Wilfredo Morales

Decomposition of Perfluoroalkylpolyethers (PFPE) in Ultra-High Vacuum Under Sliding Conditions

Reactions of three different types of perfluoroalkylpolyether (PFPE) liquids were studied during sliding contact with stainless steel (440C) specimens under ultra-high vacuum conditions. All three liquids reacted with the steel specimens during sliding. One PFPE liquid, which has acetal linkages, decomposed under the sliding conditions and generated gaseous products, namely, COF2 and fluorinated carbons, which were detected by a quadrupole mass spectrometer. Gaseous products were not detected for the other two PFPE liquids (these two liquids lacked the acetal linkages). The amount of gaseous products from the acetal containing PFPE liquid increased with increasing sliding speed. At the end of the sliding experiments, the specimens were removed from the vacuum chamber and the wear scar and the deposits on the specimens were examined by small-spot-size X-ray photoemission spectroscopy (XPS). The oxide layer on the specimen surface was removed during sliding, and metal fluorides were formed on the worn surfa...

Evaluation of Vapor Pressure and Ultra-High Vacuum Tribological Properties of Ionic Liquids

Ionic liquids are a class of salts that incorporate polyatomic anions and cations. These materials are typically viscous fluids at room temperature. The fluids are generally characterized as possessing negligible vapor pressures under ambient conditions. These beneficial properties have led us to study the effectiveness of ionic liquids containing both organic cations and anions for use as lubricants with space applications. This article presents vapor pressure measurements for four ionic liquids as well as friction coefficient data from a spiral orbit tribometer in the boundary lubrication regime under simulated space conditions using stainless steel tribocouples. In addition, we present the first tribological data on mixed ionic liquids and an ionic liquid additive. Postmortem infrared and Raman analyses of the balls and races indicates that the major degradation pathway for these organic ionic liquids is similar to those of other carbon-based liquid lubricants; that is, deterioration of the organic structure into amorphous graphitic carbon. The coefficients of friction and lifetimes of these lubricants are comparable to or better than those of several commonly used space oils.

Tribological Testing and Thermal Analysis of an Alkyl Sulfate Series of Ionic Liquids for Use as Aerospace Lubricants

Due to their low vapor pressures, low melting points, high boiling points, high radiation resistance, and high thermal stability, room-temperature ionic liquids (ILs) appear to be suitable candidates as new aerospace lubricants for the upcoming return to the Moon and eventual Mars missions and for air and rotorcraft applications. In this study, three ILs with the same cation, 1-butyl-3-methylimidazolium, but different sulfate anions were tested using an ultra-high vacuum spiral orbit tribometer (SOT) and their thermal properties were determined by thermogravimetric analysis (TGA). Specifically, 1-butyl-3-methylimidazolium methyl sulfate, 1-butyl-3-methylimidazolium ethyl sulfate, and 1-butyl-3-methylimidazolium octyl sulfate were tested. The SOT experiments revealed that the lifetimes of the three ILs decreased with increasing alkyl substituent length on the sulfate anion. Infrared and Raman spectra were taken to detect unused ILs and graphitic degradation products, respectively, on worn parts. Post-run spectroscopic analysis indicated residual degraded, but still usable, ILs in all runs, coupled with varying amounts of amorphous graphitic material produced as the final degradation product of all ILs. SOT testing indicated that these ILs have lower friction coefficients and lifetimes greater than those of two commonly used perfluoropolyalkylether (PFPE) space lubricants. TGA showed that the methyl sulfate IL had the highest thermal stability in air and nitrogen. The vapor pressure of the methyl sulfate IL is as at least as low as Fomblin 815Z at 20°C.

Permanent Magnetic Bearing for Spacecraft Applications

A passive permanent magnetic bearing rig prototype was designed and constructed. The suspension of the rotor was provided by two sets of radial permanent magnetic bearings operating in the repulsive mode. The axial support was provided by jewel bearings on both ends of the rotor. Preliminary testing led to successful operation of the bearing prototype to speeds of 5500 rpm using an air impeller. Radial and axial stiffnesses of the permanent magnetic bearings were experimentally measured and then compared to finite element results. The natural damping of the rotor was measured and a damping coefficient was calculated. Scheduled for Presentation at the 58th Annual Meeting in New York City April 28–May 1, 2003

Current Status of Hybrid Bearing Damage Detection

Advances in material development and processing have led to the introduction of ceramic hybrid bearings for many applications. The introduction of silicon nitride hybrid bearings into the high-pressure oxidizer turbopump on the space shuttle main engine led NASA to solve a highly persistent and troublesome bearing problem. Hybrid bearings consist of ceramic balls and steel races. The majority of hybrid bearings utilize Si3N4 balls. The aerospace industry is currently studying the use of hybrid bearings and, naturally, the failure modes of these bearings become an issue in light of the limited data available. In todays turbine engines and helicopter transmissions, the health of the bearings is detected by the properties of the debris found in the lubrication line when damage begins to occur. Current oil debris sensor technology relies on the magnetic properties of the debris to detect damage. Because the ceramic rolling elements of hybrid bearings have no metallic properties, a new sensing system must be developed to indicate the system health if ceramic components are to be safely implemented in aerospace applications. The ceramic oil debris sensor must be capable of detecting ceramic and metallic component damage with sufficient reliability and forewarning to prevent a catastrophic failure. The objective of this research is to provide a background summary on what is currently known about hybrid bearing failure modes and to report preliminary results on the detection of silicon nitride debris in oil using a commercial particle counter.

