| abstract |
Glass bubbles of increased collapse strength are prepared. The bubbles have an average particle density of 0.4 or more and are made of glass that consists essentially of SiO2 (60-90 weight-percent), alkali metal oxide (2-20 weight-percent), B2O3 (1-30 weight-percent), sulfur (0.005 to 0.5 weight-percent), and other conventional glass-forming ingredients. |