Nickel Arsenide

This project was submitted for the Spring 2019 3D Printing and Design Competition. Participants were asked to respond to the following prompt: “We want to know how you created your project, what inspired you, what you learned along the way, and where it might lead you. In short we want you to tell us the story behind the project and reflect on the process.”

Response:

In a display case, on the second floor of the Clement Chemistry Building at Trinity College, are a number of hand-made models of ionic compounds. Ionic compounds form crystals, which consist of many alternating positive and negative ions bonded together in a matrix. These original models were made out of cardboard paper and were glued together in the mid-1970’s; as a result, they have begun to deteriorate with time. Professor Parr, our Inorganic Chemistry professor, developed the idea to re-create these model structures with the modern technology of our era: 3D printers. The model we re-created using the 3D printers was the crystal structure of Nickel Arsenide (NiAs). NiAs has a common structural arrangement shared by many sulfides of the transition metals. The octahedron orientation of this structure visually depicts the tetrahedral vacancies. This structure has a hexagonal close packing of arsenic anions (As3-) with all the octahedral holes occupied by nickel cations (Ni2+). This hexagonal close packing structure consists of a repeat of two layers, which can be referred to as layers A and B. Layer A was printed in green, while layer B was printed in white to distinguish between the two. For those who are not familiar with the arrangement of crystal structures on an ionic level, it is important to note that the structural properties mentioned above provide important information about the way a given ion interacts with other ions.

This was our first time ever using SketchUp and the 3D printers, so it was exciting to see our concept come to life. However, the process of creating our full model was not the easiest. First, we created our octahedron shape in SketchUp from scratch (we had not realized that there were programs with shapes that could just be downloaded and inserted into the program). Then, it took several tries to get the sizing/dimensions of the octahedron correct because the MakerBot printing program would automatically resize the octahedron made in SketchUp. However, once the dimensions were figured out and established, we had to print out a total of 34 octahedrons. The total printing time for this project was over 36 hours. Once all of the pieces were printed, we had to hand-glue each octahedron piece together to assemble the entire crystal structure of Nickel Arsenide. Overall, this project was time-consuming but was very much worth it. Our structure will now be a part of a new generation of models to be included in the display case in the chemistry building to help educate other students about crystal structures for many years to come.” Created by Brianna Crawley and Sarah Donahue

David Tatem