Effect of mechanical stresses on marine organic coating ageing approached by EIS measurements

In this work, the role of a stress-strain state (visco-elastic domain) on the protective properties of two marine epoxy coatings (with and without VOC) applied onto mild steel was studied. Different stress values were applied on coated substrates and bent samples were immersed in 3 wt.% NaCl solution at different temperatures. Non-bent coated samples were also immersed in the same conditions as references. Electrochemical Impedance Spectroscopy was used to evaluate the organic coating degradation on the compressed and the stretched sides periodically.The degradation kinetics showed that the tensile mode was very damaging for one coating while a slight effect was observed on the other coating. In the first case, the water uptake was found to be more important in the tensile mode for higher stress values. A particular attention was focussed on the initial relative permittivity which appeared as a thermo-activated function of the absolute value of the applied stress, for both coatings. Using a thermodynamic approach, the influence of the enthalpic and entropic part of the permittivity was discussed. The diffusion coefficient of the solution into the coating was also measured. The results showed that the diffusion coefficient is strongly modified by the mechanical stress but different behaviours were obtained with both coatings. It is proposed that the entropic contribution plays a major role on the modification of this coefficient.     

Effect of curing time on the physicomechanical characteristics of the hardened cement pastes containing limestone

The effect of curing time on the physico-mechanical properties of the hardened Portland cement pastes containing limestone was studied. Five cement-limestone blends were prepared using 0%, 5%, 10%, 15%, and 20% of limestone as a partial substituent of Portland cement. The cement pastes were prepared using the standard water of consistency of 0.255, 0.255, 0.258, 0.261, and 0.263, respectively. The fresh pastes, thus produced, were moulded into 2×2×2-cm cubes. The pastes were first cured within the moulds at 100% relative humidity for 24 h, then the specimens were demoulded and cured under tap water for 3, 7, 14, and 28 days. At each hydration age, the hardened pastes were tested for bulk density, compressive strength, differential scanning calorimetery (DSC), and X-ray diffraction analysis (XRD). The results obtained were related as much as possible to the mechanical properties of the hardened cement pastes. The inclusion of limestone results in a notable improvement of the mechanical properties of the cement pastes containing limestone.     

Ageing of marine coating in natural and artificial seawater under mechanical stresses

In order to study the effect of a visco-elastic stress (tension and compression mode) onto the performances of a thick marine organic coating, free films and coated panels were immersed in natural seawater and in NaCl 3 wt.% solution at room temperature (20 °C), fixed temperature (45 °C) or under cyclic temperatures. Free films were analysed using uniaxial elongation and Dynamic Mechanical Analysis (DMA) and the degradation of coated samples was investigated using Electrochemical Impedance Spectroscopy (EIS).     

Resistance of metallic substrates protected by an organic coating containing aluminum powder

The corrosion behavior of an epoxy primer containing aluminum powder (10 vol.%) applied on carbon steel and on galvanized steel was examined by electrochemical impedance spectroscopy (EIS). The data show that this coating is more protective when applied onto carbon steel substrates, and that on galvanized steel thicker coatings allow to achieve similar protection levels as those obtained for carbon steel. These effects are probably due to aluminum pigments providing a cathodic protection of the substrate, and to the resulting products precipitating inside the pores of the polymeric coating. Three stages can be distinguished during exposure of the coated specimens. Upon immersion of the coated samples in the test solution, a pre-saturated stage is observed. After a certain period of immersion, which strongly depends on the thickness of the applied coating, a saturation stage is reached in which an effective protection of the metallic substrate against corrosion is achieved. Finally, at sufficiently long exposure times, swelling through the coating eventually leads to the detachment of the coating.     

The effect of micro and nano-sized particles on mechanical and adhesion properties of a clear polyester powder coating

In this study, the effect of various micro and nano-sized particles on the mechanical and adhesion properties of a commercial non-pigmented polyester-TGIC powder coating was studied. Different coating formulations containing various wt.% of aluminum hydroxide (alumina) particles, TiO₂ and two different types of fumed silica nanoparticles were prepared via a two-stage process. Tensile strength measurements, DMTA analyses and vertical pull off adhesion test were conducted to evaluate mechanical and adhesion properties of the powder coating samples.     

