Indian Journal of Materials Science

Volume 2014 (2014), Article ID 787306, 5 pages

http://dx.doi.org/10.1155/2014/787306

Research Article

Kinetics of Thermolysis of Nickel(II) Perchlorate Complex with n-Propylamine

Chandra Prakash Singh and Abhishek Singh

Department of Chemistry, DBS College, Kanpur 208006, India

Received 25 November 2013; Accepted 10 January 2014; Published 19 February 2014

Academic Editors: J. Luo and H. S. Yathirajan

Copyright © 2014 Chandra Prakash Singh and Abhishek Singh. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Complex of nickel perchlorate with n-propylamine has been synthesised with molecular formula [Ni(n-pa)₃(ClO₄)(H₂O)]ClO₄. It has been characterised by elemental analysis, thermogravimetry, UV-VIS, and IR spectroscopic data. Thermal properties have been investigated by thermogravimetry (TG) in static air and by simultaneous thermogravimetry-derivative thermogravimetry-differential thermal analysis (TG-DTG-DTA) in flowing nitrogen atmosphere. Kinetics of thermolysis has been analysed applying model-fitting and model-free isoconversional method on isothermal TG data recorded at five different temperatures. To observe the response of complex towards fast heating, explosion delay time has been recorded at various temperatures and kinetics of explosion has been studied using these data.

1. Introduction

Metal perchlorates have strong oxidizing properties and amines are reducing in nature. Amines have strong e⁻ donation power due to presence of lone pair e⁻ on their nitrogen atom. These two oxidizing and reducing groups can be easily incorporated in a single molecule by reacting metal perchlorate with amine resulting in the formation of metal amine perchlorate coordination compounds. Any composition having strong oxidizing and reducing groups simultaneously in a molecule will exhibit the properties of high energetic materials. Thus, metal perchlorate amine complexes will exhibit the properties of energetic material and undergo autotransmitted decomposition reactions [1–3] when subjected to a stimuli (heat, friction, shock, wave, etc.). Owing to their energetic properties these types of complexes have found applications in explosives, pyrotechnics, and propellants. Such type of complexes has been proved to be a strong burning rate modifier for hydroxyl terminated polybutadiene-ammonium perchlorate (HTPB-AP) based propellants [4, 5]. In search of insensitive high energetic materials, a strong interest is being given by the researches on such type of complexes (having oxidizing and reducing group in one molecule) and they have been synthesized and their properties have been extensively investigated [5–14]. In the present paper, we report the preparation, characterisation, thermolysis, and explosion characterisation of nickel perchlorate complex with n-propyl amine, water, and as ligands. Kinetics of early thermolysis was also investigated by applying model-fitting and isoconversional method.

2. Experimental

2.1. Materials

Nickel carbonate, perchloric acid, n-propyl amine (sd.fine), ethanol (Changshu Yangyuan Chemical, China), petroleum ether (Merk), and all of AR grades were used as received.

2.2. Preparation

The complex was prepared via two-step procedure. In first step hexahydrate nickel perchlorate was obtained by reacting nickel carbonate with 60% perchloric acid followed by recrystallisation. In second step, ethanolic solution of nickel perchlorate and n-propyl amine was mixed together, stirred well at room temperature, and filtered out some obtained light green ppt. From the filtrate, after 2-3 days light green crystals of desired complex were obtained. The crystals were washed with alcohol and dried.

Caution. Perchlorates are explosives. They should be handled with care. However, I have not found any problem during all experimental procedures.

2.3. Characterisation

Characterisation of complex was done by elemental analysis (C, H, N; Thermo Finnigan Flash EA 1112 CHNS analyzer), infrared [15–17] (Perkin Elmer FT-IR spectrometer), UV-VIS spectroscopy and thermogravimetry (Table 1).

Table 1: IR frequencies and elemental analysis data for the complex.

