Poster presented at the Seventh Yugoslav Materials Research Society Conference - YUCOMAT 2005, Herceg Novi, Crna Gora, September 12-16, 2005

Aleksić, Obrad

Luković, Danijela

Pejović, V. Ž.

Savić, Slavica

Savić, Slavica M.

Aleksić, Obrad S.

Serbian Academy of Science and Arts Digital Archive (DAIS)

YUCOMAT 2005 - 7th Conference of the Yugoslav Materials Research Society, September 12-16 2005, Herceg Novi, Serbia and Montenegro Thermal diffusivity and electron transport properties of NTC samples obtained by photoacoustic methodS.M. Savić1, D.T. Luković1, O.S. Aleksić2, V.Ž. Pejović21Institute of Technical Sciences of SASA, Knez Mihailova 35/IV, 11 000 Belgrade, Serbia and Montenegro2Center for multidisciplinary studies of the University of Belgrade, Kneza Višeslava 1, 11000 Belgrade, Serbia and MontenegroAbstractThermal diffusivity and electron transport parameters of sintered NTC samples were  determined by the photoacoustic technique. Powder mixtures composed of MnO, NiO, CoO and Fe2 O3 were milled to nanometer particle size. NTC discs were dry powder pressed and sintered at different temperatures in the range from 9000C to 12000C for 30 minutes. A second group of NTC discs was sintered at 12000C with the sintering time varying from 30 to 240 minutes.  These NTC samples were polished and exposed to a chopped laser beam in order to plot a response in the acoustic range. The thermal diffusivity of sintered NTC layers based on a metal oxide powder mixture was measured at room temperature by the photoacoustic (PA) technique. An increase of thermal diffusivity with sintering temperature and time of sintering was observed.Experimental¾Powder preparation:Calcinating (10500C, 60 min)Ball milling (particle size-0.9μm)Pressing (2.5 MPa)Sintering conditions (9000C, 10500C, 12000C- 30 min;  12000C –30, 60, 120, 240 min)¾SEM (JEOL JSM 6460LV)¾Photoacoustic measurements101 102020406080100120140160180200220   S 1, 9000C, 30 min S 2, 10500C, 30 min S 3, 12000C, 30 min S 4, 12000C, 60 min  S 5, 12000C, 120 min S 6, 12000C, 240 minPA phase [0]Frequency [Hz]101 10210-310-210-1100101   S1, 9000C, 30 min S2, 10500, 30 min S3, 12000C, 30 min S4, 12000C, 60 min S5, 12000, 120 min S6, 12000, 240 minPA amplitudeFrequency [Hz]Experimental phase and amplitude PA diagrams for NTC samples sintered in different  conditions101 102050100150200  S1, 9000C, 30 min Exp. points Theor. curvePA phase [0]Frequency [Hz]101 10210-410-310-210-1 S1, 9000C, 30 min Exp. points Theor. curvePA amplitudeFrequency [Hz]Experimental (points) and theoretical (dashed line) phase and amplitude PA diagrams for a NTC  sample sintered at 9000C for 30 minutes.Values of calculated parameters for sintered NTC samplesSample T [°C] /t [min] DT [m2/s] τ [s] D [m2/s] μ [cm2/Vs]1 900 / 30 0.35x10-6 0.85x10-2 0.47x10-7 1.8x10-22 1050 / 30 0.68x10-6 0.78x10-2 0.27x10-8 2.7x10-43 1200 / 30 0.73x10-6 0.20x10-1 0.34x10-7 1.3x10-24 1200 / 60 0.83x10-6 0.10x10-1 0.82x10-8 3.2x10-35 1200 / 120 0.87x10-6 0.14x10-1 0.32x10-8 1.3x10-36 1200 / 240 0.88x10-6 0.12x10-1 0.30x10-8 1.2x10-3    SEM images obtained from surfaces of samples sintered for 30 minutes at different temperatures: 900°C (a), 1050°C (b) and 1200°C (c).900 1000 1100 12003,03,54,04,55,05,56,06,57,07,5t=30 min  DT x 107 [m2 /s]T [0C]0 50 100 150 200 2507,27,47,67,88,08,28,48,68,89,0T=12000C  DT x 107 [m2 /s]t [min]a) b) c)a) b) c)SEM images obtained from surfaces of samples sintered at 1200°C for different times: 60 min (a), 120 min (b) and 240 min (c)Thermal diffusivity vs. temperature (a) and time of sintering (b) for different NTC samplesa) b)Conclusion¾ The behavior of sintered NTC thermistors and changes in the microstructure after sintering are connected with thermal diffusivity and electronic transport properties¾ Thermal diffusivity increases when the temperature and time of sintering rise ¾ This is a consequence of a corresponding microstructure-increase  in interparticle contact, average grain size, material density and reduction of porosity when temperature and time of sintering rise

English

"Thermal diffusivity and electron transport properties of NTC samples obtained by photoacoustic method

Digital Repository of the Institute of Technical Sciences of SASA

YUCOMAT 2005 -
 
7th Conference of the Yugoslav Materials Research Society, September 12-16 2005, Herceg
 
