Hirokazu Muramoto

Supporting PtRu catalysts on various types of carbon nanomaterials for fuel cell applications

PtRu catalysts were supported on five types of carbon nanomaterials of various shapes, sizes, and graphitic properties and the catalyst supports evaluated. The carbon nanomaterial used included three types of nanoparticles: Arc Black (AcB), Vulcan XC-72 (Vulcan) and graphene oxide (GO), and two types of nanofibers: carbon nanocoil (CNC) and carbon nanotube (CNT). Pt and Ru were supported by the reduction method using sodium borohydride. The metal catalyst loading was confirmed by thermo-gravimetric analysis (TGA), electron microscopy, and X-ray diffraction (XRD). Transmission electron microscopy (TEM) and XRD revealed that the diameter of PtRu catalyst nanoparticles loaded on reduced GO (rGO) and AcB were ~2 nm and was the smallest among all the samples. Shifts in Pt (111) XRD peaks of CNC and CNT were larger than those of AcB, Vulcan, and rGO. These results suggest that the diameters of catalyst nanoparticles became smaller by loading on the carbon nanoparticles with a large surface area including rGO, AcB, and Vulcan. Loading onto the carbon nanofibers enhanced the degree of PtRu alloying.

Crystallographic orientation analysis of cleavage facets adjacent to a fracture trigger in low carbon steel

The microstructure and crystallographic orientation under a cleavage crack trigger point, which was detected on a fracture toughness specimen of low carbon steel, were investigated. SEM fractographs of an etched cleavage facet reveal that a flat cleavage facet between facet ridges spreading from the trigger point is divided by a grain boundary between ferrite and pearlite. Even a different phase boundary does not occasionally create any steps and ridges on the cleavage facet: it suggests this phase boundary is not an obstacle to cleavage cracking. Electron diffraction analysis for the thin foil sample milled out from this phase boundary demonstrates that the crystallographic orientation of the ferrite grain is consistent with that of the ferrite in the adjacent pearlite block. It is strictly examined that the ferrite/pearlite boundary does not act as a local resistance to cleavage crack growth when the crystallographic orientation of the ferrite in the pearlite block is aligned with an adjacent ferrite grain.