Crystals of melaminium benzoate dihydrate (MBDH) have been grown from aqueous solution by slow solvent evaporation method at room temperature. Powder X-ray diffraction analysis confirms that MBDH crystallizes in the monoclinic system (
Supramolecular chemistry is the chemistry of molecular aggregates assembled via noncovalent interactions [
MBDH crystal was synthesized from melamine and benzoic acid in the stoichiometric ratio 1 : 1. To the hot solution of melamine, benzoic acid solution was added gently and stirred continuously well for 5 hours to get the homogenous solution. Then the solution was allowed to evaporate at room temperature, which yielded needle shaped crystals within a period of 20–25 days.
The grown crystals of MBDH have been characterized by X-ray powder diffraction technique using Rich Seifert X-ray powder diffractometer with CuK
Figure
Powder X-ray diffraction pattern of MBDH.
TG-DTG curves of MBDH at three different heating rates 10, 15, and 20°C/min in the temperature range of 30–1000°C are shown in Figure
TG-DTA curves of MBDH in nitrogen atmosphere; heating rate of 10, 15 and 20°C min−1.
In order to obtain the thermal kinetic parameters (activation energy
For nonisothermal experiments, the reaction rate at all times depends on both
The temperature dependent function is generally assumed to follow an Arrehenius type dependency:
A typical plot of
Activation energies of thermal degradation of MBDH by Arrhenius, Kissinger, and Kim-Park methods.
Method | Heating rate/°C min−1 | Stage I | Stage II | Stage III | |||
---|---|---|---|---|---|---|---|
|
ln |
|
ln |
|
ln |
||
Arrhenius | 10 | 41.92 | 13.60 | 89.97 | 27.52 | 115.11 | 27.82 |
15 | 40.01 | 12.25 | 62.96 | 20.15 | 85.32 | 21.25 | |
20 | 29.27 | 8.02 | 63.41 | 20.64 | 82.59 | 21.02 | |
Kissinger | 83.54 | 20.67 | 122.48 | 26.39 | 184.23 | 26.01 | |
Kim-Park | 78.93 | 45.65 | 129.84 | 37.88 | 199.81 | 44.56 |
Fraction reacted,
Flynn-Wall plots for three different heating rates against the temperature for the stages I, II, and III are shown in Figures
Kinetic parameters of non-isothermal decomposition of MBDH by Flynn-Wall and Friedman methods.
|
Flynn-Wall | Friedman | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Stage I | Stage II | stage III | Stage I | Stage II | Stage III | |||||||
|
ln |
|
ln |
|
ln |
|
ln |
|
ln |
|
ln |
|
0.1 | 43.59 | 11.26 | 42.13 | 12.87 | 95.37 | 21.48 | 11.65 | 3.77 | 47.79 | 14.25 | 30.83 | 7.56 |
0.2 | 45.76 | 11.93 | 56.68 | 16.50 | 88.32 | 19.86 | 19.34 | 6.46 | 49.82 | 14.88 | 37.36 | 9.08 |
0.3 | 48.62 | 12.82 | 70.04 | 19.87 | 82.49 | 18.54 | 25.13 | 8.47 | 43.99 | 13.35 | 40.44 | 9.81 |
0.4 | 48.49 | 12.71 | 82.44 | 22.99 | 78.93 | 17.71 | 27.34 | 9.22 | 28.57 | 9.21 | 42.56 | 10.33 |
0.5 | 48.86 | 12.76 | 93.02 | 25.64 | 75.54 | 16.94 | 27.22 | 9.16 | 14.43 | 3.19 | 41.78 | 10.21 |
0.6 | 45.91 | 11.72 | 62.34 | 17.55 | 72.73 | 16.29 | 24.75 | 8.28 | 14.91 | 2.42 | 36.62 | 9.10 |
0.7 | 34.27 | 7.88 | 113.93 | 30.86 | 69.78 | 15.64 | 19.56 | 6.46 | 61.59 | 14.98 | 23.71 | 6.29 |
0.8 | 12.25 | 1.19 | 122.09 | 32.86 | 66.45 | 14.91 | 12.79 | 4.09 | 91.21 | 22.93 | 8.92 | 0.92 |
0.9 | 39.89 | 14.88 | 130.86 | 35.00 | 62.41 | 14.05 | 11.02 | 1.25 | 79.69 | 19.94 | 44.27 | 8.54 |
Flynn-Wall plot for stage I in nitrogen atmosphere for the nonisothermal decomposition of MBDH using TG data.
Flynn-Wall plot for stage II in nitrogen atmosphere for the nonisothermal decomposition of MBDH using TG data.
Flynn-Wall plot for stage III in nitrogen atmosphere for the nonisothermal decomposition of MBDH using TG data.
Figure
(a) Variation of effective activation energy (
Best models can be selected by introducing the various analytical forms of
Plot of
Figure
DSC traces of MBDH.
Single crystals of melaminium benzoate dihydrate (MBDH) crystallize in the monoclinic system (