Back to Basics of Laser Diffraction – Q&A from Masterclass Part 2
Welcome back to the second installment of our blog series answering questions from the back-to-basics of laser diffraction webinar. If you missed the first Q&A blog, please find it here. In this blog series, we are addressing some of the key topics raised during the webinar, providing further insights and clarifications to enhance your understanding.
Mastering your materials – dispersion methods and choices
Next, we turn our attention to the materials and methods used in laser diffraction. Your inquiries about sample preparation, measurement techniques, and equipment calibration were insightful. Here, we provide detailed answers to enhance your practical knowledge.
Q – Should we use a dry method or a wet method for battery materials?
Q – How do you determine which dispersion unit is best for different applications, for example, oil and gas sector when analysing sand particles?
A – When choosing between wet and dry dispersion methods for material characterization using laser diffraction, key considerations include the physical and chemical properties of the sample and the goals of the dispersion process. Wet dispersion is ideal for cohesive, fine, or hygroscopic particles, and for handling toxic substances safely. It involves dispersing particles in a liquid medium, which relies on liquid-particle interactions to promote dispersion. Dry dispersion, on the other hand, is suitable for materials that dissolve in liquids, for magnetized particles, or for products designed to be dispersed in air. It uses compressed air to disperse particles and is quicker with minimal cleaning required.
More specifically for battery materials the main points to consider are: (1) the proportion of fines; (2) the risk of dust explosions or inhalation; and (3) the suitability and availability of a liquid dispersant. Some battery materials have a high carbon black content which is better suited to wet dispersion. On the other hand, further upstream some metal components of battery formulations may be coarse (>50 µm) metal powders that disperse well dry.
Choosing the correct dispersion unit for measuring sand particles will be determined by the criteria discussed above (wet versus dry) and then also the size and volume of sample available. We have a range of wet and dry dispersion units that have been designed to work with either small or large volumes of material and dispersant. Please get in touch with us today so we can help configure the best system for your requirements.
Q – What is the best way to measure water-soluble active ingredients accurately in a saturated solution? Even when the solution is saturated, the [Mastersizer] still detects high standard deviation in measurement results. We used Fraunhofer, but do not know if we are missing anything else.
A – Using saturated solutions in the Mastersizer 3000 is not recommended. Super-saturated solutions can promote crystallization or seeding and have a refractive index close to the particles, reducing optical contrast, which is not ideal for laser diffraction measurements. The Fraunhofer approximation may also lead to poor repeatability due to it being a simplified model which requires a high refractive index contrast.
Instead, we recommend you control the sample preparation by carefully managing the dilution/concentration and preparation duration. Initially, some material may dissolve, requiring additional sample to stabilize the obscuration. Significant dissolution can be identified by a marked reduction in obscuration and an increase in Dv10 across six repeats. According to ISO13320 (2020), the relative standard deviation (RSD) tolerances for a repeatable method are less than 3% (Dv10), 2.5% (Dv50), and 4% (Dv90). If significant dissolution persists, an alternative dispersant may be required or a dry dispersion option should be considered.
Q – Can the laser diffraction experiment be used to analyse particles such as liquid in liquid (micellular emulsions) or gas in solid, for example, where the “particle” is highly transparent or even more transparent than the bulk suspending medium?
A – The consideration for whether you can analyse a particle in a dispersant using laser diffraction is whether there is sufficient contrast between the refractive index of the particle and the refractive index of the dispersant. For instance, emulsions are frequently analysed on the Mastersizer 3000 range, however, there must be sufficient contrast between refractive indices of the droplet and dispersing phase. Laser diffraction cannot measure ‘gas in solid’ systems, as the dispersing phase must be a liquid or gas. However, gas bubbles in liquid can be measured with the Mastersizer 3000, and liquid droplets in air can be measured using the Spraytec.
Q – Can laser diffraction can be on-line in cement manufacturing?
Q – Is there any availability of online analysis in cement manufacturing?
A – Yes, laser diffraction can be used on-line for cement manufacturing. This technique is highly effective for measuring particle size distributions, which is crucial for optimizing the grinding efficiency and final properties of cement.
For on-line applications, Malvern Panalytical offers solutions from the Insitec range, which is suitable for real-time process monitoring in various environments, including those with hazardous conditions. The integration of such systems into the production process allows for continuous monitoring and control, ensuring optimal performance and quality of the cement. If you need more specific information or have any other questions, please get in touch.
Q – Can the instrument handle basic/acidic solutions? I might need to use a buffer for some applications.
Q – Is it possible to measure particles on volatile solvents such as ethanol or chloroform?
