Hollow spherical glass particles

A process for the preparation of hollow spherical glass particles, comprising the steps of

• a) providing a composition comprising
• i) at least 30 wt.-% of Al2O3,
• ii) at least 35 wt.-% of SiO2, and
• iii) at least 18 wt.-% of at least one alkali metal oxide,
• based on the overall weight of the composition,
• b) mixing the composition obtained in step a) with water, thereby obtaining a slurry,
• c) spray-drying the slurry obtained in step b), thereby obtaining spray-dried particles and
• d) feeding the spray-dried particles obtained in step c) into a heating system to obtain the hollow spherical glass particles, wherein the heating system comprises at least one heating device where in one or more of the at least one heating devices the particles are blown upwards while the temperature is maintained above 1000° C.;
• wherein the spray-dried particles fed into the heating system in step d) have a particle size of at or below 80 μm, and
• wherein a carrier gas stream flow rate used to blow the particles upward in step d) is from 40 L/min to 80 L/min.