Densification of Alumina Powder by Using PECS Process with Different Pulse Electric Current Waveforms

Abstract

Densification and sample temperature of alumina (Al2O3) powder during pulsed electric current sintering with different pulse power generators, inverter type and pulsed direct current type were investigated. The sample temperature for inverter generator was higher than that for pulsed direct current generator in same die temperature ranging form 800 to 1400oC. The relative density increased with increasing of the sample temperature.

Pulsed Electric Current Sintering of Transparent Alumina Ceramics

“…The waveform of applied current is probably an important factor to the sintering process of Al 2 O 3 . An effect of two types of pulse current waveforms, inverter and pulsed DC, on sample temperature and densification of Al 2 O 3 powder by using the PECS process has been clarified in [33][34][35]. The magnitude of the voltage peaks increased with an increase of the "OFF" time relative to the "ON" time for all of pulse power generator.…”

“…Temperature difference in Al 2 O 3 sample is generated in PECS [33][34][35]. When PECS of Al 2 O 3 sample with ϕ15 in diameter and 3 mm in thickness was conducted, temperature of sample outside was 20 -30 K higher than that of the inside sample.…”

“…For an insulating material, the applied current does not flow through the sample when a pulse current power is applied to the die-sample, but could only flow from one punch to the other punch via the die. The current forms a magnetic field in the near surface of punches and the die inside where is close to the sample surface, and this magnetic field affects current density [19,[33][34][35][36][37]. The highest current density should be located close to the sample surface as can be illustrated in Figure 2.…”

“…Thus, during the PECS process, the Al 2 O 3 powder must be sintered by the heat transferred from the die inside close to the sample surface and punches by means of heat conduction. Given that heat generation and transfer lead to a temperature distribution, temperature outside is higher than that inside the sample [33][34][35]. In the punch-compression direction, the die temperature is lower than the sample because the punches are in contact with water-cooled jacket and the die is cooled by radiation from the die outer surface.…”

“…This difference suggests that higher temperature could be achieved due to higher applied voltages, and the required energy for heating a sample with an inverter is higher than that with pulsed DC generator [19,[33][34][35][36][37]. The relative density as a function of the outside/inside sample temperature was discussed in [33][34][35][36][37]. These results show a consistent relative density increase trend with an increase in the sample temperature, independent of the applied pulse current waveforms and ON/OFF patterns.…”