Durability of Vacuum Infusion Tooling Produced from Fused Granular Fabrication Additive Manufacturing.

Fused Granular Fabrication Additive Manufacturing (FGF AM) has the capability to create tooling that is lower cost than conventionally manufactured tooling and still has sufficient properties for many applications. A vacuum infusion (VI) mold was printed from fiberglass-acrylonitrile butadiene styrene (ABS) and evaluated for wear and suitability for small VI runs. The mold was designed to accentuate high wear as a "worst case" scenario. The mold was able to produce 10 parts successfully before any noticeable change occurred to the surface finish. By 14 parts, the surface finish had roughened sufficiently that demolding was difficult and resulted in damage to the part. Profilometry measurements showed a 7 × increase in roughness over the run. No significant tool wear or change in geometry was detected. Even longer life would be expected for typical tooling designs since the test mold was deliberately designed to accentuate wear and demolding issues. Based on these results, similar FGF molds are a feasible option for short run VI production for prototyping or low-volume composites manufacturing, possibly at lower cost and quicker turnaround time than machined aluminum molds.

Temperature-Dependent Selectivity and Detection of Hidden Carbon Deposition in Methane Oxidation.

Reaction products in heterogeneous catalysis can be detected either on the catalyst surface or in the gas phase after desorption. However, if atoms are dissolved in the catalyst bulk, then reaction channels can become hidden. This is the case if the dissolution rate of the deposits is faster than their formation rate. This might lead to the underestimation or even overlooking of reaction channels such as, e.g., carbon deposition during hydrocarbon oxidation reactions, which is problematic as carbon can have a significant influence on the catalytic activity. Here, we demonstrate how such hidden deposition channels can be uncovered by carefully measuring the product formation rates in the local gas phase just above the catalyst surface with time-resolved ambient pressure X-ray photoelectron spectroscopy. As a case study, we investigate methane oxidation on a polycrystalline Pd catalyst in an oxygen-lean environment at a few millibar pressure. By ramping the temperature between 350 and 525 °C, we follow the time evolution of the different reaction pathways. Only in the oxygen mass-transfer limit do we observe CO production, while our data suggests that carbon deposition also happens outside this limit.

Rosai-Dorfman disease of the cauda equina: illustrative case.

BACKGROUND: Rosai-Dorfman disease (RDD) is a rare, nonmalignant histiocytosis. It typically occurs in lymph nodes, skin, and soft tissues, but numerous reports of central nervous system involvement exist in the literature. The peripheral nervous system has rarely been involved. In this study, the authors present a case of RDD isolated to the cauda equina. The presentation, management, surgical technique, and adjunctive treatment strategy are described. OBSERVATIONS: A 31-year-old female presented with 6 months of progressive left lower-extremity numbness involving the lateral aspect of the foot and weakness of the left toes. Magnetic resonance imaging of the lumbar spine demonstrated a homogeneously enhancing intradural lesion involving the cauda equina at the L2-3 levels. Histopathology after resection revealed a histiocytic infiltrate, positive for CD68 and S100, and emperipolesis consistent with RDD. No adjuvant therapy was administered, and the patient had full remission at the 1-year follow-up. Only five other cases of intradural RDD lesions of the cauda equina have been reported in the literature. LESSONS: RDD of the cauda equina is an especially rare and challenging diagnosis that can mimic other dura-based lesions, such as meningiomas. A definitive diagnosis of RDD relies on pathognomonic histopathological and immunohistochemical findings.

Formation of Epitaxial PdO(100) During the Oxidation of Pd(100).

The catalytic oxidation of CO and CH4 can be strongly influenced by the structures of oxide phases that form on metallic catalysts during reaction. Here, we show that an epitaxial PdO(100) structure forms at temperatures above 600 K during the oxidation of Pd(100) by gaseous O atoms as well as exposure to O2-rich mixtures at millibar partial pressures. The oxidation of Pd(100) by gaseous O atoms preferentially generates an epitaxial, multilayer PdO(101) structure at 500 K, but initiating Pd(100) oxidation above 600 K causes an epitaxial PdO(100) structure to grow concurrently with PdO(101) and produces a thicker and rougher oxide. We present evidence that this change in the oxidation behavior is caused by a temperature-induced change in the stability of small PdO domains that initiate oxidation. Our discovery of the epitaxial PdO(100) structure may be significant for developing relationships among oxide structure, catalytic activity, and reaction conditions for applications of oxidation catalysis.

