Design, Construction, and Operation of a Supersonic Pyrolysis Nozzle Brian Lajiness Dr. Polik Hope College Chemistry Department

Background - Pulsed Nozzle Cools and simplifies spectrum Cools and simplifies spectrum –Molecules moving in same direction with same speed –Fewer collisions lower temperature sample vacuum

Design and Construction Study literature precedents (Chen, Rev Sci Inst 63, 4003, 1992) Study literature precedents (Chen, Rev Sci Inst 63, 4003, 1992) Select materials Select materials Consult with machinist Dave Daugherty Consult with machinist Dave Daugherty Design criteria Design criteria –Adjustable heating (length, temperature) –Temperature monitor –Cooling sink –Minimize scattered light –Fit in vacuum chamber

SiC tube Carbon blocks Tube clamp Water-cooled block Pulsed nozzle Water inlet/outlet 1”

Light shield Light shield holder

Materials Withstand high temperatures, °C Withstand high temperatures, °C Very hard since most metals melt at this temperature Very hard since most metals melt at this temperature –Al - 600°C –Cu °C –Fe °C –C – does not melt; conductor –Ceramic (SiC, BN, alumina silicate) – does not melt, max working temp of 1900°C, 2000°C, and 1100°C Machineability – must be able to shape material Machineability – must be able to shape material Relatively inexpensive Relatively inexpensive

Heating SiC tube is heated resistively. A current limiter must be used since the resistance of the SiC tube drops significantly at high temperatures. SiC tube is heated resistively. A current limiter must be used since the resistance of the SiC tube drops significantly at high temperatures. An adjustable heating length was desirable, therefore carbon clamps were used to heat the tube An adjustable heating length was desirable, therefore carbon clamps were used to heat the tube 80 V 0 V Current limiter M M M Ceramic tubing

Temperature Measurement Optical Pyrometer Optical Pyrometer –Can only measure temperatures above ~700 °C Type C thermocouple Type C thermocouple –Hard to attach directly to SiC tubing

Scattered Light When heated, the SiC tube gives off visible blackbody radiation When heated, the SiC tube gives off visible blackbody radiation Two ways to protect experiment Two ways to protect experiment –Light shield –Imaging optics

Characterization Multiple heating runs have been performed to determine the reproducibility and stability of the equipment Multiple heating runs have been performed to determine the reproducibility and stability of the equipment It was discovered that the heating runs should be performed under high vacuum (10 -6 torr) to preserve the SiC tube It was discovered that the heating runs should be performed under high vacuum (10 -6 torr) to preserve the SiC tube Si + O 2 SiO 2 (insulator)

Results - Temperature Optical Pyrometer Thermocouple

Future Plans Literature search for possible fluorescing radicals and necessary experimental conditions Literature search for possible fluorescing radicals and necessary experimental conditions –Ex: NH 2, HCO, CH 3 O, HO 2, HNCN What precursor is needed to produce the radical? What precursor is needed to produce the radical? –CH 3 CHO HCO + CH 3 –CH 3 ONO CH 3 O + NO Purchase/synthesize the precursor Purchase/synthesize the precursor FE and DF spectroscopy on desired radical FE and DF spectroscopy on desired radical –Start with HCO

Acknowledgements Dr. Polik Dr. Polik Dave Daugherty Dave Daugherty Polik group members Polik group members Hope College Chemistry Department Hope College Chemistry Department Dreyfus Foundation Dreyfus Foundation