This research was performed at the Pacific Northwest National Laboratory (PNNL), which is operated by Battelle Memorial Institute for the Department of Energy (DOE) under Contract No. DE-AC05-76RL01830.

The experiment described here requires the use of hydrogen gas which is odorless, colorless, and thus undetectable by human senses. Hydrogen is highly flammable and burns with a nearly invisible blue flame and can form explosive mixtures in the presence of oxygen. High pressures in excess of 6.9 MPa add additional explosion hazards that must be appropriately planned for in preparation for any testing. This amount of stored energy represents a serious safety hazard and therefore due diligence, planning, and a safety evaluation must be performed before performing such an experiment to ensure that these hazards are mitigated. The experiment presented here is performed in accordance with appropriate safety precautions in an American Society of Mechanical Engineers (ASME) certified pressure vessel with a burst disk set to 34.5 MPa with proper ventilation.
1. Preparing Polymer Sheet Stock
<ol>
	<li>Apply detergent to the EDPM polymer sheet stock using a non-abrasive sponge and rinse under water for approximately 3 min to remove oils and talc powder applied during the manufacturing and shipping process.</li>
	<li>Dry polymer sheet in a drying oven at 85% of the material&#39;s working temperature, about 75 &#176;C for EPDM, for approximately 72 hours to drive of any water remaining from washing.</li>
	<li>Turn off the oven and allow polymer sheet stock material to cool to room temperature inside the oven.</li>
	<li>Mark one corner of the sheet stock with an arrow pointing to the top of the polymer sheet. This arrow will assist with identifying orientation of the sheet during the sample coupon generation, ensuring that samples cut from the polymer sheet will be consistently of the same orientation.</li>
	<li>Store the polymer stock sheet in a room temperature, humidity-controlled environment near 25% relative humidity prior to tribological testing.</li>
</ol>
2. Generating and Mounting Sample Coupons
<ol>
	<li>While wearing powder free gloves, mark the polymer sheet stock with an arrow in the intended coupon area near the arrow marked during preparation of the polymer sheet stock such that both arrows have the same orientation.</li>
	<li>Using a 2.222 cm diameter circular die and a mallet, stamp out a sample coupon around the arrow mark.</li>
	<li>Loosen the hex cap screws securing the sample clamp on the in situ tribometer, remove the hex cap screw and precision spring from the most easily accessible corner of the sample clamp.</li>
	<li>Slide sample coupon into sample clamp, taking care to make sure the sample is oriented with the arrow pointed face down and towards the back of the clamp which is the side closest to the back-plate of the tribometer.</li>
	<li>Replace the precision spring and hex cap screw in the empty corner of the sample clamp and proceed to hand tighten all four of the hex cap screws of the clamp until snug such that the elastomer sample is compressed by 10% of its original height. Assuming a 0.318 cm sample height, 10% compression can be achieved by using a 0.287 cm gauge block between the two plates of the clamp.</li>
</ol>
3. Preparing the In Situ Tribometer
<ol>
	<li>Place a 2.413 cm gauge block between the wall of the tribometer and the sample sled, directly below the drive screw. Make sure the data collection box is turned off, then turn the drive chain in a clockwise motion to back the sample sled such that the edge of the sled is 2.413 cm from the tribometer wall.</li>
	<li>Gently wipe the steel ball of the counter surface with a soft cloth or lint-less paper towel and an appropriate solvent such as acetone for approximately 30 seconds until the surface of the counter surface appears free of any debris.</li>
	<li>Slide the bronze counter surface carrier and bronze weight, a total normal load of 7.5 N, onto the rail perpendicular to the sample sled, allowing the counter ball to slide between into the keyhole and rest on the polymer sample.</li>
	<li>Using a hex key and two bronze screws, reattach the linear variable differential transformer (LVDT) measurement arm to the bronze counter surface holder such that the freely floating cylinder of the LVDT rests on the arm.</li>
	<li>Adjust the clamp holding the LVDT in place up or down such that the LVDT is measuring near it&#39;s zero point then tighten the clamp to secure the LVDT in place.</li>
	<li>Lower the tribometer assembly into the pressure vessel, ensuring that the thermowell in the top flange of the vessel will lower into the gap between the tribometer and the wall of the vessel.</li>
	<li>Wrap the sealing o-ring with a total of two and a half layers of PTFE tape. This is accomplished by wrapping the PTFE tape such that each additional wrap overlaps approximately half of the proceeding lap until going around the diameter of the o-ring twice. Then wrap the diameter of the o-ring a final time without any overlap. Once the o-ring is wrapped, place it in the groove in the lip of the pressure vessel.</li>
	<li>Taking into account the wiring labels, reconnect the five power wires for the tribometer motor, four data wires for the load cell, and five data wires for the LVDT.</li>
</ol>
4. Sealing the Pressure Vessel
<ol>
	<li>Lower the top flange of the pressure vessel to close it, taking care to lower the top flange gently onto the PTFE wrapped sealing o-ring.</li>
	<li>Insert the bolts into the numbered holes on the top flange indicated by the manufacturer in ascending order until they are finger tight.</li>
	<li>Using a manual hex key, torque the flange bolts in ascending order to hand tight and repeat until the bolts can no longer be tightened.</li>
	<li>Starting at 120 Nm and increasing in ~40 Nm increments, use a torque wrench to torque the flange bolts in ascending order for each ~40 Nm increment until they are torqued to 280 Nm.</li>
</ol>
5. Filling the Pressure Vessel
<ol>
	<li>Now that the pressure vessel is sealed, connect the gas fittings to the autoclave lid and flush the pressure vessel with low pressure (~0.55 MPa) argon gas for approximately 1 h until the oxygen content of the vessel drops below 10 ppm using an oxygen sensor plumbed into the output of the pressure vessel.</li>
	<li>Slowly (&#60;0.25 MPa/s) flush the vessel with hydrogen gas up to 6.9 MPa, then slowly vent the gas to atmospheric pressure. Repeat the flushing process two more times.</li>
	<li>After flushing the pressure vessel, slowly (&#60;0.25 MPa/s) fill the pressure vessel with hydrogen gas up to 13.75 MPa and allow the vessel to rest for 10 min such that the temperature of the gas within the vessel equilibrates to room temperature.</li>
	<li>Fill the vessel to 20.7 MPa and wait another 10 min.</li>
	<li>Bring the vessel up to the target 27.6 MPa and close off all valves.</li>
	<li>Allow the polymer sample to soak for at least 12 h in the hydrogen gas before starting the experiment to allow for complete permeation.</li>
</ol>
6. Running Experiment
<ol>
	<li>Double check that all the pass-through wires exiting the pressure vessel are correctly connected to the labelled wiring harness attached to the tribometer control box, and then turn on the tribometer.</li>
	<li>In the tribometer software set the experiment time to 1 hour at 0.1 cm/s velocity with a path length of 0.140 cm. This corresponds to a distance of approximately 3.5 m.</li>
	<li>Tare the load cell, and ensure that the LVDT is reporting an appropriate depth in the tribometer software which should be near 0 mm.</li>
	<li>Start the experiment.</li>
</ol>
7. Post-Experiment
<ol>
	<li>Once the experiment has completed, slowly vent the pressure vessel of hydrogen gas at approximately 0.35 MPa/s, ensuring that the pressure vessel temperature does not drop below 0 &#176;C.</li>
	<li>Finally, flush the pressure vessel volume with argon gas at atmospheric pressure for 10 minutes to ensure that there is no remaining hydrogen within the vessel.</li>
</ol>

