The glass based glass ceramics is set in the control of specific components of heating rate, temperature and time conditions, the crystal vitreous body, a kind of composite material of glass phase and crystal to generate phase coexistence.
Glass ceramics have the properties of low expansion rate, high mechanical strength, acid and alkali corrosion resistance and good thermal stability. Glass ceramics were prepared from blast furnace slag, steel slag, fly ash and tailings. The main components of the ironmaking process of blast furnace slag production (in mass fraction) CaO=35 ~ 44%, SiO2=32 ~ 42%, Al2O3=6 ~ 16%, MgO=4 ~ 13% and a small amount of MnO, FeO and CaS, in the blast furnace feeding conditions and smelting slag composition under normal conditions, small fluctuation, is a good raw material preparation glass ceramics. The blast furnace slag is the raw material for the development of slag glass ceramics, which has a history of more than and 40 years.
The British Kemantaski in 1965 by using blast furnace slag glass ceramics were prepared by G.Agarwel et al, a compact winding fibrous magnesium Wollastonite Glass ceramics were prepared by using blast furnace slag for high CaO, the experimental results showed that it has good abrasion resistance, is 2 times the basic glass. Z.E.Erkmen et al., prepared by the addition of TiO2 and Cr2O3 in the blast furnace slag with 18h at 780 DEG C, and the crystallization of 20min at a temperature of 910 DEG C, produced the glass ceramics with the main crystal phases of calcium feldspar and magnesium feldspar.
Blast furnace slag glass ceramics with nucleating agent selected from thermodynamic point of view, the glass is an amorphous material, the system is in a metastable state in energy, glass to crystal transformation with thermodynamic conditions; from kinetic conditions, with the decrease of temperature, the glass viscosity rapidly increases, the diffusion and crystal nucleus the growth of atoms and rearrange the process becomes very slow. Therefore, it is necessary to provide a strong kinetic condition to accelerate the transformation of the glassy state to the crystalline state. The effect of nucleating agent is in the process of melting glass, can be uniformly dissolved in molten glass, glass in crystallization stability zone to reduce the activation energy of crystallization, the glass can be at a relatively low temperature bulk crystallization.
Stookey suggested that the nucleating agent should have the following properties: excellent in melt molding conditions of glass, with good solubility, but during heat treatment the solubility is small, and can reduce the nucleation activation energy, promote the overall crystallization; nucleation agent diffusion activation energy is small, easy to spread in the glass; nucleating agent composition and interfacial tension of small crystal.
At present, TiO2, CaF2 and P2O5 are mainly used as nucleating agents for blast furnace slag glass ceramics.
Some scholars believe that TiO2 is a good nucleating agent, which can effectively promote the separation of the blast furnace slag glass ceramics. Some scholars have pointed out that with the increase of TiO2 content, the crystallization temperature decreases with the increase of CaOMgO-Al2O3-SiO2 content. It is generally believed that Ti4+ ions are intermediate cations in different states in the form of four coordination [TiO4] or the presence of in the form of [TiO6]. At high temperature, four coordination bonds exist, and with the decrease of temperature, the transition of the four coordination bond to the coordination of the six. Six the coordination form [TiO6] and the vitreous body do not melt mutually, causes it to separate from the silicon oxygen tetrahedron, thus forms the crystal nucleus. Yue Qinyan et al. Studied the relationship between the content of TiO2 and the activation energy of crystallization and the existence of titanium. The results show that the activation energy of TiO2 at 3.1% is the lowest, and the content of is in the form of the "six" when the content of TiO2 is from 3 to.
F- is very close to the radius of O2-, so the F- can replace the O2- in the silicon oxygen tetrahedron, which breaks the silicon oxygen tetrahedron, which plays a significant role in the destruction, and reduces the viscosity of the glass. When CaF2 is cooled, it can be separated from the glass and become the center of nucleation.
P2O5 has two kinds of functions in the glass: one is to combine with [AlO4]5- into the silicon oxygen network, play the role of the network, inhibit the crystallization, on the other hand, P5+ field is strong, the phase separation ability is strong, play the role of induced crystallization. When the content of P2O5 is low, the former plays an important role, while the latter plays a major role when the content is high. Luo Guoping and other studies showed that the content of P2O5 was lower than 4%, and the crystallization temperature increased. When the content was more than 4%, the crystallization temperature decreased. Tian Qingbo et al. In the study of the effect of P2O5 on the crystallization of CaOMgO-Al2O3-SiO2 glass ceramics, the results show that when the content of P2O5 is 10%, the glass is completely crystallized, and the grains are fine and uniform.
According to the characteristics of the complementary advantages of nucleating agents, the selection of composite nucleating agent can get better results. The compound nucleating agent CaF2 and TiO2 can reduce the activation energy E of CMAS glass ceramics to 392.2KJ/mol, which leads to the rapid crystallization of the crystal, and the crystal growth index n is increased to 2.87 by CaF2 and P2O5.
In order to reduce the viscosity of the glass and reduce the melting point, Na2SO4, K2O and other materials are often added. In order to reduce the bubble in the process of melting glass, improve the density of the glass, also often add some clarification agent, such as sodium nitrate and cerium oxide, etc.. In order to increase the thermal insulation, sound absorption and sound insulation properties of the glass ceramics, an appropriate amount of foaming agent can be added to prepare the glass ceramics.
The basic ingredients of glass composition of blast furnace slag glass ceramics is an important factor affecting heat treatment, crystal phase of glass ceramic and glass phase, and the performance of the glass ceramics is mainly determined by the content of glass ceramics in the crystal phase, crystal morphology, crystal content and glass phase, so the basis for determining the appropriate chemical composition of glass is very necessary.
Determination of chemical composition of blast furnace slag glass ceramics
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