Effect Of Doping On The Solid Solution Character Of MgO And The Microstructure Of Alite In High-magnesium Clinker

With more and more high-magnesium limestone being used for clinker, the problem with high growth of early strength and low growth of later strength in these high-magnesium clinkers has always perplexed the industial application. So once this problem is solved, it will be of important significance for producing high quality clinkers by using high-magnesium limestone.This article relied on the National Key Bisic Research Program (NKBRP) 2009CB623100, and tried to provide the theoretical basis to solve the above problem by starting from solid solution of MgO and the crystal transformation of C3S. Several conclusions could be abtained according to these experiments and analysis:(1) In single mineral, the increase of MgO, SO3 or temperature could be beneficial to the solid solution of MgO in C3S unit cell. The highest solid solution of MgO at 1450℃was about 2%, when MgO was 5%or MgO was 4%and SO3 was 4.8%.(2) In high-magnesium clinker, with the increase of F/SO3 and ZnO, f-MgO decreased. However, f-MgO deceased rapidly when SO3 was lower than 2.4%and the effect of ZnO appeared only when SO3 was lower than 1.6%; with the temperature increase, f-MgO decreased significantly, and there was a specific range of f-MgO at different temperature, f-MgO was between 2.5%-3.5%at 1250℃, between 2.0%-2.5%at 1350℃, and between 1.6%-2.0%at 1450℃; in the clinker with 5% MgO, the minimum of content of f-MgO was about 1.6%at 1450℃.(3) In high-magnesium clinker, with SM increase, the solid solution of MgO increased. Especially at 1450℃, f-MgO decreased from 1.7%to 1.2%when MgO was 3%and from 2.2%to 1.9%when MgO was 5%in clinker respectively. This meant MgO was more likely to form the solid solution with silicate phase at high temperature, compared to the intermediate phase.(4) In single mineral, the variation of cell parameter of C3S was related to the quantity and style of impurities; when F/SO3 was 0.7%/0.8%, Cu2+ replacing Ca lead to an apparent change on crystal axis a, while Zn2+replacing Ca2+lead to a change on crystal axis c; with MgO increase, the crystal axis a of C3S was stretched and theβdecreased; with SO3 increase, only crystal axis a was a little larger; the increase of temperature could decrease all the cell paremeters of a, b, c andβ.(5) In the Alite extracted from high-magnesium clinkers, the increase of SO3 led to a smallerβwhile ZnO resulted a larger one; the cell parameters of a, b, c and (3 were also decreased significantly when the temperature increased.(6) In high-magnesium clinker, with the increase of SM and MgO, f-CaO decreased at 1250℃while increased when the temperature was higher than 1350℃; with the increase of SO3 and temperature, the aluminum compound changed from CnA7-CaF2 to C12A7 and then C3A; the doping of MgO and ZnO could affect the formation of minerals only through their fluxing action; when content of SO3 introduced from CaSO4 was larger (>3.2%), C4A3 S had formed at 1250℃and decomposed completely at 1450℃while CaSO4 could be found heavily at 1250℃and decomposed partly at 1450℃; when F/SO3 was 0.7%/0.8%, there was a pefect petrographic structure in clinkers.