Unraveling silica auto-condensation and dissolution chemistry in engine coolant fluids: Applications in automotive coolant organic additive technology (OAT)

• G. Skordalou¹, S. Clerick², G. Buytaert², I. Verlent², S. Lievens² and K.D. Demadis¹

¹ Crystal Engineering, Growth and Design Laboratory, Department of Chemistry, University of Crete, Voutes Campus, Heraklion, Crete, GR-71003, Greece
² Arteco NV, B-9051 Sint-Denijs-Westrem, Belgium

Abstract: Engine coolants are mixtures of water and glycols (most commonly monoethylene glycol, MEG), formulated with corrosion inhibitors to protect the system materials. Nowadays, organic corrosion inhibitors are generally used in combination with inorganic corrosion inhibitors, such as silicates. To effectively formulate such engine coolant, it is of crucial importance to understand the behavior of silicate in a “semi-aqueous” environment. Silicate polycondensation has been thoroughly studied in aqueous solutions and the key factors influencing its aqueous chemistry are well defined (i.e. pH, temperature, concentration, etc.). In this paper the polycondensation chemistry of silicate in a wide range of MEG/water mixtures is thoroughly studied and the influence of several experimental parameters, such as working pH, condensation time and the MEG:water ratio, is investigated. The presence of MEG in MEG/water mixtures enhances silicate auto-condensation to form amorphous silica, at all pH values studied. Silicate condensation starts to occur within 10 minutes of pH adjustment and is faster with increasing MEG. The lowest levels of active silicate were observed in the pH region 8.0 to 8.5 (most common pH for engine coolants). The behavior of silicate was also studied in a generic coolant (which contains organic corrosion inhibitors in addition to MEG). In both cases condensation is severely enhanced. Temperature-driven amorphous silica particle dissolution was studied in selected MEG/water mixtures and it was found that it is negligible at ambient temperature regardless of the MEG:water ratio, whereas it is substantial at 90°C in pure water. Delineating silicate chemistry in coolant matrices will be valuable information for designing better-performing formulations for engine coolant applications.

Keywords: silicate, engine coolant, monoethylene glycol, MEG, polycondensation, corrosion inhibitor

Int. J. Corros. Scale Inhib., 2023, 12, no. 2, 621-644
doi: 10.17675/2305-6894-2023-12-2-13

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