"Intermission!" A short-term social media fast reduces self-objectification among pre-teen and teen dancers.

Social media use is pervasive among youth and is associated with body image disturbance and self-objectification. The present study investigated whether a 3-day social media fast in a sample for whom social media is especially salient, female adolescent dancers, can mitigate such negative effects. Through an online survey, 65 pre-teen and teen girls, aged 10-19, completed measures of self-objectification (body surveillance and body shame), self-esteem and self-compassion both prior to and following three days of abstaining from all social media. During the fast, girls reflected on their experiences in group messages on the messaging app, WhatsApp. Overall, the fast had positive effects on participants, for whom body surveillance and body shame was significantly reduced after the fast. Self-compassion significantly mediated the change in both body surveillance and body shame, and self-esteem was a significant mediator of improvements in body shame. The content of girls' group messages revealed a number of themes, such as more positive mental states during the fast. Future research should continue to examine the potential of brief social media fasts as a means to alleviate appearance pressures adolescent girls face on these platforms in daily life.

Dilute Alloys Based on Au, Ag, or Cu for Efficient Catalysis: From Synthesis to Active Sites.

The development of new catalyst materials for energy-efficient chemical synthesis is critical as over 80% of industrial processes rely on catalysts, with many of the most energy-intensive processes specifically using heterogeneous catalysis. Catalytic performance is a complex interplay of phenomena involving temperature, pressure, gas composition, surface composition, and structure over multiple length and time scales. In response to this complexity, the integrated approach to heterogeneous dilute alloy catalysis reviewed here brings together materials synthesis, mechanistic surface chemistry, reaction kinetics, in situ and operando characterization, and theoretical calculations in a coordinated effort to develop design principles to predict and improve catalytic selectivity. Dilute alloy catalysts─in which isolated atoms or small ensembles of the minority metal on the host metal lead to enhanced reactivity while retaining selectivity─are particularly promising as selective catalysts. Several dilute alloy materials using Au, Ag, and Cu as the majority host element, including more recently introduced support-free nanoporous metals and oxide-supported nanoparticle "raspberry colloid templated (RCT)" materials, are reviewed for selective oxidation and hydrogenation reactions. Progress in understanding how such dilute alloy catalysts can be used to enhance selectivity of key synthetic reactions is reviewed, including quantitative scaling from model studies to catalytic conditions. The dynamic evolution of catalyst structure and composition studied in surface science and catalytic conditions and their relationship to catalytic function are also discussed, followed by advanced characterization and theoretical modeling that have been developed to determine the distribution of minority metal atoms at or near the surface. The integrated approach demonstrates the success of bridging the divide between fundamental knowledge and design of catalytic processes in complex catalytic systems, which can accelerate the development of new and efficient catalytic processes.

Decoding reactive structures in dilute alloy catalysts.

Rational catalyst design is crucial toward achieving more energy-efficient and sustainable catalytic processes. Understanding and modeling catalytic reaction pathways and kinetics require atomic level knowledge of the active sites. These structures often change dynamically during reactions and are difficult to decipher. A prototypical example is the hydrogen-deuterium exchange reaction catalyzed by dilute Pd-in-Au alloy nanoparticles. From a combination of catalytic activity measurements, machine learning-enabled spectroscopic analysis, and first-principles based kinetic modeling, we demonstrate that the active species are surface Pd ensembles containing only a few (from 1 to 3) Pd atoms. These species simultaneously explain the observed X-ray spectra and equate the experimental and theoretical values of the apparent activation energy. Remarkably, we find that the catalytic activity can be tuned on demand by controlling the size of the Pd ensembles through catalyst pretreatment. Our data-driven multimodal approach enables decoding of reactive structures in complex and dynamic alloy catalysts.

Masking our risky behavior: how licensing and fear reduction reduce social distancing behavior.

Licensing and fear reduction can explain why people only partially adopt health precautions while still believing that they are remaining compliant with recommendations during the COVID-19 pandemic. We assessed individuals' attitudes regarding social distancing and personal protective practices, as well as concern about COVID-19 and behaviors in April of 2020. Concern about COVID-19 had dual, competing effects on social distancing behavior. Concern predicted increased social distancing behavior via more positive social distance policy attitudes. However, concern also predicted decreased social distancing behavior via more positive attitudes toward personal protective practices, such as mask wearing. Licensing and/or fear reduction allows individuals to view personal protective practices as substitutable rather than additive measures of safety that should complement social distancing, and this effect is not explained by partisanship or working from home. Policy makers should be cautious when advocating for multiple health precautions of varying effectiveness that are intended to be additive.

