Surface Of Coupons Research Articles

Heat treatment of 6H-SiC under different gaseous environments

Silicon carbide is a useful material for the reactors in chemical processes. In recent years, microreactors have gained significant attentions due to the high demand for process miniaturization. As heat and mass-transfer are highly improved inside the gas flow channels in microreactors, any change on the surface of inner channels under heating becomes critical to the performance of microreactors. To investigate the surface changes of silicon carbide during the heat treatment, 6H-SiC coupons were processed in five different gases—Ar, N2, air, 0.9% O2 in Ar and 50% H2O in air—that are commonly encountered in high temperature chemical processes. While the formation of oxide film was found to be dependent on the partial pressure of oxidizing gas, surface decomposition was found from the treatment in nitrogen environment. Characterization of the SiC surface by Raman spectroscopy and SEM–EDX revealed that a graphitic layer has formed at the oxide film/SiC interface. Crystallinity of graphitic layer at the interface seemed to be dependent on the partial pressure of oxidizing gas, which was revealed by the relationship between G peak position and R(ID/IG). The intensity ratio of FTO(0)/FTO(2/6) bands showed that stacking faults on the surface of SiC coupons were reduced after heat treatment.

Research on corrosion perforation on pipeline by media of high salinity acidic oil–water mixture

Corrosion perforation and scaling occur frequently in pipeline of Tuha oil field. After being exposed to crude oil in petroleum transmission pipeline for 120days, corrosion rate of weight loss of the steel disc was calculated. Scanning Electron Microscope (SEM) was employed to observe the microscopic corrosion morphology of coupon, and the compositions of the oily water mixture and pipes were analyzed. The microstructure of the corrosion products and the reason of corrosion were investigated by Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD). The result showed that non-uniform corrosion occurred on the surface of coupon, and corrosion rate of weight loss was 0.187mm/y The corrosion products was mainly ferrous sulfide (FeS) and silicon disulfide (SiS2), and the scaling was mainly calcium carbonate (CaCO3). The corrosion-cell reaction, calcium ion (Ca2+) and bicarbonate ion (HCO3-) in formation water, and sulfuretted hydrogen (H2S) were the major factors which caused pipeline corrosion and scaling. H2S and Ca2+ weakened carbon dioxide (CO2) corrosion of pipeline in oil–water mixture medium.

Experimental investigation of microbiologically influenced corrosion of selected steels in sugarcane juice environment

In the current study, ferritic stainless grades AISI 439 and AISI 444 were investigated as possible construction materials for machinery and equipment in the cane-sugar industry. Their performance in corrosive cane-sugar juice environment was compared with the presently used low carbon steel AISI 1010 and austenitic stainless steel AISI 304. The Tafel plot electrochemical technique was used to evaluate general corrosion performance. Microbiologically influenced corrosion (MIC) behaviour in sugarcane juice environment was studied. Four microbial colonies were isolated from the biofilms on the metal coupon surfaces on the basis of their different morphology. These were characterized as Brevibacillus parabrevis, Bacillus azotoformans, Paenibacillus lautus and Micrococcus sp. The results of SEM micrographs showed that AISI 439 and AISI 304 grades had suffered maximum localized corrosion. MIC investigations revealed that AISI 444 steel had the best corrosion resistance among the tested materials. However from the Tafel plots it was evident that AISI 1010 had the least corrosion resistance and AISI 439 the best corrosion resistance.

Effects of chloride, sulfate and natural organic matter (NOM) on the accumulation and release of trace-level inorganic contaminants from corroding iron

