**2. Materials and Methods**

#### *2.1. Sample Preparation*

A commercial talc powder with high purity (>99%, XTA-400, KOCH corp., Shenyang, China) was used in this study. The mean particle size of an as-received powder is approximately 12 μm. The sample was mechanically deformed using a high-energy ball mill (Emax, Retsch, Haan, Germany), which generates ultrafine particles by combining impact and shear stress. Wet milling was performed by loading the talc powder, distilled water, and zirconia balls in the volume ratio of 2:3:4 into a 50 mL zirconia (ZrO2) jar. Rotation speed was fixed at 2000 rpm and grinding time varied from 10 to 360 min. The time interval for grinding was selected by considering the trends in particle size and crystallinity of the talc following preliminary experiments. Zirconia balls of various sizes (2, 1, and 0.1 mm) were used. During grinding, the temperature of the milling jar was maintained at approximately 50 ◦C by a water-cooling system.
