Fabrication of Nano - Size Nickel Ferrites for Gas Sensors...

I. A. Abdel-Latif JOURNAL OF PHYSICS VOL. 1 NO. 2 July (2012) PP. 50 - 53

Copyright 1996-2012 Researchpub.org. All rights Reserved. 50

Abstract — Nano-size nickel Ferrites are used for a sensors

applications for different gases. In the present work, synthesis

of nano crystalline NiFe2O4 and its characterization have been

studied. NiFe2O4 is prepared using co-precipitation method

from the chemical reaction of solution of pure chloride of

nickel and iron with solution of pure Sodium hydroxide. The

co precipitated powder at ph =12.5 and at temperature 85oC is

formed to be NiFe2O4. The X-Ray diffraction test reveals that

this powder has the well known spinel cubic structure. The

crystalline size of the co precipitated powder without any

annealing is 74.93nm while the crystalline size of the annealed

powder at temperature 1000oC for 6h is 225.45nm. The

resistivity of the NiFe2O4 of crystalline size of 74.93nm at

temperature 30oC is 6.598××××10

7 Ω.m. The resistivity decreased

100 times after annealing (The resistivity at temperature 30oC

after annealing at 1000oC is 5.596××××105 Ω.m. That is means that

the increase in the crystalline size leads to decrease in the

resistivity.

Keywords: Gas sensors, Nickel Ferrites, Spinel,

Characterizations.

I. INTRODUCTION

he global warming of the earth, which is a serious environmental problem, is caused by emission of greenhouse gases such as carbon dioxide (CO2),

methane, nitrous oxide and perfluorocarbons [1]. Recently, it was shown that CO2 could be actively decomposed to

Manuscript received May 12, 2012 and accepted june 20, 2012. Physics Dept., Najran Ubniversity, Najran P.O. 1988, KSA. On leave from Physics Dept., NRC, Atomic Energy Authority,

Abou Zabaal P. O. 13759 Cairo, Egypt. E-mail: [email protected].

The current research is carried out in the frame of Najran

University Grant NU 07/10.

carbon and oxygen around 300 °C on the surface of oxygen-deficient ferrites MxFe3-xO4-δ (M~ divalent metallic ion), where δ is the oxygen deficiency [2]. Nanometer sized materials which are associated with a high surface activity due to their small particle size and enormous surface area, have been widely studied as gas sensors [3–7]. A large number of metal oxides, mixed oxides and ferrites have shown sensitivity to certain gas species. Spinel compounds, with a general formula of AB2O4, have also been proved as important oxides in gas sensors, and have been investigated for the detection of both oxidizing and reducing gases [7].

There are a few reports in the literature of attempts to develop sensors for chlorine based on semiconducting oxides. Palladium doped SnO2 [8] is shown to detect Cl2 gas but a sparker is necessary to improve the sensing characteristics. Thin films of indium tin oxide (ITO) [9] and hetero-contacts of SiC:ZnO [10] have also shown sensitivity to Cl2. In the latter case the sensitivity has been explained to be due to the interaction between the test gas and the humidity. There is also a galvanic cell type Cl2

sensor that makes use of an Ag_-ion conductivity electrolyte coated on one side with a thin film of AgCl containing material [11].

Different spinel ferrites such as NiFe2O4, CdFe2O4, ZnFe2O4 and CuFe2O4 have been studied for various gas-sensing applications [2,6,12,13]. Nickel ferrite (NiFe2O4) has been widely studied as a magnetic material [14-16] but information related to its gas-sensing properties towards reducing gases is still limited.

Recently Korotcenkov [17] suggested that the shape control of the nano-crystallites can provide energetically different adsorption sites for the test gases on different crystal facets. Thus existence of large surface to volume ratio in the typical nano-structured material facilitates better response towards specific gases. Moreover, morphology and particle size of nano-materials depend upon their method of preparation and sintering temperatures, and hence one can observe different responses towards gases for the similar composition.

Nano-crystalline Nickel ferrites were fabricated using chemical reaction method and characterization was carried out in the present work.

Fabrication of Nano - Size Nickel Ferrites for Gas Sensors Applications

Ihab A. Abdel-Latif

T



II. EXPERIMENTAL DETAILS

Nano-crystalline NiFe2O4 were synthesized using co-

precipitation method from the chemical reaction of solution of pure chloride of nickel and iron with solution of pure sodium hydroxide. These solutions were mixed using magnetic stirrer with heating at temperature 85°C for 4h. The co precipitated powder obtained at ph =12.5 and during stirring process. The obtained powder was pressed asa disc at 3T and then fired at different temperatures; 500°C and at 1000°C for 6h. The XRD measurements were performed using a PANalytical X’pert Pro MPR diffractometer with Cu radiation. The elemental analysis, EDXS spectra, and micrograph measurements were carried out using Field Emission Scanning Electron Microscope FE-SEM – JEOL (JSM-5600) with acceleration voltage 15kV and magnification of x43000. The DC resistivity – temperature dependence measurements were carried out using two and four points probe technique (Scientific Equipment & Services) in the temperature range from room temperature to 573 K.

