Influence of pulse current during Spark Plasma Sintering evidenced on reactive alumina–hematite powders

Hardness and friction behavior of bulk CoAl2O4 and Co–Al2O3 composite layers formed during Spark Plasma Sintering of CoAl2O4 powders

“…Applying the pressure early in the cycle at low temperature (US4 and US5) may favor the closing of porosity, which would decrease the possibility of O 2 and/or CO 2 leaving the sample, before the formation of Co by reaction (2) and/or (3) is thermally activated. The reaction zone and thus the composite layer are thinner, as observed in a previous study on the formation of Fe-Al 2 O 3 layers [9]. This also reveals that the relationships between transformation and densification are quite complex, because each one is able to hamper the other.…”

“…Specimen US6 was consolidated in conditions similar to that used for US2 (9). Specimen US7 and COMS2 were consolidated in conditions similar to that used for US4, except that the dwell time was doubled (6 min).…”

“…For the surface of the specimens, or even the bulk of the sample from the more reactive powder (CA), the aluminum-rich spinel becomes unstable and the precipitation proceeds with the formation of aAl 2 O 3 along with more Co particles. Note that reduction processes as described by reactions (3) and (4) cannot be ruled out, although reaction (4) is considered, from the analysis of earlier results [9], to be quite unlikely except for the extreme topmost surface of the sample:…”

“…The preparation of metalAl 2 O 3 composites usually involves firstly the synthesis of a metal-Al 2 O 3 composite powder and then its consolidation by hot-pressing or Spark Plasma Sintering (SPS). However, it was shown that materials with a Fe-Al 2 O 3 or Fe/Cr-Al 2 O 3 composite layer at the surface could be directly prepared by SPS of a powder of a reactive oxide solid solution (a-Al 1.86 Fe 0.14 O 3 or a-Al 2À2x (Fe 0.8 Cr 0.2 ) 2x O 3 , respectively) [5,8,9]. The core of the material is made up of the spinel FeAl 2 O 4 and Al 2 O 3 (and the surface may contain FeAl 2 O 4 too depending on the experimental conditions).…”

Microstructure and Thermoelectric Properties of Bulk Cobalt Antimonide (CoSb3) Skutterudites Obtained by Pulse Plasma Sintering

“…Both methods, i.e., PPS and SPS, use electric current as a direct source of heat, generated in the graphite punches, die, and sintered powder by the Joule effect. Despite the ongoing debate regarding whether plasma is induced during SPS consolidation, 17 both methods offer certain advantages over conventional sintering techniques (e.g., hot pressing), including: 18 (a) faster heating rate, (b) shorter annealing time, and (c) enhanced diffusion in the electric field. A comparison of the basic parameters of PPS and SPS is presented in Table I.…”