This study examined effects of varying levels of anions (chloride and sulfate) and natural organic matter (NOM) on iron release from and accumulation of inorganic contaminants in corrosion scales formed on iron coupons exposed to drinking water. Changes of concentrations of sulfate and chloride were observed to affect iron release and, in lesser extent, the retention of representative inorganic contaminants (vanadium, chromium, nickel, copper, zinc, arsenic, cadmium, lead and uranium); but, effects of NOM were more pronounced. DOC concentration of 1 mg/L caused iron release to increase, with average soluble and total iron concentrations being four and two times, respectively, higher than those in the absence of NOM. In the presence of NOM, the retention of inorganic contaminants by corrosion scales was reduced. This was especially prominent for lead, vanadium, chromium and copper whose retention by the scales decreased from >80% in the absence of NOM to <30% in its presence. Some of the contaminants, notably copper, chromium, zinc and nickel retained on the surface of iron coupons in the presence of DOC largely retained their mobility and were released readily when ambient water chemistry changed. Vanadium, arsenic, cadmium, lead and uranium retained by the scales were largely unsusceptible to changes of NOM and chloride levels. Modeling indicated that the observed effects were associated with the formation of metal–NOM complexes and effects of NOM on the sorption of the inorganic contaminants on solid phases that are typical for iron corrosion in drinking water.

Impact of flow rate on corrosion of cast iron and quality of re-mineralized seawater reverse osmosis (SWRO) membrane product water

Remineralization of desalinated water as part of post-treatment has attracted great attention lately because of the need for high quality water and for the protection of the network pipelines. Laboratory experiments of remineralization using Ca2+ and Mg2+ containing substances were carried out to investigate the effect of flow rates on corrosion behaviour of cast iron coupons and water quality of re-mineralized SWRO product under tropical conditions. Experiments demonstrated the clear effect of increased corrosion rate at higher flow rate, i.e., the flow rate of 1, 10 to 20L/d increased the corrosion rate from 4.72, 6.74 to 9.17mpy, respectively. The turbidity and apparent colour of flow rate at 1L/d were much higher than those of 10 and 20L/d because of iron rusting materials formation and accumulation at the low flow rate. Cast iron corrosion and various flow rates did not significantly influence water quality parameters associated with SWRO product remineralization, such as total alkalinity and hardness. Microstructure observation showed that the main corrosion product was small crystalline globules of lepidocrocite, which formed a thick orange layer on coupon surface. Crystal fiber of white calcium composite was also found on some areas of the coupon surface which functioned as a protective layer.

Reduction by Competitive Bacteria of Listeria monocytogenes in Biofilms and Listeria Bacteria in Floor Drains in a Ready-to-Eat Poultry Processing Plant

The ability of Listeria monocytogenes and two competitive exclusion (CE) bacteria, Lactococcus lactis subsp. lactis strain C-1-92 and Enterococcus durans strain 152, to form biofilms on coupons composed of different materials (stainless steel, plastic, rubber, glass, and silicone) was determined at 4 and 8 °C. Biofilm characteristics were determined by scanning electron microscopy. L. monocytogenes produced well-formed biofilms within 24 h at 37 °C on coupon surfaces. Treating Listeria-laden biofilms with the CE isolates individually at either 4 or 8 °C for 3 weeks substantially reduced or eliminated listeriae in the biofilms. Treatment with L. lactis subsp. lactis strain C-1-92 and E. durans strain 152 at 4 °C for 3 weeks reduced the population of L. monocytogenes in a biofilm from 7.1 to 7.7 log CFU/cm2 to 3.0 to 4.5 log CFU/cm2 and to 3.1 to 5.2 log CFU/cm2 , respectively, and treatment at 8 °C for 3 weeks reduced L. monocytogenes from 7.5 to 8.3 log CFU/cm2 to 2.4 to 3.5 log CFU/cm2 and to 3.8 to 5.2 log CFU/cm2, respectively, depending on the coupon composition. These two CE isolates were combined and evaluated for control of Listeria bacteria in floor drains of a ready-to-eat poultry processing plant. The results revealed that treating the floor drains with CE four times in the first week eliminated detectable Listeria bacteria from five of six drains, and the drains remained free of detectable Listeria bacteria for 13 weeks following the first four treatments. These studies indicate that CE can effectively reduce Listeria contamination in biofilms and in flow drains of a plant producing ready-to-eat poultry products.

