Particle Size Measurement Methods – Laser Diffraction? Sieve Method?

10 Considerations for Laser Diffraction and Technical Differences with Sieves 

Overview: 

 


Laser diffraction has established itself as a standard method for routine particle size analysis in various industries. Due to its powerful advantages, laser diffraction has begun to replace traditional methods like sieving for particle size analysis. 

 


Switching from sieves to laser diffraction requires evaluating the advantages of laser diffraction and comparing the results with sieve measurements. When considering laser diffraction as an alternative or replacement for sieving, important aspects for comparison include: 

1. Repeatability and Reproducibility

Using laser diffraction, the repeatability and reproducibility of results are significantly improved compared to using sieves. 

 


In typical laser diffraction measurements, reproducibility errors do not exceed 1%, and repeatability is within 0.5%, with minimal operator variability.  

This is in stark contrast to sieving, where reproducibility can vary greatly with different users and over time. The statistical superiority of laser diffraction is one of the key arguments for transitioning from sieving to analytical methods. 

2. Small Samples 


Laser diffraction allows for measurement with smaller samples compared to sieving, and in some cases, larger sample sizes can also be used. 

 


For reliable results in dry dispersion tests with laser diffraction, 10mg to 30g of sample is sufficient, with several grams typically used in general experiments. 

 

The only practical limitation to particle size analysis by laser diffraction is the duration for which samples can be continuously or online fed into the instrument. 

 

This is contrasted with sieving, where results vary with sample volume, thus providing significant flexibility in analyzing highly dispersed samples using laser diffraction. 

 

 


3. Experiment Time of Just Seconds 

 


Unlike sieving, which takes minutes, laser diffraction completes in seconds. Speed of analysis is one of the most important factors when choosing an analytical method, especially for recent material tests and process monitoring. 

 

The difference between seconds and minutes is often monetized, with material wasted from suboptimal process conditions potentially costing thousands of dollars. 

 

A typical laser diffraction test requires about 15 seconds of analysis time with approximately 10g of sample, allowing for almost real-time measurements even without in-process equipment, with results provided immediately upon test completion. 

 

Therefore, an operator with prescribed training can test over 100 samples per 8-hour shift without significant difficulty. 

 

In contrast, sieving requires several minutes each time along with cleaning, causing bottlenecks in analytical laboratories, wasting samples, and limiting the number of tests possible within one shift. 

 

Laser diffraction not only improves control over process conditions but also enhances laboratory efficiency and throughput. 

4. Running Costs 

 

Additionally, the operating cost of diffraction systems is minimal compared to sieve replacement. 

 


Maintaining a laser diffraction system requires simple cleaning of the window cell and occasional replacement. 

 

For dry dispersion systems, vacuum bags must also be replaced regularly to maintain performance, in contrast with the use of sieve stacks where sieves must be replaced due to wire breakage and tears to maintain continuity with previous measurements. 

 

 


5. Report Customization 

 


Mastersizer products allow users to customize and translate data into sieve-equivalent reports for easy interpretation. 

 


Utilizing Mastersizer 3000 software, the reports can be provided in formats tailored to the user’s information requirements with simple manipulations. 

 

When comparing results with sieving, select the relevant size range and add it to the report to easily obtain the proportion within the range. 


 

Particle size distributions and common statistical parameters can be easily displayed in a single report, allowing specifications to be conveyed to demanding customers. 

 

Additionally, data can be swiftly converted into common Excel-compatible formats using customizable Export templates. 

 

 


6. Size Range 

 


The size range of diffraction is 0.1 – 3500μm, which is much wider than that of sieves. 

 


Laser diffraction equipment like the Mastersizer 3000 provides substantial dynamic ranges in a single measurement, whereas sieving is limited to a range to tens to hundreds of microns, with poor performance under 45 microns. 

 

Additionally, for sieves, flaky or needle-shaped particles can pass through the sieve openings even if they are several times larger, leading to potential misinterpretation of actual particle sizes in samples. 

 

 


7. Maintenance and Cleaning 

Difraction allows for faster, simpler, and easier maintenance and cleaning between sample replacements. 

 


For dry dispersion laser diffraction methods, simply brushing the system prepares it for the next sample loading and measurement. 

 

For the Aero S disperser available for Mastersizer 3000, a pre-coded cleaning routine is included to assist users. Generally, the cleaning time is around 30 seconds during sample replacements, reducing wasted time between experiments. 

 

In contrast, with sieves, screens must be cleaned and weighed between tests, extending total time beyond 10 minutes, while laser diffraction offers more uptime and simpler cleaning compared to sieving. 

 

 


8. Automation 

 


Automating test conditions in Mastersizer products ensures optimal sample measurement. 

 


Malvern’s overall laser diffraction technology is designed around standard operating procedures (SOP) to maximize efficiency while minimizing user-induced variation. 

 

Once an SOP is established for sample measurement, users only need to load and appropriately name the sample. 

 


The rest is performed autonomously by the equipment. SOPs encompass all computer-controlled parameters, cleaning, report printing, and result report settings, allowing for rapid completion without expert assistance. 

While automated sieving methods are possible, problems like long cleaning times, user variation, and extended experiment times persist.  

 

Mastersizer products provide the fastest and most accurate method to obtain particle size results. 

 

 


9. Sealed Samples 

 


In dry laser diffraction methods, seals using vacuum prevent contact risks. 

 


Mastersizer’s dry dispersion accessory range is fully sealed from sample loading to the vacuum bag. Utilizing sealed systems minimizes user exposure risk to samples. 

 

Vacuum collection simplifies waste disposal and the equipment is compact enough to fit inside a hood or enclosure to maximize safety when testing dry samples. 

 

Sieving, with its open design, is more vulnerable to exposure risks and does not collect samples in convenient containers for disposal. 

 

 


10. Quiet Laboratories and More Space 

 


Diffraction occupies smaller spaces like benches and cabinets in laboratories, with less noise. 

 


The Mastersizer 3000 laser diffraction system requires a total of 27 inches of space, half that of the Mastersizer 2000 and operates with almost any HVAC line, with vacuum units installed outside the lab to minimize noise. 

 

In contrast, sieve devices are noisy, messy, vibrate significantly, and take up as much space as a large bench, with laser diffraction having clear advantages in creating a comfortable working environment in laboratories.