Initial Stages of Sintering of Alumina by Thermo‐Optical Measurements

Abstract

The behavior of nanostructured and submicrometer α‐Al2O3 powders during the initial stages of field‐assisted sintering technique (FAST), conventional, and microwave sintering was investigated using the laser‐flash technique for thermo‐optical measurements (TOM). An enhanced neck formation due to surface diffusion at very early stages of sintering was found in FAST samples. No significant difference due to heating rate has been found in these various samples.

Current Isolation in Spark Plasma Sintering of Conductive and Nonconductive Ceramics

“…The objective of this paper is to highlight observations of Al 2 O 3 in the SPS using direct (current passes through the sample) and indirect heating (current passes through the die). Al 2 O 3 is a suitable test material as there is a plethora of work describing SPS processing of Al 2 O 3 with which to compare our findings 1–4,6,8,11–13 …”

“…SPS is heralded for its promise in retaining nanostructural features, producing grain boundaries devoid of impurities, densifying refractory materials, producing layered or composite structures as well as many other benefits. The short processing times make SPS desirable over conventional sintering methods such as hot pressing, pressureless sintering, and hot isostatic sintering 1–5 . However, the mechanism is not fully agreed upon.…”

“…The short processing times make SPS desirable over conventional sintering methods such as hot pressing, pressureless sintering, and hot isostatic sintering. [1][2][3][4][5] However, the mechanism is not fully agreed upon.…”

Low Temperature Sintering of Nanocrystalline Zinc Oxide: Effect of Heating Rate Achieved by Field Assisted Sintering/Spark Plasma Sintering

“…For example, uncontrolled heating rate before pyrometer control in FAST has proven to be efficient in enhancing the sinterability of ultrafine powders. This rapid temperature overshoot of up to about 600°C leads to a higher total interparticle contact area in the partially sintered samples, characterized by higher Young's modulus or thermal diffusivity measured by the laser flash method . Using the concept of the Master Sintering Curve it is possible to show that for heating rates up to 150°C/min the densification mechanism is not changed for alumina and fully stabilized zirconia .…”

“…This rapid temperature overshoot of up to about 600°C leads to a higher total interparticle contact area in the partially sintered samples, characterized by higher Young's modulus or thermal diffusivity measured by the laser flash method. 17,19,21 Using the concept of the Master Sintering Curve it is possible to show that for heating rates up to 150°C/min the densification mechanism is not changed for alumina and fully stabilized zirconia. 22 This means that densification curves obtained by FAST show the same behavior as that observed under free sintering conditions and much lower heating rates.…”