Polished Stainless Steel Surface Research Articles

Thermal hysteresis in wettability and the Leidenfrost phenomenon

The Leidenfrost temperature (TL), at which the liquid drop lifetime peaks on a superheated surface, is believed to be wettability dependent. Here, we show that the wettability effect on TL is subject to the history of the surface temperature. Observing a water drop evaporating on a polished stainless-steel surface heated from 100 to 400∘C in argon gas, we find TL≈265∘C. We then repeat the experiment along decreasing temperature and find a TL increase by 10 K, i.e., TL≈275∘C. This thermal hysteresis is due to a reduced contact angle during heating. Once hydrophilized, the hysteresis disappears until the contact angle recovers. Similar observations are made in the air where oxidation is possible. Published by the American Physical Society 2024

Spray Coated Cellulose Nanofiber (CNF) Film as an Eco-Friendly Substrate for Flexible and Printed Electronics

Cellulose nanofiber is an eco-friendly nanomaterial used for fabricating various functional materials. It is an alternative for synthetic plastic and other petroleum derived materials. Due to demand of CNF film, fast and rapid method for fabrication of CNF film is required. A new method on spray coating to prepare smooth cellulose nanofiber (CNF) films was developed. In this method, spraying CNF suspension onto a smooth and polished metal surface was carried out and then allowed the spray coated wet film to dry in air under standard laboratory conditions. Spraying has notable advantages such as contour coating and contactless coating with the base substrate. The basis weight and thickness of the CNF film is tailorable by adjusting CNF suspension in spraying process. CNF film prepared via spray coating has unique two-sided surface roughness with the surface in contact with the base substrate or metal side much smoother than the air-contact side. The surface roughness is one of the controlling parameter in the application of the CNF film as a substrate for flexible and printed electronics. The RMS roughness of the two surfaces investigated by Optical Profilometry [OP] was found to be 2087 nm on the rough side and 389 nm on the spray coated side, respectively. The spray coated CNF film has ultra-high smoothness on the side exposed to the polished stainless steel surface. The factors including the size of cellulose fibrils and surface smoothness of base surface that control the roughness of the film are currently being investigated and will be discussed in this chapter. The surface smoothness requirements for substrate applications in flexible and printed electronics will be discussed.

Interfacial tension and equilibrium contact angle of corn oil on polished stainless steel in supercritical CO2 and N2

Abstract Lipids and bioactive components have been isolated using supercritical fluid fractionation (SFF) and packed columns with carbon dioxide from complex lipid mixtures. Lack of information about the wettability of the packing materials by different lipids was the motivation for this study. The interfacial tension (IFT) and equilibrium contact angle (CAeq) of corn oil in air, supercritical carbon dioxide (SC-CO2) and SC-N2 on polished stainless steel (SS) metal sheet were measured at 20, 40, 60, 80 °C and 0.1, 16, 20, 24 MPa in triplicate. IFT and CAeq were determined using Young-Laplace equation and height/width method, respectively. CAeq values of less than 10° demonstrated the complete wetting of corn oil on polished SS surface under unsaturated SC-N2 and SC-CO2, and saturated SC-CO2, but pressure and temperature had a significant effect on IFT and CAeq under these environments. Bouncing of drops on a completely wettable surface was observed under CO2 environment. The findings contribute to better understanding of wetting behaviour of SS surfaces by lipids, with implications for process design.