A – The Mastersizer 3000(+) is a highly versatile instrument but it’s essential to understand its chemical compatibility to ensure optimal performance and longevity. When it comes to basic and acidic solutions or volatile solvents, please check the chemical compatibility guidance in the instrument manuals before using with your instrument. It is important to check the compatibility of the measurement cell, dispersion accessory and tubing that connects the accessory to the cell. If in doubt, please contact Malvern Panalytical support and we can advise you on specific dispersants.
Q – Can you tell how to use the additives: Igepal CA-360, Tween 20, Span 20, Natriumlaurylsulfaat, Nonidet P40, natrium hexametaphosphate, Ammonium citrate dibasic?
A – Using surfactants and additives in wet laser diffraction methods can enhance the dispersion and stability of samples. Broadly we recommend using low concentrations of surfactants and additives (0.1-4% by weight) to minimize the risk of foaming (bubble formation) and destabilizing the dispersion. They can be added directly to the sample or dispersant.
Igepal CA-360, Tween 20, Span 20 and Nonidet P40 are all non-ionic surfactants that are long chain molecules that adsorb onto the particle surface. Natriumlaurylsulfat, also known as Sodium Lauryl Sulfate (SLS), is an anionic surfactant. It is a charged long chain molecule that increases repulsion between particles. They can all be used to improve the dispersion of particles in aqueous solutions.
Natrium hexametaphosphate, also known as Sodium hexametaphosphate (SHMP) is a dispersing agent used to prevent agglomeration of particles in aqueous solutions. Ammonium citrate dibasic is a chelating agent used to stabilize particles in aqueous solutions.
Q – What reference standard can you recommend for measuring large particles > 1000 um?
A – When sourcing standard materials, we recommend using polystyrene latex standards, glass beads, or certified reference materials for the most accurate and reliable measurements. Polystyrene latex standards and glass beads are commonly used for their high precision and consistency. Certified Reference Materials (CRMs) are also available in various sizes, including those suitable for large particles, providing traceability to national or international standards for the highest accuracy.
Although Malvern Panalytical does not supply standards for particles >1000 µm directly, other suppliers offer NIST traceable standards. Ensure that your dispersion accessory is suitable for measuring large particles, such as the Aero S and Hydro LV for 1000 µm particles.
Q – We use Malvern for PSA of anode materials. Our particles are usually under 32 microns, we use wet sampling. Which solvent would you advise us to use- water or IPA?
A – Without knowing the specific anode material, it is difficult to comment on what is the best option for dispersing the material. Fundamentally we want to achieve conditions where our particles are stable and well dispersed – it might be the case that you can achieve this in water or IPA! In my experience, typical anode materials such as graphite and SiOX measure well in water and small amounts of surfactant, such as Igepal CA-630. Water could also be a lot less costly to use and disposed of in the long run if it is a suitable dispersant.
Q – Can the dispersing liquid for chocolate be sunflower oil?
A – Yes, sunflower oil is a common dispersant when measuring chocolate. Other options are coconut oil, Volasil, Akomed and Isopar G. When using these dispersants, it is important to be aware of some challenges. These dispersants are generally viscous such that aggressive stirring can introduce air and produce bubbles. Additionally, insufficient equilibration time when measuring in oils can cause beam steering, leading to phantom peaks in the PSD typically at sizes >1000 µm. To avoid these issues, ensure the dispersant is thermally equilibrated before measuring the sample and/or after applying ultrasound.
Q – Can you advise how to take a representative sample from a clay suspension?
A – To prepare a representative sample of a clay suspension, ensure all particles are suspended and homogeneously mixed. This can be achieved by rolling and inverting the container, followed by continuous agitation of the sample. Then use a pipette to add an aliquot to the Mastersizer 3000(+). The amount added to the dispersion unit depends on particle size and polydispersity; larger and more polydisperse particles require higher obscuration. Consider using a high-volume dispersion unit, such as the Hydro EV or LV, to sample more material. Preparing a representative sample is more challenging when dealing with larger quantities of material.
Further resources and webinar recordings
Thank you again for your engagement throughout the Mastersizer Masterclass. If you would like to revisit the webinars please find the recordings on our website. For more information on laser diffraction applications and method development, please visit our knowledge center where you can find a library of application notes, technical notes and blog posts on a range of topics. And if you would like to ask more specific questions, please do get in touch via our customer support portal where your enquiry will be passed on to the relevant technical expert. Stay tuned for the final blog in the series where we cover adaptive diffraction and understanding size distributions.
Further reading
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