A consecutive decomposition–sintering dilatometer method to study the effect of limestone impurities on lime microstructure and its water reactivity

In this paper we develop a consecutive decomposition–sintering dilatometer method (CDSD) to study the effect of limestone impurities on lime microstructure features that are formed during the limestone decomposition. Two experimental parameters, the changing in slope of the dilatometer trace (β) and the total shrinkage of the produced lime in the subsequent sintering stage (Σ), have been shown to be influenced by the impurities. The first limestone investigated was poorly recrystallized with heteroblastic texture and a total amount of impurities equal to 2.2 wt%. The second limestone was strongly recrystallized limestone with equigranular xenotopic fabric and with 0.7 wt% total impurities. ˙β and Σ turns-out to be 13×10−4 [min−1] and 1.43 wt% for the lime from the first sample, and 3×10−4 [min−1] and 11.2 wt% for the calcium oxide from the second one. Sintering steps among CaO grains catalysed by the escaping CO2 lead, in the first lime–limestone matrix, to lime grains of irregular shapes and average dimensions between 3 and 7 micron. In the second lime–limestone matrix, liquid phases between CaO and impurities promote locally denser oxides regions mixed with others where solid-state sintering steps occurs. In these regions the average grain dimensions are 6–10 micron. CDSD methods allow to understand the lime water-reactivity vs. the emperature of lime formation tests in term of competition between coarsening and densification phenomena occurring in the temperature range 700–1200 ◦C and in air. Keywords: Sintering; Thermal expansion; Calcination; CaO; Dilatometry