Microstructure analysis with quantitative phase mapping using SEM-EDS and Phase Recognition and Characterization (PARC) Software: Applied to steelmaking slag

The amount, spatial distribution, and composition of phases determine the physical and chemical properties of a material and reveals information about its processing, its reactivity, or its changes due to corrosion and weathering. The characterization challenge, especially with heterogeneous multiphase materials, is to acquire quantitative microstructural data that is relevant for material properties on the macroscale. This often requires microscopy of extensive surface areas and yields very large datasets for X-ray microanalysis (Spectral Images) obtained with Scanning Electron Microscopy (SEM-EDS). The PARC (PhAse Recognition and Characterization) approach is a solution for dealing with such large Spectral Image datasets and can generate new insights about a material and lay a foundation for understanding it by close visualization of its phase distribution. In this chapter, PARC is applied to converter slag and its partial alteration products from hydration and carbonation. Converter slag, synonymous with basic oxygen furnace (BOF) slag and Linz-Donawitz (LD) slag, is a by-product of steelmaking, globally produced at about 0.2 Billion tons annually, and forms when hot metal from the blast furnace is converted into raw steel. Unlike blast furnace slag itself, converter slag is fully crystalline and not widely used as a building material. It contains C2S (Ca2SiO4,) as the most common phase, followed by Mg-wuestite ((Fe,Mg)O) and C2(A, F) (Ca2(Fe,Al)2O5) and shows no pozzolanic reactivity but instead is slightly hydraulic and easily carbonated. Analysis of unreacted converter slag as well as hydrated and carbonated systems are discussed to demonstrate how the quantitative evaluation of microstructure with PARC can be comprehensively integrated with bulk analytical observations from quantitative X-Ray diffraction, X-Ray fluorescence, thermogravimetric analysis, and density/porosimetry.