scholarly journals Towards a Physical Description of the Role of Germanium in Moderating Cathodic Activation of Magnesium

CORROSION ◽  
10.5006/3624 ◽  
2020 ◽  
Author(s):  
Carol Glover ◽  
Ruiliang Liu ◽  
Beth McNally ◽  
Shooka Mahboubi ◽  
Joseph McDermid ◽  
...  
Keyword(s):  
Anodic Dissolution ◽  
Anodic Polarization ◽  
Film Formation ◽  
Surface Film ◽  
H2 Evolution ◽  
Physical Description ◽  
Alloying Additions ◽  
Testing Condition ◽  
Electrode Technique

The role played by surface film formation in moderating cathodic activation (i.e. H2 evolution associated with anodic dissolution in NaCl (aq)) was determined for an Mg-0.3Ge (wt%) alloy and contrasted with this process in pure Mg. Cathodic activation was not detected using the scanning vibrating electrode technique (SVET) during anodic dissolution of the Mg-0.3Ge alloy under either freely corroding or anodic polarization conditions. Filament tracks that initiated under the more aggressive testing condition remained electrochemically inert. However, volumetric H2 evolution measurements revealed that Ge alloying additions ‘switch off’ the remote cathodes observed on previously corroded pure Mg surfaces, while Ge additions did not eliminate the “local” cathode at the principal sites of anodic activity (which cannot be detected by SVET). As such, the quantity of H2 measured on the corroding Mg-0.3Ge alloy arises exclusively from cathodic H2 evolution at the anodic sites. Moderation of sustained cathodic activation by alloying with Ge was associated with the incorporation of Ge into the inner MgO/Mg(OH)2 layer during anodic dissolution of Mg. It is possible that entrapped Ge particles or GeO2 serve as an effective poison for H recombination in the overall H2 evolution reaction that would otherwise readily occur on freshly formed Mg(OH)2 at anodic dissolution sites.

Inhibiting Corrosion of Mg Alloy AZ31B-H24 Sheet Metal with Lithium Carbonate

CORROSION ◽  
10.5006/3625 ◽  
2020 ◽  
Author(s):  
Basem Zaghloul ◽  
Carol Glover ◽  
John Scully ◽  
Joey Kish
Keyword(s):  
Sheet Metal ◽  
Anodic Dissolution ◽  
Surface Film ◽  
Lithium Carbonate ◽  
H2 Evolution ◽  
X Ray ◽  
Corrosion Rates ◽  
Macro Scale ◽  
Corrosion Mode ◽  
Electrode Technique

The objective of this work was to determine the effectiveness of dissolved Li2CO3 as a corrosion inhibitor for AZ31B-H24 sheet metal when immersed in NaCl (aq) at ambient temperature. Corrosion rates were determined by gravimetric mass loss and volumetric H2 evolution measurements and the observed inhibition was investigated further using potentiodynamic polarization, scanning vibrating electrode technique and X-ray photoelectron surface analytical measurements. We show that dissolved Li2CO3 significantly inhibits corrosion as it reduces the corrosion rate by a factor of 10. The manner in which inhibition is achieved is rationalized by the role played by the surface film produced during corrosion in inhibiting both the anode (anodic dissolution) and cathode (H2 evolution) kinetics. Inhibition involves the suppression of the filament-like corrosion mode, albeit on the macro-scale, and associated cathodic activation. By process of elimination, we propose that the Li+ cations play a key role in inhibiting the anodic dissolution and associated cathodic activation that is required to drive the filament-like corrosion.

Effect of pH on the Grain Size Dependence of Magnesium Corrosion

CORROSION ◽  
2012 ◽  
Vol 68 (6) ◽  
pp. 507-517 ◽  
Author(s):  
K. D. Ralston ◽  
G. Williams ◽  
N. Birbilis
Keyword(s):  
Grain Size ◽  
Corrosion Rate ◽  
Anodic Polarization ◽  
Localized Corrosion ◽  
Anodic Reaction ◽  
Left Behind ◽  
Kinetics Of ◽  
Electrode Technique

