Nitric Acid Bath Research Articles

Electrochemical Corrosion Behavior of Passivated Precipitation Hardening Stainless Steels for Aerospace Applications

Precipitation-hardening (PH) stainless steels (SS) are widely used in various aerospace applications. These steels exhibit good mechanical and corrosion resistance. The electrochemical behavior of 15-5PH, 17-4PH, Custom450 and AM 350 stainless steels passivated with citric and nitric acid baths for 60 and 90 min at 25 and 49 °C were evaluated in 5 wt.% sodium chloride (NaCl) and 1 wt.% sulfuric acid (H2SO4) solutions. The electrochemical behavior was studied with potentiodynamic polarization curves (PPC) according to the ASTM G5-13 standard. The results indicated that there are two characteristic mechanisms that are present in the potentiodynamic polarization curves. When the PHSS is immersed in an H2SO4 solution, there is a secondary passivation, and in the NaCl solution, there is a pseudo-passivation (not stable passivation film). The current densities in the NaCl solution were between 10−4 and 10−5 mA/cm2, while those of H2SO4 were recorded around 10−2 and 10−3 mA/cm2. Citric acid does work as a passivating solution, and in some cases, the corrosion resistance of the stainless steel was comparable to that of nitric acid.

Corrosion Behavior of Passivated Martensitic and Semi-Austenitic Precipitation Hardening Stainless Steel

This research aimed to conduct a passive layer state study on martensitic and semi-austenitic precipitation hardening stainless steels (PHSS) passivated in citric acid and nitric acid baths at 49 and 70 °C for 50 and 75 min and subsequently exposed in 5 wt.% NaCl and 1 wt.% H2SO4 solutions. Corrosion behavior of the passivated material was observed by using potentiodynamic polarization (PP) according to the ASTM G5-11 standard. The microstructural analysis was performed by optical microscopy and scanning electron microscopy (SEM), while the passivated layer was characterized by X-ray photoelectron spectroscopy (XPS). The results indicated that the semi-austenitic-NA-50 min-70 °C sample showed the best corrosion resistance behavior in both solutions. The XPS characterization confirmed that the martensitic and semi-austenitic surface film presented a mixture of chemical compounds, such as Cr2O3 and Fe(OH)O, respectively.

Determination of Nitrate and Fluoride in Spent Pickling Baths for Stainless Steel by Spectrophotometry and Potentiometry

Hydrofluoric and nitric acid baths are widespread in pickling of stainless steel due to their rapid performance and excellent quality of treated surfaces. The concentrations of nitrate and fluoride play an important role in the process and therefore require regular monitoring. Simple methods for spectrophotometric determination for nitrate and potentiometric determination for fluoride were verified based upon current procedures for water analysis. After removing metals by cation exchange, the recoveries were 98.25–98.83% for nitrate and 98.15–100.6% for fluoride. These values were obtained by comparison between these methods and a reference ion chromatography procedure for real baths and the material balance measurements of artificial mixtures. Due to high metal contents in the bath, the proposed methods fail without sample pretreatment; the spectrophotometry of nitrates with sulphosalicylic acid is impossible, and fluoride potentiometry provides the results 20% lower compared to the references samples. The conditions for ion exchange pretreatment (i.e., exchanger capacity, specimen dilution, and flow rate) were optimized. The combination of simple fluoride and nitrate determination with sample pretreatment by cation exchange is suitable for monitoring the bath quality in small pickling plants, where an automatic analyzer would represent a high investment.

The Impact of Acid Treatments and Electropolishing Stainless-Steel Surfaces on Tritium Inventories

The concentration of tritium in the adsorbed water layer on stainless-steel type 316 is notably higher than that present in the metal lattice. The absorbed waters play a key role in the migration of tritium into the metal. In this work, stainless-steel (type 316) surfaces were subjected to various pretreatments designed to alter the surface in order to probe the relation between surface conditions and total tritium inventories. These pretreatments included electropolishing and soaking in nitric-acid baths. Stainless-steel samples were loaded with tritium by exposure to a deuterium–tritium gas mixture at 25°C for 24 h. Total tritium inventories were measured using temperature-programmed desorption. The thermal desorption data show a reduction of 65% in total tritium inventory by electropolishing stainless-steel surfaces as compared to unmodified samples. It is also shown that treating the surfaces with nitric acid resulted in an increase in the tritium content by ~200%.