On the Solid Lubricity of Electrophoretically Deposited Carbon Nanohorn Coatings

In this study, dahlia-type carbon nanohorns (CNH) have been deposited onto a stainless steel substrate by using electrophoretic deposition. Secondly, the lubrication properties of the carbon nanohorn coating have been researched by tribometry and compared to an uncoated reference. Wear track analysis has been conducted to identify the underlying tribo-mechanisms. Additionally, Raman spectroscopy was employed to study the structural changes of the CNH during dispersion and tribological testing. Furthermore, energy dispersive X-ray spectroscopy (EDX) was used in order to investigate the chemical composition of the wear tracks’ surface. This work has shown that CNH coatings have the ability to maintain effective solid lubrication on a polished stainless steel surface. A temporary friction reduction of 83% was achieved compared to the uncoated reference. Moreover, the lubricity was active for significant periods of time due to the formation of a Mg(OH)2 layer which provides a certain degree of substrate adhesion as it holds the CNH in the wear track. Once this holding layer wanes, the CNH are gradually removed from wear track resulting in an increase of the coefficient of friction. The complete removal of CNH from the wear track as well as considerable oxide formation was confirmed by EDX. Moreover, the amount of defects in the CNHs’ structure increases by being exposed to tribological strain. Adhesion has been identified as the dominant wear mechanism.

Biofilm Removal Using Carbon Dioxide Aerosols without Nitrogen Purge.

Biofilms can cause serious concerns in many applications. Not only can they cause economic losses, but they can also present a public health hazard. Therefore, it is highly desirable to remove biofilms from surfaces. Many studies on CO2 aerosol cleaning have employed nitrogen purges to increase biofilm removal efficiency by reducing the moisture condensation generated during the cleaning. However, in this study, periodic jets of CO2 aerosols without nitrogen purges were used to remove Pseudomonas putida biofilms from polished stainless steel surfaces. CO2 aerosols are mixtures of solid and gaseous CO2 and are generated when high-pressure CO2 gas is adiabatically expanded through a nozzle. These high-speed aerosols were applied to a biofilm that had been grown for 24 hr. The removal efficiency ranged from 90.36% to 98.29% and was evaluated by measuring the fluorescence intensity of the biofilm as the treatment time was varied from 16 sec to 88 sec. We also performed experiments to compare the removal efficiencies with and without nitrogen purges; the measured biofilm removal efficiencies were not significantly different from each other (t-test, p > 0.55). Therefore, this technique can be used to clean various bio-contaminated surfaces within one minute.

Aging effect on the wettability of stainless steel

Abstract Commercial metals have recently been reconsidered as useful materials for functionalized surfaces with controlled wettability, yet the intrinsic wettability of various metal surfaces remain uncertain. In this study, we report that the wettability of a stainless steel (Type 304) surface exhibits a time-dependent transition, initially from a hydrophilic state to a relatively hydrophobic state. The static contact angle of a water droplet was monitored on polished stainless steel surfaces every 24 h, and a rapid increase in the contact angle, from 44° to 81°, was found during the first three days. The contact angle reached 98° in 40 days. To clarify the main factor causing the phenomenon, we compared the contact angles of water stored in four different environments for five days, where the oxygen and moisture levels were controlled. From the difference in contact angles depending on the amount of oxygen, we reached the conclusion that oxygen is likely the main cause of the aforementioned phenomenon. Finally, we demonstrated time-dependent wettability on a micro-grooved stainless steel surface whose initial superhydrophilicity became superhydrophobic after 30 days.

Polarisation-dependent generation of fs-laser induced periodic surface structures

Abstract The formation of laser induced periodic surface structures (LIPPS) was investigated on polished stainless steel surfaces under irradiation with fs-laser pulses characterised by a pulse duration τ = 300 fs, a laser wavelength λ = 1025 nm, a repetition frequency f rep = 250 Hz and a laser fluence F = 1 J/cm 2 . For this purpose line scans with a scanning velocity v = 0.5 mm/s were performed in air environment at normal incidence utilising a well-defined temporal control of the electrical field vector. The generated surface structures were characterised by optical microscopy, by scanning electron microscopy and by atomic force microscopy in combination with Fourier transformation. The results reveal the formation of a homogenous and highly periodic surface pattern of ripples with a period Λ exp ≈ 925 nm aligned perpendicular to the incident electric field vector for static linear polarisation states. Utilising a motor-driven rotation device it was demonstrated that a continuously rotating electric field vector allows to transfer the originally well-ordered periodic ripples into tailored disordered surface structures that could be of particular interest for e.g. absorbing surfaces, plasmonic enhanced optoelectronic devices and biomedical applications.

