Electromagnetic radio frequency heating in the pulsed electric current sintering (PECS) process
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Electromagnetic radio frequency heating in the pulsed electric current sintering (PECS) process Yufei Liu and D. H. Liebenberg, Clemson University, 118 Kinard Hall, Clemson, SC 29634, USA Address all correspondence to D. H. Liebenberg at [email protected] (Received 18 April 2017; accepted 19 May 2017)
Abstract Pulsed electric current sintering offers rapid sintering of many materials compared with hot press sintering. Earlier studies had demonstrated that neither sparks nor plasma formation occur in a typical apparatus such as Dr. Sinter™. Hitchcock et al. showed that electromagnetic radio frequency (rf) emission occurred during the pulsing current and suggested this emission was a relevant augmentation to the hot press sintering in addition to the current flow in the specimen. In this report the importance of rf emission in the sintering process is demonstrated and opportunities to further exploit this approach to improve the sintering process are suggested.
Introduction Pulsed electric current sintering (PECS) as developed in the Dr. Sinter™ apparatus (Dr. Sinter™ SPS-515S made by Fuji Electronic Industrial Co. 6-2-22 Fujimi Tsurugashima, Saitama 350-2201, Japan.) has demonstrated faster and higher compaction of sintered specimens compared with the hot press technique. In part, this improvement is due to pulsed current flow through the specimen providing in-specimen Joule heating and also to what has been called spark plasma sintering (SPS). However, SPS in the Dr. Sinter™ has been demonstrated[1,2] to exhibit neither sparks nor plasma. In Ref. 2 the electromagnetic emission at radio frequencies (rf) of 10 to 160 kHz was observed and suggested to be an additional difference to the hot press sintering technique. These two techniques are generally applicable to smaller specimens and microwave sintering has been developed for heating and sintering with electromagnetic radiation at tHz frequencies for larger samples.[3] Thus PECS represents an intermediate step between hot pressing and microwave sintering. This report extends the rf emission frequency measurement to above 600 kHz although the peak in the emission is 12 kHz or lower. To examine the influence of the electromagnetic radiation on the sintering process a technique is presented to limit the current through the specimen while providing the electromagnetic radiation to envelop the specimen. The electromagnetic radiation importance to the PECS process is demonstrated.
value P = 10E(dBM/10) mW.)[2] spectrum analyzer was used together with the thermocouple antenna (TCa) (The thermocouple antenna was previously demonstrated (see Ref. 1) to detect sparks from a small arc welder. The TCa was used outside the vacuum to detect FM radio signals to 100 MHz including measurement to 1 GHz with the Tektronix MDO4104B-6 instrument.) located inside the Dr. Sinter™ vacuum chamber and external to the die as seen in Fig. 1. The frequency range was expanded from the 10 kHz lower limit of the analyzer to 2 MHz. Figure 2(a) (lower panel) shows the signal fades in
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