Comparison of Two Methods for Measuring the Temperature Dependence of H2 Permeation Parameters in Nitrile Butadiene Rubber Polymer Composites Blended with Fillers: The Volumetric Analysis Method and the Differential Pressure Method.

Hydrogen uptake/diffusivity in nitrile butadiene rubber (NBR) blended with carbon black (CB) and silica fillers was measured with a volumetric analysis method in the 258-323 K temperature range. The temperature-dependent H2 diffusivity was obtained by assuming constant solubility with temperature variations. The logarithmic diffusivity decreased linearly with increasing reciprocal temperature. The diffusion activation energies were calculated with the Arrhenius equation. The activation energies for NBR blended with high-abrasion furnace CB and silica fillers increased linearly with increasing filler content. For NBR blended with medium thermal CB filler, the activation energy decreased with increasing filler content. The activation energy filler dependency is similar to the glass transition temperature filler dependency, as determined with dynamic mechanical analysis. Additionally, the activation energy was compared with that obtained by the differential pressure method through permeability temperature dependence. The same activation energy between diffusion and permeation in the range of 33-39 kJ/mol was obtained, supporting the temperature-independent H2 solubility and H2 physisorption in polymer composites.

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.

Characterizing the Diffusion Property of Hydrogen Sorption and Desorption Processes in Several Spherical-Shaped Polymers.

We developed a method for characterizing permeation parameters in hydrogen sorption and desorption processes in polymers using the volumetric measurement technique. The technique was utilized for three polymers: nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), and fluoroelastomer (FKM). The total uptake (C∞), total desorbed content (C0), diffusivity in sorption (Ds), and diffusivity in desorption (Dd) of hydrogen in the polymers were determined versus the sample diameter used in both processes. For all the polymers, the diameter dependence was not detected for C∞ and C0. The average C∞ and C0 at 5.75 MPa were 316 wt∙ppm and 291 wt∙ppm for NBR, 270 wt∙ppm and 279 wt∙ppm for EPDM, and 102 wt∙ppm and 93 wt∙ppm for FKM. The coincidence of C∞ and C0 in the sorption and desorption process indicated physisorption upon introducing hydrogen molecules into the polymers. The larger Dd in the desorption process than Ds could be attributed to an increased amorphous phase and volume swelling after decompression. The equilibrium time to reach the saturation of the hydrogen content in both processes was experimentally confirmed as proportional to the squared radius and consistent with the COMSOL simulation. This method could be used to predict the equilibrium time of the sorption time, depending on the radius of the polymers without any measurement.

Characterization technique of gases permeation properties in polymers: H2, He, N2 and Ar gas.

We demonstrate a simple experimental technology for characterizing the gas permeation properties of H2, He, N2 and Ar absorbed in polymers. This is based on the volumetric measurement of released gas and an upgraded diffusion analysis program after high-pressure exposure. Three channel measurements of sorption content of gases emitted from polymers after decompression are simultaneously conducted, and then, the gas uptake/diffusivity as a function of exposed pressure are determined in nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM) rubbers, low-density polyethylene (LDPE) and high-density polyethylene (HDPE), which are used for gas sealing materials under high pressure. The pressure-dependent gas transport behaviors of the four gases are presented and compared. Gas sorption follows Henry's law up to 9 MPa, while pressure-dependent diffusion behavior is not observed below 6 MPa. The magnitude of the diffusivity of the four gases decreases in the order DHe > DH2 > DAr > DN2 in all polymers, closely related to the kinetic diameter of the gas molecules. The dependence of gas species on solubility is in contrast to that on diffusivity. The linear correlation between logarithmic solubility and critical temperature of the gas molecule was newly observed.

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.

Electrical transport properties and Kondo effect in La1-xPrxNiO3-δ thin films.

The Kondo effect has been a topic of intense study because of its significant contribution to the development of theories and understanding of strongly correlated electron systems. In this work, we show that the Kondo effect is at work in La1-xPrxNiO3-δ (0 ≤ x ≤ 0.6) thin films. At low temperatures, the local magnetic moments of the 3d eg electrons in Ni2+, which form because of oxygen vacancies, interact strongly with itinerant electrons, giving rise to an upturn in resistivity with x ≥ 0.2. Observation of negative magnetoresistance, described by the Khosla and Fisher model, further supports the Kondo picture. This case represents a rare example of the Kondo effect, where Ni2+ acts as an impurity in the background of Ni3+. We suggest that when Ni2+ does not participate in the regular lattice, it provides the local magnetic moments needed to scatter the conduction electrons in the Kondo effect. These results offer insights into emergent transport behaviors in metallic nickelates with mixed Ni3+ and Ni2+ ions, as well as structural disorder.

Structural, Optical and Electrical Properties of HfO2 Thin Films Deposited at Low-Temperature Using Plasma-Enhanced Atomic Layer Deposition.

HfO2 was deposited at 80-250 °C by plasma-enhanced atomic layer deposition (PEALD), and properties were compared with those obtained by using thermal atomic layer deposition (thermal ALD). The ALD window, i.e., the region where the growth per cycle (GPC) is constant, shifted from high temperatures (150-200 °C) to lower temperatures (80-150 °C) in PEALD. HfO2 deposited at 80 °C by PEALD showed higher density (8.1 g/cm3) than those deposited by thermal ALD (5.3 g/cm3) and a smooth surface (RMS Roughness: 0.2 nm). HfO2 deposited at a low temperature by PEALD showed decreased contaminants compared to thermal ALD deposited HfO2. Values of refractive indices and optical band gap of HfO2 deposited at 80 °C by PEALD (1.9, 5.6 eV) were higher than those obtained by using thermal ALD (1.7, 5.1 eV). Transparency of HfO2 deposited at 80 °C by PEALD on polyethylene terephthalate (PET) was high (> 84%). PET deposited above 80 °C was unable to withstand heat and showed deformation. HfO2 deposited at 80 °C by PEALD showed decreased leakage current from 1.4 × 10-2 to 2.5 × 10-5 A/cm2 and increased capacitance of approximately 21% compared to HfO2 using thermal ALD. Consequently, HfO2 deposited at a low temperature by PEALD showed improved properties compared to HfO2 deposited by thermal ALD.