Exploitation of thermophoresis effect to prevent re-deposition of expelled particulates in laser assisted surface cleaning

Evidence in the improvement of the cleaning efficiency in the case of laser assisted surface decontamination wherein the phenomenon of thermophoresis has been exploited to prevent re-deposition of minute particulates is reported. The thermophoresis effect was made to set in by providing an appropriate temperature gradient in the vicinity of the laser exposed surface. The effectiveness of thermophoresis towards improving the laser assisted cleaning efficiency of polished stainless steel (SS) surface contaminated with copper telluride metal chalcogenide nanoparticles has been studied and compared with that obtained under ambient and dynamic vacuum conditions.

A ring area formed around the erosion pit on 1Cr18Ni9Ti stainless steel surface in incipient cavitation erosion

After a 1 min cavitation experiment performed in an ultrasonic vibration system, needle-like erosion pits appeared on a polished stainless steel surface, and a special ring area was formed around each pit. The shape of the pit and the plastic deformation of the ring area indicate that the mechanical impaction on the surface is the main reason for the cavitation erosion. On the other hand, the iridescent color, the decreased surface hardness and the appearance of the precipitated carbon ring prove that the ring area has experienced a tempering process with the temperature higher than 300 °C. Also, the lack of oxygen in the ring area proves that it is not a chemical oxygen result.

Numerical study for the impact of liquid droplets on solid surfaces

The impinging behaviour of liquid droplets on solid surfaces is studied using a computational approach. The analysis comprises the unsteady three-dimensional conservation equations of mass and momentum, with the surface tension effect treated by the continuous surface force model. Gas-liquid interfacial motions are simulated by the volume-of-fluid method in conjunction with the piecewise linear interface construction technique. In the computer code validation for a water droplet impacting on a polished stainless steel surface, computer-generated images of the time evolution of the droplet impingement dispersal shape are compared with magnified photographs by Pasandideh-Fard et al. The flow and transport phenomena in the impingement flowfield are further examined in detail. In order to respond to the need for its use in practical applications, the study is extended to explore the spreading progression to achieve a better understanding of the interaction of a 30 μm diameter polyethylenedioxy thiophene liquid droplet with a 50 × 50 μm indium tin oxide-coating square cavity at an impact velocity of 6 m/s.

Surfactant and Electric Field Strength Effects on Surface Tension at Liquid/Liquid/Solid Interfaces

We performed a series of experiments designed to elucidate the effects of the presence of sodium dodecyl sulfate (SDS) surfactant and an applied electrical field on the wetting behavior in a system containing a sessile droplet of phenylmethyl polysiloxane (PMPS) oil on a polished stainless steel surface submersed in aqueous solution. The voltage difference ranged from -3 to +3 V, which is at least 3 orders of magnitude smaller than from comparable recent work. We report the measured equilibrium contact angle of the droplet as a function of surfactant concentration and field strength. We then modeled the system. We solved the Laplace equation to obtain the 3D field within our system. We expanded the three surface tensions (oil droplet-aqueous solution (oa), oil droplet-metal surface (os), and aqueous solution-metal surface (as)) in a Taylor series with respect to surfactant concentration and local field strength. We use these three surface tensions in Young's equation to obtain the theoretical contact angle of the organic droplet. We demonstrate that the large changes in contact angle due to the simultaneous presence of small concentrations of surfactant and small voltage differences can be accounted for by changes in the oa and as surface tensions.

Collection of liquid flame spray generated TiO2 nanoparticles on stainless steel surface

Abstract Nanosized titania (TiO 2 ) powder has been generated using a turbulent H 2 –O 2 flame with a spray of liquid Ti-precursor (TEOT). The collection was performed on a polished stainless steel surface inside the flame or outside the flame very close to the flame tip. According to the XRD-analysis, a large fraction of the titania was found to consist of anatase when collected further away from the flame but, when collected inside the luminous part of the flame, the material layer was seen to be gradually transforming into rutile. Also sintering of the sub 10 nm particles into larger particles on the collection plate was observed, mostly within the flame where the temperature zone was 1100–1500 °C. When utilising the process, formation of rutile can be avoided by performing the collection sufficiently far away from the flame tip. As a result of the study, an estimate of particle size on the collection substrate, crystal size and anatase/rutile fraction on different material production rates and as a function of collection distance can be given. Also an estimate for the rate of transformation from anatase into rutile can be given.

