*2.5. Powder Hygroscopicity*

Dry glass weighing bottles (outside diameter 50 mm, height 25 mm) were placed in a dryer with ammonium chloride saturated solution at 25 ◦C ± 1 ◦C and weighed (m1) after 24 h of storage. Then, about 100 mg samples were put into the bottles and weighed accurately (m2), respectively. After storage at the aforementioned conditions with the caps opened for 24 h, each sample was weighed again (m3). The hygroscopicity could be calculated by the following equation.

$$\text{Mass Charge (\%)} = (\text{m3} - \text{m1}) \, / \, (\text{m2} - \text{m1}) \times 100\%.$$
