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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Enhancing the Range and Reliability of the Spacer Layer Imaging Method

The spacer layer imaging method (SLIM) is widely used to measure the thickness of additive and lubricant films, in lubricant development and evaluation, and for fundamental research into elastohydrodynamic lubrication and tribofilm formation mechanisms. The film thickness measurement, as implemented on several popular tribometers, provides powerful, non-destructive in-situ mapping of film topography with nanometre-scale height sensitivity. However, the results can be highly sensitive to experimental procedure, machine condition, and image analysis, in some cases reporting unphysical film thickness trends. The prevailing image analysis techniques make it challenging to interrogate these errors, often hiding their multivariate nonlinear behaviour from the user by spatial averaging. Herein, several common ‘silent errors’ in the SLIM measurement, including colour matching to incorrect fringe orders, and colour drift due to the optical properties of the system or film itself, are discussed, with examples. A robust suite of novel a priori and a posteriori methods to address these issues, and to improve the accuracy and reliability of the measurement, are also presented, including a novel, computationally inexpensive circle-finding algorithm for automated image processing. In combination, these methods allow reliable mapping of films up to at least 800 nm in thickness, representing a significant milestone for the utility of SLIM applied to elastohydrodynamic contact.

EHL film geometry↗
DOE OSTI2021

Lignin monomer conversion into biolubricant base oils

Despite progress in the depolymerization of lignin, only a few studies convert the obtained monomers to value-added products. Here we introduce a strategy to synthesize branched benzene lubricant (BBL) and branched cyclic lubricant (BCL) base oils from lignin-derived monomers and aldehyde. We perform carbon–carbon coupling via Brønsted acid-catalyzed hydroxyalkylation/alkylation (HAA) then hydrodeoxygenation (HDO). Optimum HAA reaction conditions achieve up to 90% guaiacol conversion and an HAA product containing 76% BBL and 24% enal condensation product over a P-SiO 2 catalyst. Subsequent HDO of HAA products over an Ir-ReO x /SiO 2 catalyst produces a lubricant-ranged mixture of BCL (C 24 ) up to yield (82%) and small fractions of dodecyl cyclohexane and C 10 and C 15 carbons alkanes. The kinematic viscosity, viscosity index, and Noack volatility of these base oils are comparable to commercial petroleum-derived poly α-olefin Group IV and refrigerant base oils. In conclusion, this approach provides a sustainable pathway for replacing petroleum-derived base oils.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Engine Operating Conditions, Fuel Property Effects, and Associated Fuel–Wall Interaction Dependencies of Stochastic Preignition

This work for the Coordinating Research Council (CRC) explores dependencies on the opportunity for fuel to impinge on internal engine surfaces (i.e., fuel–wall impingement) as a function of fuel properties and engine operating conditions and correlates these data with measurements of stochastic preignition (SPI) propensity. SPI rates are directly coupled with laser–induced florescence measurements of dye-doped fuel dilution measurements of the engine lubricant, which provides a surrogate for fuel–wall impingement. Literature suggests that SPI may have several dependencies, one being fuel–wall impingement. However, it remains unknown if fuel-wall impingement is a fundamental predictor and source of SPI or is simply a causational factor of SPI. In this study, these relationships on SPI and fuel-wall impingement are explored using 4 fuels at 8 operating conditions per fuel, for 32 total test points. The fuels were directly injected at two different injection timings: an earlier injection timing that initially targets the piston crown and a later injection timing that targets the cylinder liner. At each injection timing, the engine was operated at both 90°C and 70°C coolant and lubricant temperatures, and 185 and 200 kPa absolute intake manifold pressure. This work serves as an exploratory effort to down select conditions and provide initial fuel properties of interest for a secondary study to explore fuel property specific effects on fuel-wall interaction and SPI propensity. Significant findings from this initial operating condition and fuel property exploratory work are: 1. reduced engine operating coolant and lubricant temperatures, along with 2. retarded injection timings were required to increase SPI propensity. Moreover, at these conditions some fuel specific effects were also observed; specifically, increased ethanol content increased measured dye–wall (i.e., fuel–wall) interaction. However, despite increased dye–wall interaction, the increased volatility of the ethanol containing fuels also reduced the estimated fuel retention in the top-ring zone and associated measured SPI propensity. Thus, the findings of this unique approach to explore relationships between fuel-wall impingement and SPI highlight that SPI propensity is more directly proportional to retained fuel, and not simply fuel–wall impingement. Furthermore, fuel retention was found to be directly influenced by complex fuel property and engine operating condition relationships. Either retarded injection timings and/or increased fuel volatility increased fuel wall-impingement, while less volatile fuels and/or reduced coolant temperatures increased fuel retention. Therefore, for a given operating condition, the data highlights that greater volatile fuels exhibit increased fuel wall impingement without increased fuel retention or SPI propensity, while less volatile fuels could exhibit reduced fuel-wall impingement but increased fuel retention and SPI propensity rates.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2021

