*3.2.5 Composite finned foams*

Loading of new phases is achieved by building an assembly consisting of packed or self-standing porous leachable preforms alternated with packed beds of the new phases in finely divided form (inclusions). After infiltration and removal of the leachable materials, a final material with a layered distribution of components and continuous matrix is obtained (**Figure 6**).

### **Figure 5.**

*Schematic drawings showing a mold with preexistent self-standing porous leachable preforms (a) and the structure of the final material (b) for monolithic finned foams.*

### **Figure 6.**

*Schematic drawings showing an assembly consisting of packed or self-standing porous leachable preforms alternated with packed beds of finely divided inclusions (a) and the structure of the final material (b) for composite finned foams.*

**9**

**Figure 7.**

*Reproduced with permission from [8].*

*Open-Pore Foams Modified by Incorporation of New Phases: Multiphase Foams for Thermal…*

**4.1 Composite foams/foams with guest phases with preload of new phases in the** 

Open-pore magnesium foams, which have traditionally been discarded for active thermal management due to their low thermal conductivity values, can be appropriate for heat dissipation applications if they incorporate thermal inclusions such as diamond particles coated with a TiC layer of nanometric dimensions. These multiphase open-pore composite foams can be manufactured by the replication method following a strict processing control. First, a correct distribution of the preform components (NaCl and diamond particles) has to be achieved to ensure homogeneity and complete connectivity of the pores after dissolution. For this purpose, the selection of the composition of bimodal particle mixtures has been studied in detail following a predictive method described in [8, 34–37]. The results of these calculations are depicted in **Figure 7a** for the entire spectrum of NaCl particle fraction in the bimodal mixtures. The complete pore connectivity is achieved when the composition of NaCl in the bimodal (NaCl-diamond) mixture falls in the region of interest represented in **Figure 7a**. In this region the large NaCl particles are touching each other, and the smaller diamond particles are filling the voids left by

Another critical processing step is the proper control of TiC coating on diamond particles, which allows for high thermal conductance at the interface between the diamond particles and the matrix. The scanning electron microscopy (SEM) images in **Figure 8** illustrate some microstructural features of Mg/diamond composite foam. **Figure 8a** shows the diamond particles homogeneously distributed in the struts of the Mg matrix. **Figure 8b** depicts Si and Fe precipitates on diamond surfaces. During the metal solidification, traces of Si and Fe present in the nominal composition of magnesium segregate toward the interface, enhancing together with the TiC coating the magnesium-diamond interfacial thermal

*Contour diagram of the total volume fraction of inclusions (considering diamond and salt particles mixtures) over the whole range of NaCl particle fraction (XNaCl) as a function of R (ratio of the diameters of coarse NaCl particles to small diamond particles) (a); (b) is a magnification of the region of interest show in (a).* 

**4. Multiphase open-pore foams: examples and properties**

*DOI: http://dx.doi.org/10.5772/intechopen.88977*

*4.1.1 Magnesium/diamond composite foams*

the sodium chloride particles.

conductance.

**preform**
