  Some hot, massive, population-I Wolf-Rayet (WR) stars of the carbon subclass
are known to be prolific dust-producers. How dust can form in such a hostile
environment remains a mystery. Here we report the discovery of a relatively
cool, extended, multi-arc dust envelope around the star WR112, most likely
formed by wind-wind collision in a long-period binary system. We derive the
binary orbital parameters, the dust temperature and the dust mass distributions
in the envelope. We find that amorphous carbon is a main constituent of the
dust, in agreement with earlier estimates and theoretical predictions. However,
the characteristic size of the dust grains is estimated to be ~1 micron,
significantly larger than theoretical limits. The dust production rate is
6.1*10^[-7] M_Sun / yr and the total detectable dust mass is found to be about
2.8*10^[-5] M_Sun (for d=4.15 kpc). We also show that, despite the hostile
environment, at least ~20% of the initially-formed dust may reach the
interstellar medium.