Prior works show that grain size can play a role in the corrosion of a metal; however, such works are nominally executed in a single electrolyte/environment at a single pH. In this work, the anodic and cathodic reaction kinetics of pure Mg specimens with grain sizes ranging from approximately 8 μm to 590 μm were compared as a function of pH in 0.1 mol dm−3 sodium chloride (NaCl) electrolytes using anodic polarization experiments and an in situ scanning vibrating electrode technique (SVET). Anodic polarization experiments showed that grain size is important in determining overall electrochemical response, but the environment dictates the form of the grain size vs. corrosion rate relationship (i.e., pH is the overall controlling factor). Consequently, the role of grain size upon corrosion cannot be fully assessed unless a variation in environment is simultaneously studied. For example, the anodic reaction, which dictates active corrosion, also dictates passivation, so the corrosion rate vs. grain size relationship has been shown to “flip” depending on pH. Further, SVET analysis of unpolarized Mg immersed in 0.1 mol dm−3 NaCl electrolyte at neutral pH showed that breakdown of passivity of cast Mg occurred after ~1 h immersion, giving filiform-like corrosion tracks. The front edges of these corrosion features were revealed as intense local anodes, while the remainder of the dark-corroded Mg surface, left behind as the anodes traversed the surface, became cathodically activated. In contrast, grain-refined Mg samples were significantly less susceptible to localized corrosion, and breakdown was not observed for immersion periods of up to 24 h.

scholarly journals Surface film formation in vitro by infant and therapeutic surfactants: role of surfactant protein B

2014 ◽  
Vol 77 (2) ◽  
pp. 340-346 ◽  
Author(s):  
Olivier Danhaive ◽  
Cheryl Chapin ◽  
Hart Horneman ◽  
Paola E. Cogo ◽  
Philip L. Ballard
Keyword(s):  
Film Formation ◽  
Surface Film ◽  
Surfactant Protein ◽  
Surfactant Protein B ◽  
Protein B

scholarly journals Surface Film Formation in Static-Fermented Rice Vinegar: A Case Study

Mycobiology ◽  
2019 ◽  
Vol 47 (2) ◽  
pp. 250-255
Author(s):  
Jeong Hyun Yun ◽  
Jae Ho Kim ◽  
Jang-Eun Lee
Keyword(s):  
Film Formation ◽  
Surface Film ◽  
Rice Vinegar

Localized Corrosion of Binary Mg-Nd Alloys in Chloride-Containing Electrolyte Using a Scanning Vibrating Electrode Technique

CORROSION ◽  
2012 ◽  
Vol 68 (6) ◽  
pp. 489-498 ◽  
Author(s):  
G. Williams ◽  
K. Gusieva ◽  
N. Birbilis
Keyword(s):  
Localized Corrosion ◽  
Radial Expansion ◽  
Alloying Additions ◽  
Corrosion Rates ◽  
Surface Breakdown ◽  
Density Values ◽  
Intact Surface ◽  
Mean Current ◽  
Electrode Technique

The influence of neodymium (Nd) alloying additions in the 0.47 wt% to 3.53 wt% range on the localized corrosion behavior of Mg, when freely corroding in aqueous sodium chloride (NaCl) electrolyte, is investigated using an in situ scanning vibrating electrode technique (SVET). For all samples, the point of surface breakdown is an intense focal anode that expands radially with respect to time, revealing a cathodically activated interior, which is galvanically coupled with the local anode at the perimeter. However, for Nd compositions of ≤0.74%, radial expansion ceases within ca. 2 h of initiation, whereupon dark filiform-like corrosion features are observed, which traverse over the exposed Mg surface. For Nd additions of ≥1.25%, the radial expansion continues with time up to a point where the entire intact surface becomes consumed. The intensity of the local anode ring of circular corroded regions is seen to increase as more cathodically activated corroded surface becomes exposed. Mean current density values measured within these corroded areas increase progressively with Nd content, leading to a progressive rise in localized corrosion rates. The cathodic activation of corroded regions is proposed to derive from an enrichment of noble, Nd-rich intermetallic grains caused as the alpha-Mg phase becomes attacked at local anode sites.

scholarly journals Mechanisms of passivation and chloride-induced corrosion of mild steel in sulfide-containing alkaline solutions

2021 ◽  
Author(s):  
Shishir Mundra ◽  
John L. Provis
Keyword(s):  
Mild Steel ◽  
Surface Film ◽  
Critical Role ◽  
Chloride Concentration ◽  
Alkaline Solutions ◽  
Sulfide Concentration ◽  
Chloride Induced Corrosion ◽  
Alkaline Sulfide ◽  
High Sulfide

AbstractThe pore fluid within many concretes is highly alkaline and rich in reduced sulfur species, but the influence of such alkaline-sulfide solutions on the surface film formed on steel reinforcement is poorly understood. This study investigates the critical role of HS− in defining mild steel passivation chemistry. The surface film formed on the steel in alkaline-sulfide solutions contains Fe(OH)2 and Fe–S complexes, and the critical chloride concentration to induce corrosion increases at high sulfide concentration. However, this behavior is dependent on the duration of exposure of the steel to the electrolyte, and the nature of the sulfidic surface layer.

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