디지털 이미지 분석을 이용한 지오텍스타일 공극 분포의 정량화

본 논문에서는 지오텍스타일 공극 크기 분포를 이미지 분석방법을 이용하여 정량적으로 산출하였다. 연구과정은 실내시험을 통해 지오텍스타일-지오멤브레인 층으로 된 재료를 에폭시 레진으로 포화시킨 후, 양생, 절단하여 그 표면을 디지털 광학현미경으로 관찰하고 정량화함으로 이루어졌다. 여기서는 재료공학에서 주로 사용하는 공간학(stereology)의 개념을 사용하였으며, 지오텍스타일 필라멘트에 의해 둘러싸인 공극의 크기를 최대내접공극크기분포(LIOS)로 표현하였다. 지오텍스타일 내부 축적빈도 50%에 해당하는 공극직경이 압축응력이 10kPa에서 300kPa로 증가함에 따라 <TEX>$45{\mu}m$</TEX>가량 감소하였으며, 다시 압축응력을 10kPa로 되돌렸을 경우 초기치의 90%정도 수준으로 회복하였다. 마찰형 지오멤브레인 표면에서 연직응력 100, 300 kPa을 받으며 전단되었을 경우 평균 공극의 크기가 각가 32, 16.5% 감소하였다. 본 논문의 시험 및 분석 결과는 지오텍스타일 내부의 최대내접공극 크기분포가 표면거칠기가 다른 지오멤브레인 표면에서 압축 및 인터페이스 전단됨에 따라 어떻게 변화하는지를 보여준다. This paper presents results from a study undertaken to quantitatively evaluate the geotextile pore sizes using optical image analysis. The evaluation was conducted by observing surfaces of coupons cut from resin-impregnated specimens of geotextile-geomembrane layered under various load conditions. Stereological concepts were applied to collect representative specimens from a series of laboratory tests. The sizes of voids enclosed by filaments were expressed in terms of the largest inscribing opening size (LIOS) distribution. The opening diameter corresponding to the 50% cumulative frequency decreased by about 45mm as the load increased from 10 to 300kPa and recovered to about 90% of its initial state on unloading back to 10kPa. The average void size was reduced by 32 and 16.5% as the geotextile was sheared against a textured geomembrane under normal stresses of 100 and 300kPa, respectively. The results showed how the LIOS distribution varied as a function of normal stress and interface shear displacement against a smooth and a textured geomembrane surfaces.

Chemical polishing of aluminum coupons in support of vacuum chambers

Success of third and fourth generation light sources is highly dependent upon the smoothness of internal surfaces in small aperture undulators. The ratio of the undulator length to the chamber aperture is very large, making mechanical polishing difficult to implement. Chemical polishing is a viable alternative option. This study investigates the effectiveness of a chemical polishing step as a finishing treatment in lieu of mechanical polishing. Limited to no quantitative data exists in the literature that links specific chemical polishing processes to profilometer-measured surface roughness. This study examines the effectiveness of using two chemical solutions at various temperatures to treat the surfaces of aluminum coupons and reduce their surface roughness. Results indicate that certain chemical polishing steps can reduce the root mean square roughness of the surface by as much as 40%; however, careful control of the solution temperature, composition, and immersion time is critical.

Numerical modeling and experimental study of thermally induced residual stress in the direct diode laser heat treatment of dual-phase 980 steel

The direct diode laser application has been found useful in the localized heat treatment of metal parts because of its wider beam and more uniform energy distribution with respect to other lasers with Gaussian-like energy distribution. In this study, an uncoupled thermomechanical finite element model is developed to study the temperature field and thermally induced stress evolution in high-strength dual phase (DP) 980 steel during its direct diode laser heat treatment. Thermal analysis results are experimentally validated through thermocouples and then input into a mechanical model as transient temperature loading in order to acquire the thermally induced stresses and strains. The effect of martensite phase transformation on residual stress distribution in heat-treated DP980 steel is considered. An X-ray diffraction technique is used to measure the residual stress distribution at the top surface of the heat-treated coupons of DP980 steel. The numerical results show that compressive stresses are located at the laser–material interaction zone. After heat treatment, tensile stresses are retained at the heat-treated DP980 steel coupons. There is qualitative agreement between the numerically predicted and experimentally measured residual stresses. The effect of the overlapping ratio on the residual stress and hardness of the heat-treated DP980 steel is also experimentally and numerically investigated.

