Thermal Decomposition of Hexaamminenickel(II) nitrate and …shodhganga.inflibnet.ac.in/bitstream/10603/13162/13/13... · 2015-12-04 · Thermal Decomposition of Hexaamminenickel(II)

Chapter 5

Thermal Decomposition of Hexaamminenickel(II)

nitrate and Tris(ethylenediamine)nickel(II) nitrate

5.1 Introduction

In chapter 5, results of the investigations on the thermal decomposition of

hexaamminenickel(II) nitrate and tris(ethylenediamine) nickel(II) nitrate

are discussed. Thermal decomposition studies of nitrate containing

transition metal amine complexes are of significance because of its

exothermic decomposition and can be used in propellants, explosives and

pyrotechniques.1-4

The explosive decomposition of these complexes is

attributed to the simultaneous presence of both oxidising (nitrate) and

reducing (en or ammonia) groups in the same compound.1

At present TG-MS and TR-XRD studies have extensively been used to

follow the intermediates and various species formed during heating.5-6

Present investigation focus on the TG-MS and TR-XRD studies of

these complexes. The kinetics and mechanism were also evaluated for

the different decomposition reactions of hexaamminenickel(II) nitrate

and tris(ethylenediamine) nickel(II) nitrate. Model free isoconversional

methods viz., Flynn-Wall-Ozawa (FWO),7-8

Friedman,9 Kissinger-

Akahira-Sunose (KAS)10-11

in combination with non-mechanistic and

mechanism based equations were employed for the kinetic analysis.

148 Chapter 5

5.2 Experimental

5.2.1 Preparation of the complexes

The complexes were synthesized as per the standard procedure reported in

the literature.12

Hexaamminenickel(II) nitrate and tris(ethylenediamine)

nickel(II) nitrate were prepared by adding stoichiometric amount of

ammonia and ethylenediamine respectively to nickel(II) nitrate solution.

Ethyl alcohol was then added to precipitate the complex. The crystals were

separated and washed with water and dried in a vacuum desiccator. Nickel

content in the complexes was determined by gravimetry.13

The complexes

were further characterized by other spectral and chemical analysis.

5.2.2 Instrumentations

TG/DTA-MS studies were carried out in a thermogravimetric apparatus

(TG; Rigaku, TG-8120) combined with mass spectroscopy (Anelva, M-

QA200TS) under high-purity He (99.9999%) at a flow rate of 200 ml min-1

.

The heating rates employed were 5, 10, 15 and 20ºC min-1

.

DSC studies were carried out using a Shimadzu DSC-60 instrument at a

heating rate of 10ºC min-1

under flowing nitrogen (50 ml min-1

).

The elemental analyses were carried out using Vario El III instrument and

the analysis details are given in Table 3.1. X-ray powder patterns were

recorded on a Bruker D8 Advance diffractometer attached with a

programmable temperature device (TTK 450) from Anton Paar, (using Cu

Kα radiation, λ = 1.542 Å). The measurements were performed by placing

the sample on a flat sample holder, while the samples were heated by a

programmable temperature controller. Crystallite size was calculated

using Scherrer equation,

Thermal Decomposition of Hexaamminenickel(II) nitrate … 149

t = 0.9 λ / β cos θ,

where t is the thickness of the particle, λ is the wave length, β is the line

broadening (FWHM) and cos θ is the corresponding angle.

5.3 Mathematical Treatment of Data

The kinetic and mechanistic aspects of the thermal decomposition of these

nickel amine nitrate complexes were investigated by means of

isoconversional methods, mechanism non-invoking and mechanism based

equations. The details are given in Chapter 4.

