Measurement and modelling of electrical resistivity by four-terminal method during flash sintering of 3YSZ

Abstract

Flash sintering is a newly developed technique to quickly densify conductive ceramics in the presence of an electric field. At a critical combination of field and temperature, densification takes place in a few seconds. This paper investigates the electrical resistivity during flash sintering of 3YSZ by the four-terminal method in combination with numerical modelling of electrical heating and temperature distributions. Densification rates were similar to those observed previously in specimens rapidly heated by methods not involving direct electrical heating. Temperature gradients caused by heat loss from the surface and non-uniform electrical heating led to differential sintering, specimen distortion and non-uniform grain size. The four point measurements revealed significant contact resistance at the power supply electrodes and allowed accurate measurement of the resistivity under the high current conditions of flash sintering. The specimen resistivity was lower for a given temperature under high current conditions and this was attributed to electronic conduction. Concurrent sintering led to a progressive reduction of resistivity during heating causing an increase in the apparent activation energy for electrical conduction. When the effect of sintering on resistivity was accounted for, the onset conditions for the "flash event" were accurately predicted on the basis of thermal runaway.

Modelling the particle contact influence on the Joule heating and temperature distribution during FLASH sintering

“…Grasso et al [25] have shown through the use of computational modelling, that the macroscopic temperature distribution in a YSZ dog-bone shape is uniform within the gauge section but heterogeneous in the electrode contacting areas. In contrast with Grasso's work, M. Yoshida and co-workers found that dog-bone-like specimens present an non-homogeneous macroscopic distribution of current density, power dissipation and temperature during stage III of FLASH [26].…”

Induced p‐type semiconductivity in yttria‐stabilized zirconia

“…The mechanisms that occur during flash are still under debate, although certainly, samples show a dramatic increase of both temperature and conductivity during the flash event and less dramatically, in a premonitory period before the onset of flash. The increase in conductivity is electronic in nature and the associated increase in sample temperature is attributed to Joule heating . What is unclear is whether additional changes in intrinsic properties of the material occur in response to the bias, leading to an enhanced Joule heating effect, rapid sintering, and associated luminescence; however, there continues to be a debate as to whether electroluminescence occurs or whether the observed luminescence is caused by black‐body radiation …”

“…The increase in conductivity is electronic in nature and the associated increase in sample temperature is attributed to Joule heating. 19,[23][24][25][26][27] What is unclear is whether additional changes in intrinsic properties of the material occur in response to the bias, leading to an enhanced Joule heating effect, rapid sintering, and associated luminescence; however, there continues to be a debate as to whether electroluminescence occurs 28 or whether the observed luminescence is caused by black-body radiation. 29 The aim of the present work was to investigate further the effect of both atmosphere and a small dc bias, simultaneously, on the electrical properties of 8YSZ.…”

Electrical Conductivity Behavior of the Aluminum Alloy 2024 during Artificial Aging

“…Aluminum manufacturers for the aeronautical industry have invested in technology in order to make their product more competitive in the market compared to composite materials by improving the properties of aluminum and the quality of its production [1][2][3]. Al-Cu alloys of the 2000 series have their application in aircraft structures, mainly in the wings, as they present the excellent mechanical resistance obtained by heat treatment accompanied by good toughness [4][5][6].…”

“…The analysis of electrical conductivity was performed in real time using the four-terminal method during the heat treatment process and a correlation between hardness and aging times was stablished. This method is used in electronics to analyze the electrical resistivity of metallic materials [7][8][9], but it is little explored to monitor the behavior of electrical conductivity during artificial aging. During the monitoring and characterization of the 2024 alloy, analyses of hardness, electrical conductivity and material image were performed from samples as received, solubilized at 495 °C for 3 h, and with artificial aging treatment.…”