Steel Pitting Corrosion Analysis, Using a High Vaccum Epoxy Penetration Technique

An epoxy penetration technique was used to reproduce and analyze the pitting corrosion process occurred at a steel coupon surface. The samples were exposed to the resin under high vacuum conditions, in order to fulfill the pits caused by the corrosion process. With this technique, a 3D image of the corrosion damages was obtained. Once the image of the damaged surface was obtained, a Scanning Electron Microscope (SEM) was used to analyze the morphology of the pits exhibited by the steel sample. The results were satisfactory, as different parameters such as the diameter, shape and depth of the pits originated, along with the corrosion preferential path, could be established. According to the results, the use of the epoxy penetration technique may be considered as alternating pitting corrosion analysis technique.

The Effects of Device Geometry and TCO/Buffer Layers on Damp Heat Accelerated Lifetime Testing of Cu(In,Ga)Se$_{\bf 2}$ Solar Cells

In Cu(In,Ga)Se 2 solar cells encapsulated with polyethylene terephthalate (PET) or glass top sheets, the effects of damp heat (D-H) accelerated lifetime testing (ALT) depend on water vapor transmission rate (WVTR) of both transparent conducting oxide (TCO) and the intrinsic zinc oxide (i-ZnO) buffer, as well as device geometry. PET top sheets have a WVTR of ∼10 g/m2·day, and glass has a WVTR of 0. Previously, coupons encapsulated with PET degraded to 50% of initial efficiency after 1000 h D-H ALT. We show that PET encapsulated coupons degrade at the same rate as glass encapsulated coupons after 2000 h D-H ALT to 92% of initial efficiency. The only change from previous work is that, here, i-ZnO covers the entire coupon surface, not the just active area. The WVTR of the i-ZnO/TCO stack is 2 × 10−3 g·H 2 O/m2·day. A set of unencapsulated devices went through D-H ALT, one where scribing was used to define the active area of the device and another without scribing; both were protected only by 50-nm i-ZnO. The bare-unscribed device performed as well as the previous glass and PET encapsulated coupons after 1500 h D-H ALT; the bare-scribed device degraded to 78% of initial efficiency, indicating that TCO integrity is a critical ALT parameter.

Modeling to predict growth/no growth boundaries and kinetic behavior of Salmonella on cutting board surfaces.

This study developed models to predict the growth probabilities and kinetic behavior of Salmonella enterica strains on cutting boards. Polyethylene coupons (3 by 5 cm) were rubbed with pork belly, and pork purge was then sprayed on the coupon surface, followed by inoculation of a five-strain Salmonella mixture onto the surface of the coupons. These coupons were stored at 13 to 35°C for 12 h, and total bacterial and Salmonella cell counts were enumerated on tryptic soy agar and xylose lysine deoxycholate (XLD) agar, respectively, every 2 h, which produced 56 combinations. The combinations that had growth of ≥0.5 log CFU/cm(2) of Salmonella bacteria recovered on XLD agar were given the value 1 (growth), and the combinations that had growth of <0.5 log CFU/cm(2) were assigned the value 0 (no growth). These growth response data from XLD agar were analyzed by logistic regression for producing growth/no growth interfaces of Salmonella bacteria. In addition, a linear model was fitted to the Salmonella cell counts to calculate the growth rate (log CFU per square centimeter per hour) and initial cell count (log CFU per square centimeter), following secondary modeling with the square root model. All of the models developed were validated with observed data, which were not used for model development. Growth of total bacteria and Salmonella cells was observed at 28, 30, 33, and 35°C, but there was no growth detected below 20°C within the time frame investigated. Moreover, various indices indicated that the performance of the developed models was acceptable. The results suggest that the models developed in this study may be useful in predicting the growth/no growth interface and kinetic behavior of Salmonella bacteria on polyethylene cutting boards.

