2019 年 105 巻 5 号 p. 522-529
In steelmaking industry of Japan, one-third steelmaking slag is reused for road constructions. Steelmaking slag contains a few weight percent of calcium oxide, which is termed as free-lime. Free-lime expands its volume by the reactions with water and carbon dioxide, leading to collapse of road substrates. To prevent the road collapse, free-lime in steelmaking slag is now treated to be transformed to Ca(OH)2 and CaCO3 by an aging process; however, the residual free-lime still causes the road collapse. Therefore, it is necessary to detect free-lime in steelmaking slag to safely reutilize it for road constructions. In the present study, we carried out a cathodoluminescence (CL) analysis for identification of free-lime in steelmaking slag. For this purpose, we prepared a synthesized slag sample including free-lime by heating mixtures of reagents. A part of the sample was soaked in water at 70°C for 3 h (aging process). Crystallized free-lime in the sample illuminated orange due to an emission peak of Mn2+ at 600 nm regardless of the precipitation forms of free-lime. Undissolved free-lime illuminated blue due to an emission peak of oxygen vacancy at 460 nm. The sample after the aging process illuminated orange because of CaCO3 having with an emission peak of Mn2+ at 620 nm. We could identify free-lime and CaCO3 by camera detecting light over 680 nm selectively because the luminescence of CaCO3 also appeared on longer wavelength side over 690 nm. Thus, we could detect free-lime in steelmaking slag by capturing CL images within 30 s.