Ultrafast-Contactless Flash Sintering using Plasma Electrodes

Abstract

This paper presents a novel derivative of flash sintering, in which contactless flash sintering (CFS) is achieved using plasma electrodes. In this setup, electrical contact with the sample to be sintered is made by two arc plasma electrodes, one on either side, allowing current to pass through the sample. This opens up the possibility of continuous throughput flash sintering. Preheating, a usual precondition for flash sintering, is provided by the arc electrodes which heat the sample to 1400 °C. The best results were produced with pre-compacted samples (bars 1.8 mm thick) of pure B4C (discharge time 2s, current 4A) and SiC:B4C 50 wt% (3s at 6A), which were fully consolidated under a heating rate approaching 20000 °C/min. For the composite a cylindrical volume of 14 mm3 was sintered to full density with limited grain growth.

Review of flash sintering: materials, mechanisms and modelling

“…Several types of furnaces have been used including vertical tubular [37,38], quadrupole lamp [39,40], vertical tubular split [41], a modified box furnace with molybdenum silicide (MoSi 2 ) heating elements [42] and induction heating [43]. Other possible alternatives based on flame heating [44] and arc torch [36] have been also been proposed. It is important to achieve a homogenous sample heating at T Onset , a temperature difference within the sample might result in preferential current flow contributing to inhomogeneous densification.…”

Flash sintering of ceramic materials

“…Alternative approaches are to attach the wires to meshes of platinum wire placed in the same position as the discs [24], to paint the top and bottom surfaces of the discs with conductive paint/paste (often platinum [48], but silver has also been used [49,50]), or to sputter coat each side of the discs with platinum [51]. Finally, Saunders et al [52] have described a flash sintering approach which used arc plasma electrodes rather than any additional material to realise a contactless setup, and successfully fully densified B4C and SiC/B4C composite materials. This technique simplifies the process, but causes considerable heating in the samples which can cause deleterious effects such as excessive grain growth and microstructural inhomogeneities.…”

Growth of SiC platelets using contactless flash technique

“…In the case of 50%wt boron carbide instead, full consolidation was achieved in ³3 s and current at 6 A. 6) As detailed in the experimental procedure, the powder used in the present study is a sinterable grade even in pressureless conditions, however, platelet growth was observed instead of consolidation. Platelet formation was observed at higher currents (26 A) and longer times (33 s) compared to the previous study.…”

“…Platelet formation was observed at higher currents (26 A) and longer times (33 s) compared to the previous study. 6) The results suggest that a higher power density (current), prolonged discharge time and material composition containing limited amount of liquid phase would promote platelet growth induced by the SiC sublimation.…”

“…The tendency of SiC to sublime at high temperature (>2100°C) makes it an ideal material to demonstrate the potential of the newly developed Contactless Flash Technique (CFT) (described in detail in Ref. 6) to produce material consisting of large plate-like SiC particles.…”