Surface Of Coupons Research Articles

Effect of Sulfate-Reducing Bacteria (SRB) on the Corrosion of Buried Pipe Steel in Acidic Soil Solution

The influence of sulfate-reducing bacteria (SRB) on the corrosion behaviors of X80 pipeline steel was investigated in a soil environment by electrochemical techniques and surface analysis. It was found that SRB grew well in the acidic soil environment and further attached to the coupon surface, resulting in microbiologically influenced corrosion (MIC) of the steel. The corrosion process of X80 steel was significantly affected by the SRB biofilm on the steel surface. Steel corrosion was inhibited by the highly bioactive SRB biofilm at the early stage of the experiment, while SRB can accelerate the corrosion of steel at the later stage of the experiment. The steel surface suffered severe pitting corrosion in the SRB-containing soil solution.

Microbiologically influenced corrosion of TiZrNb medium-entropy alloys by Desulfovibrio desulfuricans

The microbiologically influenced corrosion of TiZrNb medium-entropy alloys (MEAs) by Desulfovibrio desulfuricans was investigated. Pitting corrosion was found on coupon surface after 14-day immersion in the inoculated medium. Electrochemical tests demonstrated that the corrosion of coupon was enhanced by the D. desulfuricans. The corrosion current density (icorr) in the inoculated medium is approximately 12 times as much as that in the abiotic medium. In the presence of biofilms, the selective dissolution of Ti occurred, particularly when the organic nutrients were insufficient. Ti0 can be used as an electron donor by microbes in their energy metabolism once other donors are not readily available.

Investigation on the Tensile and Compressional Behavior of Inconel 625 Fabricated through Laser Powder Bed Fusion

Laser powder-bed fusion (L-PBF) is one of the well-suited additive manufacturing methods for producing industrial components from Inconel 625; however, there is still lack of knowledge in the course of the mechanical properties of the products. In order to gain deeper knowledge on the tensile and compressional behavior of L-PBFed Inconel 625, eight sets of test coupons in two principal directions were manufactured through various process parameters and tested. The results show a correlation between mechanical properties and the value of volumetric energy density (VED), as well as direction-dependent properties. Fractography was also performed on the tensile specimens to investigate the evidence of failure within the fractured surface of tensile test coupons. According to the results, increasing the VED led to a higher mass density and higher tensile and compressional properties. Fractography analysis revealed a mixed brittle and ductile fracture mechanism in the majority of specimens in both directions, while the effect of structural defects was also significant. Compression results showed higher strength for L-PBFed specimens than the other AM-based methods.

Lessons learned in the design of reference fiducials for layer-wise analysis of test coupons made by laser powder bed fusion

The ability to align ex-situ inspection data of an additively manufactured (AM) part to its build geometry can be helpful, for example, to correlate observed in-situ monitoring events or features to measured discontinuities, such as pores and cracks, in ex-situ inspection. In some cases, the original part design does not lend itself to such an alignment due to the absence of datum surfaces. In this study, the concept of incorporating inclined, cylindrical protrusions as reference fiducials in the design of cylindrical AM test coupons is investigated. Six coupons with proposed fiducials were built and inspected using X-ray computed tomography (CT). Dimensional measurements performed on the fiducials expose shortcomings in the proposed fiducial design—mainly a result of limited dimensional fidelity of small features by AM—and allow us to make suggestions on how the design can be improved. Nevertheless, an alignment scheme based on the reference fiducials is compared with an approach based on inherent coupon surfaces on layer-wise porosity measurements by X-ray CT on one of the test coupons.

