External corrosion of oil and gas pipelines: A review of failure mechanisms and predictive preventions

A review on corrosion detection and protection of existing reinforced concrete (RC) structures

Carbonation of concrete at ambient CO2 concentration is a slow process. This makes the testing of the resistance of concrete against carbonation often too slow to be applicable for service life assessments of new structures. Raising the CO2-concentration will accelerate the test but the validity of an increase CO2 -level is debated. If not valid, the service life can be seriously underestimated. In this paper, the effects of accelerating on the carbonation process are discussed. It is shown that a change in CO2 concentration will not change the carbonation process. Since carbonation occurs instantly, a zero CO2 concentration at the carbonation front is maintained. Moreover, it has been concluded that all hydrated and unhydrated cement ultimately carbonate. This implies that the amount of carbonatable matter can be determined on the basis of the amount of calcium in the unreacted cement.

Influence of the carbon dioxide concentration on the resistance to carbonation of concrete

The edge-functionalization of graphene nanoplatelets (GnP) was carried out exploiting diazonium chemistry, aiming at the synthesis of edge decorated nanoparticles to be used as building blocks in the preparation of engineered nanostructured materials for enhanced heat transfer. Indeed, both phenol functionalized and dianiline-bridged GnP (GnP-OH and E-GnP, respectively) were assembled in nanopapers exploiting the formation of non-covalent and covalent molecular junctions, respectively. Molecular dynamics allowed to estimate the thermal conductance for the two different types of molecular junction, suggesting a factor 6 between conductance of covalent vs. non-covalent junctions. Furthermore, the chemical functionalization was observed to drive the self-organization of the nanoflakes into the nanopapers, leading to a 20% enhancement of the thermal conductivity for GnP-OH and E-GnP while the cross plane thermal conductivity was boosted by 150% in the case of E-GnP. The application of chemical functionalization to the engineering of contact resistance in nanoparticles network was therefore validated as a fascinating route for the enhancement of heat exchange efficiency on nanoparticle networks, with great potential impact in low-temperature heat exchange and recovery applications

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adfm.201706954

Edge‐Grafted Molecular Junctions between Graphene Nanoplatelets: Applied Chemistry to Enhance Heat Transfer in Nanomaterials

The spontaneous grafting of diazonium salts on gold may involve the carbocation obtained by heterolytic dediazonation and not necessarily the radical, as usually observed on reducing surfaces The mechanism is addressed on the basis of DFT calculations and experiments carried out under conditions where the carbocation and the radical are produced selectively The calculations indicate that the driving force of the reaction leading from a gold cluster, used as a gold model surface, and the carbocation to the modified cluster is higher than that of the analogous reaction starting from the radical The experiments performed under conditions of heterolytic dediazonation show the formation of thin films on the surface of gold The grafting of a carbocation is therefore possible, but a mechanism where the cleavage of the Ar–N bond is catalyzed by the surface of gold cannot be excluded

Some Theoretical and Experimental Insights on the Mechanistic Routes Leading to the Spontaneous Grafting of Gold Surfaces by Diazonium Salts

https://hal-brgm.archives-ouvertes.fr/hal-02979786/document

Reinforced concrete structures: A review of corrosion mechanisms and advances in electrical methods for corrosion monitoring

Gold nanostructures (GNS) were chemically functionalized using four different diazonium salts: benzene-diazonium-tetrafluoroborate (DS), 4-decylbenzene-diazonium-tetrafluoroborate (DS-C10H21), 4-carboxybenzene-diazonium-tetrafluoroborate (DS-COOH), and 4-(aminoethyl)-benzene-diazonium-tetrafluoroborate (DS-(CH2)2NH2). Effective chemical grafting on GNS was shown by surface-enhanced Raman spectroscopy (SERS); aromatic ring deformations in the range of 1570–1591 cm–1 are of particular interest. The very strong band observed around 1075 cm–1, related to CH in-plane bending for mono- and para-substituted benzenes (coupled with ring-N stretching mode), provided further irrefutable evidence of the grafting. SERS enhancement of these two bands ascertains the perpendicular orientation of the aromatic rings on the GNS. X-ray photoelectron spectroscopy (XPS) analyses of chemically grafted flat gold surfaces suggest azophenyl radical pathways when using DS, DS-(CH2)2-NH2, or DS-C10H21. It was shown that coating at t...

/pdf/evidence-of-the-grafting-mechanisms-of-diazonium-salts-on-17sd3shelq.pdf

Evidence of the Grafting Mechanisms of Diazonium Salts on Gold Nanostructures

The use of indirect electrical techniques is gaining interest for monitoring the corrosion of steel in concrete as they do not require any connection to the rebar. In this paper, we provide insights into the physical aspects of the indirect galvanostatic pulse (GP) method in the Wenner configuration. Considering uniform corrosion, the instantaneous ohmic drop is decreased due to the presence of the rebar, which acts as a short-circuit. However, we observed that this phenomenon is independent of the electrochemical parameters of the Butler–Volmer equation. They are, however, responsible for the nonlinear decrease of the current that polarizes the rebar over time, especially for a passive rebar due to its high polarization resistance. This evolution of the resulting potential difference with time is explained by the increase of the potential difference related to concrete resistance and the global decrease of the potential difference related to the polarization resistance of the rebar. The indirect GP technique is then fundamentally different than the conventional one in three-electrode configuration, as here the steady-state potential is not only representative of polarization resistance but also of concrete resistance. Considering non-uniform corrosion, the presence of a small anodic area disturbs the current distribution in the material. This is essentially due to the different capability of anodic and cathodic areas to consume the impressed current, resulting in slowing down the evolution of the transient potential as compared to uniform corrosion. Hence, highly corroding areas have a greater effect on the transient potential than on the steady-state one. The use of this temporal evolution is thus recommended to qualitatively detect anodic areas. For the estimation of their length and position, which is one of the main current problematic issue when performing any measurement on reinforced concrete (RC) structures with conventional techniques, we suggest adjusting the probe spacing to modulate the sensitivity of the technique.

https://www.mdpi.com/2624-5558/1/3/18/pdf

Indirect Galvanostatic Pulse in Wenner Configuration: Numerical Insights into Its Physical Aspect and Its Ability to Locate Highly Corroding Areas in Macrocell Corrosion of Steel in Concrete

Stéphane Gaboreau

Papers

Reinforced concrete structures: A review of corrosion mechanisms and advances in electrical methods for corrosion monitoring

Evidence of the Grafting Mechanisms of Diazonium Salts on Gold Nanostructures

Indirect Galvanostatic Pulse in Wenner Configuration: Numerical Insights into Its Physical Aspect and Its Ability to Locate Highly Corroding Areas in Macrocell Corrosion of Steel in Concrete