Touch‐free flash sintering with magnetic induction within a reactor activated by the usual flash method

Abstract

We describe a new system for flash sintering where a reactor is built with walls made from dog-bone specimens that are held in Stage III of flash under current control. The reactor is placed within a cylindrical space, like a tube, with axial access, for camera, pyrometer, and optical spectrometer. A free-floating green sample (without electrodes) is placed within; it is physically separated from the walls of the reactor. In the present experiments, the reactor wall as well as the "touch free" workpiece were constituted from yttria-stabilized zirconia. The workpiece is shown to flash, luminesce, and sinter (in a few seconds) when a modest magnetic field is superimposed over the reactor. The final density depends on the strength of the magnetic field, eventually rising to ∼98%. The grain size is highly uniform and nanoscale. Samples of different and arbitrary three-dimensional shapes have been so sintered. We propose that the walls of the reactor, which are in a constant state of flash, may generate an evanescent plasma that becomes concentrated around the center line of the reactor by the applied magnetic field. The plasma field helps to transfer energy from the reactor walls into the green sample. When the magnetic induction is turned on, the conductive load of the reactor walls on the power supply increases proving the presence of an energy transfer mechanism. The question of impedance matching between the walls, the specimen, and the free space in between is outlined.

Reactive flash sintering in a bilayer of zirconia and lanthana: Measurement of the diffusion coefficient in real time

“…Most likely this result is general and probably also occurs in the usual single‐phase flash sintering experiments. This result is particularly relevant to touch free sintering where flash plasmas are forced to migrate into a free‐standing workpiece by magnetic field 23 . In order to obtain self‐similar sintering in three dimensions, it would be necessary for the workpiece to be engulfed in the plasma before it starts to sinter.…”

On the confluence of ultrafast high‐temperature sintering and flash sintering phenomena

“…69 (vi) Flash with magnetic fields: New work shows that the flash energy can be transported from the surface of a reactor into a free-standing workpiece, without electrodes, causing it to flash and sinter. 70 A large investment into this process is needed to sort out the science and application of this method. With it, three-dimensional bodies of arbitrary shapes can be produced.…”

“…Reactive FS has significant commercial potential: Primitive powders of oxides when flashed produce a single‐phase multicomponent phase that is also well sintered, all in a few seconds 69 Flash with magnetic fields : New work shows that the flash energy can be transported from the surface of a reactor into a free‐standing workpiece, without electrodes, causing it to flash and sinter 70 . A large investment into this process is needed to sort out the science and application of this method.…”

Formation of Al2O3–GdAlO3 eutectic ceramics with a fine anisotropic structure in a flash event

“…A uniform mixing of the raw powder may be necessary to avoid the inhomogeneous microstructure of the calcined specimen as shown in Figure 3a. In addition, the use of contactless flash sintering [23][24][25] might be helpful for yielding larger melted area by applying more homogeneous current to the specimen.…”