The time-temperature-transformation diagram (TTT diagram) of CaO-SiO 2 -TiO 2 slag has been determined by using differential thermal analysis (DTA) in order to investigate the crystallization of the slag as a candidate for fluorine free mold flux. The incubation time of CaOSiO 2 TiO 2 in CaO-SiO 2 -TiO 2 slag is as small as that of cuspidine (3CaO 2 SiO 2 CaF 2 ) in commercial mold fluxes. This finding indicates that the CaOSiO 2 TiO 2 crystallizes rapidly in the slag film between the mold and the steel in the continuous casting machine, similar to cuspidine in commercial mold fluxes. CaOSiO 2 TiO 2 in CaO-SiO 2 -TiO 2 slag is substituted for cuspidine in commercial mold fluxes. The thickness of the crystalline layer of CaOSiO 2 TiO 2 is smaller than that of cuspidine. In order to improve the heat transfer control of CaO-SiO 2 -TiO 2 slag, it is necessary to decrease the incubation time of CaOSiO 2 TiO 2 at high temperature.KEY WORDS: heat transfer control; TTT diagram; CaO-SiO 2 -TiO 2 slag; fluorine free mold flux. on the mold side with lower temperature and dendrite structure from middle to the shell side with higher temperature. It is considered that cuspidine with the dendrite structure crystallizes rapidly from liquid on the shell side and cuspidine with the cubic structure precipitates from once quenched glass on the mold side. As shown Table 1, although the amount of the dendrite and the cubic structures varies with each commercial mold flux, most of the crystalline layer takes the dendrite structure. This finding that cuspidine is able to crystallize from liquid rapidly as primary crystal. Actually, Hanao et al. 21) reported that the rapid crystallization of cuspidine brings the great effect on the heat transfer control i.e. the crystallization of cuspidine from liquid as primary crystal brings the great effect on the heat transfer control. Thus, it is necessary that the crystallization rate of the crystals in CaO-SiO 2 -TiO 2 slag is compared with that of cuspidine in commercial mold fluxes. The crystallization rate of the crystals is defined as the incubation time in the time-temperature-transformation diagram (TTT diagram) of CaO-SiO 2 -TiO 2 slag.The aim of this study is to investigate TTT diagram of CaO-SiO 2 -TiO 2 slag and to examine whether CaO-SiO 2 -TiO 2 slag is proposed as a candidate for fluorine free mold flux. Figure 2 shows the equilibrium phase diagram of CaOSiO 2 -TiO 2 system. 18) In this study, two series of glassy sample were prepared. The samples of glass CST series with the basicity of 0.83 were prepared in the initial field of CaOSiO 2 TiO 2 and the samples of glass CS series with the basicity of 0.84 were prepared in the initial field of CaOSiO 2 . Table 2 shows the chemical compositions of the samples. The compositions of the samples were selected from the reason that the liquidus temperature and the viscosity of the samples are similar to those of commercial mold fluxes in CaO-SiO 2 -CaF 2 system. The samples of glass CST series have the same composition but have the differe...

The mechanism by which crystallization of mold flux reduces the heat transfer between the steel shell and the mold has been investigated from the viewpoint of physical properties and characteristics of mold flux and air gap on the basis of a heat transfer model involving conduction and radiation processes. It has been found that, in mold fluxes for medium carbon steel, the reflectivity of the crystalline slag layer formed in mold flux film is an efficient factor for further reducing the total heat flux in the film. The heat transfer reduction based on this finding would be possible according to the following mechanism: Crystallization of mold flux film increases the reflectivity of the crystalline slag layer in the film owing to enhanced scattering of light by introduction of crystal grain boundaries, and thereby more radiation energy returns from the crystalline slag layer to the steel, leading to reduction in the total heat flux across the film.

The effect of Na 2 O on the behavior and mechanism of the precipitation of cuspidine from the CaO-SiO 2 -CaF 2 -Na 2 O quaternary slags has been investigated by solid-state 19

Platinum group metals (PGMs) are indispensable materials for the automotive catalyst as these metals have excellent catalytic properties. However, these metals have serious problems in terms of resource security. This is because the production amount is limited, and moreover the primary supply of the metals is restricted to the mines located in certain countries. In this article, current status of PGMs is reviewed, and recent topics on recycling technologies for recovering PGMs from the surface of the scraps are introduced.