NaCl Acid Solutions Research Articles

Partial characterization of a bacteriocin-like inhibitory substance produced by Streptococcus equinus C6I9, a bovine rumen isolate.

The present study aimed to evaluate the production and the factors that influence the antimicrobial activity of a bacteriocin-like inhibitory substance (BLIS) produced by Streptococcus equinus C6I9, a bovine rumen isolate. The antagonist activity was evaluated by the spot-on-lawn assay. Antimicrobial activity of the crude extracts obtained using NaCl acidic solution (pH 2, 100 mM) was evaluated along the bacterial growth and in growth medium containing different carbon and nitrogen sources, by agar diffusion method. Crude extract was evaluated regarding temperature stability, storage conditions, and pH sensitivity. S. equinus C619 inhibited both Gram-positive and Gram-negative strains. The crude extract was sensitive to proteinase K, and showed great stability to different temperatures and pH (2 to 12). The presence of meat extract (1.5 g/L) and sucrose (8 g/L) resulted in higher production of BLIS by S. equinus C6I9. The BLIS molecular mass was determined as approximately 3.5 kDa. The results obtained in this study evidenced the production of a broad spectrum activity, thermo- and pH stable BLIS by the ruminal isolate S. equinus C6I9, important features for its biotechnological application.

A New Imidazole Derivative for Corrosion Inhibition of Q235 Carbon Steel in an Acid Environment.

Q235 carbon steel is a commonly used engineering material, but its application in marine environments is limited by its susceptibility to corrosion, especially localized corrosion that can lead to material perforation. Effective inhibitors are crucial to addressing this issue, particularly in acidic environments where localized areas become increasingly acidic. This study reports the synthesis of a new imidazole derivative corrosion inhibitor and evaluates its effectiveness in corrosion inhibition performance using potentiodynamic polarization curve and electrochemical impedance spectroscopy techniques. High-resolution optical microscopy and scanning electron microscopy were employed for surface morphology analysis. Fourier-transform infrared spectroscopy was used to explore the protection mechanisms. The results demonstrate that the self-synthesized imidazole derivative corrosion inhibitor offers an excellent corrosion protection performance for Q235 carbon steel in a 3.5 wt. % NaCl acidic solution. This inhibitor can provide a new strategy for carbon steel corrosion protection.

Study of Glycerol as an Additive in Ni-Mo Electrodeposition

This paper evaluates the effect of adding glycerol to the electrodeposition bath on the deposition efficiency and characteristics of Ni-Mo coating in concentrations ranging from 0.07 to 0.82 mol.L-1. Evaluation of the corrosion resistance was performed by means of weight loss tests in four different periods of immersion. Electrochemical techniques, such as obtaining polarization curves, linear polarization resistance, corrosion current density, corrosion potential, and electrochemical impedance spectroscopy were applied. Corrosion measurements were obtained in 0.5 mol.L-1 NaCl acid solution and 0.5 mol.L-1 NaOH alkaline solution. The morphology and microstructures of electrodeposited were analyzed using Scanning Electron Microscopy and Spectrometry X-Ray Diffraction. The effect of glycerol on Ni-Mo hardness was evaluated by Vickers microhardness measurements. The presence of glycerol in the electrodeposition bath increased the grain size and decreased the hardness of the coating. However, it promoted the formation of a more compact and less porous coating, increasing the corrosion resistance of the coating. Moreover, the addition of 0.82 mol.L-1 glycerol increases current efficiency, thereby reducing the amount of energy consumed during electroplating.

Combined Experimental and Theoretical Insights into the Corrosion Inhibition Activity on Carbon Steel Iron of Phosphonic Acids.

The inhibition effect of N,N′-phosphonomethylglycine (PMG) and vinyl phosphonic acid (VPA) on the 3% NaCl acidic solution corrosion of carbon steel iron was studied at different immersion times by potentiodynamic polarization, electrochemical impedance spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and computational methods. It is found from the polarization studies that PMG and VPA behave as mixed-type inhibitors in NaCl. Values of charge transfer resistance (Rct) and double layer capacitance (Cdl) in the absence and presence of inhibitors are determined. The PMG and VPA inhibitors were capable of inhibiting the corrosion process up to ≈91% and ≈85%, respectively. In the presence of PMG, the synergic effect of chlorine ions was observed. Density functional theory (DFT) was engaged to establish the adsorption site of PMG, VPA, and their deprotonated states. For studied compounds, the resulted values of ELUMO, EHOMO, energy gap (∆E), dipole moment (μ), electronic hardness (η), global softness (σ), electrophilic index (ω), and the electronic potential map are in concordance with the experimental data results regarding their corrosion inhibition behavior and adsorption on the metal surface.