Electrochemical deposition of bismuth telluride thick layers onto nickel

Bismuth telluride (Bi2Te3) is the currently best performing thermoelectric (TE) material in commercial TE devices for refrigeration and waste heat recovery up to 200°C. Up to 800μm thick, compact, uniform and stoichiometric Bi2Te3 films were synthesized by pulsed electrodeposition from 2M nitric acid baths containing bismuth and tellurium dioxide on 1cm2 nickel (Ni) substrates at average film growth rates of ~50μm/h. Pre-treatment of the Ni substrate was found to significantly enhance the adhesion of Bi2Te3 material onto Ni while pulsed electrodeposition was used to increase the compactness of the material. To maintain a homogeneous composition across the thickness of the films, a sacrificial Bi2Te3 anode was employed. All deposits produced were n-type with a Seebeck coefficient of up to −80μV/K and an electrical conductivity of ~330S/cm at room temperature.

Preparation of Bi2Te3/Nano-SiC Composite Thermoelectric Films by Electrodeposition

Bi2Te3/nano-SiC composite thermoelectric films were prepared by electrodeposition in a nitric acid bath. The effects of SiC concentration and annealing treatment on the Seebeck coefficient and electrical resistivity of the films were investigated. The morphology, composition, and structure of the films were studied by scanning electron microscopy, x-ray fluorescence spectroscopy, and x-ray diffraction. The results showed that SiC nano-particles in electrodeposited Bi2Te3/nano-SiC composite films have readily apparent effects on the crystal orientation of the Bi2Te3 matrix and the morphology of the electrodeposited composite films. For nano-SiC particle concentrations <2 g/L the Seebeck coefficients of as-deposited films decrease with increasing nano-SiC particle concentration and decrease further after annealing treatment. Improvement in electrical conductivity compensated for the decrease in Seebeck coefficient and resulted in an enhanced power factor. Addition of nano-SiC particles to the composite films introduces more interfaces, which endows the composite films with lower electrical resistivity.

Macroscopic, thermodynamic, kinetic and microscopic study of nitric acid pickling of Elektron 21 (EV31A) magnesium alloy

The study of pickling of the EL21T6 substrate in a nitric acid bath firstly provided knowledge of the influence of the different experimental parameters (concentration of acid, temperature and stirring of the solution) in relation to the etching rate. This experimental part led to the choice of standard pickling (Tbath = 25 °C, moderate stirring (250 rpm), [HNO3] = 1.20 mol/L, duration of 2 min) so as to obtain constant removal of material, even after several uses of the pickling bath. SEM observations also confirmed that in these operating conditions, pickling concerns both the grains of the matrix and the precipitates of type Mg3(Nd, Gd), leading to uniform removal of material from the surface. Working from a number of assumptions, thermodynamic and chemical kinetic studies then allowed a pickling mechanism to be proposed and led to obtaining values for the corresponding kinetic parameters (order of reaction, constant of mean rate, activation energy) to be obtained.

Electrodeposition of BixTey thin films for thermoelectric application

Electrochemically deposited bismuth telluride (BixTey) thin films were grown from nitric acid baths on sputtered Au/Ni/Si substrates. The film compositions and morphology were strongly dependent on the deposition conditions. Surface morphologies varied from granular to needle-like structures depending on the Te content of the films. The power factor improved with the increase of Bi ions in electrolytes, and this may be due to the improvement of the crystal structure and no inclusion of excess Te phases. Annealing up to 200°C in a reducing H2 atmosphere did not improve the power factor due to the interdependence of the Seebeck coefficient and the electrical conductivity.

