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WC-10wt%Co-Al2O3 ceramic composites, using both the SHS (Self-propagating High Temperature Synthesis) synthesized WC powder method and commercial WC powder, were prepared by varing WC-Co/Al2O3 vol% ratio and sintering temperature (1350℃∼1650℃) for 1 hr in Ar atmosphere. Mechanical characterization has been investigated by Instron meterial testing system and Vicker's hardness test. Compositional and structural chracterizations were carried out by energy-dispersive analysis of X-ray (EDAX) data and scanning electron microscope (SEM). Electrical characterization was carried out by the electrical resistivity measurement using 4-point probe method. As sintering period increased and Al2O3 contents decreased in WC-10wt%Co-Al2O3 ceramic composite, shrinkage and relative density increased, resulting in maximum values at 1600℃. Also the major matrix phase changed with increasing Al2O3 content from 0 to 100 vol%. It was also identified by SEM, EDAX, and electrical resistivity measurement. Based on the results of analysis of flexural strength, toughness and hardness, the mechanical properties of WC-10wt%Co-Al2O3 ceramic composites using the SHS synthesized WC powder were better than those WC-10wt%Co-Al2O3 ceramic composites using commercial WC powder because WC-10wt%Co-Al2O3 ceramic composites using the SHS synthesized WC powder were sintered very well due to small initial particle size. By the addition of 40 vol% Al2O3 [60(WC=10wt%Co)-40Al2O3], it was possible to obtain a proper candidate as a superalloy.
TiB2 was simultaneously synthesized and densified with concurrent self-propagating high-temperature synthesis and direct contact-heating by electrcial power input and pressure. Density of TiB2 synthesized by self-propagating high-temperature synthesis and consolidated simultaneously by direct contact-heating and pressure was maximum 80% of the theoretical density (4.52g/㎤). Temperature profile was analyzed by solving heat balance equation with numerical method (FTCS method). The temperature of the sample was sufficiently raised to that temperature sufficient to be densified. It was ascertained that the density of the SHS synthesized TiB2 is exponentially proportinal to the input thermal energy per mass.
We powders were synthesized from W powders in differnet particle sizes by Self-propagating High-temperature Synthesis process (SHS) using a chemical furnace. The effects of the mole ratio of chemical fuel content, pellet thickness and the mole ratio between carbon and tungsten (C/W Ratio) on synthesis were investigated with the tungsten powders have different particle size each other. Compositional and structural characterization of these powders was carried out by scanning electron microscope (SEM0 and x-ray diffractometer. Powder characterization was carried out by the measurement of particle size distribution with laser-particle size analyzer. The amounts of WC obtained by SHS process depend very much on the particle size of tungsten powder and heat contents given in a product, i.e. as the particle size of W powder is smaller, the amounts of WC produced increase. Also the more heat contents is given, the more amounts of WC increase. By optimizing the synthesis conditions, it is possible to fabricate WC powders which have little secondary phases (W2C, C).
Although Ni-Zn battery has high energy density, low material cost and excellent performance in the wide range of temperatures, it still has problems to be solved for EV application. The problems are short cycle life and change of quality with variation of season. In this paper, reaction mechanism in Ni-Zn battery and the factors which affect the mechanism have been studied. Firstly, density of electrolyte was studied. It was observed that a number of OH- affects the activation potential in the Ni electrode. The longer cycle life and higher capacity were obtained when the cocentration of electrolyte(KOH) was 35wt% Secondly, the temperature effect was studied and the best result in capacity was obtained when the battery was charged at 25℃. If it is proposed to improve efficiency of EV, the battery has to be charged at the ambient temperature. And thirdly, Ni/Zn electrode has also been tested by cyclic voltammetry measurement. When the Ni electrode is tested at low temperature, more amount of r-NiOOH is formed. This state caused the swelling in the Ni electrode, which lowers the battery performance. When the battery is charged at higher than 40℃, gas evaporation was accelerated and charging efficiency dropped. As the temperature rises, the more amount of Zn is soluble in electrolyte as like Zn(OH)₄^(2-), so that the cathode and anode capacity are increased. However, the capacity of Ni-Zn battery decreased at higher than 40℃ because the capacity is controlled by Ni electrode.