Kinetics and selectivity of methane oxidation on an IrO2(110) film.

Undercoordinated, bridging O-atoms (Obr) are highly active as H-acceptors in alkane dehydrogenation on IrO2(110) surfaces but transform to HObrgroups that are inactive toward hydrocarbons. The low C-H activity and high stability of the HObrgroups cause the kinetics and product selectivity during CH4oxidation on IrO2(110) to depend sensitively on the availability of Obratoms prior to the onset of product desorption. From temperature programmed reaction spectroscopy (TPRS) and kinetic simulations, we identified two Obr-coverage regimes that distinguish the kinetics and product formation during CH4oxidation on IrO2(110). Under excess Obrconditions, when the initial Obrcoverage is greater than that needed to oxidize all the CH4to CO2and HObrgroups, complete CH4oxidation is dominant and produces CO2in a single TPRS peak between 450 and 500 K. However, under Obr-limited conditions, nearly all the initial Obratoms are deactivated by conversion to HObror abstracted after only a fraction of the initially adsorbed CH4oxidizes to CO2and CO below 500 K. Thereafter, some of the excess CHxgroups abstract H and desorb as CH4above ∼500 K while the remainder oxidize to CO2and CO at a rate that is controlled by the rate at which Obratoms are regenerated from HObrduring the formation of CH4and H2O products. We also show that chemisorbed O-atoms ('on-top O') on IrO2(110) enhance CO2production below 500 K by efficiently abstracting H from Obratoms and thereby increasing the coverage of Obratoms available to completely oxidize CHxgroups at low temperature. Our results provide new insights for understanding factors which govern the kinetics and selectivity during CH4oxidation on IrO2(110) surfaces.

Nitinol Release of Nickel under Physiological Conditions: Effects of Surface Oxide, pH, Hydrogen Peroxide, and Sodium Hypochlorite.

Nitinol is a nickel-titanium alloy widely used in medical devices for its unique pseudoelastic and shape-memory properties. However, nitinol can release potentially hazardous amounts of nickel, depending on surface manufacturing yielding different oxide thicknesses and compositions. Furthermore, nitinol medical devices can be implanted throughout the body and exposed to extremes in pH and reactive oxygen species (ROS), but few tools exist for evaluating nickel release under such physiological conditions. Even in cardiovascular applications, where nitinol medical devices are relatively common and the blood environment is well understood, there is a lack of information on how local inflammatory conditions after implantation might affect nickel ion release. For this study, nickel release from nitinol wires of different finishes was measured in pH conditions and at ROS concentrations selected to encompass and exceed literature reports of extracellular pH and ROS. Results showed increased nickel release at levels of pH and ROS reported to be physiological, with decreasing pH and increasing concentrations of hydrogen peroxide and NaOCl/HOCl having the greatest effects. The results support the importance of considering the implantation site when designing studies to predict nickel release from nitinol and underscore the value of understanding the chemical milieu at the device-tissue interface.

Formation of a Ti-Cu(111) single atom alloy: Structure and CO binding.

A single atom Ti-Cu(111) surface alloy can be generated by depositing small amounts of Ti onto Cu(111) at slightly elevated surface temperatures (∼500 to 600 K). Scanning tunneling microscopy shows that small Ti-rich islands covered by a Cu single layer form preferentially on ascending step edges of Cu(111) during Ti deposition below about 400 K but that a Ti-Cu(111) alloy replaces these small islands during deposition between 500 and 600 K, producing an alloy in the brims of the steps. Larger partially Cu-covered Ti-containing islands also form on the Cu(111) terraces at temperatures between 300 and 700 K. After surface exposure to CO at low temperatures, reflection absorption infrared spectroscopy (RAIRS) reveals distinct C-O stretch bands at 2102 and 2050 cm-1 attributed to CO adsorbed on Cu-covered Ti-containing domains vs sites in the Ti-Cu(111) surface alloy. Calculations using density functional theory (DFT) suggest that the lower frequency C-O stretch band originates specifically from CO adsorbed on isolated Ti atoms in the Ti-Cu(111) surface alloy and predicts a higher C-O stretch frequency for CO adsorbed on Cu above subsurface Ti ensembles. DFT further predicts that CO preferentially adsorbs in flat-lying configurations on contiguous Ti surface structures with more than one Ti atom and thus that CO adsorbed on such structures should not be observed with RAIRS. The ability to generate a single atom Ti-Cu(111) alloy will provide future opportunities to investigate the surface chemistry promoted by a representative early transition metal dopant on a Cu(111) host surface.

