Junhua Dong

Corrosion Evolution of Reinforcing Steel in Concrete under Dry/Wet Cyclic Conditions Contaminated with Chloride

The corrosion evolution of rebar in concrete was monitored by electrochemical impedance spectroscopy (EIS) under dry/wet alternated accelerated corrosion test. Four stages with different dynamic characteristics were observed during the corrosion evolution. They were passive stage, local corrosion controlled by the charge transfer step, accelerated corrosion controlled by the mass transfer step, and constant rate corrosion controlled by the mass transfer step through a barrier layer. X-ray diffraction (XRD) analysis showed that the corrosion product of rebar in mortar was composed of alpha-FeOOH, gamma-FeOOH and Fe3O4. The corrosion mechanisms of all four stages were discussed and the corrosion reactions were proposed according to the corrosion product and corrosion evolution characteristics.

Introduction to atmospheric corrosion research in China

Abstract In this paper, we introduce the research on atmospheric corrosion in China. We describe the climate characteristics and the classification of atmospheric corrosivity across the whole country. We also describe the rusting evolution under simulated wet/dry cyclic conditions.

Effect of Al alloying on corrosion performance of steel

Abstract To clarify some features of the atmospheric corrosion mechanism, the corrosion performance of Al bearing steels after wet/dry cyclic corrosion tests were studied by gravimetry, SEM, X-ray diffraction (XRD), potentiodynamic polarisation tests and electrochemical impedance spectra (EIS). The results showed that rusted Al bearing steel presented a better corrosion resistance than that of rusted plain carbon steel (Q235) in 0·3%NaCl (i.e. simulating a marine environment) solution; moreover, the corrosion resistance of Al bearing steel increased with increasing Al content. The formation of a spinel double oxide containing Al(FeAl2O4) in Al alloying steels was observed, which refined the structure of the inner rust layer, suppressed the anodic dissolution and accelerated the cathodic reduction. In addition, Al alloying increased the content of γ-FeOOH and decreased that of β-FeOOH. However, in NaHSO3 solution (i.e. simulating an industrial environment), the rust layer on Al bearing steel did not possess a protective ability, and the rust layer formed was not physically or chemically stable.

A New Experimental Method for in Situ Corrosion Monitoring Under Alternate Wet-Dry Conditions

A new experimental method was applied in in situ corrosion monitoring of mild steel Q235 under alternate wet-dry conditions. The thickness of the electrolyte film during the wet cycle was monitored by a high-precision balance with a sensibility of 0.1 mg. At the same time, an electrochemical impedance technique was employed to study the effect of film thickness on corrosion rates. Experimental results showed that there was a critical electrolyte film condition for which the corrosion rate reached a maximum during wet-dry cycles. For the substrate, the critical condition could be described by a film thickness of about 17 μm. For the rusted specimen, the critical condition could be described by an electrolyte amount of about 0.038 g, which is equivalent to a film thickness of 38 μm. This monitoring system was very useful for studying atmospheric corrosion of metals covered by corrosion products.

Rusting Evolution of MnCuP Weathering Steel Submitted to Simulated Industrial Atmospheric Corrosion

The rusting evolution of MnCuP weathering steel in a simulated industrial atmosphere as a function of corrosion duration was investigated by corrosion weight gain, scanning electron microscopy, X-ray diffraction, and electrochemical methods. The results indicate that the corrosion kinetics is related closely to the rust composition and electrochemical properties. The corrosion rate is higher during the first corrosion stage, and it is lower during the second corrosion stage. During the first corrosion stage, the rust layer is in low density, discontinuous, and loose, with a lower relative abundance of α-FeOOH. During the second corrosion stage, a compact and protective inner rust layer forms with a higher relative abundance of α-FeOOH, contributing to enhanced rust layer resistance. The rust initially enhances and then stabilizes the cathodic process, but the anodic process tends to be inhibited by the protective rust layer. Electrochemical impedance spectroscopy tests indicate that it is more scientific to evaluate the rust layer protective ability by charge transfer resistance.

