These cations also connect non-bridged oxygen of the various structural units. However, considering the field strength, size and bridging with silicate network, cations have a significant role in the structural modification of slag structure. Effective ionic radii and corresponding cation field strength. Zhang, K. Chou, G. Xue and K. Mills: Metall. Maekawa, T. Maekawa, K.
Kawamura and T. Yokokawa: J. The structure of blast furnace slag has great importance because it can affect the properties of slag as well as the performance and productivity of furnace. So a variety of different parameters have been used to understand the structure of slag. It is the ratio between network modifier component and network former component of the slag composition. The SiO 2 in slag behaves as acidic by accepting electrons and alkali or alkaline metal oxides concentrations are denoted as basic because they donate electrons.
Thus, network formers are acidic and network breakers are basic in nature. The basicity values will become problematic when dealing with amphoteric oxides like Al 2 O 3. A parameter Q is used for slag network to represent its degree of polymerization. This problem can be resolved by introducing the concept of optical basicity. It was shown that the optical basicity can be calculated from Pauling electronegativity.
The link between optical basicity and electronegativity makes the numerical values more understandable. Duffy and M. Ingram: J. Solids , 21 , Nakamura, Y. Ueda and J. Toguri: J. The optical basicity parameter has some disadvantages, e. The trend in predicted viscosities for different cations is the reverse of that found experimentally.
The spectroscopic study of slag structure shows the abundance of different structural units present in melt. Usually, Q n represents structural unit of slag, where n denotes number of bridging oxygen BOs and degree of polymerization of these units significantly vary with n. A structural unit fully linked with four bridging oxygens is expressed as Q 4 , while a single tetrahedron unit having no BO is represented as Q o and so on.
Schramm, B. De Jong and V. Parziale: J. New techniques such as X-ray and neutron diffraction, nuclear magnetic resonance, Raman and XPS spectroscopy played pivotal role to develop knowledge bank about structure of slag in last few decades. Our knowledge about structure of silicates developed rapidly due to precise data from these state of the art technologies which is integrated with structural thermodynamic models and physical property data.
In order to obtain information about the short range and intermediate range order in materials diffraction and spectroscopic methods are used.
Most of the information of slag structure such as bond lengths, bond angles, and the coordination orientation and behavior of specific atoms is obtained from X-ray near edge absorption spectroscopy XANES and extended X-ray absorption fine structure EXAFS using derived values of the radial distribution function RDF subjected to Fourier transformation. When X-rays strike a sample, electrons are emitted from it. The energy of emitted electron is determined and the energy levels are utilized to determine both the coordination number and the valence state of atoms. Marumo, Terra Science Publishing, Tokyo, , Warren, H.
Krutter and O. Morningstar: J.
Bancroft, M. Fleet, X. Feng and Y. Pan: Am. Kasrai, M. Feng, K. Tan and B. Yang: Solid State Commun. The vibrational, rotational, and other low frequency modes in a slag system are investigated using Raman spectroscopy. The analysis of Raman spectra identified the different structural components of system. Excitation of the sample produces vibrations as well as rotations, with Raman spectroscopy these excitations can be detected in the visible region.
The vibrations produce intense and partly polarized Raman lines, or produce weak polarized lines. In crystalline phases the lattice vibrations are dominated by the silicate species and the vibrations produce well defined Raman lines. However, in both quenched glass and liquids, the vibrations produce broad bands which must be deconvoluted into the various polymeric species.
Individual bands correspond to individual Q species and the concentrations of these species can be determined by calculating the areas under the individual peaks. Deconvoluted a Raman 43 b XPS 2 spectra of blast furnace type slag. Wang, Q. Shu and K. Chou: Steel Res.
Fourier transform infrared spectroscopy utilizes infrared spectrum absorption or emission technique to obtained raw data which is further converted into actual spectrum by Fourier Transformation.
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FTIR technique is normally use for qualitative analysis instead of other analytical techniques because the deconvolution of the spectra is relatively easy. It remains a fundamental tool to identify structural units present in melts. On the other hand, FTIR utilizes the dipole moment change as working principle.
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XPS is a technique used to determine the chemical and physical composition, and electronic state of a constituent element in sample to a depth of 10 nm. In order to obtain XPS spectra, the target materials are exposed to X-rays. The number of electrons coming out of the material surface and their respective energies are recorded. Nuclear magnetic resonance is a phenomenon which is observed in nuclei of certain atoms which are placed in a magnetic field to absorb electromagnetic radiations and then exposed to an alternating magnetic field. NMR spectroscopy has been used extensively, for the identification of silicate melt structures.
Smith, R. Kirkpatrick, E. Oldfield and D. Henderson: Am. Sukenaga, N.
Understanding the Structure and Structural Effects on the Properties of Blast Furnace Slag (BFS)
Saito, K. Kawakami and K. Numerical simulations are also an important tool to study the atomic level structure of slags. The information obtained from simulation is utilized to study the structure of slags. The advantage of these approaches, ab initio and molecular dynamics is that they provide access to the melt structure which is not reachable with experimental methods. Ab initio simulation is an important tool to study the electronic structure and related properties of materials.
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McConnell, A. De Vita, S. Kenny and V. Heine: Phys. The metal-slag separation, reaction kinetics, permeability of the intermediate gases used for reduction and heat transfer efficiency are affected by properties of BFS. The viscosity of silicate slags is depending upon degree of polymerization of slag structure, cation effects and temperature.
Arrhenius or Weymann equations are used to express the relationship between viscosity and temperature, given as follow:. The viscosity of BF slag is probably the most valuable property in industrial high temperature processes. The degree of polymerization has positive effect on viscosity of slag which means that viscosity increases with increasing degree of polymerization of slag structure and vice versa.
The viscosity also increases with increasing concentrations of network formers oxides, decreasing concentrations of both network breakers and fluxes. Bockris, J. Mackenzie and J. Kitchener: Trans. Faraday Soc.