The effect of certain promoters on TiO2 crystal structure transformation was studied by mean thermal and X-ray analyses. It was found that the addition of rutile nuclei and potassium, phosphorus, zinc, magnesium, and aluminium compounds to hydrated titanium dioxide before calcination process influences on the initial temperature and anatase transformation.
The results of theoretical analysis of the crystal structure and bonding in relation to thermal decomposition process in anhydrous
mercury oxalate are presented. The methods used Bader’s Quantum Theory of Atoms in Molecules formalism with bond order model
(by Cioslowski and Mixon), applied to electron density obtained from ab initio calculations carried out with FP-LAPW Wien2k
package (Full Potential Linearized Augmented Plane Wave Method) and Brown’s Bond Valence Model are described. The analysis
of the obtained results shows that most probably the thermal decomposition process of mercury oxalate should lead to metal
and CO2 as products (as it is experimentally observed). Presented results (as well as the results of our similar calculations carried
out previously for zinc, cadmium silver, cobalt and calcium oxalates) allow us to state that such methods (topological and
structural), used simultaneously in analysis of the crystal structure and bonding properties, provide us with the additional
insight into given compound’s behavior during thermal decomposition process. As a result, these methods can be considered
as valuable supporting tool in the analysis of thermal decomposition process in given compound.
It is well known that by the coordinated action of atoms arranged in rows and planes in the crystal lattice, the motion of
charged particles such as protons, alpha particles and heavier ions can be influenced so that their range in the single crystals
is considerably enhanced in low-index directions. A technique has been developed based on such enhanced penetration (channeling)
of radioactive atoms (220Rn) emitted by recoil with a 100 keV energy from a224Ra point source to record channeling patterns which show the crystal structure. The radioactive recoil atoms impinging from
this source on the surface of a single crystal penetrate deeper in places where their direction of impact is identical with
low index crystal directions and planes. These places can be visualized by autoradiography when having first stripped a thin
layer from the surface corresponding to the random range of the atoms. This technique is generally applicable in close packed
crystals and gives information about the crystal structure of very thin surface layers.
Authors:T. Sato, F. Ambe, K. Endo, M. Katada, and H. Sano
The crystal structures of oxo-centered trineclear cobalt-iron chloroacetate complex [CoIIFe
O(CH2ClCO2)6(H2O)3]·3H2O (1) was compared with that of previously reported trinuclear iron complex [FeIIFe
O(CH2ClCO2)6(H2O)3]·3H2O (2) which has an isomorphous structure to 1. Compound 1 crystallizes in space group P21/n with Z=4 in a unit cell of a=14.826 (4) Å, b=4.536 (8) Å, c=14.000 (4) Å, =100.32 (2)0 and V=2968 (11) Å3. The structure was refined to R=0.75 and Rw=0.82. The coordination geometries of the three iron atoms are observed equivalent in 1 indicating a static disorder of the position among cobalt and iron atoms. Two distinct FeIII doublets observed in Mössbauer spectra of 1 become an indistinguishable broad doublet by dehydration of crystal water. On the other hand, no significant line-broadening is observed after the dehydration in complex 2. The results indicate that the dehydration in 2 induces a local environmental change reordering of an electronic configuration around iron atoms, whereas the remaining disordering is reflected in Mössbauer spectrum after the dehydration in 1.
, 16 ]. Recently, it has been greatly developed for directly determining heat capacities for various materials successfully [ 17 – 20 ].
In this article, the preparation and the crystalstructure of DPFEB were reported. In addition, the molar
Authors:Ž. Jaćimović, V. Leovac, G. Giester, Z. Tomić, and Katalin Szécsényi
Molecular and crystal structure of diaqua-sulphato(pyridoxal semicarbazone-ONO)iron(II) and dichloroaqua(pyridoxal semicarbazone-ONO)iron(III)
complexes with tridentate ONO pyridoxal semicarbazone ligand, PLSC, of formula [FeII(PLSC)(H2O)2SO4] and [FeIII(PLSC)(H2O)Cl2]Cl is reported. Thermal decomposition of the compounds was followed in argon and air gas carriers. The dequation mechanism
is discussed in the view of the crystal structure, emphasizing the complexity of the related parameters and processes.
