The present study aims to investigate the possibility of reduction of radiative heat flux in the continuous casting process by valence control of iron ions in mould flux. The compositions of samples were designed on the basis of a practical mould flux, where the basicity defined as CaO/SiO2 was also varied from 0.6 to 1.4 to change the valence of iron ions. Mixtures of oxide and fluoride powders were melted in platinum crucibles in air and then the melts were quenched into brass moulds to obtain glassy samples. In addition, graphite crucibles were also used to melt samples having the basicity of 1 at lower partial pressure of oxygen. Some glassy samples were heat-treated for crystallisation. Glassy and crystallised samples were subjected to chemical analyses and optical measurements of apparent reflectivity and transmissivity. The concentration ratio of Fe 3+ /Fe 2+ increased with increasing basicity but decreased by melting in graphite crucibles. Increasing concentration ratio of Fe 3+ /Fe 2+ leads to an increase of radiative heat flux for the glassy samples but to a decrease for the crystallised samples: the effect of valences of iron ions is more prominent in the glassy samples. In the crystallised samples, on the contrary, the degree of crystallinity affects radiative heat flux more strongly than the valence of iron ions.KEY WORDS: mould flux; mild cooling; basicity; valence of iron ions; degree of crystallinity.

No abstract

No abstract

No abstract

In the end of 2019, the emergence of COVID-19 was reported and confirmed for the first time, and it triggered an international pandemic. In Japan, the strong tendency to spread of infection is still continuing. The Japanese Government has been raised two concepts to overcome this difficulty. One is the thorough measures to control of the spread of infection and the other is the economic recovery. The government has carried out the corresponding two policies: the use of COVID-19 Contact-Confirming Application (COCOA) and the application of “GoTo Travel Campaign”. We focus on these two policies and study an ideal situation, which enables us to balance more economic recovery and control of the spread of infection. To pursue this goal, we propose a mathematical model to estimate these policies’s effects and conduct simulations of 28 scenarios. In addition, we analyze each result of the simulation and investigate characteristics of each situation. As a result, we clearly find that it required that not only the increasing the using rate of COCOA but also a positive change of people’s behaviors and awareness.