Influence of Plasma Radiation Scattered by In-flight Particles on Temperature

Measurement in Suspension Plasma Spraying

Bishoy Aziz and Prof. Christian MoreauThermal Spray Laboratory

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Outlines

IntroductionThermal and Non-thermal RadiationTheoretical Framework

Experimental SetupResultsConclusions

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Introduction

Particle diagnostics are useful and widely used in the thermal spray processes for various purposes.

The temperature of in-flight particles has a direct influence on the coating’s microstructure.

It’s useful for optimizing the spraying conditions.Researchers investigated the temperature of in-flight

particles in HVOF, VPS and APS.

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Thermal and Non-thermal Radiation

The main sources of radiation are:

1. The radiation emitted directly from the plasma and surrounding the particles.

2. The radiation produced in the core of the plasma torch and scattered by the particles in-flight.

3. The radiation emitted by the particles themselves while they are in-flight.

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Sensor Head

Plasma Radiation

Non-thermal Plasma radiation scattered by the particles in-flight

Non-thermal Plasma radiation surrounding the particles in-flight

Thermal radiation emitted by the

particles in-flight

Thermal and Non-thermal Radiation

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Theoretical FrameworkTemperature measurement is conducted using spectroscopic

analysis and two color pyrometer.20 wt% YSZ particles in pure ethanol were sprayed (TBC and

Fuel cells).Measurements were carried out for an ensemble of particles.The emission spectra in the VIS/NIR range (600 nm to 1000

nm) was investigated.

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Blackbody Radiation

Assumptions:Particle’s average

diameter is assumed 1.5 μm.

Particles behave as grey body ϵ = 0.73.

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Particle emissions are determined according to Planck’s Law:

Wikipedia.org

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Two Color PyrometerTwo color pyrometer

formulaRatio

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Inte

nsity

Rati

o

8

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Experimental SetupSpectrometer:Silicon Detectors (350 nm to

1050 nm).Entrance slit size 50 μm.Blazed grating at 500 nm.

Fiber Optic 200 μm Core Diameter.

The radiometric calibration was carried out using Tungsten Halogen lamp (NIST).

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

600 700 800 900 1000(C

ount

s/uS

)/[uW

/cm

^2.n

m]

Wavelegnth in nm

Calibration Factor as function of wavelength

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Front MeasurementND Filters for attenuation.Long pass filters (600 nm).The particle’s average

trajectory was aligned to the torch centerline using Acuraspray.

The aim is to assess the power density incident on the particles

ITSC MAY 2015Measurement acquired from the front

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Spraying ConditionsParameter Rate

Plasma Torch 3MB Sulzer MetcoArgon Flow Rate 30 slmHelium flow rate 30 slm

Suspension flow rate 10 g/minPower 24 KW

Injector 200 μmPowder YSZ (200 nm to 300 nm)

Powder Concentration 20% Wt

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These conditions produced good coatings

Results of Front Spectra at 80 cm

Plasma only.Plasma +

Ethanol.Plasma + Ethanol

+ Powder.

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Dominant plasma radiation.

Local cooling for the plasma

C II

Ar I

970 975 980 985 990 995 10000.6

0.8

1

1.2

1.4

1.6

1.8

2

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Power Density Vs Distance

ITSC MAY 2015Intensity ratio at different axial locations Log-Log Scale to extrapolate the intensity ratio at 10 cm

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.90

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

f(x) = − 1.99191914314592 x + 3.80450966450383R² = 0.999093964700942

10 20 30 40 50 60 70 800

2

4

6

8

10

12

14

16

18785 nm 877 nm 995 nm

Axial Distance (cm)

Inte

nsity

Rati

o

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Intensity scattered at 995 nm

It’s a function of :1. Particle diameter 1.5 μm.2. Incident power density at 10

cm.3. Wavelength 995 nm.4. n = 2.18 – 0.02i

The scattered intensity was taken at 90°.

Same rational for 785 nm and 877 nm.

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0.10

1.00

10.00

100.00

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Scattering Angle

Inte

nsity

Sca

tter

ed (n

W/S

r)

Scattering Effect

15

1200

1700

2200

2700

3200

3700

4200

1200 1700 2200 2700 3200 3700 4200

995/785

995/877

True Particle’s Surface Temperature (°C)

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Appa

rent

Par

ticle

’s Su

rfac

e Te

mpe

ratu

re (°

C)

True Surface temperature

1st Window

2nd Window

2700 (°C) Negligible Negligible

2500 (°C) 16° Negligible

1st Window 995±25 nm / 785±25 nm.

2nd Window 995±25 nm / 877±25 nm.

Error Influence

Radial Measurement

Measurement was carried out with and without the powder.

Achromatic lens (F = 40 mm) with optical transmission 650 nm to 1050 nm).

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PC

20 cm

Lens Head

20 cm

Spectrometer

Window

Measurement acquired radially

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Fiber Optic

Spectrums collected Radially

Significant increase in the continuum when the powder is injected.

Zr peak because of the vapors (Meta stable atoms at 10 cm).

T is around 2200 °C at (995/785)

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608 658 708 758 808 858 908 958 1008 10580

500

1000

1500

2000

Zr

870 875 880 885 890 895 9000

50

100

150

200

250

300

350

400

Plasma only.Plasma + Ethanol.Plasma + Ethanol +

Powder.

Wavelength (nm)

Spec

tral

Irra

dian

ce (μ

W/

.nm

)

Conclusions

The influence of plasma radiation scattered by in-flight YSZ particles at their melting point on temperature measurement is almost negligible.

The scattering effect on temperature measurement is reduced while repositioning the wavelength window from 995/785 nm to 995/877 nm.

The main and dominant source of error on temperature measurement is the plasma radiation, the vapors and the free electrons in the background of the continuum.

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Acknowledgement

Dr. Fadhel Ben Ettouil who provided sincere efforts and extensive support during the experimental work with the plasma system.

Dr. Patrick Gougeon for the enriching discussions and insight.

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Thanks …

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