DOI: https://doi.org/10.55373/mjchem.v27i2.54

Keywords: Sodium metasilicate; silicate dropout; solubility; functional groups; morphology

Abstract

Ethylene glycol (EG)-based coolants help dissipate excess heat generated by engines, with sodium metasilicate often added as a corrosion inhibitor. However, adding metasilicate to EG coolant can lead to the formation of silicate gel, which compromises the coolant's efficiency. This gel-like precipitate is known as silicate dropout. This paper reports on the characteristics of silicate dropout from EG coolant under varying dosages of metasilicate and temperatures. The silicate precipitates were extracted and analyzed using Fourier Transform Infrared (FTIR) Spectroscopy to identify molecular bonding and structural changes. Field Emission Scanning Electron Microscopy (FE-SEM) was employed to examine the surface morphology and microstructural features of the precipitates. The study found that silicate dropout occurred when the metasilicate concentration reached 3% at room temperature. As the metasilicate dosage increased, the solubility of the silicate precipitates decreased due to saturation. This was evidenced by a reduction in absorption at 780, 850, and 1001 cm^-1. Elevated temperatures further facilitated silicate precipitation as a result of the exothermic nature of the reaction. The IR spectra demonstrated shifts in Si-O-Si bands to higher (954-845 cm^-1 to 1001 – 854 cm^-1) and lower frequencies (811-699 cm^-1 to 783 – 583 cm^-1), indicating the formation of a silicate network and the disruption of monomeric structures. The SEM images showed monomeric silicates at lower concentrations and temperatures, while polymeric structures dominated at higher temperatures and dosages. Energy Dispersive X-ray (EDX) analysis confirmed an increase in Si content within the precipitates at higher temperatures.