Corrosion Resistance In Acidic Environments Research Articles

Effect of Zr content on microstructure, mechanical properties and corrosion behaviour in hydrochloric acid for as-cast Ti-Zr alloy

In this work, the aim was to develop a Ti alloy with improved mechanical properties and improved corrosion resistance in acidic environments. The results show that the thicknesses of the α' phase first increases and then decreases with increasing Zr content. The elastic modulus (E) first decreases and then increases, while the hardness (H), wear resistance, and plasticity index (Up/Ut) gradually increase. Moreover, the corrosion resistance of Ti-Zr alloys was improved significantly as the Zr concentration increased, which was mainly reflected in an increase in the polarization resistance and a decrease in the corrosion rate.

Tailoring flexible-segment-rich resin network structure by multi-step copolymerization for improved composite bipolar plate of proton exchange membrane fuel cell

Composite bipolar plates composed of conductivity fillers and resins are widely employed in stationary proton exchange membrane fuel cell (PEMFC) due to their high corrosion resistance in acidic environments. Phenol-formaldehyde resin is a commonly used adhesive in composite bipolar plates; while numerous benzene rings in phenol-formaldehyde resin result in the poor flexibility of composite bipolar plates. Embedding the flexible segment (–CHOH–CH2-O-) in the resin network structure of phenol-formaldehyde resin by copolymerization with epoxy resin is an effective method for improving the defects of phenol-formaldehyde resin. In this contribution, to tailor flexible-segment-rich (–CHOH–CH2-O-) resin network structure, the co-polymerization mechanism of phenol-formaldehyde resin and epoxy resin is investigated in detailed by in-situ Fourier Transform Infrared (FTIR), based on which an Alter-T strategy is proposed for flexible-segment-rich (–CHOH–CH2-O-) resin network structure during composite bipolar plates fabrication process. The obtained composite bipolar plates consisted of graphite and flexible-segment-rich resin network structure delivers improved flexural strength (86.97 MPa), electrical conductivity (203.22 S cm−1) and areal resistance (3.41 mΩ cm2) in comparison to previously reported composite bipolar plates with same components, which are also over the technical standard of the DOE. It is further demonstrated that enriching the flexible segment for improving the poor flexibility of resin network structure is of great importance to enhance the performance of the composite bipolar plates.

Pumpkin (Cucurbita maxima) seed-derived nitrogen, phosphorus, and sulfur carbon quantum dot as an inhibitor of corrosion for mild steel in HCl solution

In this work, an endogenous self-doping N,P,S-CQDs was synthesized by the acid hydrolysis of pumpkin seeds (Cucurbita maxima) and its performance as a corrosion inhibitor was evaluated. Mild steel (MS) is one of the most used materials in the industry; however, it has low corrosion resistance in acidic environments. Pumpkin is cultivated worldwide, and this compositional characteristic makes pumpkin seeds a great alternative as a raw material to produce CQDs. The results show that endogenous self-doping CQD was successfully obtained with a size distribution smaller than 10 nm. The N,P,S-CQDs presented 91.3% at 60 ppm and 94.6% at 10 ppm as maximum inhibition efficiency after 2 and 24 h immersion, respectively. Activation energy studies, XPS analysis, and isotherm studies show that the inhibition mechanism occurs through physical interaction. These results show an excellent alternative for using pumpkin seeds (Cucurbita maxima), an agroindustry waste, as a corrosion inhibitor.

Effect of boronizing process of AISI 321 stainless steel surface on its corrosion resistance in acid environment (pH = 1)

The paper presents results of research under the effect of surface thermo-chemical treatment on the cor-rosion resistance of X6CrNiTi18-10 steel. The corrosion resistance of the surface layers of stainless steel obtained as a result of thermo-chemical treatment (boronizing process) was assessed using the method of progressive thinning, which consists in performing corrosion tests on deeper and deeper areas of the surface layer. This method allowed for the determination of changes in individual characteristic corro-sion parameters read from the potentiokinetic polarization curves and the determination of the depth profiles of these parameters. In the paper, results of tests of X6CrNiTi18-10 steel resistance to general corrosion, performed in acidified sulphate solutions (pH = 1) have been presented. The thickness of the surface layer was assessed on the basis of structural tests and changes in microhardness on the cross-section of the material. It has been found that the extremely high hardness of the boron layer was accompanied by deterioration of the corrosion resistance. The general corrosion rate of the surface layer is 3-4 times higher than the corrosion rate of the material core (substrate). The characteristics of the pas-sive state of steel are particularly worsened, which is manifested by an increase in the value of the critical passivation current, the minimum current in the passive range and by limiting the tendency to secondary passivation.

Water Harvesting of Bioinspired Microfibers with Rough Spindle-Knots from Microfluidics.

