Investigation of calcium carbonate scaling inhibition and scale morphologyby AFM

The calcium carbonate scale inhibition by two inhibitors, polyacrylic acid (PAA) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), has been stud ied in two heat transfer systems: recirculating cooling water and pool boil ing systems. It is found that PBTCA has a better inhibition effect than PAA under identical conditions. The inhibition effect increases with increasin g fluid velocity for the cooling water system, whereas in the presence of i nhibitors, the fluid velocity has less effect on the scaling behavior. When the initial surface temperature increases, the inhibition efficiency decre ases. In the presence of inhibitors, the scaling behavior is insensitive to the change of surface temperature. The relationship between the inhibition effect and the fractal dimension has also been investigated. The results s how that the fractal dimension is higher in the presence of inhibitors. The better the inhibition effect, the higher the fractal dimension. XRD and FT IR analyses demonstrate that for the CaCO3 formed in the pool boiling syste m, the content of vaterite increases with the increase of inhibition effect s. The metastable crystal forms of vaterite and aragonite are stabilized ki netically in the presence of inhibitors. The step morphology has been obser ved by atomic force microscopy. It is shown that the step space on the CaCO 3 surface increases in the presence of inhibitors. Moreover, with the incre ase in inhibition effect, both the step space and the fractal dimension inc rease. Step bunching is also found and discussed in this paper. (C) 2001 Ac ademic Press.