Colored paints containing nir-reflective pigments exposed to accelerated ultraviolet radiation aging with possible application as roof coatings

This study aims to evaluate the difference in thermal behavior among paints with the presence of traditional and NIR pigments by means of a simple and cheap laboratory-scale test. Considering these goals, the thermal and esthetical properties of two different cool coatings were assessed, highlighting their positive and limited aspects. Two different complex near-infrared inorganic reflective (NIR) pigments with yellow and black respectably colors were mixed in an acrylic waterborne copolymer binder. The paint formulations were applied on steel panels. The thermal performance of the coatings was investigated in the NIR-region of the light spectrum by exposing the samples to an IR-lamp. The outer and inner surface temperatures of the painted panels were recorded using thermocouples and an IR camera. The samples were aged by artificial UV-B light exposure. Color and specular gloss changes at different exposure times were evaluated. The behavior of the cool coatings was compared with that of conventional coatings with similar color characteristics. The black cool coating achieved a maximum temperature decrease, compared to the conventional black one, of approximately 12◦C. The stability for the cool coatings was very similar to that of the conventional coating, indicating that black pigment could be a potential candidate for cool-coating applications. The yellow cool coatings did not show a significant decrease in temperature compared to the conventional paint. The gloss and color changes resulted as influenced by the types and amount of pigments

Synthesis of novel cone-shaped CaAl-LDH directly on aluminum alloy by a facile urea hydrolysis method

The urea method is one of the unique approaches to synthesize highly crystalline-layered double hydroxides (LDHs). Herein, we synthesized calcium-based layered double hydroxide (CaAl–LDH) directly on Al AA6082 substrate by using the urea hydrolysis reaction, in an effort to obtain highly potential novel cone-shaped unique LDH structure. The as-prepared CaAl-LDH thin film is characterized by X-ray diffraction, Fourier transform spectroscopy, scanning electron microscopy, transmission electron microscopy and further investigated the thermal properties and electron impedance spectra behavior. That simple in situ synthetic approach will be helpful to design environmentally friendly CaAl-LDH thin films that can be further investigated for numerous potential applications like environmental science, catalysts and biomedical applications

Sorption of As(V) from aqueous solution using in situ growth MgAl–NO3 layered double hydroxide thin film developed on AA6082

In this work, the MgAl–NO3 layered double hydroxide (LDH) developed by the single-step in situ growth method is used as a robust sorbent to remove arsenic from aqueous solution. The MgAl-LDH exhibiting two different distinct morphologies (platelet structure and cauliflower-shaped structure) was developed on the AA6082 substrate with the variation in synthesis parameters, where AA6082 specimen acts as both the reactant and support. The structural characterizations were investigated through scanning electron microscopy, X-ray diffraction analysis, and energy dispersion spectroscopy, while the adsorption of arsenic on MgAl-LDH was studied through Langmuir and Freundlich models. The Langmuir isotherms have shown a maximum adsorption capacity of around 213 and 239 mg/g for platelet and cauliflower-like MgAl-LDH, respectively. The pseudo-first-order and pseudo-second-order Lagergren kinetic models were studied for the understanding of the adsorption kinetics. The results depicted that anion exchange and the electrostatic interaction are the possible reasons of arsenic sorption on MgAl-LDH, but the ion exchange mechanism is found to be the dominant mechanism. The maximum adsorption capacity of cauliflower-shaped MgAl-LDH was found to be slightly higher than platelet structure, but overall maximum arsenic adsorption uptake values of both in situ growth structures have found to be exceeded the mostly reported MgAl-LDH maximum adsorption capacities

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

Environmentally friendly hybrid coatings for corrosion protection: silane based pre-treatments and nanostructured waterborne coatings

