X-ray Amorphous Particles Research Articles

Ir spectroscopic and crystal morphology studies of the structure of alakli metal fluorophosphatozirconates (hafnates)

Potassium, rhubidium, and caesium fluorophosphatozirconates (hafnates) and oxo(hydroxo)fluorophosphatonitratometalates with PO 4 3− /Zr molar ratios of 2.0, 1.5, 1.0, 0.66, 0.5, and 0.33 are synthesized for the first time. Most of them form either fine crystalline or X-ray amorphous particles. In order to characterize them IR spectroscopy and SEM are used. For the crystalline compounds the types of PO4 groups and the character of bonds between fluorine and water are revealed. The occurrence of triple MeF4·Rb(PO4)0.33·RbNO3 (Me = Zr, Hf) salts and also M3Me3(PO4)5·3HF crystalline solvates is found. The layered habit of K3Hf3(PO4)5·3HF, RbHfF2PO4·0.5H2O, Rb3Hf3(PO4)5·3HF, CsHfF2PO4·0.5H2O, CsHf2F6PO4·4H2O, and CsH2Hf2F2(PO4)3·2H2O crystals gives grounds to suppose that the structure of these compounds is layered unlike the structure of triple MeF4·Rb(PO4)0.33·RbNO3 salts.

Synthesis and optical properties of cadmium sulfide in perfluorosulfonic membrane

Synthesis of nano-dimensional particles of cadmium sulfide in the pores of perfluorosulfonic membrane by means of the ion-exchange fixation of Cd2+ cations and the subsequent treating with gaseous hydrogen sulfide is carried out. As a result of gradual “step-by-step” accumulation of the guest substance monotonous downfield shift of the absorption bands in the visible spectrum is observed. In the luminescence spectra a set of bands is registered characterizing the dimensional distribution of small X-ray amorphous particles. Contrary to that one-step capsulation of cadmium sulfide by means of sulfidation of membrane with the content of Cd2+ ions close to the saturated state provides the formation of nano-dimensional particles of cubic structure. Their absorption band is maximally close in its position to that of the bulk CdS, and in the luminescence spectrum characteristic long-wave radiation with λmax 670 nm dominates. Optical properties of cadmium sulfide and their dimensional specific features are described considering the population of (Cd-S)-antibonding orbitals resulting from photoexcitation.

Tungsten oxide nanoparticles synthesised by laser assisted homogeneous gas-phase nucleation

Tungsten oxide nanoparticles were generated by excimer (ArF) laser assisted chemical vapor deposition from WF 6/H 2/O 2/Ar gas mixtures. The deposited particles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The deposition rate as a function of the partial pressures of the reactants and of the laser fluence was measured by X-ray fluorescence spectroscopy. The mean diameter of the deposited tungsten oxide particles varied with the experimental parameters and was typically 23 nm. Particles with a higher degree of crystallinity were observed at a laser fluence exceeding 130 mJ/cm 2, and X-ray amorphous particles were obtained below 110 mJ/cm 2. The amorphous tungsten oxide had a stoichiometry ranging from WO 2.7 to WO 3. Deposits were formed only when hydrogen was present in the gas mixture.

Geochemical differentiation in laterite and bauxite formation

The geochemical differences between laterite and bauxite formation are discussed under the aspect that both weathering products are predominantly formed by residual enrichment of iron and aluminium. Residual enrichment is corroborated by various arguments and clearly proved for laterite formation on ultramafic rocks. Tropical weathering of the most widespread acidic rocks leads, in spite of their high Al/Fe ratio, generally to formation of laterites showing a high enrichment of iron whereas aluminium is not or only slightly enriched. This chemical variation indicates that high amounts of Al are removed additionally to Si in soil solutions when saprolites on acidic rocks are transformed into laterites containing goethite, hematite and kaolinite as main constituents. Dissolved free aluminium exist in equilibrium with kaolinite only in minimal contents, hence the removal of Si and Al probably takes place in form of freshly formed colloidal or subcolloidal, X-ray amorphous particles with kaolinitic or similiar composition. The frequently observed occurrence of two generations of secondary kaolinite in laterites corroborates this conclusion. There is general agreement that bauxites are formed by stronger leaching compared with laterites. Increased leaching lowers the concentration of dissolved silica, thus enabling gibbsite instead of kaolinite stability. The concentration of dissolved free aluminium, however, is increased in equilibrium with gibbsite. Free aluminium shows in contrast to iron an effective solubility atpH= 5, giving rise to downward leaching and re-precipitation at higher pH below a laterite crust which covers the bauxite zone in most of the bauxite deposits. In spite of the stronger leaching, bauxite formation implies a lower mass loss (mainly Si) during weathering than the formation of laterites (loss ofSi + Al) related to their highly increased iron content.

X-ray characteristics of iridium and platinum blacks of various dispersity

X-ray and structural characteristics of iridium and platinum blacks of various dispersity in the coherent scattering region from 40 to 700 A have been studied. High dispersity blacks are shown to contain crystalline and X-ray amorphous particles with a disordered structure and decreased coordination number. For such blacks a 0.003 A increase in the unit cell parameter is observed.