PowerPoint Presentation

[Audio] Preparing XRF samples using pressed pellets.

[Audio] XRF is known as X-ray Fluorescence. It is non-destructive analytical method. Besides that, it is used to identify the elemental composition of materials. By detecting the fluorescence or secondary X-ray that a sample emits when it is activated by a main X-ray source, XRF analyzers may determine the chemistry of a sample. XRF is also a great technology for qualitative and quantitative examination of material composition since each element in a sample emits a distinct collection of characteristic fluorescent X-rays which is called "a fingerprint"​.

[Audio] For XRF, there are different types of sample preparations and we will be focusing on pressed pellets today. ​.

[Audio] The first step of the sample preparation process is to select a suitable press for the sample. Different press model has a different requirement. For example, PR- 25A is used when the samples have a very large volume with a very small mass. So that the pressing can be performed in one step. Otherwise, several steps are necessary.​ ​ During the pressing process, if the pressing procedure is conducted too quickly, trapped air causes part of the pellet to flake later. Besides, if too much force can lead to the pressed pellet remaining stuck to the pressing plate. However, these problems can be overcome by using a programmable 40-ton press by slowly building up the pressure in up to three steps, whereby it is also possible to specify a waiting time after each pressing step.​.

[Audio] Then a pressing die is selected for the sample. It can be classified into 2 categories which are with rings or without rings. Different diameter pressing die has different maximum pressing force. Therefore, it is important to choose a pressing die with correct design according to the press we are using. ​.

[Audio] After that, we grind the sample in different ways to achieve a grain size of less than 100µm which is recommended for XRF analysis of pressed pellets. Different kind of sample uses different type of equipment to grind the sample. For example, jaw crusher, mortar grinder and ball mill can be used to grind a hard and brittle materials. ​.

[Audio] When the sample has been ground, the necessary amount of sample is weighed with the analytical balance. ​.

[Audio] Binding materials can be added to hold the sample together. The optimal binder that homogenize with the sample during grinding and will recrystallize under pressure to bind the sample together. Moreover, the amount of binder added must be in correct ratio to avoid dilution errors.​ ​.

[Audio] Next, the sample is mixed together with the binder. During the mixing process, the binder is homogeneously mixed with the sample to ensure a mechanically stable pressed pellet. The mixing process can be performed manually in a mortar with the pestle or automatically using an electric mixer. ​ An electric mixer is more effective and timesaving The mixing process guarantees the binding material is evenly distributed throughout the entire sample. Thus, the pressed pellet is stable in all areas during the pressing process. ​.

[Audio] After we have done preparing the sample, we proceed with the assembly of the pressing die. First, the pressing die sleeve is placed onto the bottom pressing rod. Then the first support plate is plate is placed into the housing and the sample material is introduced and the second support plate is placed on top. Before placing the support plate, make sure the polished sides face the sample. Finally, the plunger is placed into the die and the entire pressing die is placed into the press and proceed with the pressing process. Other accessories like pellet films can be used to prevent contamination and sticking of pellets onto the pressing die. ​.

[Audio] After placing the pressing die into the press, the press spindle is lowered until it touches the pestle and can no longer be lowered by hand. Then, the pressing process can be started. Pressure is built up during pressing and it can be performed manually using a lever or automatically until the required pressure is reached. Figure shown in the right is the example of software documents used for the pressing procedure. ​.

[Audio] When the pressing process is finished, the die is removed from the press and turn over and set it down. Then carefully lower the spindle by hand until the pressed pellet is pressed out of the die. Suction tool is recommended to be used so that the sample is easily and cleanly remove from the pressing die. ​.

[Audio] With the result from XRF, the composition of the element present in the material is analysed. ​.

[Audio] The example for the sample preparation process is shown in the figure above. ​.

[Audio] In conclusion, pressed pallets can be considered one of the sample preparation methods for XRF because it is cost-effective and convenient. By comparing to other methods such as the loose powder method, it is a reliable sample preparation method that delivers better results with greater consistency as it produces homogeneous samples for XRF analysis. ​.

[Audio] Now let's look into our case study for XRF sample preparation by using pressed pellet. The title for the case study is Fired pressed pellet as a sample preparation technique of choice for an energy dispersive X-ray fluorescence analysis of raw clays, and in this study, they tested 3 types of sample preparation procedures which are the loose powder, pressed pellet, and fired pressed pellet for raw clay and comparing each methods based on the recoveries, limit of detection , limit of quantification and precision.​.

[Audio] From the result obtained, the fired pressed pellet is the most practical and precise approach for sample preparation of raw clays​..

[Audio] Thank you for watching. ​. Duration: 95 min.

References. Scientist Staff, A. A. (2020, January 28). What is XRF (X-ray Fluorescence) and How Does it Work? Ask a Scientist. Retrieved January 24, 2023, from https://www.thermofisher.com/blog/ask-a-scientist/what-is-xrf-x-ray-fluorescence-and-how-does-it-work/ Tomassi . (2019, May 29). The Importance of Pressed Pellets and Pellet Dies in XRF Analysis Sample Preparation . AZoM.com. Retrieved January 24, 2023, from https://www.azom.com/article.aspx?ArticleID=18077 Dave C. (2017). 6 Things to Consider when Making Pressed Pellets for XRF Analysis . Retrieved January 25, 2023, from https://www.armi.com/blog/6-things-to-consider-when-making-pressed-pellets-for-xrf-analysis#:~:text=The%20process%20of%20making%20pressed,of%20between%2015%20and%2035T. Xrfscientific . (2021). How to Prepare Samples for XRF Analysis using a Hydraulic Press . Retrieved January 25, 2023, from https://www.youtube.com/watch?v=ZEEHaH8kum8.