Lube-Tech
detected upfront minimising equipment downtime or damages. [6]
In addition, newer machinery will potentially have a different result from that of existing formulated lubricants, in terms of the additives used, the quantity of lubricant consumed and the resulting profit. Detailed analysis is required to determine the lifetime of the appropriate oil. [7]
As indicated above, standard used oil analysis is a viable tool for the safe and continuous operation of machinery. However, such an analysis does not necessarily reveal the state of anti-wear (AW) and/ or extreme-pressure (EP) additives. The typically conducted ICP-OES analysis does yield a reliable statement about the concentration of typical elements present in AW and EP additive formulations, such as phosphorus, zinc and sulphur. Knowing the abundance of additive elements present in the lubricant allows to judge whether a lubricant must be refreshed or even exchanged if, for example the level of additives have fallen below a certain threshold. [1]
But, besides the concentration of additive elements, a structure-function-relationship is present. Thus, only certain structures of the molecules exhibit their engineered properties. As the additive structure is altered during use, changed molecules may fall back in their protective posture.[8] However, such alteration is not directly visible when using only spectroscopic methods. The concentration of additive elements may still be the same or only slightly lower than in the fresh product. As additives are typically surface active, surface wear may impact upon additive concentration whereas its effectiveness can no longer be expected at the same given percentage. Thus, knowledge about the structure and therefore the effectiveness of these additives is crucial for the prediction of the remaining useful lifetime of a lubricant, among the other parameters as for example the viscosity (class), water content or wear metals. FTIR spectroscopy allows, to a
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.147 page 2
certain extent, the monitoring of such properties. [9] However, its application is limited due to interferences.
Subsequently, OELCHECK has developed together with the Karlsruhe Institute of Technology (KIT) a method that allows the determination of the concentration of active anti-wear and extreme pressure species based on Nuclear Magnetic Resonance Spectroscopy in the course of routine used oil analysis.
Nuclear Magnetic Resonance (NMR) is the most powerful analytical method known in organic chemistry today. The principle has been developed in the 1940s and their inventors have been awarded with the Nobel Prize for Physics in 1952. [10]
For more than 40 years, the technology has been used for the analysis of petroleum products. Numerous methods have been developed and standardised such as: - Determination of hydrogen content in fuels (i.e. ASTM D7171, ASTM D4808, ASTM D3701
- Polyurethane Raw Materials (i.e. ASTM D4273, ASTM D4875)
- Determination of Aromatic Carbon content in Hydrocarbon oil according to ASTM D5292
Furthermore, NMR has its application in borehole analysis of crude oil reservoirs. [11] [12] [13]
As lubricants are comprised of organic and metal-organic compounds, it is reasonable applying NMR in lubricant analysis. [14] [15]
The principle of NMR relies on resonant adsorption and subsequent irradiation of magnetic energy in form of radio frequency. Only nuclei with a non-zero magnetic moment such as 1
H, 13 C, 15 N, 19 F, 31 P and
others are so- called NMR-active nuclei. The magnetic moment is responsible for the spin which is necessary for a successful NMR experiment. For a 1
H or 31 two possible spin orientations are known: α (+1/2) or LUBE MAGAZINE NO.176 AUGUST 2023 31 P atom,
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