<ol>
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Int. 92, 162-171 (2015).</li><li>Sawae, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Friction+and+wear+of+bronze+filled+PTFE+and+graphite+filled+PTFE+in+40+MPA+hydrogen+gas.">Friction and wear of bronze filled PTFE and graphite filled PTFE in 40 MPA hydrogen gas.</a> Proceed. , 249-251 (2011).</li><li>Fujiwara, H., Ono, H., Nishimura, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Degradation+behavior+of+acrylonitrile+butadiene+rubber+after+cyclic+high-pressure+hydrogen+exposure.">Degradation behavior of acrylonitrile butadiene rubber after cyclic high-pressure hydrogen exposure.</a> Int. J. Hydrogen Energy. 40 (4), 2025-2034 (2015).</li><li>Zhang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+low+temperature+prestrain+on+hydrogen+gas+embrittlement+of+metastable+austenitic+stainless+steels.">Influence of low temperature prestrain on hydrogen gas embrittlement of metastable austenitic stainless steels.</a> Int. J. Hydrogen Energy. 38 (25), 11181-11187 (2013).</li><li>Weber, S., Theisen, W., Mart&#305;, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+stable+high-aluminum+austenitic+stainless+steel+for+hydrogen+applications.">Development of a stable high-aluminum austenitic stainless steel for hydrogen applications.</a> Int. J. Hydrogen Energy. 38 (14), 5989-6001 (2013).</li><li>Papavinasam, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Corrosion control in the oil and gas industry. , (2013).</li><li>Yamamoto, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+Embrittlement+of+Nuclear+Power+Plant+Materials.">Hydrogen Embrittlement of Nuclear Power Plant Materials.</a> Mat. Trans. 45 (8), 2647-2649 (2004).</li><li>Rymuza, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tribology+of+polymers.">Tribology of polymers.</a> Arch. Civ. Mech. Eng. 7 (4), 177-184 (2007).</li><li>Mckeen, L. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 1 Introduction to Fatigue and Tribology of Plastics and Elastomers. , (2010).</li><li>Lorge, O., Briscoe, B. J., Dang, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gas+induced+damage+in+poly(vinylidene+fluoride)+exposed+to+decompression.">Gas induced damage in poly(vinylidene fluoride) exposed to decompression.</a> Polymer. 40, 2981-2991 (1999).</li><li>Sawae, Y., Yamaguchi, A., Nakashima, K., Murakami, T., Sugimura, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+Hydrogen+Atmosphere+on+Wear+Behavior+of+PTFE+Sliding+Against+Austenitic+Stainless+Steel.">Effects of Hydrogen Atmosphere on Wear Behavior of PTFE Sliding Against Austenitic Stainless Steel.</a> Proceed. , 1-3 (2008).</li><li>Sawae, Y., Nakashima, K., Doi, S., Murakami, T., Sugimura, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+high+pressure+hydrogen+on+wear+of+PTFE+and+PTFE+composite.">Effects of high pressure hydrogen on wear of PTFE and PTFE composite.</a> Proceed. , 233-235 (2010).</li><li>Duranty, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+in+situ+tribometer+for+measuring+friction+and+wear+of+polymers+in+a+high+pressure+hydrogen+environment.">An in situ tribometer for measuring friction and wear of polymers in a high pressure hydrogen environment.</a> Rev. Sci. Instrum. 88 (9), (2017).</li></ol>

