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    Analysis of Lube Oils per ASTM D6481

    Application Note EDXRF1249

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    Scope

    The measurement of phosphorus (P), sulfur (S), calcium (Ca), and zinc (Zn) in lube oil is demonstrated as per ASTM D6481-99(2010).

    Background

    ASTM D6481 is a standard test method for measuring lube oil using EDXRF. The elements and concentration ranges are specified in Table 1 of the method.

    Element Range
    Phosphorus 0.02 to 0.3 mass %
    Sulfur 0.05 to 1.0 mass %
    Calcium 0.02 to 1.0 mass %
    Zinc 0.01 to 0.3 mass %

    ASTM D6481-99(2010)
    ASTM Table 1 Elements and Range of Concentrations Determined

    Quality control and quality assurance during the lube oil manufacturing process is essential. A fast, simple method of analyzing lube oils is important throughout the QC/QA process. Rigaku meets this industry need with a high performance, low-cost benchtop EDXRF system. Rugged and reliable, NEX QC is an ideal tool with simple and intuitive software for the non-technical operator.
    800x610 NEX QC+ (S in Crude screen)_picture_2020.06.25Model: NEX QC

    Calibration

    Empirical calibrations were built using a suite of 16 commercially available calibration standards. 

    Element Concentration range
    P 0.020 – 0.300 %
    S 0.050 – 1.000 %
    Ca 0.005 – 1.000 %
    Zn 0.010 – 0.300 %

    Repeatability

    Three representative samples from the calibration suite were chosen to demonstrate typical instrument repeatability (precision). Ten repeat analyses were performed with the sample in static position.

    Sample: ASI 16b
    Units: %
    Element Standard value Average value Std. dev % Relative
    P 0.020 0.0235 0.0026 13
    S 0.240 0.2374 0.0014 0.6
    Ca 0.200 0.2080 0.0025 1.3
    Zn 0.100 0.1040 0.0007 0.7
    Sample: ASI 6
    Units: %
    Element Standard value Average value Std. dev % Relative
    P 0.250 0.2555 0.0095 3.8
    S 0.800 0.7954 0.0090 1.1
    Ca 0.005 0.0042 0.0006 12
    Zn 0.300 0.3044 0.0032 1.1
    Sample: ASI 10
    Units: %
    Element Standard value Average value Std. dev % Relative
    P 0.150 0.1485 0.0020 1.3
    S 0.200 0.1968 0.0010 0.5
    Ca 0.100 0.1021 0.0010 1.0
    Zn 0.200 0.2041 0.0013 0.7

    Conclusion

    The results demonstrate excellent performance for basic lube oil formulations using NEX QC. Given standards assayed for Ba, the Ba content can also be measured over similar concentration ranges. Fast and simple, the NEX QC is an ideal tool for monitoring and controlling lube oil add packs and lube formulations during blending and process QC. 

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