New insights into creep characteristics of calcium silicate hydrates at molecular level

The fundamental mechanisms under concrete creep are far from being fully understood, especially at the molecular level. Hereby, a calcium-silicate-hydrate (C-S-H) molecular model is developed to explain, for the first time, the creep characteristics at various stress states, temperature levels and water contents, which are not accessible experimentally. Rather tensile and compressive loadings, C-S-H only creeps under shear loadings originating from the sliding of the calcium silicate layers over each other as the interlayer component (water and ions) acts as a lubricator. A heterogeneous creep characteristic is observed. Elevated temperature reduces the interlayer lubricator viscosity and weakens the interfacial adhesion between the layers and the interlayer lubricator, which accelerates C-S-H creep. The removal of interlayer water enhances the creep resistance, resulting from the reduced interlayer space and enhanced interfacial adhesion. The atomic-level mechanisms explain the inter-CSH-particle behaviours at the microscale, which bridges the gap between atomistic simulation and microcosmic phenomenon.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Achieving clean production with nanostructured coated milling tools dry machining low carbon steel

The advancement of clean production using nanostructured materials in subtractive manufacturing processes has focused on replacing the use of liquid lubrication with solid lubricants coated to conventional cutting tools machining low carbon steel (~ 0.2 wt. % carbon). However, little is known about the wear mechanisms that dominate such tools when coated with functional graded nanostructured coatings. The present study follows an international standard for characterizing such wear (ISO 8688) but uses advanced measurement techniques such as x-ray fluorescence technology to measure the diffusion of chemical species from tool to workpiece and vice versa, that contributes to tool wear with the view to enhance the principles of cleaner production. The results show that when commercially-available tools coated with the appropriate functionally graded industrial coating, diffusion does not take place and creates an effective chemical barrier during machining. The experimental methods used in the study include machining workpieces using a CNC milling machine, tachometer for measuring spindle speed, dynamometer for measuring cutting forces, infra-red camera for measuring cutting temperatures, chemical species diffusion wear using x-ray florescence detector, and an optical microscope for measuring tool wear. Coupled with the physical measurement of wear, it is concluded that mechanical wear dominates the milling of a low carbon steel and that thermal properties of the coatings do not correlate with such wear. It is also concluded that flank wear as a function of volume of workpiece removed and machining duration (machining index) is a sound method for assessing the transition of the stages of wear during clean machining operations. The present study not only has implication for the design of better cutting tools, but also advances dry machining processes that eliminate the use of liquid lubricants making subtractive production processes cleaner. The main conclusions drawn from this study show that coated tools have a longer life under dry conditions compared to uncoated tools and that there is no correlation between coating properties and tool wear. In conclusion, diffusion of chemical species into the cut chips did not occur because of the lack of thermally induced chemical wear of the cutting tool and that wear is caused by the gradual erosion of the flank face due to the chip abrading the cutting tool.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Comparing energy and water use of aqueous and gas-based metalworking fluids

Gas-based metalworking fluids (MWFs) have been proposed as alternative coolants and lubricants in machining operations to mitigate concerns surrounding water use and pollution, industrial hygiene, occupational health, and performance limitations associated with water-based (aqueous) MWFs that are ubiquitously used in the metals manufacturing industry. This study compares the primary energy and water use associated with the consumptive use, delivery, and disposal of aqueous MWFs with three gas-based MWFs in the literature-minimum quantity lubricant-in-compressed air (MQL), liquid/gaseous N-2, and liquid/supercritical CO2. The comparison accounts for reported differences in machining performance in peer-reviewed experimental studies across several machining processes and materials. The analysis shows that despite the reported improvement in tool life with N-2 and CO2-based MWFs, the electricity- and water-intensive separation and purification processes for N-2 and CO2 lead to their higher primary energy and water use per volume of material machined relative to water-based MWFs. Although MQL is found to have lower primary energy use, significant consumptive water use associated with the vegetable oil commonly used with this MWF leads to higher overall water use than aqueous MWF, which is operated in a recirculative system. Gas-based MWFs thus shift the water use upstream of the manufacturing plant. Primary energy and water use of gas-based MWFs could be reduced by focusing on achieving higher material removal rates and throughput compared to aqueous MWF instead of solely targeting improvements in tool life. Additionally, the consumptive use of CO2 and N-2 MWFs could be minimized by optimizing their flow rates and delivery to precisely meet the cooling and lubrication needs of specific machining processes instead of flooding the tool and workpiece with these gases. This article met the requirements for a gold-gold JIE data openness badge described at http://jie.click/badges.