5.4 Results and Discussion

5.4.1 Thermal decomposition studies

5.4.1.1 Hexaamminenickel(II) nitrate

From thermogravimetry (TG) it can be seen that hexaamminenickel(II)

nitrate undergoes a three stage thermal decomposition. The different

stages of thermal decomposition are as follows:

[Ni(NH3)6](NO3)2 → Ni(NH3)5(NO3)2 + NH3 (Stage I)

Ni(NH3)5(NO3)2 → Ni(NH3)4(NO3)2 + NH3 (Stage II)

Ni(NH3)4(NO3)2 → NiO + 4NH3 + NO3 + NO2 (Stage III)

Simultaneous TG/DTA coupled online with mass spectral plot of

hexaamminenickel(II) nitrate is shown in Fig. 5.1.

150 Chapter 5

Fig. 5.1. TG/DTA-MS plot of [Ni(NH3)6](NO3)2 at 10ºC min-1

The complex starts to lose mass at 78ºC with the liberation of one

molecule of ammonia. The second stage at 116ºC is also a deamination

stage in which one molecule of ammonia is liberated to give an

intermediate tetraammine complex. Third stage involves (164-300ºC) the

simultaneous deamination and decomposition of the tetraammine complex

to give NiO as the final residue. The phenomenological details regarding

the decomposition viz., temperature of inception Ti, final temperature Tf,

temperature of summit Ts and the mass loss data are shown in Table 5.1.

Temperature / ºC

200 400 600 800

-100

-80

-60

-40

-20

0

Inte

nsi

ty /

a.

u.

ma

ss l

oss

/%

m/z 14m/z 15m /z 2

m/z 44

m/z 30

m/z 28

m/z 18

m/z 16

m/z 17

e

nd

o

∆T

ex

o


Table 5.1

Phenomenological data for the thermal decomposition of nickel

amine nitrate complexes at = 10ºC min-1

in He atmosphere

TG results Percentage weight loss

Stages Ti

(°C)

Tf

(°C)

Ts

(°C) Theoretical Observed Residue

[Ni(NH3)6](NO3)2 Step

wise Cumulative Stepwise Cumulative

I 78 116 87 5.97 5.97 5.7 5.7 Ni(NH3)5(NO3)2

II 116 164 136 5.97 11.9 5.8 11.5 Ni(NH3)4(NO3)2

III 164 300 266 61.9 73.8 61.3 72.8 NiO

[(Ni(en)3] (NO3)2

220 300 262 79.4 78 NiO

The DTA and DSC profiles are shown in Fig. 5.1 and Fig. 5.2

respectively. Both the DTA and DSC traces show three endotherms and

one intense exotherm.

Fig. 5.2. DSC plot of [Ni(NH3)6](NO3)2 at 10ºC min-1

0 50 100 150 200 250 300

-5

0

5

10

15

he

at f

low

/mw

flo

w/m

w

o Temperature / C

152 Chapter 5

The temperature of inception (Ti), temperature of completion (Tf) and the

peak temperature (Tp) from DTA and DSC are given in Table 5.2.

Table 5.2

DTA and DSC peak temperatures for the thermal decomposition of

hexaamminenickel(II) nitrate

Stages Ti (°C) Tf (°C) Tp (°C)

I

DTA

87 116 107

II 116 162 157

III 162 230.8 211.5

IV 230.8 295 278

I

DSC

94.5 121.1 113.5

II 125.2 158.5 142.2

III 204.1 223 208.7

IV 268.9 294.5 281.3

The first two endotherms correspond to the liberation of one molecule of

ammonia each to form tetraammine complex. The third small endotherm

is immediately followed by a sharp exotherm and is due to the initial

decomposition of the tetraammine complex.

The sharp exothermic peak can be explained on the basis of the

decomposition of Ni(NO3)2, overlapping the deamination reaction. Nickel

nitrate on decomposition gives rise to oxides of nitrogen and oxygen as

detected by TG-MS (vide infra) (scheme 1) which in turn would oxidize

the liberated ammonia.1 In TG curve, simultaneous deamination and

decomposition appear as a single stage whereas in DTA and DSC traces

the initial deamination appear as an endotherm.


