New sol-gel formulations to increase the barrier effect of a protective coating against the corrosion of steels

Films were deposited onto AISI 430 stainless steel substrates by dip-coating technique. The aim is to reach the AISI 304L stainless steel anti-corrosion properties by a coated AISI 430 stainless steel system. Sol formulation is done from the starting precursors tetraethylorthosilicate (TEOS) and 3(trimethoxysilyl) propyl methacrylate (MAP). After the hydrolysis of these precursors, sol-gel reactions occur before the addition (or not) of a controlled quantity of cerium nitrate. The addition of the PEG (polyethylene glycol), used as plasticizer has been studied in this paper and both physical and chemical properties of the synthesized hybrid films were studied by varying PEG ratios. Based on SEM observations and mass gain measurements, the thickness of the films has been adjustable. Another parameter plays a key role: the drying step of the whole system. It has been investigated and optimized in this paper to lead to coatings with a high barrier effect. The efficiency of the anti-corrosion protection of hybrid-coated stainless steel was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) after immersion of the material in a 3.5% NaCl solution. Double-layered systems were successfully developed and a good compromise between PEG content and drying conditions has been found. Potentiodynamic polarization curves showed that the hybrid coating prepared using a TEOS/MAP/PEG yielded the best anti-corrosion performances. It acts as an efficient barrier similar to AISI 304 stainless steel used as reference, increasing the total impedance and significantly reducing the current densities

The Electrochemical Behavior of α,β′-Brass in Basic NaNO3Solutions

The electrochemical behavior of an α,β'-brass CuZn40Pb2 (CW617N) was studied in basic nitrate solutions with various basic pHs and nitrate ion concentrations. In all the chosen experimental conditions, corrosion at the open circuit potential proceeded by the galvanic coupling of the α and β' phases, leading to a surface dezincification of the β' phase. The study showed that the extent of the dezincification was affected by the presence of lead in the alloy but the pH was the major parameter. During polarization tests, a pseudo-passive or a passive stage followed by a breakdown was observed: corrosion phenomena mainly involved copper and zinc dissolution from the β' phase. At pH 11, a Cu2O/PbO layer was efficient in achieving passivity of the brass. At pH 12, a Cu(OH)2-rich surface layer was formed: it was not protective enough, and complete dissolution of the β' phase was observed leading to the removal of lead particles

Development of Representative Tests to Quantify the Susceptibility to Stress Corrosion Cracking of , '-Brass Used for Gas Transfer Devices

Corrosion susceptibility of an α,β'-brass CuZn40Pb2 (CW617N), used for gas transfer devices, was investigated through accelerated corrosion tests at a constant anodic potential in NaNO3 solution with basic pHs. The anodic dissolution behavior of the α,β'-brass was characterized by a two stages-mechanism, with each stage including both dezincification and simultaneous dissolution phenomena of the β' phase but with different kinetics at each stage. Compressive or tensile stresses applied on brass specimens during the accelerated tests were observed largely to influence the anodic dissolution kinetics. Stresses were assumed to open or close the pores present in the dezincified β' phase, which promoted or slowed the dezincification mechanism, including with the Zn diffusion into the solution trapped inside of the pores

Corrosion Behavior of α,β'-Brass in NaNO3 Solutions

The corrosion behavior of an α,β'-brass CuZn40Pb2 (CW617N) was studied in solutions with basic pHs and various nitrate ion concentrations. Corrosion at the open circuit potential was observed to proceed by the galvanic coupling of α and β' phases, leading to a surface dezincification of the β' phase and the evolution of the passive layer. When the alloy was polarized in the anodic domain, a pseudo-passive or a passive stage followed by a passive breakdown was observed

Dissolution Kinetics of α,β′-Brass in Basic NaNO3 Solutions

Corrosion tests at a constant anodic potential, referred to as dissolution tests, were performed to determine the dissolution kinetics of an α,β′-brass CuZn40Pb2 (CW617N) in a basic nitrate solution with and without mechanical loading. The corrosion behavior of the α,β′-brass was characterized by a two-step mechanism, with an initiation step for which the simultaneous dissolution of all the alloying elements of the β′ phase occurred only and a propagation step including at first, the afore-mentioned simultaneous dissolution process before a critical time tc and then, both simultaneous dissolution and dezincification of the β′ phase after tc. The pH and Cu concentration of the electrolyte near the brass surface were determined to be two of the major factors influencing the occurrence of the dezincification process. The dezincification of the β′ phase extended in depth by a percolation dissolution mechanism. Mechanical loading during the dissolution tests was observed to largely influence the dezincification process. It was assumed to open or close the pores present in the dezincified β′ phase, which promoted or slowed down the dezincification mechanism depending on the sign of the stress

Mechanical properties and tribological behavior of a silica or/and alumina coating prepared by sol-gel route on stainless steel

