As another measurement method, the AS value of the bulk
powder was measured by using the powder flow analysis kit of
the texture analyzer (Stable Micro Systems Co., Ltd., TA.XT
Plus Texture Analyzer), as shown in Fig. 4(a). The testing
temperature and humidity were fixed at 29 °C and 60% RH,
respectively. Each type of spherical silica powder after or before
the cleaning of the surface-adhered nanoparticles and mica
powder was mixed at 50 wt.% by a blender (Chubu
Corporation, PS-3000S) for 1 min. The mixed powder obtained
was packed in the container of the measuring vessel. The
apparent volume of the packed sample was fixed at 140 ml. A
rotor was introduced into the packed powder sample at a blade
angle of 170° with a rotation speed of 20 rpm and a vertical
velocity of 50 mm/s. When the top of the rotor reached a
distance of 5 mm from the bottom of the container, as part of the
entering process, the rotor was vertically lifted from the powder
layer at a rotation speed of 19 rpm at a blade angle of 178°.