Biofilm formation and exopolysaccharide (EPS) production by Cronobacter sakazakii depending on environmental conditions

Biofilm matrices are formed largely of extracellular polymeric substance (EPS). This study was conducted to investigate biofilm formation and EPS production by Cronobacter sakazakii under various conditions (media, nutrition, and relative humidity (RH)) by quantification of EPS and cell populations, Field Emission Scanning Electron Microscope (FE-SEM), and colony observation. Various agar media conditions (TSA without dextrose (W/D), M9 minimum salt medium (MSM) agar, and M9 MSM agar with 3% glucose, 3% NaCl, 3% Tween 80, 3% sucrose, and adjusted to pH 5 with HCl) were prepared. C. sakazakii biofilm formed on the surface of stainless steel coupons (SSCs) immersed in TSB W/D and M9 MSM with or without 0, 1, 3, and 5% sucrose and subsequently exposed to various RH levels (23, 43, 68, 85, and 100%). EPS production by C. sakazakii on TSA W/D was significantly higher than that on other media after 1 and 2 days. However, C. sakazakii ATCC 12868 produced the highest levels of EPS (209.18 ± 16.13 and 207.22 ± 4.14 μg/mL after 1 and 2 days, respectively) on M9 MSM agar with 3% sucrose. Regarding C. sakazakii ATCC 12868 biofilm formed on the surface of SSCs immersed in M9 MSM with 0, 1, 3, and 5% sucrose and subsequently exposed to various RHs, populations were significantly different among the various RHs and sucrose concentrations, and EPS production was significantly higher (4.69 mg/L) compared to other sucrose concentrations (0%:0.71 mg/L and 1%:0.98 mg/L), except for M9 MSM with 3% sucrose (2.97 mg/L) (P ≤ 0.05). From these results, biofilm formation and EPS production by C. sakazakii differed depending on the nutrient or environmental conditions provided to the cells.

General and crevice corrosion study of the in-wall shielding materials for ITER vacuum vessel

Vacuum vessel In-Wall Shield (IWS) will be inserted between the inner and outer shells of the ITER vacuum vessel. The behaviour of IWS in the vacuum vessel especially concerning the susceptibility to crevice of shielding block assemblies could cause rapid and extensive corrosion attacks. Even galvanic corrosion may be due to different metals in same electrolyte. IWS blocks are not accessible until life of the machine after closing of vacuum vessel. Hence, it is necessary to study the susceptibility of IWS materials to general corrosion and crevice corrosion under operations of ITER vacuum vessel. Corrosion properties of IWS materials were studied by using (i) Immersion technique and (ii) Electro-chemical Polarization techniques. All the sample materials were subjected to a series of examinations before and after immersion test, like Loss/Gain weight measurement, SEM analysis, and Optical stereo microscopy, measurement of surface profile and hardness of materials. After immersion test, SS 304B4 and SS 304B7 showed slight weight gain which indicate oxide layer formation on the surface of coupons. The SS 430 material showed negligible weight loss which indicates mild general corrosion effect. On visual observation with SEM and Metallography, all material showed pitting corrosion attack. All sample materials were subjected to series of measurements like Open Circuit potential, Cyclic polarization, Pitting potential, protection potential, Critical anodic current and SEM examination. All materials show pitting loop in OC2 operating condition. However, its absence in OC1 operating condition clearly indicates the activity of chloride ion to penetrate oxide layer on the sample surface, at higher temperature. The critical pitting temperature of all samples remains between 100° and 200°C.

Wrought Aluminium Alloy Corrosion Propensity in Domestic Food Cooking Environment

The study on corrosion behaviour of wrought aluminium alloy in domestic food cooking conditions has been examined using the gravimetric approach. Flat cold rolled and annealed sheets were subjected to solutions of Capsicum annuum, L. esculentum, Allium cepa, and their blend under three conditions, namely, heating and cooling in still air, heating and cooling in refrigerator, and leaving some in open still atmosphere. Results show that corrosion occurred within the test period (288 hours) in the test environments. There was severe degradation within the first 70 hours of test when coupons were heated and cooled while unheated coupon showed low corrosion propensity. Microstructural analysis show the presence of corrosion pits on coupon surface with second phase particles sandwiched in α-aluminium matrix. Immersed coupon in the blend media show higher number of pits on the surface. Rapid corrosion of wrought aluminium alloy in Capsicum annuum, L. esculentum and Allium cepa media is attributed to the presence of corrosion aggressive elements such as allicin, diallyl-disulphide, and allyl-propyl disulphide present in the corrosion media.

