Outer and inner35S-labelled S3O
are prepared and then hydrolyzed at different temperatures. The separation of the reaction mixture is made by high-voltage
paper ionophoresis. The amount of activity is determined directly on the paper by liquid scintillation. The ratios of activity
of the reaction products are compared with those calculated on the basis of three different reaction mechanisms. All experimental
results agree very well with the authors' proposed reaction mechanism via the unsymmetrical intermediate−O3S−SOH. The influence of the isotope exchange between S2O
on the ratio of activity is examined at different temperatures. Attempts have been made also to capture the SO
which orginates from the first step of the S4O
Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount
of CaO and MgO in Li2O-Al2O3-2SiO2 were investigated. With CaO and MgO addition, the crystallization temperature (Tp) decreased, the value of Avrami constant (n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy (E) increased from 299±3 kJ mol−1 to 537±5 kJ mol−1. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk
crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength
and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated
with crystallization and morphology of glass ceramics.
Authors:G. Panneerselvam, R. Venkata Krishnan, K. Nagarajan, and M. Antony
Dysprosium hafnate is a candidate material for as control rods in nuclear reactor because dysprosium (Dy) and hafnium (Hf)
have very high absorption cross-sections for neutrons. Dysprosium hafnate (Dy2O3·2HfO2-fluorite phase solid solution) was prepared by solid-state as well as wet chemical routes. The fluorite phase of the compound
was characterized by using X-ray diffraction (XRD). Thermal expansion characteristics were studied using high temperature
X-ray diffraction (HTXRD) in the temperature range 298–1973 K. Heat capacity measurements of dysprosium hafnate were carried
out using differential scanning calorimetry (DSC) in the temperature range 298–800 K. The room temperature lattice parameter
and the coefficient of thermal expansion are 0.5194 nm and 7.69 × 10−6 K−1, respectively. The heat capacity value at 298 K is 232 J mol−1 K−1.
The thermal decomposition of FeSO46H2O
was studied by mass spectroscopy coupled with DTA/TG thermal analysis under
inert atmosphere. On the ground of TG measurements, the mechanism of decomposition
of FeSO46H2O is:
i) three dehydration steps
ii) two decomposition
The intermediate compound was identified as Fe2(SO4)3 and the final product as the hematite Fe2O3.
The third-law method has been applied to determine the enthalpies, ΔrHT0, for dehydration reactions of kaolinite, muscovite and talc. The ΔrHT0values measured in the equimolar (in high vacuum) and isobaric (in the presence of water vapour) modes (98015, 371039 and
279334 kJ mol-1, for kaolinite, muscovite and talc, respectively) practically coincide if to take into account the strong self-cooling effect
in vacuum. This fact strongly supports the mechanism of dissociative evaporation of these compounds in accordance with the
reactions (primary stages): Al2O32SiO22H2O(s)→Al2O3(g)↓+2SiO2(g)↓+2H2O(g); K2O3Al2O36SiO22H2O(s) →K2O(g)↓+3Al2O3(g)↓+6SiO2(g)↓+2H2O(g) and 3MgO4SiO2H2O(s) →3MgO(g)↓+4SiO2(g)↓+H2O(g). The values of the Eparameter deduced from these data for equimolar and isobaric modes of dehydration are as follows: 196 and 327 kJ mol-1for kaolinite, 309 and 371 kJ mol-1for muscovite and 349 and 399 kJ mol-1for talc. These values are in agreement with quite a few early results reported in the literature in 1960s.
for the preparation of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 3-methoxy-4-methylbenzoates
were investigated and their quantitative composition and magnetic moments
were determined. The IR spectra and powder diffraction patterns of the complexes
prepared of general formula M(C9H9O3)2nH2O (n=2
for Mn, Co n=1 for Ni, Cu, n=0
for Zn, Cd) were prepared and their thermal decomposition in air was studied.
Their solubility in water at 293 K is of the order 10–2
(Mn)–10–4 (Cu) mol dm–3.
IR spectra of the prepared 3-methoxy-4-methylbenzoates suggest that carboxylate
groups are bidentate bridging. The magnetic moments for the paramagnetic complexes
of Mn(II), Co(II), Ni(II) and Cu(II) attain values 5.50, 4.45, 3.16 and 1.79
B. M., respectively. During heating the hydrated complexes lose crystallization
water molecules in one step and then the anhydrous complexes decompose directly
to oxides MO and Mn3O4. Only Co(II) complex decomposes to Co3O4
with intermediate formation CoO.
Authors:Shidi Tang, Yuanfu Deng, and ShuZhong Zhan
A new heterobimetallic nitrilotriacetatoperoxotitanate complex of titanium and lead [Pb(H2O)3]2[Ti2(O2)2O(nta)2]·4H2O (C6H6O6N=H3nta) was isolated in pure crystals directly from the solution containing tetrabutyl orthotitanate, hydrogen peroxoide, lead acetate, and nitrilotriacetic acid at pH = 2.0–4.0. The isolated complex was characterized by elemental analyses, IR spectrum, thermal analysis (TG), and single-crystal X-ray diffraction. The single-crystal X-ray structural analysis revealed that the titanium atom is N,O,O′,O′′-chelated by the nitrilotriacetate and O,O′-chelated by the peroxo group and was coordinated to the bridging O atom in an overall pentagonal-bipyramidal geometry. The thermal decomposition of this precursor led to the formation of phase-pure lead titanate (PbTiO3) at ≥450 °C. The morphology, microstructure, and crystalline of the resulting PbTiO3 product have been characterized by BET, transmission electron microscopy, and powder X-ray diffraction. The TEM micrographs revealed that the size of the as-synthesized crystallines to be 50–100 nm range. The BET measurement revealed that the PbTiO3 powders had a surface area of 5.6 m2/g.
Authors:Ana Braileanu, Maria Zaharescu, D. Crişan, and E. Segal
The scientific interest for the Bi2O3-PbO system has increased due to the importance of the PbO in the high-Tc superconducting phase formation in the Bi2O3-SrO-CaO-CuO system. Also Bi2O3-PbO system contains compounds with some specific semiconductor and dielectric properties and Bi2O3-based solid solutions are well known as high oxygen ion conductors.
Previously, several low melting defined compounds have been identified in the system: 6Bi2O3·PbO; 3Bi2O3·2PbO; 4Bi2O3·5PbO; 4Bi2O3·6PbO and Bi2O3·3PbO.
This work deals with the phase formation and thermal stability of these compounds. Under non-isothermal conditions, in all mixtures regardless of the Bi2O3/PbO ratio, the compound 6Bi2O3·PbO is preferentially formed, followed by the compound 4Bi2O3·5PbO. The formation of the compound 4Bi2O3·6PbO was not confirmed while the formation of the compound Bi2O3
3PbO occurs through a complex mechanism which includes an intermediate step in which a solid solution with the litharge structure was identified. Under isothermal conditions in the same temperature range the tendency to form the stoichiometric compounds increases. All compounds form, decompose and melt at temperatures between 530–780°C.