chapter 4 synthesis of mg- ferrite -...

Chapter 4 Synthesis of Mg- ferrite

D. Y. Patil University, Kolhapur 72

4.1. Introduction

Spinel MgFe2O4 nanoparticles have been extensively used in various

technological and biomedical applications in the past decades. It covers wide

range of applications including humidity sensor, switching circuits, contrast

agent in magnetic resonance imaging, tissue repair, immunoassays,

detoxification of biological fluids, targeted drug delivery and magnetic

hyperthermia [1-3]. The effective applicability of such ferrimagnetic/

superparamagnetic nanoparticles is driven by their physical and chemical

property which is highly sensitive to their shape and sizes. The shape and size of

these nanoparticles can be effectively controlled by the synthesis route [4-5]. In

recent years, various physical and chemical techniques such as co-precipitation,

forced hydrolysis, polyol [6], sol-gel [7], ball milling [8] and combustion [9a and

9b] have been successfully used for the synthesis of MgFe2O4 nanoparticles.

Although chemical co-precipitation method is suitable for mass production of

magnetic nanoferrites, it does require careful adjustment of the pH value of the

solution for particles formation. On the other hand, combustion synthesis

(glycine-nitrate process) offer many distinct advantages for synthesizing

magnesium ferrites as it produces high-surface-area with less reaction time,

compositionally homogeneous powder, usually with low levels of residual

carbon. These advantages are mainly due to the nature of the fuel-oxidant

combustion reaction, which is rapid, self-sustaining and exothermic in nature.

The surface area, size-distribution and agglomeration of the particles in

final product depend on the adiabatic flame temperature which in turn related to

nature of fuel as well as fuel to oxidant ratio (F/O). Adiabatic flame temperature

helps in crystallization and formation of desired phase of compound. However,

high adiabatic flame temperature adversely affects the particle characteristics

like increase in crystallite size and increased agglomerates. Very little work is

done to figure out the effect of F/O ratio on characteristics of product in terms of

thermodynamic considerations including adiabatic flame temperature and heat

absorbed by the products i. e. heat of reaction [10-12]. The fuel used in reaction



should be able to maintain homogeneity among constituents and also undergo

combustion with oxidizer at low ignition temperature.

The choice of fuel and amount of fuel plays a crucial role in obtaining the

desired magnetic nanoparticles. The present chapter deals with the optimization

of combustion method for the synthesis of MgFe2O4 nanoparticles with desired

structural and magnetic properties. The amount fuel is varied and the effect of

glycine to nitrate ratio on powder characteristics of MgFe2O4 was studied in

detail in terms of thermodynamic considerations. The powder obtained was

characterized by XRD, SEM, TEM and VSM. Adiabatic flame temperatures

were calculated theoretically for the combustion reactions for different G/N

ratios and systematically discussed.

4.2. Experimental

4.2.1. Synthesis of MgFe2O4 nanoparticles

Analytical grade Ferric nitrate nonahydrate Fe (NO3)3⋅ 9H2O, Magnesium

nitrate hexa hydrate Mg (NO3)2⋅ 6H2O were used as oxidants and glycine as a

fuel to accomplish the combustion reaction. All the reagents used were of high

degree purity.

In the present work, glycine (NH2CH2COOH) was used as a fuel because

it turns out to be a cost effective alternative to urea and citric acid. It has a

relatively negative heat of combustion (−3.24 Kcal/g) as compared to urea

(−2.98 Kcal/g) or citric acid (−2.76 Kcal/g) [13]. The oxidation valences of

metal nitrates were balanced by reducing valences of the fuel so that equivalence

ratio was unity and energy released was maximum [14]. In a typical procedure

the stoichiometric amount of reactants were calculated as described above and

hand mixed in large beaker. The mixture was turned into the slurry due to

hygroscopic nature of metal nitrates. The beaker was then kept on hot plate

preheated to 300 °C. During combustion, the spark was occurred at one corner

which spread over the mass resulting brown fluffy product that gets transformed

into powder by slightest touch. As the amount of glycine (fuel) plays an

important role in combustion synthesis; in present case, the glycine to nitrate



ratio (G/N) was varied as 0.48, 0.74, 1.48, 2.22 and 2.56. This respectively

makes three combustion systems: fuel lean, fuel efficient and fuel rich wherein

G/N=1.48 represents stoichiometric ratio for combustion. The samples were

indexed as V1, V2, V3, V4 and V5 for G/N ratios 0.48, 0.74, 1.48, 2.22 and 2.56

respectively.

