Influence of the Minute Quantity of Impurities on the Transformation of Dicalcium Silicates

Abstract

β-C2S may be obtained by water quenching from the temperatures higher than the α_??_α′ transformation. In this case, however, the batch should contain the impurities which stabilize the modifications of higher temperatures, β or even α, α′, by the substitution within crystal lattices.This paper concerns with the X-ray investigation of the stabilizing action of various amount of different impurities. Moreover, the authors discussed the stabilizing action from the results of the measurement of the change of the transformation temperatures of α′, β and γ.Cr, V, P, and B showed the marked effect especially for stabilizing β, so that it was possible to obtain β even by very slow cooling. Furthermore, the increasing substitution of Cr, V, and P for Si produced α, while that of B stabilized α′ form.Al, Fe, used alone were not powerful. They stablized β by water quenching from high temperature, but they were not able to produce α and α′ crystal.Ti, Mn have practically no power, and even the water quenched samples were contaminated by γ modification.From the results of the investigations of the series of batches containing comparatively large amount of substituting elements the authors concluded that Cr substitutes for Si4+ as the pentavalent ion. This result was compared with the action of other pentavalent ions, V, P and also with E. F. Osborn's work which showed that author's conclusion is reliable. Cr stabilizes α, β forms by the same action with V and P.The ionic radii of the stabilizing elements produce an effect on the expansion and contraction of the b-axis of β-C2S. Al3+, Fe3+, whose ionic radii are fairly larger than Si4+ are able to stabilize only β-C2S. Cr5+, V5+, P5+, the ions of nearly the same size as Si4+, may easily-substitute Si4+ and stabilize the α crystal of hexagonal symmetry from the monoclinic β form.B3+, an ion smaller than Si4+, stabilize α′ with the change of axial angle. Taking into consideration of the fact that Ba2+, a larger ion than Ca2+, can also stabilize α′, the author came in the same conclusion as that of the theory of stabilization advanced by A. Dietzel. We have discussed also the change of the size of lattices of α, α′ and γ brought about by substitution.Transformation temperatures of the modifications were measured by thermal analysis with a result that the transformation temperatures of β→α′ and α′→β were lowered in proportion to the amount of substituting agents. It was observed that the stabilization at high temperature was influenced by the nature and amount of impurities.