Numerical Approach for Atmospheric Corrosion Monitoring Based on EIS of a Weathering Steel

Electrochemical impedance spectroscopy (EIS) and film thickness measurement have been employed to study the atmospheric corrosion of a weathering steel covered with a thin electrolyte layer in a simulated coastal–industrial atmosphere. The results indicate that the corrosion rate is a function of the covered electrolyte thickness and the wet/dry cycle. Within each wet/dry cycle, the increased corrosion rate is related to the increased Cl− and SO42− concentration and an enhancement of oxygen diffusion rate with the evaporation of the electrolyte. In addition, the corrosion rate increases during the initial corrosion stage and then decreases as the wet/dry cycle proceeds. Moreover, one mathematical approach based on the numerical integration method to obtain corrosion mass loss of steel from the measurements of EIS has been developed, and this would be useful for the development of indoor simulated atmospheric corrosion tests.

EIS study on corrosion evolution of chemical quenched rebar in concrete contaminated with chloride

Abstract The corrosion evolution of scaled rebar cooled by a chemical reagent FM in concrete immersed in 3·5%NaCl aqueous solution was studied by electrochemical impedance spectra and compared with bare rebar. The results show that the corrosion evolution process of FM cooled rebar consists of three stages during the immersion: the passive stage, the accelerated corrosion stage dominated through the charge transfer step and the steady corrosion stage dominated through the mass transfer step. The corrosion rate of FM cooled rebar reaches a steady rate (<0·7 μA cm−2) after 80 days. However, the corrosion rate of bare rebar always increases at all immersion times. After immersion for ∼1 year, the corrosion rate of bare rebar is nine times larger of that of FM cooled rebar. Therefore, the corrosion resistance of the rebar has been improved significantly by applying the FM cooling process.

The corrosion inhibition effect of phytic acid on 20SiMn steel in saturated Ca(OH)2 solution with 1 mol L−1 NaCl

ABSTRACT A wise strategy to hinder the degradation of the steel rebar in concrete is finding a corrosion inhibitor to resist pitting corrosion at passive state as well as the general dissolution at active dissolution state. In this paper, the corrosion inhibition effect of phytic acid (IP6) on 20SiMn steel was investigated in the simulated concrete solution with chlorides, Sat.Ca(OH)2+1 mol/L NaCl(pH=12.9), by electrochemical methods and surface analysis techniques. The results show that IP6 could prolong the incubation time of 20SiMn steel from passive to pitting corrosion and enhance the charge-transfer resistance to a certain extent with the inhibition efficiency of around 30~50%. This is ascribed to the preferential adsorption of IP6 over chloride ion on the passive film through PO4 functional groups, which lead to the formation of a compact chelation film.

Crevice Corrosion of Several Supper Stainless Steels in the Simulated LT-MED Environment

Susceptibility and morphological characteristics of crevice corrosion for SS316, SS904L, SS254sMo and SS2507 in the simulated low-temperature multi-effect distillation environment were investigated by cyclic polarization test, scanning electron microscope and laser microscope. The results show that the crevice corrosion resistance of four kinds of stainless steel is ranked as SS254sMo ≈ SS2507 > SS316 > SS904L. There are “cover” structures over the edge of active crevice corrosion regions of SS904L, SS254sMo and SS2507, but SS316 is an exception. Galvanic corrosion characteristics appeared in the crevice of duplex supper stainless steel SS2507.

Rusting Evolution and Anti-Corrosion Mechanism of MnCuP Weathering Steel in Simulated Atmospheres

This paper summaries the corrosion resistance of a low-cost MnCuP weathering steel in simulated coastal, industrial, and coastal-industrial atmospheric environments submitted to wet/dry cyclic acceleration corrosion tests. The results indicate that MnCuP weathering steel exhibits ideal corrosion resistance, and a protective rust layer can be formed on the steel with increasing the corrosion cycles in the three environments. The corrosion rate during the initial corrosion process is much higher than it is during the subsequent process. The corrosion rate decreases and then maintains at a steady decreasing value with prolonging the exposure duration. Form echanism, Mn and Cu contribute to the ion-selectivity of the rust layer formed in the coastal atmosphere. Cu and Pare responsible for the enhanced atmospheric corrosion resistance in the industrial atmosphere. The combined effects of Mn, Cu, and Pelements may be the key reason for the improved corrosion resistance of the steel in coastal-industrial atmosphere.