水垢晶体的形成及变化规律研究

Study on the Formation Process and Transformation of Fouling Crystal

加热含有0.001 mol/L的CaCl2和NaHCO3的水样,在保持蒸发与补水速度相同的条件下,利用扫描电子显微镜（SEM）研究碳钢挂片表面沉积水垢颗粒的生长过程,聚集形态和晶体结构的变化。结果表明：挂片表面首先析出无规则聚集的球状和片状颗粒;15 min后微小的球状或片状颗粒出现定向排列的趋势,形成表面十分粗糙的针棒状堆积体,其轴向生长速度达1.0-1.5μm/min;随着蒸发时间的延长,在加热2 h时,针棒状堆积体由根部开始晶化,逐步形成棱角分明的六棱柱状晶体。晶体表面也会吸附新生球形颗粒不断的沉积,同时在挂片的表面还会形成许多直径约为2μm,厚度约0.1μm的六边形片状球霰石颗粒,片层颗粒无规则的相互支撑和聚集,部分颗粒以直立方式生长。6 h后已形成的六棱柱状晶体颗粒的顶部形态开始发生变异,形成顶端带有数十根针状分枝的孪生晶体。而部分球霰石颗粒的聚集体在加热3 h后逐步向斜六面体方解石转变。

The changes of growth process, aggregation morphology and crystal structure of fouling on the surface of Carbon Steel pieces were investigated by scanning electron microscope （SEM）. The concentration of CaCl2 and NaHCO3 solution were all 0. 001 moL/L and the evaporation rate and complement rate kept balance during heating. The results show irregular spherical and flaky aggregates precipitate on the surface at first. The rough surface of aggregates show oriented arrangement and form needle-like and rod-like accumulation body which is the rudiment of the aragonite after fifteen minutes. The growth rate of axial direction is 1.0-1.5 μm/min. After heating for two hours the needle-like and rod-like accumulation body starts to crystallized from the root and gradually form hexagonal complex. The crystal adsorbs newborn spherical particles and deposits continuously on the surface, meanwhile hexagon sheety vaterite with diameter of 2 μm and thickness of 0. 1 μm appears on the pieces. The sheety particles support each other irregularly and accumulate. Some particles grow straightly. After six hours the top of the hexagonal complex changes Some of vaterite gradually turn to rhombic to twin crystal whose the top has numbers of needle branches. hexahedron after heating for three hours.