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Synthesis and Effective Thermal Conductivity Measurements of Hollow Mesoporous SiO 2 Spheres for Heat‐Insulating Applications
Author(s) -
Winkelmann Frederik,
Albert Rene,
Felderhoff Michael
Publication year - 2021
Publication title -
energy technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.91
H-Index - 44
eISSN - 2194-4296
pISSN - 2194-4288
DOI - 10.1002/ente.202001048
Subject(s) - thermal conductivity , materials science , thermal conduction , mesoporous material , calcination , dispersity , conductivity , spheres , mesoporous silica , composite material , chemical engineering , polymer chemistry , chemistry , organic chemistry , physics , astronomy , engineering , catalysis
Mesoporous silica hollow spheres are an excellent model system to investigate the thermal conductivity for an efficient heat‐insulating material with respect to its geometry. Four different monodisperse silica hollow spheres are synthesized via a three‐step synthesis consisting of emulsifier‐free emulsion polymerization, modified Stöber condensation process, and subsequent calcination. In this approach, cetyltrimethylammonium bromide (CTAB) is used as a structure directing component to produce a highly porous silica shell. The systematic investigations of the effective thermal conductivity (ETC) allow distinguishing the respective conduction pathways, such as solid conduction and gas conduction. The carried out thermal conductivity measurements reveal for all four samples promising low ETC values of ≈36 mW m −1 K −1 at 1013 mbar and 35 °C. In vacuum (0.03 mbar) all four samples showed, independent of shell thickness and inner diameter, a comparable reduced ETC of about 10 mW m −1 K −1 . The comparison with previous studies on unstructured silica hollow spheres indicates that the solid state conductivity within the bulk is more dependent on the contact strengths and the number of contacts than on the thermal conductivity within the silica material, as the scattering probability of phonons is not influenced by an increased density of defects.