AiiA Quorum-Sensing Quenching Controls Proteolytic Activity and Biofilm Formation by Enterobacter cloacae

The aim of this work was to evaluate a quorum-quenching approach to identify functions regulated by quorum sensing in Enterobacter cloacae. We employed an aiiA transconjugant strain of E. cloacae that synthesizes a lactonase enzyme that hydrolyzes N-acyl homoserine lactone signaling molecules to compare bacterial phenotypes in the presence and absence of quorum signals. The aiiA-expressing strain displayed increased proteolytic activity and intensity of a milk-clotting reaction when compared to the wild-type strain. Although both strains growing on polystyrene plates in rich media and a minimal medium of salts formed biofilms, the wild-type strain exhibited a higher number of adhered cells. On the surface of stainless steel coupons that were submerged in culture media, the number of adhered cells of the wild type contained up to one log more cells compared with the aiiA transconjugant. However, after 48 h of incubation, there was no significant difference between the strains. The results demonstrated that the quorum-sensing system negatively regulates proteolytic activity and is likely involved in the early steps of biofilm formation by E. cloacae 067.

Comparison of titanium soaked in 5 M NaOH or 5 M KOH solutions

Commercially pure titanium plates/coupons and pure titanium powders were soaked for 24h in 5M NaOH and 5M KOH solutions, under identical conditions, over the temperature range of 37° to 90°C. Wettability of the surfaces of alkali-treated cpTi coupons was studied by using contact angle goniometry. cpTi coupons soaked in 5M NaOH or 5M KOH solutions were found to have hydrophilic surfaces. Hydrous alkali titanate nanofibers and nanotubes were identified with SEM/EDXS and grazing incidence XRD. Surface areas of Ti powders increased >50–220 times, depending on the treatment, when soaked in the above solutions. A solution was developed to coat amorphous calcium phosphate, instead of hydroxyapatite, on Ti coupon surfaces. In vitro cell culture tests were performed with osteoblast-like cells on the alkali-treated samples.

General and Crevice Corrosion Study of the Materials for ITER Vacuum Vessel Inwall Shield

Vacuum vessel inwall shield (IWS) (VV-IWS) which consists of block assemblies will be inserted between the inner and outer shells of the ITER vacuum vessel. The vacuum vessel will be operating at the following: 1) 100 °C and 2) 200 °C. The temperature of the vacuum vessel will be maintained by flowing water between the shells of the vessel. To achieve the temperature of the vessel, the water will be flowed at two operation phases: 1) normal operation condition (OC1), i.e., 100 °C temperature and 1.1-MPa pressure, and 2) off-normal condition, i.e., 200 °C temperature and 2.4-MPa pressure. The water flow rate is locally rather low in the VV-IWS block assemblies, and low flow rates generally promote local attacks on the stainless steel (SS). In addition, local accumulation of the aggressive compounds like chloride and other anions might be higher for ITER condition due to the different operational modes. IWS blocks are not accessible until the life of the machine after closing of the vacuum vessel. Hence, it is necessary to study the susceptibility of IWS materials to general corrosion and crevice corrosion under operations of the ITER vacuum vessel. Corrosion properties of IWS materials were studied by using the following: 1) immersion technique and 2) electrochemical polarization techniques at OC1, baking condition (OC2), and draining and drying operations of the ITER vacuum vessel. Before and after the immersion test, all the sample materials were subjected to a series of examinations, like loss/gain weight measurement, scanning electron microscopy (SEM) analysis, optical stereomicroscopy, and measurement of surface profile and hardness of materials. After the immersion test, SS 304B4 and SS 304B7 showed slight weight gains of 0.0593 and 0.0286 g, respectively, which indicate oxide layer formation on the surface of coupons. The SS 430 material showed a negligible weight loss of 0.0160 g which is equivalent to a corrosion rate of 0.00267 mm/year, indicating mild general corrosion effect. On visual observation with SEM and metallography, all materials showed pitting corrosion attack. During the electrochemical polarization test, all sample materials were subjected to a series of measurements, like open-circuit potential, cyclic polarization, pitting potential, protection potential, critical anodic current, and SEM examination. Under the OC1 condition, the ICC value (critical current density) is found lowest for SS 304B7 and highest for SS 430, and under the OC2 condition, the ICC value is found lowest for XM-19 and highest for SS 304B7 which indicates that SS 430 and SS 304B7 showed the highest general corrosion rates under the OC1 and OC2 conditions, respectively. All materials show a pitting loop in the OC2 operating condition. However, its absence in the OC1 operating condition clearly indicates the activity of chloride ion to penetrate the oxide layer on the sample surface, at higher temperature. The critical pitting temperature of all samples remains between 100 ° and 200 °C.

