Corrosion Behavior of Alloyed Cast Iron in Ethylene Glycol-Based Engine Coolants at Elevated Temperature

Gaurav Argade,Monica Viers,Jacob Debusk,Jacob Steenhoek,Corey Trobaugh,Justin Perry,Anusha Chilukuri,Chinpei Wang

doi:10.3390/coatings11030357

Abstract

For enhanced engine performance, corrosivity of the engine coolants would play a significant role. In this work, corrosion investigation was performed on cast iron material in pre-mixed engine coolant environment to understand the threshold limits of contaminants. The pre-mixed coolant contained combination of organic additives viz. sebacate (SA), 2-ethylhexanoate (2-EH), and tolyltriazole (TTA) with varying concentrations of chloride contaminant. Constant immersion of cast iron samples in engine coolant with different chloride levels at 90 °C was followed by room temperature electrochemical tests. The potentiodynamic polarization tests showed no instability until 100 ppm chloride additions exposed up to 28 days. At lower frequencies in electrochemical impedance spectroscopy (EIS) spectra, inhibition layer characteristics changed from highly capacitive to highly resistive and concurrently a sharp decrease in charge transfer resistance was observed with time for samples exposed to >100 ppm chloride levels. In the longer duration corrosion tests, higher pit depths with increased number density of attacks were observed for cast iron samples exposed to engine coolants containing >100 ppm chloride. For elevated temperature exposures a threshold limit of <200 ppm chloride was established for cast iron samples.

Highlights

From environmental point of view the demands to enhance the efficiency of diesel engines are increasing and this creates new challenges for development of materials [1].Chemical nature of engine coolant and its interaction with the materials in contact can significantly influence the overall engine performance
It was observed that the corrosion current was in the similar range (~2–4 μA/cm2 ) for cast iron samples irrespective of the chloride concentration and exposure time
This includes cast iron samples pre-exposed to 90 ◦ C temperature and different immersion times and the day 0 samples

Summary

Introduction

From environmental point of view the demands to enhance the efficiency of diesel engines are increasing and this creates new challenges for development of materials [1].Chemical nature of engine coolant and its interaction with the materials in contact can significantly influence the overall engine performance. Cast irons have been used as materials for multiple engine components viz. It is known that cast irons on their own are less corrosion resistant even in atmospheric conditions and could be susceptible to corrosion by small concentrations of corrosive species viz. To protect cast irons from corrosion, the engine coolants typically contain corrosion inhibitors e.g., organic acids, inorganic additives, or combinations of both to simultaneously boost the corrosion resistance and heat transfer performance [3,4]. Pellet et al compared the corrosion inhibition of cylinder liners in engine coolants containing nitrites and carboxylates which reported improved liner protection in presence of carboxylates and showed no necessity of refortification of the additives [5]. Taking in to account the freezing point requirements, the engine coolants invariably contain fractions of ethylene glycol in its composition. The ingress and leaching of corrosive contaminants during operation and likelihood of formation of glycol degradation acids like glycolic acid, oxalic acid, formic acid, acetic acid, etc. due to oxidation of ethylene glycol has potential to lead to corrosive

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