Interstitial material in oilwell cements: evidence from X-ray microanalysis

New X-ray microanalysis data are reported on the composition of the interstitial material in a set of eight oilwell cement clinkers and one ordinary Portland cement clinker used as a comparison. Results on the OPC clinker support the aluminate and aluminoferrite phase compositions proposed by Taylor. In the oilwell cements, the interstitial composition varies considerably from point to point. For clinkers with bulk MgO < 1·5% approximately, the compositions scatter along the line joining the Taylor ferrites. In clinkers with MgO > 1·5% the compositions deviate from the Taylor line towards lower Fe contents. The results are evidence for non-uniform aluminoferrite solid solution or fine-grained (submicron) mixtures of aluminoferrites. There was no evidence of discrete tricalcium aluminate in regions large enough for reliable microanalysis. The degree of Mg substitution in the interstitial material follows the bulk MgO concentration. The Taylor aluminoferrite phase compositions can be generalized to allow for Mg, Si and Ti substitution. The generalized alumina ratio of the interstitial material and the degree of substitution vary considerably from clinker to clinker.