F. El-Kabbany

Electrical and thermal investigations of the phase transitions in ammonium purpurate “murexide” C8H4O6N5 · HN4

Abstract Based on some electrical properties (resistivity, dielectric constant and pyroelectric current) measured between 40 and 300°C, combined with the DTA thermogram in the same temperature range, we observed two structural phase transitions in ammonium purpurate (APP) “murexide’ C8H4O6H5 · NH4 at temperatures of about 100 and 257°C. The data are correlated to the reorientation and distortion of the NH4 ions, which are closely related to the different possibilities of the N-H … X hydrogen bonding scheme.

Physical properties and phase transitions in sodium tartrate dihydrate

We report here on the electrical properties (resistance, dielectric constant and pyroelectric current behaviour), magnetic susceptibilityXM and differential thermal analysis (DTA) for the polycrystalline powdered samples of sodium tartrate dihydrate (STD), Na2C4H4O6·2H2O. These mentioned properties are used as a probe for the detection and the studying of the different transitions that have been found in this salt. It has been observed that the various results (electric, magnetic and thermal) strongly support each other and confirm the actual presence of the phase transformations in this compound.

Non-ferroelectric phase transitions in potassium hydrogen sulphate [mercallite, KHSO4]

Abstract Accurate measurements of some electrical properties combined with the differential thermal analysis (DTA) were made from room temperature up to 200°C for single crystals of KHSO 4 (KHS). The data reveal the existence of two (non-ferroelectric) phase transitions around 100°C and 175°C. The first structural phase transition may involve only minor change in atomic positions and therefore it is not easy to detect. The existence of this phase is confirmed by the X-ray diffraction pattern. The data are correlated with the arrangement of the molecules in the unit cell including the hydrogen bonding system due to the two distinct HSO 4 ions as well as the onset of the reorientational motion of the sulphate group.

Infrared study for the phase transition of re-heated diphenyl carbazide C13H14N4O

Abstract The temperature dependence of IR spectra of re-heated diphenyl carbazide C13H14N4O have been investigated under normal pressure. The data is reported here between room temperature and up to the melting point (∼ 160°C) of diphenyl carbazide (DPC) and the IR spectra are recorded up to 4000 cm−1. This study is an extensive of a recent one, which detected the presence of a phase transition by DTA and DSC at ∼90°C. It includes measurements and interpretations of the IR spectral band shape, frequencies of modes and absorbance as a function of temperature. Special attention is paid to the most sensitive mode which reflects the phase transformation process in detail. These modes are 3055 cm−1, 1658 cm−1, 1567 cm−1 and 1308 cm−1 in which the variations confirm the gradual phase transition due to the growing of the disordering state in the crystals. The data obtained by IR spectroscopic analysis strongly indicates the presence of three different phase states for DPC organic compound. The first is the room temperature phase (orthorhombic), the second is that obtained after melting and even at room temperature (amorphous), and finally the third is that obtained by reheating as the temperature exceeds 90°C (high temperature phase). These structural changes are checked by X-rays and the high temperature phase is found to be triclinic with a = 4.5077 A , b = 4.9010 A and c = 24.0637 A .

A study of the phase transition of reheated diphenyl carbazide (DPC) by using UV spectroscopy

Phase transition phenomenon in reheated diphenyl carbazide (DPC) is studied here using UV spectroscopy. The optical band gap for reheated DPC is obtained by measuring the optical diffused reflectance (DR) and equals to 3.55 eV. Also, the optical band gap is calculated using UV technique and equals to 3.548 eV. The absorbance of reheated DPC is studied at some selected temperatures in order to check the presence of phase transitions at 90°C and 125°C. According to the present work, the band gaps are calculated at 80°C, 110°C and 130°C and equal to 3.548 eV. But at 100°C, the optical band gap has changed to 4.139 eV. It was found that each phase of reheated DPC belongs to a certain definite crystal structure. The presence of the phase transitions are checked and confirmed by scanning electron microscopy (SEM). The structural properties and morphology of reheated diphenyl carbazide are investigated by SEM. The SEM images are taken at some selected temperatures to confirm the presence of phase transitions.