Modeling ash deposit growth rates for a wide range of solid fuels in a 100 kW combustor

This work details a model for evaluating the relative ash deposition propensity of various solid fuels without the complicated spatial considerations included in CFD modeling. Four deposition mechanisms are included, namely: inertial impaction, thermophoresis, condensation, and eddy impaction. This model has been validated and shown to effectively predict ash deposit rates for a wide range of solid fuels including coal, biomass, and their blends, burned in a 100 kW rated downflow combustor. Specifically, this work presents and compares two separate models for the sticking efficiency of impacting ash particles on a coupon surface: the melt fraction stickiness model (MFSM), which is developed here and includes a novel approach to determine sticking efficiency, and the kinetic energy stickiness model (KESM), an existing model used for comparison. To apply the MFSM model, the equilibrium composition of vapor species are calculated by thermodynamic modeling using FactSage. By comparing the root-mean-square-errors of the MFSM and KESM over the wide variety of fuels, it is shown that the MFSM is more accurate than the KESM in predicting the ash deposit rate. This shows that NaCl and KCl are expected to be the main alkali vapor species in the flue gas, for the fuels evaluated.

The Ability of Staphylococcus spp. Isolated from Minced Meat to Adhere and form Biofilm on the Aluminum and Stainless-Steel Surfaces

The research included isolation and diagnosis of 19 bacterial isolate from 10 samples (minced meat and meat mincer), as 15 isolates belonging to the Micrococcaceae were diagnosed including 8 Staphylococcus spp. Isolates depending on the phenotypic properties and biochemical test, and in order to investigate the bacterial ability of the Micrococcaceae family to the formation of biofilms, two methods are used, the tube method and the Congo red agar method, as the results showed that all of the 15 isolates possess the ability to form biofilms as 100% depending on The tube method compared to the results of the Congo red agar test, which gave 13 positive result of 15 isolates in ratio 86.6% of the Micrococceae family. The highest rate of biofilm formation attributed to the Staphylococcus spp. which it gives 8 positive result for both tests as 100%. When comparing the adhesiveness of Staphylococcus spp. on the surface of the aluminum and stainless steel coupons as the materials used in the manufacture of meat mincers, our results showed that the adhesion and formation of biofilms were high on the surface of the aluminum coupons compared to the stainless steel coupons in the turbidity test using sonication and when investigating the total number of bacteria attached to the aluminum and steel coupons after exposing them to sonication, it was found that the number of units forming colonies CFU / cm2 for the aluminum coupons is 97 × 106, while it was found that CFU / cm2 of stainless steel coupons is 172 x 105, which enhances the turbidity comparison results.

Fatigue damage analysis of GFRP composites using digital image correlation

Glass fibre reinforced polymer composites are frequently used in marine applications where the combined effects of cyclic loads and the seawater environment limit their fatigue life. This paper aims to demonstrate the degradation that seawater causes to the stiffness of the composites. Three-point bending fatigue properties of cross-ply woven glass fibre composites commonly used to manufacture tidal turbine blades are reported for both wet and dry conditions. Failure analysis based on the Digital Image Correlation method was performed to identify damaged zones on the test coupon surface and to follow failure progression during the fatigue tests. To characterize the damage in the composite, stiffness degradation has been monitored during the entire fatigue history. Scanning electron microscopy was used to identify multiple failure mechanisms on the specimen fracture surface. In addition, for further verification of microscopy results, X-Ray Micro-computed tomography, was used to characterize the internal damage such as delamination. From the full-field strain measurement technique and microscopic examination of failed samples, it was found that distributed localized strains are evidence of the number of resin cracks and de-bonded areas. SEM examination shows a degraded fibre/matrix interface region due to the action of seawater.

Distributed optical sensing for monitoring strain evolution during mechanical testing of composite laminates

A Distributed fiber Optical Sensor (DOS) was embedded inside and attached to the surface of a multi-directional continuous fiber composite laminate coupon, along with the traditional foil of Strain Gages (SG) and Digital Image Correlation (DIC), to compare the DOS measure strain response to traditional strain acquisition methods. Tensile and bending tests were performed on an Open Hole composite laminate coupon to study different modes of loading and the performance of the DOS in the presence of a strain gradient. Tensile test results show good agreement between the SG, the DIC, and the DOS strain measurements in the region far from the strain concentration. Near the hole, the DOS repeatably measured the strain concentration during tensile and bending tests. The DOS was able to measure the residual strain in the composite laminate coupon through the hole-drilling method. Finite Element Analysis was performed to obtain the theoretical distribution of axial strain along the locations corresponding to the physical placement of the DOS in the coupon. As the results indicate, the DOS readings agree well with the theoretical results for the strain distribution in the test coupons. The results obtained during these evaluations provide confidence that the DOS strain measurement method and equipment are a robust strain acquisition option with the capability to overcome some of the limitations of the traditional foil SG and DIC methods.

