Determination of changes of the dissolved oxygen content after silicon deoxidation by the use of the radioactive silicon

Changes of the dissolved oxygen content after deoxidation with 0.1% and 0.42% silicon have been determined by fixing the oxygen as the radioactive SiO2 with the radioactive silicon (silicon-31) previously charged in the sampler and counting radioactivity of the inclusions extracted from the sample. In both cases, the dissolved oxygen content decreases rapidly below the equilibrium value, and then increases gradually to reach it. The mechanism of the silicon deoxidation has been discussed from the viewpoint that such changes of the dissolved oxygen is due to the non-uniform distribution of silicon formed in liquid iron immediately after silicon addition. The conclusions are as follows: (1) In the regions where the silicon contents are high, SiOsub(x) (x<2) is produced, owing to the fast rate of reaction between silicon and oxygen, and the oxygen contents decrease to lower value than the equilibrium one. (2) The minimum of the dissolved oxygen attained immediately after silicon addition is regarded as a mean oxygen content at the time when silicon and oxygen dissolved uniformly in the melt. (3) The oxygen content increases again by the reaction SiO2 (crucible) =Si+2 O and the deoxidation processes such as growth of the deoxidation products and adhesion of them to the crucible wall are rate controlled by this reaction. (4) The composition of SiOsub(x) is not widely different from that of SiO2. (auth.)