No abstract

In selective catalytic reduction (SCR) technology, aggregation of the catalyst generally degrades the performance for converting nitrogen oxides into harmless gases. To avoid such performance degradation and to achieve a noticeable improvement in the SCR performance, good dispersion of the catalyst on the support is required. In this study, we synthesized MnO x −CeO x catalytic nanoparticles on surface-modified supports and studied the dispersion behavior of the catalyst on the support. Hexagonal boron nitride (h-BN) was adopted as the catalyst support, which was modified by catalytic etching to create vacancy defects on the support. To enhance the effect of surface modification, the etched h-BN flakes were exfoliated by ultrasonication treatment and were further modified by controlling the pH of the surface. As a consequence of surface modification, the specific surface area increased from 41.89 to 67.29 m 2 /g. Microscopic analysis revealed that the size of the catalytic particles was mainly distributed with an average of 5 nm in modified h-BN. Surprisingly, the conversion efficiency of NO x gas approached 97% at a relatively low temperature (175−225 °C) when surface-modified h-BN was used as the support. The noticeable improvement in the catalytic performance is attributed to the high dispersion of active materials with the use of a porous support.

No abstract

Powder bed 3D printing can be applied to sandcasting mold manufacturing to ensure high quality and economy through process innovation. In this study, refractory alumina cement was used as an aqueous binder to ensure high-temperature thermal stability to minimize the addition of organic matter to reduce gas generation. In addition, spherical silica sand, the study material, was selected to a size of 30 µm to improve the casting mold resolution. To improve the surface quality through the post-treatment process, we confirmed the change in the surface roughness of the mold depending on the surface treatment of colloidal silica and the presence or absence of heat treatment, and finally made the mold through actual casting. Changes in the surface roughness and flowability of the cast body after mold post-treatment were confirmed. For aluminum castings, the shrinkage rate and surface roughness were confirmed in a box-shaped mold via gravity casting, and the flowability of the molten metal in the mold was confirmed in a hand-shaped mold. There was a change in the roughness and porosity of the mold, owing to the post-treatment, and the influence of the surface roughness and flowability of the cast body during actual casting was confirmed.

No abstract

No abstract

No abstract

Goethite, α-FeOOH have various applications such as absorbent, pigment and source for magnetic materials. Goethite particles were synthesized in a two step process, where Fe(OH) 2 were synthesized in nitrogen atmosphere using FeSO 4 as a raw material in the first process, and after that acicular goethite particles were obtained in an air oxidation process of Fe(OH) 2 in highly alkaline aqueous solution. Their phase and microstructure were investigated with XRD and FE-SEM. It was found that the morphology of goethite and the ratio of length-to-width (aspect ratio) of acicular goethite are dependent on the some factors such as R value (OH -/Fe 2+ ), air flow rate and pH conditions. In particular, R value has the strongest influence on the synthesized goethite morphology. It is considered that the optimal value R is 4.5 because X-ray diffraction peaks of goethite have the highest intensity at that value. Morphology of goethite particles was controlled by air flow rates, showing that their size and aspect ratio are getting smaller and decrease, respectively as air flow rate increases.The largest goethite particle obtained is about 1,500 nm in length and 150 nm in diameter.