Polymeric materials are commonplace in the natural gas infrastructure as distribution pipes, coatings, seals, and gaskets. Under the auspices of the U.S. Department of Energy HyBlend program, one of the means to reduce greenhouse gas emissions is with replacing natural gas, either partially or completely, with hydrogen. This approach makes it imperative that we conduct near-term and long-term materials compatibility research in these relevant environments. Insights into the effects of hydrogen and hydrogen gas blends on polymer integrity can be gained through both ex-situ and in-situ analytical methods. Our work represented here highlights a study of the behavior of pipeline polyethylene (PE) materials, including HDPE (Dow 2490 and GDB50) and MDPE (Ineos and legacy Dupont Aldyl A), when exposed to hydrogen by means of in-situ X-ray scattering and ex-situ Raman spectroscopy techniques. These methods complement each other in analyzing polymer microstructure. Data collected revealed that the aforementioned polymers did not show significant changes in crystallinity or morphology under the exposure conditions tested. These studies help establish techniques to study real-time effects of hydrogen gas on polymer structure and chemistry, which is directly related to pipeline mechanical strength and longevity of service.
Polymers used in hydrogen transportation, production, storage, and dispensing operations of the hydrogen infrastructure are subject to demanding performance temperatures (-60°C to +140°C) and pressures (0.9 MPa to 87 MPa), under static and cycling conditions of hydrogen exposure. Cycling exposures which include pressurization and depressurization stages can particularly affect properties of these soft materials. Other factors such temperature of exposure in hydrogen environments can also play an influential role on polymer degradation behaviors. In this work, we evaluated the influence of varying rates of depressurization (1, 10, 20, 40 MPa/min and uncontrolled) with model elastomer compounds exposed to high-pressure hydrogen cycling (17 MPa to 87 MPa) at ambient temperature. The goal was to develop an understanding of factors that affect rapid gas decompression in elastomers, which is a phenomenon common in hydrogen fueling operations. Cycling was followed by ex-situ characterization for changes in properties. Dynamic Mechanical Thermal Analysis (DMTA), density, compression set, Attenuated Total Reflectance-FTIR (ATR-FTIR), nanoindentation, and X-ray computer tomography were characterization techniques used to compare polymers before and after cycling. Polymer degradation in the form of internal damage was found to increase with rate of depressurization. EPDM showed the most dependence on rates of depressurization, compared to FKM and HNBR formulations. Additionally, filled, and unfilled model compounds of EPDM, FKM, HNBR, and NBR were tested in high-pressure (17 MPa to 87 MPa) and low-pressure (10 MPa to 31 MPa) cycling conditions at -40°C and +85°C. These experiments were performed at a fixed depressurization rate. The goal of these experiments was to better understand temperature effects under pressure cycling conditions for elastomeric polymer seals. Filled formulations of EPDM, HNBR, and NBR exhibited increased compression set and decreased storage modulus under cold cycling exposures to a greater extent than when cycled at ambient. For filled polymers cycled at low pressures at 85°C and -40°C, FKM showed the most resistance to blistering. HNBR and NBR showed heavy swelling and blistering under both these conditions. Micro CT imaging of one of the polymers (EPDM) subjected to high-pressure cycling at 85°C showed great damage in the form of cracks in the center of the sample. Filled formulations exhibited decreased compression set and storage modulus under hot cycling exposures to a greater extent than with cold and ambient cycling. The findings from these studies will help build a strong understanding of polymer behaviors in cycling hydrogen under rapid gas decompression and thermal conditions encountered in fueling operations and storage. Proper material selection for appropriate use-conditions within components is also enabled.
Additive manufacturing (AM) is a relatively new technological advancement that allows for rapid prototyping, development of intricate shapes, and reduction in manufacturing time. The materials of interest for this project are Ultem 1010, ABS M30, FDM Nylon 12, PC, and PPSF. However, little is known regarding the aging behavior of these AM materials. The limited aging study outlined herein was designed to compare the chemical, physical, and mechanical properties of AM parts as they experience accelerated aging at 70 °C for a total of 24 weeks. In general, ABS M30 stood out as it appeared to undergo chemical and physical changes leading to increase in density and an overall more brittle material, making this commonly used material not attractive for long-term use.
