Measuring method for theemissivity using FTIR

and infrared radiometer

22 June, 2010

Morikazu Sagawa, Dr. Eng.Executive Director of JIRA

1

1. What is emissivity?2. Features of hot sources3. What is FTIR?4. Preparation of measurement5. Measurement procedure by FTIR6. Measuring temperature7. Measuring emissivity by infraredradiometer

8. Conclusions

Presentation Items

2

What is emissivity? （１）

Pρ＋ Pα＋Pτ＝P

ρ＋ α＋τ＝１

ρ：reflectanceα: absorption ratioτ: transmissivity

ρ＋ α＝１ when Pτ1)

P

Pα

Pρ

Pτ

t

Relationship of radiation and absorption

3

Kirchhoff’s law

α＝εα：absorption ratio ε：ｅｍｉｓｓｉｖｉｔｙ

Black body

Virtual object which completely absorbs radiatedenergy

Emissivity is defined as a ratio of the energyradiated from the surface of materials witha certain temperature and that of a blackbody.

What is emissivity? （２）

4

Planck’s law

C1=2πhc2=3.7418×108 W･µm4/m2

C2=hc/k=1.4388×104 µm･K

1

1,

251

Tλ

C

eλ

CTλW

Features of hot sources（1）

The relationship between the radiated power andthe wavelength depends on the temperature ofthe material. This relationship is called Planck’s law.

0

5

UVvisible rays

NIR FIRIR

peak wavelength(Wien’s displacement law)

wavelength 〔μm〕

sp

ectr

alra

dia

nt

energ

yd

en

sity

〔W

/cm

２/μ

m〕 UV

visible rays

NIR FIRIR

peak wavelength(Wien’s displacement law)

wavelength 〔μm〕

sp

ectr

alra

dia

nt

energ

yd

en

sity

〔W

/cm

２/μ

m〕 UV

visible rays

NIR FIRIR

peak wavelength(Wien’s displacement law)

wavelength 〔μm〕

sp

ectr

alra

dia

nt

energ

yd

en

sity

〔W

/cm

２/μ

m〕

Planck’s law with Wien’s displacement law

Features of hot sources（２）

6

Blackbody

Radiated energy and emissivitycharacteristics of Quartz

分光

放射

エネル

ギー密

度

石英(SiO2)

黒体

40℃

〔W

/cm

２/μ

m〕

分光

放射

エネル

ギー密

度

石英(SiO2)

黒体

40℃

〔W

/cm

２/μ

m〕

分光

放射

エネル

ギー密

度

石英(SiO2)

黒体

40℃

〔W

/cm

２/μ

m〕

Wavelength 〔µm〕分

光放

射率

(%)

波長 〔μm〕

石英(SiO2)

40℃

分光

放射

率(%

)

波長 〔μm〕

石英(SiO2)

40℃

分光

放射

率(%

)

波長 〔μm〕

石英(SiO2)

40℃

Wavelength 〔µm〕

Quartz(SiO2)

Quartz(SiO2)

Blackbody

Em

issiv

ity

〔%〕

Spectr

alra

dia

nt

energ

ydensity

〔W

/cm

2/µ

m〕

W(λ,T)=ε(λ,T) W０(λ,T)

Features of hot sources（３）

ε(λ,T)=W(λ,T)/W０(λ,T)7

What is FTIR？（１）

FTIR:Fourier TransformInfrared Spectroscopy

Distributed Infrared Spectroscopy

Light source

Testbox

Detector

Computer

AD converter

Interferometer

MM

FM HM

Detector

Display

Light source

Test box

Diffraction grating

Inputslit

Output slit

http://www.jeol.co.jp/technical/ai/ir/ft-ir/ft-ir-01.htm 8

What is FTIR？（２）1.Sample on warming equipment2.Blackbody3.Mirror for measuring background radiation

Pyroelectric elements such as TGSwith broad bands and low sensitivity

Control of interferometerand data processing

MM

FM

L1

L2

HM

Light source

Interferometer

Detector

AD converter

Computer

Structure of FTIR

Test box

9

Preparation of measurement（１）

Environment of the measurement roomTemperature: 20～26℃,Tem. Stability: ±1.5℃Humidity: less than 60%

10

Light source

to Interferometer

Blackbody

SampleWarmingequipment

Attached emissivity measuring partConfirmation ofthe symmetrical passin the optical part of FTIR

Confirmation the tem.stability of the samplewarming equipment andthe contact between thesample and the warmingequipment

Absorption spectrum of the atmosphere(Mauna Kea mountain in Hawaii Island )

Preparation of measurement（２）

Atmosphere replacement in the optical part of FTIRReplacement by dried nitrogen to remove theinfluence of H2O and CO2 in the optical part of FTIR

Wavelength (μm)

Transmissivity(%

)

11

Calibration of FTIR（Horizontal）

Absorption spectrum of Polystyrene

Preparation of measurement（３）Transmissivity(%

)

Wavenumber (cm-１)

