Particle Size Distribution Measurement

[itsagoal89]

I am interested in how PSD (particle size distribution) affects the transmittance of a material and I am trying to find an accurate process to measure it so that I can test and gather data on how it affects it.

I don't know if transmittance is the proper word for what i want to study, but all i know is the PSD affects the amount of energy that gets through it and want data on how and why.

Does anyone know any instruments that i can use to examine the particle size distribution?
Im looking to study the PSD in materials like wood, leather, steel.

what would be good for that...

Optical Granulometry. Electron micrographs. Laser Diffraction. or any other ideas or examples of instruments would be appreciated...

 

[Cthugha]

That depends on what kind of material you are interested in.

You could use dynamic light scattering which is a kind of photon correlation spectroscopy. If you trace the autocorrelation of laser light scattered from your sample it will show fluctuations depending on your particle size distribution. However, for this method to work you usually need particles in suspension or solution. Then the Brownian motion will cause the particles to move around, causing the mentioned fluctuations. So you could only apply this technique to powders of metals, but not to bulk crystals or such.

 

[itsagoal89]

That is a phenomenal concept Because the leathers/polypropelenes are what i have the most samples of. I was looking a "Wyatt" instruments and didn't find any good candidates. Or you i just have to analazye the graphs after numerous trials?

thank you for your reply by the way, very intelligent!

 

[itsagoal89]

And as i am still studying and only a sophomore engineer/physicist, could you please dumb this down, "If you trace the autocorrelation of laser light scattered from your sample it will show fluctuations depending on your particle size distribution."

 

[Cthugha]

Ok, I will try to explain that a bit more in detail.

The scattered intensity from your sample at some given angle will depend on the exact positions of your scattering particles inside your volume of interest. These positions will change constantly as the particles are undergoing Brownian motion. As a consequence the instantaneous scattered intensity at some moment can be quite different from the mean scattered intensity when averaged over large times.

That also means that if you measure the scattered intensity now and measure it again shortly afterwards, the two intensities measured will be very similar, no matter whether they are both below, near or above the average scattered intensity. If you, however, measure now, wait a longer time and then perform another measurement of the intensity, the two measured intensities will be independent of each other. One can be above average, while the other one is below or vice versa or whatever. Now the timescale of the waiting time between two measurements on which similar behavior turns to independent behavior depends on how quickly your particles move around. If their shape is a bead or something similar than you can easily relate that speed of movement to the particle size and can relate the timescale of the delay, on which the intensity "randomizes" to the particle size distribution.

You might also want to google for Dynamic light scattering. There are several texts and tutorials out there which can definitely explain this much better than I could as I never performed such experiments in order to determine particle sizes myself. I hope this explanation helped at least a bit.

 

[itsagoal89]

Good advice, i did,

So, as the DLS machine is on it measures particle size over time correct? Do i keep measuring over time to see when the value strays from the norm?

 

[Cthugha]

It does not really measure the particle size directly. You get a different scattered intensity depending on the distances between the scattering particles. These change as the particles move around. It is this change that is measured by the instrument. However, as smaller particles will move around faster you can draw conclusions on the particle size distribution by knowing how fast the signal changes. Then you just keep measuring for a long time, create a timetrace of the scattering intensity. From this timetrace you can calculate the PSD.
Maybe perform a google search on "an introduction to DLS in 30 minutes". I think there is some good explanation called similar to that somewhere around the net. There is a bit of advertisement inside, but it gives an okish basic overview.

 

[GT1]

At many labs Malvern is used to measure PSD
http://www.malvern.com/labeng/products/iwtm/particle_size_analysis.htm"

 

[adrian423]

Quantachrome in the UK also provide a range of particle size instruments:
http://www.quantachrome.co.uk/en/Particle_Size_Analysis_and_Measurement.asp

Their website also has some useful links to particle size research papers and a dictionary.