Kui Xiao

Corrosion Products and Formation Mechanism During Initial Stage of Atmospheric Corrosion of Carbon Steel

The formation and development of corrosion products on carbon steel surface during the initial stage of atmospheric corrosion in a laboratory simulated environment have been studied by scanning electron microscopy (SEM) and Raman spectroscopy. The results showed that two different shapes of corrosion products, that is, ring and chain, were formed in the initial stage of corrosion. MnS clusters were found in the nuclei of corrosion products at the active local corrosion sites. The ring-shaped products were composed of lepidocrocite (γ-FeOOH) and maghemite (γ-Fe2O3) transformed from lepidocrocite. The chain-type products were goethite (α-FeOOH). A formation mechanism of the corrosion products is proposed.

Electrochemical Migration Behavior of Copper-Clad Laminate and Electroless Nickel/Immersion Gold Printed Circuit Boards under Thin Electrolyte Layers

The electrochemical migration (ECM) behavior of copper-clad laminate (PCB-Cu) and electroless nickel/immersion gold printed circuit boards (PCB-ENIG) under thin electrolyte layers of different thicknesses containing 0.1 M Na2SO4 was studied. Results showed that, under the bias voltage of 12 V, the reverse migration of ions occurred. For PCB-Cu, both copper dendrites and sulfate precipitates were found on the surface of FR-4 (board material) between two plates. Moreover, the Cu dendrite was produced between the two plates and migrated toward cathode. Compared to PCB-Cu, PCB-ENIG exhibited a higher tendency of ECM failure and suffered from seriously short circuit failure under high relative humidity (RH) environment. SKP results demonstrated that surface potentials of the anode plates were greater than those of the cathode plates, and those potentials of the two plates exhibited a descending trend as the RH increased. At the end of the paper, an electrochemical migration corrosion failure model of PCB was proposed.

Effects of mould on electrochemical migration behaviour of immersion silver finished printed circuit board

The role played by mould in the electrochemical migration (ECM) behaviour of an immersion silver finished printed circuit board (PCB-ImAg) under a direct current (DC) bias was investigated. An interesting phenomenon is found whereby mould, especially Aspergillus niger, can preferentially grow well on PCB-ImAg under electrical bias and then bridge integrated circuits and form a migration path. The cooperation of the mould and DC bias aggravates the ECM process occurring on PCB-ImAg. When the bias voltage is below 15V, ECM almost does not occur for Ag coating. Mechanisms that explain the ECM processes of PCB-ImAg in the presence of mould and DC bias are proposed.

Corrosion Behavior of Silver-Plated Circuit Boards in a Simulated Marine Environment with Industrial Pollution

The electrochemical corrosion behavior of a silver-plated circuit board (PCB-ImAg) in a polluted marine atmosphere environment (Qingdao in China) is studied through a simulated experiment. The morphologies of PCB-ImAg show some micropores on the surface that act as the corrosion-active points in the tests. Cl− mainly induces microporous corrosion, whereas SO2 causes general corrosion. Notably, the silver color changes significantly under SO2 influence. EIS results show that the initial charge transfer resistance in the test containing SO2 and Cl− is 9.847 × 103, while it is 3.701 × 104 in the test containing Cl− only, which demonstrates that corrosion accelerates in a mixed atmosphere. Polarization curves further show that corrosion potential is lower in mixed solutions (between −0.397 V SCE and −0.214 V SCE) than it in the solution containing Cl− only (−0.168 V SCE), indicating that corrosion tendency increases with increased HSO3− concentration.

Stress corrosion cracking behavior of PH13-8Mo stainless steel in Cl– solutions

The stress corrosion cracking (SCC) behavior of PH13-8Mo precipitation hardening stainless steel (PHSS) in neutral NaCl solutions was investigated through slow-strain-rate tensile (SSRT) test at various applied potentials. Fracture morphology, elongation ratio, and percentage reduction of area were measured to evaluate the SCC susceptibility. A critical concentration of 1.0 mol/L neutral NaCl existed for SCC of PH13-8Mo steel. Significant SCC emerged when the applied potential was more negative than—0.15 VSCE, and the SCC behavior was controlled by an anodic dissolution (AD) process. When the applied potential was lower than—0.55 VSCE, an obvious hydrogen-fracture morphology was observed, which indicated that the SCC behavior was controlled by hydrogen-induced cracking (HIC). Between —0.15 and —0.35 VSCE, the applied potential exceeded the equilibrium hydrogen evolution potential in neutral NaCl solutions and the crack tips were of electrochemical origin in the anodic region; thus, the SCC process was dominated by the AD mechanism.

