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• Particle diagnostics are useful and widely used in the thermal spray process

for various purposes. However, temperature measurement of in-flight

particles was found to be challenging because of the potential contribution

of the non-thermal signals affecting the measurement process and

perturbing the obtained signals. In that context, temperature measurement

for in-flight particles in suspension plasma spraying becomes even more

difficult because of the small diameter of the particles, the metallic vapors

and the radiation of the plasma surrounding the particles. In order to

evaluate the temperature of inflight particles, two color pyrometer and

spectroscopic analysis are useful tools that have been applied before on

different thermal spraying processes. In this work, the emission spectra in

the visible/near infrared optical range (600nm to 1000nm) were investigated

from two different positions. Firstly, emission spectrum was recorded from

the front direction in order to assess the influence of the plasma radiation

emitted from the core of the plasma torch that is reflected by the in-flight

particles in all spatial directions, on the temperature measurement.

Secondly, emission spectra were collected radially relative to the torch axis

at different axial locations. To conduct those measurements, 20wt% YSZ

particles in pure ethanol were sprayed and characterized.

Method

Conclusions

Influence of the Plasma Radiation Scattered by Inflight Particles on

Temperature Measurement in Suspension Plasma Spraying

B. Aziz and C. MoreauMechanical Engineering Department, Concordia University

Thermal Spray Laboratory

• The radiation of the in-flight particles was assumed to be a black body

radiation according to Planck’s law of radiation

Introduction Results

• Mie Solution at scattering angle of θ

= 90° and λ = 995nm. The refractive

index of 𝑌𝑆𝑍 particles was taken to

be 𝑛 = 2.18 − 0.02𝑖. On the other

side, the mean particle size

distribution was taken to be 1.5μ𝑚with 20% standard deviation.

According to Mie solution, the

scattered radiation at 995nm

calculated at 1m from the torch axis

is illustrated in (Fig.1).Fig. 1: Radiation intensity in (nW/Sr) as

a function of the scattering angle

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

600 700 800 900 1000

Ca

lib

rati

on

Fa

cto

r (C

ou

nts

/uS

)/[u

W/c

m^

2.n

m]

Wavelegnth in nm

• The spectrometer was

radiometrically calibrated using a pre-

calibrated light source with known

emission at each wavelength

associated with the responsivity of the

CCD camera(350nm to 1050nm) as

it’s illustrated in (Fig.2).

Fig.2 Calibration Factor [Counts/ uS]

/ [uW/cm^2.nm]

• To calculate the power incident

on the particles, the emitted

spectra for the plasma only, then

(Plasma + Ethanol), and finally

(Plasma + Ethanol + Powder) at

80cm axial distance from the

torch plane were conducted

(Fig.3).

Fig. 4 Spectrum Collected from the front direction

Fig. 5 Spectrum collected radially

relative to the spray direction, at 10 cm

from the torch exit

Zr

Fig. 6 Apparent particle’s surface

temperature as a function of true particle’s

surface temperature

1200

1700

2200

2700

3200

3700

4200

1200 2200 3200 4200Ap

pa

ren

t S

urf

ace

Te

mp

era

ture

(°

C)

True Surface Temperature (°C)

995/785

995/877

• At 10 cm from the torch exit, the calculated error in temperature

measurement due to the scattered radiation by the in-flight particles at their

melting temperature (2700ºC) was found to be 1º; however, at 2500°C the

amount of error was quantified to be 16°. On the other hand, the calculated

error is negligible at the 2700ºC while taking the intensity ratio at λ1 =995±25nm; λ2 = 877±25nm nm (995/877) as illustrated in Fig.6

• In this work, a methodology was explained to investigate the influence of

the plasma radiation scattered by YSZ particles in suspension plasma

spraying on the particle temperature measurement. It was demonstrated that

the error resulted from this source varies strongly with the detection

wavelengths. The error between the true and apparent surface temperature of

the zirconia particles was estimated 1°C at its melting point depending on

the selected wavelength bandwidths, and 16° at true particle’s surface

temperature of 2500°C

Fig. 3 Schematic for experimental setup

Acknowledgement1. Dr. Fadhel Ben Ettouil who provided an extensive support and sincere efforts

during the experimental work with the plasma spray system.

2. Dr. Patrick Gougeon for enriching discussions and advices on the content of

this paper