Polymers such as PTFE (polytetrafluorethylene or Teflon), EPDM (ethylene propylene diene monomer) rubber, FKM fluoroelastomer (Viton), Nylon 11, Nitrile butadiene (NBR) rubber, hydrogenated nitrile rubber (HNBR) and perfluoroelastomers (FF_202) are commonly employed in super critical CO2 (sCO2) energy conversion systems. O-rings and gaskets made from these polymers face stringent performance conditions such as elevated temperatures, high pressures, pollutants, and corrosive humid environments. In FY 2019, we conducted experiments at high temperatures (100°C and 120°C) under isobaric conditions (20 MPa). Findings showed that elevated temperatures accelerated degradation of polymers in sCO2, and that certain polymer microstructures are more susceptible to degradation over others. In FY 2020, the focus was to understand the effect of sCO2 on polymers at low (10 MPa) and high pressures (40 MPa) under isothermal conditions (100°C). It was clear that the same selectivity was observed in these experiments wherein certain polymeric functionalities showed more propensity to failure over others. Fast diffusion, supported by higher pressures and long exposure times (1000 hours) at the test temperature, caused increased damage in sCO2 environments to even the most robust polymers. We also looked at polymers under compression in sCO2 at 100°C and 20 MPa pressure to imitate actual sealing performance required of these materials in sCO2 systems. Compression worsened the physical damage that resulted from chemical attack of the polymers under these test conditions. In FY 2021, the effect of cycling temperature (from 50°C to 150°C to 50°C) for polymers under a steady sCO2 pressure of 20 MPa was studied. The aim was to understand the influence of cycling temperatures of sCO2 for typical polymers under isobaric (20 MPa) conditions. Thermoplastic polymers (Nylon, and PTFE) and elastomers (EPDM, Viton, Buna N, Neoprene, FF202, and HNBR) were subjected to 20 MPa sCO2 pressure for 50 cycles and 100 cycles in separate experiments. Samples were extracted for ex-situ characterization at 50 cycles and upon the completion of 100 cycles. Each cycle constituted of 175 minutes of cycling from 50°C to 150°C. The polymer samples were examined for physical and chemical changes by Dynamic Mechanical and Thermal Analysis (DMTA), Fourier Transform Infrared (FTIR) spectroscopy, and compression set. Density and mass changes immediately after removal from test were measured for degree of swell comparisons. Optical microscopy techniques and micro computer tomography (micro CT) images were collected on select specimens. Evaluations conducted showed that exposures to super-critical CO2 environments resulted in combinations of physical and/or chemical changes. For each polymer, the dominance of cycling temperatures under sCO2 pressures, were evaluated. Attempts were made to qualitatively link the permanent sCO2 effects to polymer micro- structure, free volume, backbone substitutions, presence of polar groups, and degree of crystallinity differences. This study has established that soft polymeric materials are conducive to failure in sCO2 through mechanisms of failure that are dependent on polymer microstructure and chemistry. Polar pendant groups, large atom substitutions on the backbone are some of the factors that are influential structural factors.
Conathane EN-7 (referred to as EN-7) has been used for decades to pot electrical connectors, providing mechanical support for solder joints in cables. Unfortunately, the EN-7 formulation contains a suspect carcinogen and chemical sensitizer, toluene diisocyanate (TDI). Because of this, various groups have been formulating replacement materials, but all have come up short in final properties or in processing. We propose Arathane 5753 HVB as a replacement for EN-7. The properties compare very well with EN-7 and the processing has both advantages and disadvantages over EN-7 as discussed in detail below.
A copolymer of maleic anhydride and styrene is functionalized with Diels–Alder (DA) capable pendant groups to enable the study of this material with different crosslink densities. This constituent is synthesized using commercially available starting materials and relatively simple and uncomplicated chemistries which open the possibility for its use in large-scale applications. The 10%, 25%, 50%, and 100% DA nominal crosslinking based on available pendant furan groups on the polymeric component is investigated. The reaction kinetics are monitored using infrared spectroscopy and rheology. Based on the rheological results, carbon nanotube (CNT) incorporation into the DA matrix is explored in order to determine its effects on the complex modulus of the material. This work is meant as a proof of concept for this DA material with the possibility of its incorporation into other commonly used bulk materials and/or adhesives to allow for an easily reversible product formulation.