IR
Element %, observed/calculated

(cm⁻¹)
Assignments

448
M–N
C
22.4/22.1

627
Ionic perchlorate
N
8.6/8.5

753
C–H def
H
6.1/6.4

990
C–N str.
Ni
12.95/13.27

1089
Ionic perchlorate

1112
Bidentate

1145

1395
C–NH₂

1503
N–H bend.

1570

2705
C–H str.

2994

3034
NH₂ (Pri)

3434
O–H (H₂O)

2.4. Thermal Analysis

2.4.1. TG in Air

Thermogravimetry in static air with heating rate of 10°C/min (Figure 1) was recorded using an indigenously fabricated TG apparatus [18] (sample mass 20 mg).

Figure 1: TG curve of complex in static air atmosphere.

2.4.2. Simultaneous TG-DTG-DTA

These traces were obtained in flowing nitrogen atmosphere (100 mL/min), sample was ~2.5 mg at a heating rate of 10°C/min (Figure 2, Table 2).

Table 2: TG-DTA data of the complex.

Step
TG
DTA

Temperature range (°C)
% decomposition
Peak position (°C)
Nature of peaks

I
92–121
4
169
Endo

II
121–288
12
—
—

III
290–305
70
299
Exo

Figure 2: TG-DTG-DTA curve of complex in flowing nitrogen atmosphere.

2.4.3. Isothermal TG

Isothermal TG (Figure 3) was recorded in static air atmosphere using the same indigenously fabricated TG apparatus as mentioned earlier at five different temperatures (200, 210, 220, 230, and 240°C). Sample mass taken was 10 mg and readings were recorded for 30% decomposition.

Figure 3: Isothermal TG of complex in static air atmosphere at different temperatures.

2.4.4. Kinetic Analysis

Kinetics of decomposition has been investigated using isothermal TG data using model fitting (Table 3) [19] and isoconversional method [20, 21]. Variation of activation energy with extent of conversion is shown in Figure 4.

Table 3: Activation energy , Arrhenius factor, and correlation coefficients for the isothermal decomposition of the complex.

Serial number
Model

Slope
/kJ mole⁻¹

Mean deviation
Standard deviation

1
Power law3/4
1.1382
2128.2
17.7
0.9702
2.728
2.877

2
Power law2/3
1.2143
1978.1
16.4
0.9641
2.613
2.756

3
Power law1/2
0.6130
2148.7
17.8
0.9714
2.486
2.628

4
Power law−1/2
0.0605
2207.1
18.3
0.9740
2.269
2.384

5
Power law⁻¹
−0.0051
2224.6
18.5
0.9742
2.254
2.378

6
Mampel
−1.1053
2275.1
18.9
0.9610
1.755
1.853

7
a-e3/4
0.7241
2177.1
18.1
0.9748
2.570
2.711

8
a-e2/3
−0.0275
2249.8
18.7
0.9599
2.268
2.390

9
a-e1/2
−0.4144
2260.2
18.8
0.9605
2.085
2.201

10
cs
0.2240
2249.1
18.7
0.9686
2.393
2.525

11
T-d-diff
0.2629
2305.1
19.1
0.9614
2.470
2.605

12
cc
0.1869
2223.4
18.5
0.9713
2.349
2.478

13
P-T
−1.6300
2237.5
18.6
0.9592
1.454
1.536

14
G-B
1.2040
2256.1
18.7
0.9698
2.891
3.049

Figure 4: Variation of activation energy of thermolysis for the complex with extent of conversion ().

2.4.5. Explosion Delay Experiments

This experiment was performed using tube furnace technique [22] (sample mass 10 mg) at temperatures of 280, 300, 320, 340, and 360°C within experimental limit of ±1°C (Table 4). data were fitted in Arrhenius equation

where is the Arrhenius factor, is the activation energy for explosion, is absolute temperature, and is the gas constant. A plot of versus is presented in Figure 5.

Table 4: Explosion delay, activation energy for thermal explosion , and correlation coefficient of complex.

   at temperature (°C)
(kJ mol⁻¹)

123
93
83
58
54
30.9
0.9842
−1.915

Figure 5: Graph representing versus for the complex.

