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Chapter IV Thermal Studies of …..
setup from room temperature to 800 o C at a heating of 15 C/min in nitrogen
atmosphere at SICART, Vallabh Vidyanagar, Gujarat. Powdered samples
were used for this study. A typical TGA set up used is shown figure (4.3).
4.3 TGA Study of Pure and Amino Acids Doped KDP Crystals:
Many workers have reported thermal studies of pure and doped KDP
crystals and also identified phase changes at higher temperatures. The
techniques like TGA, DTA, DTG and DSC have been employed for these
studies. Abdel-Kader et al [7] employed simultaneous TGA, DTA and DTG in the
temperature range from 25 o C to 600 o C and showed that KDP crystal
decomposed into potassium pyrophosphate and then to metaphosphate as an
end product. DTA studies at higher heating rates of 50 o C/min to100 o C/min
showed clear resolution of the first peak into two peaks; the first was
attributed to the phase transition at 200 o C and the second due to
decomposition of the sample. It is worth noting that the high temperature
phase transition (HTPT) of KDP was also obtained at 175 o C by DSC studies
at 2 o C/min. The activation energies for the thermal process of KDP crystals
occurring at 230 o C, 267 o C, 310 o C were estimated as 155.56 kJ mol -1 ,
286.56 kJ mol -1 and 81.46 kJ mol -1 , respectively, by Kissinger method,
however, the values of activation energies were 164.01 kJ mol -1 , 294.97 kJ
mol -1 and 91.34 kJ mol -1 for Ozawa method, respectively. The authors also
confirmed the high temperature phase transitions by X-ray diffraction and IR
spectra.
In another study the HTPT was reported by Ortiz et al [8] and argued
strongly for partial polymerization instead of a structural phase transitions.
These authors employed X-ray diffraction and TGA to study the kinetic
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