4.2.2. Characterizations

Thermal properties of precursor gel were recorded by the Trans-analytical

instrument (SDT 2960) operated in temperature 35 ⁰C to 1000 ⁰C with heating

rate of 10 ⁰C/min in flowing air ambiance to investigate the decomposition

behavior of nitrate and fuel mixture. All the samples were characterized by

Philips PW-3710 automated X- ray diffractometer equipped with crystal

monochromator employing Cr-Kα radiation of wavelength 2.28970 Å for

structural and phase identification. The crystallite size of the as-synthesized

product was estimated from the full-width at half-maximum (FWHM) of the

strongest diffraction peak using the Scherrer formula given in equation 3.5. [15]

The particle shape, size and morphology were investigated by Scanning electron

microscope (JEOL JSM 6360) and Transmission Electron Microscope (Philips

CM 200 model, operating voltage 20-200 kV, resolution 2.4 Å). Fourier

transform Infra Red spectrum was recorded with the help of Perkin-Elmer

spectrometer, (Model No. 783, USA) in the range of 400 to 2000 cm-1 to confirm

the formation of spinel phase and purity of the samples. Magnetization and

coercivity for all the samples was measured by vibrating sample magnetometer

(VSM) at room temperature [Lake Shore 7307].



4.3. Results and Discussion

4.3.1. Thermodynamic analysis

4.3.1.1. Thermal analysis

Figure 4.1. TG-DTA curve for stoichiometric precursors gel (a) and as

prepared MgFe2O4 nanoparticles

The simultaneous TG-DTA curves for stoichiometric precursor gel and as

prepared MgFe2O4 nanoparticles were recorded in temperature range of room

temperature to 1000 °C in air ambiance (Figure 4.1a and 4.1b respectively). The

TG-DTA in Figure 4.1a consists of three stages corresponding to different

reaction mechanisms. TG shows a primary weight loss of about 30% below 194

°C which is due to complete evaporation of water and organic contents in the

precursor gel. The sudden weight loss of 56% was observed between temperature

range of 194 °C to 200 °C which is attributed to rapid chemical reaction between

metal nitrates and glycine. This maximum weight loss occurs in narrow

temperature range which corresponds to decomposition step. The overall weight

loss of 86% for sample was observed which is in good agreement with

theoretically predicted weight loss of (84%).

The theoretical weight loss was calculated by using atomic weights of

reactants and products in combustion reaction. (Mg=24.31, N=14.01, O=15.99,

H=1.008, C=12.01, Fe=55.85 )

a b



The weight of reactants:

Mg(NO3)2•6H2O = WMg + 2 WN + 12 WO + 12WH

= 24.31 + 28.02 + 191.88 + 12.096

= 256.306

Fe (NO3)3•9H2O = WFe + 3 WN +18 WO+ 18 WH

= 55.85 + 42.03 + 287.82 + 18.144

= 403.84

CH2NH2COOH = 2 WC + 5 WH + 2WO + WN

= 24.02 + 5.04 + 31.98 + 14.01

= 75.05

Total weight of reaction mixture:

W[Mg(NO3)2•6H2O] + 2 W[Fe (NO3)3•9H2O] + 4.44 W[CH2NH2COOH]

= 256.306 + 2 x 403.84 + 4.44 x 75.05

= 1353.8916 g

Weight of product (MgFe2O4 powder):

= WMg + 2 WFe + 4 WO

= 24.31 + 111.7 + 36.96

= 199.97

Therefore the yield of combustion reaction can be predicted as:

Yield = (W product/ W reactant mixture) x 100

= (199.97 / 1343.8916) x 100

= 14.87 %

This amounts to the overall reaction yield of about 14%.

The sharp exothermic peak observed in DTA curve around 194 °C was

attributed to ignition of precursors at this temperature. The acceleration of

reaction rate and lowering of ignition temperature results in combustion reaction

between metal nitrates and glycine.

On the other hand, TGDTA curve for as prepared sample does not show

any significant weight loss. Observed weight loss of about 6 % in case of as

prepared samples may correspond to the evaporation of physical adsorbed water

or uncombusted carboneous materials. The results show that combustion



synthesis is able to produce stable and pure ferrite nanoparticles. These as

prepared nanoparticles are further used for characterization without any

subsequent heating treatment.

4.3.1.2. Thermodynamic considerations

As the nature of fuel and fuel to oxidizer ration plays an important role

in determining the structural and magnetic properties of prepared magnetic

materials, the thermodynamic analysis has been taken into consideration.

