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At least 559 records · Page 31Linked to original sources
PubMed2003

The effect of frictional heating and forced cooling on the serum lubricant and wear of UHMW polyethylene cups against cobalt-chromium and zirconia balls.

Hip simulator tests of femoral balls of cobalt-chromium alloy or zirconia against acetabular cups of UHMW polyethylene were run with and without a coolant circulated inside the femoral balls. Without cooling, the wear of polyethylene against zirconia was about 48% lower than with cobalt-chromium alloy, but the steady-state temperature of the zirconia ball was higher (55 degrees C vs. 41 degrees C), and there was more precipitation of protein from the serum, which sometimes formed an adherent layer on the surface of the zirconia. Circulating coolant at 1-20 degrees C markedly reduced the bearing temperatures and the protein precipitation. With coolant at 4 degrees C, wear of the polyethylene against cobalt-chromium alloy was about 26% lower than against zirconia, but the macroscopic and microscopic appearance of the worn polyethylene surfaces were unlike that typically generated in vivo. With or without coolant, the morphology of the polyethylene wear debris was comparable to that generated in vivo, but the ratio of fibrillar to granular debris was higher at the reduced temperature. These results suggested that circulating coolant at an appropriate temperature could avoid overheating (due to non-stop running of the simulator), preventing excessive protein precipitation while providing wear surfaces and wear debris with morphologies closely comparable to those generated in vivo.

Artifacts↗
PubMed1997

A kinetic study on crystallization of an amorphous lubricant.

PURPOSE: The purpose of the work was to study the crystallization kinetics of amorphous sterotex K at different temperatures and with different methods, and to compare the obtained kinetic and thermodynamic results. METHODS: Isothermal microcalorimetry was the principal technique to determine the crystallization behavior of sterotex K. X-ray powder diffraction and differential scanning calorimetry were employed to interpret the microcalorimetric heat flow curves and compare the kinetics and the calculated value for the transition enthalpy. RESULTS: The best way to analyze the x-ray diffractograms was the statistic Wakelin's correlation method. The method gave consistent quantitative results with microcalorimetry and both methods showed crystallization to consist of two partially parallel part-processes, which attached probably to the different growing rates of the forms consisting of different lattice planes having the same spacing. The quantitative analysis of differential scanning calorimetry scans was troublesome to perform but the obtained average value of -51 J/g for the enthalpy of the crystallization was in good agreement with the values obtained with the other methods, the average being -52 J/g. Calculating heat flow versus released energy plots from the microcalorimetric data the crystallization mechanism was observed to change as a function of temperature. CONCLUSIONS: A sensitive isothermal microcalorimeter can give precise and fast knowledge about possible solid state transition mechanism, but the source of the heat flow signal must be verified with other analytical methods to avoid incorrect conclusions. Due to the sensitivity and the real-time data the microcalorimetry can show up the mechanism of the transition for varying as a function of temperature and reveal the uselessness of the conventional Arrhenius relationship for extrapolations.

Calorimetry, Differential Scanning↗
PubMed1994

Lubricated lungs.

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Dental High-Speed Equipment↗
PubMed2003

European hazard classification advice for crude oil-derived lubricant base oils compared with the proposed mineral oil mist TLV.

The notice of intended change for the threshold limit value (TLV) for mineral oil mist contains a notation for human carcinogenicity. A description is provided of the current European regulatory approach used to distinguish between carcinogenic and non-carcinogenic mineral base oils on the basis of oil refining process and chemical marker information. This approach has proven effective in creating a market situation in the countries of the European Union where many customers require severely refined, non-carcinogenic oils. It is recommended that ACGIH consolidate the distinction between poorly and severely refined base oils in the recommended TLV for mineral oil mist and use different toxicological considerations to derive exposure control guidelines.

Air Pollutants, Occupational↗