TG-MS plot reveals the presence of ion peak with mass number 17 in the

temperature range 78-164ºC, indicating the evolution of ammonia. Along

with the peaks of ammonia, ion peaks with mass numbers 15 and 16 were

also observed during this temperature range. This could be due to the

presence of NH and NH2 ion species. These fragments were formed by the

thermal fragmentation of the evolved ammonia. The peaks corresponding to

m/z values 14, 16, 28, 30, 32 and 44 indicate the presence of ions like N, O,

N2, NO, O2 and N2O formed by the fragmentation of NO3 group. The

possible fragmentation pattern for NO3 is shown below.

Scheme 1. Fragmentation of NO3

The oxidation of ammonia also generates gaseous species like NO and N2O.

The presence of ion peak with m/z value 18 can be attributed to the formation

of water. The formation and evolution of water has been reported during the

thermal decomposition of Co(NH3)6(NO3)2, Pd(NH3)2(NO2)2 and

Pt(NH3)2(NO2)2 complexes.14-15

The formation of water due to the reaction

between the evolved gaseous products is shown below.15

2 NH3 + 3 O2 + N2 → 2 NO + N2O + 3 H2O

or 2 NH3 + 2.5 O2 → 2 NO + 3 H2O

Scheme 2. Formation of water from gaseous products

2 NO3

N2 (28) or 2N (14) + 3 O2 (32) N2O (44) + 5O (16)

I

II

2 NO (30) + 2O2 (32)

III

154 Chapter 5

5.4.1.2 Tris(ethylenediamine)nickel(II) nitrate

Fig. 5.3 shows the simultaneous TG/DTA coupled online with MS for

tris(ethylenediamine)nickel(II) nitrate. The complex starts to decompose

at 220ºC with an initial mass loss of ~ 7% followed by a large mass loss

of 65.3% to give nickel oxide as the residue. In general, the

decomposition of the complex is as follows

[Ni(en)3](NO3)2 NiO + gaseous products

The gaseous products include the oxides of nitrogen and ethylenediamine.

It is seen from the mass spectra (scheme 1) that the possible gaseous

products like NO3 and NO2 are fragmented to different species like N, O,

N2, NO and N2O at elevated temperature. The fragmentation possibility of

nitrate group and ethylenediamine are shown in scheme 1 and 3

respectively.

Fig. 5.3. TG/DTA-MS plot of [(Ni(en)3] (NO3)2 at 10ºC min-1

e

nd

o

∆T

ex

o

200 400 600 800

-100

-80

-60

-40

-20

0

m/z 18

m/z 2

m/z 30

m/z 44m/z 17

m/z 16

m/z 14

m/z 28

In

ten

sity

/a.

u.

mas

s lo

ss/

%

Temperature / ºC


0 50 100 150 200 250 300

-10

0

10

20

30

40

Hea

t fl

ow

/mw

Temperature / o

C

The thermal stability of tris(ethylenediamine)nickel(II) complex is high

compared to that of nickel hexaammine complex and is due to the

chelating effect.1

The phenomenological data regarding the decomposition

of tris(ethylenediamine)nickel(II) nitrate are given in Table 5.1.

The DTA and DSC curves are shown in Fig. 5.3 and Fig. 5.4 respectively.

Both the DTA and DSC curves show one small endotherm followed by a

sharp exothermic peak.

Fig. 5.4. DSC plot of [Ni(en)3](NO3)2 at 10ºC min-1

The small endotherm is due to the partial initial deamination (loss of

ethylenediamine) in the tris(ethylenediamine) complex and the exotherm

is due to the insitu oxidation of the liberated ethylenediamine.

Thermoanalytical data from DTA and DSC for tris(ethylenediamine)

complex are given in Table 5.3.

