Inhibition of Aluminum Alloy Corrosion in 0.5 M Nitric Acid Solution by 4-4-Dimethyloxazolidine-2-thione

The corrosion inhibition of Al-Alloy (Al2024) in 0.5 M nitric acid solution at 30 °C was achieved using 4-4-dimethyloxazolidine-2-thione (DMT) as a corrosion inhibitor. The electrochemical performance of the DMT was studied by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization measurements, and scanning electron microscopic study (SEM). The results indicated that DMT acts as an inhibitor for Al2024 in 0.5 M nitric acid. Polarization curves indicated that DMT was a mixed-type inhibitor. Inhibition efficiencies were observed to be increased with an increase in DMT concentration and attains approximately to 93.4% at 2 mM of DMT in 0.5 M nitric acid. The adsorption of DMT model on Al2024 surface obeyed in accordance with Langmuir adsorption isotherm model. The value of the free energy of adsorption ΔG _ads indicated that the adsorption of DMT molecule was a spontaneous process and was typical of physical and chemical adsorption.     

Protective Aftereffect of IFKhAN-92 Inhibitor for Corrosion of Nickel–Chromium Steel in Hydrochloric Acid

It is shown that the multimolecular protective layer of an organic inhibitor formed on the surface of chromium–nickel steel in an HCl solution containing a triazole derivative, the inhibitor IFKhAN-92, has a protective aftereffect in background solutions of the same acid. Such a protective layer is chemically bonded to the Fe, Cr, and Ni oxide and hydroxide phase adjacent to the metal phase. The lower part of the polymolecular protective layer of the organic inhibitor consists of a polymer complex formed by IFKhAN-92 molecules, metal cations (Fe, Cr, and Ni), and chloride anions, and the outer part consists of physically adsorbed IFKhAN-92 molecules, which are easily removed from the metal surface during ultrasonic washing of samples.

     

Pitting Corrosion in Copper Tubes – Cause of Corrosion and Counter-Measures

Abstract

An investigation of failures of hard-drawn copper water pipes (phosphorus-deoxidised copper) in service due to pitting corrosion was conducted from November, 1962 to February, 1965. Fifteen cases were reported. All those about which information could be obtained came from hot water installations and occurred in water with a low pH (≤7) and a HCO_3- content of, at the most, 100 mg/l but generally below 50 mg/1. Failures not due to pitting corrosion (i.e. caused by erosion and corrosion or corrosion fatigue) occurred in waters with a higher pH and higher HCO₃- content.

A laboratory investigation into the ability of the corrosion products to counteract further corrosion in different types of water was also carried out, using an electrolytic cell which, in principle, was a model of an active pit in a copper tube. This led to the following conclusions, which are in good agreement with the results obtained from the examination of service failures:

If the pH value of the water is high enough, the copper dissolved by the corrosion can be precipitated as basic copper salt. At low pH values such precipitation does not take place.

If the [HCO₃^?]/[SO₄^2?] ratio in the water is high, dissolved copper can be precipitated as basic copper carbonate in the neighbourhood of the corrosion site and counteract further corrosion.

At a low [HCO₃^?]/[SO₄^2?] ratio, crusts of basic copper sulphate will be precipitated at some distance from the corrosion site and may lead to a high corrosion rate.

Pitting is not likely to occur in hot water tubes of hard copper if the pH is ≥ 7·4 and the [HCO₃^?]/[SO₄^2?] ratio ≥1 (the concentrations given in mg/1). The critical values mentioned are approximate and may be adjusted in the light of future experience.     

Adsorption Properties and Inhibition of Mild Steel Corrosion in 0.5 M H2SO4 Solution by Some Triazol Compound

The effect of 3,5-dimethylbenzoic acid [1,2,4]triazol derivative (DBTE) on the corrosion of mild steel in 0.5 M H₂SO₄ solution was evaluated in this study by means of weight loss test, EIS, potentiodynamic polarization, and SEM. The results revealed that DBTE acted as a mixed-type inhibitor without change of the mechanism of hydrogen evolution. The inhibition efficiency increased with the increase in concentration of DBTE, and the adsorption behavior of DBTE on the mild steel surface followed the Langmuir adsorption isotherm. The thermodynamic parameters reveal that the chemisorption was the dominant adsorption process, and good inhibition performances in the studied range of temperatures were observed.     