Mitigation of eco‐unfriendly and costly microbial induced corrosion using novel synthesized Schiff base cationic surfactants

AbstractBACKGROUNDSulfate‐reducing bacteria (SRB) are considered to be the major cause of microbial‐induced corrosion. It contributes to many environmental and other costly industrial problems in the petroleum industry. Thus there is always a great need for producing new efficient biocides and biocorrosion inhibitors.RESULTSIn this work, three Schiff base surfactants (coded Q12, Q14 and Q18) were synthesized and characterized using Fourier transform infrared and 1H‐nuclear magnetic resonance techniques. A mixed culture of SRB was collected from an oil field production tank located at the North Bahrya Petroleum Company (NORPETCO), Egypt. The antimicrobial effect of the newly synthesized surfactants was studied against sessile and planktonic SRB over their different growth phases by various methods: viable cell count via most probable number method, estimation of biogenic sulfide concentrations, weight loss of iron coupons in microbial growth medium and biofilm examination on coupon surfaces using scanning electron microscopy. The synthesized surfactants expressed a high inhibition effect on bacterial growth, recording a minimum inhibitory concentration of 750 mg L−1 for Q18 and 1000 mg L−1 for both Q12 and Q14, with a considerable decline in biogenic sulfide productivity from a dose of 500 mg L−1 until complete suppression at a dose of 1000 mg L−1. Also the synthesized surfactants showed an effective metal corrosion inhibition at a concentration of 500 mg L−1.CONCLUSIONSchiff base cationic surfactants with long hydrophobic chains can be recommended as biocorrosion inhibitors for industrial application in the petroleum sector. © 2020 Society of Chemical Industry (SCI)

ANTI-CORROSION PERFORMANCE OF 2-ISONICOTINOYL-N-PHENYLHYDRAZINECARBOTHIOAMIDE FOR MILD STEEL HYDROCHLORIC ACID SOLUTION: INSIGHTS FROM EXPERIMENTAL MEASUREMENTS AND QUANTUM CHEMICAL CALCULATIONS

The corrosion inhibition performance of novel synthesized thiosemicarbazide derivative namely, 2-isonicotinoyl-N-phenylhydrazinecarbothioamide (IPC) on the mild steel coupon surface in 1[Formula: see text]M hydrochloric acid solution is investigated by weight loss measurements. The adsorption parameters of the IPC on the mild steel coupon surface have been evaluated and the surface morphology of the tested mild steel is studied by scanning electron microscope (SEM) technique. The results of this study demonstrate a significant inhibitor (IPC) for mild steel and showed the highest inhibitive efficiency of 96.3% at 5[Formula: see text]mM as optimum studied inhibitor concentration. The adsorption of IPC molecules on a mild steel coupon surface is obeyed completely by the model of Langmuir adsorption isotherms. SEM has been applied to analyse the layer of IPC molecules which formed on a mild steel coupon surface as a protective layer. The inhibition efficiency (IE) of IPC from weight loss techniques and SEM analysis was harmonic with each other. The Density Functional Theory (DFT) computations have been applied to evaluate the adsorption sites of the IPC molecules and the quantum chemical calculations correlation of IPC molecules with methodological results are discussed. The energy of the highest occupied molecular orbital (EHOMO) shows a significant tendency of the IPC molecules to donate pairs of electrons to the iron atoms on the surface of mild steel. The energy of the lowest unoccupied molecular orbital (ELUMO) for IPS molecules reveals a high tendency to accept electrons from iron atoms on the surface of mild steel.

