Corrosion Inhibition of Sodium Silicate with Nanosilica as Coating in Pre-Corroded Steel

This study was conducted to investigate the potential of using sodium silicate with nanosilica as a treatment to inhibit the progress of corrosion in steel specimens that are already corroded. Steel specimens measuring 16 mm in diameter and 4 mm in thickness were prepared and subjected to pre-corrosion by immersion to 3.5% NaCl solution. Two sets of specimens were then dip-coated with sodium silicate containing nanosilica. One set was coated with 1% nanosilica, and the other was coated with 2.5% nanosilica. The coated specimens were then subjected to Complex Impedance Spectroscopy (CIS) at 20 Hz to 20 MHz frequency range. Compared with the sodium silicate coating with 1% nanosilica, the sodium silicate coating with 2.5% nanosilica had a larger semi-circle curve in the Nyquist plot. Similarly, the sodium silicate coating with 2.5% nanosilica also showed larger magnitudes of impedance at the low-frequency region and larger phase angles at the high-frequency regions in the Bode plot. These results imply that the sodium silicate coating with 2.5% nanosilica coating demonstrated better capacitive behavior. In addition, equivalent circuit modelling results also showed that the sodium silicate coating with 2.5% nanosilica had higher coating resistance and lower coating capacitance as compared to the sodium silicate coating with 1% nanosilica. Doi: 10.28991/cej-2021-03091761 Full Text: PDF

Synthesizing and Evaluating the Photocatalytic and Antibacterial Ability of TiO2/SiO2 Nanocomposite for Silicate Coating

The TiO2/SiO2 nanocomposite has been synthesized by a sol-gel method and investigated the effect of the SiO2 content (0, 5, 10, 15, 20, and 50%) on the rutile-to-anatase phase transition of TiO2 NPs. In order to increase the photocatalytic efficiency of the nanocomposite and decrease the price of material, the TiO2/SiO2 Nc with content SiO2 of 15% sample is chosen for preparing silicate coating. The efficiency of photocatalytic MB and antibacterial ability in the air of W silicate coating (adding TiO2/SiO2 Nc (15%)) achieve almost 100% for 60 h and 94.35% for 3 h, respectively. While the efficiency of photocatalytic MB and antibacterial ability of WO silicate coating (adding commercial TiO2/SiO2) is about 25–30% for 60 h and 6.02% for 3 h, respectively. The presence of TiO2/SiO2 Nc (15%) with a larger surface area in W silicate coating can provide increased centers for absorption, photocatalytic reaction, and the contact between sample and bacteria lead to enhance the photocatalytic and antibacterial ability of W silicate coating.

The Study’s Chemical Interaction of the Sodium Silicate Solution with Extender Pigments to Investigate High Heat Resistance Silicate Coating

Silicate coating is water-based paint with many advantages and wide applications in many different industries. However, there are still some problems with silicate coating: how to increase its resistance to heat at high temperatures and prolong the life of the coating. Silicate paints have high durability and longevity dependent mainly on the chemical interaction of the silicate binder with extender pigments. Therefore, our groups have studied the geopolymerization process of the sodium silicate solution with extender pigments to investigate high heat resistance silicate coating. The effect of curing time on the chemical interaction between sodium silicate solution and extender pigments (ZnO, TiO2, Fe2O3, CaCO3, and Na2SiF6) was investigated by Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), and X-ray diffraction (XRD). The shift of antisymmetric stretching vibration of the Si-O-Si bond (1060 cm−1) to low frequency and increase of the intensity of the Si-O-Si stretching as curing time increases from 1 to 20 days are due to the increased chemical interaction between extender pigments (ZnO, TiO2, Fe2O3, CaCO3, and Na2SiF6) and sodium silicate solution. Moreover, TG results of ZnO-silicate, TiO2-silicate, CaCO3-silicate, Na2SiF6-silicate, and Fe2O3-silicate coating at 1 and 20 days of curing show high residual geopolymer about 69–90% at 800°C. Thus, we proposed that the geopolymerization process between sodium silicate solution and extender pigments (ZnO, TiO2, Fe2O3, CaCO3, and Na2SiF6) increases when the curing time from 1 to 20 days leads to forming geopolymer silicate with high thermal stability. In addition, the optimal mixing ratio between sodium silicate solution and extender pigments (ZnO, TiO2, Fe2O3, CaCO3, and Na2SiF6) is as follows: 25% binder (sodium silicate solution), 8% ZnO; 5% TiO2, 5% Fe2O3, 1% Na2SiF6, 21% CaCO3, 34% H2O, and 1% additives to make high heat resistance silicate coating with temperature resistance at 1000°C.