Hybrid silica-carbon bilayers anchoring on FeSiAl surface with bifunctions of enhanced anti-corrosion and microwave absorption

Most of the magnetic microwave absorbers are ineffective in extreme corrosive environments of acids and alkalis which abruptly reduce their performance. Therefore, it is urgent and worthwhile to produce the bifunctional materials with excellent corrosion resistance and microwave absorption property. This work presents the in-situ growth of double shells of silica and carbon on FeSiAl (FSA) alloy surface to obtain an integrated FSA@SiO2@C hybrid structure via combined Stöber and catalytic chemical vapor deposition (CCVD) techniques. The hybrid structure acquires the strengthened bi-functional for anti-corrosion and microwave absorption due to the excellent corrosion shielding protection and well dielectric properties of SiO2 and carbon hybrid structure. Importantly, the hybrid morphology retains excellent stability of more than 150 h in 5.0 wt% NaCl acid solution. Moreover, FSA@SiO2@C hybrid possesses enhanced microwave absorption performance with a minimum reflection loss (RLmin) of −46.75 dB at 5.74 GHz with a matching thickness of 3.5 mm, and the effective bandwidth (RL < −10 dB) up to 7.73 GHz at 2.5 mm thickness. While considering the excellent corrosion resistance and microwave absorption characteristics, the novel hybrid organization opens up the opportunity to design materials for valuable addition at commercial level.

Fractionation of REE, U, and Th in natural ore-forming hydrothermal systems: Thermodynamic modeling

This contribution presents a thermodynamic model revealing the mechanisms responsible for separation of Heavy and Light Rare Earth (HREE and LREE) phosphates in natural hydrothermal systems at temperatures of 250–350 °C. Our calculations were performed for an isothermal column of rock containing 0.5 wt% of apatite (Ca phosphate), which served as an immobilizing agent for REE dissolved in the solution. REE were transported by 10 wt% NaCl acidic solution. The model accounted for formation of REE phosphate solid solutions through a regular mixing model. It demonstrates that hydrothermal flushing can efficiently separate REE forming xenotime (HREE phosphate solid solutions) at the beginning of the column, and re-transportation of monazite (LREE rich) to the end of the column. This separation is primarily due to the fact that at elevated temperatures stability LREE chloride complexes is significantly higher than that for HREE. The model also evaluates behavior of U and Th, which accompany REE in vast majority of natural locations. It was found that U strongly fractionates to xenotime, whereas Th fractionates to monazite. This phenomenon can be explained by the differences in crystal-chemical characteristics between monazite and xenotime, and the mobility of Th in aqueous solutions at elevated temperatures.

Adsorption and corrosion inhibition properties of floxapen compound on the electrochemical characteristics of type-A5-series aluminium in sodium chloride solution

The inhibition performance of floxapen compounds on the electrochemical corrosion behaviour of A5 series aluminium in 3.5% NaCl acid solutions was studied through weight loss method and potentiodynamic polarisation test. The results obtained showed that the organic drug compound performed effectively in sodium chloride solutions with average floxapen compounds inhibition efficiency of 68% from weight loss and potentiodynamic polarisation test respectively. Results from corrosion thermodynamic calculations showed that the adsorption of floxapen compounds onto the aluminium was through chemisorption mechanism whereby the redox electrochemical progression responsible for corrosion initiation and the electrolytic transport of corrosive anions were concurrently suppressed. Adsorption of the compound was determined to obey the Langmuir and Frumkin isotherm model.

Influence of Li addition to passivity behavior of pure Al in NaCl acidic solution

The passive films on pure Al, Al‐1Li alloy, and Al‐2Li alloy were formed at a passive potential of −0.75 VSCE by potenyiostatic polarization for 30 min in 0.1 mol/L NaCl acidic solution (pH = 2). The corrosion resistances, semiconducting properties, and compositions of the passive films were, respectively, investigated by electrochemical impedance spectrum (EIS), Mott–Schottky (M–S) approach, and X‐ray depth photoelectron spectroscopy (XPS). The results showed that 1 and 2 wt% Li addition to pure Al improved its passivity resistance, especially for 2 wt% Li. Moreover, Li participated in the passive film formation process. The incorporation of Li2O by filling in the lattice interstitial position of Al2O3 could decrease oxygen vacancy concentration but did not change the n‐type semiconductor character of the passive films on pure Al. The increasing of passivity resistance was attributed to the decreasing of oxygen vacancy concentration and the increasing of Fermi energy of the passive films due to Li addition to pure Al.

