Effect of intermittent cathodic protection on potential and corrosion rate of carbon steel in soil simulating solution

Carbon steel in aerated soil operates in cathodic protection (CP) condition if the IR-free potential is more negative than –0.850 V CSE, which corresponds to a corrosion rate lower than 0.01 mm·a-1. CP is applied by a stationary current, which effectiveness depends on a thermodynamic effect, which reduces (or stops) corrosion rate, and on a chemical effect due to the alkalinisation at the metal-to-electrolyte interface. The increase of pH is promoted by the cathodic reactions (oxygen reduction and, at lower potential, hydrogen evolution) occurring on the polarized metal and can promote passive condition. In this paper, a preliminary study of intermittent CP has been carried out in order to investigate the effect of a temporary current interruption on potential monitoring and on residual corrosion rate of steel in soil simulating solution. Test has been performed applying two cathodic current densities (0.2 and 1.0 A·m-2), varying the current-off period daily duration (6, 12 and 16 hours) and monitoring weekly the potential. During the on period (i.e. CP on), oxygen is consumed and alkaline pH is established; during the off period (i.e. when CP is interrupted), the alkalinity and the slow oxygen replacement assure corrosion rates lower than in free corrosion condition, especially if high cathodic current density is previously applied

Surface treatment to improve corrosion resistance of pure titanium

The corrosion behavior of pure titanium UNS R50250 and UNS R50400 were investigated and compared with electrochemical behavior of Ti-0.2Pd and Ti-0.3Mo-0.8Ni alloys (UNS R52400 and UNS R53400 respectively). Surface treatments, especially anodic oxidations, were conducted in order to enhance the corrosion resistance of pure titanium up to the corrosion resistance of titanium alloys one. Samples were then tested with potentiodynamic analyses in chloride and fluoride containing solutions, in order to find critical pitting potentials for each condition and treatment. The results show that, despite all anodization treatments increased titanium corrosion resistance to different extents, no treatment was able to increase it up to UNS R52400 level. A suggestion on the best anodization procedure to increase corrosion resistance while maintaining ease of treatment is given based on potentiodynamic test results

Can an intermittent cathodic protection system prevent corrosion of buried pipeline?

Carbon steel pipelines are provided with corrosion prevention systems, namely an insulating coating and a cathodic protection (CP) system that reduces corrosion rate below 10 μm/a. CP is applied by a stationary cathodic current, which effectiveness on the metal surface is twofold: oxygen consumption and alkalinization (pH > 10) at the metal-to-electrolyte interface. The increase of pH is beneficial, promoting passive condition. In this paper, a preliminary study of the effect of intermittent CP has been carried out in order to investigate the effect of a temporary current interruption on the potential monitoring and on the residual corrosion of the metal. During the on period, oxygen is consumed and alkaline pH is established, during off period, the alkalinity and the slow oxygen replacement assure corrosion rates lower than in free corrosion condition. Test has been performed both in normal and overprotection condition, varying the off period duration, monitoring weekly the protection potential

Modellazione molecolare di inibitori organici nel cemento (Molecular modeling of organic inhibitors in concrete)

Corrosion inhibitors are largely used to prevent chloride-induced corrosion in reinforced concrete structures. The interaction mechanisms with the passive film present on steel still requires deeper understanding. In a previous work [1] based on molecular mechanics and molecular dynamics methods [2-5] we considered organic inhibitors adsorbed on γ-FeOOH, comparing theoretical results with experimental data [1]. Here we considered the initial interaction with the inhibitor film and chlorides. In particular, the adsorbed tartrate monolayer show the best behavior thanks to the repulsions by the COO- groups exposed to chlorides, more distant from the γ-FeOOH surface, whereas the dimethylethanolamine film doesn’t have the same repulsion. The molecular simulations are a useful tool to better understand the behaviour of inhibitors in presence of chlorides that can start the corrosio

Memristive Anodic Oxides: Production, Properties and Applications in Neuromorphic Computing

Memristive devices generally consist of metal oxide elements with specific structure and chemical composition, which are crucial to obtain the required variability in resistance. This makes the control of oxide properties vital. While CMOS compatible production technologies for metal oxides deposition generally involve physical or chemical deposition pathways, we here describe the possibility of using an electrochemical technique, anodic oxidation, as an alternative route to produce memristive oxides. In fact, anodization allows to form a very large range of oxides on the surface of valve metals, such as titanium, hafnium, niobium and tantalum, whose thickness, structure and functional properties depend on process parameters imposed. These oxides may be of interest to build neural networks based on memristive elements produced by anodic oxidation

Application-wise nanostructuring of anodic films on titanium: a review

open3noopenDiamanti, Maria Vittoria; Ormellese, Marco; Pedeferri, MariapiaDiamanti, MARIA VITTORIA; Ormellese, Marco; Pedeferri, Mariapi

Experiences on corrosion inhibitors for reinforced concrete

Corrosion of carbon steel reinforcement is the most important cause of premature failure on reinforced concrete structures. Prevention of corrosion is primarily achieved in the design phase by using high quality concrete and adequate cover. Additional prevention methods are adopted when severe environmental conditions occur or on structures requiring very long service life. Among these methods, corrosion inhibitors seem to offer a simple and cost effective prevention technique. They may be used both as a preventative techniques, if added to fresh concrete, and as a repair system, if applied on hardened concrete. The performance of corrosion inhibitors for reinforced concrete structures affected by chloride induced and carbonation corrosion has been studied at PoliLaPP, Laboratory of Corrosion of materials "P. Pedeferri" of the Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, in the last 15 years. Organic commercial admixed corrosion inhibitors delayed the occurrence of chloride induced corrosion. This result is related to two effects: reduction of the rate of chloride transport into concrete and increase of the critical chloride threshold. Commercial migrating corrosion inhibitors (MCI) are able to delay time-to-corrosion of passive rebars in concrete subjected to chlorides ponding; this effect is mainly related to the reduction of chlorides diffusion coefficient. MCI can reduce the corrosion rate after corrosion initiation only in carbonated concrete, nevertheless efficiency is low and residual corrosion rate is not negligible. Commercial MCI can penetrate into concrete mainly through capillary sorption but penetration depth is limited to 20 mm. The results obtained with nitrite-based inhibitor confirm literature data: the inhibitor is effective if the molar ratio [NO2 ]/[Cl ] is higher than 0.5-0.6; in carbonated concrete, due to insufficient amount of inhibitor, no significant effect has been observed on corrosion rate. Among the tested organic substances, compounds containing carboxylic group showed the best results solution tests: pitting potential, time-to-corrosion and critical chloride content are similar to those obtained with sodium nitrite. In concrete tests, only one amine and one amino acid showed good performance increasing the critical chlorides threshold with respect to the reference condition. For carboxylate substances, a strong link was found between inhibiting properties and molecular structure