Authors:S. Naidu, N. Bhide, K. Prabhakaran, and E. Kurian
Nitroaminoguanidine (NAG) has been investigated as regards its thermal decomposition characteristics using simultaneous thermal analysis, infrared
spectroscopy, X-ray diffraction and polarising microscopy. XRD studies show thatNAG crystal belongs to the tetragonal system. The crystal structure parameters are found to be:a=17.063±0.005Å,b=17.063±0.005Å,c=5.155±0.005Å andc/a axial ratio=0.302. Under non-isothermal conditions,NAG decomposed apparently in one stage with a loss in weight of 80%. But the thermal decomposition ofNAG in the solid phase under isothermal conditions proceeded through three stages. Both the first and the second stages obeyed
theA-E (Avrami Erofee'v) equation forn=1. The 3rd stage is too slow and kinetics has not been attempted. The rate parameters for the first and second stages have
been evaluated. Gaseous decomposition products detected using the IR gas cell are NH3, NO2, HCN, N2O, CO and CO2. High temperature IR studies indicate preferential deamination reaction initially indicating breaking of N−NH2 and C−NH2 bonds leading to NH2 radical formation. Addition of diphenylamine, a known chain inhibitor, decelerated the thermal decomposition, supporting
a radical chain reaction.
Authors:S. Petit, F. Mallet, M. Petit, and G. Coquerel
A combined analysis of structural data and experimental results (DSC, temperature-resolved XRPD and hot stage optical microscopy)
revealed that the dehydration mechanism of cortisone acetate monohydrate (CTA·H2O) involves a collective and anisotropic departure of water molecules followed by a cooperative structural reorganization
toward the anhydrous polymorph CTA (form 2). In spite of the lack of crystal structure data, it can be postulated from experimental
data that thermal decomposition of the dihydrated form (CTA·2H2O) and of the tetrahydrofuran solvate (CTA·THF) toward another polymorph (CTA (form 3)) also proceeds according to a cooperative
mechanism, thus giving rise to probable structural filiations between these crystalline forms of CTA. The crystal structure
determination of two original solvates (CTA·DMF and CTA·DMSO) indicates that these phases are isomorphous to the previously
reported acetone solvate. However, their desolvation behaviour does not involve a cooperative mechanism, as could be expected
from structural data only. Instead, the decomposition mechanism of CTA·DMF and CTA·DMSO starts with the formation of a solvent-proof
superficial layer, followed by the partial dissolution of the enclosed inner part of crystals.
Hot stage optical microscopy observations and DSC measurements showed that dissolved materials (resulting from a peritectic
decomposition) is suddenly evacuated through macroscopic cracks about 30°C above the ebullition point of each solvent. From
this unusual behaviour, the necessity to investigate rigorously the various aspects (thermodynamics, kinetics, crystal structures
and physical factors) of solvate decompositions is highlighted, including factors related to the particular preparation route
of each sample.
Summary The unit cell parameters of virgin and thermally treated potassium hexacyanoferrate(II)trihydrate (KFCT) crystals are measured at room temperature. Considerable changes in the lattice constants are observed for as-grown or pre-cooled to the liquid nitrogen temperature samples after heating up to selected higher temperatures for different times. The detected variations may be due to partial or total removal of the three water molecules of crystallization and the transformation of Fe2+ to Fe3+. DSC, DTA and TG are used to study physical and chemical changes associated with the observed crystallographic variations. The effect of γ-irradiation with a dose of 5×105 Gy on the crystal structure of KFCT is also examined. Two computer software programs are used to analyze the data of the X-ray diffraction patterns and the results are compared.
Authors:Hideki Saitoh, Satoaki Ikeuchi, and Kazuya Saito
Summary Crystal structures of the room-temperature (RT) and low-temperature (LT) phases of p-methylbenzyl alcohol were reexamined by single-crystal X-ray diffraction method while paying special attention to detect structural disorder in the RT phase involved in successive structural phase transitions at 179 and 210 K. In the RT phase at 250 K, positional disorder of oxygen atoms was detected in contrast to the previous structure report. The structure of the LT phase coincided to the previous one. Heat capacities were measured by adiabatic calorimetry below 350 K, which covers the structural phase transitions and fusion at 331.87 K. The structural phase transitions were of first-order and required long time for completion. The combined magnitude of entropies of transition was ca. 5 J K-1 mol-1, a part of which can be ascribed to the positional disorder observed in the structure analysis. Standard thermodynamic functions are tabulated below 350 K.