Corrosion and Electrochemical Behavior of Ni–P Coatings in 0.5 M H2SO4

An increase in the phosphorus content in Ni–P coatings (from 6.6 to 13.4%) is shown to be accompanied by amorphization of their structure and a decrease in the anodic dissolution rate (at low overvoltages) by two–three orders of magnitude, whereas the corrosion rate is decreased to a lesser degree. Polarization curves of the coatings measured in 0.5 M H₂SO₄ comprise two linear segments and no passive range. In the first segment, the b _a coefficient is shown to be anomalously high (0.4–0.5 V for amorphous alloys), and the dissolution is controlled by transient volume diffusion of nickel and accompanied by surface accumulation of phosphorus. Being added as a stabilizer, thiourea reduces the corrosion resistance of the coatings and increases the dissolution currents, which can be to a considerable degree eliminated by increasing the phosphorus content in the coatings. The adverse effect of Pb incorporation into the coatings manifests itself as a substantial acceleration of their anodic dissolution.     

Electrochemical Evaluation of Corrosion on Borided and Non-borided Steels Immersed in 1 M HCl Solution

In this study the corrosion resistances of AISI 1018 and AISI 304 borided and non-borided steels were estimated using polarization resistance and electrochemical impedance spectroscopy (EIS) techniques. Boriding of the steel samples was conducted using the powder-pack method at 1223 K with 6 h of exposure. Structural examinations of the surfaces of the borided steels showed the presence of a Fe₂B layer with isolated FeB teeth on the AISI 1018 steel, whereas a compact layer of FeB/Fe₂B was formed on the AISI 304 steel. Polarization resistance and EIS of the borided and non-borided steels surfaces were performed in a corrosive solution of 1 M HCl. The EIS data were analyzed during 43 days of exposure to the acid solution. Impedance curves obtained during this period for the borided and non-borided steels were modeled using equivalent electrical circuits. The results of both electrochemical techniques indicated that boride layers formed at the steel surfaces effectively protect the samples from the corrosive effects of HCl. The main corrosion processes observed on the boride layers were pitting and crevice corrosion.     

Estimation of the Corrosion Resistance of ВНС-17 and ЭИ-69 Steels after Nitriding Them in a Magnetic Field

The corrosion resistance of composite phosphate–nitride layers on -17 and -69 stainless steels nitrided in a magnetic field is discussed. The protection of the steels in a 3%NaCl solution is shown to be of a predominantly electrochemical mechanism.     

Ring--Like Solidification Structure Of Mnbi Phase In Bi—Mn Alloy Under A High Magnetic Field

对强磁场作用下Bi-Mn合金分别从全熔态和从固液两相区开始的凝固过程及其组织的实验研究表明，磁场使初生MnBi相在试样外侧呈环状偏聚，其自身生长为棒状，棒的长轴沿磁场方向呈定向规则排列，而试样心部基本无初生MnBi相。在Curie点以上开始进行较慢的凝固时，由片状聚合而成的棒状MnBi具有单晶特征。对以上现象的形成原因进行了分析。     

Oxygen Incorporation in Czochralski Growth of Silicon under a Horizontal Magnetic Field

A mechanism of oxygen transportation in Czochralski growth of silicon crystals under a horizontal magnetic field(HMCZ)is proposed.Oxygen depleted surface melt,driven to the growth interface by the thermal Marangoni flow.determines oxygenconcentration in the grown crystals.Systematic study was carried out to investigate effects of growth parameters on oxygen in-corporation into crystals.     

Curcumin Derivatives as Green Corrosion Inhibitors for α-Brass in Nitric Acid Solution

1,7-Bis-(4-hydroxy-3-methoxy-phenyl)-hepta-1,6-diene-4-arylazo-3,5-dione I-V have been investigated as corrosion inhibitors for ??-brass in 2?M nitric acid solution using weight-loss and galvanostatic polarization techniques. The efficiency of the inhibitors increases with the increase in the inhibitor concentration but decreases with a rise in temperature. The conjoint effect of the curcumin derivatives and KSCN has also been studied. The apparent activation energy (E _a*) and other thermodynamic parameters for the corrosion process have also been calculated. The galvanostatic polarization data indicated that the inhibitors were of mixed-type, but the cathode is more polarized than the anode. The slopes of the cathodic and anodic Tafel lines (b _c and b _a) are maintained approximately equal for various inhibitor concentrations. However, the value of the Tafel slopes increases together as inhibitor concentration increases. The adsorption of these compounds on ??-brass surface has been found to obey the Frumkin??s adsorption isotherm. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitors.     