Heterostructure rough spindle-knot microfibers (HRSFs) are fabricated via a flexible parallel-nozzle microfluidic method. In this method, the bioinspired HRSF with a roughness gradient between spindle-knots and joints, can be manufactured in large-scale, and with which the size of the spindle-knots and joints can be precisely adjusted by regulating flow rates. The HRSFs, fabricated with chitosan and calcium alginate, have strong mechanical properties and corrosion resistance in acid environment (pH = 5) and alkaline environment (pH = 9), respectively. More attractively, under controlled treatment conditions, the morphology of the spindle-knots on the HRSFs can be effectively managed by changing the composite content of calcium chloride in the fluid. During the water collection process, tiny droplets of moisture can be captured on the surface of the HRSFs, subsequently, the droplets can coalesce and be transported from joint to spindle-knot sections. It is demonstrated that the surface morphology of spindle-knots directly influences the water collection efficiency, where a higher roughness gradient generates higher water collection efficiency. This parallel-nozzle microfluidic technology provides a low-cost and flexible method to manufacture high biocompatibility bioinspired rough spindle-knot microfibers, which has many potential applications in large-scale water collection, sustained drug release, and directional water collection.

Powder metallurgical production of 316L stainless steel/niobium composites for Proton Exchange membrane electrolysis cells

ABSTRACTIn this study, a composite made of a porous stainless steel (SS) 316L substrate coated with Nb was investigated as a novel porous transport layer (PTL) for proton exchange membrane electrolysis cells (PEMECs). The fabrication of such SS316L/Nb composites using scalable and automatable powder metallurgical techniques as tape casting, screen-printing and field assisted sintering technology/spark plasma sintering (FAST/SPS) was described. Sintering behaviour and the interdiffusion at the SS316L/Nb interface were investigated. Powder metallurgical techniques such as screen-printing are the preferred method to achieve a porous Nb coating, while FAST/SPS is the preferred method for a better control of the SS316L/Nb interface by lowered interdiffusion. First electrochemical performance tests with SS316L/Nb composites demonstrate they have potential to replace the state-of-the-art titanium-based PTLs. The use of SS316L is expected to decrease manufacturing costs of PTLs, while the addition of niobium layer, due to its excellent corrosion resistance in acid environment, aims to improve PEMECs lifetime and performance.

Corrosion Behavior of Plasma-Nitrided 904L Austenitic Stainless Steel in Hydrofluoric Acid

A new type of high-chromium nickel molybdenum super austenitic stainless steel, 904L, has excellent corrosion resistance in acidic environments. However, the service life of 904L decreases significantly in a mixed acid system that includes hydrogen fluoride and sulfuric acid. In this article, different plasma nitriding processes were used to modify the surface of 904L stainless steel. X-ray diffraction was used to analyze the phase composition after nitriding; scanning electron microscopy and atomic force microscopy were used to examine the surface morphology after nitriding; electrochemical noise and electrochemical methods were used to study the localized corrosion behavior and the damage mechanism of the ion nitride layer; and the effect of the plasma nitride layer on the corrosion resistance was explored. The results show that with increasing nitriding time, the thickness of the nitride layer increased. Ion nitriding resulted in the coarsening of the 904L austenitic stainless steel surface. A long nitriding treatment time resulted in the precipitation of CrN in the modified layer, depleting the chromium from the matrix and remarkably reducing the corrosion resistance.

Experimental investigation and optimization of PAC parameters on Monel 400™ superalloy

ABSTRACTNickel-based superalloys are predominantly used to manufacture marine, automotive, and aerospace parts due to its excellent corrosion resistance in acidic environments and high-strength characteristics. Machining of these alloys are extremely difficult through conventional process because of their tendency to quickly work harden and poor thermal conductivity. Plasma arc cutting (PAC) is a disruptive metal-cutting process to perform cutting of difficult to cut materials even for intricate profiles. The present work examines the effect of PAC process variables such as arc current, gas pressure, cutting speed, and stand-off distance on evaluating the surface roughness, kerf width, and micro hardness of Monel 400™ superalloy. Experiments are designed and conducted using Box–Behnken design (BBD) of response surface methodology. The quadratic models are developed and assessed for its performance using analysis of variance (ANOVA). Optimal machining process conditions, cutting speed of 2427.08 mm/min, gas pressure of 3.83 bar, arc current of 45 A, and stand-off distance of 2.14 mm are obtained through multiobjective desirability approach. From the confirmation experiments, the relative error is found to be 2.68% for surface roughness, 4.45% for kerf width, and 4.36% for micro hardness which confirms the feasibility and efficiency of proposed methodology.

