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Design, Construction, Design, Construction, and Operation of a and Operation of a
Supersonic Pyrolysis Supersonic Pyrolysis NozzleNozzle
Brian LajinessBrian Lajiness
Dr. PolikDr. Polik
Hope College Chemistry DepartmentHope College Chemistry Department
Background - Pulsed Background - Pulsed NozzleNozzle
Cools and simplifies Cools and simplifies spectrumspectrum– Molecules moving in same Molecules moving in same
direction with same speeddirection with same speed– Fewer collisions lower Fewer collisions lower
temperaturetemperature
sample
vacuum
Room Temperature
28320 28322 28324 28326 28328Frequency
Inte
nsity
22.37 K BP .1 atm
28320 28322 28324 28326 28328Frequency
Inte
nsi
ty
6.70 K BP 1.0 atm
28320 28321 28322 28323 28324 28325 28326 28327 28328
FrequencyIn
tens
ity
Design and Design and ConstructionConstruction
Study literature precedents Study literature precedents (Chen, (Chen, Rev Sci InstRev Sci Inst 6363, 4003, 1992), 4003, 1992)
Select materialsSelect materials
Consult with machinist Dave DaughertyConsult with machinist Dave Daugherty
Design criteriaDesign criteria– Adjustable heating (length, temperature)Adjustable heating (length, temperature)
– Temperature monitorTemperature monitor
– Cooling sinkCooling sink
– Minimize scattered lightMinimize scattered light
– Fit in vacuum chamberFit in vacuum chamber
MaterialsMaterials
Withstand high temperatures, 0-1900°CWithstand high temperatures, 0-1900°C Very hard since most metals melt at this Very hard since most metals melt at this
temperaturetemperature– Al - 600°CAl - 600°C– Cu - 1083°CCu - 1083°C– Fe - 1539°CFe - 1539°C– C – does not melt; conductorC – does not melt; conductor– Ceramic (SiC, BN, alumina silicate) – does not melt, Ceramic (SiC, BN, alumina silicate) – does not melt,
max working temp of 1900°C, 2000°C, and max working temp of 1900°C, 2000°C, and 1100°C1100°C
Machineability – must be able to shape materialMachineability – must be able to shape material Relatively inexpensiveRelatively inexpensive
HeatingHeating
SiC tube is heated resistively. A current SiC tube is heated resistively. A current limiter must be used since the resistance of limiter must be used since the resistance of the SiC tube drops significantly at high the SiC tube drops significantly at high temperatures.temperatures.
An adjustable heating length was desirable, An adjustable heating length was desirable, therefore carbon clamps were used to heat therefore carbon clamps were used to heat the tubethe tube
80 V
0 V
Current limiter
M
M
M
Ceramictubing
Temperature Temperature MeasurementMeasurement
Optical PyrometerOptical Pyrometer– Can only measure temperatures above ~700 °CCan only measure temperatures above ~700 °C
Type C thermocoupleType C thermocouple– Hard to attach directly to SiC tubingHard to attach directly to SiC tubing
Scattered LightScattered Light
When heated, the When heated, the SiC tube gives off SiC tube gives off visible blackbody visible blackbody radiation radiation
Two ways to protect Two ways to protect experimentexperiment– Light shieldLight shield– Imaging opticsImaging optics
http://www.egglescliffe.org.uk/physics/astronomy/blackbody/bbody.html
CharacterizationCharacterization
Multiple heating runs have been performed Multiple heating runs have been performed to determine the reproducibility and stability to determine the reproducibility and stability of the equipmentof the equipment
It was discovered that the heating runs It was discovered that the heating runs should be performed under high vacuum (10should be performed under high vacuum (10--
66 torr) to preserve the SiC tube torr) to preserve the SiC tube
Si + O2 SiO2 (insulator)
Temperature of SiC Tube
0
200
400
600
800
1000
1200
1400
1600
1800
0 10 20 30 40 50 60 70 80 90 100
Variac Position
Te
mp
era
ture
(d
eg
C)
Results - TemperatureResults - Temperature
Optical PyrometerThermocouple
Future PlansFuture Plans
Literature search for possible fluorescing Literature search for possible fluorescing radicals and necessary experimental conditions radicals and necessary experimental conditions – Ex: NHEx: NH22, HCO, CH, HCO, CH33O, HOO, HO22, HNCN, HNCN
What precursor is needed to produce the What precursor is needed to produce the radical?radical?– CHCH33CHO HCO + CHCHO HCO + CH33
– CHCH33ONO CHONO CH33O + NOO + NO
Purchase/synthesize the precursorPurchase/synthesize the precursor
FE and DF spectroscopy on desired radicalFE and DF spectroscopy on desired radical– Start with HCOStart with HCO