According to the principle of propellant chemistry, when stoichiometric amount

of fuel is mixed with metal nitrates then product of reaction consists of

environment friendly gases like H2O, N2 and CO2. The combustion reaction

between metal nitrates and glycine can be expressed as:

(4.1)

where Φ is molar ratio between glycine and nitrates. Here Φ = 4.44/3=

1.48 is the stoichiometric ratio which implies that product can be formed directly

from the reaction without consuming external oxygen. Thus different values of Φ

in above equation represent the different G/N ratios. The theoretical calculations

based on thermodynamic consideration such as enthalpy of reaction and flame

temperature helps in estimation of exact ignition condition and initiation of

combustion reaction. Enthalpy of reaction depends on the heat of formation of

products and reactants. The following equation is used to calculate the enthalpy

of reaction:

(4.2)

where n is the number of moles, ∆Hf° is heat of formation and ∆H° is

enthalpy of reaction. The thermodynamic data for various reactants and products

involved in combustion is available in literature [11-13 and 16] and listed in

Table 4.1. The Enthalpy of reaction as a function of Φ can be calculated by using

thermodynamic data (Table 4.1) and eq. 4.1 as follows:

3 2 2 3 3 2 2 2 2

2 4 2 2 2

Mg (NO ) 6H O +2 Fe (NO ) 9H O +4.44 CH NH COOH + (9.99 -10) O

MgFe O + 8.88 CO + (4 +2.22 ) N + (24 + 11.1 ) H O

Φ Φ →

Φ ↑ Φ ↑ Φ ↑

0 o of products f reactantsH = ( n H ) - ( n H ) ∆ ⋅ ∆ ⋅∆∑ ∑



(4.3)

The heat absorbed by product during combustion reaction can be

theoretically approximated as:

(4.4)

Eq. 4.4 can be modified to calculate adiabatic flame temperature (Tad) as follows,

(4.5)

where Q is the heat absorbed by products under adiabatic condition, T is the

reference temperature (T= 298 K) and Cp is the heat capacity of the products at

constant pressure.

Table 4.1. Thermodynamic data required for calculation of adiabatic flame

temperature [11-13 and 15]

a all values considered at ambient temperature T=25°C

Using data from Table 4.1, eq. 4.1, eq. 4.4 and eq. 4.5; the adiabatic flame

temperatures and heat absorbed by products for various G/N ratios were

calculated and tabulated in Table 4.2. As expected, the values of theoretically

calculated Tad and heat absorbed by product are increase with increase in amount

of glycine. The reaction temperature and Tad increases with increase in G/N ratio.

However beyond the optimum value of temperature, the decrease in reaction

temperature with further increase in G/N ratio is observed attributed to the

amount of gases released during reaction which may dissipates heat. This gives

Compound Heat of formationa

∆Hf° (kcal/mol)

Heat capacitiesa

cp (cal/mol K)

Fe(NO3)3 9H2O (s) -785.2 -

Mg(NO3)2 6H2O (s) -624.48 -

CH2NH2COOH (s) -79.71 -

H2O (g) -57.79 7.2+0.0036T

CO2 (g) -94.05 10.34+0.00274T

N2(g) 0 6.5+0.001T

O2 (g) 0 5.92+0.00367T

MgFe2O4 (s) -343.69 34.16

adT0p298 products

Q= - H = ( n c ) dT ∆ ⋅∑∫

QT = T +ad Cp

0H = 464.23 + (-1122.72) (25°C, kcal)∆ Φ



rise to lower values of reaction temperature than that of theoretically calculated

Tad.

Table 4.2. Variation of Adiabatic flame temperature (Tad), heat absorbed (Q) by

product and number of moles of gases evolved during combustion at different

G/N ratio

4.3.2. Structural analysis

4.3.2.1. X-ray diffraction

.

.