Electrodeposition of MWNT/Bi2Te3 Composite Thermoelectric Films

The effect of multiwalled carbon nanotubes (MWNTs) on the electrochemical behavior of the Bi-Te binary system in nitric acid baths was investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy. Based on the results, MWNT/Bi2Te3 composite thermoelectric films were prepared by potentiostatic electrodeposition at room temperature. The morphology, composition, and structure of the MWNT/Bi2Te3 composite films were analyzed by environmental scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction. The results show that addition of MWNTs to the electrolyte did not change the electrochemical reduction mechanisms of Bi3+, HTeO2+ or their mixture, but the reduction processes of Bi3+, HTeO2+, and their mixture become easier. MWNT/Bi2Te3 composite thermoelectric films can be obtained by potentiostatic electrodeposition at a wide range of potentials with subsequent annealing. The MWNTs in the films act as nucleation sites for Bi2Te3 compound and thereby elevate the film deposition rate. The content of Bi element and MWNTs in the films increased as the potential was shifted negatively. In addition, the MWNTs can enhance the crystallization of Bi2Te3 film.

Creation of Superhydrophobic Stainless Steel Surfaces by Acid Treatments and Hydrophobic Film Deposition

In this work, we present a method to render stainless steel surfaces superhydrophobic while maintaining their corrosion resistance. Creation of surface roughness on 304 and 316 grade stainless steels was performed using a hydrofluoric acid bath. New insight into the etch process is developed through a detailed analysis of the chemical and physical changes that occur on the stainless steel surfaces. As a result of intergranular corrosion, along with metallic oxide and fluoride redeposition, surface roughness was generated on the nano- and microscales. Differences in alloy composition between 304 and 316 grades of stainless steel led to variations in etch rate and different levels of surface roughness for similar etch times. After fluorocarbon film deposition to lower the surface energy, etched samples of 304 and 316 stainless steel displayed maximum static water contact angles of 159.9 and 146.6°, respectively. However, etching in HF also caused both grades of stainless steel to be susceptible to corrosion. By passivating the HF-etched samples in a nitric acid bath, the corrosion resistant properties of stainless steels were recovered. When a three step process was used, consisting of etching, passivation and fluorocarbon deposition, 304 and 316 stainless steel samples exhibited maximum contact angles of 157.3 and 134.9°, respectively, while maintaining corrosion resistance.

Properties of PbO&lt;sub&gt;2&lt;/sub&gt; Electrode Modified by AEO-7 for Electrocatalytic Degradation of Crystal Violet

In order to improve the performance of PbO2electrode, A kind of surface active agent – AEO-7 was added into nitric acid bath and modified PbO2electrode was prepared on stainless steel substrate by anodic oxidation. The modified variations on surface morphology of the electrodes were examined by Scanning Electron Microscopy(SEM); The polarization curves, Tafel curves and Cyclic voltammograms of modified and unmodified PbO2electrodes were compared in Crystal violet solution; The electrocatalytic activities were inspected by electrocatalytic degradation of crystal violet. It was found that the modified electrode showed higher oxygen evolution potential, better corrosion resistance, and more excellent electrocatalytic activity than the unmodified electrode.

Preparation of Ti/PTFE-F-PbO 2 Electrode with a Long Life from the Sulfamic Acid Bath and Its Application in Organic Degradation

A polytetrafluoroethylene (PTFE)-doped PbO 2 electrode on a Ti substrate was prepared by galvanostatic method from the sulfamic acid bath (Ti/PTFE-F-PbO 2-I) or nitric acid bath (Ti/PTFE-F-PbO 2-II). Scanning Electron Microscopy revealed that the Ti/PTFE-PbO 2-I electrode had a more regular morphology with smaller size crystals than the Ti/PTFE-F-PbO 2-II electrode. On the basis of the results of both the accelerated electrolysis test and the empirical formula for estimating the service life of an electrode, the service life of the Ti/PTFE-PbO 2-I electrode was predicted to be more than 7 years under conventional electrolysis conditions (0.1 A·cm −2). During the treatment of 4-chlorophenol- contaminated water, the Ti/PTFE-PbO 2-I anode showed both a good electro-catalytic activity and high electrochemical stability, exhibiting an excellent potential application.

