Determination of the Critical Potentials for Pitting, Protection, and Stress Corrosion Cracking of 67‐33 Brass in Fluoride Solutions

Abstract

Pitting potentials E~, and protection potentials, E~p, have been determined for a-brass (33% Zn) using a cyclic polarlzahon method. Increasing the F concentratmn shlJ~s the crlhcal potential to more active values. The pitting potentials, Ep, and protection potentials, Ep depend on the logarithmic concentration of F-ions according to the equations: Ep = a + b log [F ] and Epp = a + b log [F ~. Slow strain rate tests (SSRT), at a strain rate of 5 • 10 5 s-~, were performed under open-circuit and potentiostatic conditions to study the stress corrosion cracking (SCC) characteristics of the a-brass in NaF solutions of various concentrations (pH 6.8) at 25~ The minimum concentration of NaF that caused intergranular stress corrosion cracking (IGSCC) was 1 • 10-4M. This concentration, was also the critical level for repassivation, observed in cyclic polarization tests. These results demonstrate a good correlation between the electrical and the mechanical breakdown of the passive film. In the presence of 10 ~M NaF the potential range for IGSCC was -150 to -50 mV (SCE). These critical potentials were restricted to the stable passive potential range and also fell within the potential-pH region where Cu~O was stable. The formation of a Cu20 film on the brass after polarization in the passive region was confirmed by x-ray diffraction (XRD). At more noble potentials and at cathodic potentials below the Cu20 domain, the failure mode was ductile fracture. These observations of IGSCC of the brass in fluoride solutions support a film rupture-dissolution mechanism.

Selective Dissolution of Alpha Brass in Acid Noncomplexing Media

“…Several workers have addressed the mechanism and consequences of the selective dissolution of zinc. [1][2][3]11,13,14,22,[26][27][28] The process leads to relative enrichment of the alloy surface with copper atoms, which become more mobile than they were in the parent alloy. Consequently, the alloy surface becomes unstable by virtue of the mole fraction of copper ͑which is higher than the equilibrium value in the parent alloy͒, the vacancies injected in the lattice, and the lower forces binding these remaining copper atoms to the alloy surface.…”

“…The behavior of the concentration of Zn +2 is related to the fate of the Cu* atoms on the surface. [1][2][3]11,13,14,[26][27][28] At potentials below E t , Cu* atoms remain on the surface and hence block the dissolution of Zn atoms from the underlying layers of the alloy. Above E t , copper atoms also dissolve out of the alloy into the electrolyte, exposing the underlying Zn atoms, which ionize under a high driving force.…”

Electroless Nickel-Phosphorus Composite Coatings

“…Hence, how to improve the particle dispersion in electroless bath is a key problem. Lee (2012a) has found that the dispersion of nano-TiO 2 particles in the plating bath is affected by the concentration of nano particles in the plating bath and magnetic stirrer speed. The agglomeration of TiO 2 particles in plating solution is reduced by ultrasonic dispersion of particles for 15 min followed by agitation of the bath at a constant speed of 100 rpm for one hour deposition period.…”

Study of Hardness and Corrosion Resistance of Electroless Ni-P-TiO2 Composite Coatings

“…Such coatings are extensively used in industries due to their excellent mechanical, tribological, soldering and brazing properties (Sahoo and Das, 2011; particles present in the coated layer. Coating with fewer amount of titanium particle has lower hardness and vice versa (Momenzadeh and Sanjabi, 2012;Lee, 2012).…”