Active Magnetic Regeneration - Magnetocaloric Energy Conversion: From Theory to Applications - page 154

Those methods enable the fabrication of parallel-plate AMRs or even some more
advanced geometries. The largest effort in this eld was placed on La-based (La -

-

Fe MnO 3 ) mag-

netocaloric materials, which in addition to Gd and some of its alloys show the greatest
potential for application in a magnetic refrigerator in the near future. The most
promising fabrication methods are brie

Co Si) and perovskite-type manganese oxides-based (La Ca Sr

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y presented below.
Katter et al. [ 134 ] proposed a process termed thermally induced decomposition
and recombination (TDR) for the fabrication of an AMR with La

fl

Si alloys.
Fully dense, bulk samples of La(Fe,Co,Si) 13 were initially prepared by the reactive
sintering of powder mixtures. Due to the high thermal expansion and low bending
strength, the conventional machining caused cracks in the material, which prevents its
machining to a

Fe Co

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ne element suitable for use in an AMR. After a heat treatment at
about 1073 K the material is in the decomposed (magnetocalorically passive) state,
and the material possesses enhanced mechanical properties (low thermal expansion)
and is easier to machine. Then, after the material has been machined (using EDM
cutting) in the decomposed state, it is recombined back into the magnetocalorically
active state (recombination heat treatment at about 1323 K) and its magnetocaloric
properties are fully recovered. This technique enables the production of relatively

ne
magnetocaloric elements suitable for use in an AMR. Figure 4.37 shows the AMR
part produced by the wire EDM cutting of an initial block of magnetocaloric material
using the TDR technique. The block was produced by Vacuumschmelze [ 31 , 135 ].
In 2013, Moore et al. [ 136 ] proposed a selective laser melting (SLM) method for
the production of a more sophisticated AMR geometry (compared to most widely
applied, packed-bed and parallel-plate geometries). SLM is a rapid prototyping
technique to form a variety of three-dimensional shapes. The same technique was
applied already by Tura et al. [ 137 ] using bronze powder to produce passive
regenerators with small (0.7 s geome-

tries. However, Moore et al. [ 136 ] used La(Fe,Co,Si) 13 as a starting powder and
produced two types of AMRs: a wavy-channel block and the block of an arrays of

× 0.7 mm) channels suitable for the AMR '

rst had a channel diameter of 0.8 mm, a high surface-
to-volume ratio and excellent thermohydraulic properties [ 138 , 139 ], while the

n-shaped rods. The

Fig. 4.37 A photograph of a La Si AMR part produced by wire EDM cutting using the

TDR technique. The plate thickness is 0.5 mm and the spacing is 0.2 mm. The AMR was
manufactured by the German company Vacuumschmelze

Fe Co

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