**Acknowledgements**

*Foams - Emerging Technologies*

obtained in argon environment.

**5. Conclusions**

**Figure 7.**

From visual observations and the performed analysis, one can clearly note that the porosity in the bulk of both samples is predominantly of closed type and amounts to about 80–85% in both species. It is also evident that the walls of the samples are abundant of pores. Another interesting feature is that the closed cells of the species foamed in air are larger than the cells in the volume of the sample foamed in argon. Moreover the thickness of the walls in the sample synthesized in air is on average lower than the wall thickness in the glass-ceramic foam material

*X-ray computed tomography, (a) 3-D reconstruction of the surface and the bulk of a glass-ceramic foam synthesized in air (left); volume cross sections (right), and (b) 3-D reconstruction of the surface and the bulk of* 

In current investigation the authors have shown the possibility for carrying out successful synthesis depending on the temperature and the applied atmosphere of

It was shown that synthesis in inert environment leads to the production of

If properly engineered, the practice and experience show that a glassy-crystalline material with low density and high porosity of about 80% can be obtained, which can be considered as more than a satisfactory result [1, 22]. In addition thus obtained foams are characterized by fire resistance features up to 1100°C as well. By applying a double-stage heat treatment, first stage, low temperature sintering at 950°C, and second stage, foaming at 1100°C, foam materials with improved properties and differences in the structure have been successfully obtained.

The SEM images from the fractures of both glass-ceramic foam species reveal a well-sintered material. They show a good degree of sintering and total porosity

well-sintered glass-ceramics and/or glass-ceramic foams.

*a glass-ceramic foam synthesized in argon (left); volume cross sections (right).*

materials with higher degree of sintering.

**82**

below 10–15%.

N.B. Jordanov gratefully acknowledges the financial support of the National Program Young Scientists and Post-docs of the Ministry of Education and Science of Republic of Bulgaria under the project "Sintered self-glazed glass-ceramics and foams from iron-rich industrial wastes." D. Tatchev and A. Karamanov express their gratitude for the support of Project BG05M2OP001-1.002-0019: "Clean technologies for sustainable environment—waters, waste, energy for circular economy." All authors are thankful for the financial support for realization of the closed experimental setup for measurements in a dual environment of the Bulgarian Science Fund (FNI) under Project DN 19/7 "Theory and application of sinter-crystallization."