3027.1(3.30)2924.0(3.42)2850.7(3.51)1944.0(5.14)1871.0(5.34)1801.6(5.55)1601.4(6.24)

1583.1(6.32)1181.4(8.46)1154.3(8.66)1069.1(9.35)1028.0(9.73)906.7(11.03)698.9(14.31)

12

Calibration of FTIR（Vertical）・Control the optical pass（through and stop）・Use of known materials such as SiC

Preparation of measurement（４）

Spectral emissivity of SiC

0

2 0

4 0

6 0

8 0

1 0 0

01 0 0 02 0 0 03 0 0 04 0 0 05 0 0 06 0 0 0

W a v e n u m b e r (c m- 1)

Intensity（％

）Emissivity

(%)

Wavenumber (cm-１) 13

Measurement procedure by FTIR(１)

1. After Confirmation the plasticity and stability ofmeasurement, set up mirror for measuringbackground radiation

2. Measure the background radiation: Vm(λ,T)

3. Set up the sample on warming equipment

4. Measure the surfe temperature of the sample

5. Measure the radiation of the sample: VS(λ,T)

5. Set up the temperature of a blackbody same as

the measuring surface temperature of the sample

Measuring spectral emissivity using FTIR

（To be continued） 14

6. Measure the radiation of the blackbody: Vb(λ,T)

7. Calculate the emissivity using below equation

( )( ) ( )( ) ( ),λλ

,λ,λ=,λε

TV-T,V

TV-TVT

S

Sｍｂ

ｍ

Source: JIS R1801(Method of measuring spectral emissivity of ceramic radiatingmaterials for infrared heaters using FTIR)

Measuring spectral emissivity using FTIR

15

Measurement procedure by FTIR(２)

Example of radiated energy andemissivity characteristics of Quartz

分光

放射

エネル

ギー密

度

石英(SiO2)

黒体

40℃

〔W

/cm

２/μ

m〕

分光

放射

エネル

ギー密

度

石英(SiO2)

黒体

40℃

〔W

/cm

２/μ

m〕

分光

放射

エネル

ギー密

度

石英(SiO2)

黒体

40℃

〔W

/cm

２/μ

m〕

Wavelength 〔µm〕分

光放

射率

(%)

波長 〔μm〕

石英(SiO2)

40℃

分光

放射

率(%

)

波長 〔μm〕

石英(SiO2)

40℃

分光

放射

率(%

)

波長 〔μm〕

石英(SiO2)

40℃

Wavelength 〔µm〕

Quartz(SiO2)

Quartz(SiO2)

Blackbody

Em

issiv

ity

〔%〕

Spectr

alra

dia

nt

energ

ydensity

〔W

/cm

2/µ

m〕

16

Measurement procedure by FTIR(３)

Measuring temperature（１）

Contact thermometer

Measure the temperature of the material surface

example）

K type thermocouple：

Temperature range:-200～1000℃

・Nickel and chromium alloy consisting mainly of・Nickel alloy consisting mainly of

17

Stefan-Boltzmann law

σ=(π4/15)(C1/C24)=5.6703×10－8 W/m2K4

The amount of radiated energy (E) emitted bya blackbody of absolute temperature (T) is given asStefan-Boltzmann law.

0

4),()( TdTWTE σλλ

18

In the case of real materials, the amount of radiatedenergy (E) emitted by absolute temperature (T)is given as follows;

( ) ( ) ( ) 40

TdTWTTE εσ=λ,λ,λε=∞

∫

Measuring temperature（２）

Infrared radiometer

Heater for warming

Change the part ofa blackbody and a sample

Detector

A straying lightshading board

Measuring emissivityby infrared radiometer（1）

19

Measuring equipmentPattern on the sample

Blackbody paintwith known emissivity

Part ofwith unknown emissivity

Measuring emissivityby infrared radiometer（２）

20

Measuring procedure (１)

1. Set up the sample on warming equipment2. Measure the surface temperature of the blackbody arton the sample setting emissivity in a known value: Tb1

3. Measure the surface temperature of the non-lackbodypart remaining emissivity in a known value: T1

4. Rising the temperature of warming equipment about10 ℃ remaining the emissivity in a known value:

5. Measure the surface temperature of the blackbodypart: Tb2 and non-blackbody part: T2

(To be continued)

Measuring emissivityby infrared radiometer（３）

21

Source: JIS A1423(Simplified test method for emissivity by infrared radiometer)

Measuring procedure (１)

6. Calculate the emissivity using below equation

=ε12

1

b

2

S T-T

T-T

ｂ

Measuring emissivityby infrared radiometer（４）

Measuring procedure (２)

22

1. Measure the temperature of the blackbody part2. Change the emissivity to agree with thetemperature of the blackbody part and read itsvalue

Conclusions

23

1. EmissivityImportant index of hot sources

2. FTIRSummarize the theory and thenote of preparation and operationIndicate the measurement procedureand the measuring example

3. Methods of measuring temperature4. Simplified measuring method foremissivity by infrared radiometer

Thank you for your kind attention