Electrodeposition of Sb2Se3 on indium-doped tin oxides substrate: Nucleation and growth

The mechanisms related to the initial stages of the nucleation and growth of antimony selenide (Sb2Se3) semiconductor compounds onto the indium-doped tin oxides (ITO) coated glass surface have been investigated using chronoamperometry (CA) technique. The fabrication was conducted from nitric acid bath containing both Sb3+ and SeO2 species at ambient conditions. No underpotential deposition (UPD) of antimony and selenium onto ITO substrate was observed in the investigated systems indicating a weak precursor–substrate interaction. Deposition of antimony and selenium onto ITO substrate occurred with large overvoltage through 3D nucleation and growth mechanism followed by diffusion limited growth. FE-SEM and XRD results show that orthorhombic phase Sb2Se3 particles with their size between 90 and 125nm were obtained and the atomic ratio for antimony and selenium was 2:2.63 according to the EDX results.

Investigations on the electrodeposition behaviors of Bi 0.5Sb 1.5Te 3 thin film from nitric acid baths

The electrochemical reduction process of Bi 3+, HTeO 2 +, Sb III and their mixtures in nitric acid medium was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The reduction products electrodeposited at various potentials were examined using X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results show that cathodic process in the nitric acid solution containing Bi 3+, HTeO 2 + and Sb III involves the following reduction reactions in different polarizing potential ranges: In low polarizing potential ranges, Te 0 is formed firstly on the electrode surface through the electrochemical reduction of HTeO 2 +; with the negative shift of the cathodic polarizing potential, the reduction reaction of Bi 3+ with Te 0 to form Bi 2Te 3 takes place; when the cathodic polarizing potential is negative enough, Bi 3+ and Sb III react with Te 0 to form Bi 0.5Sb 1.5Te 3. The results indicate that Bi 0.5Sb 1.5Te 3 films can be fabricated by controlling the electrodepositing potential in a proper high potential ranges.

Electrochemically deposited thermoelectric n-type Bi2Te3 thin films

Electrochemically deposited n-type BiTe alloy thin films were grown from nitric acid baths on sputtered Bi x Te y /SiO/Si substrates. The film compositions, which varied from 57 to 63 at.% Te were strongly dependent on the deposition conditions. Surface morphologies varied from needle-like to granular structures depending on deposited Te content. Electrical and thermoelectric properties of these electrodeposited Bi x Te y thin films were measured before and after annealing and compared to those of bulk Bi 2 Te 3 . Annealing at 250 °C in reducing H 2 atmosphere enhanced thermoelectric properties by reducing film defects. In-plane electrical resistivity was highly dependent on composition and microstructure. In-plane Hall mobility decreased with increasing carrier concentration, while the magnitude of the Seebeck coefficient increased with increasing electrical conductivity to a maximum of −188.5 μV/K. Overall, the thermoelectric properties of electrodeposited n-type BiTe thin films after annealing were comparable to those of bulk BiTe films.

Reducing blank values for trace analysis of ionic organotin compounds and their adsorption to different materials

Organotin compounds (OTC) are highly toxic pollutants strongly affecting many ecosystems. As analytical techniques for OTC have improved in the past, problems with blank values and adsorption to container walls have been revealed. In this study, OTC adsorption to different materials was studied, and different methods such as derivatization, complexation, extraction, UV-light treatment, nitric acid baths, glowing at high temperatures, and rinsing with detergents and distilled water were tested to reduce OTC blank values from chemicals, solutions, and containers of different materials. Rinsing with detergents and distilled water was effective for decontaminating containers of different materials. Glowing at high temperatures was specifically suitable for glassware and chemicals with high melting points. UV-light treatment was suitable only for solutions. However, OTC underwent disproportionation, and tin became methylated under high temperatures and UV-light treatment. Methods combining sodium tetraethylborate and organic solvent extraction had the best decontamination effects among all methods but were not economical. Sodium borohydride provided another alternative but was less effective. However, use of sodium tetraethylborate and sodium borohydride was restricted to aqueous solution and in certain pH ranges. No material was found without adsorption of all OTC in this study. Tributyltin and dibutyltin adsorbed strongly in the Teflons, polyethylene, and silanized glass. Monomethyltin and monobutyltin had strong adsorption in most materials. Different materials should be used for different OTC in adsorption studies. The use of extraction reagents to recover OTC from container walls is suggested to avoid underestimation of OTC concentrations in waters.

