Progress in Color, Colorants and Coatings
Volume:13 Issue: 4, Autumn 2020

In this paper, electrochemical behavior of epoxy paints embedded by modified calcium carbonate particles was investigated during exposure to 3.5 wt% NaCl solution. The precipitated calcium carbonate (PCC) and ground calcium carbonate (GCC) particles were utilized as inexpensive filler for epoxy paints. Electrochemical impedance spectroscopy (EIS), polarization tests and pin-on-disk method were used to determine the protective properties of epoxy paints on carbon steel substrates. GCC particles with the concentration of 20 wt% were more effective than PCC particles in increasing the corrosion resistance of epoxy paints; however, PCC particles affected obviously the reduction of friction coefficient of epoxy paints under wet condition (3.5 wt% NaCl solution). This behavior may be attributed to the small size and spherical shape of such particles. Values of the friction coefficient for epoxy paints were about 0.5-0.6 under dry condition. The coating resistance increased by about 99 % in the presence of GCC particles in 20 wt% after 3 days of the immersion. In addition, equivalent electrical circuits suggested that the ion transport through defects in the paint layer is the controlling factor in the corrosion process after immersion for 7 days.

In this study, vanadium conversion coating(VCC) was deposited on the surface of soft-cast steel (St-37).  A thermoset coating was enforced on the VCC and blank substrates. The surface was characterized by field emission scanning electron microscope (FE-SEM), elemental mapping of energy dispersive X-ray (EDX) and atomic force microscopy (AFM). The adhesion strength of the thermoset coating on the surface of the treated samples was measured before and after 35 days of submergence in 3.5 wt. % NaCl solution via a pull-off device. Meanwhile, the effect of VCC treatment on the thermoset coating (epoxy) was examined by electrochemical impedance spectroscopy (EIS) and cathodic delamination (CD) tests. FE-SEM, EDX and AFM studies of treated surfaces showed a homogeneous vanadium oxide/hydroxide layer precipitated on the metal which increased the surface roughness. It was shown that VCC significantly improved the corrosion resistance of the epoxy coating. The vanadium compounds also reduced the cathodic activity on steel resulting in lower cathodic disbandment. The lower adhesion loss was also observed on the vanadium treated sample in comparison with the blank one.

Sophisticated manipulation of surface roughness and solid surface energy are widely used to design super-hydrophobic layers. In this work, we designed highly porous silica layer with contact angle (CA) of 145°, and its robustness was promoted with thermal treatment. Wettability of coated layer is studied with CA measurement for different liquid surface tensions using diluted organic solvents (ethanol, acetone or ethylene glycol) with distilled water. Zisman plot is also used to estimate the surface energy of the porous silica. The results are compared with coated black soot as a hydrophobic layer. Moreover, thin layer of Au (~10 nm) was coated on the porous silica layers to study the effects of chemical properties on the wetting behavior. The thickness of the Au thin layer is negligible compared to the surface roughness, so the drastic decrease in CA rates can be related to the layers' porosity and the affinity of solvents to liquid/air and liquid/solid interfaces.

In this work, photostability, absorption and emission intensity of coated polycarbonate (PC) sheets with optical brightener (OB) as a wavelength converter material have been investigated. In addition, this coated sheet was used as a wall for microalgae culture flask, as a small scale photobioreactor, for studying the spectral conversion of UV-A radiation to blue light region and its effect on the biomas productivity of microalga Chlorella sp. For this purpose, the PC sheets coated by different concentrations of OB dissolved in thermoplastic acrylic resin were prepared and placed between the UV-A radiation source and the culture flasks. Results showed that the photostability increases under UV-A and solar radiation by applying two coating systems. Also, higher surface concentration causes an increase in emission intensity of coated sheet. Furthermore, compared with the uncoated sheets, the sheet coated with OB layer exhibited up to 70% higher biomass production of microalga Chlorella sp.

In this research, graphene oxide (GO) nanoparticles were modified by second and fourth generations of poly(amidoamine) dendrimers in order to improve the particle dispersion quality in the epoxy matrix and therefore its barrier anti-corrosion performance. Confirmation on the GO surface modification by Polyamidoamine generation 2 (PAMAM2) and polyamidoamin generation 4 (PAMAM4) was carried out by Fourier transforms infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA). The corrosion protection properties of the epoxy composites against corrosive electrolyte (3.5 wt.% NaCl solution) was investigated by salt spray and electrochemical methods. The dispersion of unmodified and modified GO sheets in the epoxy matrix was studied by FE-SEM analysis. The FT-IR test results evidenced that the GO sheets were successfully modified with PAMAM 2 and 4 via the covalent binding mechanism.  Salt spray and EIS test results revealed that the epoxy composites loaded with GO-PAMAM4 and PAMAM4 showed the highest improvement in the corrosion resistance. FE-SEM images from the fracture surface of the coatings revealed that the dispersion of GO sheets within the epoxy coating was improved after modification by PAMAM4.

A novel nanocomposite consisted of nanomaterials as (CuO:NiO) and carbon (fuel ash) were designed to absorb solar energy. Thin films were made via casting and spin coating of the dopants nanocomposite thin films, containing different concentration ratios of CuO:NiO. These thin films are precipitated on a glass and copper substrates. The optical properties of the doped fuel ash films with nanoparticles were measured in the range of 250-1300 nm. The intensity of solar radiation was measured too. The data were analyzed and interpreted in terms of the theory of phonon-assisted direct electronic transitions. The Eg of the doped C was measured with different concentration ratios of (CuO:NiO) (A=0.5:2.5, B=1:2, C=1.5:1.5, D=2:1, E=2.5:0.5) wt. %, with a fixed concentration of  C of  (7) wt.%. The results of the doped samples revealed an energy gap of (2.5-3.9 eV) and the absorptivity ranged from (85-99 %) for all nanocomposites. The energy gap of this nanocomposite system is very similar to those of semiconductor and has high efficiency to absorb the solar energy radiation. In addition, the results showed that the heat absorbed by the samples subjected to solar energy on the surface would be a selective surface. Thus, the synthesized coating will be utilized on a flat plate collector as a trap to absorb solar energy.