Master of Science (MS)
First Committee Member
Pamela C. Burnley
Second Committee Member
Elisabeth M. Hausrath
Third Committee Member
Fourth Committee Member
Number of Pages
Understanding basic material properties of rare earth element (REE) bearing minerals such as the temperatures and pressures at which different phases are thermodynamically stable and how they respond to changes in temperature and pressure can assist in understanding how economically viable deposits might form, thereby potentially leading to the discovery of new deposits. Bastnaesite is the most common REE bearing mineral mined. The lanthanum-fluoride end member, bastnaesite-(La), was synthesized. Synthetic bastnaesite-(La) and lanthanum oxyfluoride was investigated using thermal analysis at ambient pressure and high temperature through the methods of thermogravimetric analysis, differential scanning calorimetry, and heated stage powder X-ray diffraction. Bastnaesite-(La)’s thermodynamic behavior from ambient pressure to 11.3 GPa at ambient temperature and from 4.9 to 7.7 GPa up to 400°C temperature was investigated through in-situ single crystal X-ray diffraction in diamond anvil cells. Bastnaesite-(La)’s decomposition reaction to lanthanum oxyfluoride and CO2 was investigated from ambient pressure to 1.2 GPa and temperatures up to 900°C was investigated in an oven and in a Griggs modified piston cylinder apparatus. A phase diagram illustrating this region of pressure and temperature space was constructed. High temperature X-ray diffraction data were used to fit the Fei thermal equation of state and the thermal expansion coefficient α298 for all three materials. Bastnaesite-(La) was fit from 25°C to 450°C (298 K to 723 K) with V0 = 439.82 Å, α298=4.32×10-5 K-1, a0 = -1.68×10-5 K-1, a1 = 8.34×10-8 K-1, and a2 = 3.126 K-1. Tetragonal γ-LaOF was fit from 450°C to 675°C (723 K to 948 K) with V0 = 96.51 Å, α298 = 2.95×10-4 K-1, a0 = -2.41×10-5 K-1, a1 = 2.42×10-7 K-1, and a2 = 41.147 K-1. Cubic α-LaOF was fit from 674°C to 850°C (973 K to 1123 K) with V0 = 190.71 Å, α298 = -1.12×10-5 K-1, a0 = 2.36×10-4 K-1, a1 = -1.73×10-7 K-1, and a2 = -17.362 K-1. At ambient temperature, a 3rd-order Birch-Murnaghan equation of state was fit for bastnaesite-(La) with Vo = 439.82 Å3, Ko = 105 GPa, and K’ =5.58.
compressibility; phase equilibria; thermal analysis
University of Nevada, Las Vegas
Rowland, Richard Lee, "Phase equilibria, compressibility, and thermal analysis of bastnaesite-(La)" (2017). UNLV Theses, Dissertations, Professional Papers, and Capstones. 3164.
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