Crystallization Fouling in Domestic Appliances and Systems

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 analyzed 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