Figure 4.2. XRD patterns of samples V1, V2, V3, V4 and V5 using different

G/N ratio: 0.48, 0.74, 1.48, 2.22 and 2.96

Sample G/N Q (kcal/mol) Tad (K) Number of

moles of gases

evolved

V1 0.48 -94.18 11 35.32

V2 0.74 97.13 565 39.1

V3 1.48 658.49 1711.34 50.2

V4 2.22 1219.85 2442.15 61.3

V5 2.96 1781.21 2948.89 72.4



Figure 4.2 exhibits, X- ray diffraction patterns of MgFe2O4 powder prepared by

combustion method at various G/N ratios. The diffraction peaks corresponding to

planes (220), (111), (311), (400), (422) and (511) were well matched with

JCPDS card No. 36-0398 which confirms the formation of pure MgFe2O4 phase

with space group fd3m

The variation of crystallite size (D) and X-ray density (dxrd) with different

G/N ratio are shown in Figure 4.3. From figure, it is seen that the crystallite size

decreases with increasing G/N ratio, attains minimum value at sample V3 and

then slightly increases. It is also interesting to note that the intensity of Bragg

peak is also minimum for stoichiometric sample corresponding to smaller

crystallite size of sample compared to other variations.

Figure 4.3. Variation of crystallite size and X-ray density with G/ N ratio

Figure 4.3 indicates a small dependence of crystallite size on the synthesis

conditions such as adiabatic flame temperature, number of mole of gases escaped

during combustion and enthalpy of reaction. The large amount of gases produced

during the combustion may carry heat from system and thereby hindering the

growth of particles. The properties observed for stoichoimetric condition are due

to dominant effect of number of gas molecules escaped over adiabatic flame

temperature. The dependence in values of crystallite size and lattice parameter



with G/N ratios is probably due to competition between adiabatic flame

temperature and number of gases evolved during synthesis [10].

4.3.2.2. FT-IR

The formation of the spinel phase in the nanocrystalline MgFe2O4 samples

is supported by FT-IR spectra. The FT-IR spectra for variable G/N ratios were

recorded in the range 400 to 2000 cm-1 (Figure 4.4.). The absorption bands

appeared at ~450 cm-1 and ~565 cm-1 corresponding to stretching vibration of

metal-oxygen bonds at tetrahedral and octahedral sites respectively are observed

in case of spinel ferrites. The band observed at 1638 cm-1is due to N-O stretching

and the intensity of band is found to increase with increase in the G/N ratio.

Figure 4.4. FT-IR spectra of V1, V2, V3, V4 and V5 samples at different G/N

ratios: 0.48, 0.74, 1.48, 2.22 and 2.96 respectively

From Figure 4.5, the shift in values of absorption bands from lower

wavenumber (559 cm-1) to higher wavenumber (567 cm-1) with increasing G/N

ratio can be attributed to shifting of Fe3+ and Mg2+ ions towards oxygen ion on

occupation of tetrahedral and octahedral sites, which decreases the Fe3+-O2- and



Mg2+-O2- distances [16]. On the basis of this data it can be suggested that the

MgFe2O4 spinel phase is formed with cation distribution,

where x is inversion parameter while A and B are tetrahedral and

octahedral places in spinel structure respectively. The inversion parameter is

equal to 0 for inverse spinel and is 1 when structure is normal spinel. The

observed values illustrates that the frequency band appeared at ~560 cm-1 and

~450cm-1 are responsible for the formation of spinel MgFe2O4 [17]. The

remarkable increase in the intensity and area of investigated bands with increase

in G/N ratio suggests the enhancement in MgFe2O4 production.

Figure 4.5. Variation of octahedral wavenumber with glycine to nitrate

ratio

4.3.2.2. SAED pattern

The presence of ring pattern in selected area electron diffraction (SAED)

pattern assures the formation of polycrystalline MgFe2O4 (Figure 4.6). From

figure exhibits strong diffraction rings which supports the formation of pure and

highly crystalline MgFe2O4 nanoparticle by low temperature combustion method.

3+ 2+ 2+ 3+ 2-

1-x x A 1-x 1+x B(Fe Mg ) [Mg Fe ] O



The rings are consistent with Braggs diffraction peaks in XRD pattern and are

indexed accordingly.

Figure 4.6. Selective Area Electron Diffraction pattern for stoichiometric

sample (V3)

4.3.3. Microstructural analysis

4.3.3.1. SEM

The SEM images of MgFe2O4 nanoparticles with different G/N ratio are

shown in Figure 4.7. Obtained images show remarkable change in the

microstructure regarding porosity, grain size of samples. This shows the

dependence of microstructure on different reactant composition [16]. From

figure 4.7a and b it can be concluded that lower G/N ratio favors frothy and

small holes within structure, which may be due to escaping large number of

gases during the combustion. While for intermediate G/N ratio, small spherulitic

porous structure dominates.

