Vladimír Machovič

Structure of silicon oxycarbide glasses derived from poly(methylsiloxane) and poly[methyl(phenyl)siloxane] precursors

Abstract The preparation of silicon oxycarbide glasses and structure changes of polysiloxane precursors during heat-treatment in oxidative and nitrogen atmosphere are studied by 13 C and 29 Si magic angle spinning (MAS) NMR, Fourier-transform infrared (FTIR) spectroscopy and thermogravimetry analysis (TG). The reaction mechanisms in inert and oxidation conditions are discussed with respect to the chemical composition of the used precursors. We focused on the formation of new silicon oxycarbide units as well as a highly condensed aromatic carbon phase, the structure of which is discussed. A correlation of thermo-oxidative properties with chemical structure of prepared materials as well as with conditions of their preparation is given.

Preparation of iron, aluminium, calcium, magnesium, and zinc humates for environmental applications

A few non-conventional humate sorbents, i.e. iron humate (FeH), aluminium humate (AlH), calcium humate (CaH), magnesium humate (MgH), and zinc humate (ZnH), were prepared from a commercial product Fortehum L/K (Humatex, Bílina, Czech Republic). The metal content in humates was determined by X-ray fluorescence analysis, the organic elements (C, H, N, and S) were analysed by an Elementar Vario III and the functional groups were determined by classical methods using KBr pellets and diffuse reflection infrared spectroscopy (DRIFTS). FeH, AlH, and ZnH were tested as sorbents for the removal of inorganic or organic pollutants (metals, inorganic ions, dyes, and chlorophenols) from waste water. Sorption properties decreased in order: ZnH, AlH, FeH. CaH and MgH are partly soluble and therefore they are not usable as sorbents. However, their ion-exchange abilities for heavy metals are excellent which makes them usable for phytoremediation and bioremediation.

Hypogene Features in Sandstones: An Example from Carboniferous Basins of Central and Western Bohemia, Czech Republic

Concave and cavernous forms including rising wall channels, rising sets of coalesced copula, ceiling half-tube channels, separate ceiling copula, ceiling chimneys, and half-spherical upward-convex arches locally occur in surface outcrops of Carboniferous arkose sandstones in central and western Bohemia. Many of these negative forms conventionally described as tafoni and/or honeycombs have been traditionally interpreted as products of various exogenous weathering processes. Based on the line of indirect evidence, we propose an alternative interpretation in which these features represent transitional and outlet members of the morphologic suite of rising flow (MSRF), indicative of their subsurface hypogene origin. The negative forms are commonly associated with bedding planes and subvertical fractures mineralized with goethite and jarosite. The reflectance of coal particles embedded in sandstone along mineralized bedding planes (0.91–1.03% R r ) is appreciably higher with respect to those of adjacent unaltered arkose host rocks (0.61–0.85% R r ), pointing to the thermal overprint by hot fluids. Moreover, the walls of many cavities are covered by sandy-disintegrated alterite locally mineralized with gypsum, dickite, goethite, authigenic quartz, pickeringite, and bischofite. We suggest that these phenomena, including the origin of characteristic concave forms and mineralogical alterations of arkose host rocks, may have been due to warm, CO2-saturated and possibly H2S-rich brines that ascended from the deepest stratigraphic units of the Carboniferous succession via the network of subvertical tectonic fractures and migrated laterally outward along permeable bedding planes. As indicated by the apatite fission track analysis and wider geological observations, the alteration of arkose sandstones probably occurred at relatively shallow depth of burial, during the Tertiary uplift of the Bohemian Massif 15–20 Ma ago. In this environment, the alteration may have been accelerated by the effects of mixing corrosion where heated deep basinal fluids interacted with shallower interstratal waters. When the uplifted sandstone sequences eventually reached the surface, the hypogene cavities and altered cliff walls were subjected to subaerial weathering and fluvial erosion processes the effects of which were superimposed on older hypogene features.

Comparison of Nanofiber and Particle Form of GELATINE/HA Biocomposites

This report is about composites used for bone grafting. Targets the composites compact of organic chemical compounds (biopolymers) and anorganic chemical compounds (nanoparticles). These composites must be, among others, biocompatible, nontoxic for organism and their mechanical properties must be near to mechanical properties of bone. This report focused on biodegradable composites based on gelatine and nanopowder of hydroxyapatite in nanofiber and particle form.