Effect Of Nucleating Agent On The Microstructure Of Glass-ceramics From Blast Furnace Slag

The method of the treatment with the blast furnace slag?hereafter referred to as BFS?, a byproduct of ironmaking, is water-granulated slag. BFS, whose main chemical composition are SiO₂, CaO and so on, is mainly used to produce cement, slag fiber, which is uneconomical and underutilized to the sensible heat. Preparing glass-ceramics with molten BFS has remarkable economic and social benefits.In this paper, the BFS, coming from the iron making site, is used as the main raw materials together with chemical reagents such as SiO₂, Al₂O₃, Mg O, K₂ O, Na₂SO₄, TiO₂ and CaF₂ to prepare glass-ceramics by melting method. Effect of CaO/SiO₂, TiO₂ and CaF₂ on glass melting, glass structure, nucleation and crystallization temperature and microstructure were characterized by melt properties tester, LRS, DSC, XRD and SEM respectively. The density, water absorption, corrosion resistance of acid and alkali are also tested.The crystal of glass-ceramics from BFS are diopside, augite and akermanitegehlenite. With the increasing of CaO/SiO₂, the content of akermanite-gehlenite increases, leading high water absorption and poor acid and alkali corrosion. The optimum ratio of CaO/SiO₂ is 0.44 based on the utilization rate of BFS and the properties of glass-ceramics.When TiO₂ and CaF₂ are added, [Si O4] network in glass is damaged due to the Si₄⁺ andO₂^- being replaced by Ti₄⁺?from TiO₂? and F^-?from CaF₂?, which decreases the viscosity of the liquid glass and increases the chemical instability of the parent glass. In the process of heat treatment, titanium and fluoride are immiscible in glass, leading to two-phase glass separation. So TiO₂ and CaF₂ can lower the nucleation and crystallization temperature and enhance the crystallizability of the glass. Adding 4% TiO₂, the glass-ceramics has the characteristics of high crystal, fine grains and homogeneous microstructure. When CaF₂ content is greater than 4%, there would be a new phase—cuspidine. The average particle size of the crystal is 100 nm and the glass-ceramics has the best corrosion resistance to acid and alkali with 6% CaF₂.