Physicochemical, Thermal and Cooling Curve Characterisation of Sulfate Salt–Modified Sesame Oil as a Potential Bio-Based Quenching Medium

The development of environmentally safe quenching media is critical for sustainable heat treatment operations. Vegetable oils have emerged as promising bio-based alternatives to petroleum-derived quenchants due to their renewability, biodegradability and favourable thermal characteristics; however, their direct industrial application is often limited by inadequate thermal stability and sub-optimal cooling behaviour. In this study, raw sesame oil and sesame oil modified with potassium sulfate (K₂SO₄) and sodium sulfate (Na₂SO₄) additives were systematically characterised to evaluate their suitability as potential bio-based quenching media. Physicochemical properties, including density, viscosity, acid value and iodine value, were evaluated. Thermal safety characteristics (smoke point, flash point and fire point) were determined using a digital infrared pyrometer, while thermal degradation behaviour was assessed through thermogravimetric and differential thermal analyses (TGA/DTA) to obtain decomposition onset temperatures and maximum mass loss rate temperatures. Cooling behaviour was examined using temperature–time cooling curve analysis. The results show that the incorporation of sulfate salt additives modifies the physicochemical and thermal behaviour of sesame oil, generally leading to improved thermal safety limits and enhanced thermal stability compared with the raw oil. Cooling curves reveal noticeable differences in heat extraction behaviour among the modified oils, indicating that additive concentration improves the cooling characteristics of sesame oil, especially at the vapour blanket stage (0 – 5 sec). The combined findings demonstrate that sulfate salt modification provides an effective route for modifying the properties of sesame oil and establishing its potential as a bio-based quenching medium. The data generated in this study serve as essential baseline information for future application-oriented heat treatment studies.