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Lubricants, Volume 3, Issue 4 (December 2015) , Pages 628-711

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Open AccessArticle
Mechanism of Friction and Wear in MoS2 and ZDDP/F-PTFE Greases under Spectrum Loading Conditions
Lubricants 2015, 3(4), 687-711; https://doi.org/10.3390/lubricants3040687
Received: 26 July 2015 / Revised: 8 December 2015 / Accepted: 9 December 2015 / Published: 18 December 2015
Cited by 4 | Viewed by 2446 | PDF Full-text (1197 KB) | HTML Full-text | XML Full-text
Abstract
Two different greases formulated using MoS2 and a combination of ZDDP and functionalized PTFE (F-PTFE) were examined under spectrum loading conditions where loads, frequency, and duration of the steps were treated as variables. Combination of ZDDP and F-PTFE were synergistic resulting in [...] Read more.
Two different greases formulated using MoS2 and a combination of ZDDP and functionalized PTFE (F-PTFE) were examined under spectrum loading conditions where loads, frequency, and duration of the steps were treated as variables. Combination of ZDDP and F-PTFE were synergistic resulting in a significant reduction in the wear and friction under spectrum loading condition. Decreasing the time step during the ramp up and ramp down cycles resulted in larger wear for the grease containing MoS2 particles in comparison to ZDDP/F-PTFE in grease. The tribofilm formed on the surface was analyzed using various characterization techniques like SEM, EDS, and Stereo Optical Microscopy. Tribofilms from MoS2 additives had extensive amounts of abrasive and adhesive wear and showed the formation of MoS2 on the surface on the other hand the tribofilms from ZDDP/F-PTFE had smaller amounts of severe wear and exhibited patchy tribofilms of Zn-phosphates as well as sulfides of Zn and Fe. Full article
(This article belongs to the Special Issue Tribofilms and Solid Lubrication)
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Open AccessArticle
Development of a Synthetic Synovial Fluid for Tribological Testing
Lubricants 2015, 3(4), 664-686; https://doi.org/10.3390/lubricants3040664
Received: 10 July 2015 / Revised: 9 November 2015 / Accepted: 18 November 2015 / Published: 1 December 2015
Cited by 13 | Viewed by 2531 | PDF Full-text (915 KB) | HTML Full-text | XML Full-text
Abstract
Wear tests of joint prostheses are usually performed using bovine calf serum. The results from different laboratories are hardly ever comparable as, for example, the protein concentration and the protein composition of the serum-based test liquids vary. In addition, the viscosity of these [...] Read more.
Wear tests of joint prostheses are usually performed using bovine calf serum. The results from different laboratories are hardly ever comparable as, for example, the protein concentration and the protein composition of the serum-based test liquids vary. In addition, the viscosity of these test liquids is similar to that of water and does not match the more viscous synovial fluid. The present work was aimed at developing a synthetic synovial fluid as an alternative to the existing test liquids. Improved consistency and reproducibility of results at a similar price were required. Hyaluronic acid (HA), the lyophilized proteins bovine serum albumin (BSA) and immunoglobulin G (IgG), the phospholipid lecithin (PL) and salts were applied in a stepwise approach to replace the actually used test liquid based on newborn calf serum. The in vitro results obtained with ultra-high-molecular-weight polyethylene (UHMWPE) pins sliding against CoCrMo discs revealed that the developed synthetic synovial fluid fulfils the set requirements: increase of viscosity, reasonable cost, improved consistency and wear particles which resemble the ones found in vivo. The developed synthetic synovial fluid with 3 g/L HA, 19 g/L BSA, 11 g/L IgG, 0.1 g/L PL and Ringer solution is a more realistic alternative to the used serum-based test liquid. Full article
(This article belongs to the Special Issue Friction and Lubricants Related to Human Bodies)
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Open AccessReview
Ionic Nanofluids in Tribology
Lubricants 2015, 3(4), 650-663; https://doi.org/10.3390/lubricants3040650
Received: 15 September 2015 / Revised: 22 October 2015 / Accepted: 22 October 2015 / Published: 27 November 2015
Cited by 14 | Viewed by 1916 | PDF Full-text (638 KB) | HTML Full-text | XML Full-text
Abstract
This overview covers the most recent developments in the field of ionic nanofluid lubricants, defined as dispersions of nanoparticles with ionic liquids through the activation of nanophases. The nanophases range from metal nanoparticles and ceramic inorganic nanoparticles, to different carbon nanophases. The combinations [...] Read more.