In situ measurement of water at the organic coating/substrate interface

In situ and quantitative information on the water layer at the organic coating/substrate interface is crucial for understanding and preventing the failure of organic coating systems. A technique, based on a two-layer model derived rigorously from internal reflection theory, has been developed for measuring in situ the thickness and amount of the water layer at the organic coating/substrate interface. The technique gives new insight into the processes by which water degrades the coating/substrate bonds. In this technique, a transparent or an opaque organic coating of sufficient thickness is applied to an internal reflection element (IRE) with or without a thin metallic film, which is used as the substrate. A water chamber is attached to the organic-coated specimen. After adding water to the chamber, Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectra are taken automatically at specified time intervals without disturbing the specimens or the instrument. Water uptake in the coating and FTIR-MIR spectra of water on the coating-free substrate are also used for the analysis. Examples of clear and pigmented coatings on untreated and treated substrate surfaces are given to demonstrate the technique. Results of water accumulation at the coating/iron interface with and without applied electrical potentials are given. In addition to measuring water at the coating/substrate interface, the technique provides a means for studying the transport of water through a coating adhered to a substrate. Information on water at the interface and its transport properties through coatings applied to a substrate is valuable for interpreting corrosion, blistering and delamination of organic coating systems, and for developing models for use in predicting the serivce lives of protective coatings.     

Crack-bridging ability of organic coatings for concrete: influence of the method of concrete cracking, thickness and nature of the coating

Some concern about the determination of a standardised test for crack-bridging ability (CBA) measurements exists. The present work focuses on the analysis of the results of experimental tests performed to simulate the mechanical behaviour of a coating when a crack in the beneath concrete opens and grows. The influence of the method of concrete cracking, thickness and nature of the coating on the CBA are studied. Experimental results suggest that: (i) the same coating has higher CBA when the crack in the beneath concrete is produced through slight bending rather than through tensile loading; (ii) the CBA clearly depends on the nature (then mechanical properties) of the applied coating; (iii) power law relationships between CBA and thickness of the coating exist.     

Resistance of metallic substrates protected by an organic coating containing glass flakes

The resistance against corrosion of an epoxy-polyamine-based coating immersed in a 3 wt.% sodium chloride solution was investigated by electrochemical impedance spectroscopy (EIS). The organic coating contained glass flakes as pigment in order to enhance its barrier characteristics. The data show that this coating is more strongly adhered and exhibits higher protection characteristics when applied onto carbon steel substrates than on galvanized steel. Though the capacitance of the coating (C_C) does not show any appreciable variation with immersion time, the resistance (R_PO) of the film is observed to increase with time upon immersion. The analysis of the data sustains that the organic film behaves as a porous, non-barrier coating. Two time constants are observed even at earlier exposures, and the improved corrosion resistance developed after the coating system was exposed to the test electrolyte is considered to originate from the precipitation of corrosion products within the pores in the film.     

Ingress of water into organic coatings: Real-time monitoring of the capacitance and increase in mass

Water ingress into a cataphoretic coating employed in the car industry was studied using real-time mass and capacitance measurements. The results showed the presence of three well-differentiated time constants associated with the process. The corresponding time scales were 2–3 min, 1 and 10 h. The first time constant (fastest process) was assumed to be associated with the filling of surface pores by water. This process involved about 50% of the total water uptake. The second time constant was assumed to be due to the water occupancy of pores in the bulk of the coating. Finally, the slowest process was assumed to be due to water diffusion through the bulk coating. This process presented capacitive effects only if fillers were present in the coating.     

Effect of high temperature or fire on heavy weight concrete properties

Temperature plays an important role in the use of concrete for shielding nuclear reactors. In the present work, the effect of different durations (1, 2 and 3 h) of high temperatures (250, 500, 750 and 950 °C) on the physical, mechanical and radiation properties of heavy concrete was studied. The effect of fire fitting systems on concrete properties was investigated. Results showed that ilmenite concrete had the highest density, modulus of elasticity and lowest absorption percent, and it had also higher values of compressive, tensile, bending and bonding strengths than gravel or baryte concrete. Ilmenite concrete showed the highest attenuation of transmitted gamma rays. Firing (heating) exposure time was inversely proportional to mechanical properties of all types of concrete. Ilmenite concrete was more resistant to elevated temperature. Foam or air proved to be better than water as a cooling system in concrete structure exposed to high temperature because water leads to a big damage in concrete properties.     

