PHASE FORMATION MECHANISM AND KINETICS IN SOLID-STATE SYNTHESIS OF Ba-DOPED YE'ELIMITE: THE EFFECT OF Ba-DOPING CONCENTRATION ON C_(4-x)B_xA_3$ SYSTEMS

摘要

Calcium barium sulfoaluminate (abbr.C(4)(-)(x)B(x)A(3)$), one of the special cementitious minerals originated from ye 'elimite (abbr.C(4)A(3)$), has superior hydration and hardening performance. In this paper, a series of C(4)(-)(x)B(x)A(3)$ with different Ba-doping concentrations (x = 0, 0.5, 1, 1.5 and 2) were prepared, and the effect of the Ba-doping concentration on the formation was systematically investigated by the Rietveld/XRD quantitative phase analysis. The results show that BaSO4 is the essential intermediate phase for the formation of the Ba-doped ye'elimite. The solid-state reaction process of C(4)(-)(x)B(x)A(3)$ is separately expressed as two main forms, corresponding to the cases in which the Ba-doping concentration (x) is larger than and less than "1", respectively. The Jander diffusion model shows the optimal fitting for C(4)(-)(x)B(x)A(3)$ and it clearly proves that the C(4)(-)(x)B(x)A(3)$ formation becomes increasingly difficult as the Ba-doping concentration increases. The correlation between the apparent activation energy (E-a) and the Ba-doping concentration is positively well related, which can be expressed as 'E-a = 71.9x + 304' (kJ.mol(-1)).