Corrosion Behavior of Copper–Nickel Alloys in Neutral Chloride and Sulfide Containing Solutions

The corrosion behavior of Cu30Ni and 30-1-1 alloys in oxygen-containing chloride solutions (0.1–0.5 N NaCl) with and without Na₂S additive (2–1000 mg/l) is studied with radiometric and electrochemical methods by taking into account the amount of oxygen sorbed in the course of corrosion. In blank solutions, a film of corrosion products is formed on the alloy surface; the thickness and copper content of the film increase with a decrease in chloride concentration. The corrosion rate in sulfide-containing solutions is higher than in sulfide-free ones. In the initial corrosion period, nickel compounds are accumulated in the film. With an increase in sodium sulfide concentration, corrosion accelerates. Additionally alloying the Cu30Ni alloy with manganese and iron reduces its rate by half.     

Scanning Electrochemical Microscopy for the Investigation of Galvanic Corrosion of Iron with Zinc in 0.1 M NaCl Solution

Scanning electrochemical microscopy was used to monitor microscopic aspects of the electrochemical processes at the iron-zinc couple immersed in 0.1 M NaCl aqueous solution. The SECM measured the concentration of chemical species relevant to the corrosion processes. The electrochemical behavior of galvanic Fe/Zn coupling was investigated as a function of time using SECM microelectrode both as Fe/Zn joined together as well as away from each other. SECM amperometric line scan curves were obtained over the Fe/Zn at a constant distance. In the first case, the chemical species participating in the corrosion reactions at the sample are detected at the SECM tip by applying appropriate potential values to the microelectrode. The release of Zn²⁺ ionic species into the solution phase from local anodic sites, as well as the consumption of dissolved oxygen at the corresponding cathodic locations, was successfully monitored. The results revealed that the galvanic couple where Fe/Zn is close to each other will show higher corrosion rate of zinc than that of galvanic couple away from each other. The Fe/Zn couple away from each other showed a decrease in current values with time. This is due to the formation of oxide layer of Zn over the Fe followed by the protection of the corrosion products with further exposure times.     

High-Temperature Corrosion Behaviour of Aluminized-Coated and Uncoated Alloy 718 Under Cyclic Oxidation and Corrosion in NaCl Vapour at 750 °C

To evaluate the suitability of HR3C and 22Cr–25Ni–2.5Al AFA steels as the heat-resistant alloys, the oxidation behavior of them was investigated in air at 700, 800, 900 and 1000 °C. The evolution of oxide layer on the surface and subsurface was investigated using a combination of compositional/elemental (SEM, EDS) and structural (XRD, GDOES) techniques. A dense and continuous Cr₂O₃ healing layer on the HR3C was formed at the temperature of 700 or 800 °C, but the Cr₂O₃ oxide film on HR3C was unstable and partly converted into a less protective MnCr₂O₄ with the increase in temperature to 900 or 1000 °C. The composition and structure of oxide film of 22Cr–25Ni–2.5Al AFA steels are significantly different to the HR3C alloys. The outer layer oxides transformed from Cr₂O₃ to Al-containing oxides, leading to a better oxidation resistance at 700 or 800 °C compared to HR3C. Further, the oxide films consist of internal Al₂O₃ and AlN underneath the outer loose layer after 22Cr–25Ni–2.5Al AFA oxidized at 900 or 1000 °C. It can be proved that the internal oxidation and nitrogen would make 22Cr–25Ni–2.5Al AFA steels have worse oxidation resistance than HR3C alloys at 900 or 1000 °C.     

Acid Corrosion of an AД-1M Alloy under a Contact Deposition of Tin

The effect of a concurrent substitution of tin for aluminum on the corrosion rate of the latter in hydrochloric acid solutions is studied. In the case of an insignificant contribution of the contact exchange current (shortly named metal depolarization), the aluminum corrosion rate is determined by its surface coverage with tin and the deposition time. Nonmonotonic time dependence of the corrosion rate can be associated with the kinetics of tin deposition. The equation estimating the inhibition coefficient as a function of the aluminum surface fraction occupied by the tin deposit is given.     

