THE MODERN APPROACH TO THE QUALITY INCREASE OF CASTING BLOCKS AND HIGH-PERFORMANCE COMPOUNDS FOR PROCESSING OF MELTS ON THE BASIS OF ALUMINUIM

In the article there is given the group of measures, aimed at increase of quality of cast ingots and of high-performance compounds for processing of melts on the basis of aluminium

Hydrothermal structure control of polyoxofluoromolybdates(VI)

The predictive hydrothermal synthesis of polyoxometalates (POMs) is an important challenge for their targeted production and for the design of new POM motifs and organic−inorganic POM materials. In this context, the systematic fluorination of POMs remains to be fully explored. Therefore, the structure-directing influence of cation pairs on the primary and secondary structure of polyoxofluoromolybdates(VI) is explored in the present study. In the first step, new types of mixed alkali difluorooctamolybdates ((M, M′)Mo8O26F2·nH2O; M, M′ = K−Cs) illustrate how the choice of the alkali cations controls the resulting structure type. This structure-directing potential of the cations is investigated in terms of electrostatic calculations. The concept of cation pairs as structural “spacers” and “scissors” is then applied to construct new secondary structures from the recently discovered [Mo6O18F6]6− and [Mo7O22F3]5− fluoromolybdate anions. The use of selected bicyclic organic cations (asn = 1-azoniaspiro[4,4]nonane; adu = 1-azonia-4,9-dioxaspiro[5,5]undecane) led to the new organic−inorganic fluoromolybdates asn2Na4Mo6O18F6·6H2O, adu3Na3Mo6O18F6·3H2O and adu4NaMo7O22F3·4H2O. The steering effect of the organic cations in the formation of the layered organic−inorganic structures is compared for all three compounds with respect to their potential as building blocks for constructing POM-based materials

Hydrothermal Formation of W/Mo-Oxides: A Multidisciplinary Study of Growth and Shape

The hydrothermal formation of mixed nanoscale W/Mo-oxides with the hexagonal tungsten bronze (HTB) structure has been investigated by in situ EDXRD (energy dispersive X-ray diffraction). Compared to the binary oxide systems, they display intermediate kinetics with a nucleation-controlled mechanism dominated by the slow growing tungsten component. Furthermore, the thermal stability of nanostructured W/Mo-HTB compounds has been monitored through combined in situ X-ray absorption spectroscopy (XAS) and XRD in reducing and oxidizing atmospheres. Their transformation into other mixed nanostructures was only observed above 300 °C in O2- and H2-containing atmospheres. In addition, the shape of nanoscale hexagonal W/Mo-oxides can be expanded into a variety of morphologies via the use of alkali chlorides as hydrothermal additives. The alkali cations exert a two-fold role as internal stabilizers and external shape control agents. Their mobility within the channels of the W/Mo-oxide host framework has been investigated by solid state NMR spectroscopy

W/Mo-Oxide nanomaterials: structure-property relationships and ammonia-sensing studies

W/Mo-oxides of the hexagonal tungsten bronze (HTB) type have been investigated by X-ray absorption spectroscopy to obtain detailed insight into the substitution process of W by Mo that leads to mixed HTB frameworks. Both the morphology of the nanostructured W/Mo-HTBs as well as the oxidation state of Mo are significantly influenced through the incorporation of different alkali cations into the hexagonal channels of this open structure. A variety of complementary analytical methods, including TG, in situ and ex situ XRD, SEM, and solid-state NMR analyses, were applied to determine the thermal stability of the obtained W/Mo-HTB materials with respect to their alkali cation and NH(4)(+) contents. A strong correlation between composition and stability was found with the Rb-W/Mo-HTBs exhibiting the highest structural and morphological resistance among the series (up to 580 degrees C). The NH(3)-sensing properties of selected W/Mo-oxides in test atmospheres furthermore point to promising features of the Rb-stabilized hexagonal framework materials