This thesis considers a nanotechnology approach based on the production of metals pre-treatments and organic coatings (a complete protection system at all) designed from the nanoscale. The final aim is to develop protection systems with improved corrosion protection properties and a low environmental impact. In particular, multifunctional silane hybrid molecules were used to design sol-gel pre-treatments for metals and to modify the inner structure of UV curable waterborne organic coatings. In the first part of this thesis thin (hundreds of nanometers) sol-gel films consisting of an experimental mixture of hybrid silicon alkoxides molecules were applied onto aluminium and hot dip galvanized (HDG) steel for the development of effective and environmentally friendly corrosion protection systems A chemical and electrochemical characterization of the sol-gel films highlighted their good corrosion protection properties both for aluminium and HDG steel. To test the effectiveness of the sol-gel coatings as coupling agent between metallic substrates and organic coatings (paints) both a powder coating paint and a cataphoretic coating paint were applied on the silane pre-treated substrates. The electrochemical measurements and the accelerated tests carried out on these protection systems proved the capability of these sol-gel conversion coatings to improve the corrosion protection properties of the traditional protective cycles. The performance of the silane pre-treatments was also compared to commonly used surface conversion coatings for metals. The result of this comparison evidenced that the corrosion protection properties ensured by the sol-gel conversion treatment is comparable or higher than most of the commonly used pretreatments. A study about the incorporation of inorganic nanoparticles into these sol-gel films gave evidences of an improved corrosion resistance due to the addition of certain amount of montmorillonite nanoparticles in the sol-gel matrix. The same hybrid silicon alkoxide molecules used to perform the pre-treatments were used modify the inner structure of UV curable waterborne coatings in order to improve the corrosion protection properties maintaining the environmental compatibility of the protecting system. The design, application and characterisation of urethane, acrylic and epoxy waterborne UV curing coatings modified with the hybrid silicon molecules in order to obtain nanostructured waterborne films with improved corrosion resistance and thermomechanical properties were studied. The characterization proved the great potential of the silicon alkoxide molecules as a tool to modify the properties of the organic matrix of the paint: silicon alkoxides can promote the self assembly of inorganic nanoparticles into the matrix or can act as an effective coupling agent between inorganic nanoparticles and the polymeric matrix. Silicon alkoxide molecules were proved to be an efficient tool to design a protection system from the nanoscale leading to the prospective of an accurate control of the overall properties of the macroscopic systems

Insight into the Role of Cerium (III) Addition to a MgAl-LDH Coating on AA6082

In this work, Ce doped MgAl-LDHs layers have been developed through an in-situ synthesis method on 6082 aluminum surface. The aim was to gain mechanistic insight into the role of Ce(III) as an active corrosion inhibitor embedded in the LDHs layer. The development of the LDH structure was verified by checking the presence of the characteristic XRD peaks, the platelet morphology (evaluated by SEM-EDXS) and the functional groups (by FTIR-ATR analyses). The same techniques were employed to assess the effect of a prolonged immersion time in 0.1 NaCl on the Ce doped MgAl-LDH coatings. Electrochemical impedance spectroscopy (EIS) was employed to monitor the evolution of the electrochemical properties of the coatings during prolonged immersion in saline solutions. The findings suggest a crystallization/dissolution/precipitation mechanism which implies: (i) the formation of crystalline cerium compounds, such as Ce(OH)3, in the LDH structure during the synthesis; (ii) the dissolution upon exposure to the NaCl solution, thus leading to cerium ions release; (iii) the precipitation of amorphous Ce oxides/hydroxides at the cathodic sites when the metal starts to corrode; (iv), the consequent mitigation of the electrochemical activity of the metal and, thus, the reduction of the extent of corrosion

Thermal behaviour and weathering resistance of coil coatings for energy-efficient buildings

In recent years, the aspects of energy-savings in buildings have become increasingly important. Coil coatings are frequently used for roof and façade construction in order to reduce the cost, the building time and the maintenance. In recent years different near infrared (NIR) reflectivity pigments have been developed to increase the capability of paint to reflect the sun’s radiation thus minimizing the amount of energy absorbed by the building. Coil coatings containing both traditional and NIR pigments are considered for the assessment of their thermal behaviour. The same painted system produced by three different producers was considered. Using a small scale house model, a W-IR emitting lamp and thermocouples, the amount of energy absorbed by the painted metallic coupons has been evaluated in order to assess the efficiency of the different pigments under investigation. To evaluate effect of ageing, all the different samples were subjected to five accelerated degradation cycles consisting in 168 h of UV-B irradiation followed by 168 h of salt spray exposure. The thermal properties of samples were collected. The cool pigments resulted effective to decrease the heat absorbance (difference between standard and NIR paints up to 18°C). The thermal properties were found not to be affected by degradation

Effect of Synthesis Conditions on the Controlled Growth of MgAl–LDH Corrosion Resistance Film: Structure and Corrosion Resistance Properties

In this study, a series of MgAl–layered double hydroxide (LDH) thin films were synthesized by a single step hydrothermal process at different synthetic conditions on AA6082, and the combined effect of reaction temperatures and crystallization times on in situ growth MgAl–LDH structural geometry, growth rate, and more importantly on the corresponding corrosive resistance properties are briefly discussed. The synthesis of LDH was performed at reaction temperatures of 40, 60, 80, and 100 °C, while the treatment time was varied at 12, 18, and 24 h. The as-prepared synthetic coatings were characterized by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), while the corresponding corrosion protection efficiency of the developed coating was studied through potentiodynamic polarization studies and electrochemical impedance spectra. The findings demonstrated that extended crystallization time and reaction temperature impart a significant effect on the oriented growth of layered double hydroxide, the surface morphology, and on the film thickness, which had a remarkable influence on the LDH corrosion resistance ability. The LDH coated specimen developed at 100 °C for 18 h reaction time showed a more compact and dense structure compared to the traditional platelet structure obtained at 80 °C for 24 h crystallization time, and interestingly that compact structure exhibited the lowest corrosion current density, up to five orders of magnitude lower than that of bare AA6082