Analysis of microstructure of two-component powder compact by electrical conductivity measurement (Part 2)

Particle connection in two-component powder compact was quantitatively evaluated by electrical conductivity measurement. As a model system, an Al 2 O 3 powder (median size 0.33 μm or 0.51 μm, insulator) was mixed with an indium tin oxide powder (ITO, 90 mass% In 2 O 3 -10 mass% SnO 2 , median size 0.20 μm, electronic conductor) in aqueous solutions with and without polyacrylic acid (dispersant) at pH 3.3-10.0. The packing density of the powder compacts consolidated by filtration depended on the pH of the suspension, the size of Al 2 O 3 particles and the volume fraction of ITO. The above green density was well simulated using the fractional collision frequency and packing density of Al 2 O 3 -Al 2 O 3 , Al 2 O 3 -ITO and ITO-ITO clusters in the powder compact. A continuous connection of ITO particles in the consolidated green compact formed at 25 vol% ITO fraction in both the powder compacts with 0.33μm- and 0.51μm-Al 2 O 3 median size, respectively. On the other hand, particle connection of ITO-ITO formed at 95% relative density for 20 vol% ITO fraction after the sintering at 1400°C. At 10 vol% ITO fraction, no ITO-ITO connection was formed in the dense compact with a relative density above 95%. The conduction path in the green and sintered compacts was formed at Df=0.15 (D: relative density of the compact, f: ITO volume fraction), which corresponded to 0.66 cm of the critical length of connecting ITO particles in a 1 cm-cube of the compact. It is possible to interpret that one string of connecting ITO particles is in contact three-dimensionally with another string to make the conduction path.