화학공학소재연구정보센터
Journal of Chemical Thermodynamics, Vol.116, 185-196, 2018
Thermal stability of aprotic ionic liquids as potential lubricants. Comparison with synthetic oil bases
Thermal stability of three ionic liquids (ILs) and five base stock lubricants was analysed using a Perkin Elmer thermogravimetric device and compared with that of the 19 ILs previously studied. The ILs are 1 -(2-methoxyethyl)-1-methyl-pyrrolidinium tris(pentafluoroethyl) trifluorophosphate, [1-(2-methoxye thyl)-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl) imide, and trihexyl(tetradecyl) phosphonium tris(pentafluoroethyl) trifluorophosphate, and the bases are dipentaerythritol hexaheptanoate, a polypropyleneglycol dimethylether, and three perfluoroalkylpolyethers. Firstly, dynamic scans were performed, under air atmosphere and at a heating rate of 10 degrees C.min(-1), to estimate the short-term thermal stability. Anion influence on the short-term thermal stability is higher than the cation one, and those ILs with bis(trifluoromethylsulfonyl) imide anion [NTf2](-) are the most stable. All the ILs here studied showed higher onset temperatures than the five base oils. The influence of the water content on the short-term thermal stability was analysed through the onset temperature variation between two different water contents, as supplied and after saturation, observing that the influence of this impurity is not significant for the studied ILs. From isothermal experiments performed at temperatures lower than the onset ones, the kinetic of the degradation was studied and the activation energy for the ILs and two lubricant bases was determined. The values obtained were used to estimate the maximum operation temperature of these fluids using three different methodologies. Finally, qualitative studies were performed based on the colour change after heating at different temperatures and on the character endo or exothermic of the DSC peaks associated to the different mass loss steps under N-2 atmosphere. These studies showed that the degradation mechanism depends on the atmosphere. (C) 2017 Elsevier Ltd.