The Coulter Principle or Electrical Sensing Zone (ESZ) method may be used to measure the particle concentration and size distribution in an oil sample, with the help of an appropriate organic electrolyte solution to dissolve the oil.
If the oil sample is insoluble in the electrolyte solution, then a solvent is used to dissolve the sample. A sample is then taken from the resulting solution and diluted with the electrolyte solution. This article discusses the application of a Beckman Coulter Multisizer™ 3 to measure the particle concentration and size distribution in an oil sample.
Significance of Particle Content Analysis in Oil
According to the ISO 4406 standard, the oils are classified based on their particle content in the range of particles /ml = 4 µm, = 6 µm, and = 14 µm. This is the commonly used range for particle content analysis in oils. A 100µm aperture tube is ideal for this purpose, as it can analyze the particle concentration and size distribution from 2-60 µm. Other aperture tubes may be required for different analysis ranges.
Experimental Setup and Procedure
The aperture tube suitable for the analysis size range is selected. The Multisizer™ 3 is configured and calibrated as described in the user manual. Volumetric Mode is set as the control mode for the Multisizer™ 3 to measure the particle concentration. The run volume can be any value up to 2000µL. The volume needed for the analysis is experimentally determined based on the state of the oil sample and the duration of the analysis.
For most of the oils, a 2% NH4SCN (Ammonium Thiocyanate) solution in Isopropyl alcohol (IPA) is ideal. The electrolyte solution is prepared through dissolution of 20 g NH4SCN in 1.0L of Isopropyl alcohol. A0.45µm alcohol-compatible membrane filter is used to filter the solution.
For oils that are soluble in Isopropyl alcohol, exactly 20 mL of electrolyte solution is measured into a 20 mL Accuvette® II, followed by pipetting 2.0 mL of oil into the electrolyte solution. However, the amount may vary depending upon the state of the oil. The Accuvette is then gently stirred for thorough dissolution of the sample without introducing bubbles.
For oils that are insoluble in Isopropyl alcohol, exactly 10 mL of Methyl Isobutyl Ketone (MIK) is measured into an appropriate size glass flask, followed by pipetting 2.0 mL of oil into the flask. The amount may vary depending upon the state of the oil. The flask is then gently stirred for thorough dissolution of the sample with no bubbles. Exactly 20 mL of electrolyte solution is measured into a 20 mL Accuvette® II, followed by pipetting 2.0 mL of the oil-MIK mixture into the Accuvette. The Accuvette is then gently stirred for thorough dissolution of the sample without introducing bubbles.
The Multisizer™ 3 Software is loaded with sample information, including analytical volume, dilution factor, and oil volume used for sample preparation, to determine the particle concentration in the original oil.
Hydraulic Fluid Sample Analysis
A black is prepared using the same procedure in accordance with the type of oil to be investigated but without the addition of oil. The blank is run and subtracted from all the subsequent runs using the Multisizer™ 3 Software. Then, the oil samples are run. The results are shown in Figure 1.
Figure 1. Experimental results. Image credit: Beckman Coulter
The Interpolation feature in the Multisizer™ 3 Software allows representing the results as the total number of particles, size distribution, and number of particles within, below or above the size classifications in the size distribution range.
From the results, it is evident that the Beckman Coulter Multisizer™ 3 can be used to measure the concentration and size distribution of particles present in oils.
This information has been sourced, reviewed and adapted from materials provided by Beckman Coulter, Inc. - Particle Characterization.
For more information on this source, please visit Beckman Coulter, Inc. - Particle Size Characterization.