Novi, Serbia and Montenegro
 
Thermal diffusivity and electron transport properties of NTC samples 
obtained by photoacoustic
 
method
S.M. Savić1, D.T. Luković1, O.S. Aleksić2,
 
V.Ž. Pejović2
1Institute of Technical Sciences of SASA, Knez Mihailova 35/IV, 11 000 Belgrade, Serbia and Montenegro
2Center for multidisciplinary studies of the University of Belgrade, Kneza
 
Višeslava
 
1, 11000 Belgrade, Serbia
 
and Montenegro
Abstract
Thermal diffusivity and electron transport parameters of sintered NTC samples were
 
 
determined by the photoacoustic
 
technique. Powder mixtures composed of MnO, NiO, CoO
 
and Fe2
 
O3
 
were milled to nanometer particle size. NTC discs were dry powder pressed and 
sintered at different temperatures in the range from 9000C to 12000C for 30 minutes. A 
second group of NTC discs was sintered at 12000C with the sintering time varying from 30 
to 240 minutes.  These NTC samples were polished and exposed to a chopped laser beam in 
order to plot a response in the acoustic range. The thermal diffusivity of sintered NTC 
layers based on a metal oxide powder mixture was measured at room temperature by the 
photoacoustic
 
(PA) technique. An increase of thermal diffusivity with sintering temperature 
and time of sintering was observed.
Experimental
¾Powder preparation:
Calcinating (10500C, 60 min)
Ball milling (particle size-0.9μm)
Pressing (2.5 MPa)
Sintering conditions (9000C, 10500C, 12000C- 30 min;  12000C –30, 60, 120, 240 min)
¾SEM (JEOL JSM 6460LV)
¾Photoacoustic measurements
101 102
0
20
40
60
80
100
120
140
160
180
200
220
 
 
 S 1, 9000C, 30 min
 S 2, 10500C, 30 min
 S 3, 12000C, 30 min
 S 4, 12000C, 60 min 
 S 5, 12000C, 120 min
 S 6, 12000C, 240 min
P
A
 p
ha
se
 [0
]
Frequency [Hz]
101 102
10-3
10-2
10-1
100
101
 
 
 S1, 9000C, 30 min
 S2, 10500, 30 min
 S3, 12000C, 30 min
 S4, 12000C, 60 min
 S5, 12000, 120 min
 S6, 12000, 240 min
P
A
 a
m
pl
itu
de
Frequency [Hz]
Experimental phase and amplitude PA diagrams for NTC samples sintered in different
 
 
conditions
101 102
0
50
100
150
200
 
 
S1, 9000C, 30 min
 Exp. points
 Theor. curve
P
A
 p
ha
se
 [0
]
Frequency [Hz]
101 102
10-4
10-3
10-2
10-1
 
S1, 9000C, 30 min
 Exp. points
 Theor. curve
P
A
 a
m
pl
itu
de
Frequency [Hz]
Experimental (points) and theoretical (dashed line) phase and amplitude PA diagrams for a NTC
 
 
sample sintered at 9000C for 30 minutes.
Values of calculated parameters for sintered NTC samples
Sample T [°C]
 
/t [min] DT
 
[m2/s] τ [s] D [m2/s] μ [cm2/Vs]
1 900 /
 
30 0.35x10-6 0.85x10-2 0.47x10-7 1.8x10-2
2 1050 /
 
30 0.68x10-6 0.78x10-2 0.27x10-8 2.7x10-4
3 1200 /
 
30 0.73x10-6 0.20x10-1 0.34x10-7 1.3x10-2
4 1200 /
 
60 0.83x10-6 0.10x10-1 0.82x10-8 3.2x10-3
5 1200 /
 
120 0.87x10-6 0.14x10-1 0.32x10-8 1.3x10-3
6 1200 /
 
240 0.88x10-6 0.12x10-1 0.30x10-8 1.2x10-3
  
  
SEM images obtained from surfaces of samples sintered for 30 minutes at different temperatures:
 
900°C (a), 1050°C (b) and 1200°C (c).
900 1000 1100 1200
3,0
3,5
4,0
4,5
5,0
5,5
6,0
6,5
7,0
7,5
t=30 min
 
 
D
T x
 1
07
 [m
2 /s
]
T [0C]
0 50 100 150 200 250
7,2
7,4
7,6
7,8
8,0
8,2
8,4
8,6
8,8
9,0
T=12000C
 
 
D
T x
 1
07
 [m
2 /s
]
t [min]
a) b) c)
a) b) c)
SEM images obtained from surfaces of samples sintered at 1200°C for different times:
 
60 min (a), 120 min (b) and 240 min (c)
Thermal diffusivity vs. temperature (a) and time of sintering (b) for different NTC samples
a) b)
Conclusion
¾ The behavior of sintered NTC thermistors and changes in the microstructure 
after sintering are connected with thermal diffusivity and electronic transport 
properties
¾ Thermal diffusivity increases when the temperature and time of sintering rise 
¾ This is a consequence of a corresponding microstructure-increase  in 
interparticle contact, average grain size, material density and reduction of 
porosity when temperature and time of sintering rise


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"Thermal diffusivity and electron transport properties of NTC samples obtained by photoacoustic method

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