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PhD Defense by Martin Bonderup Østergaard

Martin Bonderup Østergaard, Department of Chemistry and Bioscience will defend his thesis on: "Preparation and characteristics of glass foam"


05.04.2019 kl. 13.00 - 16.00



"Preparation and characteristics of glass foam"


Glass foams are attractive materials that can be used for different applications such as lightweight fillings and thermal or sound insulation. As thermal insulator, the thermal conductivity is a crucial property that should be kept as low as possible without compromising other properties. However, the understanding of thermal conductivity of glass foams is still limited due to lack of reported data. Therefore, the aim of this PhD project was to enhance the understanding by investigating the effects of solid and gas phases and porous structure on the thermal conductivity of glass foams. We prepared glass foams from obsolete cathode ray tube (CRT) panel glasses throughout the present thesis as it has a low thermal conductivity compared to other waste silicate glasses such as flat glass and bottle glass, and large amounts of CRT glass is landfilled, and thus, being harmful to our environment.

First, we studied the foaming of a common CRT panel glass, Mn3O4, and carbon mixture while adding different alkali (Li, Na, K) phosphates to the mixture. Various types of sodium phosphates are claimed to have a foam stabilizing effect, however, this is not proved in literature. We found no effect of the alkali phosphates on pore size, pore shape, or wall thickness. However, we showed that K3PO4 is promising to obtain closed pores of highly porous glass foams.

Second, we investigated the effect of pressure and gas specie on the foaming behavior using a physical foaming approach. Glass powder was sintered under high pressure of inert gases (He, Ar, N2) which resulted in a pellet with high gas pressure in closed pores. Subsequent reheating of the pellet caused expansion due to the combination of decreasing viscosity of the glass and the release of the high gas pressure. We found that the kinetic diameter of the gas species greatly affected the foaming onset, maximum expansion, and thus, the final foam characteristics. On the contrary, the pressure dependence showed an optimum pressure of 20 MPa.

Third, we studied the effect of solid phase, gas phase, and macrostructure on the thermal conductivity of glass foams. In order to optimize the insulating ability of glass foams, it is necessary to enhance the knowledge of the contribution of different phases and structure to the thermal conductivity of glass foams. We found that the thermal conductivity of the solid phase increases with increasing content of foaming agent dissolved in the glass structure. Moreover, the thermal conductivity increases with increasing crystal content in the samples. The gas phase contribution to thermal conductivity of glass foams was investigated by entrapping Ar or N2 by physical foaming, however, CO2 was present giving binary gas mixtures. Theoretical calculations of the thermal conductivity of gas mixtures proved that the Ar-rich gas phases had a lower thermal conductivity than that of the N2-rich ones resulting in a lower thermal conductivity of the glass foams. Finally, we found that an increase in average pore size from 0.10–0.16 mm decreases the thermal conductivity by >10 %.


  • Professor Yuanzheng Yue, Dept. Chemistry and Bioscience, AAU, Denmark


  • Associate Professor Rasmus Lund Jensen (Chairman) fra Department of Civil Engineering, AAU, Denmark
  • Professor Paolo Colombo,Department of Industrial Engineering, University of Padova, Italy
  • Senior Advisor for Strategic Affairs Manoj K. Choudhary, Glass Service, USA, Inc., USA





Department of Chemistry and Bioscience, AAU, Section of Chemistry


Fredrik Bajers Vej 7H, 9220 Aalborg Ø, room number: Auditorium