발간논문

Home > KJMM 논문 > 발간논문

Directional solidification experiments were conducted on the Al-Fe-Mn ternary eutectic alloys to investigate the growth mechanism and the mechanical behaviors at temperature gradient 80℃/㎝. The effects of the growth rate and the alloying elements, such as manganese and iron, on the composite structures and the mechanical properties of Al-Fe-Mn ternary composites were investigated. The results obtained were as follows: 1) As the growth rate increases, the growth morphology of the composites changes from the plate type into the rod one in Al-Fe alloys, but from the blade type into the square -pillar one in Al-Mn alloys. 2) In the case of Al-Fe alloys the interphase spacing increases with the increase of manganese content, but in the case of Al-Mn alloys it decreases with the increase of iron content. 3) The faster growth rate causes the higher mechanical strength. But the effect of the growth rate on the mechanical properties was larger for Al-Fe alloys than for Al-Mn alloys.

keyword :

In order to investigate the effect of squeeze pressure on the spingback and mechanical properties of sand mold with various clay content, moisture and size of sand grains, permeability, green compressive strength and green mold hardness were tested and dimensional change was also measured. From this experiment, the results were summarized as follows: 1) Spingback of mold was affected significantly by the magnitude of pressure but not size of grains, clay and moisture. 2) Permeability of mold decreased as the squeeze pressure and clay content of the foundry sand increased but it increased as size of sand grains increased. 3) Green compressive strength of mold increased as the squeeze pressure, clay content of the foundry sand and size of sand grains increased. 4) Green mold hardness of mold increased as the squeeze pressure, clay content of the foundry sand and size of sand grains increased. 5) Density of mold increased as the squeeze pressure, clay content of the foundry sand and size of sand grains increased.

keyword :

A study on the leaching of stibnite was carried out in acidified ferric chloride solution at temperature ranging from 30℃ to 90℃. Possible leaching mechanism for the reaction was discussed with the experimental kinetic data obtained in this investigation. To evaluate the rate equation satisfying the data of the reaction, various kinetic models were discussed. The results obtained in this work are as follows; 1) The leaching rate of stibnite was enhanced by increasing the temperature and the concentration of solvent, and by making the particle size smaller. 2) In case of fine particle finer than 270 mesh, the leaching reaction is controlled by the diffusion of reactant (Fe(III)) through sulfur layer. The leaching reaction of coarse particle coarser than 270 mesh is controlled by chemical reaction in early stage and shift to diffusion controlled reaction according as the reaction progresses. 3) The apparent activation energy for pore diffusion reaction is 17 ㎉/㏖. 4) The initial leaching rate of 270/325 mesh stibnite can be expressed by the following empirical equation, d[Sb(III)]/dt = k ·[Fe(III)]^0.3 ·[HCl]^0.6

keyword :

The effects of sodium hydroxide concentration, particle size, temperature and leaching atmosphere have been studied in leaching of stibnite with sodium hydroxide solution. The results in this work are as follows. 1) The extraction rate of antimony from stibnite was enhanced by increasing the temperature and the concentration of sodium hydroxide. 2) The reaction control step is shifted from chemical reaction control in low concentration of sodium hydroxide (below 0.05M) to diffusion control in high concentration (above 0.5M). 3) In case of the chemically controlled reaction, the initial leaching rate can be expressed by the following empirical equation. [d Sb(III)/dt]_(t=0) = k ·(C_(NaOH))³ 4) When the leaching of stibnite with sodium hydroxide was carried out under the oxidizing atmosphere, the higher oxide of antimony is precipitated and this causes the loss of antimony.

keyword :

The corrosion of Fe-25w/o Cr steel, containing of 0-4.2 w/o Al, has been investigated over the temperature range of 700℃ to 1000℃ in the salt of 90 w/o Na₂SO₄-10 w/o NaCI. The result is as follows: 1) At 700-800℃, the corrosion is hardly proceeded after 24 hrs. But, above 900℃, an addition of 2.3-4.2 w/o Al is desired for protecting the corrosion attack. 2) The corrosion attack is proceeded through the grain boundary. 3) When the specimen of O w/o Al is corroded for 36 hrs, CrS is detected above 800℃. But, in case of 1.1-4.2 w/o Al, CrS is detected above 900℃. 4) By SEM, a larger addition of Al leads α-Al₂O₃scale to be protective, and it decreases the velocity of corrosion. 5) By EPMA, the scale is produced in order of iron-oxide, chrome-oxide, and aluminum-oxide. It arises because each atoms migrates to the surface of specimen on the high temperature.

keyword :

keyword :

keyword :

keyword :