For higher G/N ratio, (Figure 4.7d and e) foamy agglomerated particles

with a wide distribution and larger voids in their structure are observed. It can be

seen from figure that all samples exhibit larger grains in the range of 200-500 nm

and having a network with voids and pores. The porosity in all cases is found to

be entirely intergrannular. The formation of pores is attributed to the release of



d

e

a b

c

large amount of gases during combustion process. The formation of multigrain

agglomerates observed in all samples consists of very fine crystallites as they

show strong tendency to form agglomerates [18]. The appearance of spongy

structure with increasing G/N ratio was attested a better crystallinity of spinel

phase.

.

Figure 4.7. SEM images of [a] V1, [b] V2, [c] V3, [d] V4 and [e] V5 using

different G/N ratios: 0.48, 0.74, 1.48, 2.22 and 2.96 respectively



The minimum amount of fuel used in the case of the fuel-lean results in a

small enthalpy and hence the local temperature of the particles remains low,

which may prevent the formation of a dense structure. Associated gas evolution

results in highly porous structure, i.e., as the amount of gas increases

agglomerates are more likely to break up and more porosity will be observed as

in case of higher G/N ratio. Figure 4.8 shows the TEM image recorded for the

stoichiometric sample V3 which revealed the particle size of MgFe2O4 powder in

the range of 20 to 40 nm.

Figure 4.8. TEM image for stoichiometric MgFe2O4 NPs

4.3.4. Magnetic properties

4.3.4.1. M-H loop analysis

The specific magnetization curves of the investigated samples, obtained

from room temperature VSM measurements are shown in Figure 4.9. These

curves are typical for a soft magnetic material and indicate hysteresis loops [9].

From these measurements magnetization (Ms), Remenance (Mr) and coercivity

(Hc) are derived and listed in Table 4.3. It can be seen that the magnetization of

sample V5 is much smaller as compared to other samples. This is attributed to its

poor crystallization and relatively small grain size at fuel rich combustion.



Sample V1 has an average grain size of about 40 nm and magnetization

about19emu/g at room temperature. The magnetization of stoichiometric sample

V3 is about 31.56 emu/g which is close to that of bulk MgFe2O4 material

(approximately 30 emu/ g) [19]. It should also be noted that the Mr value is also

maximum for stoichiometric MgFe2O4. From figure it is clear that the

magnetization, remanance and coercivity increases with increase in G/N ratio

attains maximum at stoichiometric condition then decrease further for higher

glycine amount. The change in the magnetic properties may be attributed to the

low crystalline anisotropy, which arises from crystal imperfection and the high

degree of aggregation. G/N ratio strongly influences, the maximum reaction

temperature Tm: when Φ (thus G/N) increases, Tm first increases until (Φ=1)

stoichiometric condition is reached and then decreased in fuel-rich conditions

because large amounts of gases (CO2, H2O, N2) are released which dissipates the

heat of the process [19].

Figure 4. 9. M-H measurements at room temperature for V1, V2, V3, V4 and V5

at different G/N ratios: 0.48, 0.74, 1.48, 2.22 and 2.96 respectively



As a consequence, for the highest G/N values, the released energy was not

sufficient to burn all the organic matter which in turn affects the magnetic

properties of MgFe2O4. Also it has been proved that combustion method is able

to induce the redistribution of cations along A and B sites. The variations in

magnetic properties can also be attributed to the change in the distribution of

Mg2+ and Fe3+ ions at A and B site of the spinel structure with increase in G/N

ratio and surface structure disorder [3, 15].

Table 4.3 Effect of variation in G/N ratio on Magnetization (Ms), Coercivity (Hc) and

Remenance (Mr) of MgFe2O4

4.3.4.2. M-T measurements

The optimized sample stoichiometric MgFe2O4 is further subjected to

temperature dependant magnetization characterizations. The M-H curve of

MgFe2O4 nanoparticles is measured at 300 K and 10 K in order to investigate the

effect of temperature on magnetic properties like magnetization and coercivity

[Figure 4.10]. The magnetization is recorded under the applied of about 15kOe.

The saturation magnetisation of the bulk MgFe2O4 was found to be 33.6 emu/g at

300 K. It is interesting to note that the combustion process leads to increase the

saturation magnetization.

The result indicates that the magnetization of sample is increased by 24 %.

The samples have Ms of 33.83 emu/g at room temperature which increases up to

41 emu/g when temperature is reduced to 10 K. Similarly the Hc of sample

increases from 90 Oe to 127 Oe with decreasing temperature from RT to 10 K.

