Spreading Mechanism of PFPE Lubricant on the Magnetic Disks

[+] Author and Article Information
Hiroshi Tani, Hiroyuki Matsumoto

Data Storage & Retrieval Systems Division, Hitachi, Ltd., 2880, Kozu, Odawara-shi, Kanagawa-ken, 256-8510, Japan

J. Tribol 123(3), 533-540 (Jul 06, 2000) (8 pages) doi:10.1115/1.1308030 History: Received February 02, 2000; Revised July 06, 2000
Copyright © 2001 by ASME
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Surface roughness of sample disks measured by using 3-D roughness profiler. (a) Roughness profile of sample disks. (b) Surface topography of sample disks.
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Time chart of drag testing consists of continuous drag cycles and interval rest periods. Continuous drag cycles and interval rest periods are periodically repeated.
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Experimental method using etching technique to remove the lubricant in order to measure the thickness profiles of the lubricant replenishment.
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Dependence of the frictional force on the interval rest period of drag test. Sliding velocity is 0.5 m/s.
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Dependence of the lubricant decrease thickness at sliding position with relation of the interval rest period.
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Dependence of the asperity wear on the interval rest period. Wear depths were measured using 3-D profiler.
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Schematic images of the lubricant reflow into the top area of asperity. Lubricant film was decreased by the contact of the magnetic head.
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Dependence of the friction on the average diameter of texture asperity on the disk surface. Average diameter was derived from the apparent contact area.
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Durability of the drag test depended on the environmental temperature. Lubricant thickness of sample disks was 2.0 nm and the average diameter of texture asperity was 1.2 μm.
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Lubricant depletion measured with the ellipsometer on drag tests. Average radius of asperity was 1.2 μm, the head sliding velocity was 1.0 m/s.
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Profiles of lubricant replenishment into the area of removal lubricant by etching measured with the ellipsometer. Diameter of removal area was 1.4 mm. In right figures, the dark area shows that the lubricant thickness is thick.
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AFM topographies of the lubricant film surfaces before and after etching 8. At bottom right corner in each figure, the white area shows lubricant surface and the black area shows carbon surface.
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Contact angle to water depended on the lubricant thickness. The saturation thickness was defined as the thickness of lubricant at the saturated point with contact angle.
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Calculation model consisted of an adsorption model and a transition model of PFPE lubricant molecules on the carbon overcoat surface. (a) Adsorption model of lubricant on the carbon surface. (b) Transition model of lubricant molecules applied for Eyring model.
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Arrangement of lubricant molecules in Monte Carlo simulation to estimate the behavior of the lubricant reflow into the removal area by etching. Number of grids are (i,j,k)=(100×100×2).
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Flowchart of Monte Carlo simulation to calculate the behavior of lubricant reflow around the removed lubricant area
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Comparison between the measured profiles of lubricant reflow and the calculated profiles by Monte Carlo simulation. The dots show the measured profiles as the same as shown in Fig. 11, and the solid lines show the calculated profiles.
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Thickness of lubricant reflow into the removed areas with the different radii. The dots show the experimental results and the solid lines show the results of calculation.
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Thickness of lubricant reflow into the removed area on the top of texture asperity. Thickness of lubricant is 2.0 nm, and the environmental temperature is 25°C.
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Dependence of the lubricant replenishment on the environmental temperature. The dots show the experimental results and the solid lines show the results of calculation.
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Replenishment of lubricant on the disks with different thickness of lubricant. The critical reflow time (tc) was defined as the time when the lubricant coverage saturated (θ=1.0) at transitional state.
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Durability of drag tests (as shown in Fig. 10) for disks with lubricant of different thickness versus critical reflow time
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A model of lubrication mechanism of PFPE lubricant in the head disk interfaces



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