The authors have nothing to disclose.

Current ex situ techniques for tribological testing of polymer materials require samples to be exposed to high pressure hydrogen which are then depressurized before being tested using a commercial tribometer.15,24,25 The test methodology in this protocol was designed to permit testing of the tribological properties of polymer samples in a high pressure environment in situ. By testing polymer materials such as the EPDM samples presented above while they are pressurized, this protocol allows for a more realistic measurement of the dense pressure-compressed polymer sample found in components of the hydrogen delivery infrastructure. Since the tribological properties of the material are measured in situ, data anomalies caused by depressurization effects such as explosive decompression present in ex situ methods are mitigated. 
This protocol requires adequate sample soak times of the polymer sample attached to the tribometer instrument in order to ensure that the hydrogen gas has completely diffused throughout the polymer sample, which in the case of EPDM was approximately 12 hours. As a result measurement of the polymer sample's tribological properties while being exposed to high pressure hydrogen gas, the metallic functional and structural components of the tribometer used in this protocol were required to be hydrogen gas compatible. Therefore, the in situ tribometer was mostly constructed out of aluminum and the use of stainless steel was minimized. Functional components such as the motor driving the sample stage and a capacitive load cell used to measure the frictional load in the tribometer constructed using hydrogen-compatible components and were specially ordered for this project. These components increased the cost of performing this in situ methodology as compared to the ex situ alternatives.
The in situ test methodology described here has been developed to quantitatively measure the friction and wear of polymer samples while in a hydrogen gas environment similar to the high pressure conditions that exist within the hydrogen delivery infrastructure. The results of this testing can be used to help determine the suitability of a given polymer material for use in hydrogen infrastructure and storage applications. The data generated using this methodology and presented above for EPDM polymer samples suggests that the surface coefficient friction of these samples along with the wear EPDM samples experienced was increased in a high pressure hydrogen environment. This methodology was not able to determine whether these trends were due to the pressure effects of the in situ environment or the interaction between the hydrogen gas and the EPDM polymer. Future study is required to deconvolute the effects of pressure and hydrogen compatibility in these elastomeric samples with in a high-pressure hydrogen environment.

