Investigation of Physical and Mechanical Characteristics of Rubber Materials Exposed to High-Pressure Hydrogen.

Rubber materials play a key role in preventing hydrogen gas leakage in high-pressure hydrogen facilities. Therefore, it is necessary to investigate rubber materials exposed to high-pressure hydrogen to ensure operational safety. In this study, permeation, volume swelling, hydrogen content, and mechanical characteristics of acrylonitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), and fluorocarbon (FKM) samples exposed to pressures of 35 and 70 MPa were investigated. The results showed that the volume recovery and hydrogen desorption behavior of EPDM with the highest permeation were fast whereas those of FKM with the lowest permeation were slow. The volume of NBR with the highest hydrogen content expanded after decompression. In contrast, FKM swelled the most despite having the lowest hydrogen content. After exposure to high-pressure hydrogen, the compression set (CS) slightly increased due to internal cracks, but the tensile strength decreased significantly with increasing pressure despite the absence of cracks in the fracture area of all tensile specimens. It was concluded that the decrease in tensile strength is closely related to the volume increase because of the relationship between the relative true strength and the volume ratio.

Effect of the High-Pressure Hydrogen Gas Exposure in the Silica-Filled EPDM Sealing Composites with Different Silica Content.

With the increasing interest in hydrogen energy, the stability of hydrogen storage facilities and components is emphasized. In this study, we analyzed the effect of high-pressure hydrogen gas treatment in silica-filled EPDM composites with different silica contents. In detail, cure characteristics, crosslink density, mechanical properties, and hydrogen permeation properties were investigated. Results showed that material volume, remaining hydrogen content, and mechanical properties were changed after 96.3 MPa hydrogen gas exposure. With an increase in the silica content, the crosslink density and mechanical properties increased, but hydrogen permeability was decreased. After treatment, high-silica-content composites showed lower volume change than low-silica-content composites. The crack damage due to the decompression caused a decrease in mechanical properties, but high silica content can inhibit the reduction in mechanical properties. In particular, EPDM/silica composites with a silica content of above 60 phr exhibited excellent resistance to hydrogen gas, as no change in their physical and mechanical properties was observed.

H2 Uptake and Diffusion Characteristics in Sulfur-Crosslinked Ethylene Propylene Diene Monomer Polymer Composites with Carbon Black and Silica Fillers after High-Pressure Hydrogen Exposure Reaching 90 MPa.

We investigated the influence of two fillers-CB (carbon black) and silica-on the H2 permeation of EPDM polymers crosslinked with sulfur in the pressure ranges 1.2-90 MPa. H2 uptake in the CB-blended EPDM revealed dual sorption (Henry's law and Langmuir model) when exposed to pressure. This phenomenon indicates that H2 uptake is determined by the polymer chain and filler-surface absorption characteristics. Moreover, single sorption characteristics for neat and silica-blended EPDM specimens obey Henry's law, indicating that H2 uptake is dominated by polymer chain absorption. The pressure-dependent diffusivity for the CB-filled EPDM is explained by Knudsen and bulk diffusion, divided at the critical pressure region. The neat and silica-blended EPDM specimens revealed that bulk diffusion behaviors decrease with decreasing pressure. The H2 diffusivities in CB-filled EPDM composites decrease because the impermeable filler increases the tortuosity in the polymer and causes filler-polymer interactions; the linear decrease in diffusivity in silica-blended EPDM was attributed to an increase in the tortuosity. Good correlations of permeability with density and tensile strength were observed. From the investigated relationships, it is possible to select EPDM candidates with the lowest H2-permeation properties as seal materials to prevent gas leakage under high pressure in H2-refueling stations.

Impedance spectroscopy for in situ and real-time observations of the effects of hydrogen on nitrile butadiene rubber polymer under high pressure.

Nondestructive impedance spectroscopy (IS) was developed and demonstrated to detect the effects of hydrogen on nitrile butadiene rubber exposed to hydrogen gas (H2) at high pressures up to 10 MPa. IS was applied to obtain an in situ and real-time quantification of H2 penetration into and its desorption out of rubber under high pressure. The diffusion coefficients of H2 were also obtained from the time evolution of the capacitance, which were compared with those obtained by thermal desorption gas analysis. The in situ measurements of the capacitance and the dissipation factor under various pressures during cyclic stepwise pressurization and decompression demonstrated the diffusion behaviour of H2, the phase of the rubber under high pressure, the transport properties of H2 gas, and the physicochemical interaction between H2 and the rubber. These phenomena were supported by a COMSOL simulation based on the electric current conservation equation and scanning electron microscopy (SEM) observations.

Mechanical test method and properties of a carbon nanomaterial with a high aspect ratio.

