The Benefits of Automated Particulate Analysis by SEM-EDS

Automated Particle Analysis by SEM/EDS

When encountering puzzling particulate results, questions arise such as:

What species of particulate are in this sample?

What is the chemical composition of these particles?

What is the particle size distribution of this sample?

Automated particle analysis by Scanning Electron Microscopy and Energy Dispersive X-ray Spectrometry (SEM-EDS) provides a method to answer questions about particle populations that arise in a very wide range of industries. Some examples of SEM-EDS application include: wear particle analysis, size distribution of pharmaceutical ingredients, source determination of airborne particulate, and nanoparticle characterization.  SEM-EDS can also determine whether non-process related particulate is biasing the catch through identification of particle species and chemical composition.

SEM-EDS is a powerful analytical tool for obtaining concise information about a particulate sample.

Figure 1: Representative Automated Particle Analysis High Contrast

Figure 1: Representative Automated Particle Analysis High Contrast

The first step in SEM/EDS automated particle analysis is to acquire a background image with sufficient contrast between the background and the particles so that image analysis can differentiate between them (Figure 1).  For automated image analysis systems, a “particle” is defined as a set of contiguous pixels all of which are brighter (or more rarely, darker) than the threshold brightness used to define the surrounding “background” pixels.

Next, particles are recognized by the image analysis system (which is a part of the SEM/EDS software).  Figure 2 shows the same field of view as Figure 1, except that there is indication of the particle count that the system has identified.  The analysis system saves the location of each particle and then two-dimensional size and shape parameters for each particle are determined. Typical parameters include maximum, minimum and average diameters, perimeter, and aspect ratio.

Figure 2: Representative Automated Particle Analysis

Figure 2: Representative Automated Particle Analysis

Once the particles in the field of view are recognized, the automation system of the microscope conducts a chemical analysis of each particle to acquire the signature on an EDS spectrum.  A typical example appears as Figure 3.  A peak in the EDS spectrum indicates the presence of the corresponding element in the particle which can then be classified based on its composition.  In Figure 3, the spectrum shows the particle to be composed of Iron (Fe) and Oxygen (O), indicating an Iron Oxide particle.

Once every particle in the field of view is recognized and its dimensions and composition saved, the microscope moves to a new field of view and the process is repeated until a set number of particles or a predetermined number of fields of view have been analyzed.  Using this systematic analysis sampling allows for the characterization (size, shape, composition) of hundreds and even thousands of particles in just a few hours without operator involvement beyond the initial setup.

Figure 3: Representative EDS Spectrum of Automated Particle Analysis

Figure 3: Representative EDS Spectrum of Automated Particle Analysis

Finally, the results are tabulated, giving a complete picture of the particle types, sizes, and shapes.  The tabulation is entirely customizable since all of the data (size, shape, composition) is stored for each individual particle.

Table A: Percent Distribution of Particles by Mass with Corresponding Emission Rate

Amount of Particulate Emitted in One (1) Hour = 10 lbs


Particle Size
(microns)

Distribution
(%)

Particle Emission Rate
(lb/hr)

0.5 – 1.0


53.05


5.305

1.0 – 2.5 37.25 3.725
2.5 – 5.0 7.57 0.757
5.0 – 7.5 1.44 0.144
7.5 – 10 .40 0.04
10 – 25 0.28 0.028
25 – 50 0.00 0
50– 100 0.01 0.001
>100 0.00 0
TOTALS 100 10

ESS provides emissions testing, air quality analysis, and consulting services for manufacturers, municipal water treatment plants, public utilities, paper mills, and other industrial facilities in the US and overseas.  Since its inception in 1979, ESS has conducted thousands of emissions tests and provided countless hours of environmental consulting services.  ESS specializes in conducting the EPA testing methods for all applicable EPA subparts, such as: NSPS (40 CFR 60), NESHAP (40 CFR 63), RATA (40 CFR 75), and various other federal and state regulations.

We are committed to the highest standards of integrity, excellence and customer service.  ESS continues to invest in facilities, equipment, education, and safety to provide a broad range of services to meet our clients’ varying needs.

Adapted from information available at: http://mvascientificconsultants.com/

 

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