In the recent years, there has been great interest in hydrogen as a potential zero emission or near-zero emission fuel in vehicles and stationary power sources. Since hydrogen exists as a low density gas at room temperature, most applications use some form of compressed hydrogen for fuel.1,2 A potential drawback of using compressed, high pressure hydrogen gas is incompatibility with many materials found within infrastructure2,3,4 and vehicular applications5 where compatibility issues are combined with repeated pressure and temperature cycling. A pure hydrogen environment is known to damage metal components including certain steels and titanium through different mechanisms including hydride formation, swelling, surface blistering, and embrittlement.2,6,7,8 Non-metallic components such as lead zirconate titanate (PZT) used in piezoelectric ceramics have also proven susceptible to degradation due to hydrogen incompatibility effect such as surface blistering and lead migration.9,10,11,12 While these examples of damage due to hydrogen exposure have been previously studied, the compatibility of polymer components within hydrogen environments has only recently become of interest.13,14,15,16 This is largely a result of metallic components providing structural integrity in nuclear and oil and gas applications whereas the polymer components usually act as barriers or seals.17,18,19,20 As a result, the friction and wear properties of polymer materials within components such as polytetrafluoroethylene (PTFE) valve seats and nitrile butadiene rubber (NBR) O-rings become important factors in their ability to function.
In the case of the hydrogen infrastructure, components such as valves, compressors, and storage tanks contain polymer materials that are in contact with metallic surfaces. The frictional interaction between the polymer and metallic surfaces results in wear of each of the surfaces. The science of the relationship between the friction and wear of two interacting surfaces is known as tribology. Polymers tend to have lower elastic moduli and strength than metallic, therefore the tribological properties of polymer materials differ greatly from metallic materials. As a result, polymer surfaces tend to exhibit greater wear and damage after frictional contact with a metallic surface.21,22 In a hydrogen infrastructure application, rapid pressure and temperature cycling causes repeated interaction between the polymer and metallic surfaces, increasing the likelihood of friction and wear on the polymer component. Quantifying this damage can be challenging ex situ due to possible explosive decompression of the polymer sample after depressurization which may cause non-tribological damage.23 Additionally, many commercial polymer products contain many fillers and additives such as magnesium oxide (MgO) that may interact negatively with hydrogen gas through hydriding, further complicating ex situ analysis of wear in these materials.24,25
Due to the complexity of differentiating between damage to the polymer material caused during depressurization and damage due to tribological wear ex situ, there is a need to directly study the frictional properties of non-metallic materials in situ within a high-pressure hydrogen environment that is likely to exist within the hydrogen delivery infrastructure. In this protocol, we demonstrate a test methodology developed to quantify the friction and wear properties of polymer materials in a high-pressure hydrogen environment utilizing a purpose-built in situ tribometer.26 We also present representative data acquired using the in situ tribometer and ethylene propylene diene monomer (EPDM) rubber, a common polymer sealing and barrier material. The EPDM material for which representative data was generated using the protocol below was purchased in 60.96 cm square sheets with a 0.3175 cm thickness and was reported by the vendor to have a 60A hardness rating.

<table><tbody><tr><td>EPDM Polymer Stock Sheet</td><td>McMaster-Carr</td><td>8525T68</td><td>24&quot; x 24&quot;, 1/8&quot; Thick</td></tr><tr><td>Pressure Vessel, Autoclave</td><td>Fluitron Inc.</td><td>8308-1788-U</td><td>5&quot; diameter, 1&#039; height</td></tr><tr><td>High Purity Hydrogen Gas</td><td>Praxair</td><td>HY4.5</td><td>Grade 4.5, 5ppm O2, 5 ppm H20</td></tr><tr><td>O2 Sensor</td><td>Advanced Micro Instruments</td><td>T2</td><td>0-5ppm min. range, 10,0000ppm max.</td></tr><tr><td>Pre-purified Argon Gas</td><td>Oxarc</td><td>LCCO-HP818</td><td>High-purity, 99.998%</td></tr><tr><td>Liquid Dishwashing Detergent</td><td>McMaster-Carr</td><td>98365T89</td><td>32 oz pour bottle, lemon scented</td></tr><tr><td>Mildew Resistant Sponge</td><td>McMaster-Carr</td><td>7309T1</td><td>6&quot; long x 3 -1/2&quot; Wide x 1&quot; High, yellow</td></tr><tr><td>PTFE Pipe Thread Sealant Tape</td><td>McMaster-Carr</td><td>4591K12</td><td>1/2&quot; wide, white color</td></tr><tr><td>Gas Tube Fittings</td><td>Swagelok</td><td>SS-400-1-4</td><td>1/4&quot; OD, stainless steel, male NPT threading</td></tr><tr><td>Hammer Driven Die</td><td>McMaster-Carr</td><td>3427A22</td><td>7/8&quot; Hammer driven hole punch</td></tr><tr><td>Linear Variable Differential Transformer</td><td>Omega</td><td>LD320-2.5&amp;nbsp;</td><td>2.5mm, AC output, guided w/spring</td></tr><tr><td>Autoclave O-ring Seal</td><td>Fluitron Inc.</td><td>A-4511</td><td>Hastelloy C-276, 5-3/4&quot; OD x 5&quot; ID x 3/8&quot;</td></tr><tr><td>Torque Wrench</td><td>McMaster-Carr</td><td>85555A422</td><td>Adjustable Torque-Limiting Wrench, Quick-Release, 1/2&quot; Square Drive, 50-250 ft.-lbs. Torque</td></tr><tr><td>Mallet</td><td>McMaster-Carr</td><td>5939A11</td><td>Hard and Extra-Hard Rubber Hammer, 2-1/4 lbs.</td></tr><tr><td>iLoad Mini Capacitive Load Sensor</td><td>Loadstar Sensors</td><td>MFM-050-050-S*C03</td><td>50 lb, U Calibration, 0.5% Accuracy, Steel</td></tr></tbody></table>

