Materials Performance

DEC 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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53 NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIALS PERFORMANCE DECEMBER 2014 Effect of Iron Oxide Concentration on Polymer Performance To understand the impact of Fe 2 O 3 con centration on the performance of a poly mer, several precipitation experiments were made in the presence of 3.50 mg/L of HP1 and varying amounts of Fe 2 O 3 . Figure 2 presents Ca 2+ vs. time for experiments made in the absence of HP1 and varying amounts of Fe 2 O 3 (Curves A, B, and C). In the absence of HP1, the addition of 25 or 100 mg of Fe 2 O 3 to the CaCO 3 supersatu rated solution did not exhibit any signifi cant effect on the rate of CaCO 3 precipita t i o n . F i g u r e 2 a l s o p r e s e n t s C a 2 + concentration vs. time collected for experi ments conducted in the presence of 3.5 mg/L of HP1 and 0 mg and 50 mg of Fe 2 O 3 (Curves D and E). In the absence of Fe 2 O 3 , CaCO 3 precipitation is preceded by an induction time. Under similar precipitation conditions, the addition of 50 mg of Fe 2 O 3 resulted in a marked impact on the induc tion time. Induction time obtained in the presence of 50 mg of Fe 2 O 3 is ~2.5 h (Curve D) compared to >10 h (Curve E) observed w hen Fe 2 O 3 is absent. The decrease in induction time and corresponding %I val ues (83% vs. 44%) may be attributed to the depletion of HP1 via adsorption on Fe 2 O 3 particles, causing decreased performance of HP1. The inf luence of var ying amounts of Fe 2 O 3 on the performance of HP1 was also investigated. Results presented in Figure 3 shows that adding a small amount (10 mg) of Fe 2 O 3 exhibits antagonistic effects on the performance of HP1. With 5.0 mg/L of HP1 and 10 mg of Fe 2 O 3 the %I value obtained is 80%. This compares to 88% obtained with out Fe 2 O 3 . Figure 3 also shows that HP1 performance decreased with an increasing amount of Fe 2 O 3 in th e CaC O 3 sup er saturated solutions. To overcome the negative impact of Fe 2 O 3 on HP1, a series of precipitation experiments were conducted at constant supersaturation and with 50 mg of Fe 2 O 3 and varying concentrations of HP1. Figure 4 presents the results of these experiments. With and without 50 mg of Fe 2 O 3 , CaCO 3 FIGURE 1 Effect of mixing time on the performance of HP1 (5 mg/L) in the presence of Fe 2 O 3 . FIGURE 2 Performance of HP1 (3.5 mg/L) in the presence and absence of Fe 2 O 3 . inhibition increased with increasing HP1 concentrations. To achieve a similar %I value (>85%) it required 3.5 mg/L of HP1 without Fe 2 O 3 and ~15 mg/L of HP1 with Fe 2 O 3 . To overcome the antagonistic influ ence of Fe 2 O 3 on the performance of the inhibitor, almost ~4 times the amount of HP1 would be required to inhibit CaCO 3 precipitation. In a calcium sulfate (CaSO 4 ) dihydrate scaling system, ~2.5 times the amount of HP1 in the presence of Fe 2 O 3 was required to achieve >85% inhibition. 2 While it is known that homopolymers containing –CO OH group are ef fective inhibitors for various scales (e.g., calcium fluoride [CaF 2 ], CaCO 3 , and barium sulfate [BaSO 4 ]), 35 copolymers containing –COOH a n d o th er fu n c ti on al g ro up s su c h a s –COOR, –SO 3 H, –CONR 1 R 2 , etc., are excel lent inhibitors for tricalcium phosphate [Ca 3 (PO 4 ) 2 ] and also effective dispersants for Fe 2 O 3 . 67 To investigate the influence of Fe 2 O 3 on the performance of homo, co, and terpolymers, a number of experiments

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