The Decomposition of a Commercial Perfluoropolyalkylether on Alpha and Gamma Catalytic Aluminas

The decomposition of a commercial perfluoropolyalkylether liquid lubricant (PFPE Z) was studied using a thermal gravimetric and differential scanning calorimetry unit. Small porous alumina pellets (alpha and gamma forms) were charged with approximately 5 mg of PFPE Z, and the charged pellets were then placed inside the thermal units where decomposition started to occur over the. narrow temperature range of 198° to 210°C under a nitrogen atmosphere. At the end of a test, 1,1,2-trichlorotrifluoroethane solvent was used to extract PFPE Z and decomposition products from the pellets. This extract was analyzed using high-pressure liquid chromatography in the size exclusion mode. The alumina pellets were examined using X-ray photoelectron spectroscopy. Analysis of the thermal, chromatography, and X-ray photoelectron spectroscopy data support evidence that there are two different decomposition mechanisms for PFPE Z. The data indicated, that active surface sites, other than Lewis acid sites, were responsible for P...

X-ray photoelectron spectroscopy peak assignment for perfluoropolyether oils

Perfluoroalkylpolyether (PFPE) oils are increasingly being used as vacuum pump oils and as lubricants for magnetic recording media and instrumentation for satellites. In this paper, the relative binding energies of three PFPE oils are determined. When sample oils are continuously irradiated during X-ray spectroscopy (XPS) measurements, the relative peak intensity of the spectra is altered significantly, indicating that gaseous products form from the oils during XPS measurements. Thus, attention should be paid to chemical changes when XPE is used to characterize fluorinated carbons such as PFPE oils.

Feasibility Study of Vapor-Mist Phase Reaction Lubrication using a Thioether Liquid

Aerospace drive systems are required to survive a loss-of-lubrication test for qualification. In many cases emergency lubrication systems need to be designed and utilized to permit the drive system to pass this difficult requirement. The weight of emergency systems can adversely affect the mission capabilities of the aircraft. The possibility to reduce the emergency system weight using vapor-mist phase lubrication (VMPL) technology has been considered by NASA and the Army Research Laboratory (ARL). Phosphate esters have been the lubricant of choice in most VMPL studies primarily because they do provide adequate lubrication for short periods of time. However, during the lubrication process, the phosphate esters react continuously with the surface iron in gears and bearings, resulting in excessive wear. To minimize this problem an alternative non-phosphate liquid, a thioether, was used to mist phase lubricate a spur gearbox rig operating at 10,000 rpm under highly loaded conditions. After 21 million shaft revolutions of operation the gears exhibited only minor wear.

Simulation of lubricating behavior of a thioether liquid lubricant by an electrochemical method

An electrochemical cell was constructed to explore the possible radical anion forming behavior of a thioether liquid lubricant. The electrochemical behavior of the thioether was compared with the electrochemical behavior of biphenyl, which is known to form radical anions. Under controlled conditions biphenyl undergoes a reversible reaction to a radical anion, whereas the thioether undergoes an irreversible reduction yielding several products. These results are discussed in relation to boundary lubrication.

Evaluation of Vapor Pressure and Ultra-High Vacuum Tribological Properties of Ionic Liquids (2) Mixtures and Additives

Ionic liquids are salts, many of which are typically viscous fluids at room temperature. The fluids are characterized by negligible vapor pressures under ambient conditions. These properties have led us to study the effectiveness of ionic liquids containing both organic cations and anions for use as space lubricants. In the previous paper we have measured the vapor pressure and some tribological properties of two distinct ionic liquids under simulated space conditions. In this paper we will present vapor pressure measurements for two new ionic liquids and friction coefficient data for boundary lubrication conditions in a spiral orbit tribometer using stainless steel tribocouples. In addition we present the first tribological data on mixed ionic liquids and an ionic liquid additive. Post mortem infrared and Raman analysis of the balls and races indicates the major degradation pathway for these two organic ionic liquids is similar to those of other carbon based lubricants, i.e. deterioration of the organic structure into amorphous graphitic carbon. The coefficients of friction and lifetimes of these lubricants are comparable to or exceed these properties for several commonly used space oils.