which is crucial to maintaining the performance and life of PEMFC.

An Experimental Study of the Frictional Behavior at the Interface Soil-Structure with Regards to Wall Friction Effect and Clogging Related to Surface Roughness Form

Abstract The interactions between soil-structure are largely governed by the shear strength at the soil-structure interface, particularly in situations involving large displacements, known as shear residual strength. This latter can be influenced by a range of factors, including normal stress, physical properties, surface roughness, wall friction. The main objective of this study is to investigate clogging related to surface roughness form, in addition to wall friction arises from consolidation. In order to investigate the impact of wall friction, experiments involving ring shear tests were carried out on kaolin. Four different consolidation durations were employed to induce varying settlements of the upper platen, while three distinct testing procedures, including single stage, multistage, and preshearing, were utilized. Additionally, different levels of surface roughness were incorporated to investigate the effect of clogging. The test results obtained from various testing procedures indicate that employing a single stage procedure with zero consolidation time is the most suitable approach for mitigating the influence of wall friction. For clogging effect, is dependent on the materials used, namely, the kaolin and the mixture, as well as, the interfaces involved.

Polycaprolactone (PCL)-based films integrated with hairy cellulose nanocrystals and silver nanoparticles for active Tilapia packaging applications

The migration of metal ions to the food matrix has been always a challenge in the production of active food packaging films. In this study, it was tried to evaluate the idea of using hairy cellulose nanocrystals (HCNs) in controlling the migration of Silver Nanoparticles (AgNPs) from polycaprolactone (PCL)-based films to the Tilapia fish. HCNs and the final films (integrated with various amounts of HCNs and AgNPs) were evaluated physicochemically and mechanically. Tilapia fish were packed using the films and after specific periods, the fish samples were assessed microbiologically and physiochemically. According to the results, incorporating NPs into PCL films enhanced tensile strength, elasticity, and toughness making the films more resistant to breakage and deformation under stress. The introduction of HCNs reduced the surface roughness level, decreasing AgNPs migration, but also accelerated the degradation rate. Films with [1% AgNPs +2% HCNs] and [1% AgNPs] had the lowest and highest water vapor transmission rate. The use of AgNPs (1%) + HCNs (2%) incorporated into PCL films resulted in a lower pH value, TVB-N, TBARs, and PV. It also decreased microbial activities in samples in comparison to the control. Therefore, the idea of using HCNs along with antibacterial metal-based nanoparticles can control the rate of ion migration.

Electrical detachment of triboelectrically charged bumpy particles from rough surfaces

The detachment of bumpy particles from smooth and rough surfaces through electrostatic fields was studied. The Johnson–Kendall–Roberts (JKR) adhesion model for elastic interface deformations was used to account for the individual bump adhesion, including the electrostatic forces. It was assumed that the elastic deformation of asperities determines the real contact area, and the effect of topographic properties of substrates was included in the analysis. For a fixed charge per unit mass, the Coulomb, the image, the dielectrophoretic, and the polarization forces acting on the particle in the presence of an imposed electric field were evaluated. The electrostatic detachment of bumpy toner particles for various applied electrostatic fields was studied. The triboelectric charges were concentrated on the hemispherical bumps, and the critical electric field strength needed to detach charged particles from surfaces with varying roughness levels was evaluated. It was shown that the particle charge, surface roughness, and the number of bumps significantly affect the removal of particles from surfaces. For higher charges (∼5 × 10−15 C ), decreasing the number of bumps from 22 to 14 and the roughness parameter from 0.83 to 0.77 approximately doubled the detachment field needed to remove 8.3 μ m polystyrene (PSL) particles from the aluminum oxide substrate. The model predictions are compared with the available experimental data, and good agreement was observed. The study’s findings predicting the electric field needed for charged particle removal could lead to more efficient copiers and electrostatic cleaning devices.

A Comparative Study of Zinc Phosphate and Zirconium-Based Conversion Coatings on Galvannealed Steel: Effect on Corrosion Performance of Electrocoated Systems

The efficacy of an electrocoated system that uses a Zr-based conversion coating was assessed to protect galvannealed (GA) steel. The aim was to determine if a Zr-based system has the potential to replace a system with a traditional zinc phosphate (ZnP) conversion coating, where there are concerns for the environmental and economic sustainability. A comparative study between the two conversion coatings, and a control system with no conversion coating, is presented. Data from AC and DC electrochemistry are utilized with surface analysis investigations of pristine specimens, where scanning electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction have been used to determine the mechanism through which protection, or coating failure, occurs. Further investigations study surface morphology and stability of specimens during immersion in a simulated electrocoat bath, and their effect on the performance of fully electrocoated systems. The corrosion current density (icorr) for bare, ZnP, and Zr-based conversion coated specimens in chloride-containing solution with no electrocoat were found to be approximately 1.90 µA/cm2, 0.30 µA/cm2, and &amp;lt;0.01 µA/cm2, respectively. Rp values of 0.05 kΩ, 4.2 kΩ, and 20.7 kΩ were recorded for bare, ZnP and Zr-based specimens, respectively. The corrosion current density (icorr) for bare, ZnP, and Zr-based conversion coated specimens under chloride-containing conditions with electrocoat were found to be 3.82 µA/cm2, 0.53 µA/cm2, and 0.06 µA/cm2, respectively. |Z| values at 0.01 Hz (|Z|0.01 Hz) were measured, yielding 45.5 GΩ, 47.4 GΩ, and 31.6 GΩ for bare, ZnP, and Zr-based pretreatments respectively, demonstrating excellent barrier properties after electrocoating. Hydrogen evolution reaction (HER) rate values of 3.52 × 10−2 mol·m−2·s−1, 3.12 × 10−2 mol·m−2·s−1, and 2.94 × 10−2 mol·m−2·s−1 were recorded for the bare, ZnP, and Zr-based systems, respectively. This study produced a ranking order of HER rate. This was bare &amp;gt; ZnP &amp;gt; Zr-based. These results suggest that the Zr-based system is less prone to HER, interfering with the electrocoat deposition process. A performance ranking order for pretreated and electrocoated systems was established, where Zr-based &amp;gt; ZnP &amp;gt; control. The level of thickness and roughness provided by the conversion coating is speculated to be the controlling factor for coating performance, where the ZnP conversion coating was found to provide a thicker layer with greater surface coverage beneficial for a uniform electrocoat film build.