Preparation and characterization of a greenish yellow lackluster coating with low infrared emissivity based on Prussian blue modified aluminum

Greenish yellow lackluster coatings with low infrared emissivity were prepared by Prussian blue (PB) surface modified Al powders and polyurethanes. The morphology and component of PB/Al powder were characterized by scanning electron microscopy and X-ray diffractometer. The infrared emissivity, surface gloss and visible light color of PB/Al composite coating were investigated by an infrared emissometer, a glossmeter and a colorimeter, respectively. Mechanical properties of PB/Al composite coatings were studied by using adhesion test and impact strength test. The results indicate that PB/Al powder decreases not only the gloss of the coating, but also its emissivity within the wavelength range of 8–14 μm. The composite coatings have good adherence and impact strength at PB/Al content below 50 wt.%, and then the mechanical properties decrease in the PB/Al content range from 50 wt.% to 60 wt.%. By comparing PB/Al composite coating and Al powder tinting coating with the same color and surface gloss, PB/Al composite coating exhibits significant lower infrared emissivity, which is attributed to closer inter-powder distances of metallic fillers and higher electrical conductivity in the coating.     

Effect of the passivating coating type, particle size, and storage time on oxidation and nitridation of aluminum powders

Processes of nonisothermal oxidation, nitridation, and ageing of aluminum powders with different particle sizes (nano-sized powder, ASD-1 powder, and PAP-2 powder) are considered. Application of non-oxide coatings onto particles of aluminum nanopowders reduces their thermal stability. Owing to scale-shaped particles, the PAP-2 powder after long-time storage preserves high activity of oxidation and nitridation, which is commensurable with that of the aluminum nanopowder. The activity of the coarse ASD-1 powder consisting of spherical particles in terms of oxidation and nitridation is low and only slightly changes during ageing. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 61–69, March–April, 2006.     

Effects of curing program on mechanical behavior and water absorption of DGEBA/TETa epoxy network

Water uptake in organic coatings remains an interesting challenge for fundamental and applied researches because chemical, physical, and mechanical properties are concerned. The polymer network, which is affected by the curing program, is a key factor for water absorption. In this work, an epoxy network based on diglycidyl ether of bisphenol A and a hardener triethylentetramine was cured at different temperatures: below T_g (protocol 1) and above T_g (protocol 2). DMA, Differential Scanning Calorimetry (DSC), and FT‐IR measurements showed that both protocols allow to obtain totally cured networks. However, DSC and DMA results revealed that both cured networks present different levels of homogeneity, depending on the different curing conditions, which affect the free volume and the activation volume associated with visco‐elastic properties. The mechanical properties of free films and water sorption behaviors were investigated as function of cured conditions. It was found that protocol 1‐cured networks present higher mechanical properties and was less affected by water ingress than protocol 2‐cured systems, leading to better barrier properties. These results highlight the influence of the curing program onto the heterogeneous distribution of the epoxy network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Critical effect of pH on the formation of organic coatings on mild steel by the aqueous electropolymerization of 2-vinylpyridine

Coatings of poly(2-vinylpyridine) have been formed on mild steel substrates in aqueous medium by electrochemical polymerization of the 2-vinylpyridine monomer. The pH of the solution has been found to be critical for this electropolymerization coating process. At low pH (below 3.5), even with an efficient initiation reaction, the propagation process was impeded and no substantial polymer film was formed. At high pH (above 6.0), only a thin and irregular film formed due to the lack of an effective initiation reaction. Only when the solution pH is in the range of 4 to 5.5 can good quality coatings be formed on mild steel substrates. The detailed effects of the pH on the electropolymerization are discussed in terms of a proposed free radical polymerization mechanism. This research has also resolved the issue of some of the non-reproducible experimental results reported in the literature and confirmed the feasibility of forming poly(2-vinylpyridine) coatings on a mild steel substrate by electropolymerization of the monomer.     

Research on improving the heat insulation and preservation properties of small-size concrete hollow blocks

To solve the problems of poor thermal insulation and heat preservation properties that exist in the walls made of small-size concrete hollow blocks, a new type of compound small-size concrete hollow blocks has been developed. As shown in tests and calculations, the compound blocks not only improve significantly the thermal insulation effect, heat preservation properties, and impermeability of the walls, but also show good decorative results.     

