Corrosion In Cl Research Articles

Ethylene Glycol (EG)-Derived Chlorine-Resistant Cu0/TiO2-x for Efficient Photocatalytic Degradation of Nitrate to N2 without Sacrificial Agents at Near-Neutral pH Conditions: The Synergistic Effects of Cu0 and EG Radicals.

The selective photoreduction of nitrate to nontoxic nitrogen gas has emerged as an energy-efficient and environmentally friendly route for nitrate removal. However, the coexisting high-concentration chloride ions in wastewater can exert a significant influence on nitrate reduction due to the competitive adsorption and corrosion of Cl- on photocatalysts. Herein, we prepared ethylene glycol-Cu/TiO2-x (EG-Cu/TiO2-x) through a solvothermal reaction of Cu-doped TiO2 in an EG solution. The photodegradation of nitrate using EG-Cu/TiO2-x without adding sacrificial agents can efficiently occur in near-neutral pH solutions containing 50 mM Cl- with 95.26% of NO3- removal and 76.52% of N2 selectivity. Moreover, the photocatalyst performance remained at a high level after 8 cycles. In this work, NO3- was first converted to NH4+ by Cu0 and Ti3+, followed by the NH4+-to-N2 conversion by photogenerated chlorine free radicals. Compared to HO•, Cl•, and Cl2•-, ClO• is proved to play the predominant role in transforming NH4+ to N2. The EG radicals produced by UV light impede Cl- adsorption on Cu, protecting Cu0 from being corroded. What's more, photoelectrons can reduce Ti4+ to Ti3+ and protect Cu0 from being oxidized, enabling the stability of reactive sites. This work provides novel insights and understanding on designing photocatalysts for NO3- removal in solutions containing chloride ions, highlighting the significance of eliminating Cl- by EG radicals and adjusting the conversion process of NO3- for the efficient removal of NO3-.

INHIBITION PROFICIENCY OF Al 3+ ON MILD STEEL CORROSION IN DIFFERENT pH AQUEOUS MEDIUM

The effect of pH on the inhibition performances of Al3+ on mild steel corrosion in Cl- aqueous solution has been investigated by immersion tests and electrochemical tests. Immersion tests results showed that the rate of corrosion in higher pH solution was decreased as compared to the lower and intermediate pH. Scanning electron microscopic observation elucidated that the lower number of pits and grain boundaries on the sample immersed in higher pH solution as compared to lower pH solutions. The electrochemical impedance spectroscopic results showed the highest charge transfer resistance in higher pH solution, and supported the results obtained from the immersion tests. X-ray photoelectron spectroscopic results elucidated a protective layer was formed on the steel surface immersed in the higher pH solution that was associated with Al(OH)3. Therefore, it was suggested that the protective layer on the steel surface immersed in the higher pH solution inhibited the corrosion reactions.

Binder-integrated Bi/BiOI/TiO2 as an anti-chloride corrosion coating for enhanced photocathodic protection of 304 stainless steel in simulated seawater

Preparing Bi/BiOI catalysts for efficient photocathodic protection of metals in the marine environment has been always a tricky problem because of Bi oxidation and I- ion release under Cl- ion corrosion. Herein, by integrating sodium carboxymethyl cellulose (CMC) into the composites, petal-like Bi/BiOI-modified TiO2 (TBB) p-n heterostructure coatings with a "truncated schema" were successfully fabricated. The as-prepared coatings (CTBB) provided stable photocathodic protection for 304 stainless steel (304SS) in simulated seawater. Compared with TiO2, CMC integrated Bi/BiOI/TiO2 p-n heterostructure coatings showed enhanced photocathodic protection performance with a large photocurrent response of 43 μA cm−2 and a stable potential drop of − 250 mV in simulated seawater without the participation of hole scavengers, which was attributed to the improvement of visible-light utilization and fast electron-hole pair migration at the p-n heterojunction interface. Furthermore, CMC effectively protected Bi nanoparticles against oxidation and BiOI from corrosion of Cl- ions in the electrolyte due to electron density redistribution in the vicinity of I- ions. The as-fabricated CTBB coatings showed great potential as photoanodes for photocathodic protection of 304SS in simulated seawater.

Effect of Laser Strengthening on Electrochemical Corrosion of AA6082 Aluminum Alloy

In this study, the surface of 6082 aluminum alloy was machined by laser heat treatment, and the microstructure and properties of the affected zone of laser surface were discussed by scanning electron microscope (SEM). The experimental results show that the laser treatment has an obvious second phase fine grain strengthening effect on the surface of aluminum alloy. The local hardness of the surface laser action zone has been improved obviously. Combined with the polarization curve data and microscopic corrosion morphology, with the addition of laser, the corrosion resistance mechanism of aluminum alloy has been well optimized, and the number and continuity of pitting pits on the surface of aluminum alloy have been restrained. The intergranular corrosion and the maximum corrosion depth behavior decreased under the corrosion of Cl−. The comprehensive properties of aluminum alloy surface have been effectively optimized under the action of laser heat treatment.the effect of laser heat treatment on the corrosion resistance and the surface mechanical properties of AA6082 aluminum alloy was investigated.

