Corrosion behaviour of AISI 304 stainless steel with Cu coatings in H2SO4

The work addresses the influence of cementation and electrodeposition of copper coatings on the corrosion resistance of AISI 304 stainless steel immersed in 30 wt.% H₂SO₄ at temperatures of 25 and 50 °C. Corrosion process was evaluated by gravimetric tests, DC measurements and electrochemical impedance spectroscopy (EIS). The specimen surfaces were analysed by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. The corrosion performance of AISI 304 stainless steel in sulphuric acid solution was greatly improved by copper coatings. The amount of copper deposited by the cementation process was sufficient to protect the stainless steel of corrosion. A greater amount of copper obtained by electrodeposition treatments does not supply further improvement in the corrosion behaviour. The improved corrosion resistance is related to copper dissolution at the initial stages of immersion tests and the presence of Cu²⁺ in the solution, which makes the medium more oxidizing, increasing the stability of the passive layer. In addition, the presence of copper at the surface reduces the overpotential of cathodic reaction, enabling the transition from an active region to the passive one.     

Electrochemical synthesis and characterization of polyaniline-coated PEMFC metal bipolar plates with improved corrosion resistance

This article reported the electrochemical deposition of polyaniline (PANI) on 316-L stainless steel (316LSS) to improve the anti-corrosion performance as PEMFC metal bipolar plates. The results indicate that PANI can increase the corrosion potential of 316LSS by more than 410.57 mV and effectively decrease the corrosion current density by four orders of magnitude in comparison with the uncoated 316LSS. The experimental results showed that the PANI increased the open-circuit potential of the steel by about 140 mV. The polarization current value of PANI-coated 316LSS reduced to 2.3 × 10^?7 A/cm² under the PEMFC cathode working condition. During exposure for 12 h, Nyquist plots of PANI-coated 316LSS did not change substantially. This indicates that the PANI coating was an effective barrier against the inward penetration of corrosive species.     

Improving the empirical model for plasma nitrided AISI 316L corrosion resistance based on M?ssbauer spectroscopy

Traditional plasma nitriding treatments using temperatures ranging from approximately 650 to 730 K can improve wear, corrosion resistance and surface hardness on stainless steels. The nitrided layer consists of some iron nitrides: the cubic ?? ^?? phase (Fe₄N), the hexagonal phase ?? (Fe_2???3N) and a nitrogen supersatured solid phase ?? _N . An empirical model is proposed to explain the corrosion resistance of AISI 316L and ASTM F138 nitrided samples based on Mössbauer Spectroscopy results: the larger the ratio between ?? and ?? ^?? phase fractions of the sample, the better its resistance corrosion is. In this work, this model is examined using some new results of AISI 316L samples, nitrided under the same previous conditions of gas composition and temperature, but at different pressure, for 3, 4 and 5 h. The sample nitrided for 4 h, whose value for ??/?? ^?? is maximum (=?0.73), shows a slightly better response than the other two samples, nitrided for 5 and 3 h (??/?? ^?? = 0.72 and 0.59, respectively). Moreover, these samples show very similar behavior. Therefore, this set of samples was not suitable to test the empirical model. However, the comparison between the present results of potentiodynamic polarization curves and those obtained previously at 4 and 4.5 torr, could indicated that the corrosion resistance of the sample which only presents the ?? _N phase was the worst of them. Moreover, the empirical model seems not to be ready to explain the response to corrosion and it should be improved including the ?? _N phase.     

Tribological characterization of TiCN coatings deposited by two crossed laser ablation plasma beams

The simultaneous laser ablation of two targets (graphite and titanium) in an Ar-N₂ gas mixture was carried out to deposit thin films of the ternary compound TiCN at room temperature. The base conditions used to produce the TiN without carbon were taken from our previous studies. The experimental conditions for the ablation of the carbon target were varied so that the carbon content in the films could be changed depending on the carbon ion energy. The control of the experimental conditions was carried out using a Langmuir planar probe which permitted the determination of the mean kinetic ion energy. The maximum hardness value of 35 GPa, was obtained with a carbon ion energy of about 250 eV, which corresponds to a film with 5 at% carbon content. In order to perform tribological and scratch tests, two types of substrate were used: nitrided AISI 316 stainless steel and AISI 316 stainless steel previously coated with a thin titanium layer (～50 nm). Values of the wear rate in the range of 1.39×10^?6 to 7.45×10^?5 mm³?N^?1?m^?1, friction coefficient from 0.21 to 0.28 and adhesion from scratch test measurements up to 80 N for final critical load, were obtained.     

