Transmission electron microscopic study of ferrite in sulfate-resisting Portland cement clinker

The oxide interstitial material in industrial clinker for sulfate-resisting Portland cement was extracted using salicylic acid and investigated by tra nsmission electron microscopy and X-ray powder diffraction (XRD). The ortho rhombic unit cell parameters of the ferrite phase were determined for two s amples by XRD: (1) a = 5.529, b = 14.542, c = 5.347 Angstrom; and (2) a = 5 .550, b = 14.526, c = 5.347 Angstrom. Energy dispersive X-ray microanalysis indicated that the ferrite normally had an atomic Al/Fe ratio of 0.7-0.9 a nd an average composition of Ca2.03Al0.72Fe0.87Mg0.11Mn0.05Si0.17Ti0.03O5 ( 13 analyses). Sometimes the composition varied on the micrometer scale, and areas with Al/Fe approaching 2 were observed. Electron diffraction indicat ed the basic structure to be of symmetry Ibm2, each layer of Bragg spots pe rpendicular to c* being accompanied by a sheet of diffuse intensity. It is proposed that the diffuse scattering is generated by a disordered array of single tetrahedral chains with reversed polarity in the brownmillerite-type crystal structure. (C) 1999 Elsevier Science Ltd. All rights reserved.