Metal-Based Ionic Liquids in Oxidative Desulfurization: A Critical Review.

Ionic liquids (ILs) as novel functional desulfurization materials have attracted increasing attentions. Metal-based ionic liquids (MILs) are classified into three types of metal chloride ILs, metal oxide ILs, and metal complex ILs based on the definition and basic structure of MILs in this critical review. On the basis of the properties of ILs such as structure designability, super dissolution performance, good thermal and chemical stability, nonflammability, and wide electrochemical window, MILs exhibit unique advantages on hydrophobicity, oxidation performance, and Brönsted-Lewis acidity. Therefore, MILs possess both the absorption and oxidation centers for the intramolecular adsorption and oxidation to improve the oxidative desulfurization (ODS) process. During the novel nonaqueous wet oxidative desulfurization process (Nasil), H2S can be oxidized into elemental sulfur with hydrophobic MILs, which can be regenerated by oxygen for recycle, to solve the problems of low sulfur capacity, low sulfur quality, and severe secondary pollution in the aqueous Lo-Cat wet oxidative desulfurization process. Another outstanding feature of MILs in ODS is biomimetic catalysis, which has the function of activating molecular oxygen and improving the oxidation performance. Metal oxide ILs and metal complex ILs are used in combination with hydrogen peroxide or oxygen with the existing water to generate a Fenton-like reaction to convert hydrophobic organic sulfur or SO2 into hydrophilic sulfoxide/sulfone or sulfur acid, respectively. However, the corrosion of Cl- to the equipment and emulsification phenomenon in the extraction process of sulfoxide/sulfone separation still need further study. Furthermore, the promising strategies to construct highly efficient and green desulfurization processes for large-scale applications are provided.

Effects of pack chromizing on the microstructure and anticorrosion properties of 316L stainless steel

To extend the applications of 316L stainless steel in corrosive environments and correlate the corrosion resistance with composition and microstructure, homogeneous Cr-rich layer with the thickness of 75 μm was fabricated on 316L stainless steel by pack chromizing and post heat treatment. The chromizing layer was mainly composed of FeCr solid solution. Post heat treatment eliminated the precipitates and Cr-depletion in the chromizing layer. The corrosion behaviors were studied by electrochemical measurements and corrosion morphology observation. The pitting corrosion in Cl− containing solutions was avoided after chromizing treatment, which was ascribed to the reduced sensitivity of Cr-rich surface to Cl− ions. The higher Cr concentration in the modified layer also improved the long-term stability of corrosion resistance. After immersion in NaCl solution for 24 days, the charge transfer resistance of chromizing sample was higher than that of 316L by a factor of 8.19. In addition, the free corrosion potential shifted to the positive direction after post heat treatment, and the corrosion current density was also reduced to 0.066 μA/cm2. The further improvement on anticorrosion performance was attributed to the homogeneous microstructure.

AN ELECTROCHEMICAL PROCESSING STRATEGY FOR IMPROVING TRIBOLOGICAL PERFORMANCE OF AISI 316 STAINLESS STEEL UNDER GREASE LUBRICATION

In order to improve the tribological performance of AISI 316 stainless steel (316 SS) under grease lubrication, electrochemical processing was conducted on it to obtain a rough (surface texturing-like) surface by making use of the high sensitivity of austenitic stainless steel to pitting corrosion in Cl --rich environment. Numerous corrosion pits or micro-ditches acted as micro-reservoirs on the obtained surface. While the grease could offer consistent lubrication, and then improve the tribological performance of 316 SS. Tribological behaviors of raw 316 SS and the treated sample were measured using a reciprocating type tribometer sliding against GCr 15 steel counterpart under dry and grease lubrication conditions. The results showed that the mass losses of the two samples were in the same order of magnitude, and the raw sample exhibited lower friction coefficient in dry sliding. When the tests were conducted under grease lubrication condition, the friction coefficients and mass losses of the treated sample were far lower than those of the raw 316 SS. The tribological performance of 316 SS under grease lubrication was drastically improved after electrochemical processing.

Deposition, characterization and electrochemical properties of silica-phosphate composite coatings formed over A6092/SiC/17.5p aluminum metal matrix composite

This paper investigates the effect of 2.5wt.% (NH4)3PO4 post-treatment after silica treatment on the formation of silica-phosphate (Si-P) composite coatings over A6092/SiC/17.5p aluminum metal matrix composite (AMMC). In previous studies, the optimum concentration, treatment time and pH of silica treatment have been determined. The aim of the current paper is to determine the optimum conditions under which Si-P composite coatings can provide a maximum localized corrosion protection to AMMC. The surface morphology of Si-P composite coatings and the ability to protect AMMC substrate from localized corrosion in Cl− media were examined as a function of phosphate treatment time (0, 2, 5 and 10min). Results showed that phosphate post-treatment after silica coating significantly affects the microstructure and the pitting corrosion resistance of the ultimate coated composites. The coating deposited on AMMC post-treated for 2min provides better pitting corrosion resistance than that post-treated for 5 and 10min. It is largely because the morphologies of the coatings are remarkably different under the three post-treatment conditions.

