A temperature-sensitive coating,
based on hematite (iron III oxide), has
been developed to measure surface temperature
using spectral techniques. The
hematite powder is added to a binder
that allows the mixture to be painted on
the surface of a test specimen. The coating
dynamically changes its relative spectral
makeup or color with changes in
temperature. The color changes from a
reddish-brown appearance at room temperature
(25 ºC) to a black-gray appearance
at temperatures around 600 ºC.
The color change is reversible and
repeatable with temperature cycling
from low to high and back to low temperatures.
Detection of the spectral
changes can be recorded by different
sensors, including spectrometers, photodiodes,
and cameras. Using a-priori
information obtained through calibration
experiments in known thermal
environments, the color change can
then be calibrated to yield accurate
quantitative temperature information.
Temperature information can be
obtained at a point, or over an entire
surface, depending on the type of equipment
used for data acquisition.