Hiromu Kusuda

High sound absorption of porous aluminum fabricated by spacer method

Porous aluminum with a density of 0.27g∕cm3 was produced by the spacer method. The sound absorbency of the material is significantly improved by inserting an air gap between the sample and the rigid back surface; in this manner, a sound absorption coefficient near unity can be achieved over a significant portion of the audible range. The present data agree with the theoretical analysis in the previous study by Lu et al. [J. Acoust. Soc. Am. 108, 1697 (2000)]; this in turn shows that the present results can largely be attributed to the size (= approximately 50μm) of apertures connecting pores in the material.

The examination of fracturing process subjected to triaxial compression test in Inada granite

The behavior of a granite subject to a triaxial compression test ranging from the prefailure stage to the postfailure stage was studied using a fluorescent technique from the geological point of view. Microscopic observations of the specimens at different stages showed changes in the failure process. The start of formation of new microcracks paralleled the compression direction through their propagation until the onset of faulting and ended with the failure of shear zones after the strength failure point. Pores chiefly identified in the feldspar increased in length and width in the early stages, but not in number. It seems that the effect of pore spaces did not have any effect of failure. The microcracks generated on angular edges of quartz or feldspar grains and around biotite grains with increasing compression force. The phenomenon appearing on the crystal boundaries among biotite and quartz or feldspar agrees with the result calculated based on the theory on stress fields with ellipsoidal inhomogeneity suggested by Eshelby.

Sound absorption characteristics of porous aluminum fabricated by spacer method

Porous Al specimens with porosities of 85%–95% and pore sizes of 212–300to610–700μm were fabricated by the spacer method, and their sound absorption coefficients were investigated by the transfer function method. The sound absorption coefficient increased with porosity. However, there was no apparent correlation between pore size and sound absorption coefficient. Also, the sound absorption coefficient depended on the thickness. The sound absorption coefficient of a specimen was significantly improved by the modification of aperture size, even if the porosity and pore size were unchanged. Therefore, it is suggested that sound absorption behavior is strongly affected by not only the porosity and pore size but also the aperture size for porous Al fabricated by the spacer method.

Application of a fluorescent technique to the study of the weathering process

Processes and rates of weathering in representative tuff obtained from a Green Tuff region were directly examined using a new fluorescent approach. This approach was developed to visualize microscopically the microcracks and micropores that contribute to deterioration. The following observations were made. Progression of tuff weathering is caused by a delicate balance between chemical alteration and physical disintegration. Weathering occurs in many hidden microcracks and micropores not detected under natural light, but which can be clearly visualized under ultraviolet light. Water pathways, such as microcracks and cavities, accelerated the chemical alteration by increasing the effective surface area of rocks in contact with water. As the reaction proceeds, the constituent materials loosen and alteration products become widespread in the matrix. Secondary amorphous to poorly crystallized materials, such as iron hydroxide and aluminosilicate, precipitate on the fracture surfaces, slowing the progress of weathering. At the ultimate stage of weathering in tuff, all cracks and most of the micropores are filled with secondary materials. These observations on a microscopic scale during tuff weathering agree with the assessment of weathering obtained by measuring porosity, P-wave velocity and tensile strength.

Surface functionalization of high free-volume polymers as a route to efficient hydrogen separation membranes

There is a sparcity of polymeric membranes with sufficient selectivity for efficient hydrogen separation from syn-gas products, primarily carbon dioxide. Despite hydrogens significantly smaller kinetic diameter, low selectivity arises as other gases are generally more condensable within typical polymeric membranes. Here we report an in situ-controllable, surface polymerization of polydopamine (PDA) and polyaniline (PANI) on high free-volume glassy polymer films, specifically the well studied polymer of intrinsic microporosity (PIM-1) and poly(1-trimethylsilyl-1-propyne) (PTMSP). The resulting nanolayer composite membranes demonstrate a remarkable hydrogen selectivity against N2, CH4 and CO2 (H2/CO2 ∼ 50). The PDA or PANI layers principally serve to increase the diffusive selectivity towards hydrogen whilst the high free volume supports of PIM-1 or PTMSP provide a highly permeable interface for defect-free growth of the selective layer. Whilst both PANI and PDA are effective, these selective layers were found to grow by heterogeneous or homogeneous modes respectively.