Interface Joint Strength between SS316L Wrought Substrate and Powder Bed Fusion Built Parts.

Metal powder bed fusion (PBF) additive manufacturing (AM) builds metal parts layer by layer upon a substrate material. The strength of this interface between the substrate and the printed material is important to characterize, especially in applications where the substrate is retained and included in the finished part. Ensuring that this interface between the original and the printed material has adequate material properties enables the use of this PBF AM process to repair existing structures and create new parts using both AM and conventional manufacturing. This paper studies the tensile and torsional shear strengths of wrought and PBF-built SS316L specimens and compares them to specimens that are composed of half wrought material and half PBF material. These specimens were created by building new material via PBF onto existing wrought SS316L blocks, then cutting the specimens to include both materials. The specimens are also examined using optical microscopy and electron backscatter diffraction (EBSD). The PBF specimens consistently exhibited higher strength and lower ductility than the wrought specimens. The hybrid PBF/wrought specimens performed similarly to the wrought material. In none of the specimens did any failure appear to occur at or near the interface between the wrought substrate and the PBF material. In addition, most of the deformation in the PBF/wrought specimens appeared to be limited to the wrought portion of the specimens. These results are consistent with optical microscopy and EBSD showing smaller grain size in the PBF material, which correlates to increased strength in SS316L due to the Hall-Petch relationship. With the strength at the interface meeting or exceeding the strength of the original wrought material, this process shows great promise as a method for adding additional features or repairing existing structures using metal PBF AM.

Temperature dependence of nickel ion release from nitinol medical devices.

Nitinol exhibits unique (thermo)mechanical properties that make it central to the design of many medical devices. However, nitinol nominally contains 50 atomic percent nickel, which if released in sufficient quantities, can lead to adverse health effects. While nickel release from nitinol devices is typically characterized using in vitro immersion tests, these evaluations require lengthy time periods. We have explored elevated temperature as a potential method to expedite this testing. Nickel release was characterized in nitinol materials with surface oxide thickness ranging from 12 to 1564 nm at four different temperatures from 310 to 360 K. We found that for three of the materials with relatively thin oxide layers, ≤ 87 nm nickel release exhibited Arrhenius behavior over the entire temperature range with activation energies of 80 to 85 kJ/mol. Conversely, the fourth ''black-oxide'' material, with a much thicker, complex oxide layer, was not well characterized by an Arrhenius relationship. Power law release profiles were observed in all four materials; however, the exponent from the thin oxide materials was approximately 1/4 compared with 3/4 for the black-oxide material. To illustrate the potential benefit of using elevated temperature to abbreviate nickel release testing, we demonstrated that a > 50 day 310 K release profile could be accurately recovered by testing for less than 1 week at 340 K. However, because the materials explored in this study were limited, additional testing and mechanistic insight are needed to establish a protective temperature scaling that can be applied to all nitinol medical device components.

Full-field microscale strain measurements of a nitinol medical device using digital image correlation.

Computational modeling and simulation are commonly used during the development of cardiovascular implants to predict peak strains and strain amplitudes and to estimate the associated durability and fatigue life of these devices. However, simulation validation has historically relied on comparison with surrogate quantities like force and displacement due to barriers to direct strain measurement-most notably, the small spatial scale of these devices. We demonstrate the use of microscale two-dimensional digital image correlation (2D-DIC) to directly characterize full-field surface strains on a nitinol medical device coupon under emulated physiological and hyperphysiological loading. Experiments are performed using a digital optical microscope and a custom, temperature-controlled load frame. Following applicable recommendations from the International DIC Society, hardware and environmental heating studies, noise floor analyses, and in- and out-of-plane rigid body translation studies are first performed to characterize the microscale DIC setup. Uniaxial tension experiments are also performed using a polymeric test specimen to characterize the strain accuracy of the approach up to nominal stains of 5%. Sub-millimeter fields of view and sub-micron displacement accuracies (9nm mean error) are achieved, and systematic (mean) and random (standard deviation) errors in strain are each estimated to be approximately 1,000µÏµ. The system is then demonstrated by acquiring measurements at the root of a 300µm-wide nitinol medical device strut undergoing fixed-free cantilever bending motion. Lüders-like transformation bands are observed originating from the tensile side of the strut that spread toward the neutral axis at an angle of approximately 55°. Despite the inherent limitations of optical microscopy and 2D-DIC, simple and relatively economical setups like that demonstrated herein could provide a practical and accessible solution for characterizing cardiovascular implant micromechanics, validating computational model strain predictions, and guiding the development of next-generation material models for simulating superelastic nitinol.

