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排序方式: 共有58条查询结果,搜索用时 62 毫秒
1.
Prof. Dr. Leszek Stoch 《Journal of Thermal Analysis and Calorimetry》1992,38(9):1947-1948
2.
L. Stoch 《Journal of Thermal Analysis and Calorimetry》1997,49(3):1433-1440
Chemical component exchange and transport phenomena accompanying the multistage phase transformations of several silicate and aluminosilicate-phosphate glasses and borates as model systems are considered. It is demonstrated that the component transport limitations modify the role of chemical affinity influence and determine the sequence of new compound formation.The work was supported by grant P040703406 from the National Committee of Scientific Research of Poland. 相似文献
3.
Physicochemical properties and compositions of KxH(3-x)PW12O40 salts, where 2 < or = x < or = 3, have been investigated. It has been found that freshly prepared K2HPW12O40 salt (drying at 313 K) contains particles of heteropolyacid and particles of the neutral potassium salt, the sample being in 78.6% amorphous. On aging at room temperature, the heteropolyacid spreads to form a surface layer covering the neutral potassium salt particles K3PW12O40. Heat treatment of KxH(3-x)PW12O40 salts, where 2 < or = x < 3, from 313 K to higher temperatures induces the transformation of the heteropolyacid-covering K(3) core into a well-dispersed, amorphous surface layer. On further heating of the acidic potassium salts, the surface layer decomposes between 855 and 915 K with the formation of a PW8O26-type bronze as a new phase, the K3PW12O40 salt remaining unchanged. The latter starts to decompose at 1093 K, and in the case of all samples, the process is completed at about 1183 K. Rietveld structure refinement, XPS, and 31P NMR measurements of acidic potassium salts indicate that the core of these salts is always formed by the K3PW12O40 salt, which is covered by a heteropolyacid. Comparison of lattice parameters of the K3 salt and HPW leads to the conclusion that the layer is composed of partially or completely dehydrated heteropolyacid molecules. The coverage of the core by HPW in the K2 sample was estimated to be equal to one monolayer. 相似文献
4.
ESCA spectra of V2O5, V2O5/TiO2 and V2O5 dissolved in TiO2 were recorded after oxidation and reduction. V4+ ions have the same effective charge in reduced V2O5 and in TiO2, whereas the effective charge of V5+ ions in TiO2 is higher than in V2O5, indicating enhanced electron acceptor properties.
V2O5, V2O5 TiO2 V2O5 TiO2 . , V+4 V2O5 TiO2 V+5 TiO2 V2O5, .相似文献
5.
Thermal decomposition of ulexite 总被引:1,自引:0,他引:1
The thermal decomposition of ulexite, NaCa[B5O6(OH)6] · 5H2O, monocrystals was investigated by thermal, X-ray, IR and optical microscopy methods at normal and elevated temperatures.It was found that the thermal decomposition has an intraframework character and proceeds in a few separate stages: 1) release of part of the molecular water coordinating the Ca and Na cations; this leads to a rearrangement of the ulexite structure; 2) release of the remaining molecular water and some part the OH groups, which causes breakdown of the ulexite structure, with the simultaneous crystallization of CaO · B2O3 and 2CaO·B2O3; 3) the slow release of the remaining OH groups up to 600°C, which causes decomposition of the borate rings and the crystallization of NaB3O5 and NaCaBO3.
Zusammenfassung Mittels thermischer, röntgenographischer, IR- und optisch mikroskopischer Verfahren wurde bei Normal- und bei hohen Temperaturen die thermische Zersetzung von Ulexiteinkristallen NaCa[BsO6(OH)6]·5H2O untersucht.Die Untersuchungen zeigten, daß die thermische Zersetzung von Ulexit einen Innergittercharakter trägt und in einigen separaten Schritten verläuft: 1) Freisetzung desjenigen molekularen Wassers, welches Ca und Na Kationen koordiniert; hierdurch geschieht eine Wiederherstellung der Ulexit-struktur, 2) Freisetzung des verbleibenden Kristallwassers und einem Teil der OH-Gruppen, wodurch eine Zersetzung der Ulexit-struktur unter gleichzeitiger Kristallisation von CaO · B2O3 und 2CaO · B2O3 erfolgt, 3) langsame Freisetzung der verbleibenden OH-Gruppen bis 600°C, was eine Spaltung der Boratringe und die Kristallisation von NaB3O5 und NaCaBO3 zur Folge hat.相似文献
6.
