4.4. Electrostatic Measurements

Triboelectrification of glass beads was measured using a capacitive probe method as reported previously.⁵⁰ Briefly, glass beads were stored in a conductive-grounded container under controlled environmental conditions (25 °C, 30–35% RH) for a minimum of 18 h before measurement. A U-shaped stainless steel spatula was used to charge and load particles into the measuring pan, as illustrated in Figure ​Figure88. The spatula was tilted at an angle of approximately 45°, placed directly above the measuring pan, and between 10 and 30 mg of the sample was loaded at a time. Charge decay was measured at 25 °C and three different humidity levels: 20% RH, 50% RH, and 75% RH. The mass of sample used was recorded. At least six repeats were performed for each sample under each selected condition.

Schematic of the tribocharging method used.

Glass beads were characterized for electrostatic properties using a charge decay time analyzer (JCI155 v6, Chilworth Technology Ltd. Southampton, UK). Samples were equilibrated under target conditions for a minimum of 18 h before measurement. Glass beads (2 g) were placed in the sample holder to form an even layer. Both a negative and a positive corona discharge of 8.0 kV were applied separately to the sample for a duration of 0.02 s. The data analysis was commenced at 0.07 s after the corona discharge, and the rate of charge decay was measured until 10% of the initial charge was reached. Four measurements were taken for each sample at 25 °C and three different humidity levels—25% RH, 50% RH, and 75% RH—in a temperature- and humidity-controlled cabinet (Safetech, Climatezone, Hampshire, UK).