in situ high pressure hydrogen tribological testing of common polymer materials used in the hydrogen delivery infrastructure

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is known about the effects of high pressure hydrogen on the polymer sealing and barrier materials also found within these components. More study is required in order to determine the compatibility of common polymer materials found in the components of the hydrogen fuel delivery infrastructure with high pressure hydrogen. As a result, it is important to consider the changes in physical properties such as friction and wear in situ while the polymer is exposed to high pressure hydrogen. In this protocol, we present a method for testing the friction and wear properties of ethylene propylene diene monomer (EPDM) elastomer samples in a 28 MPa high pressure hydrogen environment using a custom-built in situ pin-on-flat linear reciprocating tribometer. Representative results from this testing are presented which indicate that the coefficient of friction between the EPDM sample coupon and steel counter surface is increased in high pressure hydrogen as compared to the coefficient of friction similarly measured in ambient air.

Using the methodology presented, the coefficient of kinetic friction and wear factor for an elastomeric sample can be measured while in a high-pressure hydrogen environment. The representative data presented in Figure 1 show that in a high-pressure hydrogen environment greater force is required to move EPDM polymer samples under the steel counter surface. Using the relationship between the normal force FN and the frictional force FK the coefficient of friction, &#181;, between the EPDM sample and the steel ball can be determined. This data is presented in Figure 2 where the EPDM samples exhibit a higher coefficient of friction in hydrogen than samples tested in ambient air. This result indicates that there is more friction occurring due to the sliding contact between the EPDM polymer steel surfaces while in a high-pressure hydrogen environment as compared to ambient air.
Figure 3 reveals that the penetration depth of the steel counter surface into the EPDM polymer samples in high pressure hydrogen is less than the depth measured in ambient air samples. As in previous studies26, the effective wear factor, K*, describes the amount of material removed from the surface can be calculated using Equation 1 from the penetration depth XPD, the contact pressure P, the wear volume V, and the time T. This K* parameter is referred to as an &#34;effective&#34; wear factor because the combination of both removal of material and the deformation of the polymer surface that contribute to a wear depth measured by the LVDT position sensor. Figure 4 shows that the EPDM samples have a lower effective wear factor in high pressure hydrogen by the end of the experiment. This phenomenon is most likely a pressure effect and is not necessarily an indication that wear in hydrogen gas is less than in ambient air conditions.
<img alt="Equation 1" src="/files/ftp_upload/56884/56884eq1.jpg" />
Equation 1: Relationship between the effective wear factor (K*) and the penetration depth (XPD), the contact pressure (P) of the counter-surface on the polymer sample, the volume of the wear track (V), and time (T).

