발간논문

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In this study, a cold fluidized bed for sinterfeed of wide size range 1-5 ㎜ has been comprehensively characterized in terms of minimum fluidization velocity, fluidized-bed regime, variation in pressure drop, degradation and holdup of axial direction using manometers and differential pressure transmitters(DPT). From the measurement of pressure drop(△P) in the reactor using 7 DPTs installed along the vertical length of reactor, it was found that the degradation of iron ore is almost in the early stage of fluidization, within 5 min. The amount and size distribution in each section between DPTs can be predicted from the measurements of △P. Calculating the solid holdup in the bed from the measurements, the variation in the bed height with ore weight can be also predicted. Therefore it is expected that the present study can provide some useful parameters which is critical in the determination of the reactor height for scale-up of a fluidized bed system.

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The thermoelectric properties of p-type Bi_(0. 5)Sb_(1. 5)Te₃ thermoelectric materials, which were fabricated by extrusion at temperature ranged from 300 to 500℃ with various amounts of Te dopants (0 to 6 %), were studied. The microstructure of the thermoelectric materials was investigated by optical microscopy and scanning electron microscopy. The microstructure of the extruded specimen was dense, fine-grained, and elongated along the extrusion direction. The relative density increased with increasing extrusion temperature. The highest relative density (99.6 %) was obtained by extrusion at 440℃. The value of figure of merit (2.94×10^(-3)/K) was the highest at the extrusion temperature of 440℃ and at the dopant of 4 wt% Te.

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The p-type thermoelectric powders of 25%Bi₂Te₃-75%Sb₂Te₃ doped with 4wt%Te were prepared by high pressure gas atomizer. The new process with rapid solidification followed by pressing and sintering was investigated to produce homogeneous material. Characteristics of the material were examined with XRD, DSC, SEM, EPMA-line scan and bending test. Property variations of the materials were investigated as a function of variables, such as powder size, sintering temperature and annealing effect. Quenched powders and sintered materials consist of Bi₂Te₃ type of single phase. When the process parameters were optimized, the maximum figure of merit was 2.78×10^(-3)K^(-1). The bending strength of the material produced in this work was 4.68 ㎏f/㎟.

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In order to increase the growth rate of Ni Metal Induced Lateral Crystallization(MILC) of amorphous Si which shows acceptable electrical properties. Pd thin films were deposited on amorphous Si with a distance to Ni deposited area. The shorter the space between the Ni and Pd films, the faster the rate of Ni MILC, and when the space was 60 ㎛ the growth rate was 7.5 ㎛/hr. Through TEM microstructural analysis and investigation on relationships between the space and growth rate the enhanced growth rate of Ni-MILC turned out to be due to stresses generated by the formation of Pd₂Si under/at Pd deposited area. Using Pd assisted. Ni-MILC method, 0.8 ㎛/hr of MILC growth rate could be obtained at the temperature as low as 450℃.

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The stuffing effect of TaN on the diffusion barrier properties for Al was investigated. The stuffing of TaN was performed by annealing at 500℃ for 30 minutes in N₂ ambient. After Secco etching, etch pits appeared on Si surface at 575℃ in both as-deposited and stuffed TaN cases, but the number density of etch pit in stuffed case was slightly low. AES depth profile indicated that there was no noticeable difference in the distribution and concentration of oxygen in TaN layer between as-deposited and stuffed TaN. This is believed to be responsible to the insignificant improvement of diffusion barrier properties by stuffing process. The minimal incorporation of oxygen into TaN by stuffing process was attributed to the microstructure of TaN. TEM investigation reveals that the grain size and grain boundary spacing of TaN deposited by reactive sputtering are very small so that oxygen can not penetrate into TaN film by stuffing process.

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