156 Chapter 5

Table 5.3

DTA and DSC peak temperatures for the thermal decomposition of

tris(ethylenediamine)nickel(II) nitrate

Stages Ti (°C) Tf (°C) Tp (°C)

I

II

DTA 219.9 245.7 228

245.7 272 262

I

II

DSC

213.8 228.9 218

236.6 276.9 253.7

In the mass spectra (Fig. 5.3), the ion peaks with mass numbers 2, 14, 16,

17, 18, 28, 30 and 44 were observed during the thermal decomposition of

this complex. These peaks appear in the temperature range 260-290ºC and

correspond to the formation of ion species like H2, N, NH2, NH3, H2O,

N2/C2H4, NO and N2O. The detection of oxides of nitrogen formed from

the fragmentation of NO3- group in the temperature range 260-290ºC,

surmise the presence of Ni(NO3)2 phase during the thermal decomposition

of the tris(ethylenediamine) complex. The formation of Ni(NO3)2 as an

intermediate phase has been further confirmed by TR-XRD analysis (vide

infra). Among the ion peaks H2, N, NH3 and N2 are formed by insitu

fragmentation of the evolved ethylenediamine as shown below.

3 NH2-CH2-CH2-NH2

Scheme 3. Fragmentation of ethylenediamine

4 NH3 (17) + 3 CH2 = CH2 (28) + N2 (28) or 2 N

2 N2 (28) or 4 N + 6 H2 (2)


20 40 60

*

oo

##

##

#

#

##

#

##

#

##

***

**

**

*

**

*

*

*

*

*

280oC

260oC

240oC

220oC

180oC

160oC

140oC

120oC

100oC

80oC

60oC

o NiO

# Ni(NO3

)2

* [Ni(NH3

)]6

(NO3

)2

(200)

***(222)*

*

two theta/ degrees

Inte

nsi

ty/

a.u

40oC

300oC

*

(111)

200oC

(111) (220)(311) (420)

(511)

(222) (400)

(400)

Mass numbers 16, 30 and 44 correspond to the presence of O, NO and

N2O formed by the fragmentation of NO3- group

as shown in scheme 1.

Detection of water (m/z 18) possibly formed by the reaction between the

gaseous products (scheme 2) was also observed in the mass spectral

analysis of tris(ethylenediamine) complex.

5.4.2 Temperature resolved X-ray diffraction studies


In order to complement the TG-MS results, insitu temperature resolved X-

ray diffraction patterns (TR-XRD) were recorded to identify the

structure/stability of the phases formed during the deamination stages of

the hexaamminenickel(II) nitrate. The typical non isothermal diffraction

series with a step wise heating of 20ºC per patterns from 40-300ºC for

[Ni(NH3)6](NO3)2 are shown in Fig. 5.5.

Fig. 5.5. TR-XRD pattern of [Ni(NH3)6](NO3)2

158 Chapter 5

The temperature resolved X-ray diffraction patterns in the range 40-80ºC

contain peaks corresponding to (111), (220), (222), (311), (400), (420)

and (511) planes and can be indexed to the cubic lattice of the complex

(JCPDS No. 45-0027). The temperature resolved XRD patterns in the

temperature range 100-140ºC show the structural changes occurred due to

the deamination resulting in the formation of nickel nitrate at 160ºC. The

peak corresponding to (420) plane at 2θ 37.2º of hexaammine complex

appears with very low intensity in the temperature range (100-140ºC),

indicating that this plane forms part of the lattice plane of the intermediate

complex structure formed due to the deamination. The intermediate

complex decomposes to give Ni(NO3)2 at 160ºC and is stable up to 280ºC

and the peaks at 42.68 and 49.92º 2θ are indexed as (222) and (400)

planes of Ni(NO3)2 (JCPDS no. 74-2261). At 300ºC, NiO is formed as the

residue by the decomposition of Ni(NO3)2 and the peaks at 37.39 and

43.44º 2θ correspond to the (111) and (200) planes of NiO (JCPDS no.

