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/

 

Understanding Upstream and Downstream

The terms “upstream” and “downstream” are frequently used in the stack testing industry to describe direction within a stack.  However, these terms are often confused and used opposite of their intended meaning.

The key to remembering upstream and downstream when talking about flow is to think about another flowing object—a river!

Rivers generally flow from a source, like a mountain lake, to an outlet, like the ocean where the freshwater disperses into the saltwater.  In terms of stack air flow, the air emissions originate from an emissions source and travel through the stack to the stack exit where they disperse into the atmosphere.

The direction of travel from a source to an outlet is with the current, or downstream.  Conversely, the direction of travel from an outlet to a source is against the current, or upstream.

There are two simple mnemonic devices which can help you to remember the difference between upstream and downstream.

“Up the Creek Without a Paddle”

Imagine you are in a canoe enjoying a peaceful trip down the river when you hear the sound of a waterfall ahead.  You look around for your oars, but there are none in sight.  Frantically, you use your arms to try to paddle further upstream to safety, but it is very difficult because you are fighting the current.  This is a situation of being up the creek without a paddle.

Upstream is the direction toward the source and also against the current.

Upstream Downstream Diagram

Diagram Showing Upstream and Downstream in Relation to Current

 

“Gently Down the Stream”

Now imagine that you made it safely to the river bank and carried your canoe to bypass the waterfall on foot.  You put the canoe back into the river where you can lay back and relax because the current is carrying you gently down the stream to your destination.

Downstream is the direction away from the source and also with the current.

The diagram above is a visual aid demonstrating the relationship between current and upstream/downstream direction.

If you have questions about this topic, or any other emissions testing question, please call Environmental Source Samplers at 1-888-363-0039 and we will be happy to help you.

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