China
Africa
Explore chapters and articles related to this topic
Fabrication processes
Published in Frédéric Guittard, Thierry Darmanin, Bioinspired Superhydrophobic Surfaces, 2017
Frédéric Guittard, Thierry Darmanin
Another strategy used in the literature involves the production of acids in situ, which could be obtained by the replacement of acids with substituted-trichlorosilane. Hence, the hydrolysis of substituted-trichlorosilane leads to silanols functions and released HCl in the solution. The group of Boukherroub showed that the insertion of zinc substrates in hydrolyzed perfluorotrichlorosilane induces the formation of zinc oxide (ZnO), simonkolleite [Zn5(OH)8Cl2.H2O], and zinc hydroxide [Zn(OH)2] structures [8586]. The surface morphology was highly dependent on the hydrolysis rate of perfluorotrichlorosilane. They produced spherical particles of about 1.5–2.0 mm by controlling this parameter and obtained superhydrophobic surfaces with θw = 151°.
Hybrid Scanning Electrochemical Techniques
Published in Allen J. Bard, Michael V. Mirkin, Scanning Electrochemical Microscopy, 2022
Christine Kranz, Christophe Demaille
Combination of SECM with Raman spectroscopy was originally described by Etienne et al. in the framework of corrosion studies [152]. These authors combined SF regulated SECM with Raman microscopy using an original setup comprising a 25 µm Pt in glass microelectrode positioned at a 30° angle from the opaque sample surface, which is attached to a confocal microscope stage. With this arrangement, optical images of the surface showing the exact position of the tip can be acquired. The laser spot, which is the excitation source for Raman spectroscopy, can then be aligned with the tip extremity, ensuring that the exact same surface location interrogated by the tip is also probed by Raman spectroscopy. Exploration of the sample can be carried out by lateral motion of the microscope stage, without compromising the tip/laser alignment. It is worth noting that this original setup is, by design, suitable for analyzing opaque samples. Etienne et al. used it to characterize a corroding sample, consisting of a steel sample covered with metallic and organic coatings. A millimeter-wide strip of the organic coating was removed, and corrosion of the so-exposed metal was analyzed by constant distance (SF) SECM coupled to Raman, at first in the presence of a redox mediator (ruthenium hexaammine). Sample topography, electrochemical current, and Raman spectra were acquired at several locations across the metal strip. A very good correlation was observed between the topography, the tip current, and the intensity of a Raman band at 450 cm−1 evidencing depletion of the TiO2-containing coating across the strip. This was the first demonstration of the ability of SECM-Raman to correlate in situ the local chemical composition of a sample with electrochemical activity. The corrosion behavior of the sample was further studied by replacing the amperometric UME by a pH sensitive probe. The Raman spectra, acquired simultaneously with the pH profile, revealed the formation of zinc chloride hydroxide monohydrate (simonkolleite) at the corroding metal surface.
EUROCORR 2019: ‘New times, new materials, new corrosion challenges’: part 2
Published in Corrosion Engineering, Science and Technology, 2020
M. A. Knoch (Aachen University, Germany) addressed the ‘Influence of mechanical loads on the corrosion behaviour of thermally sprayed ZnAl15’. Although pure Zn coatings can offer reliable cathodic corrosion protection to steel in most atmospheres, ZnAl may confer superior protection in marine environments. Samples were exposed to mechanical loading (body impact/scratching etc.) according to ISO 17872 and subsequently exposed to a neutral salt spray test for 554 h. After testing, EDS analysis revealed that the corrosion products comprised a mixture of ZnAl-oxides (ZnxAlyOz). Whereas platelike products (assumed to be Simonkolleite crystals) were identified on the thin films, the thick-film corrosion products consisted of a porous layer (possibly zinc hydroxide or hydrozincite) on top of ZnxAlyOz. The coatings exhibited ductile deformation behaviour, which is preferable to the brittle failures often observed in organic coating systems.
Synthesis, microstructural, corrosion and antimicrobial properties of Zn and Zn–Al coatings
Published in Surface Engineering, 2019
Satish Tailor, Ankur Modi, S. C. Modi
EDS results show that 3–4% Cl was found in depth of coating, this clearly shows that corrosive media was entered in the coating as shown in Figure 5(a). Whereas Figure 5(b) shows only the coating elements (Al, Zn), no corrosive media elements were observed inside the coating. Figure 6 shows the XRD pattern of pure Zn and Zn–Al coating after the salt spray test. Analyses of the patterns indicated that the corrosion products in pure Zn coating (Figure 6(a)) consisted of mainly simonkolleite Zn5(OH)8Cl2·(H2O), hydrozincite Zn5(OH)6(CO3)2 and ZnOHCl. However, Zn rich phase is the main part. In Zincal coating, Zn and Al phases are the main phases and zinc aluminium carbonate hydroxide hydrate Zn6Al2(OH)16CO3·4(H2O) was the dominant corrosion product with hydrozincite Zn5(OH)6(CO3)2, originally existed in the coating. Similar corrosion products were also found in previous studies [19,23]. Owing to the absence of Cl− ions in the coating of Zincal [24], these corrosion products are little soluble which could not only adhere on the coating surface by forming a protective layer but also deposit in the cracks and defects to cut off the passage from electrolyte rapidly [25]. It prevents further penetration of the corrosion medium inside the coating and improves the corrosion resistance.
Long-term corrosion resistance of zinc-rich paint using functionalised multi-layer graphene-tripolyphosphate: in situ creation of zinc phosphate as corrosion inhibitor
Published in Corrosion Engineering, Science and Technology, 2019
Mona Ehsanjoo, Somayeh Mohammadi, Naz Chaibakhsh
According to the SEM images, the presence of many micro-holes in the control zinc-rich paint has led to easier penetration of Cl− into the coating. Therefore, based on Equations (1–3), the reaction of Cl− with Zn(OH)2 due to its hydrolysis led to the formation of simonkolleite (Zn5(OH)8Cl2·H2O). [44]