47-1049). Average crystallite size of NiO calculated from the peak

broadening value using Sherrer equation is 25.5 nm.


The temperature resolved X-ray diffractograms for the thermal

decomposition of [Ni(en)3](NO3)2 are shown in Fig. 5.6.

At 40ºC the pattern corresponds to the tris(ethylenediamine)nickel(II)

nitrate and the peaks at 11.74, 15.76, 20.39 and 26.24º 2θ indicate the

different planes of the complex. In the temperature range 100-200ºC the

complex undergoes thermal decomposition resulting in the intensity

reduction of these peaks. At 220ºC the deamination (release of 3

ethylenediamine molecules) process was completed resulting in the


30 60

o

##

##

##

#

o

****

*

*

*

*

*

**

***

o

280oC

260oC

240oC

220oC

180oC

160oC

140oC

120oC

100oC

80oC

60oC

two theta/ degrees

#

* * *

(222)

Inte

nsi

ty/

a.u

*

NiO

# Ni(NO3

)2

* [Ni(en)3

](NO3

)2

(400)

(111)(200)

40oC

200oC

300oC

formation of Ni(NO3)2 as intermediate in the temperature range 220-

280ºC. The peaks at 42.91 and 49.97º 2θ correspond to (222) and (400)

planes of Ni(NO3)2 (JCPDS no. 74-2261).

Fig. 5.6. TR-XRD pattern of [(Ni(en)3] (NO3)2

The intermediate Ni(NO3)2 phase is stable till 280ºC and on further

heating decomposes to NiO as the residue. The peaks at 37.29 and 43.43º

2θ correspond to the (111) and (200) planes of NiO. Average crystallite

size of NiO calculated from the peak broadening value using Sherrer

equation is 23 nm.

5.4.3 SEM analysis


The SEM images of hexaamminenickel(II) nitrate and the NiO residue

are shown in Figs. 5.7 a-b. NiO formed (Fig. 5.7 b) by the decomposition

of hexaamminenickel(II) nitrate is in the nano range (20nm).

160 Chapter 5

Fig. 5.7. SEM pictures of (a) [Ni(NH3)6](NO3)2 (d) NiO


The SEM images of tris(ethylenediamine)nickel(II) nitrate and the NiO

residue are given in Figs. 5.8 a-b. The SEM image shows that nano NiO

(20 nm) (Fig. 5.8 b) formed is highly porous in nature. The porosity of the

residue may be due to the escape of gaseous products during pyrolysis.

Fig. 5.8. SEM pictures of (a) [(Ni(en)3] (NO3)2 (b) NiO

Morphologies of the nano NiO residues formed by the thermal

decomposition of these two amine complexes are different, as they are

formed from different precursors. These findings are of significance since

the morphology of nickel oxide nanoparticles can be tailored by merely

changing the precursors.

(a) (b)

(a) (b)


0.0 0.2 0.4 0.6 0.8 1.0

110

115

120

125

130

135

140

145

150

155

160

FWO

KAS

Freidman

E/

kJ

mo

l-1

alpha

5.4.4 Kinetics and mechanism

The first two clear cut and non overlapping deamination reactions of

hexaamminenickel(II) nitrate involving the loss of one ammonia molecule

in each stages are subjected to kinetic analysis.

5.4.4.1 Kinetic analysis using isoconversional approach

Hexaamminenickel(II) nitrate

By employing isoconversional methods, a series of activation energies were

obtained as a function of conversion for the two deamination stages of the

hexaammine complex. Variations of activation energy with conversion for

the first and second deamination stages for the hexaamminenickel(II)

