The development of efficient inhibitors based on environmentally sustainable compounds for steel protection is of crucial importance for industry but also for the preservation of metallic components. This investigation reports the synthesis and characterization of a new hybrid inhibitor based on the intercalation of 6-amino hexanoic acid (6-AHA) in layered Aluminum tri-polyphosphate (ATP) and its application for corrosion protection of S235 low carbon steel in 3.5%NaCl solution . The corrosion inhibition efficiency of ATP-6-AHA was evaluated using gravimetric and electrochemical measurements (PP, EIS). The overall results demonstrated that the hybrid inhibitor system ATP-6-AHA significantly decreases the corrosion behavior of S235 steel. The inhibition effect could be related to the passivation by a phosphate protective layer as confirmed by analysis of the steel surface using X-ray photo electron spectroscopy (XPS) and scanning electron microscope (SEM) techniques.

In contrast to other additive manufacturing methods such as Wire Arc Additive Manufacturing or Laser Metal Deposition, the cold spray system designed by SPEE3D allows for structures to be printed at much lower temperatures. As a result, structures printed via cold spray often undergo post processing heat treatments which potentially alters the distribution of trace elements throughout the sample. The distribution of elements within these structures may then have a direct impact on the corrosion properties of these materials. The impact of post processing heat treatment parameters on the microstructure and distribution of Mg and Si trace elements within an Al alloy was investigated using cross section analysis of samples by SEM-EDS. From an Al powered feedstock, alloys were printed using SPEED3D’s LightSPEE3D printer utilising air as the carrier gas, at 30 Bar and 500°C; various post processing heat and water quench treatments were then applied. Results reveal a reorganisation of Mg (which subsequently becomes oxidised) towards the edges of pores, regions typically with a higher surface energy. This is in direct contrast to the largely homogenous distribution of Mg in samples which did not undergo post printing heat treatments. The addition of charcoal during the heat treatment process also resulted in the redistribution of Si within the sample, and the creation of silicon carbide structures. The impact of reorganisation of Mg within the sample as well as the creation of silicon carbide structures on the selective corrosion of these materials was then investigated by potentiodynamic corrosion testing and electrochemical impedance spectroscopy.

Corrosion behavior of Zn-Mn alloys was studied through polarization resistance test and electrochemical impedance spectroscopy in 3% NaCl solution. Compared to pure Zn, Zn-10.1%Zn coating exhibits high corrosion resistance. The evolution of R_p with the Mn content seems to be ascribed to two mechanisms of Zn-Mn deposits dissolution, leading to two surface states. The differentiation is linked to the absence or the presence of the corrosion products layer on Zn-Mn deposit surface. The Nyquist impedance plots shape depends on the Mn content. This shape difference reveals a difference in phenomena possible to occur at the deposit/corrosive environment interface

Nickel phosphorus-based coatings are considered to be an excellent option for mitigating corrosion faced by many industries. Further enhancement in the properties of Ni-P coatings are achieved by introducing property specific reinforcement in the Ni-P matrix. In this study, structural, mechanical, and electrochemical properties of Ni-P-TiC composite coatings prepared through electrodeposition techniques were investigated. Titanium particles ranging from 0 to 2 g/L were electrodeposited into Ni-P matrix and examined through state-of-the-art techniques. Prepared coatings have uniform thickness, and nodular-structure structures with no discernible defects. Vickers microhardness and nanoindentation findings indicate a clear association between hardness and TiC particle concentration, with the ultimate hardness of 593HV100 (at 1.5 g/L) . Adding more TiC particles to the mix induces a decrease in hardness since they accumulate in the Ni-P matrix. Corrosion resistance is increased by an increasing amount of TiC particles with best corrosion results for an additional 2.0 g/L of TiC which can be elucidated to reduction in active area by the presence of TiC particles. Ni-P-TiC composite coatings show various beneficial structural, mechanical, and corrosion resistance characteristics, indicating that they can be used in numerous industrial applications.

Hydrogen diffusion plays an important role in understanding how materials chemically degrade over time. Open questions regarding the underlying diffusion pathways and whether they lead to the trapping of Hydrogen provide insight into properties such as the incubation time towards hydrogen embrittlement. For the case of polycrystalline materials, answering these questions are non-trivial, as hydrogen can diffuse through two unique environments: (1) bulk crystalline region and (2) grain boundary region. In this work we approximate the grain boundaries using the amorphous bulk phase due to similarities in the short-range atomic order. Density functional theory (DFT) was used to generate amorphous configurations of titania via ab initio molecular dynamics. A spectrum of hydrogen binding energies was then calculated using a multitude of oxygen sites with varying coordination number. Classical molecular dynamics were then performed on a larger titania system using a machine learning force field. A graph-based order parameter was then used to characterize the classically derived amorphous phase space and was mapped onto the oxygen coordination number. Our results qualitatively indicate that hydrogen diffusivity can be tailored to either inhibit or induce diffusion based on the specific local oxygen environments present in the amorphous phase.

The aim of this work was to develop novel flash-PEO coatings for AZ31B magnesium alloy with similar or better performance than Cr(VI) conversion coatings (CCC) that could become an alternative corrosion protection system choice for industrial applications. DC flash-PEO coatings were developed in different electrolytes (aluminate-, phosphate-, and silicate-based electrolytes, or their mixtures without/with fluoride) using very short treatments (≤90 s) in order to limit the energy consumption as much as possible. The multidimensional screening, including electrochemical impedance spectroscopy (EIS), specific energy consumption and industrial-type neutral salt spray (NSST), and paint adhesion tests were implemented in order to verify the suitability of PEO coatings’ performance. The energy consumption of the PEO processes remained relatively low for some of the coatings, ~1 kW h m⁻² µm⁻¹, which makes only 5 kW h m⁻² of energy required to produce the overall 5 µm-thick coatings. A correlation was found between the energy consumption of the PEO process with fluorides and the corrosion resistance, demonstrating that the lower the energy consumption of the respective PEO process, the better corrosion resistance of the resulted coating. The overall evaluation of the coatings’ corrosion protection (EIS, NSST, paintability) confirmed that two of the developed PEO coatings (aluminate-phosphate-fluoride and silicate-phosphate-fluoride based ones) could be an adequate substitute for CCC.

