Synergistic effects of formaldehyde and alcoholic extract of plant leaves for protection of N80 steel in 15%HCl

Abstract

The synergistic effects of formaldehyde and an alcoholic extract of plant leaves have been studied by weight loss measurements at temperatures up to 363 K using various concentration ratios of the two inhibitors to protect N80 steel against corrosion in 15% hydrochloric acid. The inhibition efficiency was found to decrease with increasing temperature for all except two of the various concentration ratios that were studied. After identifying these two most promising mixtures, their corrosion prevention effects for N80 steel in hydrochloric acid were studied in more detail by weight loss and potentiostatic polarisation measurements. The corrosion rate of the steel was decreased by the presence of small additions of the inhibitors. The extent of decrease was found to depend on the nature of the corrosion inhibitor and its concentration. The inhibition efficiencies of the two plant based inhibitor mixtures were compared with those of two commercially available oil industry corrosion inhibitors. In all cases the adsorption of the inhibitors on the steel appeared to follow the Frumkin or Langmuir adsorption isotherm. The inhibition efficiencies of the two plant based inhibitors and the two commercial inhibitors were evaluated at a concentration level of 0.8% for temperatures in the range 303 K to 363 K) and exposure times of between 1 h and 24 h. Thermodynamic parameters including the free energy of adsorption, activation energy, enthalpy and entropy were calculated in both the absence and presence of inhibitors. Potentiostatic polarisation tests have revealed that inhibitors are primarily of the anodic type.     

Investigation of pitting potential of carbon steel using experimental design method

Abstract

The dependence of the pitting potential E_p of 1018 carbon steel on chloride concentration, pH and the temperature of the solution was studied by the potentiodynamic method in accordance with a statistical experimental design. The parameters of the empirical pitting potential model determined on the basis of Box-W ilson ex perimental design method were evaluated using the experimental data. Comparison of the predicted values from the model with the observed values showed that the model is a good fit. From the model equation the most noble pitting potential value of -225 mV (SCE) was obtained when the Cl^- ion concentration, temperature and pH of the solution were 205 ppm, 25°C, and 6·4, respectively. The Box-Wilson experimental design technique was proved to be applicable in modelling the pitting potential of carbon steel.     

Inhibition of steel and galvanised steel corrosion by zinc and calcium ions in the presence of phosphate

Abstract

Mixtures of zinc, calcium and phosphate ions have been found to be effective (>90%) in inhibiting the corrosion of steel and zinc during immersion in acid rain solution and when used as pigment additions to organic coatings. The presence of calcium ions, in addition to zinc ions, appears to be fundamental in the inhibition mechanism since, in the absence of calcium, the inhibition efficiency is 50% or less. Although some anodic inhibition occurs, the predominant mechanism appears to be classical cathodic inhibition caused by the precipitation of a sparingly soluble, thin, but persistent, solid film. Surface analysis, by XPS, confirms that phosphorus is present in the form of phosphate species containing zinc and calcium. Also, the atomic ratios of zinc:calcium:phosphorus present in the inhibitive film strongly suggest that it consists of a mixture of CaZn₂(PO₄)₂ (Scholzite) and Zn₃(PO₄)₂ (Hopeite) in a 1 : 1 ratio.     

Inhibition of mild steel by strontium chromate in artificial acid rain solution

Abstract

The inhibition of mild steel in an artificial acid rain solution (pH 4·5) in low concentrations of strontium chromate pigment has been evaluated using a range of methods: potentiodynamic polarisation, electrochemical impedance, X-ray photoelectron spectroscopy and solution analysis. The individual effects of strontium and chromate have been evaluated and have been used to estimate inhibitor efficiency and film composition, and to determine the possible inhibition mechanism. The results show that, at low concentration, strontium chromate affects the cathodic reaction, with reduction of Cr⁶⁺ to Cr³⁺, and the surface film was composed of magnetite and hydrated chromium hydroxide. The presence of strontium was not found significantly to affect the inhibitory performance.     

