Challenge

Hollow glass microspheres (HGMS), also known as microbubbles, are thin-walled spherical glass particles with a diameter of 10 to 200 micrometres and wall thicknesses of 0.3 to 2.0 micrometres. The spheres are resistant to corrosion, temperature, and chemical influences and also extremely stable: Due to their perfect shape, they can withstand pressure of up to 2,000 bar. Free-flowing microbubble powder is used as insulating material in the building sector. However, HGMS production is very energy-consuming, as it requires a glass powder that is made specifically for this purpose. Microbubble production directly from molten glass can reduce the costs but generates particles with a wide size distribution and strong variations in wall thickness. This results in varying stability and insulating properties, making the product unattractive as insulation material. The challenge for microbubble production from glass melt is to adapt the glass composition and process parameters so that the resulting HGMS quality is comparable to other HGMS products on the market.

Goals and procedure

The aim of the MicroBubble project is to reduce the energy input for HGMS production by at least 30 percent without losing the excellent mechanical properties. The project focuses on the development of HGMS made of borosilicate glass. However, the project team also experiments with using waste glass cullet as a raw material in order to increase the sustainability of the product and further reduce the costs of HGMS. Centrepiece of the work is the high-temperature coaxial nozzle system developed in the project that atomises a liquid glass strand into tiny droplets and enables a continuous process for powder production without using moving components. The process is to be developed to such an extent that it can be scaled up to industrial production scale after the end of the project.  In order to achieve an early market launch of the process and the HGMS products, extensive building structure investigations are already being carried out during the project.

Innovations and perspectives

The process to be developed in the project differs significantly from other HGMS manufacturing processes: Due to the coaxial flow guidance of the fuel gases and the glass flow, the particle properties can be controlled so that the HGMS show a narrow particle size and wall thickness distribution. These microbubbles have the potential for large-scale use in HGMS-based insulation systems. The reduced production costs resulting from energy savings increase their competitiveness compared to insulation systems based on expanded polystyrene foam (EPS) and can contribute to supplying the building materials industry with large quantities of HGMS. Microbubbles are purely mineral and thus fully recyclable, which improves the ecological footprint in the building sector and contributes to climate protection. In addition, the project team envisages applications beyond the construction industry, for example for other established HGMS-based products such as wall paints or polymer composites.