Significance and Use
Lubricating greases are used in almost all bearings used in any machinery. Lubricating grease is composed of ~90 % additized oil and soap or other thickening agent. There are over a dozen metallic elements present in greases, either blended as additives for performance enhancements or as thickeners, or in used greases present as contaminants and wear metals. Determining their concentrations can be an important aspect of grease manufacture. The metal content can also indicate the amount of thickeners in the grease. Additionally, a reliable analysis technique can also assist in the process of trouble shooting problems with new and used grease in the field.
Although widely used in other sectors of the oil industry for metal analysis, ICP-AES based Test Methods D4951 or D5185 cannot be used for analyzing greases because of their insolubility in organic solvents used in these test methods. Hence, grease samples need to be brought into aqueous solution by acid decomposition before ICP-AES measurements.
Test Method D3340 has been used to determine lithium and sodium content of lubricating greases using flame photometry. This technique is no longer widely used. This new test method provides a test method for multi-element analysis of grease samples. This is the first DO2 standard available for simultaneous multi-element analysis of lubricating greases.
1.1 This test method covers the determination of a number of metals such as aluminum, antimony, barium, calcium, iron, lithium, magnesium, molybdenum, phosphorus, silicon, sodium, sulfur, and zinc in unused lubricating greases by inductively coupled plasma atomic emission spectrometry (ICP-AES) technique.
1.1.1 The range of applicability for this test method, based on the interlaboratory study conducted in 2005, is aluminum (10–600), antimony (10–2300), barium (50–800), calcium (20–50 000), iron (10–360), lithium (300–3200), magnesium (30–10 000), molybdenum (50–22 000), phosphorus (50–2000), silicon (10–15 000), sodium (30–1500), sulfur (1600–28 000), and zinc (300–2200), all in mg/kg. Lower levels of elements may be determined by using larger sample weights, and higher levels of elements may be determined by using smaller amounts of sample or by using a larger dilution factor after sample dissolution. However, the test precision in such cases has not been determined, and may be different than the ones given in Table 1.
1.1.2 It may also be possible to determine additional metals such as bismuth, boron, cadmium, chromium, copper, lead, manganese, potassium, titanium, etc. by this technique. However, not enough data is available to specify the precision for these latter determinations. These metals may originate into greases through contamination or as additive elements.
1.1.3 During sample preparation, the grease samples are decomposed with a variety of acid mixture(s). It is beyond the scope of this test method to specify appropriate acid mixtures for all possible combination of metals present in the sample. But if the ash dissolution results in any visible insoluble material, the test method may not be applicable for the type of grease being analyzed, assuming the insoluble material contains some of the analytes of interest.
1.2 Elements present at concentrations above the upper limit of the calibration curves can be determined with additional appropriate dilutions of dissolved samples and with no degradation of precision.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific warning statements are given in Sections 8 and 10.
TABLE 1 Precision of Grease Analysis
Note—X is the mean concentration in mg/kg.
|Aluminum||10–600||0.2163 X0.9||6.8156 X0.9|
|Antimony||10–2300||0.3051 X0.8191||4.6809 X0.8191|
|Barium||50–800||0.3165 X0.7528||2.9503 X0.7528|
|Calcium||20–50 000||2.2853 X0.7067||3.0571 X0.7067|
|Iron||10–360||0.8808 X0.7475||2.5737 X0.7475|
|Lithium||300–3200||0.0720 X1.0352||0.1476 X1.0352|
|Magnesium||30–10 000||0.6620 X0.6813||2.6155 X0.6813|
|Molybdenum||50–22 000||0.1731 X0.9474||0.4717 X0.9474|
|Phosphorus||50–2000||1.2465 X0.6740||4.0758 X0.6740|
|Silicon||10–15 000||1.3859 X0.9935||4.8099 X0.9935|
|Sodium||30–1500||6.5760 X0.5||11.571 X0.5|
|Sulfur||1600–28 000||1.0507 X0.8588||1.5743 X0.8588|
|Zinc||300–2200||0.1904 X0.8607||0.5912 X0.8607|
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D1193 Specification for Reagent Water
D3340 Test Method for Lithium and Sodium in Lubricating Greases by Flame Photometer
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4951 Test Method for Determination of Additive Elements in Lubricating Oils by Inductively Coupled Plasma Atomic Emission Spectrometry
D5185 Test Method for Determination of Additive Elements, Wear Metals, and Contaminants in Used Lubricating Oils and Determination of Selected Elements in Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
D6792 Practice for Quality System in Petroleum Products and Lubricants Testing Laboratories
D7260 Practice for Optimization, Calibration, and Validation of Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) for Elemental Analysis of Petroleum Products and Lubricants
additive elements; aluminum; antimony; barium; calcium; emission spectrometry; grease; ICP; inductively-coupled plasma emission spectrometry; internal standard; iron; lithium; lubricating grease; magnesium; molybdenum; phosphorus; silicon; sodium; sulfur; zinc;
ICS Number Code 75.100 (Lubricants, industrial oils and related products)
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Citing ASTM Standards
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