cutting fluids↗
DOE OSTI2026

Effect of Oil Viscosity and Impact of Ionic Liquid Additive on Electrically Induced Pitting in Rolling Contact

Electrically induced bearing damage (EIBD) is a growing concern in electric drivetrains, where electrical discharge currents generate localized pitting that accelerates wear and premature failure. While ionic liquids (ILs) have shown promise as lubricant additives due to their natural physical adsorption, strong capabilities of tribofilm formation, and high molecular tunability, their role in mitigating EIBD is little known. This gap is especially evident because lubricant viscosity and film thickness affect discharge behavior, and additive performance in these regimes has not been well explored. In this study, tribological tests were performed using a ball-on-disk pure rolling-contact system under an applied voltage on polyalphaolefin oils of three viscosities (4, 10, and 150 cSt measured at 100 °C), with and without the addition of a phosphonium-phosphate IL. Surface damage was analyzed using scanning electron microscopy (SEM) and stylus profilometry. Damage quantification was based on pit morphology analysis of SEM images. The results provide new insights into how oil viscosity governs the discharge behavior and how an IL additive could influence the pit formation. While viscosity seems to play a significant role, an IL additive shows potential to reduce EIBD and deserves further study.

electrically induced bearing damage (EIBD)↗
DOE OSTI2024

Competition Between Growth and Removal in Zirconia Nanocrystal-Derived Tribofilms: The Role of Co-additives

Antiwear additives permit energy-efficient lubrication of gearboxes, bearings, and other tribological interfaces. We study zirconia (ZrO 2 ) nanocrystal additives, which readily form protective tribofilms in tribological contacts. Our prior work demonstrated cooperative antiwear performance between ZrO 2 and the S- and P-based co-additives in fully formulated hydrocarbon gear oils. Here, we extend that work by examining the growth kinetics of the ZrO 2 tribofilms, including the influence of the co-additives. In the boundary lubrication regime for mixed rolling-sliding contacts, the initial phase of ZrO 2 tribofilm growth is soon overtaken by removal processes, phenomena whose importance has gone unnoticed in prior work. Tribofilm removal affects the steady-state thickness and morphology of the tribofilm as well as its growth kinetics. The S- and P-based co-additives are incorporated into the ZrO 2 tribofilm, and alter the competition between the growth and removal processes, increasing initial net growth rates per contact cycle and contributing to a more polished final interface. This work highlights the significance of removal processes in determining tribofilm antiwear performance, and suggests several routes for improving tribofilm growth kinetics using co-additives.

Coadditives↗
DOE OSTI2021

Temperature-dependent dynamic fouling on superhydrophobic and slippery nonwetting copper surfaces

Bioinspired, superhydrophobic and slippery liquid infused surfaces that offer nonwetting characteristics have been explored in recent years for fouling mitigation. However, most of the studies are in the context of biofouling or under static immersion at ambient temperature conditions that are not reflective of the dynamic flow environment in practice. This article presents, for the first time, a systematic study of dynamic fouling of superhydrophobic (SHS) and slippery lubricant-infused surfaces (LIS) over a range of flow and temperature conditions. In this work, copper metallic surfaces were textured via electrodeposition or etching and further functionalized to achieve SHS and, additionally, infiltrated with a lubricant to fabricate LIS. The nonwetting surfaces were studied for their fouling behavior in a rotating Couette flow of a supersaturated calcium sulfate solution at different rotational speed and temperature. Fouling mineral mass accumulation on the different surfaces was measured as a function of time over a period of days using inductively coupled plasma mass spectroscopy and the fouled surfaces were investigated using scanning electron microscopy. Both SHS and LIS showed superior anti-scaling performance at all ranges of variables. An analytical Hill-Langmuir model is presented, for the first time, to describe the time evolution of scaling within 20% accuracy over the range of parameters studied. The study is the first to juxtapose two surface texturing methods, electrodeposition and etching, and two nonwetting surface types, SHS and LIS, subject to a common suite of experiments to elucidate fundamental understanding of mineral fouling on nonwetting surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Rheological and pumping behaviour of 3D printable cementitious materials with varying aggregate content

