Characterizing Fabric Anisotropy of Air-Pluviated Sands

Sand particles depositing through air generally align their largest dimensions in horizontal plane, forming a cross anisotropic fabric. Therefore, sands display varying strength, permeability, compressibility with directions. This study characterizes fabric anisotropy in loose and dense air-pluviated sand specimens scanned by X-ray Computed Tomography (X-ray CT) using a series of image processing techniques. The principal component analysis, three-dimensional watershed analysis, and Delaunay triangulation technique are used to compute directional parameters, including particle long axes, contact normals, and branch vectors, and scalar parameters, including index void ratios, coordination number, and average branch vector length. The particle long axes and branch vectors displayed preferred horizontal directions while the contact normals displayed preferred vertical directions. The dense specimen has smaller index void ratios, larger coordination number, and smaller average branch vector length than the loose specimen.

Study on the Fabrication of Visible Light Response Type N-Doped TiO2 Photocatalyst by SPS

It is recognized that TiO2, the most popularly used photocatalyst, has a disadvantage that it only react with ultraviolet light. In this study, nitrogen-doped TiO2was selected as strategy for promoting the absorption of visible light, and SPS (spark plasma sintering) method was tried to fabricate a dense specimen without using binder materials. Preparation methods of specimen are as follows; yellow-colored N-doped TiO2powders were synthesized from a mixed aqueous solution containing TiCl3and NH3. The precipitate was air-dried for 1 week. Then dried in a drying oven for 1day(50°C). And heat-treated for 1h(400°C).N-doped TiO2powder and non-doped TiO2powder were sintered by SPS at 400 or 700°C. N-doped TiO2fabricated by SPS showed a favorable crystal structure of anatase, and successful existence of doped nitrogen was confirmed by XPS analysis. UV-vis results showed that N-doped TiO2responded to visible light, which indicates an increasing possibility of this type of photocatalyst. Further study to extend the range of absorption wavelength is carrying out.

Deformation Characteristics of Granular Materials Under Hydrostatic Compression

The deformation characteristics of sand and other granular materials under hydrostatic compression are studied in the conventional triaxial apparatus using 4 × 4 in. (10 × 10 cm) specimens. Modifications have been made for measuring small axial strains and free end platens were used. The errors in testing have been estimated and their effect was evaluated. Different kinds of granular materials were tested to study the effect of the physical properties of the material on its deformational behavior.The results showed that the total deformation of a mass of sand subjected to a hydrostatic compression is generally not recoverable, and can be divided into elastic (recoverable) and sliding (irrecoverable) components. It has also been found out that for a dense specimen of sand most of the total deformation is recoverable, since the sliding component of deformation represents only a small fraction of the total deformation. The results also showed that for the very dense specimen axial and radial strains were nearly equal which implies that the material behaves isotropically. On the other hand for a loose specimen the sliding component of deformation becomes large and thus the total deformation of the specimen cannot be considered completely elastic. Furthermore axial and radial strains of the loose specimen were not equal.