Reliability improvement of conductive adhesives on tin (Sn) surfaces

Effective organic corrosion inhibitors are introduced into a typical electrically conductive adhesive (ECA) formulation and evaluated. With the incorporation of small amounts of these additives, lower bulk resistivity and highly stable contact resistance on tin (Sn) surfaces were achieved. Contact angle, grazing angle Fourier Transfer Infrared (FT-IR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS) characterizations showed the presence of coatings of the corrosion inhibitors on the metal surfaces. A barrier passivation layer formed on Sn surfaces with the effective corrosion inhibitors. X-ray diffraction analysis confirmed that such a passivation layer protected the Sn surface and prevented oxidation and corrosion under elevated temperature and humidity environment.     

Corrosion inhibition of mild steel by polyhydric alcohol phosphate ester (PAPE) in natural sea water

Abstract

The corrosion inhibition of mild steel by polyhydric alcohol phosphate ester (PAPE) in natural sea water has been investigated by polarisation curves, electrochemical impedance spectroscopy (EIS) and surface analytical techniques. The results have shown that PAPE acts as a mixed type (anodic and cathodic) negative catalytic effect interface inhibitor and that the adsorption is of the Langmuir type. The inhibitor can adsorb immediately and compactly on the steel surface, the thickness of the film increasing with time. The adsorption behaviour involves the formation of complexes between the R1 functional group of the PAPE molecular structure and metal ions on the steel surface, such as Fe²⁺, Mg²⁺, Ca²⁺, etc.     

Corrosion and other Causes of Failure of Electric Immersion Heater Elements in New Zealand: II. Elements Tested Under Laboratory Conditions

Abstract

Factors influencing immersion heater element corrosion are investigated. It is shown that elements can continue heating water for considerable times after the insulation has become wet due to water penetration following corrosion. New corrosion palliatives are suggested—particularly cathodic protection and the electrical insulation of the element sheath from the boss and the tank.     

Inorganic interfacial engineering: processing of hard materials

Abstract

Inorganic interfacial engineering may be regarded as the core of powder metallurgical processing of hard materials. The present paper reviews recent results from an interdisciplinary research effort, BRIIE (the Brinell Centre for Inorganic Interfacial Engineering), a joint effort between five industrial companies, three universities, two research institutes and VINNOVA (the Swedish Agency for Innovation Systems). The research involves experimental work on the aqueous processing of powders and the use of surface actants is reviewed as well as the colloidal processing of ceramics. Pressing and sintering of agglomerated powders have been studied both theoretically and experimentally. Models for the simulation of pressing and sintering of hard metal powders are developed. Results on ceramic materials obtained by spark plasma sintering and their resistance to thermal shock are reported.     

Citric acid as natural corrosion inhibitor for aluminium protection

Abstract

The inhibition effect of citric acid on the corrosion behaviour of aluminium in 2M NaCl solution (pH 2) was studied with the help of potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS) and linear polarisation resistance (LPR) techniques. The experimental results showed that citric acid inhibits the corrosion of aluminium in NaCl solution and the inhibition efficiency depends on its concentration. The protection efficiency increases with citric acid concentration up to a critical value of 1·0 × 10^?5M. At higher concentrations, the inhibition efficiency reduced again with increasing concentration. The mechanism of inhibition was attributed to the adsorption of citric acid onto the metal surface.     

Comparison of pitting susceptibility of passive films formed on iron with different inorganic inhibitors

Abstract

The pitting susceptibility of passive films on iron in chloride containing solution, formed using three different inorganic inhibitors, chromate, nitrite and bicarbonate, is determined using linear sweep voltammogram. It is found that the pitting susceptibility becomes stronger in the order of the passive films formed in 0 · 01M chromate, 0 · 1M nitrite and 0 · 5M bicarbonate. The difference in pitting susceptibility is explained by the difference in electronic property of the passive films, which is determined using Mott–Schottky measurements. The donor density of the passive films formed in bicarbonate is highest, followed by nitrite and then by chromate, although the concentration of bicarbonate is five times that of nitrite and 50 times that of chromate. This suggests that the passive film formed in bicarbonate is most susceptible to attack by chloride ions.