Measuring Temperature in Adverse Environments Using Phosphors

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Measuring Temperature in Adverse Environments
Using Phosphors

• Dr. Andy Hollerman
• Associate Professor of Physics
• University of Louisiana at Lafayette
• P.O. Box 44210
• Lafayette, LA 70504
• [phone]
• hollerman_at_louisiana.edu

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Outline

• Fluorescence Based Engine Health Monitoring
• Derived from several presentations by S.W.
  Allison from Oak Ridge National Laboratory (ORNL)
  and W.A. Hollerman.
• LED Excitation of High Temperature Luminescent
  Coatings
• Derived from a presentation by S.W. Allison from
  ORNL.

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W. A. Hollerman UL Lafayette
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Summary
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Thermometry Method

• Researchers have found a method that relies on
  measuring the rate of decay of the fluorescent
  response of an inorganic phosphor as a function
  of temperature.
• Having calibrated the phosphor over the
  temperature range of interest, a small surface
  deposit of phosphor is excited with a pulsed
  laser and the fluorescent decay is measured
  (typically in less than 1 ms) to calculate the
  temperature of the substrate.
• Often temperature measurements are made using
  thermocouples or optical pyrometry. However, in
  situations where rapid motion or reciprocating
  equipment is present at high temperatures, it is
  best to use other techniques.
• The time needed to reduce the light intensity to
  e-1 (36.8) of its original value is defined as
  the prompt fluorescence decay time and is often a
  strong function of temperature.

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Phosphor Calibration
Signal (V)
575 nm
453 nm
480 nm

• Oven temperature is steadily increased and
  monitored using a Type S thermocouple located
  near the phosphor.
• At a known temperature, the fluorescent decay
  signal is captured from the oscilloscope.
• The lifetime of the response is then calculated
  using a National Instruments LabVIEW program.
• The lifetime values are then plotted (on a log
  scale) versus the temperature to obtain the
  calibration curve.
• The region past the knee of the curve has a
  nearly linear relationship between temperature
  and the lifetime and is best for temperature
  measurement.

Signal from 453, 480, 575 nm emissions from
YAGDy (0.27) at 1,039 C
1000
100
480 nm
Lifetime (µs)
575 nm
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1
0
200
400
600
800
1000
1200
1400
1600
1800
Temperature (C)
Fluorescence lifetime of 480 and 575 nm from
YAGDy (0.27) versus temperature
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Measurement Challenges

• Relatively small phosphor light emission
• Additional contribution of blackbody temperature
  to mask the light emission of the phosphor
  coating.
• Binder must withstand challenging environments
• Vibrations,
• Chemical exposure,
• Radiation, and
• Extreme temperatures.

Signal and background from 453 nm emission in
YAGDy (0.27) at 1,306 C
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Fluorescence Decay Time
ZnSMn
ZnSMn
t
t

• Temperature sensitivity is often determined
  through the characterization of the prompt
  fluorescent decay time (lifetime - ?).
• Sensitivity can range from cryogenic
  temperatures up to approximately 2000 K.
• Phosphor thermometry allows temperature
  measurement through flames and large black body
  backgrounds.

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YAGCe FluorescenceDecay Time
(Hollerman et al., IEEE TNS, August 2003)
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Fluor Paint Grain Size Measurement
S
Eu
Y
10 µm

• Y2O2SEu fluor and polysiloxane paint on a glass
  slide
• 2 MeV proton beam
• 2 x 2 µm beam area
• µPIXE images
• Y, S, and Eu - fluor
• Si and Ca - slide
• 1.7 MV 5SDH-2 Pelletron accelerator in Louisiana

Ca
Si
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Phosphor Characterization
SEM
AFM

• Y2O2SEu and polysiloxane paint sample.
• 30 x 30 µm Atomic Force Microscope (AFM) image
• Fluor grain size is less than 10 µm in extent.

• Gold-coated Y2O2SEu and polysiloxane paint
  sample.
• Small bright clusters represent individual
  yttrium fluor grains.
• Fluor grain size less than 10 µm.
• Magnification of 3,000.

