A review of the effect of metals on the thermo-oxidative stability of perfluoropolyalkylether lubricants

Abstract

The structural attributes and degradation mechanisms are reviewed for Fomblin Z®, Demnum , and space applications such as in satellites [4]. The backbone of the molecule contains only single bonds which allow free rotation of the backbone atoms producing a fluid with excellent viscosity characteristics. The high temperature oxidative stability is partly due to their high molecular weight and the shielding effect the highly electro-negative fluorine atoms have on protecting the carbon/oxygen backbone [5]. Comparing hydrocarbon chemistry in oxidative environments, hydrocarbons have the tendency to form water and OH radicals via a free radical process. This situation does not apply to perfluorinated compounds due to the resistance of the C-F bond to the attack by free radicals and the thermodynamic instability of OF 2 and OF species [6,7]. This renders PFPAEs JOURNAL OF SYNTHETIC LUBRICATION

Production of Highly Symmetrical and Branched Biolubricants from Lignocellulose-Derived Furan Compounds

“…Ether lubricants are often used in gear oils because of their stable extreme pressure. Currently, polyethers or epoxy ether lubricants prepared via oxidation of CC bonds are mostly used in the market . In this work, we hydrogenated the furan ring to prepare highly branched epoxy ether biolubricants.…”

Lithium Insertion Mechanism in Iron Fluoride Nanoparticles Prepared by Catalytic Decomposition of Fluoropolymer

“…Although PFPEs are stable up to 410 °C in an inert atmosphere and to approximately 316 °C in an oxygen-rich environment, PFPEs can be catalytically decomposed by metal, metal oxides, metal fluorides (FeF 3 , AlF 3 ), and particularly Lewis acids (such as AlCl 3 ) at lower temperatures. In the case of Krytox PFPE (CF 3 CF 2 CF 2 O­[CF­(CF 3 )­CF 2 O] m CF 2 CF 3 ), decomposition is potentially initiated by an intramolecular disproportionation reaction at the terminal pentafluoroethoxy groups (−O–CF 2 –CF 3 ) releasing trifluoroacetyl fluoride (CF 3 COF), and proceeds down the chain in an unzipping fashion by decomposition at the perfluoroisopropoxy end groups (CF 2 –O–CF­(CF 3 ) 2 ) into hexafluoroacetone ((CF 3 ) 2 CO), , which is the main decomposition product, as illustrated in Scheme .…”

“…Although the mechanism of CF 3 COF release during the first stage of decomposition is still not clear, , it is generally believed that the oxide surface is slowly fluorinated by a nucleophilic substituted CF 3 COF followed by a second stage where the rapid decomposition of PFPE commences via a chain reaction catalyzed by freshly formed strong Lewis acid (FeF 3 ) sites, resulting in complete fluorination and decomposition of PFPE fluids into volatile perfluorocarbons, carbonyl fluoride, oxidized products, and hydrogen fluoride if any water is present. Much of the documented literature reports − that the majority of the second-stage byproducts are (CF 3 ) 2 CO and low molecular weight Krytox chains but other degradation mechanisms cannot be completely dismissed.…”

“…From previous studies, the final oxidation state of iron (Fe 2 O 3 , FeO, Fe 3 O 4 , and Fe) varies with the temperature and atmosphere as shown in following reactions. 47−52 But, under inert atmosphere the primary product, FeO, is known to disproportionate to Fe 53,54 which is the main decomposition product, as illustrated in Scheme 1.…”

“…Although the mechanism of CF 3 COF release during the first stage of decomposition is still not clear, 54,55 it is generally believed that the oxide surface is slowly fluorinated by a nucleophilic substituted To obtain mechanistic insights into the metal fluoride formation, all the volatile chemical species generated during heat treatment were analyzed using mass spectrometry (MS). The presence of COF is due to ionization of COF 2 produced by oxidation of trifluoroacetyl fluoride and hexafluoroacetone, whereas CF 3 is from ionization of C 2 F 6 released by thermal decomposition of hexafluoroacetone or trifluoroacetyl fluoride.…”