煅烧工艺对天然水硬性石灰中硅酸二钙晶相转变的影响

天然水硬性石灰(natural hydraulic lime, NHL)是由钙硅质原料煅烧消化所得,主要成分是硅酸二钙(Ca₂SiO₄, C₂S)和氢氧化钙(Ca(OH)₂, CH),与我国古代岩土类建筑物的兼容性较高,是一种优秀的古建筑修复材料。为探究NHL的煅烧工艺,本文使用方解石粉和石英粉作为NHL煅烧原料,设置不同冷却方式(急冷≈500 ℃/min、随炉冷却≈60 ℃/min)、恒温时间(0~180 min)和煅烧温度(1 000~1 200 ℃),通过X射线衍射和游离氧化钙(f-CaO)测试方法评价NHL烧成制度。结果表明:在低于1 150 ℃煅烧C₂S时,改变降温速率不会使C₂S在降温过程中发生晶相转变;同一温度下,随恒温时间的增加NHL煅烧产物中C₂S含量增多,在30~45 min时其含量达到该温度下的最大值,且温度升高能增加该最大值,在恒温过程中C₂S先以β-C₂S存在,随时间延长,逐渐转变为γ-C₂S;煅烧温度1 150 ℃,恒温时间45 min,急速冷却的煅烧制度可用于制备NHL。

Influence of Calcination Process on C2 S Crystal Transformation in Natural Hydraulic Lime

Natural hydraulic lime (NHL) is obtained from calcination and digestion of calcined calc-silicate raw materials. Its main components are dicalcium silicate (Ca₂SiO₄, C₂S) and calcium hydroxide (Ca(OH)₂, CH). It fits ancient lithology buildings well, and the durability is in line with the requirements of people for the restoration of ancient buildings. Using X ray diffraction and free calcium oxide (f-CaO) test methods, this paper evaluated the NHL calcination process by investigating the mineral phase composition and conversion rate of the products obtained under different cooling methods (fast cooling speed which is about 500 ℃/min compared with cooling in the closed furnace for the cooling speed of nearly 60 ℃/min), firing time (0 min to 180 min) and calcination temperatures (1 000 ℃ to 1 200 ℃) and with calcite power and silicate power. The results show that, when the calcination temperature is lower than 1 150 ℃, changing the cooling method will not cause the crystal phase transformation of C₂S during the cooling process. At the same temperature, the content of C₂S in the NHL calcined product increases with the increase of the constant temperature time, and its content reaches the maximum value at this temperature in 30 min to 45 min, and the increase of the calcination temperature increases the maximum value. C₂S first exists in β-lattice, and gradually changes to γ-C₂S over time. With a rapid cooling speed, the calcination temperature of β-C₂S is lower than that of γ-C₂S. To prepare NHL, the calcination process could be firing at 1 150 ℃ for 45 min, and with the rapid cooling system.