Validating the particle size of metal powders: ASTM B822 or ISO 13320?

by Ulf Nobbmann, Friday, 13th October 2023

Image showing metal powder sparking and flying away from the center. ASTM defines how to measure particle size of metal powders in ASTM B822 or alternatively can use ISO 13320

Formnext 2023 is just around the corner and Malvern Panalytical will be there at the Frankfurt Messe from 7-10 November. We will be showcasing our various analytical solutions for the 3D Printing industry, alongside part manufacturers, material manufacturers and machine manufacturers. So, if you’re attending, then come visit us at booth F61 in hall 11.0, where we will he happy to show you our solutions, and answer any questions you may have.

Speaking of 3D Printing questions, we recently received this question from one of our Mastersizer customers, and we thought the answer may be helpful to others working in the industry.

We are currently using a Mastersizer laser diffraction system with wet dispersion unit to test according to ISO 13320: 2020-01. Is this test method also applicable to ASTM822? Are the two norms similar, how are they different?

Are ASTM B822 and ISO13320 the same?

Looking into the answer to this question, I consulted with several of my colleagues. To start with, a web search reveals that ASTM themselves consider the two methods equivalent:

screen snipped from ASTM indicating that ISO13320 and ASTMB822 are equivalent methods of particle size analysis by laser diffraction

In a handwaving generalization, ISO documents tend to read like a cookbook, whereas ASTM methods tend to read like a recipe. A major issue is sonication.

What guidance does ASTM give for sample preparation?

There are some specific suggestions for metal powders that you could implement when operating according to ASTM822 (and incorporating specific sample preparation instructions in ASTM821) such as

  1. Additive: Tween / Polysorbates for: Copper (Cu), Ferroalloys (Fe), Iron/steel, Manganese Sulfide (MnS), Nickel (Ni).
  2. Stabilizer: Sodium Hexametaphosphate for: Molybdenum (Mo), Tantalum (Ta), Tantalum Carbide (TaC), Tungsten / Wolfram (W), Tungsten Carbide (WC)
  3. Sonication: Recommended to use just as much ultrasound as needed/identified during the development phase.

Typical bath sonicators have a power in the range from 10mW to 100mW, and the actual power is not all that important. The applied input energy is the key parameter (feel free to listen to a webinar excursion into the world of ultrasound, cavitation and singing kettles).

Still need help with my ASTM method question!

Do the above suggestions help clarify the picture? If not, don’t hesitate to reach out to our global applications support team. We can get you in touch with a local resource to help with your concerns. And questions related to norms and standards, specifically for laser diffraction, be that ASTM or ISO. And if you are near Frankfurt in November, why not stop by our stand? We’d love to connect with you – especially if additive manufacturing and metal powders are on your mind.

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