Zhiming Gao

Sensing Atmospheric Corrosion of Carbon Steel and Low-Alloy Steel Using the Electrochemical Noise Technique: Effects of Weather Conditions

Three electrochemical probes were designed to study the effects of weather on the atmospheric corrosion of carbon steel and low-alloy steel in an urban atmosphere by using the electrochemical noise (EN) technique. The fabricated probes can be successfully applied to investigate instant atmospheric corrosion resistance in various weather conditions. Continuous 15-day EN monitoring showed that, under the same weather conditions, the corrosion resistance of Q235 carbon steel is higher than that of low-alloy steels.

Monitoring the Diffusion Layer During Passive Film Breakdown on Alloy 800 with Digital Holography

The effects of chloride and thiosulfate ions on localized corrosion of alloy 800 are investigated through dynamical observation of the change in phase image of the diffusion layer during passive film breakdown using digital holography. The results indicate that solution chemistry has a significant effect on film breakdown and diffusion layer. The phase distribution changes at different applied potentials show that in the process of film breakdown, dissolution of metal ions from pitting is not remarkable in chloride-only solution, whereas dissolution of metal ions is significantly high in thiosulfate and chloride solution. Thiosulfate has a combined effect with chloride ions in passive film degradation.

Electrochemical noise monitoring of the atmospheric corrosion of steels: identifying corrosion form using wavelet analysis

ABSTRACT The early stage atmospheric corrosion of T91 and Q235B steels exposed to Tianjin’s urban atmosphere over 20 days was studied using two electrochemical probes via an electrochemical noise (EN) technique. To identify the corrosion process and the corrosion form of the two steels, EN data were analysed by statistics and wavelet transform. The results revealed that the wavelet energy of decomposed EN mainly located at high-frequency level for Q235B steel, whereas it mainly located at the low-frequency level for T91 steel. Analyses of surface images confirmed that Q235B steel underwent uniform corrosion whereas T91 steel suffered from localised corrosion. The obtained noise resistance correlated well with weight loss data. GRAPHICAL ABSTRACT

Pitting growth rate on Alloy 800 in chloride solutions containing thiosulphate: image analysis assessment

ABSTRACT The growth rate of pits formed on Alloy 800 in chloride solutions containing various thiosulphate concentrations was assessed by potentiostatic polarisation, in situ corrosion image observation, and image analysis. The pitting growth rate was a function of solution chemistry: in chloride solution pits were small but numerous, in chloride + thiosulphate solution, the pits were large. Competitive adsorption on Alloy 800 of chloride and thiosulphate ions affected the pitting potential and therefore the pitting growth rate on the metal. The reduction of thiosulphate to elemental sulphur accelerated the pitting growth rate in chloride + thiosulphate solutions.

Characterization of a Stressed Passive Film Using Scanning Electrochemical Microscope and Point Defect Model

The corrosion resistance of passive film is investigated by in situ scanning electrochemical microscopy (SECM), and is also diagnosed by modified point defect model (PDM). Thus the constant rate related to defect reactions present in the passive film, can be obtained. SECM results indicate that both compressed and tensile stress decreases the stability of passive film, leading to an increase in surface reactivity and dissolution rate—which is possibly due to the decreased binding force between atoms caused by the stress and therefore make them more easy to dissolve. PDM results indicate that the reason of the decreased stability is an increase in the rate constant of defect reactions present in the passive layer, including transportation rate of oxygen and cation dissolution rate.

In-situ Study the Corrosion Degradation Mechanism of Tinplate in Salty Water by Scanning Electrochemical Microscopy

In this work, the corrosion degradation of tinplate in contact with salty water is investigated by scanning electrochemical microscopy (SECM) electrochemical impedance spectroscopy (EIS). Experimental results indicate tin maintains at passive state during the exposure; however, pores and defects existed in tin coating leads to an exposure of carbon steel substrate to the electrolyte, in which localized corrosion tends to occur within the pore. A phenomenological model is proposed to interpret corrosion mechanism of tinplate in contact with salty food based on the proposed electrochemical equivalent circuit.

Online Monitoring of the Atmospheric Corrosion of Aluminium Alloys Using Electrochemical Noise Technique

In this work, an electrochemical system based on electrochemical noise (EN) technique for online detection and monitoring of atmospheric corrosion of LY12CZ aluminium alloys has been established. A detecting probe and a monitoring instrument with a software have been developed to perform the electrochemical noise measurements with zero resistance ammeter (ZRA) mode. Experimental results show that the atmospheric corrosion behaviour of aluminium could be effectively detected and monitored by the analysis of the electrochemical potential and current noise, also by the noise resistance variation.

Field Corrosion Detection of Nuclear Materials using Electrochemical Noise Techinique

Some critical issues when applying electrochemical noise (EN) in field corrosion detection of nuclear materials are solved. In this work, a portable EN measurement system for field test is established by using Compact RIO modular instrument and zero resistance ammeter (ZRA) module. The electrode system for EN measurement is built by using platinum wire or stainless steels coated with thermal sprayed ceramic coatings as counter electrode. Two EN sensors are developed based on the electrode system mentioned above, and field corrosion detection is successfully achieved. The corrosion of stainless steel pipeline surface in nuclear power plant and internal-surface corrosion of continuous blowdown piping are successfully evaluated by the established new EN measurement system.

Atmospheric corrosion monitoring of field-exposed Q235B and T91 steels in Zhoushan offshore environment using electrochemical probes

This work aimed to in-situ monitor the atmospheric corrosion of steels exposed to Zhoushan offshore environment by using electrochemical noise (EN) technique. A portable EN monitoring system was established and two electrochemical probes (named as Q235B and T91) were designed. Experimental results indicated that the noise resistance of T91 steel was higher than that of Q235B steel, revealing that the corrosion resistance of T91 was higher than that of Q235B. A 60-day monitoring result indicated that the noise resistance was well correlated with the weight loss data. Wavelet analyses results of EN data indicated that Q235B underwent uniform corrosion and T91 suffered from localized corrosion, which was further confirmed by the surface observation. It is concluded that EN can be used as a new method to identify the corrosion form and corrosion resistance in atmospheric conditions.

Passivation degradation of Alloy 800 on nucleate boiling surface

ABSTRACT In this work, the passivation degradation of Alloy 800 on nucleate boiling surface was studied by using polarisation curve, electrochemical impedance spectroscopy and secondary ion mass spectrometry. Experimental results indicated that boiling bubble would significantly degrade the passive film, as indicated by a decreased pitting potential and increased passive current density. Under boiling condition, the mass transfer of electrolyte is accelerated and the temperature of Alloy 800 was increased, as a result, the cathodic reaction and the dissolution rate of the passive film were increased. The passive film was Cr-depleted but Ni- and Fe-enriched, and the decreased Cr content in the passive film led to a degraded passive film.