3D printing with cementitious materials is an emerging technology and provides an active area of research. Despite this, there are only limited studies that examine the pumping behaviour of high yield stress fluids such as printable concrete. We present a study on the rheological behaviour of 3D printable cementitious materials with different aggregate-to-binder ratios (a/b) and analyse the pumping and printing characteristics with the measured rheological parameters. We observed that an increase in a/b resulted in a significant increase of plastic viscosity, and a nominal increase in yield stress and storage modulus. The variation in plastic viscosity and yield stress with increasing aggregate content was analysed with the Krieger-Dougherty and Chateau-Ovarlez-Trung model, respectively. Also, the rheological properties of the paste rich lubrication layer during pumping were determined with the help of a tribometer. The yield stress and viscous constant of the lubrication layer increase with the increase in a/b. The pumping pressure predictions were carried out by a suitable theoretical model by considering appropriate flow conditions for different mixtures. The variation in critical height of printed elements with an increase in a/b was correlated with the observed rheological parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mineral scaling on brass and aluminum surfaces with a range of wettability

Crystallization fouling, or mineral scaling, is fundamental to various surfaces in energy and environmental applications. This paper considers, for the first time, a systematic investigation of scaling of nonwetting aluminum and brass surfaces relative to their bare counterparts. Metallic surfaces with a range of nonwetting characteristics from hydrophilic to superhydrophobic and lubricant infused surfaces were fabricated using a facile etching method. Systematic dynamic flow scaling experiments are conducted on the six different surface types at three flow levels and two temperature levels. The interactive effects of the different parameters are analyzed relative to their correspondence to the nucleation theory. The study reveals that nonwetting metallic superhydrophobic or hydrophobic surfaces reduce fouling by over 50% compared to bare counterparts. Further, lubricant infused metallic surfaces demonstrate superior anti-scaling performance by over 60% and up to 90% fouling reduction. The study is the first to present fundamental insights into the engineering and anti-scaling performance of nonwetting brass and aluminum surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Characterization of MoS 2 films via simultaneous grazing incidence X-ray diffraction and grazing incidence X-ray fluorescence (GIXRD/GIXRF)

Physical vapor deposited (PVD) molybdenum disulfide (nominal composition MoS 2 ) is employed as a thin film solid lubricant for extreme environments where liquid lubricants are not viable. The tribological properties of MoS 2 are highly dependent on morphological attributes such as film thickness, orientation, crystallinity, film density, and stoichiometry. These structural characteristics are controlled by tuning the PVD process parameters, yet undesirable alterations in the structure often occur due to process variations between deposition runs. Nondestructive film diagnostics can enable improved yield and serve as a means of tuning a deposition process, thus enabling quality control and materials exploration. Grazing incidence X-ray diffraction (GIXRD) for MoS 2 film characterization provides valuable information about film density and grain orientation (texture). However, the determination of film stoichiometry can only be indirectly inferred via GIXRD. The combination of density and microstructure via GIXRD with chemical composition via grazing incidence X-ray fluorescence (GIXRF) enables the isolation and decoupling of film density, composition, and microstructure and their ultimate impact on film layer thickness, thereby improving coating thickness predictions via X-ray fluorescence. We have augmented an existing GIXRD instrument with an additional X-ray detector for the simultaneous measurement of energy-dispersive X-ray fluorescence spectra during the GIXRD analysis. This combined GIXRD/GIXRF analysis has proven synergetic for correlating chemical composition to the structural aspects of MoS 2 films provided by GIXRD. We present the usefulness of the combined diagnostic technique via exemplar MoS 2 film samples and provide a discussion regarding data extraction techniques of grazing angle series measurements.

MoS2↗
DOE OSTI2020

Material-Dependent Antagonistic Effects between Soot and ZDDP

While soot in engine oil is known to accelerate the wear of diesel and gasoline direct-injection compression-ignition engines, there is a lack of consensus on the wear mechanism though various hypotheses have been proposed in the literature. Particularly, some recently observed antagonistic effects between soot and a common lubricant antiwear additive, zinc dialkyldithiophosphate (ZDDP), while others did not. The discrepancy is, in part, explained by the strong alloy dependence of such antagonism discovered in this study. Specifically, four alloys, 52100 steel and M2, M50, and A2 tool steels, are tested in lubricants containing carbon black (CB, a soot surrogate) with and without ZDDP present. Adding the CB alone to the oil increases the wear rate for all steel alloys as expected. However, distinct wear performance is observed for the four steel alloys when ZDDP is introduced to the CB-containing oil: while the 52100 steel has notable wear reduction, the three tool steels suffer significant wear increase. Comprehensive tribofilm characterization suggests that the Mo content in the steel alloy and the sulfur from ZDDP strongly influence wear behavior. The combination of CB/Mo-catalyzed sulfidation and CB-accelerated abrasion is hypothesized to be responsible for the high wear of the Mo-alloyed tool steels.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The effect of electrical current on premature failures and microstructural degradation in bearing steel