IR spectroscopic analysis of polymorphism in C13H14N4O

IR analysis is used here to investigate the changes in N-N, N-H, CO modes of thermally treated diphenyl carbazide (DPC) during the variation of temperature from room temperature up to ≈160°C. Polymorphism in DPC compound has been studied here by detecting the changes in some IR spectroscopic parameters (e.g., mode shift, band contour) during the elevation of temperature. Also, DSC, X-ray, NMR and atomic mass spectra are used as confirming tools for what is obtained by IR. All of the vibrations of DPC were found to be due to ionic fundamentals 3311 cm(-1), 3097 cm(-1), 3052 cm(-1), 1677 cm(-1), 1602 cm(-1), 1492 cm(-1), 1306 cm(-1), 1252 cm(-1), 887 cm(-1) and 755 cm(-1). The results revealed for the first time that the thermally treated DPC traverse four different phase transformations at 50°C, 90°C, 125°C and 140°C. The crystal structure was found to be amorphous, monoclinic, tetragonal, orthorhombic and amorphous within a temperature range (30°C-160°C). X-ray diffraction patterns support the results obtained by IR and DSC.

Exothermic phase transition in re-heated diphenyl carbazid C13H14N4O

Abstract The effect of heating and re-heating on diphenyl carbazid (DPC) organic compound is studied between room temperature and its melting point ~162 °C by a set of DTA and DSC measurements. Also, electrical measurements (including d.c. resistance, dielectric constant and pyroelectric current) are carried out in order to confirm the results of thermal analysis. Various results obtained indicate, for the first time, that diphenyl carbazid undergoes a previously unknown exothermic phase transition in the vicinity of 90 °C during re-heating, i.e. there are two different phases I and II, where: DPC(II) → 90 °C → DPC(I). The heat required for this transition is calculated and found to be 39 J/gm. This phase transition is correlated with the onset of the hydrogen bonding of the amino ions (N-H). The electrical conduction is found to be activated by energies of 0.8 eV and 0.5 eV for the phases I and II, respectively. An energy model is also suggested to account for the conduction mechanism in the revealed phase of the re-heated DPC compound.

Temperature dependence of IR analysis of Sr(NO3)2

Abstract The infrared spectra of Sr(NO3)2 have been thoroughly investigated under normal pressures and at different temperatures during its phase transition II → I at ~320 ° C. The study includes measurements and interpretations of the IR spectral band shape, intensities and frequencies of the internal modes as functions of temperature. Special attention is paid to the bending mode v2, the asymmetric stretching mode v3, the first overtones (2v1, 2v3) and the combination mode (v1 + v4). The results reveal that the transformation from the ordered state (phase II) to the disordered state (phase I) of Sr(NO3)2 can be monitored by clear variations in the spectral parameters for v2, (2v1, 2v3), v3 and (v1 + v4) modes. According to the IR analysis reported here, the energy barrier of the reorientation of the NO3−1 ions is found to be 0.29 eV in the ordered phase II and 0.28 eV in the disordered phase I.

Electrical and calorimetric properties of sodium hydrogen tartrate monohydrate

This report considers some electrical parameters (dielectric constant and resistivity) and some calorimetric properties (thermal heat capacity, thermal conductivity and thermal diffusivity) as well as the DTA thermogram in the temperature range 30 < T < 140°C of sodium hydrogen tartrate monohydrate, NaHC4H4O6·H2O (SHTMHD). The accurate measurements of these parameters have revealed the presence of a structural phase transition at about 83°C, in addition to the phase transformation that results from the loss of water (dehydration). The data are correlated to the restricted rotation of the tartrate ions as well as to the hydrogen bonding scheme.

A study of the phase transformation in anthranilic acid single crystals

The electrical properties (resistance, dielectric constant and pyroelectric current) as a function of temperature in the range 30°C < T < 120°C of anthranilic acid single crystals (o-aminobenzoic add, C6H4NH2COOH), were accurately measured and correlated to the structural phase change that has been observed at 81 °C. The activation energies of the two phases were determined. The recorded DTA thermogram supports this phase change. In addition, the mean molar susceptibility χM of the powdered sample was accurately determined in the same temperature range; the result indicates that the structural phase change takes place at 81°C.