nitrate complex are shown in Figs. 5.9-5.10 and the corresponding values

are given in Table 5.4. The activation energy calculated by FWO and KAS

equations for the deamination reaction from hexaamminenickel(II) nitrate

to pentaamminenickel(II)nitrate (Fig. 5.9) exhibited a decreasing

dependence of activation energy with conversion. This decreasing

dependence of activation energy with conversion is attributed to the

reversible nature of the reaction.16

Fig. 5.9. Variation of activation energy with conversion (α) for the

deamination reaction of [Ni(NH3)6](NO3)2 to Ni(NH3)5(NO3)2

162 Chapter 5

0.0 0.2 0.4 0.6 0.8 1.0

130

140

150

160

alpha

E /

kJ

mo

l-1

FWO

KAS

Friedman

For the deamination reaction i.e pentaamminenickel(II) nitrate to

tetraamminenickel(II) nitrate, activation energy also shows a decreasing

dependence with conversion (α). The decreasing dependence shows that

the reaction is reversible, which is very common to many solid state

reactions of the type solid ↔ solid + gas.16

Fig. 5.10. Variation of activation energy with conversion (α) for the

deamination reaction of Ni(NH3)5(NO3)2 to Ni(NH3)4(NO3)2

The shapes of the plots showing the dependence of activation energy on

the extent of conversion are similar for the three equations viz., FWO,

KAS and Friedman. However, for the Friedman method the activation

energy values are comparatively higher as this method is very sensitive to

experimental noise.17


Table 5.4

Activation energy and conversion () values for deamination reactions of

hexaamminenickel(II) nitrate

Stage 1 Stage II

5.4.4.2 Kinetic analysis using non-mechanistic approach


The kinetic parameters evaluated for the first two deamination stages of

the hexaamminenickel(II) nitrate decomposition using the non-mechanism

based equations are given in Table 5.5.

alpha E (kJ mol-1

)

FWO KAS Friedman

0.05 138.6 139.6 157.7

0.1 139.1 140.1 158.9

0.2 135.9 132.1 150.8

0.3 130.6 132.8 147.9

0.4 128.1 127.1 146

0.5 127.2 126.2 145.5

0.6 127.1 125 139.1

0.7 125.1 124 134.8

0.8 124.2 122 133

0.9 123 121 131

1 122 120 134.4

alpha E (kJ mol-1

)

FWO KAS Friedman

0.05 157.5 153.4 155.8

0.1 155.9 152.4 157.9

0.2 151.2 147.8 155

0.3 147.9 147.9 153.6

0.4 139.7 141.4 157.1

0.5 138.4 140.6 154.5

0.6 137.4 139.7 158.7

0.7 135.5 133.6 152.3

0.8 136.4 136.8 145.8

0.9 130.9 135.9 140.6

1 131.4 135.9 144.3

164 Chapter 5

Table 5.5

Kinetic parameters for the two deamination stages of hexaamminenickel(II)

nitrate decomposition from non-mechanistic equations

Stage1 Stage II

n 1.47 1.49

E (kJ mol-1)

CR 125.80 101.37

MKN 125.82 100.65

HM 161.25 105.46

MT 124.60 99.62

A (s-1)

CR 1.23×1014 5.95×1010

MKN 1.34×1014 5.01×1010

HM 2.83×1020 1.83×1011

MT 8.23×1016 3.40×1010

∆S≠ (JK-1 mol-1)

CR -2.34×101 -4.14×101

MKN -1.61×101 -4.28×101

HM -1.44×102 -3.21×101

MT -7.65×101 -4.61×101

r

CR 0.9982 0.9976

MKN 0.9982 0.9976

HM 0.9982 0.9964

MT 0.9984 0.9979

CR, Coats–Redfern; MKN, Madhusudanan-Krishnan-Ninan; HM, Horowitz-Metzger;

MT, MacCallum-Tanner.

