Loss Of Crystal Water Research Articles

Thermoanalytical investigation of layered titanium salts

The investigated materials have similar routes of thermal decomposition; i.e. they lose their crystal water first, then at a higher temperature their structural one. At least the result TiP2O7 goes through a phase change at about 1000 K. The amorphous titanium phosphate lost its crystal and structural water at higher temperature than those of crystalline forms. Both α- and γ-titanium phosphates and also their transition metal containing forms have layered structure. In case of α- and γ-forms after the loss of crystal water a phase change occurs which is followed by the decomposition of the molecule. Various transition metals containing γ-titanium phosphates lose their crystal water at the same temperature, with the exception of Ni containing ones. The process is finished in this case at temperature 90 K higher than that of the others.

Crystal structure analysis, pseudosymmetry and spectroscopic data of K4[Fe(CN)5NO2]⋅KNO2⋅H2O

Abstract K4[Fe(CN)5NO2]⋅KNO2⋅H2O crystallizes in the non-centrosymmetric orthorhombic space group Bb21 m (no. 36) with a = 2698.2(3), b = 1415.7(1), c = 849.6(1) pm and Z = 8 at 291 K. Due to a high degree of pseudosymmetry the deviations from centrosymmetry are small. The gross arrangement of the iron and potassium atoms is that of the AlB2-type, discernible from the distorted hexagons of the boron-analogous part with the composition FeK3 while further potassium atoms are replacing Al in agreement with the formulation K2[FeK3]. The disorder of the free nitrite ions affiliated to KNO2 is characterized by means of additional data sets collected at temperatures of 173 K and 363 K. The results of the structure analysis are confirmed by infra-red spectroscopy. Especially the deformation modes δ(O-N-O) of the free nitrite and those of the nitro ligand show the expected frequency splitting. Mössbauer data serve as a check on chemical composition and give an independent estimate for the mean square displacement of the iron (57Fe) atoms comparable to the results from X-ray diffraction. The loss of crystal water above 400 K is registered using ther-mogravimetry and differential scanning calorimetry.

Thermal Behaviour of Transition Metal-Containing Zirconium Phosphate

The thermal behaviour of Co(II), Ni(II) and Zn(II)-containing zirconium phosphate of α type was investigated. XRPD analysis revealed that, for the samples containing Co(II) or Ni(II), the first reflection of the solid phase is split into a doublet. In contrast, when Zn(II) is present, a single solid phase system is formed. The thermal behaviour of the materials followed this sequence. For the samples containing Co(II) or Ni(II), phase-transition processes were found and there was also a loss of crystal water, but for the sample containing Zn(II) there was only one endothermic effect, which corresponded to the decomposition of phosphate groups.

Synthesis and characterization of uranyl orthosilicate (UO 2) 2SiO 4 · 2H 2O

A new method was developed for the synthesis of uranyl orthosilicate, ( UO 2) 2 SiO 4 · 2 H 2 O. The method was derived from a procedure described by legros et al. [1]. This compound was synthesized by reacting stoichiometric amounts of 0.1 M solutions of uranyl acetate and sodium metasilicate at pH = 5 and at 383 K for about 10 days in a Parr bomb. Uranyl orthosilicate was obtained with reproducible yields of 81 ± 2%. The final product was identified and characterized by X-ray powder diffraction, IR-spectroscopy, ICP-MS, AAS, thermoanalysis (TG/DTG/DTA) and 29Si-MAS-NMR. The lattice constants were determined as a = 0.8306(3) nm, b = 1.1245(6) nm and c = 1.8622(8)nm for the orthorhombic system. The substance can be dried up to 423 K without any loss of crystal water. The 29Si-MAS-NMR investigations showed that the crystalline (UO 2) 2SiO 4 · 2H 2O contains only monomeric silicate anions.

DTA and TG analysis of heteropolyacids of the series H(3+x)PMo(12−x)VxO40·nH2O

DTA, TG and DTG of molybdovanadophosphoric acids of the series H(3+x)Mo(12−x)VxO40· nH2O (x=0, 1, 2, 3) were carried out. The samples with the highest content of water of crystallization (n=19–34) fuse above 40 °C, giving solutions of heteropolyacids which boil at 110 to 130 °C. The total loss of crystallization water occurs below 170–200 °C. The anhydrous acids decompose (dehydroxylation) at temperatures decreasing from the average value of 433 °C forx=0 to about 293 °C forx=3. For these vanadium-containing samples, an exothermic peak not accompanied by weight change appears at about 450, 430 and 390 °C forx=1,2 and 3, respectively, indicating a transformation in the solid state. Ifx=0, a weaker endothermic effect of dehydroxylation overlaps with a stronger exothermic effect, and only one exothermic effect exists, at 435 °C.

Thermal analysis of 1-Hydroxiethylidenediphosphonic acid and its salts

1-Hydroxyethylidenediphosphonic acid and its tetrasubstitutcd Li, Na, K, Rb, NH4, Ca and Ba salts were synthcsized and their thermal behaviour was studied under non-isothermal conditions by simultaneous TG-DTG-DTA at 20–1000 ‡C. The following thermal transformations were observed: loss of crystallization water, melting in the case of the acid, and intramolecular dehydration in the case of the salts, leading to the corresponding unsaturated derivatives. From the free acid, its acidic salts and the neutral ammonium salt, long-chain polycondensates are formed through intermolecular dehydration.

Kinetic analysis of thermogravimetric data. XI thermal decomposition of some metal dithionates

A thermal analytical study of Li, Na, K, Rb, Cs, NH4, Mg, Ca, Sr, Ba and Zn dithionates is reported. The decomposition of the dithionate ion is endothermic in the case of the Na, K, Rb, Cs and NH4 salts, but exothermic with Li, Mg, Sr, Ba and Zn. Kinetic parameters have been derived from the TG curves by means of the Coats-Redfern method. The validity of a linear kinetic compensation law is reported for the loss of crystal water and separately for the decomposition of the dithionate ion.