Fluorine-free mould flux has been required to reduce corrosion of continuous casters. In this paper, Na2Ca2Si3O9 has been applied to an alternative crystalline phase of Ca4Si2O7F2 (cuspidine) that crystallized in commercial flux films. Effects of basicity described as T.CaO/SiO2 and additions of Li2O, Na2O, MgO and/or MnO into Na2Ca2Si3O9 composition mould flux on viscosity and solidification temperature were studied and the solidified specimens were examined by X-ray diffraction to identified crystalline phases.The viscosity of the mould flux is reduced with increaing of the basicity or the basic components contents. The solidification temperature decreased slightly as the basicity increased from 0.47 to 0.60, whereas it increased steeply with increasing of the basicity from 0.60 to 0.70. The solidification temperature also steeply increased when large amounts of these basic components were added. With increasing of the basic components amounts, the first peak intensity of the target phase, Na2Ca2Si3O9, decreased while that of Na2Ca2Si2O7, which had higher melting point than the target phase, increased. It is indicated that the solidification temperature is related to Na2Ca2Si2O7 crystallization.Carbon steel was cast with one of the developed fluorin-free mould fluxes and slab without any surface cracking was obtained.

The unusual wetting phenomenon of liquid Bi on surface-porous copper has been studied. A porous layer was prepared at the surface of a copper substrate and the wetting behavior of liquid Bi on this layer was investigated and compared with that on a flat solid copper substrate. A surface-oxidized copper substrate was reduced at 473 K in H 2 to prepare a porous layer at the surface. Since the contact angle of liquid Bi on the flat solid copper substrate was gradually declining with increasing temperature, the behavior of liquid Bi on solid copper was shown to have good-wettability. In addition, the unusual wetting behavior of liquid Bi was observed on surface-porous copper substrate. This result is evidence that the pores in the porous layer are 3-dimensionally inter-connected. This usual wetting phenomenon of liquid Bi was then applied in the joining of copper wire with the surface-porous copper substrate. Bonding was successfully achieved with a minimized weld overlay at the joining point.

The authors found that a liquid Cu droplet wetted and spread very widely on a solid substrate of Fe in a reduced atmosphere after the surface oxidation of the substrate. The mechanism of the unusual wetting behavior was investigated by using surface-oxidized Fe substrate with liquid Cu, Ag, Sn, and In. It was found that under a reduced atmosphere condition, fine pores were formed at the surface of the substrate which had been oxidized, and that the pores were connected to each other continuously over the whole surface. The liquid metals penetrate into these pores by capillary force to cause the unusual wetting behavior.

Wettability of liquid indium and liquid bismuth on a solid iron was investigated to elucidate their different behaviors relating to the unusual wetting phenomena. Sessile drop method was performed to measure the contact angle of each liquid metal on the flat solid iron in H 2 from 700 to 1100 K. In addition, we observed wetting behaviors of liquid indium and liquid bismuth on the surface-porous iron substrate. It was found from these experiments that liquid indium wetted and penetrated into the porous layer at 773 K. On the other hand, liquid bismuth did not infiltrate the porous substrate at temperatures lower than about 950 K. The wetting behavior of these liquid metals on the porous substrates is supposed to be related to the wettability of each metal on the flat solid iron.

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