Decomposition of perfluoropolyether lubricants: A study using TGG―MS in the presence of alumina powder

• Published in: Journal of thermal analysis and calorimetry Vol. 106; no. 1; pp. 213 - 220
• Main Authors: KEATING, Mimi Y, HOWELL, Jon L
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Dordrecht Springer 01-10-2011
• Subjects: Aluminum oxide; Applied sciences; Chemical reactions and properties; Criminal investigation; Degradation; Exact sciences and technology; Fluorine compounds; Fluorocarbons; Friction, wear, lubrication; Lubrication and lubricants; Machine components; Mechanical engineering. Machine design; Organic polymers; Physicochemistry of polymers; Powders; Sulfur compounds; TG-MS; Catalytic reaction; Lubricants; Coupled method; Fluorine containing polymer; Thermogravimetry; Decomposition; Ether polymer; High-temperature; Powder; Lubricant; Polypluoropolyethers; Aluminium Oxides; Alumina powder; Thermal analysis; Alumina; Mass spectrometry
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-011-1529-2

Decomposition has been studied in the chemistry of perfluoropolyethers (PFPE), thus far no molecular structure information is reported. TG-MS is a tool to follow the off gassing of decomposition for clues. We selected two PFPEs that have different properties: Krytox[R] XHT-1000 and Fomblin Z60 heating to normal decomposition and catalytic decomposition in the presence of alumina powder. Comparing the decomposition fragment intensities, the molecular structure of the branched Krytox[R] XHT-1000 oil is more stable than the blocky Fomblin Z60. We see aluminum-containing fluorine fragments in the rapid decomposition of oils in contact with alumina powder. It has been suggested the formation of Al([O.sub.6-n][F.sub.n]), where n = 1,2, and 3, in which the fluorine atoms are selectively associated with aluminum atom. The major decomposition products are small and large fragments of fluorocarbons and perfluoroalkoxy. In the absence of alumina powder, Krytox XHT-1000 shows only a loss of 13 mass/% after several hours at 330[degrees]C, whereas in the presence of 1 mass/% alumina powder the oil has rapidly decomposed to 67 mass/% of its original mass within 15 min. Fomblin Z60, a product might not be designed for high temperature, exposing to the same conditions at 330[degrees]C for several hours and shows a loss of 98 mass/% alone, but in the presence of 1 mass/% alumina powder shows a loss of 98 mass/% in 3.6 min. When 3 mass/% of two new developmental additives were added to the both oils, the catalytic decomposition in the presence of 1 mass/% alumina powder was significantly reduced in Krytox[R] XHT-1000, showing only a loss of 23 mass/% in 4 h, but nearly all weight for Z60 in 60 min. In the oil grades that contain the new additives, we see the fragments of Al-O-S, and F-Al-O-S. The sulfur-containing compound has been reported ionically bonded to oxide in a tripod configuration of alumina surface, which shields the formation of Al-F.