The Effect of Electrochemical Chloride Extraction Combining Ultrasonic on Steel-Reinforced Mortars

A creative methodology of ultrasonic-electrochemical chloride extraction (UT) is proposed which is an improvement of the traditional electrochemical chloride extraction (ECE) through the assistant of ultrasonic wave and according experimental investigation on the viability of this method is carried out. The results indicated that the Cl- extraction efficiency of UT was approximately 19% higher than that of ECE, and the corrosion current density of UT group obtained through Linear Sweep Voltammetry was also the lowest which further demonstrates that ultrasonic wave had positive and obvious effect on halting the corrosion of Cl- on steels.

Mechanical Properties and Marine Corrosion Resistance of P-Bearing ULCB Steels

The research aims to evaluate the microstructure, mechanical properties and marine corrosion resistance of P-bearing ULCB steels. P produced stronger solution strengthening effect, but had less effect on the low temperature impact toughness of ULCB steel. With increasing P content to 0.09(mass)%, the immersion corrosion rate of ULCB steel in 3.5% NaCl obviously decreased in comparison with those steels without or with lower P content. This is attributed to that the complex effect of Cu and P promoted the formation of dense amorphous oxyhydroxide in the inner scale, which inhibited further corrosion from NaCl solution. Mo in ULCB steel played an important role in avoiding pitting corrosion in Cl- environment.

Characterisation and corrosion performance of laser-melted 3CR12 steel

Dual-phase ferritic–martensitic 3CR12 steel, exhibiting an excellent corrosion resistance under ambient conditions, is a potential substitute for FeCrNi stainless steels in many applications. However, the steel suffers pitting corrosion in Cl −-containing environments, usually associated with the presence of non-metallic inclusions. The present work investigates the possibility of improvement of the pitting corrosion performance of hot-rolled and annealed 3CR12 steel using a laser surface melting (LSM) technique. The laser processing was carried out using a 3 kW CW Nd:YAG laser with 10 and 13 mm line beam profiles. Pitting resistance in de-aerated 3.5% NaCl solution was substantially increased by LSM. The degree of improvement is associated with the formation of ferrite and reduction of martensite in the melt region, the extent of which depends on the processing parameters. Observation of pitting morphologies of the laser-melted surfaces showed that corrosion was initiated at the ferrite grain boundaries, where the martensite or possibly impurities were located, compared with more random pitting in the banded microstructure of the initial steel.

Surface modification of carbon steel with laser treated nitrogen-containing stainless steel layers

Laser surface alloying was used in this study to introduce nitrogen-containing stainless steel layers on carbon steel to improve its corrosion resistance. The alloying materials used were FeCrNiSi 3N 4 and FeCrMnSi 3N 4 powders which were pre-mixed before laser irradiation. The chemical composition, the microstructure and the electrochemical behavior of the alloyed layers were of particular interest and analyzed. Potentiodynamic polarization tests were performed to evaluate the corrosion resistance of the laser treated alloys in deaerated 3.5 wt.% NaCl solution at pH 4. Two austenitic stainless steels, namely 316L and P900N, were tested for comparison. Experimental results indicated that nitrogen contents in the laser treated FeCrNiSiN and FeCrMnSiN alloys could reach 0.38 and 0.83 wt.% respectively. The FeCrNiSiN layer exhibited higher resistance to pitting corrosion in Cl − containing solution as compared with those of 316L and P900N stainless steels. However, the pitting corrosion resistance of FeCrMnSiN layer was inferior to those of the 316L and P900N stainless steels.

18-8ステンレス鋼の腐食におよぼすアニオンおよびカクハンの影響

The effects of anions and agitating conditions on the corrosion of 18-8 stainless steel were studied by immersion tests and measurements of polarization curves.The results obtained were as follows:(1) The amount of corrosion in Cl- solution was much larger than that in ClO4- or SO42- solution and it increased with the increase of Cl- concentration up to 19, 000p.p.m.The value of corrosion rate obtained from the polarization curves was in appreciably good accordance with that calculated by the immersion test for a long time.(2) It was explained that the rest potential varied with the lapse of time; in particular, remarkably in Cl- solution.(3) It was also explained that the temperature of Cl- solution and the agitating conditions of ClO4- or SO42- solution had great effects on the limiting current density for dissolution of iron. The effects of agitating conditions on the limiting current density for reduction of oxygen were theoretically analyzed, and the relation between the diffusion current (id) and angular velocity of rotation (ω) for a rotating cylindrical electrode was derived as follows;id=Aω1/2(4) The activation energy of corrosion was discussed and the singularity of Cl- was explained.