Thermal conductivity of porous materials

Incorporation of porosity into a monolithic material decreases the effective thermal conductivity. Porous ceramics were prepared by different methods to achieve pore volume fractions from 4 to 95%. A toolbox of analytical relations is proposed to describe the effective thermal conductivity as a function of solid phase thermal conductivity, pore thermal conductivity, and pore volume fraction (νp). For νp 0.65, the thermal conductivity of kaolin-based foams and calcium aluminate foams was well described by the Hashin Shtrikman upper bound and Russell's relation. Finally, numerical simulation on artificially generated microstructures yields accurate predictions of thermal conductivity when fine detail of the spatial distribution of the phases needs to be accounted for, as demonstrated with a bio-aggregate materia

Thermal conductivity of porous materials

International audienceIncorporation of porosity into a monolithic material decreases the effective thermal conductivity. Porous ceramics were prepared by different methods to achieve pore volume fractions from 4 to 95%. A toolbox of analytical relations is proposed to describe the effective thermal conductivity as a function of solid phase thermal conductivity, pore thermal conductivity, and pore volume fraction (νp). For νp 0.65, the thermal conductivity of kaolin-based foams and calcium aluminate foams was well described by the Hashin Shtrikman upper bound and Russell’s relation. Finally, numerical simulation on artificially generated microstructures yields accurate predictions of thermal conductivity when fine detail of the spatial distribution of the phases needs to be accounted for, as demonstrated with a bio-aggregate material

Functionalization of microstructured open-porous bioceramic scaffolds with human fetal bone cells.

Bone substitute materials allowing trans-scaffold migration and in-scaffold survival of human bone-derived cells are mandatory for development of cell-engineered permanent implants to repair bone defects. In this study, we evaluated the influence on human bone-derived cells of the material composition and microstructure of foam scaffolds of calcium aluminate. The scaffolds were prepared using a direct foaming method allowing wide-range tailoring of the microstructure for pore size and pore openings. Human fetal osteoblasts (osteo-progenitors) attached to the scaffolds, migrated across the entire bioceramic depending on the scaffold pore size, colonized, and survived in the porous material for at least 6 weeks. The long-term biocompatibility of the scaffold material for human bone-derived cells was evidenced by in-scaffold determination of cell metabolic activity using a modified MTT assay, a repeated WST-1 assay, and scanning electron microscopy. Finally, we demonstrated that the osteo-progenitors can be covalently bound to the scaffolds using biocompatible click chemistry, thus enhancing the rapid adhesion of the cells to the scaffolds. Therefore, the different microstructures of the foams influenced the migratory potential of the cells, but not cell viability. Scaffolds allow covalent biocompatible chemical binding of the cells to the materials, either localized or widespread integration of the scaffolds for cell-engineered implants

Surface Functionalization of Alumina Ceramic Foams with Organic Ligands

Different anchoring groups have been studied with the aim of covalently binding organic linkers to the surface of alumina ceramic foams. The results suggested that a higher degree of functionalization was achieved with a pyrogallol derivative – as compared to its catechol analogue – based on the XPS analysis of the ceramic surface. The conjugation of organic ligands to the surface of these alumina materials was corroborated by DNP-MAS NMR measurements