D-leucine enhances antibiofilm activity of chlorhexidine against caries-causing Streptococcus mutans biofilm

Chlorhexidine (CHX) mouthwash is widely used clinically to remove the established Streptococcus mutans biofilm and prevent caries. However, the long-term use with high concentration of CHX leads to the staining of tooth and mucous membrane. In this study, d-leucine (d-leu) was used as an antimicrobial enhancer for CHX against mature S. mutans biofilm. The biocidal efficacy was evaluated by means of quantitative antibacterial test and biofilm observation. The results indicated that 100 ppm d-leu alone was ineffective to remove the S. mutans biofilm. Moreover, the biocidal effect of 1 ppm CHX was also inadequate to eradicate the biofilm. When 100 ppm d-leu was mixed with 1 ppm CHX, most of the mature S. mutans biofilm on 316L stainless steel coupon surfaces were successfully removed, and the removal efficacy was equivalent to that of 10 ppm CHX alone. The results confirmed that d-leu significantly enhanced the antibiofilm effect of CHX, dissembling the tenacious biofilm into easily killed planktonic counterparts. d-leu represents a novel strategy to reduce the dosage of CHX with a guaranteed effect for caries prevention.

Mitigations of machine-damaged free-edge effects on fiber-reinforced composites

The carbon fiber-reinforced composites were prepared in a vacuum oven using pre-preg composites, and the edge surfaces of the composite coupons were treated using high performing adhesives to eliminate the free-edge effects. The primary objective of the study was to usefully address the free-edge effects of composites used in aircraft and other manufacturing industries. The mechanical test results conducted on the untreated and edge-treated test coupons showed that the edge treatment and fiber orientations significantly affected the tensile strength and quality of the composites. It is determined that applying adhesives on the edges of the coupons could improve the mechanical properties of the composites, about 11%. Successful testing and evaluation of materials can lead to the precise analysis of a structure, and predictable behavior of the end design. This study may open up new possibilities to enhance the overall mechanical properties of fiber-reinforced composites for various manufacturing industries.

Three-Dimensional Simulation of Solution-Contact Electrolytic Dissolution

Electrochemical dissolution is a process where a metal is dissolved via oxidation and can be controlled through electrolyte properties, electrolyte flow, and applied potential. Electrochemical dissolution is employed in many manufacturing applications such as electrochemical machining, electrochemical pickling, metal refining, metal surface finishing, etc. Most of these dissolution applications use a traditional metal-contact method (metal being dissolved is in direct contact with the anode); however, some applications will have phenomena that cause operational issues, safety issues, or damage to the dissolver components. These phenomena include (1) difficulty maintaining contact, (2) arcing/sparking[1] in a flammable environment, which occurs because of a build-up of oxide, or (3) overheating, which can cause melting during dissolution. To avoid unsafe or destructive phenomena, a solution-contact electrolytic dissolution (SCED) method (metal being dissolved is only in contact with electrolyte) can be employed. Here, a three-dimensional model is developed to simulate solution-contact electrolytic dissolution in a small-scale system for the first time.A representation of a small-scale SCED system is shown in Figure 1. This system takes place within a HNO3 solution and includes a Pt anode and cathode where water-splitting and hydrogen formation occur, respectively. The sample coupon (our target for dissolution) acts as a physical barrier, so hydrogen ions gather on the anode-side of the sample coupon, forming a positively charged region, while H+ ions are consumed on the cathode-side of the coupon, leaving a negatively charged region. This imbalance of charge, along with the potential profile that forms within the system when voltage is applied to the anode, drive reactions to occur on the surface of the sample coupon. The reactions include the ejection of a metal ion, Mν+, towards the negatively charged region, while H+ ions combine with the free e-s released from the metal dissolution reaction to form hydrogen gas. The model theory developed here is able to predict stray currents in the solution-phase, a useful design tool to avoid corrosion of other components within an electrochemical system. [2-3] Discussion over important phenomena that must be properly represented to simulate this electrolytic dissolution process will take place, including electrochemical species transport, local surface reaction rates (using Butler-Volmer kinetics), and electrodynamic potential.