Fluid Conductivity of Porous Aluminum Fabricated by Powder-Metallurgical Spacer Method

Porous aluminum with well-adjusted porosity and pore size was fabricated by a powder-metallurgical spacer method, and its fluid conductivity was investigated. As the porosity and pore size increased, the Darcian permeability increased. However, the permeability of the porous aluminum was significantly lower than the expected value based on those of other similar porous materials. The low fluid conductivity is attributed to the presence of small apertures at cell walls, which is peculiar to the porous metals fabricated by the powder-metallurgical spacer method.

Influence of Density on the Compressive Properties in Porous Copper Produced by Spacer Method

Porous copper specimens with relative densities of 0.22–0.96 were produced by spacer method and their compressive properties were investigated. In the low relative density range (relative density < 0.5–0.6), porous copper showed a density exponent n of 2.3, where n represents the relative density dependence of yield strength. In this range, the bending and buckling of cell walls and the formation of macroscopic deformation bands were observed. On the other hand, porous copper with a higher relative density (0.5–0.6 < relative density < 0.9–1) had an n value of approximately 1, where the dominant deformation mode of cell walls was yielding and no clear deformation band was observed. Also, in the highest relative density range (relative density is very close to 1), the compressive properties degraded markedly with decreasing density, indicating that stress concentration around the minimal pores occurred in this density range.

Compressive Properties of Porous Metals with Homogeneous Pore Characteristics

Spacer method is excellent technique of processing porous metals with well-controlled pore characteristics such as porosity (up to 90%) and pore size (as small as several hundred micrometers). Compressive properties of porous aluminum fabricated by the spacer method are investigated. They were subjected to monotonic compression tests at room temperature, and showed less fluctuated flow stress during their compressive deformation than conventional porous aluminum alloy, reflecting their homogeneous pore characteristics. Also, shortening behavior of the porous aluminum fabricated by the spacer method during cyclic compression was significantly differed from that of conventional porous aluminum alloy. Therefore, it can be concluded that the homogeneity of pore characteristics is responsible for compressive properties of porous metals. Monotonic compression tests on porous copper specimens with various porosities, which were made by the spacer method, were also conducted. The yield stress of the porous copper with high porosity (or low relative density) depended on the relative density more strongly than that of the porous copper with low porosity (or high relative density). It is presumed that porous metals with high porosity and ones with low porosities have different deformation mechanisms.

Porous Metals Produced by Spacer Method as Ecomaterials

Porous metals, or metallic foams, are emerging ecomaterials that can be applied to structural use, shock absorber, filter, heat exchanger, etc. Their very low densities and peculiar deformation behaviors will facilitate the application. The control of pore characteristics such as porosity and pore size distribution can be successfully achieved by spacer method. In this paper, fabrication of porous aluminum via the spacer method is introduced and their excellent properties due to homogeneous pore characteristics are exhibited

Sound Absorption Behavior of Porous Al Produced by Spacer Method

Porous Al specimens with a pore size range from 212-300 to 610-700 μm, a porosity from 85 to 95% and a specimen thickness from 2 to 20 mm were produced by the spacer method, and their sound absorption capacity was investigated. For these specimens, sound absorption coefficient increased with increasing porosity. On the other hand, sound absorption coefficient varied inconsistently with the variation of pore sizes. The latter may be attributed to variation of aperture sizes of each specimen because the porous Al specimens with differerent pore sizes produced by the spacer method should have different aperture sizes. Sound absorption coefficient increased at the frequency below 2000 Hz with increasing specimen thickness.