REPOSITORY > RESULTS

Abstract

Thermal insulation materials have a strong impact on energy efficiency of buildings which are one of the main energy consumers in the EU. Thermal insulation materials are widely used and improving their properties or improving their production can therefore have a rapid impact on the efficient use of energy in buildings. Foamed glass is an interesting thermal insulation material since it can be produced from a cullet, i.e. crushed glass from the production or postconsumer source. Here, the use of carbonaceous foaming agents allows the synthesis of best quality foamed glass, while at the same time requires the implementation of the process in the inert atmosphere, which is a less environmentally friendly option in comparison to the air atmosphere.
In this thesis, different types of waste glass cullets, with the emphasis on cathode ray tube panel glass, were investigated for their expansion ability either by hydrothermal treatment or by mixing them with water glass. Chemical and crystallographic changes in the glass powder mixtures were followed by X ray diffraction and infrared spectroscopy. Mass loss and evolution of gases during the heating were analyzed with thermogravimetry coupled with mass spectrometry. Porosity of the obtained foams was analyzed with Archimedes method in water and with He pycnometer, while the structural characteristics were analyzed using scanning electron microscope. Atmosphere within the closed pores of the foamed glass was analyzed with gas chromatography.
In the first part of the research, foaming of cathode ray tube panel glass with the addition of water glass in air was investigated. Chemical and crystallographic changes in the glass powder mixtures suggest that a new carbonate phase is formed after glass powder is mixed with water glass. Analysis of the atmosphere from within the closed pores of the foamed glass has revealed that it is mostly composed of carbon dioxide. A new carbonate based foaming mechanism is proposed as an alternative to the water dominated mechanism.
In the second part of the research, glass powders were hydrothermally treated to different water content and investigated for their ability to foam in the air atmosphere. Newly obtained glass powders foam in the air atmosphere, however, this ability does not change significantly with their water content.
In the last part of the research, both possibilities of foaming with hydrosilicates were utilized for foaming with the addition of carbonaceous foaming agent in air atmosphere. Use of carbonaceous foaming agent in combination with the hydrothermally treated glass powder leads to slightly improved foaming ability in the air atmosphere. However, the use of water glass in combination with the waste glass powder results in significantly enhanced foaming ability, leading to high porosity foamed glass. Furthermore, as-obtained foams exhibit a homogeneous porous structure and low thermal conductivity. Both cases of hydrosilicate use protect the carbon from the premature burning and allow implementation of the foaming process in the air atmosphere.
This research explains a novel foaming mechanism for the foaming with water glass, which emphasizes the importance of the foaming mixture reactivity with the carbon dioxide from the surrounding atmosphere. Furthermore, the research demonstrates the applicability of hydrosilicates for the implementation of the glass foaming with the use of carbonaceous foaming agent in the air atmosphere. The dissertation consists of two articles published in scientific journals.