Adhesion and interfacial interactions of BaO–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>-based glass-ceramic seals and AISI430 interconnect for solid oxide fuel cell applications

In the present work, adhesion, leak rate, and chemical compatibility of a series of borosilicate-based glasses, belonging to the ternary BaO–SiO₂–B₂O₃ system, with AISI 430 alloys as interconnect were investigated for solid oxide fuel cell applications. Wetting angle and deformation behavior of the selected glasses with temperature and time were initially characterized with the hot-stage microscope. It was observed that the temperature ranges of wetting for all combinations were greater than 1000 °C. Significant deformation did not appear in the samples over soaking time at sealing temperature. In the next step, the leakage tests of AISI430/glass-ceramic couples were performed. The sample containing 32 % molar BaO (Ba32) had no gas leakage; a low leak rate of 10^?7to 10^?8 Pam³ s^?1 was obtained for the glass with 37 % molar BaO (Ba37) and big leak of the system (10^?3to 10^?4 Pam³ s^?1) for Ba42. Possible interfacial reactions between the as-received glass and cell ingredients and aging up to 100 h were studied by scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy and X-ray dot mapping. The results showed that the Ba32 and Ba37 glasses coupled with AISI had fine adhesion, which remained stable under these conditions and were compatible with the interconnect. So, the use of these glass-ceramics will probably be successful in joining the ceramic electrolytes to the metallic interconnect.     

Effect of molybdenum on Li<Subscript>2</Subscript>Mn<Subscript>4</Subscript>O<Subscript>9</Subscript> for rechargeable lithium ion batteries

Li₂Mn₄O₉ and molybdenum-doped Li₂Mn₄O₉ have been prepared by simple solid-state method. Molybdenum is used as a dopant since it is resistant to both corrosion and high-temperature creep deformation. The structural, morphological, and electrical performances of the samples have been analyzed. The material exhibits a cubic structure with the fd3m space group. Using EDAX, the chemical compositions of the samples have been identified. The dc electrical conductivity of the Mo-doped (LM2) sample is found to be increased to 7.44?×?10^?6 S cm^?1 at 393 K. The enhanced electrical property of the molybdenum-doped Li₂Mn₄O₉ reveals it as a feasible cathode material for rechargeable Li-ion batteries.     

Lithium manganese aluminum oxide-based full Li-ion battery using carbon fibers as current collectors

Herein, Li-ion battery using carbon fibers instead of conventional aluminum/copper foils as the current collectors is assembled. To achieve the binder-free environment, LiMn_0.97Al_0.03O₂-based fiber type cathode is prepared directly via a two-step strategy involving electroplating and hydrothermal method by forming active materials on the individual carbon fiber. Cu₆Sn₅-based fiber type anode is prepared directly via electroplating and subsequent heat treatment. The resulting LiMn_0.97Al_0.03O₂|Cu₆Sn₅ Li-ion battery using carbon fiber as the current collector functions at about 3 V, with an initial capacity of 180 mAh g^?1 (based on the cathode). The capacity retention is 90 % after 150 cycles. In particular, the battery using phosphate-modified LiMn_0.97Al_0.03O₂-based fiber type electrode demonstrates a better cycling and high rate performance compared to the unmodified counterpart.     

Preparation of LiCoO2 cathode materials from spent lithium–ion batteries

Preparation of LiCoO₂ cathode materials from spent lithium–ion batteries are presented. It started with the reclaim/recycle of metal values from spent lithium–ion batteries, which involves the separation of electrode materials by ultrasonic treatment, acid dissolution, precipitation of cobalt and lithium, followed by the preparation of LiCoO₂ cathode materials. Co (99.4%) and Li (94.5%) were recovered from spent lithium–ion batteries. The LiCoO₂ cathode materials prepared from the reclaimed cobalt and lithium compounds showed good elecrtochemical performance. The reclaiming of cobalt and lithium has a promising outlook for the recycling of cobalt and lithium from spent Li–ion batteries, thus reducing the cost of Li–ion batteries.     