Polluter's Employees Not Protected Under Clean Water Act

John Borowski was the president and owner of Borjohn Optical Technology Inc. and Galaxie Laboratory Inc. (Borjohn). Borjohn disposed of its spent nickel plating baths and nitric acid baths by dumping them directly into plating room sinks without any pretreatment. The sinks drained into underground pipes that fed into the municipal sewer system and from there to the state Water Resource Authority's treatment works. Because of this, Borjohn was subject to pretreatment regulations of the US Environmental Protection Agency that made it a felony to place another person in imminent danger from the pollutants. Borjohn's employees were unavoidably exposed to the chemicals, and Borowski and Borjohn were convicted of two counts of violating the Clean Water Act's knowing‐endangerment felony provision. However, both company and owner were acquitted on appeal.

Advantage of the scanning tunnelling microscope in documenting changes in carbon fibre surface morphology brought about by various surface treatments

The scanning tunnelling microscope (STM) was used to examine the surfaces of P-55 pitch-based carbon fibres before and after they had experienced various surface treatments (to < 1% weight loss), which included treatment in an argon plasma, as well as oxidation in air at elevated temperature, oxygen plasma at room temperature, nitric acid bath, and an electrochemical bath. The effects of these surface treatments on the filaments could be differentiated from the micrometre scale down to the nanometre scale. The STM has been shown to be a valuable tool for viewing the surface morphology of these 10 μm filaments non-destructively in air down to the atomic scale.

Adhesion studies of magnetron-sputtered copper films on chemically etched nickel substrates: Effects of the concentration and the temperature of the bath

The adhesion strength of sputtered copper films to chemically etched nickel substrates has been studied using the scratch adhesion test. The effects of the concentration and the temperature of a nitric acid bath were investigated and it was found that the critical load was very weak unless the amorphous layer produced by mechanical polishing on the substrate surface was eliminated. A chemical etching at room temperature in a nitric acid bath was shown to have only a slight efficiency in the enhancement of the adhesion, whatever the bath concentration was. High critical loads could be obtained when the temperature of the bath was increased to 80 °C. Above this temperature, the critical load enhancement was largely lost. At room temperature, the addition to the bath of small quantities of nickel sulphate (1 gl −1) gave a strong increase in the values of the critical load. A larger addition of sulphate led to poorer results. The roughness of the etched surface was measured with a profilometer and observations were made by scanning electron microscopy. It was observed that, as a general rule, the critical load increases with increasing surface roughness. However, a very important factor in the adhesion strength seems to be the morphology of the surface.

Corrosion and electrochemical characteristics of oxidized steels Kh15N5D2T and Kh15N4AM3

1. We investigated the corrosion resistance in a humid atmosphere and in NaCl solution, the breakdown potential, and the electrode potential of oxidized steel Kh15N5D2T in relation to the oxidation temperature. The steel oxidized at temperatures up to 350°C has a higher breakdown potential, the oxide films do not contain chromium, and formation of the film does not induce improverishment of the steel in chromium below the oxide film. Films formed at higher temperatures are not protective, the steel has a lower breakdown potential, and the chromium concentration below the film is low due to its transfer into the film (scale). 2. We investigated the corrosion resistance and breakdown potential of steel Kh15N4AM3 with a film formed during aging (350\dgC). The corrosion resistance of parts with an oxide film is practically the same as that for parts after removal of the oxide film by chemical means and higher than that after removal of the film by shotblasting with subsequent passivation in a nitric acid bath.