Abstract

Formation of mineral scale, particularly calcium carbonate, has long been a concern in domestic appliances such as boilers, steamers and washing machines. In this work, the formation of inorganic deposits was studied on solid surfaces and in the bulk solution as a result of evaporation of potable water. Scale precipitation was evaluated on metallic samples for various bulk temperatures, surface roughness and surface material as a function of time. The morphology of scale crystals from both surface and solution was evaluated. The microstructure and morphology of deposits on the surface were analysed using Scanning Electron Microscopy and X-ray diffraction. The present work has demonstrated that deposition rates increase as the evaporation process proceeds as expected. The nature of the material and the surface roughness both affect surface deposition kinetics. The complex relationship between the saturation ratio (as the bulk solution shows precipitation) and the kinetics of bulk and surface precipitation/deposition is demonstrated. The prevailing crystalline form of calcium carbonate is aragonite. However, the polymorphic composition of surface deposition and the bulk precipitate is influenced by temperature.

摘要

矿物质水垢的形成，尤其是碳酸钙，长期以来一直是锅炉、蒸汽机和洗衣机等家用电器中的一个问题。在这项工作中，研究了由于饮用水蒸发而在固体表面和本体溶液中形成无机沉积物。在金属样品上评估了各种体积温度、表面粗糙度和表面材料作为时间函数的氧化皮沉淀。评估了来自表面和溶液的鳞片晶体的形态。使用扫描电子显微镜和 X 射线衍射分析表面沉积物的微观结构和形态。目前的工作已经证明，随着蒸发过程按预期进行，沉积速率会增加。材料的性质和表面粗糙度都会影响表面沉积动力学。饱和比（如本体溶液显示沉淀）与本体和表面沉淀/沉积动力学之间的复杂关系得到了证明。碳酸钙的主要结晶形式是文石。然而，表面沉积和本体沉淀的多晶型组成受温度的影响。