Influence of tetraborate anions on manganese electrodeposition in an anion-exchange membrane electrolysis reactor

The influences of tetraborate anions on manganese electrodeposition in an anion-exchange membrane electrolysis reactor were investigated. The experimental results of manganese electrodeposition indicate that a certain amount of tetraborate anions can increase cathode current efficiency and initial pH 7.0–8.0 is suitable for high cathode current efficiency. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis show the nanocrystalline structure and impact morphology of electrodeposited manganese. The purity of electrodeposited manganese is above 99.88 %. The tests of tetraborate anions on buffer capacity (β) and pH value of the electrolyte near the cathode surface confirm that tetraborate anions facilitate manganese electrodeposition. Tetraborate anions can improve concentration polarization of Mn²⁺ ions and then increase the overpotential of hydrogen evolution reaction. Therefore, ammonium tetraborate can reduce the hydrogen embrittlement, pore, and pitting negative effect on electrodeposit surface, to improve the corrosion resistance of electrodeposited manganese. After tetraborate anions being added in electrolyte, weight loss measurement indicates that the corrosion resistance of electrodeposited manganese is improved. Electrochemical measurements testify that corrosion resistance of electrodeposited manganese containing tetraborate anions in electrolyte is reflected by less negative corrosion potential and higher impedance.     

Ultrathin surface coatings to enhance cycling stability of LiMn2O4 cathode in lithium-ion batteries

Spinel LiMn₂O₄ suffers from severe dissolution when used as a cathode material in rechargeable Li-ion batteries. To enhance the cycling stability of LiMn₂O₄, we use the atomic layer deposition (ALD) method to deposit ultrathin and highly conformal Al₂O₃ coatings (as thin as 0.6–1.2 nm) onto LiMn₂O₄ cathodes with precise thickness control at atomic scale. Both bare and ALD-coated cathodes are cycled at a specific current of 300 mA g^?1 (2.5 C) in a potential range of 3.4–4.5 V (vs. Li/Li⁺). All ALD-coated cathodes exhibit significantly improved cycleability compared to bare cathodes. Particularly, the cathode coated with six Al₂O₃ ALD layers (0.9 nm thick) shows the best cycling performance, delivering an initial capacity of 101.5 mA h?g^?1 and a final capacity of 96.5 mA h?g^?1 after 100 cycles, while bare cathode delivers an initial capacity of 100.6 mA h?g^?1 and a final capacity of only 78.6 mA h?g^?1. Such enhanced electrochemical performances of ALD-coated cathodes are ascribed to the high-quality ALD oxide coatings that are highly conformal, dense, and complete, and thus protect active material from severe dissolution into electrolytes. Besides, cycling performances of coated cathodes can be easily optimized by accurately tuning coating thickness via varying ALD growth cycles.     

Wear resistance of CuZr-based amorphous-forming alloys against bearing steel in 3.5% NaCl solution

Abstract

To investigate the amorphous-crystalline microstructure on the tribocorrosion of bulk metallic glasses (BMGs), 6 mm diameter rods of Cu_46-xZr₄₇Al₇Ag_x (x = 0, 2, 4) amorphous-forming alloys with in situ crystalline and amorphous phases were fabricated by arc-melting and Cu-mould casting. Using a pin-on-disc tribometer, the tribo-pair composed by CuZr-based amorphous-forming alloys and AISI 52100 steel were studied in 3.5% NaCl solution. With the increase of Ag content from 0 to 4 at.%, the compressive fracture strength and the average hardness decrease firstly and then increase. Moreover, 4 at.% Ag addition increases the amount of amorphous phase obviously and inhibits the formation of brittle crystalline phase, resulting in the improvement of corrosion resistance and the corrosive wear resistance. The primary wear mechanism of the BMG composites is abrasive wear accompanying with corrosive wear. The tribocorrosion mass loss of Cu₄₂Zr₄₇Al₇Ag₄ composite is 1.5 mg after 816.8 m sliding distance at 0.75 m s^?1 sliding velocity under 10 N load in NaCl solution. And the volume loss evaluated from the mass loss is about 20 times lower than that of AISI 304 SS. Thus, Cu₄₂Zr₄₇Al₇Ag₄ composite may be a good candidate in the tribology application under marine environment.     

Ultra-rapid combustion synthesis of Na<Subscript>2</Subscript>FePO<Subscript>4</Subscript>F fluorophosphate host for Li-ion and Na-ion insertion

Exploring soft-chemistry synthesis of Fe-based battery cathode materials, we have optimized combustion synthesis as an ultra-rapid approach to produce Na₂FePO₄F fluorophosphate cathode. It yields nanoscale, carbon-coated target product by annealing (at 600 °C) for just 1 min. The purity of the material crystallizing in the orthorhombic structure was confirmed by powder X-ray diffraction pattern and XPS analysis, while the morphology was studied by scanning electron microscopy. The as-synthesized material exhibits good electrochemical performance delivering a first discharge capacity of more than 70 mAh/g at C/10 rate versus both Li⁺/Li and Na⁺/Na, hence acting as an efficient host for both Li-ion and Na-ion insertion. Combustion synthesis can be employed as an economic route for synthesis and rapid screening of various phosphate-based insertion materials.     

