Page 196 - Chalcogenide Glasses for Infrared Optics

172 Cha pte r Se v e n

passed through the reactor, and returned through fiber to the instru-
ment optical path. Spectra are easily recorded in real time following
the course of a reactor. Besides the convenience, the reaction moved
away protects the instrument and the operator from hazards. Early
examples are described in the literature. 11, 12
In other applications, a single unclad fiber from the FTIR is placed
in a mold away from the instrument and returned to the instrument
optical path. The mold is filled with a liquid plastic prior to the liquid
undergoing a polymerization chemical reaction. Providing the reac-
tants each have observable absorption bands, the reaction may be fol-
lowed in real time as the polymerization progresses. An example
would be the polymerization of the plastic after a catalyst has been
added. The recorded spectra could be used to verify when the reac-
tion is complete so the plastic object can be removed from its mold at
the appropriate time.
The largest consumers of AMI glass fibers for chemical applica-
tions are Peter Melling and Mary Thomson of Remspec Corporation.
13
Their most unique development has been the multifiber probe. The
probe is designed to be used with most FTIR spectrometers; it utilizes
7 fibers in the bundle to input the FTIR energy and 12 fibers to return
the signal. The probe has three separate heads: an ATR crystal head,
a reflection head, and a liquid transmission. A diagram of the ATR
head is shown in Fig. 7.14. The fibers are very flexible, allowing
remote collection of spectra from 2 to almost 12 µm. The probe is 7 in
long and encased in a ¼-in stainless-steel tube, allowing easy access
to a flask or reaction vessel in the laboratory. At the end of the probe
is an ATR crystal tip. Again, real-time observation of chemical reac-
tions taking place may lead to better understanding of the reaction
and even chemical kinetics data. For an example, the polymerization
of isobutylene was studied over 80 min using the probe, and Fig. 7.15
shows the recorded data.
AMI worked very closely with personnel from Foster Miller in
Boston in their program to utilize the AMI IR fibers to solve chemical
analytical problems. The program included Mark Druy, Roy Bolduc,
Paul Glatkowski, Suneet Chada, William Kyle, and Chuck Stevenson.

ATR probe
Seal End cap

ATR crystal
FIGURE 7.14 Remspec multifi ber FTIR probe.