III. RESULTS AND DICUSSIONS

Considering that hydroxides decompose by a strong heat

of reaction [18] to produce oxides in the reaction process; the mechanism of NiFe2O4 formation is illustrated as follows: Ni Cl2.4 (H2O) + 2NaOH → Ni(OH)2 +2NaCl+ 4H2O

At room temperature 2Fe Cl3.4(H2O) +6NaOH→ 2Fe(OH)3 +6NaCl+ 8H2O

At room temperature The intermediate reaction products Ni(OH)2 and Fe(OH)3, due to their small size and high activity decompose rapidly to produce NiO and Fe2O3 nanoparticles with generation of high heat of reaction.

Ni(OH)2→NiO + H2O + heat 2Fe(OH)3→ Fe2O3+ 3H2O + heat

These nanoparticles, due to the presence of the sodium chloride facilitate formation of crystalline NiFe2O4 without any agglomeration. The XRD patterns, in the 2θ range from 20° to 90°, are shown in fig.1. The X-Ray diffraction test reveals that this powder has the well known spinel cubic structure of space group Fm3m. XRD patterns fitted according to Reitvield method and Fullprof software was used [19]. The a lattice parameter was

calculated to be 8.332Å which is in good agreement with those reported [20] and JCPDS Card No.10-325. Aluminum peaks appeared in the diffraction pattern, corresponding to the data reported by Fortes et al., [21], are attributed to the sample holder.

From XRD patterns it was noted that there are broadening in peaks which are good indication to forming the crystalline nano-size. The crystalline phase is increased with raising

a) As prepared powder

b) Fired at 500°C for 6h

c) Fired at 1000°C for 6h

Fig.1 XRD patterns for NiFe2O4 at different heat

treatment.

sintering temperature where the broadening of the peaks for the powder as prepared decreased with higher temperature treatment. The crystalline size of the co precipitated powder without any annealing is 29.2 nm. The crystalline size of the annealed powder at temperature 500oC for 6h increased to be 60.5 nm and finally reached 225.45nm for the annealing at temperature 1000oC.

From EDXS spectrum which is shown in fig. 2 one can conclude that the obtained powder consists of the proposed

I. A. Abdel-Latif

Copyright 1996-2012 Researchpub.org. All rights Reserved.

chemical formula, NiFe2O4. It is quite clear that the experimentally observed percentages of elements are in a good agreement with those theoretically calculated

Fig.. 2 EDXS spectrum of the proposed chemical

formula, NiFe2O4.

The microstructure graphs of NiFe2O4

treatment are illustrated in Fig. 3. It is quite there is homogeneity in the size of particles all over the graph. The minimum particle size is 29.2nm of the ample as prepared while the maximum particle size The mean value of the particle size is 225.45nm good agreement with the crystalline size deduced fXRD measurements.

The measured dc resistivity of the NiFesize of 74.93nm at temperature 30oC is 6.598resistivity decreased 100 times after annealing (The resistivity at temperature 30oC after annealing at 10005.596×105 Ω.m). That is means that the increase in the crystalline size leads to decrease in the resistivity.semiconducting behavior is observed.

It is well known that depending upon the morphology and operating temperatures; the oxide surface holoxygen species, such as O- ,O-

, O-2 . Their number and distribution also plays an important role in the gas sensing characteristics [18].

ACKNOWLEDGEMENTS

The Najran University grant (NU grant No acknowledged. The author expresses all the gratefulness for all members of the Center for Advanced Materials & Nano-Engineering CAMNE

JOURNAL OF PHYSICS VOL. 1 NO. 2

2012 Researchpub.org. All rights Reserved.

It is quite clear that the experimentally observed percentages of elements are in a

calculated

Fig.. 2 EDXS spectrum of the proposed chemical

4 at different heat quite clear that say

size of particles all over the is 29.2nm of the ample

particle size is 190.48 nm. 225.45nm which in

good agreement with the crystalline size deduced from

resistivity of the NiFe2O4 of crystalline C is 6.598×107 Ω.m. The

resistivity decreased 100 times after annealing (The C after annealing at 1000oC is

.m). That is means that the increase in the crystalline size leads to decrease in the resistivity. The s

It is well known that depending upon the morphology ; the oxide surface hold various

. Their number and distribution also plays an important role in the gas sensing

ACKNOWLEDGEMENTS

The Najran University grant (NU grant No 7/10) is all the gratefulness

for all members of the Center for Advanced Materials &

Fig.3 Micrograph of

treatment .

July (2012) PP. 50 - 53

52

Fig.3 Micrograph of NiFe2O4 at different heat



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Fabrication of Nano - Size Nickel Ferrites for Gas Sensors...

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