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Evaluating Temperature Limits

• A series of samples were prepared to evaluate the
  temperature limits for the various material
  combinations.
• The samples were heated to 1200 ºC. A UV lamp was
  used to excite the samples after heating to
  determine if the phosphor survived the heating.
• The process was repeated at 1300 ºC, 1400 ºC, and
  1500 ºC.
• It can be seen that with increasing temperature
  fluorescence decreases, but still produces enough
  light to make a temperature measurement.

ZYP Coatings ZAP Binder Y2O3Eu
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YAGCr phosphor paint emitted fluorescence for a
repeated exposure near a hydrogen flame at
2,200 C.
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Sample Phosphor Paint Results
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YAGDy and ZAP Results

• YAGDy phosphor powder
• 100 ZAP binder
• Applied to ceramic substrate using a standard
  airbrush.
• The mixture is airbrushed on to surface.
• The painted substrate is then heated for 1 hour
  at 900 C to cure the binder.

1,600 C
1,500 C
1,400 C
Three heated samples excited by UV light.
Three coated samples after heating.
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Example Emission Spectra
YAGCe
YAGEu
FWHM 100 nm lc 525 nm
Peaks at 592, 610, 631, 697, and 710 nm
Intensity
Intensity
Wavelength (nm)
Wavelength (nm)
Data Taken for the NASA Glenn Research Center
Fluor paints sprayed on a YSZ substrate and
excited by a UV lamp.
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LED Excitation of High Temperature Luminescent
Coatings

• S. W. Allison ORNL
• A. Heyes Imperial College
• A. Hollerman UL Lafayette

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Rationale

• Light Emitting Diodes (LEDs). For the high
  temperature and difficult environments that
  turbine engines present, until recently, an
  expensive and unwieldy laser was required for
  luminescent thermometry. However, technological
  developments have recently led to the
  availability of high brightness light emitting
  diodes (LEDs). This development expands the
  opportunities and measurement niches for this
  technique.

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Advantages

• Inexpensive (10 USD ea.)
• Price will drop
• Small and Rugged fit for tight spaces
• Performance will improve! Thanks to Lighting
  Industry drive to develop greater efficiency and
  power
• Custom Designs for higher operating temperatures
  and currents are possible.
• Long life

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Disadvantages

• Some difficulty in coupling to optical fiber vs
  lasers
• Cannot achieve high power in short bursts as
  lasers can and total energy output is less

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Demonstrations of LED Excitation of
High-Temperature Phosphors

• LED Excitation of YAGDy Powder in High
  Temperature Oven (to 1100 C)
• Of YAGDy coating (ambient)
• Of YSZDy (ambient)

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LED light directed into oven via Cu-clad fiber
bundle
Fiber bundle
Optics
Window/port
Oven
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YAGPowder signal from Cu-clad fiber bundle 2
LEDs
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Setup for Coating Fluorescence Measurements
YAGDy

• YAGDy

Lens
LED
Detector (not shown) was close
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Comparison of YAGDy and TBC
Room temperature
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Room temperature
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Test Conclusions

• LEDs can excite useful fluorescence at high
  temperatures and from coatings of interest to the
  US/UK program

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Some Keys to LED Implementation

• High current pulser required
• Multifiber for light delivery and collection
  (metal coated for highest temperatures)
• Detector (PMT) able to handle continuous
  blackbody emission and still respond linearly
• Attention to filter design for blackbody
  filtering
• Use pulse width of at least several decay
  constants in duration

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Some Keys to LED Implementation Continued

• Determine current limit of LEDs and operate just
  below that
• Use more LEDs and more delivery and collection
  fibers or use Direct Illumination
• Establish that LED wavelength/power combination
  is optimized

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Steps to an Effective Sensor System

• Define desired footprint for sensor
• Identify EngineTest Vehicle
• Identify surface of interest
• Establish distance from probe to target
• Estimate desirable operating temperature range
• Produce a sensor design to accomplish it

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Questions?

• Contact Dr. Andy Hollerman at
• Hollerman_at_louisiana.edu
• [phone]
• UL Lafayette is always looking for good graduate
  students to continue this work!