Efficient Detection of Low-Content Diamond Crystals in Sand via X-ray Powder Diffraction: A Guided-Inquiry Instrumental Analysis Laboratory Experiment

Abstract

X-ray powder diffraction (XRPD) is a highly significant analytical method for the identification of crystalline phases in powder and solid samples. In this study, we introduced XRPD analysis into a guided-inquiry laboratory experiment for students to identify large-sized, low-content diamond crystals present in sand. This task presents a significant challenge for conventional XRPD phase analysis because when the grains in the specimen are both excessively large and very few, some reflections in the XRPD pattern may be anomalously intense or absent. Under the instructor’s guidance, the students endeavored to establish a method (rocking scanning) to assess the presence of low-content diamond crystals. In this creative work, a thorough rocking scan of the (111), (220), and (311) planes revealed the presence of low-content diamonds in the sand. Additionally, the students prepared standard mixture samples using commercial diamond powder to establish the detection limit of diamond crystals under the current conditions. The rocking-scan method simplifies the identification of large, low-content crystals in mixed-phase systems, typically requiring sophisticated equipment and techniques. Therefore, this experiment can be likened to a treasure-seeking activity in the sand. The experiment provided experience with a new analytical method that demanded considerations and analysis not common to the other methods discussed in the course. Students were motivated by the opportunity to design their own projects and by the real-world potential implications of their findings. Through this project, the instructors gained experience in applying XRPD analytical techniques in the field and in the classroom. The students likewise benefited as they gained a deep understanding of fundamental concepts of XRPD. Moreover, the utility of the guided-inquiry laboratory experiment considerably motivates students, enhances student learning, and improves student critical-thinking and problem-solving ability, according to the results of a student survey.