Dicalcium silicate solid solutions

Abstract

Studies on the manner of combination of NazO in portland cement clinker have revealed crystalline phases of chemical composition near that of 2CaO.SiOz, but possessing properties quite different from those heretofore reported for the {3 form of this compound. These phases result when certain compositions in the quaternary systems NazO-CaO-AhOa-Si02 and NazO-CaO-Fe20a-SiOz are quenched from high temperatures. Optical, thermal, and X-ray diffraction data have been obtained which indicate that they are solid solutions of NazO and Ah03 and of NazO and FezOa, in a high-temperature form of 2CaO.SiOz having a hexagonal structure. There is also evidence that this hexagonal lattice is the fundamental structure of the a form of 2CaO.SiOz.In the pure compound the a-{3 inversion temperature has been reported to be 1,420° ± 2° C, whereas in the phases described in this paper the transformation temperature may be lowered by as much as 245° C, e. g., to 1,175°± 10° C. The inversion from a to {3 is accompanied by considerable ex-solution of dissolved material, showing that the extent of solid solution of these oxides in {3-2CaO.SiOz is much less than in the a form. As a result of this precipitation the grains of {3

Phase equilibrium relations in a portion of the system Na-2-O-CaO-Al-2O-3-SiO-2

“…2 If there is any solid solution in the f3-2CaO.Si02 it must be very small. However, in several compositions in the interior of the system the 2CaO.Si02 phase corresponded in properties to one of the a-2CaO.Si02 solid solutions described in a previous paper [6]. The extent of this solid solution was not determined and the relation which it may bear to the stability of the 3CaO.SiOz has not been investigated.…”

“…Consequently, it must be concluded that it is not a distinct compound but rather a solid solution phase. As mentioned in the previous paper [6], it is probable that the twinning results from the inversion of the 2CaO.Si02 from the a to the .B form.…”

“…Measurements of indices of refraction have indicated that solid solution of N a20 and Al20 a may OCClli" to a limited extent in !3-2CaO.Si02 [6]. There is evidence that such solid solution may also take place in the ternary system N a20-CaO-Si02.…”

“…Such pairs occur also with Na20.80aO.3AI20a, but to a lesser extent, while in the pattern of 30aO.A120 a only single lines occur. In table 6 are shown the interplanar spacings calculated for the charge prepared from the mixture, in comparison to the more important lines of 30aO .AI20~ and N a20 .80aO .3AI20 3• CaO-N a20.AbOa, the 2CaO.Si02 appeared to be one of the a-2CaO.Si02 solid solutions described in a previous paper [6]. No definite region of occurrence for this phase in contrast to .B-2CaO.Si02 was observed, and the amounts of N a20 and Ab03 in solid solutions were not determined.…”

“…Consequently, such data will not be considered here. A previous paper from this laboratory by one of the present authors [6] dealt with solid solutions which the compound 2CaO.Si02 may form under suitable conditions in the system N a20-CaO-AI20 a-Si02, as well as in the system Na20-CaO-Fe20a-Si02. It was shown that these solid solution phases have a hexagonal crystal structure and that this structure very likely is fundamentally that of the ex form of 2CaO.Si02.…”