The increasing importance of developments in the mechanical industry requires a constant evolution of skills, particularly in the area of functionalization and protection of metallic alloy surfaces. The wear of materials is one of the causes of loss of profitability. This study aims to develop solutions to extend the lifetime of stainless steel 304 L. In this work, we have achieved to optimize protective coatings on stainless steel against wear, using sol-gel method associated with dip-coating technique. Three routes have been proposed to achieve this type of coating, a single sol precursor of silica or alumina and a mixture of sols precursors of both oxides. The results of tribological tests show that silica coating does not provide a performance gain towards the stainless steel protection. Alumina coating even as thin film is very efficient to resist against wear. Wear track widths on the sample is reduced by a factor 2, and the wear volume of the counterface is decreased by a factor 30, corresponding to a total wear volume reduction of a factor 7. The combination of both oxides seems to be a very promising way for such kind of application. With silica/alumina coating, we have obtained a reduction ofwidths wear track of a factor 1.5 and a decrease of friction coefficient as compared to alumina coating

Carbon nanotube/alumina and graphite/alumina composite coatings on stainless steel for tribological applications

Carbon/alumina coatings on stainless steel are prepared by a sol-gel route, using either carbon nanotubes (8 walls on average) or graphite flakes. The friction coefficient against a steel ball is decreased by a factor of 4–5 compared to pure alumina and wear is reduced by a factor of 2 with graphite flakes. A Raman spectroscopy study of selected specimens outside and inside the worn surface shows that the carbon nanotubes are not dramatically damaged whereas the graphite flakes are broken into graphene layers. The reasons why graphite is more effective than the carbon nanotubes, for the same carbon content, to improve the tribological behavior are discussed

New architectured hybrid sol-gel coatings for wear and corrosion protection of low-carbon steel

The replacement of expensive stainless steel in various socio-economic sectors such as mechanical or alimentary is an issue that would be possible to solve by developing a protective coating on low-carbon steel. In these applications, complex pieces are in contact with different kinds of fluids, with or without particles when functioning. Consequently, the expected coating function is to effectively protect the equipment from corrosion, abrasion and erosion. In this work thin hybrid coatings obtained by the sol-gel process have been developed for corrosion and wear protection on low-carbon steel. This innovative system is constituted of alumino-silicate epoxy based sol-gel coatings acting as barrier layers which, when loaded with zirconia particles, improve the mechanical properties. Taking into account the specificity of the carbon steel, we developed two architectured coatings displaying corrosion and wear protection. They are built by superposition of a bi-layered hybrid primer coating and a mono-layered zirconia loaded hybrid coating. Using two different zirconia contents, 30 wt.% and 40 wt.%, thin coatings of 5 and 10 μm are achieved. What is of interest is that the combination of antiwear tests and EIS to evaluate the influence of abrasive wear on anticorrosion properties has, for the first time, been demonstrated on such thin hybrid sol-gel coatings. The loss of corrosion protection of the lower zirconia loaded coating was attributed to the formation of localized defects after removal of material. On the contrary, the higher zirconia loaded coating demonstrated an interesting corrosion and wear behavior with the formation of a compacted layer at the top of the outer layer providing a barrier effect against water and ion permeation. To further characterize the protective systems, the morphology and the microstructure of the coatings were investigated by scanning electron microscopy

Dispersion of graphite flakes into boehmite sols for the preparation of bi-layer-graphene / alumina coatings on stainless steel for tribological applications

Carbon-alumina coatings on stainless steel were prepared by a sol-gel route. The dispersion of the commercial graphite flakes by an ultrasonic bath, an ultrasonic probe and a high-shear mixer, produce thinner flakes, fewlayered-graphene and bi-layer-graphene (BLG), respectively. The coatings were examined by optical and electron microscopy, interferential rugosimetry, optical profilometry and Raman spectroscopy. The friction coefficient against a steel ball is decreased by a factor of 5–7 and the wear volume is reduced by a factor of 6–38 compared to a pure alumina coating. The best results correspond to the sample prepared using the high-shear mixer. Delamination of the graphite flakes into BLG during the friction test provides the system with debris suitable for tribofilm building up and lubrication but it is better to already have carbon dispersed as BLG in the coating before the test, notably because the carbon surface area available is much higher

Predicting haplogroups using a versatile machine learning program (PredYMaLe) on a new mutationally balanced 32 Y-STR multiplex (CombYplex): Unlocking the full potential of the human STR mutation rate spectrum to estimate forensic parameters

We developed a new mutationally well-balanced 32 Y-STR multiplex (CombYplex) together with a machine learning (ML) program PredYMaLe to assess the impact of STR mutability on haplogourp prediction, while respecting forensic community criteria (high DC/HD). We designed CombYplex around two sub-panels M1 and M2 characterized by average and high-mutation STR panels. Using these two sub-panels, we tested how our program PredYmale reacts to mutability when considering basal branches and, moving down, terminal branches. We tested first the discrimination capacity of CombYplex on 996 human samples using various forensic and statistical parameters and showed that its resolution is sufficient to separate haplogroup classes. In parallel, PredYMaLe was designed and used to test whether a ML approach can predict haplogroup classes from Y-STR profiles. Applied to our kit, SVM and Random Forest classifiers perform very well (average 97 %), better than Neural Network (average 91 %) and Bayesian methods (< 90 %)