<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56884/56884fig1.jpg" /> 
Figure 1: Representative frictional load data acquired using the in situ tribometer&#39;s load cell of an EPDM polymer sample coupon at cycle #120 as a function of time. Data acquired in high pressure hydrogen is in blue, and data acquired in ambient air is in black. <a href="/files/ftp_upload/56884/56884fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56884/56884fig2.jpg" /> 
Figure 2: Coefficient of friction data calculated from frictional load data such as in Figure 1. The amount of friction between the EPDM sample and the steel counter surface is much higher in high pressure hydrogen than in ambient air. <a href="/files/ftp_upload/56884/56884fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56884/56884fig3.jpg" /> 
Figure 3: Penetration depth data gathered from the LVDT component of the in situ tribometer from testing on EPDM polymer samples. As in the friction data, the high pressure hydrogen data is blue while the ambient air data is in black. <a href="/files/ftp_upload/56884/56884fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56884/56884fig4.jpg" /> 
Figure 4: The wear factor calculated from the penetration depth data presented in Figure 3. The wear factor of the ambient air sample is higher than the wear factor of sample tested in high pressure hydrogen, which is most likely a pressure effect. <a href="/files/ftp_upload/56884/56884fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure at JoVE.com

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

A test methodology for quantifying tribological properties of polymers used in hydrogen infrastructure service is demonstrated and characteristic results for a common elastomer are discussed.

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is ...

in-situ-high-pressure-hydrogen-tribological-testing-common-polymer

Nanyang Technological University

Research

JoVE Journal

Engineering

7.5K Views.  Pacific Northwest National Laboratory. Een test-methodologie voor het kwantificeren van de tribological eigenschappen van polymeren in waterstof infrastructuurdienst gebruikt wordt aangetoond en karakteristiek resultaten voor een gemeenschappelijk elastomeer worden besproken.

Video: In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs and condition-based maintenance. These materials are adopted in a wide range of engineering applications, from aircraft and ship structures, to bridges, wind turbine blades, biomaterials and biomedical implants. Polymers are viscoelastic materials, and their response may be highly nonlinear and thus make it challenging to predict and monitor their in-service performance. The laboratory-scale testing platform presented herein assists the investigation of the influence of concurrent mechanical loadings and environmental conditions on these materials. The platform was designed to be low-cost and user-friendly. Its chemically resistant materials make the platform adaptable to studies of chemical degradation due to in-service exposure to fluids. An example of experiment was conducted at RT on closed-cell polyurethane foam samples loaded with a weight corresponding to ~50% of their ultimate static and dry load. Results show that the testing apparatus is appropriate for these studies. Results also highlight the larger vulnerability of the polymer under concurrent loading, based on the higher mid-point displacements and lower residual failure loads. Recommendations are made for additional improvements to the testing apparatus.

The durability of polymers and fiber-reinforced polymer composites in service is a critical aspect for their designs and condition-based maintenance. We present a novel low-cost laboratory testing platform for the investigation of the influence of concurrent mechanical and environmental loadings, and may help design more efficient yet safer composite structures.

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs ...

Atomically Traceable Nanostructure Fabrication

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure.

We report a protocol for combining the atomic metrology of the Scanning Tunneling Microscope for surface patterning with selective Atomic Layer Deposition and Reactive Ion Etching. Using a robust process involving numerous atmospheric exposures and transport, 3D nanostructures with atomic metrology are fabricated.

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process ...

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of the effective friction coefficient between two sliding surfaces. This property enables adaptive systems that modify their frictional state and associated dynamic response as the operating conditions change. Surface wear can also be reduced through ultrasonic lubrication. We developed a protocol to investigate the dependence of friction force reduction and wear reduction on the linear sliding velocity between ultrasonically lubricated surfaces. A pin-on-disc tribometer was built which differs from commercial units in that a piezoelectric stack is used to vibrate the pin at 22 kHz normal to the rotating disc surface. Friction and wear metrics including effective friction force, volume loss, and surface roughness are measured without and with ultrasonic vibrations at a constant pressure of 1 to 4 MPa and three different sliding velocities: 20.3, 40.6, and 87 mm/sec. An optical profilometer is utilized to characterize the wear surfaces. The effective friction force is reduced by 62% at 20.3 mm/sec. Consistently with existing theories for ultrasonic lubrication, the percent reduction in friction force diminishes with increasing speed, down to 29% friction force reduction at 87 mm/sec. Wear reduction remains essentially constant (49%) at the three speeds considered.

We present a protocol for using a piezoelectrically-assisted tribometer and optical profilometer to investigate the dependence of ultrasonic wear and friction reduction on linear velocity, contact pressure, and surface properties.

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at ...