This work is to characterize the mechanical properties of the selected composites along both on- and off- fiber axes at the ambient loading condition (+25°C), as well as at the cold (-54°C), and high temperatures (+71°C). A series of tensile experiments were conducted at different material orientations of 0°, 22.5°, 45°, 67.5°, 90° to measure the ultimate strength and strain $σ_{f}, ϵ_{f}$, and material engineering constants, including Young's modulus Ε and Poisson's ratio ν. The composite materials in this study were one carbon composite carbon (AS4C/UF3662) and one E-galss (E-glass/UF3662) composite. They both had the same resin of UF 3362, but with different fibers of carbon AS4C and E-glass. The mechanical loading in this study was limited to the quasi-static loading of 2 mm/min (1.3x10^(-3) in/s), which was equivalent to 5x10(-4) strain rate. These experimental data of the mechanical properties of composites at different loading directions and temperatures were summarized and compared. These experimental results provided database for design engineers to optimize structures through ply angle modifications and for analysts to better predict the component performance.
This report describes the mechanical characterization of six types of woven composites that Sandia National Laboratories are interested in. These six composites have various combinations of two types of fibers (Carbon-IM7 and Glass-S2) and three types of resins (UF-3362, TC275-1, TC350-1). In this work, two sets of experiments were conducted: quasi-static loading with displacement rate of 2 mm/min (1.3x10^(-3) in/s) and high rate loading with displacement of 5.08 m/s (200 in/s). Quasi-static experiments were performed at three loading orientations of 0°, 45°, 90° for all the six composites to fully characterize their mechanical properties. The elastic properties Young's modulus and Poisson's ratio, as well as ultimate stress and strain were obtained from the quasi-static experiments. The high strain rate experiments were performed only on glass fiber composites along 0° angle of loading. The high rate experiments were mainly to study how the strain rate affects the ultimate stress of the glass-fiber composites with different resins.
An investigation of polyurethane foam filled with known flame retardant fillers including hydroxides, melamine, phosphate-containing compounds, and melamine phosphates was carried out to produce a low-cost material with high flame retardant efficiency. The impact of flame retardant fillers on the physical properties such a s composite foam density, glass transition temperature, storage modulus, and thermal expansion of composite foams was investigated with the goal of synthesizing a robust rigid foam with excellent flame retardant properties.
An assessment of the effects of cation concentration on the thermophysical properties of salts in the temperature range of 300 to 500°C was investigated. The latent heat and density exhibit a statistically relevant dependence upon mixtures, while heat capacity, viscosity, and thermal conductivity did not exhibit statistical differences among mixtures in the range of temperature studied. Heat capacity tended to be nearly flat while in the liquid state for mixtures at each temperature. Density of the mixtures decreases linearly with temperature. Mixture composition influenced density, with a relative variation up to 2% over the temperature range investigated. Viscosity decreased as a function of temperature in a non-linear fashion and methods used here tended to exhibit a higher value than literature values. Thermal conductivity used laser flash and transient wire methods. Transient wire found no differences between mixtures within repeatability of the measurement, while laser flash was found to not work well for molten nitrate salts due to the large error.
Two classes of materials, poly(methylene diphenyl diisocyanate) or PMDI foam, and cross-linked epoxy resins, were characterized using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), to help understand the effects of aging and %E2%80%9Cbake-out%E2%80%9D. The materials were evaluated for mass loss and the onset of decomposition. In some experiments, volatile materials released during heating were analyzed via mass spectroscopy. In all, over twenty materials were evaluated to compare the mass loss and onset temperature for decomposition. Model free kinetic (MFK) measurements, acquired using variable heating rate TGA experiments, were used to calculate the apparent activation energy of thermal decomposition. From these compiled data the effects of aging, bake-out, and sample history on the thermal stability of materials were compared. No significant differences between aged and unaged materials were detected. Bake-out did slightly affect the onset temperature of decomposition but only at the highest bake-out temperatures. Finally, some recommendations for future handling are made.
This report describes the development of a new detection method for electrostatic discharge (ESD) testing of explosives, using a single-lens reflex (SLR) digital camera and a 200-mm macro lens. This method has demonstrated several distinct advantages to other current ESD detection methods, including the creation of a permanent record, an enlarged image for real-time viewing as well as extended periods of review, and ability to combine with most other Go/No-Go sensors. This report includes details of the method, including camera settings and position, and results with well-characterized explosives PETN and RDX, and two ESD-sensitive aluminum powders.