Effects of artificial weathering on the mechanical properties of paper‐based materials consolidated with polymeric materials

The study of polymer behavior over time represents the crucial stage in the setup of innovative methodologies for paper restoration. In this research, a series of laboratory simulations by accelerated aging and characterization tests by chemical and physical measurements were carried out on paper samples consolidated both by grafting polymerization with acrylic copolymers and by coating with waterborne polyurethanes with the aim of determining their harmlessness and long‐term effectiveness. In this way, our purpose was not only to verify possible risks for the paper materials but also to determine the advantages and potentialities of new restoration methods through an appropriate and essential working plan of investigations. From our evaluation, both the selected consolidation methods appeared unsuitable to be used in paper restoration because of the damage that they could cause on the paper materials because of their limited durability over time. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Current distribution in double-cylinder electrolyte cells: Application to the study of corrosion properties of organic coatings

The ionic conductivity of an applied organic coating has been investigated using numerical finite element modelling and a double-cylinder electrochemical cell. The experimental results show that electrochemical impedance spectroscopy is able to account for ionic conductivity property of applied organic coatings in a flexible manner.     

Influence of B-site substituent Ce on thermophysical,oxygen diffusion,and mechanical properties of La2Zr2O7

Pyrochlore-type La₂Zr₂O₇ (LZ) is a promising candidate for high-temperature thermal barrier coatings (TBCs). However, its thermal expansion coefficient and low fracture toughness are not optimal for such application and thus, need to be improved. In this study, we systematically report the effect of CeO₂ addition on phase formation, oxygen-ion diffusion, and thermophysical and mechanical properties of full compositions La₂(Zr₁?_xCe_x)₂O₇ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1). La₂(Zr₁?_xCe_x)₂O₇ exhibits a pyrochlore structure at x ≤ 0.3, while a fluorite structure is observed outside this range. With the increase in CeO₂ content, thermal expansion coefficient and oxygen-ion diffusivity in La₂(Zr₁?_xCe_x)₂O₇ are increased. Oxygen-ion diffusivity of La₂(Zr₁?_xCe_x)₂O₇ is two orders of magnitude less than that of classical 8YSZ. Among La₂(Zr₁?_xCe_x)₂O₇ compounds, La₂(Zr_0.7Ce_0.3)₂O₇ and La₂(Zr_0.5Ce_0.5)₂O₇ exhibit relatively low oxygen diffusivities. The composition La₂(Zr_0.5Ce_0.5)₂O₇ presents the lowest thermal conductivity due to the strongest phonon scattering and also the highest fracture toughness due to the solid-solution toughening. The highest sintering resistance is achieved by the composition La₂(Zr_0.7Ce_0.3)₂O₇ because of its ordered pyrochlore structure and high atomic mass of Ce. Based on these results, the compositions La₂(Zr_0.5Ce_0.5)₂O₇ and La₂(Zr_0.7Ce_0.3)₂O₇ are alternatives for classical 8YSZ for TBC materials operating at ultrahigh temperatures.     

Effect of mechanical stress on kinetics of degradation of marine coatings

Water, UV and temperature are well-known factors for organic coating degradation. Mechanical stress can also affect long-term lifetime in marine environments and probably is conducive to synergistic effects with other ageing parameters. The present work proposes a method to estimate the role of a stress–strain state on the protective properties of two marine epoxy coatings onto mild steel (with and without VOC). Preliminary mechanical measurements on free films by Dynamic Mechanical Analysis (DMA) indicated that the two coatings have a visco-elastic behaviour for a stress level lower than 3.3 MPa. Consequently, a stress equal to 3 MPa was applied on coated substrates using bent samples which were immersed in 3% NaCl solution and in natural seawater (“Les Minimes” yachting harbour in La Rochelle). This test is innovative because a visco-elastic deformation implies that the chain motion remain unchanged after a time of recovery (total restoration of strain in unloading stage) so coatings are not disturbed without applied stress. Non-bent coated samples were also immersed in the same environments as references. The coating degradation was followed by Electrochemical Impedance Spectroscopy (EIS) on both sides of the sample (compressed and stretched sides). The results allowed evaluation of the influence of mechanical state on the coatings degradation in visco-elastic regime and also demonstrate that the mechanical effect depends on the direction of the stress loading.     

A brief history of the Athens conference on organic coatings, science and technology

On 5–9 July 1999 the 25th conference on organic coatings took place in Vouliagmeni near Athens in Greece. To celebrate this anniversary and to honor the memory of the founder and director of the conference, Professor Angelos V. Patsis, a brief review of the history of the conference is given. Typical trends in coatings technology and applications reflected in the programs throughout the years are analyzed.