The Inhibition Effect of Synthesized 4-Hydroxybenzaldehyde-1,3propandiamine on the Corrosion of Mild Steel in 1 M HCl

The corrosion inhibition of mild steel in 1 M HCl by 4-hydroxybenzaldehyde-1,3propandiamine (4-HBP) has been investigated using potentiodynamic polarization, electrochemical impedance spectroscopy and chronoamperometry measurements. The experimental results suggest that this compound is an excellent corrosion inhibitor for mild steel and the inhibition efficiency increases with the increase in inhibitor concentration. Polarization curves reveal that this organic compound is a mixed-type inhibitor. The effect of temperature on the corrosion behavior of mild steel in 1 M HCl with the addition of the Schiff base was studied in the temperature range from 25 to 65 °C. The experimentally obtained adsorption isotherms follow the Langmuir equation. Activation parameters and thermodynamic adsorption parameters of the corrosion process such as E _a, ΔH, ΔS, K _ads, and ΔG _ads were calculated by the obtained corrosion currents at different temperatures and using the adsorption isotherm. The morphology of mild steel surface after its exposure to 1 M HCl solution in the absence and in the presence of 4-HBP was examined by AFM images.     

Indole Alkaloids of Alstonia angustifolia var. latifolia as Green Inhibitor for Mild Steel Corrosion in 1 M HCl Media

The inhibition effect of mild steel (MS) corrosion in 1 M HCl was studied by the addition of indole alkaloids (crude) isolated from Alstonia angustifolia var. latifolia (A. latifolia) leaves at 303 K. Potentiodynamic polarization, impedance spectroscopy, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) analyses were used for this study. Results show that the isolated alkaloid extract of A. latifolia is a good inhibitor and exhibited maximum inhibition efficiency (above 80%) at concentrations between 3 and 5 mg/L. Polarization measurements indicated that the inhibitor does not alter the mechanism of either anodic or cathodic reactions and acted as mixed-type inhibitor. The inhibition efficiencies of both electrochemical techniques are found to be in good agreement and adsorption of inhibitor follows Langmuir isotherm. Adsorption of inhibitor over metal surface was well supported by the SEM studies, while FTIR studies evidenced the presence of indole alkaloids as green inhibitor that reduces the rate of corrosion.     

Thermodynamic and Electrochemical Investigations of Poly(Methyl Methacrylate–Maleic Anhydride) as Corrosion Inhibitors for Mild Steel in 0.5 M HCl

Protection of Metals and Physical Chemistry of Surfaces - In this research, poly(methyl methacrylate-maleic anhydride)P(MMA-MAH)s with different percentages methyl methacrylate and maleic anhydride...     

Effect of Morinda Tinctoria Leaves Extract on the Corrosion Inhibition of Mild Steel in Acid Medium

The Morinda tinctoria (MT) plant leaves extract was prepared in aqueous and hydrochloric acid media and was used as corrosion inhibitor for mild steel in hydrochloric acid medium. MT is found to be an efficient inhibitor at room temperature and the efficiency decreases with increase in temperature. Results from colorimetric studies predict the amount of iron present in the test solution and the percentage inhibition efficiency values calculated from this data fit well with the weight loss experiments. The AC impedance studies reveal that the mild steel surface is positively charged and the process of inhibition is through charge transfer. Polarisation studies indicate the mixed nature of the inhibitor. Thermodynamic parameters obtained predict that the process of inhibition is a spontaneous one.     

Electrochemical Corrosion Behavior of Magnetron-Sputtered Al-Mo Gradient-Coated Steel in 3.5 wt.% NaCl Solution

A gradient three-layer Al-Mo coating was deposited on steel using magnetron sputtering method. The corrosion properties of the coating were studied in 3.5 wt.% NaCl solution using electrochemical techniques, whereas the hydrogen-induced cracking (HIC) resistance was examined by constant-load tests using notched tensile specimens. These results were compared with conventional electroplated cadmium-coated steel. The results show that the gradient Al-Mo coating exhibits better corrosion and HIC resistance when compared to electroplated cadmium. This was due to the excellent corrosion resistance of the bottom aluminum-rich layer, while the top Mo-rich layer provided good lubrication properties.     

The Corrosion Behavior of Ni<Subscript>3</Subscript>(Si,Nb) Alloys in Boiling 70 wt.% Sulfuric Acid

Corrosion-resistant Ni₃(Si,Nb) alloys are promising materials of construction for hydrogen-production systems based on the sulfur-iodine thermochemical cycle. In this work, the corrosion rates of three different Ni₃(Si,Nb) alloys were measured in boiling 70 wt.% sulfuric acid and a three-stage corrosion mechanism was identified, based on the composition and morphology of surface scale that developed. The α(Ni) + β(Ni₃Si) eutectic constituent of the alloy microstructure was selectively attacked by acid and, when present, is detrimental to corrosion resistance. The G-phase (Ni₁₆Si₁₇Nb₆) is more passive than the β-matrix and seems to contribute to a lower steady-state corrosion rate.