(Invited) Effect of Rust on Hydrogen Uptake into Exposed Steels during Drying of NaCl Droplets

In recent years, high-strength steels have been widely used in many industrial fields such as automobiles and construction. However, hydrogen embrittlement (HE) of high-strength steels has been a great concern because HE susceptibility of the steels strongly relates to the strength of them. Since the steels are often used in atmospheric environments, hydrogen atoms generated by corrosion reaction are absorbed into steels and can cause HE. Therefore, to use the high strength steel safety, it is needed to clarify hydrogen absorption mechanism into steels in atmospheric environments. However, in atmospheric environments, corrosion reaction is considered to occur under wet/dry cyclic conditions. Especially, since corrosion product layers consisting of iron rust is formed during steel corrosion, they can affect the rates of both corrosion reaction and hydrogen uptake. In this study, the effect of rust on hydrogen uptake into steels is discussed based on the results of hydrogen permeation current and corrosion potential.A sheet of plain carbon steel (0.020 % C, 0.01 % Si, 0.018 % Mn, 0.015 % P, 0.007 % S, Bal. Fe) was used as a material. The size of steel sheet was 150 mmw x 75 mml x 0.8 mmt. Both surfaces of the sheet were ground with SiC papers down to P500 grit and then degreased. The steel sheet was exposed for 1 month at Choshi exposure test site of Japan weathering test center (Chiba, Japan). It was located about 4 km far from the coast.The steel sheet after the exposure test was covered with iron rust completely. The sheet was cut into small coupons of 25 mmw x 25 mml x 0.8 mmt. One side of coupon surfaces working as hydrogen-detection side was ground with SiC papers down to P1200 grit to remove iron rust. Then this side was electroplated with Pd ca. 400 nm in thickness. For other side of the coupon surfaces for hydrogen-entry side, iron rust was removed partly. This side of the steel surfaces was subjected to a wet/dry corrosion test. A sample was finally prepared after both surfaces were cleaned with Milli-Q water (18 MW cm at 25 oC). The exposed surface area of the sample was fixed about 1 cm2 for both hydrogen-entry and hydrogen-detection sides by coating with rubber-type masking agent.Hydrogen uptake behavior of rusted steel was investigated by Devanathan-Stachurski method [1]. A coupon of rusted steel was set in this cell. Test solution filled in the hydrogen-detection-cell was 0.1 M NaOH. In this cell, Pd-electroplated surface was polarized at a constant potential of +0.1 V vs. Ir wire. On the opposite side of steel surfaces for hydrogen-entry side, a 30-mL droplet of 10 mM NaCl was placed on the rusted steel to measure hydrogen permeation current. During the drying of the droplet, corrosion potential for the rusted steel coupon was measured with a home-made Kelvin probe (KP) simultaneously with hydrogen permeation current [2-4].On the exposure test at Choshi, iron rust was formed on the whole steel surface. XRD and FT-IR analysis revealed that the iron rust consisted mainly of a- and g-FeOOH. In addition, amorphous rust may be involved in the rust.Hydrogen uptake behavior of the rusted steel with various percentages of the rusted area was observed during the drying of NaCl droplet. The amount of hydrogen entry was calculated by integrating the transient of hydrogen permeation current during the drying. The amount of hydrogen entry, N H depended on the percentage of rusted area were . For N H of 0 % of rusted area a bare steel before exposure test was used. The N H was increased with decreasing the percentage of rusted area. When the percentages of the rusted area were 90 and 98 %, corrosion potentials during drying of a NaCl droplet were more negative than that of 100 %. The change of corrosion potential may affect the increase of N H. A.V. Devanathan, A. Stachurski, Proc. Roy. Soc., A270, 90 (1962).Stratmann, H. Streckel, Corros. Sci., 30, 681 (1990).Stratmann, H. Streckel, Corros. Sci., 30, 697 (1990).Stratmann, H. Streckel, K. T. Kim, S. Crockett, Corros. Sci., 30, 715 (1990)

Experimental Validation of a Sliding Mode Control for a Stewart Platform Used in Aerospace Inspection Applications