This overview covers the most recent developments in the field of ionic nanofluid lubricants, defined as dispersions of nanoparticles with ionic liquids through the activation of nanophases. The nanophases range from metal nanoparticles and ceramic inorganic nanoparticles, to different carbon nanophases. The combinations with room-temperature ionic liquids can be in the form of mixtures, dispersions, surface-modified nanophases, or chemically-functionalized nanophases. The new ionic nanofluids can be used as base lubricants, as lubricant additives, or as anti-friction and wear-reducing additives in new nanocomposite materials. Full article
(This article belongs to the Special Issue Nanoparticles and Ionic Liquids in Lubrication)
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Open AccessArticle
Ionic Liquids as Additives of Coffee Bean Oil in Steel-Steel Contacts
Lubricants 2015, 3(4), 637-649; https://doi.org/10.3390/lubricants3040637
Received: 2 September 2015 / Revised: 19 October 2015 / Accepted: 21 October 2015 / Published: 28 October 2015
Cited by 8 | Viewed by 2070 | PDF Full-text (1501 KB) | HTML Full-text | XML Full-text
Abstract
Environmental awareness and ever-growing restrictive regulations over contamination have increased the need for more environmentally-friendly lubricants. Due to their superior biodegradability and lower toxicity, vegetable oils are a good alternative to replace currently-used mineral oils. However, vegetable oils show low oxidation and thermal [...] Read more.
Environmental awareness and ever-growing restrictive regulations over contamination have increased the need for more environmentally-friendly lubricants. Due to their superior biodegradability and lower toxicity, vegetable oils are a good alternative to replace currently-used mineral oils. However, vegetable oils show low oxidation and thermal stability and poor anti-wear properties. Most of these drawbacks can be attenuated through the use of additives. In the last decade, ionic liquids have emerged as high-performance fluids and lubricant additives due to their unique characteristics. In this study, the tribological behavior of two phosphonium-based ionic liquids is investigated as additives of coffee bean oil in steel-steel contact. Coffee bean oil-ionic liquid blends containing 1, 2.5, and 5 wt% of each ionic liquid are studied using a block-on-flat reciprocating tribometer and the test results are compared to commercially-available, fully-formulated lubricant. Results showed that the addition of the ionic liquids to the coffee bean oil reduces wear volume of the steel disks, and wear values achieved are comparable to that obtained when the commercially-available lubricant is used. Full article
(This article belongs to the Special Issue Nanoparticles and Ionic Liquids in Lubrication)
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Open AccessArticle
Eco-Friendly Multipurpose Lubricating Greases from Vegetable Residual Oils
Lubricants 2015, 3(4), 628-636; https://doi.org/10.3390/lubricants3040628
Received: 16 July 2015 / Revised: 24 September 2015 / Accepted: 29 September 2015 / Published: 21 October 2015
Cited by 4 | Viewed by 1706 | PDF Full-text (135 KB) | HTML Full-text | XML Full-text
Abstract
Environmentally friendly multipurpose grease formulation has been synthesized by using Jatropha vegetable residual oil with lithium soap and multifunctional additive. The thus obtained formulation was evaluated for its tribological performance on a four-ball tribo-tester. The anti-friction and anti-wear performance characteristics were evaluated using [...] Read more.
Environmentally friendly multipurpose grease formulation has been synthesized by using Jatropha vegetable residual oil with lithium soap and multifunctional additive. The thus obtained formulation was evaluated for its tribological performance on a four-ball tribo-tester. The anti-friction and anti-wear performance characteristics were evaluated using standard test methods. The biodegradability and toxicity of the base oil was assessed. The results indicate that the synthesized residual oil grease formulation shows superior tribological performance when compared to the commercial grease. On the basis of physico-chemical characterization and tribological performance the vegetable residual oil was found to have good potential for use as biodegradable multipurpose lubricating grease. In addition, the base oils are biodegradable and non toxic. Full article
(This article belongs to the Special Issue Lubricating Greases)
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