Synthesis and electrochemical properties of Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> cathode material for lithium-ion battery

The layered Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ lithium-rich manganese-based solid solution cathode material has been synthesized by a simple solid-state method. The as-prepared material has a typical layered structure with R-3m and C2/m space group. The synthesized Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ has an irregular shape with the size range from 200 to 500 nm, and the primary particle of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ has regular sphere morphology with a diameter of 320 nm. Electrochemical performances also have been investigated. The results show that the cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ prepared at 900 °C for 12 h has a good electrochemical performance, which can deliver a high initial discharge capacity of 233.5, 214.2, 199.3, and 168.1 mAh g^?1 at 0.1, 0.2, 0.5, and 1 C, respectively. After 50 cycles, the capacity retains 178.0, 166.3, 162.1, and 155.9 mAh g^?1 at 0.1, 0.2, 0.5, and 1 C, respectively. The results indicate that the simple method has a great potential in synthesizing manganese-based cathode materials for Li-ion batteries.     

S/N dual-doped carbon nanosheets decorated with Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> nanoparticles as high-performance anodes for lithium-ion batteries

In this work, we have successfully synthesized the S/N dual-doped carbon nanosheets which are strongly coupled with Co _x O _y nanoparticles (SNCC) by calcinating cobalt/dithizone complex precursor following KOH activation. The SNCC as anode shows the wonderful charge capacity of 1200 mAh g^?1 after 400th cycles at 1000 mA g^?1 for Li-ion storage. The superior electrochemical properties illustrate that the SNCC can be a candidate for high-performance anode material of lithium-ion batteries (LIBs) because of the facile preparation method and excellent performance. Significantly, we also discuss the mechanism for the SNCC from the strong synergistic effect perspective.     

Preparation and electrochemical performances of nanoporous/cracked cobalt oxide layer for supercapacitors

Nanoporous/cracked structures of cobalt oxide (Co₃O₄) electrodes were successfully fabricated by electroplating of zinc–cobalt onto previously formed TiO₂ nanotubes by anodizing of titanium, leaching of zinc in a concentrated alkaline solution and followed by drying and annealing at 400 °C. The structure and morphology of the obtained Co₃O₄ electrodes were characterized by X-ray diffraction, EDX analysis and scanning electron microscopy. The results showed that the obtained Co₃O₄ electrodes were composed of the nanoporous/cracked structures with an average pore size of about 100 nm. The electrochemical capacitive behaviors of the nanoporous Co₃O₄ electrodes were investigated by cyclic voltammetry, galvanostatic charge–discharge studies and electrochemical impedance spectroscopy in 1 M NaOH solution. The electrochemical data demonstrated that the electrodes display good capacitive behavior with a specific capacitance of 430 F g^?1 at a current density of 1.0 A g^?1 and specific capacitance retention of ca. 80 % after 10 days of being used in electrochemical experiments, indicating to be promising electroactive materials for supercapacitors. Furthermore, in comparison with electrodes prepared by simple cathodic deposition of cobalt onto TiO₂ nanotubes(without dealloying procedure), the impedance studies showed improved performances likely due to nanoporous/cracked structures of electrodes fabricated by dealloying of zinc, which provide fast ion and electron transfer routes and large reaction surface area with the ensued fast reaction kinetics.     

Thermally oxidised rutile-TiO2 coating on stainless steel for tribological properties and corrosion resistance enhancement

In the present work, a novel process has been developed to improve the tribological and corrosion properties of austenitic stainless steels. Efforts have been made to deposit titanium coatings onto AISI 316L stainless steel by magnetron sputtering, and then to partially convert the titanium coatings to titanium oxide by thermal oxidation. The resultant coating has a layered structure, comprising of rutile-TiO₂ layer at the top, an oxygen and nitrogen dissolved α-Ti layer in the middle and a diffuse-type interface. Such a hybrid coating system showed good adhesion with the substrate, improved corrosion resistance, and significantly enhanced surface hardness and tribological properties of the stainless steel in terms of much reduced friction coefficient and increased wear resistance.     

