The influence of steel grade on the oxidation rate of molten steel in tundish was studied by conducting oxidation experiments on the Ti and Ti-Al deoxidized molten steel and comparing the obtained oxidation rates with that of the Al deoxidized molten steel as measured in a previous report. In the still state, the oxidation rate of the Ti deoxidized molten steel is faster than those of the Ti-Al deoxidized molten steel and the Al deoxidized molten steel, showing dependence on the steel grade. This means that in the still state, while the oxidation rates of the Ti-Al and Al deoxidized molten steel are controlled by the mass transfer of oxygen in the oxide film, the oxidation rate of the Ti deoxidized molten steel is controlled by the mass transfer of O2 gas in the gas phase because the surface is not covered with oxide films. In addition, in the stirred state, the oxidation rates of the Ti and Ti-Al deoxidized molten steel become faster than that of the Al deoxidized molten steel in the region where the O2 gas partial pressure exceeds 10 kPa. This dependence on the steel grade can be explained by the mechanism of accelerating the mass transfer in the gas phase due to active iron evaporation in the Ti and Ti-Al deoxidized molten steel, in which the surface disturbance is larger than that in the Al deoxidized molten steel.

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Powder blasting is often operated in refining process in order to achieve lower sulfur content in molten steel with high desulfurization efficiency. In this study, effects of wettability of a particle on penetration and flotation behavior were examined by water model experiment. A polypropylene particle was blasted onto water surface with Ar gas through a single-hole nozzle, and particle behavior during penetration into water to flotation to water surface was recorded by a high-speed camera. Wettability between the particle and water was changed by applying repellent or hydrophilic material on the particle. According to penetration of the particle, an air column was generated and a residual bubble was remained on the particle after rupture of the air column. The repellent particle floated to the water surface in a short time because maximum penetration depth was small and diameter of a residual bubble was large. On the other hand, the detention time of the hydrophilic particle became longer than the repellent particle because maximum penetration depth was relatively large and the residual bubble was separated from the particle. The reason that wettability between the particle and water affects penetration and f loatation behavior is that adhering position of the air column on the particle changed. In the case of repellent particle, the position changed to penetrating direction of the particle. Therefore, the force caused by surface tension of water increases, and the residual air column on the particle after rupture of the air column becomes large. Keywords: refining process; water model experiment; wettability of a particle; air column; residual bubble; detention time of a particle.

Powder blasting is often performed in refining processes for improving their reaction efficiency. Herein, the effect of wettability on penetration and flotation behavior of a particle was examined via a water model experiment. A polypropylene particle was blasted onto the water surface with Ar gas through a single-hole nozzle, and the behavior of the particle during penetration into water to flotation on the water surface was recorded using a high-speed camera. Wettability between the particle and water was changed by applying a repellent or hydrophilic material on the particle. Based on the penetration of the particle, an air column was generated and a residual bubble remained on the particle after the air column ruptured. Repellent particles floated on the water surface in a short period of time because the maximum penetration depth was short and the diameter of the residual bubble was large. Conversely, hydrophilic particles stayed longer in water than repellent particles because the maximum penetration depth was relatively long and the residual bubble detached from the particle. The mechanism which wettability affects penetration and flotation behavior was analyzed, and it was elucidated that the controlling factor of particle behavior is the adhesion point of the air column on the particle. In the case of repellent particles, the adhesion point changes toward to penetrating direction of the particle and the force caused by the surface tension of water increases. Therefore, the maximum penetration depth decreases and the diameter of the residual bubble increases. KEY WORDS: refining process; water model experiment; wettability of a particle; air column; residual bubble; detention time of a particle.

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