Sample

ID

G/N

ratio

Ms(emu/g) Hc (Oe) Mr

(emu/g)

V1 0.48 19.33 119.07 4.03

V2 0.74 27.29 93.26 4.02

V3 1.48 31.56 182 9.60

V4 2.22 21.14 110.68 3.69

V5 2.96 17.25 103.25 3.10



Such increase in magnetic properties with decrease in the temperature was found

in many reports and may be attributed to the surface effects. The effect of

increasing the temperature above room temperature was studied by Franco et al

[22]. The magnetization decreases with increasing temperature approaching zero

at ~750 K. The Curie temperature determined by means of the inverse

susceptibility versus temperature was ~738 K. In there case, coercivity and

remanence decreased with increasing temperature. It should be emphasised that

the magnetisation for the MgFe2O4 does not saturate at the maximum field

attainable. Another feature observed from the field cooled hysteresis loop

measurements at 10 K is that the loop of milled sample is not symmetrical about

the origin but is shifted to the left (the shift ∆HC is about 5 kA/m). The

nonsaturating magnetisation and shift of the hysteresis loop are typical features

of the canted magnetic structures [23].

(a) (b)

Figure 4.10 M-H curve at 300 K and 10 K at field of 15 kOe (a) and FC-ZFC

curve from 4 K to 400 K (b) at field of 500 Oe



It is seen that combustion process enhances the magnetic hardness of the

ferrite. At 10 K, the coercive field increased from 90 Oe to about 127 Oe for the

combusted material. The higher coercivity of the combusted sample is because of

the smaller crystallite size, increase in the grain boundary volume, and the

structural disorder (cation redistribution) introduced by milling. The increase of

the surface anisotropy of small crystallites also contributes to the increase in

coercivity. Similarly, at 300 K, the higher coercive field of combusted material

in comparison with that of bulk MgFe2O4 could mainly be accounted for by the

different cation distribution and spin arrangement observed in combusted and

bulk samples. Higher magnetocrystalline anisotropy, surface anisotropy and

shape anisotropy may all contribute to such a high coercivity of ultrafine

particles. Similar enhancement of the coercivity has also been reported for

nanocrystalline NiFe2O4 [24]. The smaller coercive field observed in the

combusted MgFe2O4 sample at 300 K in comparison with that observed at 10 K

could be explained by the fact that sample contains a crystallite size distribution

which is broad. The FC-ZFC measurements show that materials have their

blocking temperature above 400 K.

The results shows that presence of ferrimagnetism in combustion synthesized

MgFe2O4 may contribute to heat loss through hysteresis losses. Therefore these

optimized magnetic nanoparticles can be used for induction heating studies.

4.4. Conclusion

The nanocrystalline MgFe2O4 powder with average particle size of around

40 nm was successfully prepared by glycine nitrate synthesis with different G/N

ratios. Thermodynamic considerations show that calculated values of heat

absorbed by product, number of moles of gases evolved and adiabatic flame

temperature increase with increase in G/N ratio. XRD result reveals that amount

of glycine has no significant effect on formation of single phase MgFe2O4

powder and fuel lean condition also leads to proper MgFe2O4 phase formation.

Slight variation in crystallite size and lattice parameter with different G/N ratios

may be attributed to competition between adiabatic flame temperature and



number of gases evolved. From FT-IR analysis, the spinel structure, purity and

formation of MgFe2O4 was confirmed. Transmission electron microscopy image

shows the formation of MgFe2O4 nanocrystals with average particle size of about

~40 nm which is in good agreement with the particle size calculated from XRD

analysis. The distribution of nanoparticles is quite broad in combustion method.

The microstructural analysis of products with different G/N ratio shows very

pronounced effect on microstructure which is attributed to the effect of adiabatic

flame temperature and number of moles of gases evolved during combustion.

The magnetization for sample increases with increase in G/N ratio attains

maximum value at stoichiometric condition and then decreases with further

increase in G/N ratio. Thus glycine-nitrate process can be explored to obtain high

quality pure and homogeneous MgFe2O4 without subsequent heating treatment.

Though the amount of fuel affects the particulate characteristics, we have

obtained superior properties of MgFe2O4 nanoparticles at stoichiometric

condition. Therefore we optimized the ratio of glycine to fuel to stoichiometric in

further combustion synthesis of MgFe2O4 nanoparticles. The temperature

dependant magnetic properties of MgFe2O4 nanoparticles suggest that these

nanoparticles can be a good candidate for magnetic induction heating.



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chapter 4 synthesis of mg- ferrite -...

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