  In laboratory experiments, spherical 1 mm-wide glass and basalt particles are
heated, and the hot particles collide at about 1m/s with a flat glass target
that is at room temperature. When the particles are heated below 900 K, the
collisions are essentially elastic with coefficients of restitution of about
0.9, but above 900K collisions become increasingly inelastic and the
coefficient of restitution decreases with increasing temperature. At 1100K the
glass particles approach sticking but, simultaneously, at the same temperature
the particles melt on timescales of minutes. The basalt particles approach
sticking at 1200 K. Only above 1400K do basalt grains in contact with each
other fuse together, forming compounds on timescales of hours, and at 1500K
basalt grains completely fuse together. Therefore, cooling basalt grains only
have a 100K window for compound formation, and velocities very likely have to
be below 1m/s for sticking in the first place. We predict that this puts
constraints on compound chondrule formation and particle densities in the solar
nebula.