Microbiologically influenced corrosion (MIC) of concrete sanitary sewers is a common problem that demands a large rehabilitation investment every year. MIC is the result of dilute sulfuric acid (H₂SO₄) dissolving the cement matrix. The acid is produced by a complex series of chemical and biochemical reactions. Hydrogen sulfide (H₂S) is produced by sulfur-reducing bacteria (SRB) in the liquid phase, and then in time, this gas is converted by sulfur-oxidizing bacteria (SOB) into H₂SO₄. The last conversion occurs above the liquid level under aerobic conditions. The objectives of this paper are (1) to present a literature review of MIC processes and factors influencing them, and (2) to discuss control mechanisms and authors’ experience on development over years in understanding MIC of concrete (MICC) in a sanitary sewerage environment (SSE). Published papers were identified that reported MICC in SSE for the past 30 years. The literature review and authors’ on-site and laboratory investigations suggest that MIC of concrete is a complex process that involves varied surface interactions. The addition of liquid antimicrobial additive as per standard procedure shows the resistance of concrete to MIC and its direct relation with the mixing time of admixture. Many empirical inputs like corrosion areas, corrosion rates, the impact of cement, and aggregate types varying with installation and repair of sewer structures are identified. The review results show variation in corrosion rates and other empirical inputs obtained on-site and through laboratory studies due to different testing procedures. Further research is needed to establish quantitative relations between empirical inputs related to MICC in SSE. Identification and development of more effective coatings and safe antibacterial agents will help inhibit colonization of SOB overexposed sewers and better understand environmental microbiology.

Some dental implants present on the market contain aluminum, which represents a potential risk to the health, since aluminum is associated with neurodegenerative diseases like Alzheimer´s disease. An oral cavity, into which the implant is placed, is an aggressive environment that can, under certain circumstances, cause degradation / corrosion of the implant resulting in metal ions release in tissues, organs, and bloodstream. Therefore, control of the chemical composition as well as the surface characteristics of implants is necessary. Collagen and sodium alendronate molecules were self-assembled on surface of the commercial titanium implant containing 6% at. of aluminum. Since dental implants have to osseointegrate with surrounding bones, molecules with known positive effects on skeletal system were selected. Density Functional Theory calculation results indicated an exergonic reaction (DG^*_INT Ë‚ 0) between chosen molecules and implant surface, while electrochemical impedance spectroscopy results pointed to improved anti-corrosion properties of both collagen- and alendronate-functionalized surfaces (protective effectiveness > 92%) compared to “bare” implant surface. The proposed functionalization could provide better quality control during the implant production process and thus minimize possible negative biological effects on patient´s health.

According to currently enforced Eurocode 2 for the design of reinforced concrete structures, it is essential to protect the steel reinforcement from corrosion and concrete from degradation under aggressive environmental conditions such as marine, urban, industrial, soils, to which these are normally exposed. In this context, this experimental study investigates the enhancement of the physico-mechanical properties of common cement-based mortars and the electro-chemical properties of reinforcing steel, through the addition of nanomaterials in the mix. For the experimental set- up, cylindrical and cubic specimens of different dimensions were cast and were partially immersed in sodium chloride solution for eight (8) months. Two (2) groups were considered: cement-based mortar composites with 0.5 wt.% CNTs addition and conventional (reference) specimens without any addition of nanomaterials, for comparison. The influence of adding CNTs on chloride penetration resistance was subsequently evaluated using standardized and non-standardized testing techniques: physico-mechanical tests (flexural strength and porosity), mass loss of steel, electrochemical measurements (corrosion current, HCP) and total chloride content calculation. The test results showed that using CNTs as addition in mortar production led to protection of steel rebars against pitting corrosion; moreover, a significant improvement in flexural strength and porosity of mortars was also observed compared to the reference specimens without CNTs.

Organic corrosion inhibitors embedded in coatings play a crucial role substituting traditional anti-corrosion pigments, which can cause acute toxicity problems to human health and the environment. However, why some organic compounds inhibit corrosion and others do not, is still not well understood. Therefore, we are currently developing two complementary technological approaches to help corrosion scientists and engineers working in academia and across different industries choose the optimal inhibitor for each specific problem: 1) build an interactive exploratory data tool for the selection of the ideal corrosion inhibitor taking into account different conditions (type of alloy, electrolyte, pH, etc.) based on previously published information (https://datacor.shinyapps.io/cordata/), and 2) develop machine learning models and an online tool to perform an initial virtual screen of potential molecules for the design of more efficient organic corrosion inhibitors (1). These two approaches will contribute to the digitalization of inhibitor search, helping speed up research in the corrosion science and tailor corrosion protective technologies in a more efficient and condition specific manner.

Acknowledgements: Project DataCor (refs. POCI-01-0145-FEDER-030256 and PTDC/QUI-QFI/30256/2017, datacorproject.wixsite.com/datacor).

(1) T.L.P. Galvão, G. Novell-Leruth, A. Kuznetsova, J. Tedim, J.R.B. Gomes, J. Phys. Chem. C, 124, 2020, 5624-5635.