Low Temperature Activation of Methane on Metal-Oxides and Complex Interfaces: Insights from Surface Science.

ConspectusThe abundance of cheap, natural gas has transformed the energy landscape, whereby revealing new possibilities for sustainable chemical technologies or impacting those that have relied on traditional fossil fuels. The primary component, methane, is underutilized and wastefully exhausted, leading to anthropogenic global warming. Historically, the manipulation of methane remained "clavis aurea," an insurmountable yet rewarding challenge and thus the focus of intense research. This is primarily due to an inability to dissociate C-H bonds in methane selectively, which requires a high energy penalty and is an essential prerequisite for the direct conversion of methane into a large set of value-added products. The discovery of such processes would promise an energy gainful use of natural gas benefiting several essential chemical processes associated with C1 chemistry. This first C-H bond dissociation step of the methane molecule appears in numerous catalytic mechanisms as the rate-determining step or most essential barrier sequence for all subsequent steps that follow in the production of C-C, C-O, or Cx-Hy-Oz bonds found in value added products. A main goal is to catalytically reduce the energy barrier for the first C-H bond dissociation to be able to achieve the activation of methane at low or moderate temperatures. As such there is great value in understanding the fundamental nature of the active sites responsible for bond breaking or formation and thus be able to facilitate better control of this chemistry, leading to the development of new technologies for fuel production and chemical conversion. Surface science studies offer enhanced perspectives for a careful manipulation of bonds over the last layer atoms of catalyst surfaces, an essential factor for the design of atomically precise catalysts and unravelling of the reaction mechanism. With the advent of new surface imaging, spectroscopy, and in situ tools, it has been possible to decipher the surface chemistry of complex materials systems and further our understanding of atomic active sites on the surfaces of metals, oxides, and carbides or metal-oxide and metal-carbide interfaces. The once considered near impossible step of C-H bond activation is now observed at low temperatures with high propensity over a collection of oxide, metal-oxide, and metal-carbide systems in a conventional or inverse configuration (oxide or carbide on metal). The enabling of C-H activation at low temperature has opened interesting possibilities for the specific production of chemicals such as methanol directly from methane, a step toward facile synthesis of liquid fuels. We highlight the most recent of these results and present the key aspects of active site configurations engineered from surface science studies which enable such a simple reactive event through careful manipulation of the last surface layer of atoms found in the catalyst structure. New concepts which help in the activation and conversion of methane are discussed.

Growth and auto-oxidation of Pd on single-layer AgOx/Ag(111).

We investigated the growth and auto-oxidation of Pd deposited onto a AgOx single-layer on Ag(111) using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Palladium initially grows as well-dispersed, single-layer clusters that adopt the same triangular shape and orientation of Agn units in the underlying AgOx layer. Bi-layer clusters preferentially form upon increasing the Pd coverage to ∼0.30 ML (monolayer) and continue to develop until aggregating and forming a nearly conformal Pd bi-layer at a coverage near 2 ML. Analysis of the STM images provides quantitative evidence of a transition from single to bi-layer Pd growth on the AgOx layer, and a continuation of bi-layer growth with increasing Pd coverage from ∼0.3 to 2 ML. XPS further demonstrates that the AgOx layer efficiently transfers oxygen to Pd at 300 K, and that the fraction of Pd that oxidizes is approximately equal to the local oxygen coverage in the AgOx layer for Pd coverages up to at least ∼0.7 ML. Our results show that oxygen in the initial AgOx layer mediates the growth and structural properties of Pd on the AgOx/Ag(111) surface, enabling the preparation of model PdAg surfaces with uniformly distributed single or bi-layer Pd clusters. Facile auto-oxidation of Pd by AgOx further suggests that oxygen transfer from Ag to Pd could play a role in promoting oxidation chemistry of adsorbed molecules on PdAg surfaces.

