In this lab, students will use solid-state methods to synthesize cobalt and chromium spinels, ZnCr2O4, ZnCo2O4, CoAl2O4, and CoCr2O4. They will (1) characterize their structure with X-ray powder diffraction (XRD) and (2) characterize the color using UV-Vis diffuse reflectance spectroscopy.
|The Synthesis and Characterization of Cobalt Spinels.docx||1.2 MB|
|XRD index supplement.docx||104.84 KB|
Upon completing this lab, students will:
- Know how to synthesize polycrystalline materials using solid state synthesis techniques.
- Gain experience preparing solid samples for diffraction analysis and collecting XRD data.
- Be able to index XRD patterns from cubic materials to determine unit cell parameters.
- Relate reflectance spectra to the visible colors of materials.
Mortars and pestles (agate or porcelain)
Crucibles (alumina or porcelain)
High temperature furnace (1000˚C)
Powder X-ray diffractometer
UV-Vis spectrometer equipped to do diffuse reflectance
This lab is the first lab in an upper level inorganic laboratory course. It is completed first, because the students must weigh out reagents and grind them in a mortar and pestle and then heat them for 8 hours at 1000˚C. The synthesis does not take a full lab period, which allows time for the first-day housekeeping items to be distributed and discussed. During the second lab period, student samples are returned and the students collect their XRD data and UV-Vis data. There is enough time for students to begin working through the analysis in class.
Note: This lab lends itself to many adaptations.
- If there is no XRD access readily available for students, patterns may be provided so that students can index these, even if they have not collected the data.
- The electronic transitions of these compounds may be analyzed with more detail (ie. assigning transitions).
- Magnetic measurements may be made and the number of unpaired electrons deduced (this is Exp 3 that is referred to in the attached lab document).
Students complete pre- and post-lab questions; these are within the document. Upon completion of the lab, the student is to write a lab report. A lab report is written in a format similar to that of a paper submitted for publication. Sections include the title & authors, abstract, introduction, experimental, results, discussion, conclusion and references.
The average score for the prelab assignements was 65% with a high of 100% and a low of 35%. The average score for lab reports was 92% with a high of 100% and a low of 71%.
Students were able to index the patterns using the supplement (attached) as a guide.