microstructures are revealed by etching
in Nital (2 volume % HNO3,
balance ethanol). The optimal etching time
varies from one meteorite to another,
and can range from 30 to 300 seconds.
The etched specimen is washed with
ethanol and then dried using cold,
"time-lapse" video shows metal in Tuxtuac (LL5)
during Nital etching (horizontal field of view =
450 microns). The metal was photographed
prior to etching, and then re-photographed at 30
second etch intervals for a cumulative etch time
of 270 seconds. I used "CombineZP"
freeware to align and animate the images.
Note that taenite darkens whereas kamacite stays
relatively bright. Taenite FCC annealing
twins also become visible as etching proceeds.
Warning! Nital etchant is highly
flammable and potentially explosive,
especially at acid concentrations above
5 vol.%. Bretherick's Handbook of
Reactive Chemical Hazards describes
nitric acid-alcohol mixtures as "rocket
fuel". Even at low acid
concentrations, I have witnessed
Nital explode to produced the toxic gas
NO2 (not good). Always
prepare this etchant in small
quantities, and discard your etchant
immediately after use because dissolved
metal seems to catalyze the