Materials Performance

SEP 2018

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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32 SEPTEMBER 2018 W W W.MATERIALSPERFORMANCE.COM COATINGS & LININGS sodium chloride (NaCl) solution and the Al 2 O 3 slurry. The impeller specimen was rotated by a 0.75-kW motor with the driving speed con- trolled at 300 rpm. For all impellers tested, the specimen was removed from the tester at 24-h intervals, cleaned using an ultra- sonic bath, and air dried. The weight of each impeller was measured using an elec- tronic balance to determine mass loss. Results The weight loss of each impeller after the test is shown in Figure 5. The weight loss of the impeller coated with the WC-Ni brazing layer was almost nil. The weight loss of the impeller that wasn't brazed is significant as th e sp ecim en decreased 0.03 g after 96 h of testing time. By forming a passive film on the surface, Ni provided go o d c orro sion prot e ction prop er ti e s. Sriraman, et al. 14 reported that the forma- tion of the oxide film promoted by WC con- tent in the Ni improved corrosion resis- tance. Furthermore, the passive behavior of Ni b e cam e in crea sin g ly e v i d ent a s th e tim e of imm ersion increased . Th e {1 1 1}- oriented grains exhibit higher cor- rosion resistance than other orientations in Ni due to close-packed direction and the tenacity of the oxide layer in this orienta- tion. 15 For this reason, the Ni element con- tributed to the corrosion resistance of WC-Ni brazed coatings. Conclusions A WC-Ni brazing layer on the surface of the impeller for FGD was manufactured by conventional vacuum brazing with a rotary system in a furnace chamber with a mag- netic seal. The rpm of the rotary brazing process was estimated from FEM simula- tion and that corresponded with the actual brazing process. The serviceable lifetime of the impeller with an applied WC-Ni brazing layer on the surface measured almost eight times longer than the unbrazed impeller. References 1 X.M. Li , D. Reinhoudt, M. Crego-Calama, " What Do We Need for a Superhydrophobic Surface? A Review on the Recent Progress in the Preparation of Superhydrophobic Sur- faces," Chemical Society Reviews 36 (2007): pp. 1,350-1,368. FIGURE 3 (a) A schematic diagram of the vacuum furnace and (b) the actual furnace equipment. FIGURE 4 A schematic of the service life evaluation tester. evaporation in the WC sheet provided cap- illary action that drew the liquid Ni into the WC sheet. 10 The temperature was increased to 1,100 °C. The holding time at this tem- perature was determined from results of finite element method (FEM) simulation. Finally, the furnace was turned off and the specimen cooled to room temperature. Lifetime Evaluation Test A schematic of the impeller service life evaluation tester is illustrated in Figure 4. Impellers with and without the brazed WC-Ni layer were prepared . The initial weight of the specimens was measured with an electronic balance. Then the speci- mens were attached to the axis as shown in Figure 4. Aluminum oxide (Al 2 O 3 ) is usually used as the erodent in wear tests due to its high hardness. An Al 2 O 3 slurr y was prepared with an average Al 2 O 3 particle size of 150 μm . The slurry concentration was 10 wt%. The SS container was filled with 100 L of the slurry. The combined erosion and cor- rosion tests were conducted using 10 wt%

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