Dispersion of particles

1. Dispersion of particles

When the liquid sample is left for a long time, the particles settle due to gravity. Therefore, in order to ensure that the measurement results of particle contamination can reflect the actual pollution status of the liquid sample, it is necessary to ensure that the particles in the liquid sample are uniformly dispersed and suspended before detection.

Common solutions: The agglomerated particles can be effectively dispersed through methods such as vigorous shaking, ultrasonic vibration, and heating. The specific dispersion method is to first vigorously shake the liquid sample for 1 minute, immerse it in an ultrasonic bath for 30 seconds, and then vigorously shake the liquid sample for 5 minutes to disperse the particles in the liquid sample.

2. Detection of sample degassing

When shaking the liquid sample to evenly disperse and suspend particles, bubbles are likely to be generated. If the bubbles are not eliminated, they will be counted as particles, which will affect the accuracy of particle counting measurement results.

Common solutions:

Vibration method: Ultrasonic vibration can quickly gather small bubbles into large bubbles. The specific method can refer to the following steps: place the shaken liquid sample in the ultrasonic cleaning tank and vibrate for about 30 seconds until the layered bubbles rise to the surface of the liquid sample; Slowly rotate the liquid sample sampling container at least 5 times to raise the residual gas in the liquid sample to the liquid level;

Instrument pressurization method: Place the sample solution in a pressure sampler and adjust the negative pressure to eliminate bubbles. The specific operation is to move the toggle switch downwards, add negative pressure to the instrument up to 0.08MPa, and then let it stand (freely control the defoaming time according to the number of bubbles in the liquid sample). After the bubbles are eliminated, press the pressure relief button to release the pressure in the pressure chamber before taking out the sample solution.

PS: Pull the toggle switch upwards to apply positive pressure. When the viscosity of the liquid sample is too high, positive pressure can be used to assist in injection. Generally, when the viscosity of the liquid sample does not exceed 350cSt, this instrument can be used for injection assistance to avoid secondary pollution caused by improper dilution of the liquid sample.

Dilution of liquid sample

In practical terms, dilution of liquid samples is highly likely to cause secondary contamination and incorrect counting results by amplifying liquid particle counters. Therefore, when measuring particle contamination, it is advisable not to dilute the sample. However, if the following three situations occur in the liquid sample, dilution is necessary:

1. The number and concentration of particles in the liquid sample are higher than the limit coincidence error of the particle sensor;

2. The color of the liquid sample is too dark, which affects the particle counting results;

3. The viscosity of the liquid sample is too high, and the particle counter sampling device cannot guarantee that the liquid sample will pass through the particle sensor at the working flow rate.

When the viscosity of the liquid sample is too high, the first consideration should be to use heating to reduce the viscosity of the liquid sample, but the heating temperature should not exceed 60 ℃. If the liquid sample is heated to 60 ℃ and still cannot be guaranteed to pass through the particle sensor at the working flow rate, dilution should be used.

Selection of diluent: The diluent should preferably be a clean liquid that is the same as the liquid sample. If it is necessary to reduce the viscosity of the liquid sample or increase its transparency, a low viscosity clean solvent compatible with the liquid sample and sampling container should be selected. The commonly used diluents include YH-15 aviation hydraulic oil, toluene, analytical grade isopropanol, softened water (for water-based liquids), petroleum ether (boiling range of 90-120 ℃), etc.

The reliability of liquid particle contamination detection results depends not only on the instrument, but also on whether the liquid sample can reflect the true condition of the system. Proper pre-treatment of the liquid sample can make the detection results more accurate and reliable.