# Calculate Average Particle Size with a Particle Size Meter

The average particle size is computed by deriving the specific surface area from the flow velocity of the gas through the powder bed.

Image Credit: Shutterstock/Hanna

## The Difference Between an Average Particle Size Meter and Laser Particle Size Analyzer

The average particle size meter and laser particle size analyzer are the widely used particle size analyzers used for this process. While the results measured by both methods can be expressed in terms of microns, these individual results are not fully comparable. This is because the working principles of both methods vary vastly.

According to the principle of air transmission method, the average particle size meter is operated. Essentially, this measures the gaps between particles and not the particles themselves.

The working principle behind the laser particle size meter is the phenomenon of scattering of the particles by laser. In order to obtain the particle size distribution, the scattering signal is collected by detectors placed at different positions. Further, the shape of particles greatly influences the measurement accuracy.

Each particle is required by the average particle size meter to be approximately round and roughly an equal circle. When the particle is assumed to be round, the equivalent diameter is used in the laser particle size meter. However, the more irregular the particle shape, the less accurate the actual measurement will be.

## Applications of the Average Particle Size Meter

When it comes to the application scope of both, in some specific industries – such as magnetic materials, cemented carbide, powder metallurgy, and pharmacy – the average particle size meter is used more widely.

## Benefits of the Average Particle Size Meter

The average particle size meter is a type of instrument that has the ability to rapidly determine the average particle size of various powders, using the penetrant method. Owing to its simple structure, accurate measurement, convenient operation, stable performance and good reproducibility, it is considered advantageous.

The HMK-22 Average Particle Size Meter has been widely used in the fields of powder metallurgy, magnetic materials, hard alloy, tungsten and molybdenum materials, gunpowder, ceramics, pharmaceutical, food, water mixture, electronics, and the chemical industry. In addition, it also finds use in national defense, aerospace and other industries, along with the measurement of powder inlet and outlet. Thus, in effect, it has been recognized as one of the world’s foremost customary means of detection today.

## Average Particle Size: Physical or Chemical Analysis?

One of the most frequently asked questions is whether the average particle size is considered physical analysis or chemical analysis. The definitive answer is that the average particle size relates to physical analysis, not chemical analysis. In the testing of the average particle size, it follows that the average particle size meter will be used.

As an example, take the HMK-22 average particle size meter. In the process of preparing the powder sample, the measurements taken are simply compaction. This is followed by an analysis of the average particle size of the powder, using the air transmission method. Further, the air transmission method doesn’t alter the sample’s physical characteristics in the slightest.

## Preparing the Sample for Particle Size Analysis

Prior to the particle size analysis, the sample needs to be prepared effectively in order to ensure the analysis is accurate and repeatable. To accomplish this, generally speaking, the existing state of the sample should be maintained without causing damage to its original representativeness. Then, it should be ensured that the sample quantity is more than enough to meet the demand of particle size analysis.

Image Credit: DANDONG HMKTEST INSTRUMENT CO., LTD

Image Credit: DANDONG HMKTEST INSTRUMENT CO., LTD

Image Credit: DANDONG HMKTEST INSTRUMENT CO., LTD

Image Credit: DANDONG HMKTEST INSTRUMENT CO., LTD

For the airflow sieving resin sample, 25 g is the sample size needed for each sieving. Further, the smaller the sample’s particle size, the smaller the amount of sample required – around approximately 10 g, for example.

With few exceptions, the sieving test needs to be conducted in accordance with the sample’s receiving state. For instance, if the sample is not detected when received, it must be placed in an airtight container, fulfilling all the conditions for storing dry powder.

When it comes to resin, static electricity can have a large impact. Antistatic material such as 0.5% y-aluminum oxide can be used, in an effort to eliminate the influence of static electricity on air flow sieving. Unless otherwise specified, this must be put in the resin at the start of the sieving process.

Finally, in the case of lactose medicinally used excipient, 0.1 g aluminum oxide is usually put in when sieving.

This information has been sourced, reviewed and adapted from materials provided by AimSizer Scientific Ltd.

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