The authors introduce a new controller, aimed at industrial domains, that improves the performance and accuracy of positioning systems based on Stewart platforms. More specifically, this paper presents, and validates experimentally, a sliding mode control for precisely positioning a Stewart platform used as a mobile platform in non-destructive inspection (NDI) applications. The NDI application involves exploring the specimen surface of aeronautical coupons at different heights. In order to avoid defocusing and blurred images, the platform must be positioned accurately to keep a uniform distance between the camera and the surface of the specimen. This operation requires the coordinated control of the six electro mechanic actuators (EMAs). The platform trajectory and the EMA lengths can be calculated by means of the forward and inverse kinematics of the Stewart platform. Typically, a proportional integral (PI) control approach is used for this purpose but unfortunately this control scheme is unable to position the platform accurately enough. For this reason, a sliding mode control (SMC) strategy is proposed. The SMC requires: (1) a priori knowledge of the bounds on system uncertainties, and (2) the analysis of the system stability in order to ensure that the strategy executes adequately. The results of this work show a higher performance of the SMC when compared with the PI control strategy: the average absolute error is reduced from 3.45 mm in PI to 0.78 mm in the SMC. Additionally, the duty cycle analysis shows that although PI control demands a smoother actuator response, the power consumption is similar.

Chemical analysis and field emission study of electropolished niobium surface containing synthesized niobium oxide particles

We conducted electropolishing (EP) of a Nb superconducting RF coupon cavity containing coupons at various positions of the cavity, and laboratory EP of Nb samples. The surface of the electropolished coupons was studied by using XPS, SEM, AFM, and EDX. The XPS analysis revealed that the atomic compositions and Nb 3d peak shapes (intensity ratio of the Nb5+ and Nb0 peaks) varied for the different coupons, indicating that the chemical state was not the same over the entire cavity surface. These differences might originate from the particle clusters observed on the coupon surfaces, which mainly existed as Nb2O5 and its hydrated form in different number densities. An individual particle cluster was isolated from the surface for EDX analysis, revealing the presence of C and F impurities, where F existed mostly as CFx with traces of niobium fluoride. These particle clusters were possibly synthesized during the post-EP water rinsing process by the hydrolysis of the niobium fluoride species (H2NbOF5) that were produced in the EP process and existing in the acid viscous layer on the surface. The post-EP water rinsing conditions affected the number density of particle clusters, and strong agitation of the acid reduced the particle content on the laboratory electropolished samples. An individual particle cluster emitted electrons at a DC field of 64 MV/m after being activated at a high field of ~150 MV/m, possibly limiting the performance of the SRF cavity. An optimized post-EP water rinsing followed by HF rinsing or prolonged ultrasonic rinsing of the cavity was effective at removing undesired particles from the surface.

The examination, evaluation and comparison of corrosion effect on different metal surface by various crops based biodiesel

Biodiesel is relatively higher corrosive compared to Diesel; consequently, the concern of viability is now a foremost issue. The biodiesel is self-oxidative in the environment; thus, its characteristics might be changed as fuel. The current work investigates the behavior of numerous biodiesel corresponding to corrosion when exposed to the surface of metal coupons. A gas chromatography mass spectrometry (GC-MS) was performed on eight biodiesel and a hypothesis was proposed to corroborate the hypothesis; static immersion tests, scanning electron microscopic (SEM) and surface roughness analysis were conducted. The immersion test was conducted for 150 days at ambient temperature conditions; later on, the corrosion rate of metals was examined. Results indicate that the Bronze has a maximum corrosion rate of 0.0674 mpy with Karanja biodiesel, followed by palm biodiesel. The Karanja biodiesel has the highest susceptibility to corrosion with all metals, while the Diesel is found to be the lowest with intermediate values for Rapeseed and Castor.

