Measuring the Electrical Resistivity of Liquid Iron to 1.4 Mbar.

We determined the electrical resistivity of liquid Fe to 135 GPa and 6680 K using a four-probe method in a diamond-anvil cell combined with two novel techniques: (i) enclosing a molten Fe in a sapphire capsule, and (ii) millisecond time-resolved simultaneous measurements of the resistance, x-ray diffraction, and temperature of instantaneously melted Fe. Our results show the minimal temperature dependence of the resistivity of liquid Fe and its anomalous resistivity decrease around 50 GPa, likely associated with a gradual magnetic transition, both in agreement with previous ab initio calculations.

Microstructure Investigation of Polymer Electrolyte Fuel Cell Catalyst Layers Containing Perfluorosulfonated Ionomer.

Perfluorosulfonated ionomers are the most successful ion-exchange membranes at an industrial scale. One recent, cutting-edge application of perfluorosulfonated ionomers is in polymer electrolyte fuel cells (PEFCs). In PEFCs, the ionomers are used as a component of the catalyst layer (CL) in addition to functioning as a proton-exchange membrane. In this study, the microstructures in the CLs of PEFCs were characterized by combined synchrotron X-ray scattering and transmission electron microscopy (TEM) analyses. The CL comprised a catalyst, a support, and an ionomer. Fractal dimensional analysis of the combined ultrasmall- and small-angle X-ray scattering profiles indicated that the carbon-black-supported Pt catalyst (Pt/CB) surface was covered with the ionomer in the CL. Anomalous X-ray scattering revealed that the Pt catalyst nanoparticles on the carbon surfaces were aggregated in the CLs. These findings are consistent with the ionomer/catalyst microstructures and ionomer coverage on the Pt/CB surface obtained from TEM observations.

Laboratory-based x-ray computed tomography for 3D imaging of samples in a diamond anvil cell in situ at high pressures.

Three-dimensional (3D) visualization of a material under pressure can provide a great deal of information about its physical and chemical properties. We developed a technique combining in-house x-ray computed tomography (XCT) and a diamond anvil cell to observe the 3D geometry of a sample in situ at high pressure with a spatial resolution of about 610 nm. We realized observations of the 3D morphology and its evolution in minerals up to a pressure of 55.6 GPa, which is comparable to the pressure conditions reported in a previous synchrotron XCT study. The new technique developed here can be applied to a variety of materials under high pressures and has the potential to provide new insights for high-pressure science and technology.

Accuracy of equilibrium magnetization mapping in sliced two-dimensional spoiled gradient-recalled echo pulse sequence with variable flip angle.

PURPOSE: To evaluate the accuracy of an equilibrium magnetization (M0 ) map obtained using a two-dimensional (2D) spoiled gradient-recalled echo (SPGR) pulse sequence with variable flip angle (VFA). MATERIALS AND METHODS: Single-slice 2D SPGR images of 4% agar gel phantoms with different gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA) concentrations (0-1 mM) were obtained with a VFA (2-30°). The 2D SPGR-VFA data were acquired with different repetition times (TRs; 7.8-117.2 ms), Gaussian and sinc RF pulses, and different field strengths (4.7, 7, and 9.4 Tesla). M0 and T1 maps were calculated from the 2D SPGR-VFA data. M0 and T1 values were compared with those calculated from free-relaxed 2D gradient-recalled echo (GRE) images and inversion recovery-prepared 2D SPGR images. The M0 and T1 slice profiles were also investigated. RESULTS: Consistent M0 values were obtained, regardless of the different Gd concentrations, TRs, and pulse sequences. The M0 slice profiles calculated from the sliced SPGR-VFA data quantitatively reproduced those calculated from the free-relaxed sliced GRE. In contrast, the T1 values calculated from the 2D SPGR-VFA data were underestimated at a high Gd concentration, short TR, and Gaussian RF pulse. CONCLUSION: M0 values calculated from 2D SPGR-VFA images are highly quantitative.

Water content distribution in a polymer electrolyte membrane for advanced fuel cell system with liquid water supply.

To better understand the operation of a new fuel cell design, we used magnetic resonance imaging (MRI) to measure the water content distribution in a polymer electrolyte membrane under fuel cell operation with and without a supply of liquid water. The supply of liquid water to the membrane improved the cell performance by increasing the water content in the membrane and thus reducing the electrical resistance of the membrane. The study also showed that MRI is a promising method to investigate the distribution of water in the membrane of a fuel cell under operating conditions.

Velocity measurement of clay intrusion through a sudden contraction step using a tagging pulse sequence.

Magnetic resonance imaging (MRI) with a spatial tagging sequence was used to measure the velocity distribution of clay that was forced past a sudden contraction. A spatial tagging sequence provided magnetic resonance images of clay that allowed measurement of the velocity distribution in the clay, which can provide profound insights on the deformation process of clay during the intrusion process. The experiments were conducted using a specially-designed vessel that could operate at up to 30 MPa. The vessel offers a rectangle test section with a sudden contraction step that had a ratio of contraction of 2:1. The vessel was installed into a commercial magnetic resonance imaging equipment and then the fluid motion of clay flowing into the narrow contracted channel was quantitatively investigated to examine behaviors of flowing clay as non-Newtonian fluid. MRI results are compared with those obtained by computational fluid dynamics (CFD) calculation. Velocity distributions obtained from each tag displacement did not well agree with those predicted by CFD results near the contraction step where the fluid accelerated rapidly. However, a post-processing on calculation results, in which virtual tag displacement is calculated, gave better agreement with experiment and enabled us to compare MRI results with CFD results.