Hydrogen getters were tested for use in storage of plutonium-bearing materials in accordance with DOE’s Criteria for Interim Safe Storage of Plutonium Bearing Materials. The original studies, documented in Sandia Report SAND2008-301530150095, included HiTop getter material aged for 3 months at 70°C. This material was aged for an additional 3 months for a total of 6 months at 70°C, and the performance of the getter was evaluated again and documented in Sandia Report SAND2008-301530151789P. This material was then aged for an additional 7 months for a total of 13 months at 70°C, and the performance of the getter under recombination and gettering conditions was evaluated. A sample of the 13 months aged getter was exposed to radiation at SRNL, and the performance of this sample was also evaluated. The results of the 13 months study is reported in SAND2008-301530157165P. The HiTop material was aged for an additional 5 months for a total of 18 months. This material was split into two samples with the second sample being exposed to radiation at SRNL. The performance of the 18 month aged HiTop material is covered in this report.
Hydrogen getters were tested for use in storage of plutonium-bearing materials in accordance with DOE's Criteria for Interim Safe Storage of Plutonium Bearing Materials. The original studies, documented in Sandia Report SAND2007-0095, included HiTop getter material aged for 3 months at 70°C. This material was aged for an additional 3 months for a total of 6 months at 70°C, and the performance of the getter was evaluated again and documented in Sandia Report SAND2007-1789P. This material was then aged for an additional 7 months for a total of 13 months at 70°C, and the performance of the getter under recombination and gettering conditions was evaluated. A sample of the 13 months aged getter was exposed to radiation at SRNL, and the performance of this sample was also evaluated. The results of the 13 months study is reported in SAND2007-7165P. The HiTop material was aged for an additional 5 months for a total of 18 months. This material was split into two samples with the second sample being exposed to radiation at SRNL. The performance of the 18 month aged HiTop material is covered in this report. The 18-month aged material showed similar performance under gettering conditions to the previously aged material: the recombination rate is well above the required rate of 45 std. cc H2/h, and the gettering reaction occurs in the absence of oxygen at a slower rate. Both pressure drop measurements and 1H NMR analyses support these conclusions. 1H NMR analyses show extremely minor changes in the 18-month aged material, which can be possibly attributed to slight decomposition of the HiTop material or absorption of contaminants during the aging process.
Legacy plutonium-bearing materials are stored in shipping containers at the Savannah River Site (SRS) until their final disposition can be determined. This material has been stabilized and is maintained per the DOE’s standard for long-term storage of Pu-containing materials, DOE-STD-3013. As a part of its ongoing storage mission, Washington Savannah River Company’s (WSRC) Nuclear Materials Management (NMM) organization is tasked with a surveillance program that will ensure these materials have remained in their expected condition over the several years of storage. Information from this program will be used by multiple entities to further validate the safe storage of Pu-bearing materials per DOE-STD-3013. Part of the program entails cutting open selected 3013 containers and sampling the materials inside. These samples will then be analyzed by Savannah River National Laboratory (SRNL). The remaining material not used for samples will then be repackaged in non-3013 containers to be placed back into shipping packages for storage until disposition at SRS. These repackaged materials will be stored per the requirements of DOE’s Criteria for Interim Safe Storage of Plutonium Bearing Materials (ISSC).
Hydrogen getters were tested for use in storage of plutonium-bearing materials in accordance with DOE's Criteria for Interim Safe Storage of Plutonium Bearing Materials. The hydrogen getter HITOP was aged for 3 months at 70 C and tested under both recombination and hydrogenation conditions at 20 and 70 C; partially saturated and irradiated aged getter samples were also tested. The recombination reaction was found to be very fast and well above the required rate of 45 std. cc H2h. The gettering reaction, which is planned as the backup reaction in this deployment, is slower and may not meet the requirements alone. Pressure drop measurements and {sup 1}H NMR analyses support these conclusions. Although the experimental conditions do not exactly replicate the deployment conditions, the results of our conservative experiments are clear: the aged getter shows sufficient reactivity to maintain hydrogen concentrations below the flammability limit, between the minimum and maximum deployment temperatures, for three months. The flammability risk is further reduced by the removal of oxygen through the recombination reaction. Neither radiation exposure nor thermal aging sufficiently degrades the getter to be a concern. Future testing to evaluate performance for longer aging periods is in progress.