Materials Performance

JUN 2016

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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47 NACE INTERNATIONAL: VOL. 55, NO. 6 MATERIALS PERFORMANCE JUNE 2016 CaCO 3 inhibitors. As illustrated, increasing the dosage from 10 to 40 ppm shows a slight decrease in the performance of all phosphonates except for PAPE MP. The observed behavior of phosphonates may be explained by calcium phosphonate salt for- mation, which effectively decreases the solution concentration of phosphonates. Based on the data presented for the high SI sy st e m , t h e p h o sp h o n a t e ra n k i n g i s : PAPEMP > PBTC ≈ AMP ≈ HPA ≈ HEDP. It is interesting to note that a similar trend has been reported for calcium ion tolerance of phosphonates. 9 Calcium Phosphate During the last two decades, the prob- l e m of C a 3 ( P O 4 ) 2 s c a li n g h a s b e c o m e increasingly important. Higher orthophos- phate levels are being encountered in cool- ing water due to the use of low-quality makeup water, increased water reuse, and the use of organophosphonate as a corro- sion and scale inhibitor, which degrades to orthophosphate. The increased orthophos- phate levels, combined with alkaline oper- ating conditions, can lead to the formation of insoluble Ca 3 (PO 4 ) 2 scale that is normally attributed to hydroxyapatite (HAP). In cooling water systems, however, it is not the HAP that is initially formed; instead a precursor phase is formed, which is widely known as amorphous Ca 3 (PO 4 ) 2 (Ca/P). Us i n g t h e e x p e r i m e n t a l p r o t o c o l described earlier, a series of Ca/P precipita- tion experiments was performed in the presence of 10 and 50 ppm of phospho- nates. Data presented in Figure 3 reveal that phosphonates exhibit poor to medio- cre (<40%) performance at 10 ppm concen- trations. Increasing the phosphonate con- centration fivefold—from 10 to 50 ppm— results in a significant decrease (~30%) in HPA, AMP. HEDP, and PBTC performance. Under similar conditions, PAPEMP perfor- mance is significantly improved—from 42 to 93%. Based on the data presented, the effec- tiven ess of phosphonat es as Ca 3 (P O 4 ) 2 inhibitors follows the trend PAPEMP >> HPA, AMP, HEDP, and PBTC. As discussed before, the observed trend in phosphonate performance may be attributed to differ- ences in calcium ion tolerance of these phosphonates. FIGURE 3 Ca 3 (PO 4 ) 2 inhibition by phosphonates at varying dosages. FIGURE 4 Fe 3+ stabilization by phosphonates at varying concentrations. Iron Stabilization Among the various dissolved impurities in natural waters, metal ions, when present at a few ppm, pose the most serious prob- lems in many domestic and industrial applications. These metal ions including aluminum, copper, iron, manganese, and zinc, form insoluble hydroxides under acidic and/or alkalin e conditions and deposit on equipment surfaces. They also influence the performance of scale inhibi- tors and dispersants commonly used in water treatment formulations. Removal of these heavy metal ions from industrial wastewater is of primary concern because they cause contamination of water bodies and are also toxic to many life forms. In aqueous solutions, depending upon the water chemistry, ferric ions (Fe 3+ ) form a variety of both soluble and insoluble com- plexes. The iron stabilization used in this experiment refers to the ability of the phos- ph on at e s to for m s o lubl e c ompl e xe s , inhibit the formation of hydroxocomplexes, and/or disperse. In practice, it may be dif- ficult to differentiate between truly soluble and very finely dispersed particles. Under the conditions employed, % stabilization is defined as the concentration of the ionic species that is not removed by filtration through a 0.22-µm filter. A Multifunctional Additive for Controlling Inorganic Foulants in Industrial Water Systems

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