Superior nanomaterials have been developed and applied to many fields, and improved characteristic of nanomaterials have been studied. Measurement of the mechanical properties for nanomaterials is important to ensure the reliability and predict the service life times of products containing nanomaterials. However, it is challenging to measure the mechanical properties of nanomaterials due to their very small dimensions. Moreover, macro-scale measurement systems are not suitable for use with nanomaterials. Therefore, various methods have been developed and used to in an effort to measure the mechanical properties of nanomaterials. This paper presents a review of various evaluation systems and the measurement methods which are used to determine the mechanical properties of carbon nanotube (CNT) and carbon nanofiber (CNF), representatively. In addition, we measured the tensile strength and elastic modulus of the CNT and CNF in the scanning electron microscope (SEM) installed the nano-manipulator and the force sensor and this measurement system and results would be introduced in detail.

The Mechanical and Electrical Properties of a Single Carbon Nanofiber Induced by Applying Tensile Strain.

Carbon nanofibers (CNFs) are good candidates for nano-system applications because they have the excellent mechanical and the electrical properties. The mechanical and electrical properties of a single CNF were measured. A tensile test and a measurement of the electrical resistance of CNFs during elongation were performed inside a scanning electron microscope. We confirmed that the CNFs used in this experiment consisted of a polycrystalline structure and an amorphous phase by a result of Raman. Additionally, we observed that the crystal structure in nanofibers exhibits brittle fracture behavior and the amorphous phase make them relatively ductile. The elastic moduli of the CNFs were 9.57 to 13.6 GPa in the elastic section. The electrical resistance of the CNFs exhibited unusual behavior during elongation. The electrical resistance of the CNFs exhibited stable resistance increase like as the tensile results in the initial region. But the electrical resistance exhibited generally irregular increase after initial region because of the polycrystalline structure and amorphous phase. The strain sensitivity of the CNFs exhibited a much lower value.

Unzipped Nanotube Sheet Films Converted from Spun Multi-Walled Carbon Nanotubes by O2 Plasma.

Large-scale graphene or carbon nanotube (CNT) films are good candidates for transparent flexible electrodes, and the strong interest in graphene and CNT films has motivated the scalable production of a good-conductivity and an optically transmitting film. Unzipping techniques for converting CNTs to graphene are especially worthy of notice. Here, we performed nanotube unzipping of the spun multi-walled carbon nanotubes (MWCNTs) to produce networked graphene nanoribbon (GNR) sheet films using an 02 plasma etching method, after which we produced the spun MWCNT film by continually pulling MWCNTs down from the vertical well aligned MWCNTs on the substrate. The electrical resistance was slightly decreased and the optical transmittance was significantly increased when the spun MWCNT films were etched for 20 min by O2 plasma of 100 mA. Plasma etching for the optimized time, which does not change the thickness of the spun MWCNT films, improved the electrical resistance and the optical transmittance.

Growth of spin-capable multi-walled carbon nanotubes and flexible transparent sheet films.

Iron-catalyzed spin-capable multi-walled carbon nanotubes (MWCNTs) were grown on a SiO2 wafer by chemical vapor deposition, which was carried out at 780 degrees C using C2H2 and H2 gases. We fabricated a flexible transparent film using the spun MWCNTs. The MWCNT sheets were produced by being continuously pulled out from well-aligned MWCNTs grown on a substrate. The MWCNT sheet films were manufactured by simply carrying out direct coating on a flexible film or glass. The thickness of the sheet film decreased remarkably when alcohol was sprayed on the surface of the sheet. The alcohol spraying increased the transmittance and decreased the electrical resistance of the MWCNT sheet films. The sheets obtained after alcohol spraying had a resistance of -699 omega and a transmittance of 81%-85%. The MWCNT sheet films were heated by applying direct current. The transparent heaters showed a rapid thermal response and uniform distribution of temperature. In addition, we tested the field emission of the sheet films. The sheet films showed a turn-on voltage of -1.45 V/microm during field emission.

The mechanical properties and test of a single ZnO nanorod inside scanning electron microscopy.

The bending and tensile tests of the ZnO nanorods were carried out by controlling a force sensor and a nano-manipulator inside a scanning electron microscope (SEM). The force sensor was mounted on the nano-manipulator, was controlled with the nano-manipulate. The load response during the mechanical test for the ZnO nanorod was obtained by using the force sensor which is formed as a cantilever. The elastic modulus of the ZnO nanorods after the tensile and bending tests were calculated and compared. The elastic modulus of ZnO nanorods was depended on a size and an aspect ratio of the ZnO nanorods. The difference of the elastic modulus of ZnO nanorods was obtained with a difference of test methods performed along crystal facets direction of the ZnO nanorods. The average elastic modulus calculated after the tensile test was approximately 57.15 GPa. In case of the bending test, the average elastic modulus was approximately 29.37 GPa.