Characterization of the Passive Film and Corrosion of Martensitic AM355 Stainless Steel

ABSTRACT Electrochemistry methods were used to investigate the influence of pH on the passive film and corrosion behavior of ultrahigh strength AM355 stainless steel in chloride-containing media. Analysis of the Pourbaix diagram indicates that AM355 stainless steel exhibits higher corrosion resistance in natural and near-natural environments than that in acidic and alkaline conditions. Electrochemistry measurements and composition analysis of the passive film show that pitting potential increased due to the enhanced repassivation capacity of AM355 stainless steel with increasing pH. The mixed MnS/oxide inclusions are the main pitting sensitive locations under all conditions. Morphological observations and energy-dispersive spectroscopy showed that the influence of the gap between the martensitic laths is significant with increasing pH. The inclusions, element concentrations, and microstructures weaken the resistance of ultrahigh-strength martensitic AM355 stainless steel against corrosion.

Atmospheric Corrosion of Q235 Carbon Steel and Q450 Weathering Steel in Turpan, China

Q235 carbon steel and Q450 weathering steel were exposed to the hot and dry environment of Turpan, China for three years. The corrosion rates of both steels were calculated and compared. The morphologies of the rust layer products were observed by optical microscopy and scanning electron microscopy. Analyses of the rust layers were performed by X-ray photoelectron spectroscopy, X-ray powder diffraction, and Raman spectroscopy, and analysis results indicate that the compositions of rust are main iron rich oxide such as FeOOH, Fe3O4, and Fe2O3. The iron oxide layer content proportion was calculated through a semi-quantitative algorithm. The resistance elements (Cr, Ni, and Cu) enhanced the resistance properties of the Q450 weathering steel matrix. Moreover, the resistance elements increased the proportion of goethite crystals in the corroded rust layer.

The influence of Bacillus subtilis on tin-coated copper in an aqueous environment

The influence of Bacillus subtilis (BS) on tin-coated copper in an aqueous environment was investigated by exposing the sample to a culture medium inoculated with BS. Scanning electron microscopy, electrochemical measurements and chemical analyses were performed to study the corrosion mechanism. The experimental results show that BS can adhere and gather on the surface of the sample, resulting in oxygen consumption at the place where the bacteria are densely attached. Increases in the Rct values after the initial immersion showed that corrosion was inhibited, while decreases in the Rct values after the later immersion showed that corrosion was accelerated. Our results suggest that differences in oxygen concentration due to activity of BS are the main reason for corrosion of tin-coated copper.

Microporous corrosion behavior of gold-plated printed circuit boards in an atmospheric environment with high salinity

The microporous corrosion is the main surface failure mechanism of gold-plated components. The microporous corrosion behavior of electroless nickel and immersion gold (ENIG)-plated printed circuit boards (PCBs) in Turpan area which has an atmospheric environment with high salinity was investigated via a field exposure method for 24 months, as well as 3D analysis, FIB technology, composition analysis, and electrochemical impedance spectroscopy and corrosion mechanism model. After 6 months of exposure, the corrosion products filled up the pores and clustered on the surface as mound shape, and a possible corrosion mechanism model was displayed in the study after 24 months of exposure. The results showed that PCB-ENIG mainly suffered microporous corrosion in a high salinity atmospheric environment. The pores on the gold-plated coating were location where corrosion occurred first and the corrosion products were mostly oxides, chlorides, sulfates and carbonates of copper and nickle.

Co/Mn co-doped TiO 2 nanotube arrays for enhanced photoelectrochemical properties: experimental and DFT investigations

In this study, we used first principle calculations to investigate the electronic properties of TiO2 modified with eight different elements. Co/Mn co-doped TiO2 nanotube arrays, which had the smallest band gap, were subsequently prepared using electrochemical anodization followed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) measurements. The results showed that the TiO2 nanotube arrays were highly ordered and well aligned. Finally, the photoconversion efficiency was measured using photoelectrochemical experiments and, under the same conditions, the photoconversion efficiency under visible light increased approximately three times from 9.35% for the undoped TiO2 nanotubes to 21.25% for the Co/Mn co-doped TiO2 nanotubes. These results indicate that Co/Mn co-doped TiO2 nanotube arrays can improve the efficiency of visible-light utilization and could be a promising material in such fields as photocatalysis and solar cells.