Surface engineering of biomedical metallic materials by plasma-based low-energy ion implantation

Plasma-based low-energy ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition of thin films, for surface engineering of metallic materials was emerged as low-temperature, low-pressure surface modification technique. Plasma source ion nitriding onto AISI 316L austenitic stainless steel produced a high nitrogen face-centered-cubic phase (γ_N) layer about 10 μm thick at the temperature of 380 °C during 4 h with the high microhardness of HK_0.1 N 22.0 GPa. The microhardness of the nitrided surface from the titanium nitride phase [(Ti, Al, V)N] layer on Ti6Al4V alloy at 750 °C during 4 h achieved up to about HK_0.1 N 15.5 GPa. No pitting corrosion in the Ringer’s solution at 37 °C was detected by electrochemical polarization measurement for the nitrided AISI 316L stainless steel and Ti6Al4V alloy, respectively. Plasma source ion nitriding of the metallic materials provided the engineering surfaces with combined improvement in hardness and corrosion resistance.     

Changes in surface properties of nitrogen-implanted AISI316L stainless steel

The effect of nitrogen ion implantation with an energy of 125 keV and doses of 1 × 10¹⁷–1 × 10¹⁸ at/cm² on such tribological characteristics of AISI316L stainless steel as the friction coefficient, wear resistance, and microhardness was studied. The steel surface layer composition was studied by the methods of RBS, XRD, GXRD, SEM, and EDX. The friction coefficient and abrasion resistance of AISI316L stainless steel were measured in air, oxygen and argon atmospheres, and in vacuum. An increase in the abrasion resistance after implantation was detected, which was different for various media. The largest increase in the wear resistance was observed during testing in air. The largest decrease in the friction coefficient was observed for all implanted samples in argon atmosphere. Tribological tests resulted in an increase in nitrogen, carbon, and oxygen concentrations in worn sample fragments in comparison with their concentrations in surface layers immediately after implantation.     

Synthesis and electrochemical performance of LiFePO<Subscript>4</Subscript>/C cathode materials from Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> for high-power lithium-ion batteries

Carbon-coated olivine-structured LiFePO₄/C composites are synthesized via an efficient and low-cost carbothermal reduction method using Fe₂O₃ as iron source at a relative low temperature (600 °C). The effects of two kinds of carbon sources, inorganic (acetylene black) and organic (sucrose), on the structures, morphologies, and lithium storage properties of LiFePO₄/C are evaluated in details. The particle size and distribution of the carbon-coated LiFePO₄ from sucrose (LiFePO₄/SUC) are more uniform than that obtained from acetylene black (LiFePO₄/AB). Moreover, the LiFePO₄/SUC nanocomposite shows superior electrochemical properties such as high discharge capacity of 156 mAh g^?1 at 0.1 C, excellent cyclic stability, and rate capability (78 mAh g^?1 at 20 C), as compared to LiFePO₄/AB. Cyclic voltammetric test discloses that the Li-ion diffusion, the reversibility of lithium extraction/insertion, and electrical conductivity are significantly improved in LiFePO₄/SUC composite. It is believed that olivine-structured LiFePO₄ decorated with carbon from organic carbon source (sucrose) using Fe₂O₃ is a promising cathode for high-power lithium-ion batteries.     

The mechanism of oxide whisker growth and hot corrosion of hot-dipped Al-Si coated 430 stainless steels in air-NaCl(g) atmosphere

The mechanisms of oxide whisker growth and hot corrosion of 430 stainless steel (430SS) and aluminide 430 stainless steel hot-dipped in a Al-10 wt.%Si molten bath (430HDAS) were studied at 750 and 850 °C in air mixed with 500 and 990 vppm NaCl_(g). The results showed that the loose Cr₂O₃ scale which formed on the 430SS could not prevent the corrosion of 430SS in a 500 vppm NaCl_(g) atmosphere, resulting in the formation of Fe₂O₃ scale. Fe₂O₃ whiskers grew at the grain boundary of the Fe₂O₃ scale. However, no Fe₂O₃ whiskers formed on the Fe₂O₃ scale while 430SS was exposed in a 900 vppm NaCl_(g) atmosphere. During the initial high-temperature corrosion of 430HDAS in a 500 vppm NaCl_(g) atmosphere, a dense Al₂O₃ scale formed on the surface of the specimens. Also, Al₂O₃ whiskers grew on the Al₂O₃ scale. As exposure time increased, cyclic chlorination/oxidation degraded the protective aluminide layer and caused the formation of Fe₂O₃ scale and Fe₂O₃ whiskers. The morphology of Fe₂O₃ whiskers formed at 750 °C is more slender than those formed at 850 °C. The formation and growth of both Fe₂O₃ and Al₂O₃ whiskers may be attributed to the chloridation of both the steel substrate and aluminide layer, accelerating the diffusion rate of metallic ions in the oxide scales.