Voltage-Current Characteristics of Sintered Compacts of Flaky Aluminum Powder

Abstract

According to a hypothesis of the mechanism for varistor characteristics of semiconductor ZnO-base ceramics, i.e., current can easily flow only at high voltage through intergranular thin layers which are formed by the addition of Bi₂O₃ with high electrical resistivity (ρ), it was expected that non-linear voltage (V)-current (I) characteristics can appear in conductor Al powder sintered compacts, along grain boundaries of which thin layers of Al₂O₃ with high ρ are arranged. In this study, flaky Al powder (2.69 mass%O) compacts with the size of φ10 mm×t1∼4 mm and with the relative density of 85% were sintered at 673 K for 3.6 ks in vacuum and their V−I characteristics were measured in the range of 10⁻⁶∼2×10³ V.
The results obtained are as follows: The current at low voltage was less than 10⁻⁷ A, i.e., the electrical resistivity of the compacts was very high (ρ >5×10⁶ Ω·m), and the current non-linearly sharply increased up to 10∼10³ A over a critical voltage (breakdown voltage, V_B) of 50∼130 V, although a breakdown of air accompanied. However, the compacts became in general nearly ohmic conductor (ρ=10⁻³∼10⁻¹ Ω·m) and V_B disappeared, once the voltage higher than V_B was applied. Namely, the flaky Al powder sintered compacts were clarified to have a unique V−I characteristics which is initially non-linear, and then becomes nearly ohmic after one application of high voltage.