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

Protocol for Relative Hydrodynamic Assessment of Tri-leaflet Polymer Valves

Limitations of currently available prosthetic valves, xenografts, and homografts have prompted a recent resurgence of developments in the area of tri-leaflet polymer valve prostheses. However, identification of a protocol for initial assessment of polymer valve hydrodynamic functionality is paramount during the early stages of the design process. Traditional in vitro pulse duplicator systems are not configured to accommodate flexible tri-leaflet materials; in addition, assessment of polymer valve functionality needs to be made in a relative context to native and prosthetic heart valves under identical test conditions so that variability in measurements from different instruments can be avoided. Accordingly, we conducted hydrodynamic assessment of i) native (n = 4, mean diameter, D = 20 mm), ii) bi-leaflet mechanical (n= 2, D = 23 mm) and iii) polymer valves (n = 5, D = 22 mm) via the use of a commercially available pulse duplicator system (ViVitro Labs Inc, Victoria, BC) that was modified to accommodate tri-leaflet valve geometries. Tri-leaflet silicone valves developed at the University of Florida comprised the polymer valve group. A mixture in the ratio of 35:65 glycerin to water was used to mimic blood physical properties. Instantaneous flow rate was measured at the interface of the left ventricle and aortic units while pressure was recorded at the ventricular and aortic positions. Bi-leaflet and native valve data from the literature was used to validate flow and pressure readings. The following hydrodynamic metrics were reported: forward flow pressure drop, aortic root mean square forward flow rate, aortic closing, leakage&#160;and regurgitant volume, transaortic closing, leakage, and total energy losses. Representative results indicated that hydrodynamic metrics from the three valve groups could be successfully obtained by incorporating a custom-built assembly into a commercially available pulse duplicator system and subsequently, objectively compared to provide insights on functional aspects of polymer valve design.

There has been renewed interest in developing polymer valves. Here, the objectives are to demonstrate the feasibility of modifying a commercial pulse duplicator to accommodate tri-leaflet geometries and to define a protocol to present polymer valve hydrodynamic data in comparison to native and prosthetic valve data collected under near-identical conditions.

Limitations of currently available prosthetic valves, xenografts, and homografts have prompted a recent resurgence of developments in the area of ...

Bioengineering

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are demonstrated here. The catalyst forms a substitutional solid solution structure, with a small and uniform particle size around 2 nm. This is realized by careful control over the impregnation, calcination, and reduction steps during catalyst preparation and is identified by advanced in situ synchrotron techniques. The catalyst propane dehydrogenation performance continuously improves with increasing Cu:Pt atomic ratio.

A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are ...

Chemistry

A Coupled Experiment-finite Element Modeling Methodology for Assessing High Strain Rate Mechanical Response of Soft Biomaterials

This study offers a combined experimental and finite element (FE) simulation approach for examining the mechanical behavior of soft biomaterials (e.g. brain, liver, tendon, fat, etc.) when exposed to high strain rates. This study utilized a Split-Hopkinson Pressure Bar (SHPB) to generate strain rates of 100-1,500 sec-1. The SHPB employed a striker bar consisting of a viscoelastic material (polycarbonate). A sample of the biomaterial was obtained shortly postmortem and prepared for SHPB testing. The specimen was interposed between the incident and transmitted bars, and the pneumatic components of the SHPB were activated to drive the striker bar toward the incident bar. The resulting impact generated a compressive stress wave (i.e. incident wave) that traveled through the incident bar. When the compressive stress wave reached the end of the incident bar, a portion continued forward through the sample and transmitted bar (i.e. transmitted wave) while another portion reversed through the incident bar as a tensile wave (i.e. reflected wave). These waves were measured using strain gages mounted on the incident and transmitted bars. The true stress-strain behavior of the sample was determined from equations based on wave propagation and dynamic force equilibrium. The experimental stress-strain response was three dimensional in nature because the specimen bulged. As such, the hydrostatic stress (first invariant) was used to generate the stress-strain response. In order to extract the uniaxial (one-dimensional) mechanical response of the tissue, an iterative coupled optimization was performed using experimental results and Finite Element Analysis (FEA), which contained an Internal State Variable (ISV) material model used for the tissue. The ISV material model used in the FE simulations of the experimental setup was iteratively calibrated (i.e. optimized) to the experimental data such that the experiment and FEA strain gage values and first invariant of stresses were in good agreement.

The current study prescribes a coupled experiment-finite element simulation methodology to obtain the uniaxial dynamic mechanical response of soft biomaterials (brain, liver, tendon, fat, etc.). The multiaxial experimental results that arose because of specimen bulging obtained from Split-Hopkinson Pressure Bar testing were rendered to a uniaxial true stress-strain behavior when simulated through iterative optimization of the finite element analysis of the biomaterial.

