Award Date

12-1-2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Pamela C. Burnley

Second Committee Member

Elisabeth M. Hausrath

Third Committee Member

Shichun Huang

Fourth Committee Member

Paul Forster

Number of Pages

83

Abstract

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.

Keywords

compressibility; phase equilibria; thermal analysis

Disciplines

Geology

Language

English


Included in

Geology Commons

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