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Scale formation is a serious problem often observed in heat transfer equipments. Barite, calcite and aragonite are some of the major components of scale. Control of scale formation is usually achieved through usage of scale inhibitors/chelating agents. Here we report the effect of ethylene glycol-O,O’-bis(2-aminoethyl)-N,N,N’,N’-tetraacetic acid (EGTA) on the morphology and polymorphism of CaCO3 when synthesized from CaCl2 solution using Na2CO3 at three different temperatures, 60, 80 and 100°C. The samples were characterized using XRD, FTIR and SEM techniques. The details revealed that EGTA stabilizes aragonite more efficiently at 60°C and with raise in temperature formation of calcite is predominant. The study revealed an unusual and novel datura pod like morphology for calcite. [ABSTRACT FROM AUTHOR]

CaCO 3 scale deposition from its sludge was studied on copper substrate. Ethylenediamminetetraacetic acid was used as chelating agent and tested for its influence on the deposition. The experiments were carried out at 60 and 100 °C and the effect of direct heating and indirect heating was studied. The samples were characterized by XRD, FTIR and SEM techniques. The data revealed that the complex forming nature of EDTA, the shape of the crystallite and area of contact are the key factors for the deposition of CaCO 3 on metal surface. [ABSTRACT FROM AUTHOR]

Abstract: Calcium carbonate was precipitated from calcium chloride using sodium carbonate in the presence of diethylenetriaminepentaacetic acid (DTPA) between 60 and 230°C. The samples were characterized by FTIR, Raman, XRD and SEM techniques. CaCO3 with different crystal morphologies such as spherolite/datura pod, dumbbell, peanut, were obtained depending on the experimental conditions. The results showed that pure aragonite, calcite and vaterite were formed at low, moderate and high temperatures respectively. A binary mixture of calcite and vaterite was resulted between 150 and 200°C. The data suggested an unusual conversion of stable calcite to meta stable vaterite at higher temperature in presence of DTPA. The study revealed a novel methodology for the exclusive/individual preparation of different crystalline polymorphs of CaCO3. Formation of pure vaterite above 200°C divulged the possibility of DTPA as a potential scale inhibitor and boiler sludge conditioner at elevated temperatures. [Copyright &y& Elsevier]

The effect of different chelating agents on the crystallization of CaCO 3, polymorphism and morphology of CaCO 3 in the presence of barium were studied at 100 °C. The samples were characterized using FTIR, Raman spectroscopy, XRD and FESEM techniques. The study revealed that without any chelating agents, in the presence of different volumes of 0.1 M Ba2+ ion solution, stabilization of a binary mixture of rhombohedral calcite and flower-like vateritewas facilitated. In the presence of EDTA, the phenomenal transformation of calcite to vateritewas observed. Pure calcite has resulted in the presence of Nitrilotriacetic acid (NTA) in the presence of Ba2+ ions. Blending EDTA with NTA favored a binary mixture of spherical vaterite and calcite. The probable mechanism for stabilization of various polymorphs by the additives and effect of blending of additives for better scale inhibition efficiency has been discussed. [Display omitted] • Investigated the individual and synergistic Effects of Ba2+, EDTA and NTA on Polymorphic and Morphological changes of CaCO 3. • Presence of EDTA accentuated the vaterite directing behavior of Ba2+ ions. • EDTA-NTA combination resulted into a rare spherical morphology for calcite. [ABSTRACT FROM AUTHOR]