Active Magnetic Regeneration - Magnetocaloric Energy Conversion: From Theory to Applications - page 155

second had n-like rod diameters of about 1 mm and a spacing between them of

0.2 mm.
Even smaller dimensions of magnetocaloric elements and

uid channels (down
to 0.1 mm) are possible using the SLM technique with different starting powders.
Since La(Fe,Co,Si) 13 is brittle and has irregular shaped particles a larger starting
powder must be used (50

fl

m). It was shown that spherical particles of a few
microns in diameter would be the best choice in this regard. However, the produced
AMRs were annealed at 1,323 K for several days and further tested for their
magnetocaloric properties and cycling stability. They concluded that the adiabatic
temperature change, especially around its Curie temperature, was somewhat
reduced due to the smaller amount of 1:13 phase present (the ratio between La and
other materials). The AMRs were tested according to their cyclic stability. There-
fore, a magnetization and demagnetization with cycling frequencies of 4 Hz for 106
cycles was performed. No degradation of the magnetocaloric effect occurred during
the cycling, which makes it promising candidate for future applications in a mag-
netic refrigerator.
Tape casting is a promising method for producing thin and

80 ʼ

-

fl at plates made of

magnetocaloric materials, as recently shown for La SrMnO 3 (LCSM) per-

ovskites. As explained in Bahl et al. [ 140 ], the powders of LCSM material were
suspended in slurry with additional azeotropic additives. Using a so-called doctor
blade to control the thickness (in this case 0.3 mm), the slurries were applied from a
vessel onto a moving substrate. The resulting tapes were further sintered at 1,473 K
for 4 h. The produced plates were subsequently assembled into an AMR by using a
gluing technique (see Fig. 4.35 b) and applied in a magnetic refrigerator [ 140 , 141 ].
The tape-casting technique can also be successfully applied for making layered
(graded) magnetocaloric plates (and further layered AMRs) by using several
powders (slurries) with different Curie temperatures side by side (see [ 142 ] for
details).
Pryds et al. [ 143 ] applied a thermoplastic extrusion process to fabricate a
monolithic squared channel (honeycomb) AMR with LCSM perovskites. The
LCSM powder was mixed with stearic acid and thermoplastic (polyethylene) bin-
der. The slurry was than extruded into a honeycomb structure (AMR) with a wall
thickness of 0.5 mm and a channel thickness of 1 mm. The monolith was further
sintered to remove the binder, which causes a reduction in the speci

- Ca -

c heat and an
increase in the adiabatic temperature change. The fabricated regenerator was also
tested in a passive regenerator experiment showing similar performance to a par-
allel-plate regenerator with the same porosity. As explained by the authors [ 143 ],
the main advantages of such a fabrication method (compared to parallel-plate
regenerators) are mainly the low cost, the low time consumption and the structural
(stable thin-wall structure) bene ts, which can be produced by a one-step pro-

cessing technique.
In Pulko et al. [ 144 ] epoxy-bonded magnetocaloric plates and then the AMR
were evaluated with the goal of fabricating an AMR with thinner plates and a
smaller spacing compared to the state-of-the-art sintered AMR (produced by TDR
method). As magnetocaloric material LaFe 13 − x − y Co x Si y powder (130 ʼ m) was used.