A synergistic d-tyrosine and tetrakis hydroxymethyl phosphonium sulfate biocide combination for the mitigation of an SRB biofilm

Microbiologically influenced corrosion (MIC) is a major problem in various industries such as oil and gas, and water utilities. Billions of dollars are lost to microbiologically influenced corrosion (MIC) each year in the US. The key to MIC control is biofilm mitigation. Sulfate-reducing bacteria (SRB) are often the culprits. They are also involved in souring and biofouling. SRB biofilms are notoriously difficult to eradicate. Due to environmental concerns and increasing costs, better biocide treatment strategies are desired. Recent studies suggested that D-tyrosine and some other D-amino acids may signal biofilm dispersal. Experimental results in this work indicated that D-tyrosine is an effective biocide enhancer for tetrakis hydroxymethyl phosphonium sulfate (THPS) that is a green biocide. Desulfovibrio vulgaris (ATCC 7757) was used in biofilm prevention and biofilm removal tests. It was found that 100 ppm D-tyrosine alone and 50 ppm THPS alone were both ineffective against the SRB biofilm. However, when 1 ppm D-tyrosine was combined with 50 ppm THPS, the synergy between the two chemicals successfully prevented the establishment of the SRB biofilm on C1018 mild steel coupon surfaces in batch treatment tests. It also eradicated established SRB biofilms from coupon surfaces in both 1 and 3-h shock treatment tests.

Transfer, Attachment, and Formation of Biofilms by Escherichia coli O157:H7 on Meat‐Contact Surface Materials

Studies examined the effects of meat-contact material types, inoculation substrate, presence of air at the liquid-solid surface interface during incubation, and incubation substrate on the attachment/transfer and subsequent biofilm formation by Escherichia coli O157:H7 on beef carcass fabrication surface materials. Materials studied as 2 × 5 cm coupons included stainless steel, acetal, polypropylene, and high-density polyethylene. A 6-strain rifampicin-resistant E. coli O157:H7 composite was used to inoculate (6 log CFU/mL, g, or cm²) tryptic soy broth (TSB), beef fat/lean tissue homogenate (FLH), conveyor belt-runoff fluids, ground beef, or beef fat. Coupons of each material were submerged (4 °C, 30 min) in the inoculated fluids or ground beef, or placed between 2 pieces of inoculated beef fat with pressure (20 kg) applied. Attachment/transfer of the pathogen was surface material and substrate dependent, although beef fat appeared to negate differences among surface materials. Beef fat was the most effective (P < 0.05) inoculation substrate, followed by ground beef, FLH, and TSB. Incubation (15 °C, 16 d) of beef fat-inoculated coupons in a beef fat homogenate (pH 4.21) allowed the pathogen to survive and grow on coupon surfaces, with maximal biofilm formation observed between 2 and 8 d of storage and when air was present at the liquid-solid interface. The results indicated that the process of fabricating beef carcasses may be conducive to the attachment of E. coli O157:H7 onto meat-contact surfaces and subsequent biofilm formation. Furthermore, it is recommended that substrates found in beef fabrication settings, rather than laboratory culture media, be used in studies designed to investigate E. coli O157:H7 biofilm development and control in these environments. Findings of this study provide knowledge on the effect of type of beef carcass fabrication surface material, fabrication-floor fluids and residues, and incubation conditions on attachment/transfer and subsequent biofilm formation by E. coli O157:H7. The results highlight the importance of thoroughly cleaning soiled surfaces to remove all remnants of beef fat or other organic material that may harbor or protect microbial contaminants during otherwise lethal antimicrobial interventions.