Influence of grain size on the corrosion behavior of a Ni-based superalloy nanocrystalline coating in NaCl acidic solution

The effects of grain size on the electrochemical corrosion behavior of a Ni-based superalloy nanocrystalline (NC) coating fabricated by a magnetron sputtering technique, has been investigated in 0.5 M NaCl + 0.05 M H 2SO 4 solution. Coatings with grain sizes 10 nm, 50 nm and 100 nm were fabricated on glass and the superalloy substrates. The results indicate that a passive film with porous property, n-type semiconductive property and incorporation of chloride ions formed on the NC coating with 100 nm grain size, which increased the susceptibility to pitting corrosion. The NC coatings with 10 nm and 50 nm grain size formed compact, non-porous and p-type passive films without chloride ions, which improved resistance to pitting corrosion. The smaller grain size of the material decrease the amount of chloride ions adsorbed on the surface and promoted the formation of compact passive film, which significantly increased the material's resistance to pitting corrosion in acidic solution.

Effect of silicon content on wear resistance and corrosion behaviour of Al–Si eutectic alloy

In the present study, Al–Si eutectic alloys produced at the Aluminium Institution were studied. The alloys were cast and forged into bars of 20 mm diameter. The results obtained were compared with a pure aluminium sample. Metallographic analysis, spectral analysis, SEM and energy dispersive spectroscopy analysis, pin on disk abrasive wear tests and mass loss tests were performed. Wear resistances of alloys with various silicon contents were tested under different loads and constant abrasive speed. SiC abrasive paper of 80 grit size was used. The dry sliding tests were carried out under loads of 10, 20 and 30 N and the testing was conducted under a constant sliding velocity of 36˙8 m min–1 in a dry air atmosphere. Corrosion rates were determined in 0˙1M NaCl acid solutions. The corrosion tests were performed at 2, 4, 6 and 8 h. The wear and corrosion resistance of all the eutectic alloys increased with increasing silicon content in the matrix.

Electrochemical corrosion behaviour of microcrystalline aluminium in acidic solutions

The electrochemical corrosion behaviour of microcrystalline pure aluminium coating, fabricated by a magnetron sputtering technique, has been investigated in both 0.5 mol/l NaCl and 0.5 mol/l Na 2SO 4 acidic (pH = 2) aqueous solutions. The corrosion resistance of the microcrystalline Al coating has deteriorated more compared with that of the cast pure Al in Na 2SO 4 acidic solution. However, its oxide film has a higher pitting resistance in the NaCl acidic solution. Chloride ions play a big role in the formation of the oxide film on the microcrystalline Al coating. The higher pitting resistance was attributed to the more acidic isoelectric point which the oxide film achieved.

Influence of nanocrystallization on passive behavior of Ni-based superalloy in acidic solutions

The electrochemical corrosion behaviors of Ni-based superalloy nanocrystalline coating (NC) fabricated by a magnetron sputtering technique have been investigated in comparison with cast alloy in 0.25 M Na 2SO 4 + 0.05 M H 2SO 4 and 0.5 M NaCl + 0.05 M H 2SO 4 solution, respectively. Compared with cast alloy, the NC coating had a little higher passive current density in Na 2SO 4 acidic solution, while it had superior resistance to pitting corrosion in NaCl acidic solution. The semiconductive type of passive film of the NC coating was p-type in both acidic solutions, while, that of cast alloy changed from p-type in Na 2SO 4 acidic solution to n-type in NaCl acidic solution. XPS results indicated that Cr 2O 3 was the main component for the passive films of the NC coating as well as those of the cast alloy. No chloride ion was found in the passive film of NC coating while it was in the passive film of cast alloy. The chloride ions adsorbing on the surface of cast alloy incorporated into the passive film, which induced the formation of n-type oxide film. The nanocrystallization of Ni-base superalloy obviously weakened the adsorption of chloride ions on surface, which decreased the susceptibility of pitting corrosion in acidic solution.

Corrosion inhibition of carbon steel by an amine- fatty acid in acidic solution

The corrosion inhibition of carbon steel in 3% de-aerated NaCl acidic solution with amine–fatty acid corrosion inhibitor, KI384, was investigated at different temperatures using potentiodynamic polarization technique. The Corrosion rate was calculated in the presence and absence of inhibitor. The inhibition increased with an increase in inhibitor concentration and decreased with rise in temperature. The maximum percentage inhibitor efficiency was obtained at 35 oC. The percentage inhibition up to 99% was registered at a concentration of 10 ppm of KI384. The inhibitor acts as a mixed type at lower temperature and predominantly anodic at high temperature. The interrelationship between the surface coverage and concentration of the inhibitor was also studied. It was found that the inhibitor obeys Langmuir adsorption isotherm and adsorbs on the metal surface through physical adsorption. Tanz. J. Sci. Vol.29(1) 2003: 99-108