Premature failures associated with microstructural degradation, i.e. white etching cracks (WECS), are becoming commonplace as applications are requiring tribological components to operate under extreme conditions. Although the specific drivers of WECs are still debated, the failures are often found in applications where cyclic loading is combined with added energy from stressors such as slip, impacts, or stray current. The aim of the current work is to elucidate effect that variable current has on premature failure. Numerous commercially available lubricants were tested, and both lubricant base oil type and additive package were found to have an effect on WEC failure time.

Bearing failure↗
DOE OSTI2024

Finite domain solution of a KGD hydraulic fracture in the viscosity-dominated regime

This paper describes a numerical algorithm for solving the classic problem of a plane strain (KGD) fracture propagating in an impermeable elastic medium with zero toughness. The method, which takes advantage of the self-similar nature of the solution, combines a domain-based scheme to solve the elasticity equations and a finite volume method to solve the nonlinear lubrication equation. This work represents a first step towards developing a model able to account for pore pressure diffusion in the medium and corresponding poroelastic effects, noting that these processes are more efficiently solved using a domain-based rather than a boundary integral method. To enhance the efficiency and accuracy of the numerical scheme, the far-field crack asymptotics is embedded in the discretized elastic relationship between the fluid pressure and the crack opening, while the coupled fluid-solid tip asymptote is enforced in a weak form when solving the nonlinear lubrication equation. The proposed technique yields results that closely match the analytical solution, even with a coarse mesh. This approach offers potential for addressing more complex hydraulic fracturing problems in the future.

Domain-based method↗
DOE OSTI2023

Tribocorrosion of stainless steel sliding against graphite in FLiNaK molten salt

The molten salt reactor (MSR) concept recently gained renewed interest in developing Generation IV nuclear reactors. One MSR design uses fluoride molten salts to cool tri-structural isotropic particle fuel encapsulated by a carbon matrix into spherical pebbles, which would inevitably contact the reactor's stainless steel container wall during salt circulation. Characterizing this interaction is crucial for reactor safety. Here, in this work, we report the tribocorrosion behavior of graphite sliding against Type 316H stainless steel lubricated by a FLiNaK (LiF:NaF:KF; 46.5:11.5:42 mol %) molten salt in an argon environment. Accelerated wear loss was observed at a higher temperature because of a lower molten salt viscosity and a higher corrosion rate. The graphite had a more rapid material loss at a higher sliding speed than stainless steel because of its higher vulnerability to vibration-induced microfracture. The salt-starved condition caused more material loss than either the no-salt or the salt-flooded condition because neither a graphite transfer film nor stable boundary lubrication could be established at salt starvation. An interesting dual-layer surface film was discovered on the stainless steel worn surface: a chromium-rich top film and a nickel-accumulated but chromium-depleted interlayer. The film composition and structure provide fundamental insights to the mechanochemical interactions between stainless steel and graphite in a molten salt environment.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Long-Term Static and Dynamic Corrosion Stability of Nonwetting Surfaces

Superhydrophobic surfaces (SHSs) and lubricant-infused surfaces (LISs) are two classes of nonwetting surfaces that have drawn attention due to their advanced functional properties including corrosion inhibition. Yet there is a conspicuous lack of corrosion study of SHSs and LISs with respect to their fabrication and material parameters, especially at high temperatures and under dynamic flow conditions over long durations, which is sought to be addressed in this article. Considering copper SHSs and LISs, a full factorial combinatorial study of two facile texturing processes, electrodeposition and etching, two different functionalization agents, stearic acid and mercaptan, and two types of infused lubricants, Krytox 104 and DOWSIL 510, is presented, encompassing over 650 measurements on 90 tested surfaces. All fabricated surfaces demonstrated water repellency with a contact angle above 150° and a sliding angle below 7°. For the first time, the study examines high-temperature corrosion stability and long-term corrosion durability of the nonwetting surfaces in both static fluid and dynamic turbulent flow conditions over a period of 30 days. Here, LISs and SHSs are shown to provide excellent corrosion inhibition over all tested corrosion conditions, with negligible presence of corrosion species on the surfaces and no deterioration of the texturing. The surfaces are also shown to rejuvenate easily to the initial wettability and corrosion resistance values. This study provides valuable insights into the selection of materials and processing parameters for the fabrication of nonwetting surfaces for the application of interest.

Copper↗