Determination of the Effect of Temperature on Potassium Aluminum Sulfate

Authors:

• Students:
  • Karishma Bhatara
  • Raisa Clare David
  • Allison Jenner
  • Judith Koukol
• Teachers:
  • Valerie Rickert
• Mentors:
  • Tieyan Chang (University of Chicago, ChemMatCARS)
  • Yu-Sheng Chen (University of Chicago, ChemMatCARS)

Advanced Photon Source Sector 15: ChemMatCARS

Potassium aluminum sulfate, (AlK(SO₄)₂*12H₂O), is an inorganic salt produced in the dodecahydrate form [11]. Potassium aluminum sulfate has an octahedral crystalline shape caused by the formation of its crystal lattice through its cations (K⁺ and Al³⁺) and anions (SO₄^2-). Using the APS, the crystalline system was determined to be cubic, with a space group of Pa-3. Temperature studies (250 K to 100 K) were performed to determine the effect of temperature on the bond length and volume of the ions in the unit cell. It was determined that as the temperature increased, the bond length and volume also increased in a linear model. Study of the effect of cation replacement on this compound has been limited. A tertiary purpose of this study was to determine if cation replacement of the Al³⁺ by other 3+ cations, specifically Cr³⁺, results in different crystalline structures. In potassium aluminum sulfate, the aluminum was replaced with chromium (3+), and the possible changes in the structure, symmetry, and space group was attempted. The chromium 3+ cation is in period 4 of the periodic table, whereas aluminum is in period 3, suggesting the structure of the potassium aluminum crystal would change because of the different sizes of the cations. Potassium chromium sulfate has a hexagonal structure [3], differing from its cation partner potassium aluminum sulfate. The Sector 15 NSF’s ChemMatCARS at Advanced Photon Source (APS) has played an important role in recent scientific advancements, and the Advanced Crystallography Program can illuminate small crystal samples to determine the crystal structure at atomic resolution level. Due to difficulties in the synthesis of the potassium chromium sulfate, the effect on the structural changes due to the change in cation was not determined. In this poster, only (AlK(SO₄)₂*12H₂O) data have been presented. In addition, a temperature study (250 K to 100 K) was performed to understand the linear thermal expansion phenomenon in the crystalline.

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