When you send material to PTL for analysis, do you need your samples back? Perhaps they are difficult to produce, expensive, or highly proprietary. While we are always happy to send back any untested samples, we can’t always retain and return the portions used for analysis. This blog will explore whether your material is recoverable after specific analyses at Particle Technology Labs (PTL) and how the recovered material may be altered.
Particle Sizing
Laser diffraction (LD) and microscopy are among the most common techniques used for particle sizing. Given the relatively low quantities needed for these analyses, the samples used for these techniques are generally not recovered. The samples may simply be scraped off the plate or mount after imaging or flushed out of the LD instruments directly into the waste collection container for disposal.
On the contrary, particle sizing by sieve analyses requires much higher sample quantities, e.g., at least 10-100 g. Sieved samples are typically retained, as separated by particle size fractions, and could be shipped back at your request. There are, of course, some exceptions. For example, the fraction that passes through an air jet sieve cannot be recovered, as the material is whisked away into a vacuum bag during analysis. Likewise, if the sample is wet sieved, any dissolved solids are typically diluted in the fluids added for analysis and cannot readily be recovered. The sieving process should only produce the desired size separation and not cause unwarranted changes in the sample, e.g., breaking (or milling) or agglomeration on the sieve. Otherwise, an alternative method for particle sizing should be explored.
Pore Sizing
At PTL, the two main pore size distribution analyses are mercury intrusion porosimetry (MIP, largely for macropores) and gas physisorption (for micropores and mesopores, also provides BET specific surface area). As the name suggests, during a MIP analysis, the material is impregnated with mercury, making it impractical to separate the two from each other. This process contaminates the sample; therefore, it must be properly disposed of after analysis.
In contrast, the samples can be readily recovered after a gas physisorption analysis. The retained sample is typically dried but is generally unchanged unless it is sensitive to cryogenic temperatures and/or rapid temperature changes. Drying occurs as sample preparation involves degassing under vacuum or flowing inert gas, often with some heat, to help draw out any excess moisture and other gaseous impurities that may have adhered to the surface or inside the pores of the material. The sample tube is then submerged in liquid nitrogen, and nitrogen adsorption analysis is conducted at the boiling point of liquid nitrogen (77K).
Other Techniques
If you have a catalytic sample and you’re interested in the surface area of only the metallic sites and/or its dispersion, then you might need chemisorption analysis. Like the physisorption analysis, a sample can be readily recovered after an analysis. By design, this analysis requires a reactive gas and is typically conducted at high temperatures; the retained material is usually changed in some ways. How it is changed depends on how the sample is prepared and the analysis design. For example, the samples could be reduced and/or oxidized either before or throughout an analysis.
If you are more interested in packing and flow properties of a material, density and powder flowability analyses may be crucial. Both comprise a wide range of techniques and/or experimental setups. Very broadly speaking, while higher sample quantities are typically required, sample recovery after analysis should not be difficult. Unless the sample is friable, the recovered materials should remain largely unchanged.
Final Thought
While we can’t cover every analysis under our roof, we sure hope this general overview is helpful! Of course, if you have any questions about your specific samples and testing needs, please feel free to send us a message. We look forward to working with you!
By Julie Pohlman-Zordan, Particle Characterization Chemist III.