Improving fluid retention properties of 316L stainless steel using nanosecond pulsed laser surface texturing

Stainless steel has been used as a successful biomaterial for decades. In this study, a pulsed nanosecond laser was used to create patterned surfaces of stainless steel coupons to study the effect of patterning on fluid retention and biocompatibility studies of laser patterned and control surfaces. An AVIA 355 nanosecond pulsed laser was used with different laser parameters to create unique “peak and valley” structures (uniform textured surface) on stainless steel coupons of size of 1 × 1 × 0.1 cm3. The surface structural changes can be attributed to the Gaussian beam profile of the laser. The coupons were observed under a scanning electron microscope to understand the change of the material surface profile. An optical profilometer was used to measure the surface roughness and compare it with a nontextured or control surface. The contact angle measurement showed a decrease in the contact angle, reduced to 71.6° from 82.2° making the patterned surface more hydrophilic. A biocompatibility study of the stainless steel was performed to evaluate the effect of surface modification on its impact on biocompatibility. The cell viability of the patterned sample was 94% as compared to 84% for the unpatterned surface. A simulation of the process was run using flow3d® to understand the behavior of the material during the texturing process. The results obtained from the simulation process were compared with the experimental data and found to be in good agreement. The effects of Gaussian beam, vapor pressure, and overlapping of the beam were also analyzed in the simulation process.

Effectiveness of a Novel Rechargeable Polycationic N-Halamine Antibacterial Coating on Listeria monocytogenes Survival in Food Processing Environments

The goal of this research was to evaluate the efficacy of a novel rechargeable nonleaching polycationic N-halamine coating applied to stainless steel food contact surfaces to reduce Listeria monocytogenes contamination on ready-to-eat (RTE) foods. Four L. monocytogenes strains were inoculated onto the charged (C; chlorine activated) or noncharged (NC) N-halamine-coated steel coupon surfaces that were either intact or scratched. After inoculation, test surfaces were incubated at 2, 10, and 25°C for 0, 48, and 72 h. L. monocytogenes transfer from coated adulterated surfaces to RTE meat (beef sausages and roast beef) was also tested at 2°C. L. monocytogenes on both intact-C and scratched-C surfaces was significantly reduced at all temperatures; however, in the presence of organic material, these coatings were more effective for reducing L. monocytogenes at 2 and 10°C than at 25°C (P < 0.05). In contrast, on NC intact and scratched surfaces, reduction at 25°C increased (P < 0.05), decreasing the difference in L. monocytogenes levels between charged and noncharged intact and scratched surfaces at this temperature. Overall, greater L. monocytogenes reduction was achieved on intact-C and scratched-C (4.1 ± 0.19 log CFU/cm2) than on intact-NC and scratched-NC (2.3 ± 0.19 log CFU/cm2) surfaces at all temperatures (P < 0.05). The combination of surface condition and chlorine with coupons exposed for 2 h at 2°C in the presence of an organic load (50% meat purge) did not significantly affect the bactericidal efficacy of the N-halamine coating. Regarding transfer to RTE meat, an overall 3.7-log reduction in L. monocytogenes was observed in sausages and roast beef. These findings suggest that a novel rechargeable N-halamine coating on stainless steel surfaces can inactivate L. monocytogenes.

Glow discharge-optical emission spectroscopy for in situ analysis of surfaces in plasmas

In situ, real-time characterization of surfaces exposed to plasmas is of great interest. Common chemical analysis methods such as x-ray photoelectron spectroscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy cannot be used. Here, we discuss the use of glow discharge-optical emission spectroscopy for this purpose. A small coupon piece (aluminum coated with yttria in this study) was mounted on an rf-biased electrode and inserted into an opening in the reactor wall. Silicon or SiO2 substrates on a separately rf-biased electrode were etched in an inductively coupled plasma (ICP) of Cl2/Ar/O2 or C4F8/O2, respectively. Pulsed bias was applied to sputter the surface of the coupon piece in the wall at the edge of the ICP, either after etching in an Ar ICP or during etching in the Cl2/Ar/O2 ICP. Optical emission from the region above the coupon surface was collected and spectrally resolved. The difference in intensity between the coupon bias on and off conditions was used to determine what species were present on the surface. A quantification method for converting emission intensities into atomic composition depth profiles is presented.