Alkali activation of dif ferent type of ash as a production of combustion process

Presented study deals with the final struc ture and radiological properties of different fly-ash based geopolymers. Lig nite fly-ash (lignite Kolubara – Ser bia) and wood fly ash were obtained in combustion process together with commercial fly-ash. Synthesis of the geopolymers was con ducted by mixing fly-ash, sodium silicate solution, NaOH and water. The sam ples were strength ened 60 °C for 48 hours af ter stay ing at room temperature in covering mold for 24 hours. The X-ray dif frac tion, Fou rier trans form in fra red and SAM mea sure ments were conducted on the sam ples af ter 28 days of geopolymerization pro cess. The X-ray dif frac tion measurements of lignite fly-ash sam ples show anhydrite as the main constituent, while wood fly-ash samples consist of cal cite, albite and gypsum minerals. Besides determination of physicochemical properties, the aim of this study was radiological characterization of lignite fly-ash, wood fly-ash and the obtained geopolymer products. Ac tiv ity con cen tra tion of 40 K and radionuclides from the 238 U and 232 Th decay series, in ash sam ples and fly-ash based geopolymers, were determined by means of gamma-ray spectrometry, and the absorbed dose rate, D, and the annual effective dose rate, E, were calcu lated in accordance with the UNSCEAR 2000 report

Polarised Photoluminescence from Surface-Passivated PbS Nanocrystals

Effective surface-passivation of PbS nanocrystals in aqueous colloidal solution has been achieved following treatment with CdS precursors. The resultant photoluminescent emission displays two distinct components, one originating from the absorption band-edge and the other from above the absorption band-edge. We show that both of these components are strongly polarised but display distinctly different behaviours. The polarisation arising from the band-edge shows little dependence on the excitation energy while the polarisation of the above-band-edge component is strongly dependent on the excitation energy. In addition, time resolved polarisation spectroscopy reveals that the above-band-edge polarisation is restricted to the first couple of nanoseconds, while the band-edge polarisation is nearly constant over hundreds of nanoseconds. We recognise an incompatibility between the two different polarisation behaviours, which enables us to identify two distinct types of surface-passivated PbS nanocrystal.Comment: Preprint, 19 pages, 4 figure

Chemical, physical and radiological evaluation of raw materials and geopolymers for building applications

The main goal of this study was the evaluation of physical–chemical, as well as radiological properties of residual materials used for geopolymer synthesis and those final products as a possible application as new materials in a civil engineering industry. Concentration of 40K and radionuclides from the 238U and 232Th decay series in waste precursors, their metaphases and geopolymer samples synthetized by alkali activation were determined together with corresponding absorbed dose rate (D˙) and the annual effective dose rate. Natural activity concentrations in the alkali-activated material (geopolymer) were found to be lower than that of both residual materials and calcined ones

Sputtering yield and morphological changes of TiB2 coatings induced by different incident beams

The properties of TiB2 coatings deposited by direct electron-beam evaporation and by plasma spray deposition as well as their behavior during the interaction with the energetic beam are discussed. These coatings are considered as a plasma facing material for some parts of the next step tokamak. Sputtering yields were determined for: Ar+ ion bombardment in the energy region 3-12 keV and laser beam bombardment in the range up to 10(9) W/m(2). It was found that whatever the mechanism of sputtering is, a similarity between sputtering yield and energy dependence for used combinations of incident beams and target does exist.16th International Conference on Atomic Collisions in Solids (ICACS-16), Jul 17-21, 1995, Linz, Austri

Synthesis of fullerenes by hollow cathode arc

The formation of fallerenes in a hollow cathode arc in an inert gas atmosphere is investigated. The effects of the carbon evaporation rate, the inert gas flow rate and the are temperature on the fullerene yield, production rate and conversion rate are observed. A magnetic field of 100 Gauss is used to collimate the discharge and to improve the carbon evaporation rate. The agreement among experimental data and theoretical results of the model based on the equations of Smoluchovski is obtained

Kinetic model of metallocarbohedrene formation in arc plasma generator

A kinetic model of the formation of stable metal-carbon clusters, which have been designated metallocarbohedrenes, is developed. The metals chosen for the theoretical analysis were titanium and zirconium. An optimum starting composition of composite electrodes was found. The fullerene and Met-Car yields for different metal-to-carbon mass ratios were determined. The maximum yield of Ti8C12 was 0.4% while the maximum yield of Zr8C12 was 0.6%. The theoretical mass spectra of carbon and metallocarbon clusters were explored

SEM and EDX analysis of silicon surface irradiated by TEA CO2 laser

5th Multinational Congress on Electron Microscopy, Proceedings, Sep 20-25, 2001, Lecce, Ital

The effect of various parameters on the structure of W-Ti thin films

The properties of W-Ti thin films/coatings deposited by sputtering on various substrates have been studied. Structural analyses were made by X-ray diffraction and scanning tunneling microscopy. The results have shown that the crystal structure of W-Ti coatings has the same structure as tungsten; the presence of titanium gave rise to the expansion of the alpha-tungsten lattice. Microstructural features-grain size and morphology-mean surface roughness depend on substrate properties and thickness of the coatings. For the same thickness of deposited coatings, different inicrostructure features have been obtained as a function of substrate structure. The mean surface roughness and the grain size increase with increasing thickness of deposits on the same substrate.Progress in Advanced Materials and Processes, 5th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS 2003), Sep 15-19, 2003, Herceg Novi, Yugoslavi

Properties of tungsten-titanium sputtered coatings

Trends in Advanced Materials and Processes, 3rd Yugoslov-Materials-Research-Society Conference, Sep 20-24, 1999, Herceg Novi, Yugoslavi