Effect of Heat Treatment on theEffect of Heat Treatment on theCharacteristicsCharacteristics of SiO2 Addedof SiO2 Added--ZnFe2O4ZnFe2O4

Ceramics for NTC ThermistorsCeramics for NTC Thermistors

WiendartunWiendartun 11)), Dani Gustaman Syarif , Dani Gustaman Syarif 22))

11)) Department of Physics, UPI, Bandung. Department of Physics, UPI, Bandung. 22 )Nuclear Technology Center for Materials and )Nuclear Technology Center for Materials and

Radiometry Radiometry –– BATAN, Bandung.BATAN, Bandung.

INTRODUCTIONINTRODUCTION

R vs T- THERMISTOR

THERMISTOR Thermally Sensitive Resistor.NTC CHARACTERISTIC PRODUCT EXAMPLES APPLICATIONS

Current limiter thermistor

Specialize Thermistor

Incubator

Computer

INTRODUCTIONINTRODUCTION (Continuation)(Continuation)

Important electronic component. Important electronic component. -- Sectors: Biomedical, aerospace, instrumentation, communications, Sectors: Biomedical, aerospace, instrumentation, communications,

automotive and HVACR (Heating, Ventilation, Air conditioning and automotive and HVACR (Heating, Ventilation, Air conditioning and Refrigeration).Refrigeration).--Application : Temperature measurement, circuit compensation, Application : Temperature measurement, circuit compensation,

suppression of in rushsuppression of in rush--current, flow rate sensor and pressure sensor. current, flow rate sensor and pressure sensor. Most, Most, thermistorsthermistors are produced from are produced from spinelspinel ceramics based on ceramics based on Most, Most, thermistorsthermistors are produced from are produced from spinelspinel ceramics based on ceramics based on transition metal oxides forming general formula AB2O4transition metal oxides forming general formula AB2O4..Need alternative {Need alternative {ExpeciallyExpecially based on abundant material [based on abundant material [yarosityarositmineral( Fe3O4)] in Indonesia} mineral( Fe3O4)] in Indonesia} ZnFeZnFe22OO44 is proposed, including is proposed, including that added with SiOthat added with SiO22..Predicted that the heat treatment effect can improve the Predicted that the heat treatment effect can improve the characteristics of the ZnFecharacteristics of the ZnFe22OO44 ceramic for NTC ceramic for NTC thermistorsthermistors. .

EXPERIMENTEXPERIMENT

ZnO Fe3O4 0.5%SiO2

MIXING

Optical Microscope

CALCINATION

CRUSHING

SIEVING

PRESSING

SINTERING1200oC/2h/60C/60C

CHARACTERIZATION-XRD-Electrical-Microstructural

3,9 ton/cm2

800oC/2hSintering Furnace

XRD

Heat Treatment10000C/10’/100C/100C10000C/10’/100C/ 20C10000C/10’/100 C/quenching

Heat TreatmentHeat Treatment

T

1000C

t

1000C

10’ 20’

1000C/10’/10C/2C1000C/10’/10C/ 10C1000C/10’/10C/quenching

Visual Appearance of typical SiO2Visual Appearance of typical SiO2AddedAdded--ZnFe204ZnFe204

RESULTS (XRD Profile)RESULTS (XRD Profile)

0.5 w/o SiO2 sintered at 1200 C/2h/6 C/6 C

Inte

ns

ita

s (

a.u

.)

220

311

511 440

Inte

ns

ita

s (

a.u

.)

XRD profiles of ZnFe2O4 based-ceramics.

0 w/o SiO2 sintered at 1200 C/2h/6 C/6 C

20 30 40 50 60 70 80

2q (Derajat)

Inte

ns

ita

s (

a.u

.)

222

400422 533

622

2q (Derajat)

Inte

ns

ita

s (

a.u

.)

RESULTS (Microstructure)RESULTS (Microstructure)

Grain

Grain boundary Grain

Pore

Microstructure of the ZnFe2O4 based-ceramics.

50 m

Pore Grain boundary

0 w/o SiO2 sintered at 1200 C/2h/6 C/6 C0.5 w/o SiO2 sintered at 1200 C/2h/6 C/6 C

Electrical CharacteristicElectrical Characteristic

R = RR = R00. Exp.(B/T). Exp.(B/T)Ea = B.k Ea = B.k α = α = -- B/TB/T22

R = Thermistor resistanceR = Thermistor resistanceRR00 = Resistance at the infinite temperature= Resistance at the infinite temperatureB = Thermistor constantB = Thermistor constantT = Temperature of thermistorT = Temperature of thermistorEa = Activation energyEa = Activation energyk = The Boltzmann constantk = The Boltzmann constantα = Sensitivity of thermistorα = Sensitivity of thermistor

RESULTSRESULTS(Electrical Characteristics)(Electrical Characteristics)

10

11

12

13

14

ln R

ho

Rata

-rata

(o

hm

.cm

)

Ln resistivity () vs 1/T of SiO2 added- ZnFe2O4 ceramics.

6

7

8

9

0.0025 0.0027 0.0029 0.0031 0.0033

Suhu (Kelvin)

ln R

ho

Rata

-rata

(o

hm

.cm

)

● 10000C/10’/100C/20C■ 10000C/10’/100C/100C▲ 10000C/10’/100C/quenching

RESULTSRESULTS(Electrical Characteristics)(Electrical Characteristics)

No. Heat treatment B( 0K)

Ea(eV)

α( %/ 0K)

ρRT( kOhm-

cm)

1 Sintered at 12000C/2hours/6C/6C)

(Initial) -

- - 98

2 1000 C/10min/ 10C/ 10 C 3978 0.34 4.42 38

Market requirement for B is ≥ 2000 oK and is ≥ 2.2 %/oK[7], and for RT = 10 ohm.cm -1 Mohm.cm [4].

Tabel of The value of the thermistor constant (B), sensitivity (α) and room temperatureresistivity (ρRT) of 0.5 weight % SiO2 added-ZnFe2O4 ceramics.

2 1000 C/10min/ 10C/ 10 C 3978 0.34 4.42 38

3 1000 C/10min /10C/ 2 C 3705 0.32 4.12 154

4 1000C/10min/10C/quenching 3014 0.26 3.35 12

CONCLUSIONSCONCLUSIONSThe grain size of the ZnFeThe grain size of the ZnFe22OO4 4 ceramics ceramics tends to decrease by addition of SiOtends to decrease by addition of SiO22. .

The Heat Treatment can be adopted in The Heat Treatment can be adopted in thermistor fabrication to control the thermistor fabrication to control the thermistor fabrication to control the thermistor fabrication to control the electrical characteristics of the thermistor.electrical characteristics of the thermistor.

The values of the thermistor constant (B) The values of the thermistor constant (B) and the room temperature resistivity (and the room temperature resistivity (RT RT ))

of the ZnFeof the ZnFe22OO44 ceramics made in this ceramics made in this work fits the market requirement.work fits the market requirement.

THANK YOUTHANK YOU

ACKNOWLEGMENTACKNOWLEGMENTTheThe authorsauthors wishwish toto acknowledgeacknowledge theirtheir deepdeep gratitudegratitudetoto DIKTI,DIKTI, DepartmentDepartment ofof NationalNational EducationEducation ofofIndonesianIndonesian GovernmentGovernment forfor financialfinancial supportsupport underunderHibahHibah PekertiPekerti programprogram withwith contractcontractHibahHibah PekertiPekerti programprogram withwith contractcontractNoNo..032032/SP/SP22H/PP/DPH/PP/DP22M/III/M/III/20072007