http://www.machinerylubrication.com/Read/477/molecular-spectroscopy-lubrication
Quote:
Perhaps the simplest used oil analysis tool for monitoring additives is elemental analysis. Using either rotating disk electrode (RDE) or inductively coupled plasma (ICP) spectroscopy, elements such as zinc, phosphorus, calcium, barium and magnesium can be measured and trended to provide an indication of additive concentration. However, elemental spectroscopy has two major limitations with respect to tracking additives. First, the technique does not actually measure additives, but rather the individual elements or atoms contained within the additive molecule. While this comment may seem obvious, it has serious implications when talking about trending additive depletion.
To understand the potential problem, consider the fate of one of the most common additives, zinc dialkyl dithiophosphate (ZDDP), an antiwear and antioxidant additive. Depending on formulation, a common AW hydraulic fluid may contain anywhere from 100 ppm to 500 ppm of ZDDP, as measured by the elemental concentrations of zinc and phosphorus. Subjecting an oil containing ZDDP to high temperatures and high levels of moisture will likely result in significant additive depletion due to hydrolysis - a chemical reaction between the ZDDP molecule and water. Under such circumstances, the ultimate by-products of the hydrolysis reaction will likely be zinc salts and phosphates, which although no longer chemically ZDDP, may remain in solution in the oil. The result is that by considering only zinc and phosphorus concentrations, the difference between “good” zinc and phosphorus in the form of ZDDP and “bad” zinc and phosphorus from reaction by-products will be next to impossible to determine.
The second limitation of using elemental spectroscopy for tracking additive depletion is perhaps even more fundamental. Many common additives such as antioxidants, dispersants, VI improvers and some antifoam additives are organic molecules. Simply stated, an organic additive molecule contains carbon, hydrogen and perhaps oxygen, nitrogen or sulfur. Because none of these elements are routinely detected using elemental spectroscopy, ICP or RDE offers little or no help in monitoring organic additive health.
You might have started with 900ppm Zn, and finished with 900ppm, but that doesn't tell you how much of the Zn was still active additive.
Quote:
Perhaps the simplest used oil analysis tool for monitoring additives is elemental analysis. Using either rotating disk electrode (RDE) or inductively coupled plasma (ICP) spectroscopy, elements such as zinc, phosphorus, calcium, barium and magnesium can be measured and trended to provide an indication of additive concentration. However, elemental spectroscopy has two major limitations with respect to tracking additives. First, the technique does not actually measure additives, but rather the individual elements or atoms contained within the additive molecule. While this comment may seem obvious, it has serious implications when talking about trending additive depletion.
To understand the potential problem, consider the fate of one of the most common additives, zinc dialkyl dithiophosphate (ZDDP), an antiwear and antioxidant additive. Depending on formulation, a common AW hydraulic fluid may contain anywhere from 100 ppm to 500 ppm of ZDDP, as measured by the elemental concentrations of zinc and phosphorus. Subjecting an oil containing ZDDP to high temperatures and high levels of moisture will likely result in significant additive depletion due to hydrolysis - a chemical reaction between the ZDDP molecule and water. Under such circumstances, the ultimate by-products of the hydrolysis reaction will likely be zinc salts and phosphates, which although no longer chemically ZDDP, may remain in solution in the oil. The result is that by considering only zinc and phosphorus concentrations, the difference between “good” zinc and phosphorus in the form of ZDDP and “bad” zinc and phosphorus from reaction by-products will be next to impossible to determine.
The second limitation of using elemental spectroscopy for tracking additive depletion is perhaps even more fundamental. Many common additives such as antioxidants, dispersants, VI improvers and some antifoam additives are organic molecules. Simply stated, an organic additive molecule contains carbon, hydrogen and perhaps oxygen, nitrogen or sulfur. Because none of these elements are routinely detected using elemental spectroscopy, ICP or RDE offers little or no help in monitoring organic additive health.
You might have started with 900ppm Zn, and finished with 900ppm, but that doesn't tell you how much of the Zn was still active additive.
