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46 results on '"Junk, Christopher P."'

6. Physical and Chemical Evolution of PTFE-α-Al2O3 Composites Versus 304 SS Tribofilms During Dry Sliding.

Author

Haque, Faysal M., Junk, Christopher P., and Sidebottom, Mark A.

Abstract

Polytetrafluoroethylene (PTFE) is renowned for its remarkably low friction coefficient (µ ~ 0.1) yet exhibits notably high wear rates (K ~ 104) in dry sliding applications. To mitigate this, various metallic and non-metallic fillers have been explored, consistently demonstrating a reduction in wear rates of unfilled PTFE between 10 and 104 times. Among these fillers, α-Al2O3 is one of the most extensively studied materials. 5 wt% of α-Al2O3 filler into PTFE yields a composite material, PTFE- α-Al2O3, characterized by a wear rate a staggering 104 times lower than unfilled PTFE. This reduction in wear has been attributed to the formation of tribofilms on the PTFE composite and metal counterbody material. These tribofilms emerge due to the interaction between broken fluropolymer chains and environmental water and oxygen. This interaction results in the creation of carboxylate salt groups, which subsequently react with metal/metal oxide particles (both from the counterbody and the metal filler) to form tribofilms. Despite numerous studies scrutinizing the chemical composition of the tribofilms pre- and post-test, the chemical development of these films has remained largely unexplored. In this study, the authors utilize attenuated total reflection infrared spectroscopy (ATR-IR), transmission infrared (IR) spectroscopy, optical microscopy, and stylus profilometry to observe tribofilm development. A thorough topographical and chemical description of the tribofilm is provided via these techniques. The ratio of carboxylate salt groups directly corresponds with improved wear performance and these changes are very local to the worn polymer surface. This discovery contributes to a deeper understanding of the tribological behavior of PTFE-α-Al2O3 composites. [ABSTRACT FROM AUTHOR]

Published
2024
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17. Preparation and synthetic applications of aryl tetraflates (ArOS[O.sub.2]C[F.sub.2]C[F.sub.2]H)

Author

Rostovtsev, Vsevolod V., Bryman, Lois M., Junk, Christopher P., Harmer, Mark A., and Carcani, Liane G.

Subjects
Catalysis -- Research, Biological sciences, Chemistry
Abstract

The preparation of aryl esters of 1,1,2,2-tetrafluoroethanesulfonic acid (aryl tetraflates) that could be used in a number of palladium-catalyzed coupling reactions is described.

Published
2008

21. Perfluoroalkoxy (PFA)-α-Alumina Composites: Effect of Environment on Tribological Performance.

Author

Sidebottom, Mark A., Atkinson, Cooper A., Campbell, Kasey L., Babuska, Tomas F., Junk, Christopher P., Burch, Heidi E., and Krick, Brandon A.

Abstract

Perfluoroalkoxy polymer (PFA)-α-phase alumina (α-Al2O3) composites have dramatically (~ 10,000 ×) improved wear resistance compared to unfilled PFA when tested in air. In this study, unfilled PFA and PFA-α-Al2O3 composites were tested using a linear reciprocating tribometer in dry nitrogen (< 2.5 ppm O2 and H2O), humidity-controlled air (15%, 30%, and 45% relative humidity), and submerged water. PFA-α-Al2O3 tested in dry nitrogen (N2) and in submerged water exhibited wear rates that were two to three orders of magnitude higher than those of PFA-α-Al2O3 composites tested in humidity-controlled air. Infrared spectra of the worn PFA-α-Al2O3 surfaces tested in air exhibited peaks attributed to carboxylate salts. These peaks were severely diminished on the PFA-α-Al2O3 sample tested in dry N2 and not observed for submerged water environments. The high wear rate of PFA-α-Al2O3 tested in dry N2 and submerged water was attributed to the lack of carboxylate salts, which require oxygen and water form. These carboxylate salts bond to the α-Al2O3 filler within the PFA matrix which reinforces the polymer wear surface. Additionally, these carboxylate salts form a transfer film on the stainless steel counterface, which protects both the composite and counterface from wear and abrasion. [ABSTRACT FROM AUTHOR]

Published
2020
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24. Electron-diffraction and theoretical investigation of the molecular structure of octafluorobicyclo[2.2.0]hex-1(4)-ene in the gas phase: Another example of a molecule with an unusually long C((super 3)sp) - C((super 3)sp) single bond

Author

Richardson, Alan D., Hedberg, Kenneth, Junk, Christopher P., and Lemal, David M.

