Corrosion Study of Electroless Ni-P-Al<sub>2</sub>O<sub>3</sub>- ZrO<sub>2</sub> Nanocomposite Coatings in Paper Mill Digester

Abstract

Objectives: To acquire more production and better quality of paper. The pulp and paper mill digesters are currently operated at increased temperature and sulfidity which results from increase in uniform and localized type of corrosion attacks on digester materials. Methods/Statistical Analysis: The current study intends to search corrosion protection mechanism in non-conventional (inclusion of 2.5gpl of each synthesized Al 2 O 2 and ZrO 2 nanoparticles into acidic EL Ni-P matrix, 2 hr constant stirring, temperature range 85 to 900C)alternate materials with liquor composition, concentration, and operating parameters. The NiPAZr(MS-Ni-P-Al 2 O 2 -ZrO 2 ) nanocomposite coatings were deposited on mild steel (MS)substrate by electroless (EL) technique. To carry out an in-plant test, the coupons of conventional material (mild steel, MS) and non-conventional materials (NiPAZr as-plated and NiPAZr heat treated at 3800C) were exposed in mid part (near strainer) of 2 nd batch digester of SPML (U.P., India) for six months duration. The exposed corroded coupons after removal from the digester were cleaned mechanically and chemically (ASTM specifications) and analyzed for uniform and pitting type corrosion attack. Findings: From corrosion point among all the coupons, it is concluded that mild steel (MS)coupon experiences the highest corrosion attack while NiPAZr (as-plated and heat treated) coated coupon slow corrosion attack. The mid part of the digester where the test rack was fitted is mainly affected due to general and pitting corrosion. Therefore, this in-plant test suggests that in applied conditions, it would be better to construct/fabricate the mid part of the digester with EL NiPAZr nano-composite (as-plated or heat treated at 3800C) coatings. These EL nano-composite coatings can be a cost effective option in contrast to conventional materials (MS, SS304L, SS316L and SS2205 etc.) for the paper industrialist to construct/fabricate especially mid part of the digester. Application/ Improvement: For making/fabrication mid part of the digesters these nano-composite coatings can be a cost effective option in comparison to conventional materials as well as can be applied up to very high-temperature range