Effects of phosphorus on corrosion resistance of electroless nickel in 50% sodium hydroxide

Journal Article · Wed Jun 01 00:00:00 EDT 1994 · Corrosion (Houston); (United States)

DOI:https://doi.org/10.5006/1.3293524· OSTI ID:7072800

Zeller, III, R L ^[1]; Salvati, L ^[2]

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1. Occidental Chemical Corp., Grand Island, NY (United States)
2. Abbott Labs., Abbott Park, IL (United States)

Nickel (Ni) and electroless nickel (EN) coatings are used extensively in caustic soda (NaOH) service. The corrosion resistance of an EN coating is dependent upon phosphorus (P) content, but not in the trend expected. High-phosphorus EN (HPEN) coatings have poorer corrosion resistance in hot, concentrated sodium hydroxide (NaOH) than low-phosphorus (LPEN) and medium-phosphorus (MPEN) coatings, which have a corrosion resistance comparable to Ni. The purpose of this work was to quantify the effect of P in EN coatings on their corrosion resistance in 50% NaOH at room temperature (RT). Electrochemical techniques were used to investigate the corrosion processes. X-ray photoelectron spectroscopy (XPS) was used to characterize coating surfaces. Very low corrosion rates ([<=] [mu]m/y) were measured for all coatings. It was proposed that the detrimental effect of P in EN coatings exposed to a concentrated NaOH environment was a result of the higher solubility of nickel phosphate (Ni[sub 3][PO[sub 4]][sub 2]) relative to nickel hydroxide (Ni[OH][sub 2]) and nickel oxide (NiO). This mechanism predicted an inverse relationship between the thickness of the protective film on EN and its P content, which was consistent with experimental observations.

• OSTI ID: 7072800
• Journal Information: Corrosion (Houston); (United States), Vol. 50:6; ISSN 0010-9312
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
NICKEL
CORROSION RESISTANCE
PHOSPHORUS
METALLURGICAL EFFECTS
SODIUM HYDROXIDES
CORROSIVE EFFECTS
PROTECTIVE COATINGS
ALKALI METAL COMPOUNDS
COATINGS
ELEMENTS
HYDROGEN COMPOUNDS
HYDROXIDES
METALS
NONMETALS
OXYGEN COMPOUNDS
SODIUM COMPOUNDS
TRANSITION ELEMENTS
360105* - Metals &amp; Alloys- Corrosion &amp; Erosion