L. Stoch 《Journal of Thermal Analysis and Calorimetry》1987,32(6):1651-1658
Temperature-activated reactions of decomposition, the synthesis of new compounds, and reduction and oxidation, termed here intraframework reactions, take place within the structural framework of solids. They are distinguished in that they occur within the bulk volume of the substance, in the area of the influence of crystal fields. The atoms and ions participating in these reactions are displaced by diffusion, which is usually directional diffusion. The regularities governing some of these reactions are presented in the paper.
Zusammenfassung Im Strukturgefüge von Feststoffen treten sogenannte Intratexturreaktionen auf: durch Wärme hervorgerufene Zersetzungsreaktionen, Sýnthese neuer Verbindungen, Reduktion und Oxidation. Diese sind dadurch gekennzeichnet, daß sie im gesamten Volumen der Substanz, in einem vom Kraftfeld des Kristalles beeinflußten Raum ablaufen. Der Austausch der an den Reaktionen teilnehmenden Atome und Ionen wird durch eine stets gerichtete Diffusion verursacht. Es werden Gesätzmäßigkeiten beschrieben, denen einige dieser Reaktionen unterliegen.
- , , , . , , . . , . , , , . .相似文献
7.
The high-resolution
transmission electron microscopy HRTEM study of the atomic scale mechanism
of crystal structure organization within the amorphous polymeric structure
of the model multicomponent glass TiO2–MgO–Al2O3–SiO2– in the glass transformation temperature range has been
undertaken. In the glass transition (T
g)
temperature range, glass transforms from the solid of rigid amorphous structure
into viscoelastic state of weakened chemical bonds. This is an example of
nuclei formation and crystal growth in the polymeric amorphous structure of
low atomic scale homogeneity due to middle range ordering. It has been demonstrated
that in this case crystal structure formation proceeds by successive displacement
and local ordering of atoms in the amorphous structure, like disorder-order
transformation in crystalline solid bodies. As the consequence in the crystallization
by parent structure reorganization mechanism, traditional model of glass crystallization
as well as kinetic models of reactions in solid bodies according Avrami or
others, are worthy to be revised. 相似文献
8.
Five different doublets corresponding to W 4f electrons were observed in the course of reduction of WO3. On contact of WO3 with hydrogen, W5+ ions are formed. Reduction results at first in formation of isolated W4+ ions. Clusters of edge-sharing octahedra on shear planes are then formed, in which pairing of W4+ ions occurs due to metal-metal bonding, corresponding to an apparent 2+ oxidation state. 相似文献
9.
Birczyński A Lalowicz ZT Olejniczak Z Stoch G Petelenz B 《Solid state nuclear magnetic resonance》2005,28(2-4):142-159
Partially deuterated ammonium compounds contain ammonium ion isotopomers with relative abundances given by the binomial distribution of protons and deuterons. All isotopomers with deuterons contribute characteristic deuteron NMR spectra at 5K. Experimental NMR spectra were separated and respective contributions of isotopomers were determined. The derived contributions agree with expected values for a given deuteration in the case of ammonium hexafluorophosphate. In ammonium hexachlorotellurate both NH2D2+ and about 50% of NH3D+ ions are rigid, while the remaining NH3D+ perform limited jumps. NHD3+ and ND4+ ions undergo tunnelling rotation, NH3D+ ions perform either jumps about C2 axis or limited jumps, but some stay rigid in ammonium hexachlorostannate. NH2D2+, NHD 3+ and ND4+ undergo rotational tunnelling. In the case of ammonium perchlorate, the NH3D+ ions perform either jumps about C3 axis or limited jumps whilst some remain rigid. Very low values of activation energies were derived for all spectral components from the temperature dependence of their spectra, up to about 20K, which indicates an incoherent tunnelling nature of the observed dynamic processes. The diverse mobility of NH3D+ ions appears to be the most interesting and new feature. 相似文献
10.
The influence of silica addition and of the annealing on the structure and properties of phosphate coatings are investigated. It has been observed that silica stabilizes phosphates and reduces the transport of iron towards the surface. 相似文献