Subjects
Butylene -- Research, Butylene -- Electric properties, Butylene -- Structure, Electronegativity -- Research, Chemistry, Physical and theoretical -- Research, Chemicals, plastics and rubber industries
Abstract

The molecular structure of octafluorobicyclo[2.2.0]hex-1(4)-ene is measured in the gas phase by electron diffraction at room-temperature. The bond-altering effects of electrostatic repulsions and rehybridization arise from electronegativity differences.

Published
2003

28. A remarkable [2.2.2]propellane

Author

Yigang He, Junk, Christopher P., Cawley, John J., Lemal, David M., and Liu, Hung-wen

Subjects
Biosynthesis -- Usage, Propellanes -- Structure, Propellanes -- Research, Chemistry
Abstract

Molecules possessing the highly stained [2.2.2]propellane ring system are very rare and the first representative to be isolated, carboxamido derivative, was synthesized in 1973. The synthesis of a third[2.2.2]propellane, its structure, properties and chemistry are described.

Published
2003

37. New Amorphous Fluoropolymers of Tetrafluoroethylene with Fluorinated and Non-Fluorinated Tricyclononenes. Semiconductor Photoresists for Imaging at 157 and 193 nm

Author

Feiring, Andrew E., primary, Crawford, Michael K., additional, Farnham, William B., additional, Feldman, Jerald, additional, French, Roger H., additional, Junk, Christopher P., additional, Leffew, Kenneth W., additional, Petrov, Viacheslav A., additional, Qiu, Weiming, additional, Schadt, Frank L., additional, Tran, Hoang V., additional, and Zumsteg, Fredrick C., additional

Published
2006
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44. New Amorphous Fluoropolymers of Tetrafluoroethylene with Fluorinated and Non-Fluorinated Tricyclononenes. Semiconductor Photoresists for Imaging at 157 and 193 nm

Author

E. Feiring, Andrew, K. Crawford, Michael, B. Farnham, William, Feldman, Jerald, H. French, Roger, P. Junk, Christopher, W. Leffew, Kenneth, A. Petrov, Viacheslav, Qiu, Weiming, L. Schadt III, Frank, V. Tran, Hoang, and C. Zumsteg, Fredrick

Abstract

Twenty-two tricyclo[4.2.1.02,5]non-7-ene (TCN) or 3-oxatricyclononene monomers, having fluorinated or nonfluorinated substituents on the four-membered rings, were prepared by cycloaddition reactions of functionalized olefins with norbornadiene or quadricyclane. Radical polymerizations with tetrafluoroethylene (TFE) and/or TFE and acrylates provided amorphous polymers with high solubility in standard organic solvents. The TFE/TCN dipolymers typically have glass transition temperatures of over 200 °C, substantially higher than TFE copolymers with norbornene. Perfluoroalkyl sulfonyl fluoride groups can be incorporated in the side chains of the TCN monomers giving soluble copolymers. Polymers which also incorporated acrylate monomers were prepared using a semibatch process to control composition. Selected polymers incorporating tertiary alkyl ester groups from the TCN monomer or acrylates have shown good image formation when compounded with a photoacid generator, imaged with 157 or 193 nm light, and developed using aqueous base.

Published
2006

45. Solubility and Diffusivity of Difluoromethane in Room-Temperature Ionic Liquids

Author

B. Shiflett, Mark, A. Harmer, Mark, P. Junk, Christopher, and Yokozeki, A.

Abstract

New experimental results are presented for the solubility and diffusivity of difluoromethane in 19 room-temperature ionic liquids (RTILs). In the series of RTILs presented here, eight RTILs with five new fluorocarbon sulfonate anions have been prepared for the first time. The measurements were performed using a gravimetric microbalance at temperatures between (283.15 and 348.15) K and at pressures from (0.01 to 1.0) MPa. Experimental gas solubility data were successfully correlated with the nonrandom two-liquid (NRTL) solution model. The solubility of difluoromethane in RTILs is affected by the choice of both the cation and anion. Diffusivities obtained from the time-dependent absorption data were well analyzed using a model based on a modified Stokes−Einstein equation. The calculated molecular size for difluoromethane is 2 to 3 times larger than the known size.

Published
2006
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