This study offers a combined experimental and finite element (FE) simulation approach for examining the mechanical behavior of soft biomaterials (e.g. ...

Determining Tribocorrosion Rate and Wear-Corrosion Synergy of Bulk and Thin Film Aluminum Alloys

The increasing complexity and severity of service conditions in areas, such as aerospace and marine industries, nuclear systems, microelectronics, batteries, and biomedical devices, etc., impose great challenges on the reliable performance of alloys exposed to extreme conditions where mechanical and electrochemical attack co-exist. Finding ways for alloys to mitigate the combined attack of wear and corrosion (i.e., tribocorrosion) under such extreme conditions is thus highly critical for improving their reliability and service lifetime when used in such conditions. The challenge lies in the fact that wear and corrosion are not independent of each other, but rather work synergistically to accelerate the total material loss. Thus, a reliable method to evaluate the tribocorrosion resistance of metals and alloys is needed. Here, a protocol for measuring the tribocorrosion rate and wear-corrosion synergy of Al-based bulk and thin film samples in a corrosive environment under room temperature is presented.

Here, we present a protocol to measure the tribocorrosion rate and wear-corrosion synergy of thin film and bulk Al alloys in simulated sea water at room temperature.

The increasing complexity and severity of service conditions in areas, such as aerospace and marine industries, nuclear systems, microelectronics, ...

Hydrogen Charging of Aluminum using Friction in Water

A new method of hydrogen charging of aluminum was developed by means of a friction in water (FW) procedure. This procedure can easily introduce high amounts of hydrogen into aluminum based on the chemical reaction between water and non-oxide coated aluminum.

In order to introduce high amounts of hydrogen in aluminum and aluminum alloys, a new method of hydrogen charging was developed, called the friction in water procedure.

A new method of hydrogen charging of aluminum was developed by means of a friction in water (FW) procedure. This procedure can easily introduce high ...

Microfluidic Fabrication Techniques for High-Pressure Testing of Microscale Supercritical CO2 Foam Transport in Fractured Unconventional Reservoirs

Pressure limitations of many microfluidic platforms have been a significant challenge in microfluidic experimental studies of fractured media. As a result, these platforms have not been fully exploited for direct observation of high-pressure transport in fractures. This work introduces microfluidic platforms that enable direct observation of multiphase flow in devices featuring surrogate permeable media and fractured systems. Such platforms provide a pathway to address important and timely questions such as those related to CO2 capture, utilization and storage. This work provides a detailed description of the fabrication techniques and an experimental setup that may serve to analyze the behavior of supercritical CO2 (scCO2) foam, its structure and stability. Such studies provide important insights regarding enhanced oil recovery processes and the role of hydraulic fractures in resource recovery from unconventional reservoirs. This work presents a comparative study of microfluidic devices developed using two different techniques: photolithography/wet-etching/thermal-bonding versus Selective Laser-induced Etching. Both techniques result in devices that are chemically and physically resistant and tolerant of high pressure and temperature conditions that correspond to subsurface systems of interest. Both techniques provide pathways to high-precision etched microchannels and capable lab-on-chip devices. Photolithography/wet-etching, however, enables fabrication of complex channel networks with complex geometries, which would be a challenging task for laser etching techniques. This work summarizes a step-by-step photolithography, wet-etching and glass thermal-bonding protocol and, presents representative observations of foam transport with relevance to oil recovery from unconventional tight and shale formations. Finally, this work describes the use of a high-resolution monochromatic sensor to observe scCO2 foam behavior where the entirety of the permeable medium is observed simultaneously while preserving the resolution needed to resolve features as small as 10 &#181;m.

Microfluidic Fabrication Techniques for High-Pressure Testing of Microscale Supercritical CO2 Foam Transport in Fractured Unconventional Reservoirs

This paper describes a protocol along with a comparative study of two microfluidic fabrication techniques, namely photolithography/wet-etching/thermal-bonding and Selective Laser-induced Etching (SLE), that are suitable for high-pressure conditions. These techniques constitute enabling platforms for direct observation of fluid flow in surrogate permeable media and fractured systems under reservoir conditions.

Pressure limitations of many microfluidic platforms have been a significant challenge in microfluidic experimental studies of fractured media. As a ...

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

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