Kinetic parameters computed from the four non-mechanistic equations are

comparable. The correlation coefficient values in the table show good

linear fit. The comparatively higher values of kinetic parameters obtained

using Horowitz-Metzger equation are due to the inherent error involved in

the approximation employed in the Horowitz-Metzger equation. It can be


seen from the Table that the order parameters are fractional numbers. It is

known from the literature18

that the order parameters can have decimal

number. The entropy of activation for the two deamination stages shows

negative values. The negative values of entropy indicate that the activated

complex has an ordered structure than the reactant and the reaction in this

case is said to be slower than the normal.19

The kinetic parameters (E and

A) calculated for the first deamination stage (i.e. hexaamminenickel(II)

nitrate to pentaamminenickel(II) nitrate) show higher values compared to

the second stage of deamination (pentaamminenickel(II) nitrate to

tetraamminenickel(II) nitrate).

5.4.4.3 Deduction of reaction mechanism


The kinetic parameters (viz., E, A) and the correlation coefficient obtained

for the two deamination stages of hexaamminenickel(II) nitrate

decomposition evaluated using the mechanism based equations are given in

Table 5.6. Among the two deamination reactions of hexaamminenickel(II)

nitrate, the best linear fits (r = 0.9947 and 0.9913) are obtained for the

Mampel equation (eqn. no. 5) and therefore the rate controlling process for

these two deamination stages are assigned as random nucleation with the

formation of one nucleus on each particle.

166 Chapter 5

Table 5.6

Kinetic parameters for the two deamination stages of

hexaamminenickel(II) nitrate from mechanistic equations

Mechanistic eqns no. Stage1 Stage II

1

E

A

r

152.1

6.95×1016

0.9706

116.3

7.79×1011

0.9509

2

E

A

r

167.9

6.11×1018

0.9792

129.55

2.54×1013

0.9649

3

E

A

r

189.9

1.73×1021

0.9889

148.6

2.17×1015

0.9813

4

E

A

r

175

1.38×1019

0.9829

135.6

3.85×1013

0.9711

5

E

A

r

104.1

1.03×1011

0.9947

81.8

1.27×108

0.9913

6

E

A

r

48.8

3.21×103

0.9939

374

2.24×102

0.9893

7

E

A

r

30.3

8.08×100

0.9928

22.6

2.13×100

0.9867

8

E

A

r

86.3

1.45×108

0.9836

66.1

4.34×105

0.9714

9

E

A

r

91.7

5.79×108

0.9879

70.8

1.30×106

0.9792

E - kJ mol-1

, A - s-1

5.5 Conclusions

Investigations on the thermal behaviour of hexaamminenickel(II) nitrate and

tris(ethylenediamine)nickel(II) nitrate have been carried out using simultaneous


TG/DTA coupled online with mass spectroscopy (MS) and temperature

resolved X-ray diffraction (TR-XRD) techniques. Hexaamminenickel(II)

nitrate undergoes a three stage thermal decomposition and tris(ethylenediamine)

nickel(II) nitrate undergoes two stage thermal decomposition. Decomposition

reactions involve highly exothermic oxidation reactions. Evolved gas

analysis by MS studies shows that along with ammonia, ion species like

NH2 and NH are formed during the deamination process. These species

could be formed due to the fragmentation of the evolved ammonia during

pyrolysis. The decomposition of nickel nitrate generates gaseous products

like N, N2, NO, O2 and N2O. Oxidation of NH3 evolves N2O, NO and

water and these species are detected during pyrolysis. Thermal

fragmentation of ethylenediamine produces various ion fragments like

NH3, CH2 = CH2, N2, N and H2. The formation of the intermediates was

monitored by insitu TR-XRD. The final residues during the thermal

decomposition of both these amine complexes are highly crystalline NiO

nanoparticles. Kinetic analysis of both stages of deamination of

[Ni(NH3)6](NO3)2 using isoconversional methods show that the activation

energies vary with the extent of conversion, indicating the multi step

nature of solid state reactions. Using the mechanism based equations it is

deduced that the rate controlling processes for the thermal deamination

reactions of nickel hexaammine complex are random nucleation with the

formation of one nucleus on each particle.

168 Chapter 5

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