Comparison of Nucleation Site Density for Pool Boiling and Gas Nucleation

It has been well established that the rate of heat transfer associated with boiling systems is strongly dependent on the nucleation site density. Over many years attempts have been made to predict nucleation site density in boiling systems using a variety of techniques. With the exception of specially prepared surfaces, these attempts have met with little success. This paper presents an experimental investigation of nucleation site density measured on roughly polished brass and stainless steel surfaces for gas nucleation and pool boiling over a large parameter space. A statistical model used to predict the nucleation site density in saturated pool boiling is also investigated. The fluids used for this study, distilled water and ethanol, are moderately wetting and highly wetting, respectively. Using distilled water it has been observed that the trends of nucleation site density versus the inverse of the critical radius are similar for pool boiling and gas nucleation. The nucleation site density is higher for gas nucleation than for pool boiling. An unexpected result has been observed with ethanol as the heat transfer fluid, which casts doubt on the general assumption that heterogeneous nucleation in boiling systems is exclusively seeded by vapor trapping cavities. Due to flooding, few sites are active on the brass surface and at most two are active on the stainless steel surface during gas nucleation experiments. However, nucleation sites readily form in large concentration on both the brass and stainless steel surfaces during pool boiling. The pool boiling nucleation site densities for ethanol on rough and mirror polished brass surfaces are also compared. It shows that there is not a significant difference between the measured nucleation site densities on the smooth and rough surfaces. These results suggest that, in addition to vapor trapping cavities, another mechanism must exist to seed vapor bubble growth in boiling systems.

Assessment by XPS and electrochemical techniques of two molecular organosilane films prepared on stainless‐steel surfaces

AbstractThe ability of silane groups to chemosorb on mechanically polished stainless‐steel surfaces has been investigated. Accordingly, tridecafluoro‐1,1,2,2‐tetrahydrooctyltrichlorosilane and the tridecafluoro‐1,1,2,2‐tetrahydrooctyltriethoxysilane, two organosilanes of similar chain length terminated with hydrophobic non‐reactive functions, have been tested as probe molecules. X‐ray photoelectron spectroscopy characterization, optical microscopy imaging, electrochemistry and contact angle measurements have been performed to characterize bare and modified samples. Results reported in this work show the influence of time of immersion and coupling agent reactive group on self‐assembled monolayer formation. It emerges that silanization by triethoxysilanes in millimolar solutions is not suitable for producing chemically bonded organic films with high density. Copyright © 2004 John Wiley & Sons, Ltd.

Artifacts in AFM images revealed using friction maps

We have retrieved a clear wavy pattern form and AFM image taken in the friction mode, over a highly polished stainless steel surface, which is usually assumed to be due to an optical interference phenomenon. A clear spatial correlation has been found between the best resolved parts of the pattern observed, and the smoothest part of the original topographical image, which clearly support the idea that the observed effect (not appeared in the topographical image), is effectively due to an optical interference phenomenon.

Effect of Substrate Temperature on Splashing of Molten Tin Droplets

Tin droplets (0.6 mm diameter) impacting on a polished stainless steel surface were photographed. Droplet impact velocity was varied from 10-40 m/s and substrate temperature from 80-260°C. A molten metal droplet generator was used to produce uniform sized tin droplets. The stainless steel test surface was mounted on the end of a rotating flywheel, giving it linear velocities of up to 40 m/s. A CCD video camera was used to photograph droplets impinging on the substrate. By synchronizing the ejection of a single droplet with the position of the rotating arm and triggering of the camera, different stages of droplet impact were photographed. On a cold surface (20°C) fragments from the periphery of the droplet broke off and flew off the surface during impact. At a high surface temperature (240°C) there was much less splashing and the droplet formed a roughly circular splat. The transition from splashing to circular splats took place at a substrate temperature of approximately 160°C. A three-dimensional model of droplet impact and solidification was used to simulate droplet splashing

