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

Abstract

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.

The paste hydration of brownmillerite with and without gypsum: a time resolved synchrotron diffraction study at 30, 70, 100 and 150 °C

“…The mean particle size is 20 mm and the BET surface area 0.22 m 2 g 21 . Some minor impurities are present (Table 1), but the material is purer than the interstitial ferrite phase of oilwell cement production clinkers, 8,9,38 which typically contains several percent by weight of MgO and SiO 2 . Gypsum CS ¯H2 was BDH AnalaR laboratory reagent grade.…”

“…[5][6][7] In construction cements both phases are present while in oilwell cements C 3 A is absent or present in trace amounts only. 8,9 In oilwell cements the clinker ferrite phase is richer in iron than in most construction cements, with a mean A/F generally around 0.8.…”

The site occupancy of Mg in the brownmillerite structure and its effect on hydration properties: an X-ray/neutron diffraction and EXAFS study

“…The distinct preference of Al atoms for the tetrahedral sites (and correspondingly Fe for the octahedral sites) was ®rst proposed by Smith (1962) on the basis of the observed intensity distributions for 0k0 re¯ections. Brownmillerite in real cement is more complex as a result of additional minor substitutions for Fe and Al by Mg and Si, as well as Ti (Harrisson et al, 1985;Bergstrom et al, 1994 (Gollop & Taylor, 1994), suggesting that Fe and Al are both replaced to the same degree. There are, however, dif®culties in making synthetic brownmillerite samples with substantial Mg and Si substitution; it is claimed (Maki et al, 1995;Neubauer et al, 1996) that Mg/Si substitute up to a maximum level of about 4% by weight, but this value is not universally accepted.…”

From selective dissolution to crystal chemistry of brownmillerite in sulfate resisting cement

“…These structural formulas are similar to those found in the literature for sulfate resisting cements 8,9,10,17,[47][48][49][50] and oil well cements. [51][52][53] The microprobe results show that brownmillerite is highly inhomogeneous, with some areas very rich in Al. This was also reported by Landa-Canova et al 8 and Richardson et al 53 using transmission electron microscope.…”