Selective Deposition of Al2O3 on the Upper Side-Photoelectrode to Improve Dye-Sensitized Solar Cell Efficiency.

Charge recombination at the photoelectrode/dye/electrolyte interface decreases the energy conversion efficiency of dye-sensitized solar cells (DSSCs). To suppress charge recombination at this interface in DSSCs, an aluminum oxide (Al2O3) film can be deposited as an insulating metal oxide layer on the photoelectrode to form an energy barrier. However, the Al2O3 energy barrier can also disturb the transport of injected electrons to the working electrode through the titanium dioxide (TiO2) photoelectrode. In this study, Al2O3 was selectively deposited as an insulating metal oxide layer on the upper side of a TiO2 photoelectrode, which has a high probability of charge recombination, using plasma-enhanced atomic layer deposition. Deposition of the Al2O3 layer by this method helped to minimize the transport rate deterioration of injected electrons. This resulted in an increase of the efficiency of DSSCs containing the Al2O3 layer by 42.3% compared with that of a reference DSSC without the insulating metal oxide layer.

Development and Characterization of Non-Evaporable Getter Thin Films with Ru Seeding Layer for MEMS Applications.

Mastering non-evaporable getter (NEG) thin films by elucidating their activation mechanisms and predicting their sorption performances will contribute to facilitating their integration into micro-electro-mechanical systems (MEMS). For this aim, thin film based getters structured in single and multi-metallic layered configurations deposited on silicon substrates such as Ti/Si, Ti/Ru/Si, and Zr/Ti/Ru/Si were investigated. Multilayered NEGs with an inserted Ru seed sub-layer exhibited a lower temperature in priming the activation process and a higher sorption performance compared to the unseeded single Ti/Si NEG. To reveal the gettering processes and mechanisms in the investigated getter structures, thermal activation effect on the getter surface chemical state change was analyzed with in-situ temperature XPS measurements, getter sorption behavior was measured by static pressure method, and getter dynamic sorption performance characteristics was measured by standard conductance (ASTM F798⁻97) method. The correlation between these measurements allowed elucidating residual gas trapping mechanism and prediction of sorption efficiency based on the getter surface poisoning. The gettering properties were found to be directly dependent on the different changes of the getter surface chemical state generated by the activation process. Thus, it was demonstrated that the improved sorption properties, obtained with Ru sub-layer based multi-layered NEGs, were related to a gettering process mechanism controlled simultaneously by gas adsorption and diffusion effects, contrarily to the single layer Ti/Si NEG structure in which the gettering behavior was controlled sequentially by surface gas adsorption until reaching saturation followed then by bulk diffusion controlled gas sorption process.

Effect of Growth Temperature on the Structural and Electrical Properties of ZrO2 Films Fabricated by Atomic Layer Deposition Using a CpZr[N(CH3)2]3/C7H8 Cocktail Precursor.

The effect of growth temperature on the atomic layer deposition of zirconium oxide (ZrO2) dielectric thin films that were fabricated using a CpZr[N(CH3)2]3/C7H8 cocktail precursor with ozone was investigated. The chemical, structural, and electrical properties of ZrO2 films grown at temperatures from 250 to 350 °C were characterized. Stoichiometric ZrO2 films formed at 250-350 °C with an atomic ratio of O to Zr of 1.8-1.9 and a low content of carbon impurities. The film formed at 300 °C was predominantly the tetragonal crystalline phase, whereas that formed at 350 °C was a mixture of tetragonal and monoclinic phases. Electrical properties, such as capacitance, leakage current, and voltage linearity of TiN/ZrO2/TiN capacitors fabricated using the thin ZrO2 films grown at different temperatures were compared capacitor applications. The ZrO2 film grown at 300 °C exhibited low impurity content, predominantly tetragonal crystalline structure, a high dielectric permittivity of 38.3, a low leakage current of below 10-7 A/cm² at 2 V, and low-voltage linearity.

Ferritin-based new magnetic force microscopic probe detecting 10 nm sized magnetic nanoparticles.

A single-molecule ferritin picking-up process was realized with the use of AFM, which was enhanced by employing controlled dendron surface chemistry. The approach enabled the placement of a single ferritin protein molecule at the very end of an AFM tip. When used for magnetic force microscopy (MFM) imaging, the tips were able to detect magnetic interactions of approximately 10 nm sized magnetic nanoparticles. The single ferritin tip also showed the characteristics of a "multifunctional" MFM probe that can sense the magnetic force from magnetic materials as well as detect the biomolecular interaction force with DNAs on the surface. The multifunctional tip enabled us not only to investigate the specific molecular interaction but also to image the magnetic interaction between the probe and the substrate, in addition to allowing the common capability of topographic imaging. Because the protein engineering of ferritin and the supporting coordination and conjugation chemistry are well-established, we envisage that it would be straightforward to extend this approach to the development of various single magnetic particle MFM probes of different compositions and sizes.