Evaluation of chlorines' impact on biofilms on scratched stainless steel surfaces

Biofilms of a wild type Escherichia coli were grown on 316 stainless steel slides in a nutrient starved medium. The stainless steel surfaces were either polished to a smooth finish or scribed. The scribes consisted of lines and crosses. Biofilm samples were taken after 3, 6, 12, 24 and 48 h of growth. After sampling, the slides were soaked in deionized water or 50 or 200 ppm free chlorine prior to vital staining. Images were captured and the areas of viable and total biofilm were estimated. The individual biofilm patches, circularities, total percentage coverage, and viability percentage coverage were analyzed. The biofilms tended to increase in size between 6 and 24 h. A 3-6 h old biofilm on a polished stainless steel surface detached when 200 ppm sodium hypochlorite was applied. When grown in scribes, the circularity decreased up to 24 h, but thereafter increased. As the film grew older, it detached with or without a sodium hypochlorite treatment from the part of the surface that was polished, but remained in the neighborhood of the scribe. Based on the results, we recommend sanitizing at intervals of less than 12 h for this and similar strains of bacteria and protection of stainless steel surfaces to minimize scratching.

Splat Shapes in a Thermal Spray Coating Process: Simulations and Experiments

We studied the deposition of nickel particles in a plasma spray on a stainless steel surface using both experiments and numerical simulations. We developed a three-dimensional computational model of free-surface fluid flow that includes heat transfer and solidification and used it to simulate the impact of nickel partcles. In our experiments, particles landing on a polished stainless steel surface at a temperature below 300 °C splashed and formed irregular splats, whereas those deposited on substrates heated above 400 °C formed round disk splats. Simulations showed that formation of fingers around the periphery of a spreading drop is caused by the presence of a solid layer. Droplets that spread completely before the onset of solidification will not splash. To sufficiently delay the instant at which solidification started in our simulations to obtain disk splats, we had to increase the thermal contact resistance between the droplet and the substrate by an order of magnitude. We measured the thickness of the oxide layer on the test surfaces used in our experiments and confirmed that heating them creates an oxide layer on the surface that increases the thermal contact resistance. We demonstrated that the numerical model could be used to simulate the deposition of multiple droplets on a surface to build up a coating.

Adhesion characteristics of whole milk powder to a stainless steel surface

The deposition of dairy powders on equipment surfaces during the drying process has several undesirable effects. These include the cost of cleaning (materials and down-time), product degradation due to incorporation of oxidized debris in the product and ultimately the risk of a fire or explosion due to burning of the deposited powder. The present investigation concentrated on the adhesion force of whole milk powder to a polished stainless steel surface using an established centrifuge technique. The effects on adhesion bonding strength of particle size, temperature and consolidating force were studied. The powder used in this investigation was an agglomerated whole milk powder with particles ranging from 20 to 250 μm (based on the calibration using alumina powder). Microscope and image acquisition techniques were used to acquire data from the centrifuge experiments. Powder composition and particle size had an effect on the adhesion force and increasing powder temperature from 40 to 60°C increased adhesion.

Procedures for cleaning stainless steel weights, investigated by mass comparison and ellipsometry

Four 1 kg stainless steel weights were used to carry out comparisons to investigate the efficiency of different procedures for cleaning precision mass standards. Not only were mass comparisons carried out on a high-resolution 1 kg comparison balance but also the surface layers of 1 kg mass standards were directly determined for the first time using an automatic ellipsometer. Both measuring techniques show that ultrasonic cleaning in ethanol is the most efficient procedure for cleaning polished stainless steel surfaces. Furthermore, it was possible to prove that ellipsometry as an optical technique of surface analysis is well suited for non-contact, highly sensitive and absolute determination of the surface cleanliness of mass standards.