Corrosion Resistance of 1.4362 Steel in Boiling 65% Nitric Acid

Lean duplex stainless steels were developed for use in environments where high strength and corrosion resistance are required. Duplex stainless steels offer a cost-effective solution with high strength and corrosion resistance. Due to high chromium content and a balanced composition, 1.4362 ferritic-austenitic stainless steel possesses excellent corrosion resistance in acidic environments. General corrosion problems in duplex stainless steels at 475°C have been widely researched. Steels are most degraded at 475°C, but corrosion can still occur at both lower and higher temperatures. Corrosion resistance is influenced by chromium content and microstructural morphology. The percentage of each phase and its properties are determined by composition, technological processing and heat treatments. Machining and fabrication practices, such as welding, are also vital for performance. The objective of this study was to determine the effects of 30-minute isothermal heat treatments at 535°C and exposure time on relative mass loss and roughness parameters of 1.4362 lean duplex stainless steel. The influence of boiling nitric acid on the corrosion resistance of steel was investigated based on mass loss and roughness parameters. Corrosion properties and roughness of 1.4362 alloys are discussed in this paper.

Evaluation on the Corrosion Resistance of Three Types of Galvanizing Steels in 1% H2SO4Solution

Galvanizing method has been extensively used to the numerous constructional steels such as a guard rail of high way, various types of structural steel for ship building and various types of steels for the industrial fields etc.. However, the galvanized structures would be inevitably corroded rapidly with increasing exposed time because an acid rain due to environmental contamination has been much dropped more and more. Therefore, it has been made an effort to improve the corrosion resistance of the galvanizing film through various methods. In this study, comparison evaluation on the corrosion resistance of three types of the samples, that is, the hot dip galvanizing with pure zinc(GI), the hot dip galvanizing of alloy bath with zinc and aluminum(GL) and the pure zinc galvanizing steel immersed again to chromate treatment bath(Chro.)were investigated using electrochemical methods in 1% <TEX>$H_2SO_4$</TEX> solution. The Chro. and GI samples exhibited the highest and lowest corrosion resistance respectively in 1% <TEX>$H_2SO_4$</TEX> solution, however, the GI sample revealed the highest impedance at 0.01 Hz due to its high resistance polarization caused by corrosion products deposited on the surface, while Chro. sample exhibited the lowest impedance at 0.01 Hz because of little corrosion products on the surface. Consequently, it is suggested that the chromate treated steel has a better corrosion resistance in acid environment compared to pure galvanizing(GI) or galvalume(GL) steels.

Microstructures of hot-pressed Cr–Ti–Cu targets and their film properties for perpendicular magnetic recording application

In this study, the effect of Cr50−0.5xTi50−0.5xCux (x = 0, 10, 20, 30, 40, 50) hot-pressed target on film performance was investigated. By increasing the ratio of Cu, the target strength and anti crack properties showed significant improvements due to the decrease of brittle intermetallic compound. In addition, the target properties were found to affect the performance of sputtering process and its film. During sputtering test, the arcing behavior was significantly suppressed by reducing the incoherent defects of the target. The results of film analysis also showed the advantages with increasing Cu ratio in Cr–Ti–Cu alloy systems, including the decrease on sheet resistivity, intrinsic stress and surface roughness. Moreover, all as-deposited films were clarified as amorphous structures to meet the requirement for perpendicular recording media application, and further analyzed with Ω and δ indices, which were subjected to quasi-chemical energy and the atomic size difference, respectively. Unfortunately, the excessive Cu addition makes a side effect on the corrosion resistance in acid environment. Related results mentioned above were supported by bending strength measurement, X-ray diffraction, scanning electron microscope, atomic force microscope, Twyman–Green interferometer, and four-point probes method.

Carbon composite hybrid bipolar plates with bypass-connected gas diffusion layers for PEM fuel cells

The bipolar plates of proton exchange membrane (PEM) fuel cell systems serve many functions, such as electrically connecting cells in series, separating gases in adjacent cells and providing structural support for the stack and flow channels of water and gases. Although carbon fiber composite bipolar plates have high strength and stiffness as well as corrosion resistance in acidic environments, they do not yield a sufficiently high electrical conductance, which compromises the efficiency of PEM fuel cells.To increase the electrical conductance of the bipolar plate, a composite hybrid bipolar plate with bypass-connected gas diffusion layers (GDLs) has been developed. The graphite foil coating method, which was developed in preceded study, is applied to decrease the contact resistance between the bipolar plates and the GDLs. Moreover, to minimize the contact resistance between the hybrid bipolar plates and gas diffusion layers by allowing continuous electron conduction though the unit cell, a bypass connection is made between the bipolar plates and the GDLs. The experimental results show that the developed hybrid bipolar plate has a 98% lower electrical resistance than the conventional composite bipolar plates.

Effect of Al additives and annealing time on microstructure and corrosion resistance of Nd–Fe–B alloys

The corrosion behavior and the microstructure of thermally treated stoichiometric Nd–Fe–B alloys with 1–3 at.% Al additions have been investigated. The additions improve the corrosion resistance in acid environment as well as in humid air at 150°C whereas the smallest amount of Al resulted in the lowest corrosion rate. Large annealing times were found to increase the corrosion resistance in acid environment additionally, whereas it deteriorates the corrosion resistance in humid air.