Browsing by Author "Tu, G. C."

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Electrical discharge abrasive drilling of hard materials using a metal matrix composite electrode
(2006-07-01)
Shu, Kuen Ming
;
Shih, Hung Rung
;
Tu, G. C.
;
材料科學與工程學系
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Department of Materials Science and Engineering
The main object of the present work was to develop an electrical discharge abrasive drilling (EDAD) methodology to remove the re-solidified layer through the grinding induced by a metal matrix composite electrode prior to the re-solidification of molten material. A metal matrix composite (Cu/SiCp) electrode, with an electroless pretreatment of Cu coating on SiCp to enhance bonding status between Cu and SiCp, was made with a rotating device and this was employed to study the EDAD technology. The machinability of the mold steel HPM50 and tungsten carbide P20 was investigated by the combined technologies of EDAD. The machined surfaces of these materials were examined by scanning electron microscopy (SEM) and their surface roughness measured by a profilemeter. From the experimental results, it was found that the EDAD machining efficiency was three to seven times than that of normal EDM operation for mold steel. However, the efficiency improvement is hardly detectable for tungsten carbide. In addition, the surface roughness of both materials could be improved in comparison with that achieved after EDM.
Perturbed hydrogen permeation of a hydrogen mixture - New phenomena in hydrogen permeation by Pd membrane
(2008-04-01)
Chen, S. C.
;
Hung, Caryat C. Y.
;
Tu, G. C.
;
Rei, M. H.
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材料科學與工程學系
The newly developed constant concentration method was adopted to study the hydrogen permeation of a hydrogen mixture of H-2 + Y through a palladium membrane tube. The hydrogen permeation of the hydrogen mixture differs from that of a single hydrogen feed. For the hydrogen mixture, the well-known Sieverts equation, Q = J(H)/[(P-R(H))(1/2) - (P-P(H))(1/2)] fails to yield the correct hydrogen flux or permeance even after the pressure terms are adjusted to the partial pressure of hydrogen. The hydrogen concentration in the mixture affects both the flux and the permeance. Significant abnormal permeation of the non-hydrogen gas, Y, in the hydrogen permeates is detected during the hydrogen permeation of the mixture, H-2 + Y, even though Y-gas alone does not permeate through the defect-free palladium membrane. This Y-gas slippage in the presence of hydrogen in the mixture is tentatively attributed to the expansion of the palladium atomic lattice, enlarging inter-cluster openings. Y-gas permeates through the enlarged structure or grain boundary of the palladium atoms in the membrane. The permselectivity of a palladium membrane cannot be measured simply from the ratio of two separate permeation fluxes of H-2 and Y The permselectivity of a hydrogen mixture, H-2 + Y, measured by the constant concentration method in the retentate, is compared with that measured by the flowing-through method and with that determining from two separate measurements of H-2 and of Y. The three methods give different permselectivities of the same palladium membrane tube when the concentration ratio of H-2/Y is adjusted to 1. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Preparation of palladium membrane by electroplating on AISI 316L porous stainless steel supports and its use for methanol steam reformer
(2008-04-30)
Chen, S. C.
;
Tu, G. C.
;
Hung, Caryat C. Y.
;
Huang, C. A.
;
Rei, M. H.
A novel electroplating method of preparing Pd-membrane on an AISI 316L porous stainless steel support is successfully developed by proper control of rotation speed of the support. The use of low-current density with high-rotation speed enables us to avoid hydrogen absorption during electroplating and to prepare smooth thin surfaced membrane with defect free. The electroplated-Pd-membrane shows well property in the hydrogen permeation, flux and excellent permselectivity (H-2/He > 100,000), and is used in a membrane-assisted steam reformer of methanol for the production of high-purity hydrogen. It was also found that the membrane spontaneously exhibited to resist hydrogen embrittlement under the phase-transition temperature of 280 degrees C, when operated in the temperature range of 250-350 degrees C under the hydrogen pressure of 9 kgf/cm(2). (C) 2008 Elsevier B.V. All rights reserved.