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

SiC tube

Carbon blocks

Tube clamp

Water-cooled block

Pulsed nozzle

Water inlet/outlet

1”

Light shield

Light shield holder

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

AcknowledgementsAcknowledgements

Dr. PolikDr. Polik

Dave DaughertyDave Daugherty

Polik group membersPolik group members

Hope College Chemistry DepartmentHope College Chemistry Department

Dreyfus FoundationDreyfus Foundation