Hojin Ryu

Local ordering structure of meta-kaolinite and meta-dickite by the X-ray radial distribution function analysis

X-ray diffraction measurements on the structure of meta-kaolinite and meta-dickite have been carried out to obtain the radial distribution function (RDF). The distances and corresponding coordination numbers for Si-O and Al-O pairs were estimated by applying the pair function method. The SiO4 tetrahedron remains unchanged in the dehydrated samples presently investigated, and the oxygen coordination number around aluminium was also found to be four. This implies the overall preference of AlO4 tetrahedron at the expense of the parent AlO2 (OH)4 octahedron.

Effect of mechanochemical treatment of supported catalysts on the CVD growth of carbon nanomaterials

Various morphologies of carbon nanotubes (CNTs) grown on the Fe(NO/sub 3/)/sub 3/-Al(OH)/sub 3/ mixtures have been observed. Fe(NO/sub 3/)/sub 3/-Al(OH)/sub 3/ mixtures prepared by impregnation method have been mechanochemically treated by the high energy grinding process using a mixer mill. Long grinding duration of Fe-Al(OH)/sub 3/ induced Al(OH)/sub 3/ to amorphous form and promoted both Fe(NO/sub 3/)/sub 3/ and Al(OH)/sub 3/ to agglomerate into spheres. With as-prepared unground and ground mixtures, CNTs were grown by thermal CVD under C/sub 2/H/sub 2/ and H/sub 2/ gases at 700/spl square/. As a result, CNTs grown on ground mixtures have a more uniform diameter than those of unground mixture. In addition to this, morphological changes of CNTs grown on unground and ground mixtures show that mechanochemical treatment for supported catalyst can act as the factor of growth control.

Effects of mechanochemical treatment of Ni-Al(OH)3 on the preparation of carbon nanomaterials by thermal CVD

Abstract Carbon nanomaterials have been prepared by the thermal chemical vapor deposition (CVD) method in which C2H2 gas was deposited on the Ni–Al(OH)3 mixture pretreated by mechanochemical treatment with a high-energy mill. As the duration time of grinding for the Ni–Al(OH)3 mixture by the mixer mill is increased, amorphous Al(OH)3 and smaller Ni particles agglomerated into spheres. With unground and 120-min ground mixture of Ni–Al(OH)3, carbon nanomaterials were prepared at 500 and 600 °C. As a result, carbon nanomaterials prepared on a ground mixture have more uniform morphologies than those of the unground mixture. The characterization of Ni–Al(OH)3 mixture and as-prepared carbon samples was done by X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectroscopy and current–voltage (I–V) measurement.

Studies on the Characteristics of the Catalyst Layer of the PEMFC Electrode

The present paper highlights on the need to understand the correlation of the characteristics of the catalyst layer with the performance of the polymer electrolyte membrane fuel cell (PEMFC). This paper deals with the correlation of the platinum loading in the catalyst layer and the performance of the polymer electrolyte membrane fuel cell and also the correlation of the required hydrophilicity/hydrophobicity in the catalyst layer to get the optimum performance under given operating conditions.

Formation of mullite from ground product of a kaolinite-aluminum trihydroxide mixture by solid phase reaction

The present paper describe the effect of grinding a kaolinite/aluminum-trihydroxide mixture using a planetary ball mill on the structure of the ground product and the mean thermal expansion coefficients of samples sintered from the unground and ground mixtures. The size reduction of the mixture predominates in the early stage of grinding and the obtained fine particles aggregate subsequently with an increase in grinding time. The crystal structure of the mixture is collapsed easily into a disordered one, of which amount increases with an increase in grinding time. Only mullite phase was detected in the sintered body of the ground products at relatively lower temperature 1523K except for anatase as an inherent impurity, whereas corundum, cristobalite and Al-Si spinel phases besides mullite were formed in the sintered body of the unground mixture. The thermal expansion coefficients of sintered bodies of the 120 minutes-ground mixture are considerably lower than those of the unground mixture by about 10%. Consequently, the planetary milling enables us to improve the uniform mixing state at the atomic scale resulting in direct formation of mullite with high purity at relatively low temperature with a lower thermal expansion coefficient of the sintered body