Kishore K. Kar

A model of the dynamics of boundary film formation

Abstract The dynamics of formation and loss of the boundary films formed during sliding on steel surfaces were investigated over a range of temperature. Tests are performed on a cylinder-on-disk machine using mineral oil with various concentrations of zinc dialkyldithiophosphate (ZDP). The thickness and refractive index of the boundary films during step load test were monitored in situ with an ellipsometer, and the composition of the films was analyzed by X-ray photoelectron spectroscopy (XPS). As temperature increases, chemical reactivity increases the film formation rate, while the film removal rate increases owing to (a) the decrease of durability of the boundary film material and (b) the reduction of hydrodynamic fluid film thickness due to decreasing viscosity of the lubricant. There is a balance between these two competing mechanisms, and this balance is reflected in the boundary film thickness. The boundary films consist of a film of oxide and metallic compound (OMM) covered by an organo-iron compound (OIC). Their relative effectiveness in preventing scuffing depends on temperature and composition. In particular, the OIC is effective in reducing wear of the opposing surfaces by covering the OMM.

Development and tribological properties of new cyclotriphosphazene high temperature lubricants for aircraft gas turbine engines

A number of substituted aryloxycyclotriphosphazenes were synthesized and studied, with the objective of meeting the lubricant requirements of the Integrated High Performance Turbine Engine Technology (IHPTET) initiative. These compounds were evaluated for pour point, oxidative stability, and lubricity behavior. Further property evaluations were performed on a leading candidate fluid, bis(4-fluorophenoxy)-tetrakis(3-trifluoromethylphenoxy) cyclotriphosphazene, code-named X-1P. The results of this study are discussed, along with comparative data of other leading commercial high temperature fluids. Presented at the 46th Annual Meeting in Montreal, Quebec, Canada April 29–May 2, 1991

A model for the boundary film formation and tribological behavior of a phosphazene lubricant on steel

The dynamics of formation and loss of the boundary films formed during the lubricated sliding of steel surfaces were investigated over a range of temperature and applied load. Tests were performed on a cyldinder-on-disk machine using a phosphazene lubricant (X-1P), a polyphenyl ether, and mineral oil with and without addition of zinc dialkyldithiophosphate (ZDP). Among these lubricants, X-1P was found to have the best high-temperature, high-load performance. The thickness and retractive index of the boundary films were monitored in situ with an ellipsometer, and the composition of the films was analyzed by X-ray photoelectron spectroscopy (XPS). The performance of the lubricants was found to be closely associated with boundary film-forming ability. In order to achieve high load-carrying capacity, a boundary film must be formed. The films formed in X-1P grow more slowly than those in ZDP-containing mineral oil, but they remain thick even at high load and high temperature (250°C). These films are durable and effective in reducing friction and preventing scuffing. The film formed with X-1P consists of a mixture of compounds containing Fe, O, C, F, P, and N. Among the compounds formed, some form of iron fluoride appears to be most important in determining the performance of the film.

Cyclotriphosphazenes as Potential Lubricants for Thin Film Hard Disks

This paper explores the use of phosphazenes as alternative lubricants for thin film hard disks. Contact start/slop (CSS), stiction and drag tests were performed on five disks lubricated with a typical cyclic phosphazene lubricant, X-1p, with a thickness in the range of 0.3 nm to 0.7 nm. The coefficients of friction and stiction were found to increase initially, then level off and reach a steady-state value without a further increase after 2000 CSS cycles, ft is concluded that X-1p performs well on thin film disks with a lubricant thickness of about 0.5 nm. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Lahaina, Hawaii, October 16–20, 1994

Formation of a BN layer on the surface of B4C using nitrogen implantation

Abstract The surface of B 4 C was irradiated using nitrogen ions and then examined to determine the alterations in the surface chemical and mechanical properties following implantation. Pure boron was also implanted to compare uptakes and chemistry. The implantations were performed in situ at 10 keV in an ultrahigh vacuum system and at 100 keV using a commercial implanter. For doses up to 5.0 × 10 17 atoms cm -2 all implanted nitrogen reacted. The nitrogen implanted (10 keV) into either B 4 C or boron was chemically in the form of BN. 100 keV nitrogen implantation into boron resulted in BN formation while a boron carbide-nitride species was formed using B 4 C. Nitrogen doses of about 6.0 × 10 17 cm -2 at 100 keV for B 4 C produced chemical halos, 2 – 6 μm in diameter, around a crater owing to expulsion of a TiB 2 particulate impurity. The B 4 C surface, modified at 100 keV, (dose less than or equal to 5.5 × 10 17 cm -2 ) showed a 60% reduction in the pin wear scar diameter and a 200% increase in the coefficient of friction compared with the unimplanted surface. These changes in the surface chemical and mechanical properties suggest that a hard BN layer forms on B 4 C following nitrogen ion implantation.

Oscillation of Mixing Jets in a Long Horizontal Tank

In contrast to mixing in vertical tanks, jet mixing in long horizontal tanks is scarcely investigated in the literature. It is known that jet mixing in long horizontal tanks is more difficult when compared to short tanks, as more liquid volume must be recirculated through the jets.In this study, computational fluid dynamics (CFD) simulations are conducted for the flow in a horizontal cylindrical tank with a length-to-diameter ratio of 3:1 and a nominal volume of 112,560 L (liquid volume of 75,708 L, i.e. 20,000 gallons). A pair of back-to-back Coldrey nozzles is placed near the center of the tank bottom, and each nozzle directs its jet towards the corresponding vessel end. An intriguing phenomenon is observed in the transient simulations, where the turbulent jets oscillate in both horizontal and vertical directions with a low frequency. In order to determine the source of such oscillation, a number of simulations are conducted to explore the effects of mesh type and size, boundary condition on the free surface, turbulence model, and time step. Oscillation persists in all cases, indicating that it is unlikely the result of some numerical instability. The oscillation also appears to be insensitive to the Reynolds number or symmetry in the nozzle or tank geometry. Another simulation with a single jet also shows the oscillatory flow behavior, and thus the oscillation is more likely to be caused by interaction between the jet and the recirculating flow in the tank, rather than interaction between the two jets. Further analysis of the jet velocity profile suggests that the secondary flow on the cross section of the jets might also contribute to the oscillation.While similar confined jet oscillations due to Coanda effect and blind cavity effect have been previously observed in small cavities by both 2D numerical simulations and laboratory scale experiments, this study shows that such oscillation also exists in industrial scale horizontal tanks. The oscillatory motion of the liquid may lead to improved mixing in the tank.© 2014 ASME