Scale and Corrosion Prevention in Cooling Water Systems Part I : Calcium Carbonate
This paper presents the results of study that was undertaken to investigate the ability of a new antiscale, polyacrylamide in solving problems found in cooling water systems. The effects of the polymer on C-steel and copper dissolution in synthetic cooling water environment were studied through scale, Tafel, and Linear polarization measurements. The results obtained from this study showed that the new antiscale polymer can decrease scale build-up growth under experimental conditions. Both linear and Tafel polarization studies indicate that the polymer acted as an anodic type corrosion inhibitor on C-steel and mixed-type on copper, thus reducing metal dissolution. Morphological investigations of calcium carbonate deposits on both C-steel and copper surfaces were studied by optical microscopy. The polymer used in this study appears to have an excellent crystal modification effect on reducing calcium carbonate scale. The antiscale effect results from changes in crystallization behavior promoting bulk solution precipitation rather than formation of adherent scale.
The threshold scale inhibition phenomenon
Abstract The precipitation of calcium carbonate has been studied in the absence and presence of hydroxyethylidene-1, 1-diphosphonic acid (HEDP). At ambient temperatures, a stable, threshold inhibited solution of calcium carbonate can be made in the presence of HEDP. However, this solution is thermally unstable and its calcium ion activity is abnormally low indicating the formation of ion pairs or embrionic crystals. Heated, HEDP containing calcium bicarbonate solutions are stabilised by a different mechanism. The rate of carbon dioxide evolution (and hence of calcium carbonate precipitation) is reduced because of a pH rise caused, indirectly, by the inhibitor.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.