A Computational Study on Deformed Bioprosthetic Valve Geometries: Clinically Relevant Valve Performance Metrics.

Transcatheter aortic valves (TAV) are symmetrically designed, but they are often not deployed inside cylindrical conduits with circular cross-sectional areas. Many TAV patients have heavily calcified aortic valves, which often result in deformed prosthesis geometries after deployment. We investigated the effects of deformed valve annulus configurations on a surgical bioprosthetic valve as a model for TAV. We studied valve leaflet motions, stresses and strains, and analog hydrodynamic measures (using geometric methods), via finite element (FE) modeling. Two categories of annular deformations were created to approximate clinical observations: (1) noncircular annulus with valve area conserved, and (2) under-expansion (reduced area) compared to circular annulus. We found that under-expansion had more impact on increasing stenosis (with geometric orifice area metrics) than noncircularity, and that noncircularity had more impact on increasing regurgitation (with regurgitation orifice area metrics) than under-expansion. We found durability predictors (stress/strain) to be the highest in the commissure regions of noncircular configurations such as EllipMajor (noncircular and under-expansion areas). Other clinically relevant performance aspects such as leaflet kinematics and coaptation were also investigated with the noncircular configurations. This study provides a framework for choosing the most challenging TAV deformations for acute and long-term valve performance in the design and testing phase of device development.

Redox-mediated transformation of a Tb2O3(111) thin film from the cubic fluorite to bixbyite structure.

We used temperature programmed desorption (TPD) and low energy electron diffraction (LEED) to investigate the isomeric structural transformation of a Tb2O3 thin film grown on Pt(111). We find that repeated oxidation and thermal reduction to 1000 K transforms an oxygen-deficient, cubic fluorite (CF) Tb2O3(111) thin film to the well-defined bixbyite, or c-Tb2O3(111) structure, whereas annealing the CF-Tb2O3(111) film in UHV is ineffective in causing this structural transformation. We estimate that the final stabilized film consists of about ten layers of c-Tb2O3(111) in the surface region plus about eight layers of CF-Tb2O3(111) located between the c-Tb2O3(111) and the Pt(111) substrate. Our measurements reveal the development of two distinct O2 TPD peaks during the CF to bixbyite transformation that arise from oxidation of c-Tb2O3 domains to the stoichiometrically-invariant ι-Tb7O12 and δ-Tb11O20 phases and demonstrate that the c-Tb2O3 phase oxidizes more facilely than CF-Tb2O3. We present evidence that nucleation and growth of c-Tb2O3 domains occurs at the buried TbOx/CF-Tb2O3 interface, and that conversion of the interfacial CF-Tb2O3 to bixbyite takes place mainly during thermal reduction of TbOx above ∼900 K and causes newly-formed c-Tb2O3 to advance deeper into the film. The avoidance of low Tb oxidation states may facilitate the CF to bixbyite transformation via this redox mechanism.

Comparison of ASTM F2129 and ASTM F746 for Evaluating Crevice Corrosion.

Crevice corrosion is one of the major mechanisms that drives implant failure in orthopedic devices that have modular interfaces. Despite the prevalence of crevice corrosion in modular interfaces, very little is known with regards to the susceptibility of different material combinations to participate in crevice corrosion. In this study, we compare two electrochemical methods, ASTM F2129, Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements to Determine the Corrosion Susceptibility of Small Implant Devices, and a modified version of ASTM F746, Standard Test Method for Pitting or Crevice Corrosion of Metallic Surgical Implant Materials, in their ability to induce crevice corrosion. Four commonly used metals, 316 stainless steel, commercially pure titanium (Ti grade 2), Ti-6Al-4V (Ti grade 5), and cobalt-chromium-molybdenum per ASTM F1537, Standard Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants (UNSR31537, UNSR31538, and UNSR31539), were used to form crevices with a rod and washer combination. As a control, the metal rod materials were tested alone in the absence of crevices using ASTM F2129 and the modified ASTM F746 method. As another control to determine if crevices formed with polymeric materials would influence crevice corrosion susceptibility, experiments were also conducted with metal rods and polytetrafluorethylene washers. Our results revealed more visible corrosion after ASTM F2129 than ASTM F746. Additionally, ASTM F746 was found to falsely identify crevice corrosion per the critical pitting potential when visual inspection found no evidence of crevice corrosion. Hence, ASTM F2129 was found to be more effective overall at evaluating crevice corrosion compared to ASTM F746.