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Chapter IV Thermal Studies of ….. There are mainly two types of thermo-gravimetry available, one is a dynamic thermo-gravimetry and the other is a static or endothermic thermo- gravimetry. In the dynamic thermo-gravimetry the sample is subjected at continuous and linearly increasing temperature, whereas, in the static or endothermic thermogravimetry, the sample is maintained at constant temperature for a certain period of time during which any change in weight is recorded. The basic requirements for the analysis are a precision balance and a recorder. At present, in market the availability of automatic recording thermo-balances is, usually, ranging from 1 mg to 100 g. In general a furnace should have a linear rise of temperature with time and should be capable to work in inert, oxidizing or reducing atmosphere from ambient to 1500 o C. Often the heating and cooling rate of the furnace can be selected from slightly higher than zero to as high as 200 o C/min. Because of the continuous record of weight and temperature no features of thermograms are overlooked. The shape of thermogravimetric curve of a particular compound is influenced by the heating rate of the sample and the atmosphere surrounding it [2, 5, 6]. Figure: 4.3 A typical TGA set up. The thermo grams of pure and L-histidine, L-threonine and DL- methionine doped KDP crystals were recorded on PerkinElmer, Pyris1 TGA, 163
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 164
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Saurashtra University Re - Accredit
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Statements Under O. Ph.D.7 of Saura
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ACKNOWLEDGEMENT The author expresse
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in-law, Mother- in -law and all oth
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of NLO materials in rapidly develop
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doped samples in comparison to the
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micro-hardness decreases. Also, as
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Papers Published in National and In
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Seminar on Recent Advances in Conde
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Chapter I Brief Introduction... Cha
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Chapter II Solution Growth…. Tabl
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Chapter V Dielectric Study of …
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Chapter VI UV-Vis Spectroscopic….
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Chapter VIII Micro-hardness studies
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Load (N) Chapter VIII Micro-hardnes
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Chapter IX General Conclusion case
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