3. Results and Discussion

Table 1 containing elemental analysis and IR data shows a good agreement between observed and calculated percentages of C, H, N, and Ni. The FT-IR spectra of the complex revealed bands at 448 cm⁻¹ assigned to (M–N), 627 and 1089 cm⁻¹ assigned to ionic perchlorate, and 1112 and 1145 cm⁻¹ assigned to bidentate perchlorate ion ( symmetry) [22]. A broad peak at 3434 cm⁻¹ is due to (O–H) of coordinated water. Other peaks are according to standard text. In the UV-VIS spectrum, the absorption maxima at 263 nm is due to transition and a peak at 378 nm is assigned for overlapping with charge transfer band. A band at 870 nm is assigned for transition. Thus, as suggested by the overall evidence given above, the complex can be formulated as [Ni(n-pa)₃(ClO₄)(H₂O)]ClO₄ in which Ni²⁺ is hexacoordinated. Out of six coordination sites, three sites are satisfied with nitrogen atoms; one from each n-propylamine and three sites with O-atoms; one from water molecule and two from one of the perchlorate ions acting as a bidentate ligand ( symmetry).

A perusal of TG curve recorded in static air with linear temperature increase shows that the complex decomposes in three steps. The very first step (92–121°C) is gradual in which coordinated H₂O leaves the complex (~4% wt. Loss). In the second step (121–288°C) one of the n-propylamines is released (~12% wt. Loss). In the third step (290–305°C) the remaining residue [Ni(n-pa)₂(ClO₄)]ClO₄ (might be tetracoordinated complex of Ni²⁺) ignites with smoke and low noise giving a sharp weight loss (~70%). At lost ~15% mass is left which corresponds to NiO (calculated mass 15.27%). In flowing N₂ atmosphere (Figure 2) the decomposition pattern of complex is similar to static air. A DTG peak has been obtained corresponding to third step sudden weight loss. DTG were not obtained for first step because this step is very gradual. DTG peak for second step might be incorporated in third step of DTG peak. In DTA curve an endotherm at 169°C and this is to be in harmony with second step (removal of one of the n-pa molecule). A strong exothermic peak at 299°C has been received which suits the ignition of partially decomposed residue in the third step.

Thus, in the light of the above discussion, the thermolysis pattern of the complex can be given as

In the order to calculate activation energy () for the removal of ligands (30% wt. Loss which includes H₂O and 2 n-pa molecule), a set of reaction models (Table 3) [19] was used on isothermal TG data in the temperature range 200–240°C (Figure 3). values obtained (~18 kJ mole⁻¹) are almost equal irrespective of the reaction model used.

Kinetic analysis of isothermal TG data applying isoconversional method [20, 21] concerns with the calculation of activation energy independent of the model but corresponding to the extent of conversion () of the complex. Figure 4 shows that at different values of , values in are different. Model-free isoconversional method is a better approach to obtain reliable and consistent kinetic data as compared to model-fitting methods.

The complex when subjected to sudden high temperature explodes with noise. To determine the activation energy of explosion () explosion delay time has been recorded at five different temperatures (Table 4). Activation energy for explosion was found to be 30.9 kJ mol⁻¹. A graph of versus (Figure 5) shows that explosion delay time exponentially depends on temperatures.

4. Conclusion

The complex has been prepared and characterised by various techniques. TG-DTA study reveals that the complex decompose in three steps. After an initial weight loss (~16%) oxidiser () and fuel (reducing group i.e., n-pa) lead to ignition giving a sharp exothermic peak in DTA. End product of thermolysis corresponds to NiO. Complex explodes when kept suddenly under high temperatures.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

The authors thank the Secretary Board of Management, Principal and Head of Department of Chemistry, DBS College, Kanpur, for providing laboratory facilities, and University Grants Commission, New Delhi, for financial assistance. Thanks are also due to Sophisticated Test and Instrumentation Centre, Cochin University of Science and Technology, for CHN, FT-IR, UV-VIS, and TG-DTA analyses.

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