Grain growth of camphor as a rock analogue: microstructural development and grain growth law

Abstract

Grain growth experiments were performed on rhombohedral camphor as a rock analogue at 24 °C [i.e., room temperature (RT)] and higher temperatures of 31, 35, 43, and 50 °C. The experiments were very simple compared with those on rocks, which require special apparatuses. The ground sample of camphor was pressed on a glass slide, and a thermometer was set next to the sample. The two-dimensional see-through experiment was performed at RT under a polarizing microscope. The evolving microstructures were clearly observable and showed real-time grain boundary migration by grain growth and the consumption of smaller grains by neighboring larger grains. The result was a consistent increase in grain size from ∼ 10 to ∼ 40 µm in 2 h. The higher-temperature experiments were performed on a hot plate. A glass slide and a weight that had been preheated on the hot plate were placed on top of the glass slide that contained the pressed sample and thermometer. The increase in grain size was controlled by increasing the temperature, with the temperature being held for the same durations. The grain size data in the case of grain growth were analyzed with the grain growth law of dⁿ − d₀ⁿ = k₀ exp(−Q/RT)t, where d (µm) is the grain size at time t (s), d₀ (µm) is the initial grain size, n is the grain growth exponent, k₀ (µmⁿ/s) is a constant, Q (kJ/mol) is the activation energy, R is the gas constant, and T is the temperature in Kelvin. The determined parameters were n = 3.7 ± 0.2, k₀ = 10^−12.7±0.1, and Q = 60.4 ± 6.1.