Karla Barčová

Thermal decomposition of almandine garnet: Mössbauer study

The thermal decomposition of almandine garnet from Zoltye Vody, Ukraine, has been studied using57Fe Mössbauer spectroscopy. Room temperature Mössbauer spectrum of the initial powdered sample is characterised by one doublet corresponding to Fe2+ in dodecahedral position 24c. In the room temperature spectra of all heated almandine samples, a doublet corresponding to γ-Fe2O3 nanoparticles appeared. Depending on experimental conditions (heating temperature and time), the additional spectral lines of α-Fe2O3 and ε-Fe2O3 were observed in Mössbauer spectra.It is obvious that the thermal transformation of almandine garnet in air is related to the primary formation of γ-Fe2O3 superparamagnetic nanoparticles. γ-Fe2O3 nanoparticles are transformed into ε-Fe2O3 and consequently into α-Fe2O3 at higher temperatures. The mechanism and kinetics of the individual structural transformations depend on experimental conditions — mainly on the heating temperature and size of the particles.

Quantitative evaluation of the synergistic effects of failures in a critical infrastructure system

A critical infrastructure is a complicated system whose failure (in whole or in part) has a significant impact on national interests, including security, the economy and basic human needs. The system consists of relevant sectors, elements and their mutual linkages. In order to study critical infrastructures, it is necessary to apply a systems approach based on cross-sectoral evaluation and research into the linkages between the individual critical infrastructure sectors. Specifically, it is necessary to describe the individual vertical and horizontal levels of each critical infrastructure and the associated linkages. From this point-of-view, a critical infrastructure is embedded within the broader context of emergencies and enterprises, representing a compact and mutually-interconnected system.This paper focuses on quantitatively assessing the impacts of critical infrastructure failures. It presents a theory of synergistic linkages, their levels and the synergistic effects due to the joint action of impacts, which increase the overall impact on the critical infrastructure and on society. The concepts are formalized in the SYNEFIA methodology, which is applied in a case study involving the critical infrastructure of the Czech Republic. In particular, the methodology is applied to determine the synergistic effects of disruptions to multiple sub-sectors of the Czech infrastructure.

Characterization and thermal behaviour of garnets from almandine-pyrope series at 1200°C

The natural garnets from almandine (Fe3Al2Si3O12)—pyrope (Mg3Al2Si3O12) series with the iron to magnesium atomic ratio ranging from 0.2 to 1 were characterised and their thermal behaviour at 1200°C studied by 57Fe Mossbauer spectroscopy, X-ray powder diffraction, X-ray fluorescence, DTA, TG and electron microprobe analysis. The pyrope-type samples with a dominant magnesium content at position 24c in the cubic garnet structure undergo oxidative decomposition at 1200°C resulting in the formation of the paramagnetic spinel Mg(A1,Fe)204 structure with a low iron content, enstatite (Mg,Fe)SiO3 and anorthite CaAl2Si2O8 as the host compound for calcium. Contrary to pyropes, the iron-rich garnets exhibit complete oxidation at 1200°C conforming to the formation of magnetically ordered nanocrystalline γ-Fe2O3 or Mg(Fe,AI)2O4 spinels depending on the initial chemical composition of the garnets. In the reaction products of iron-rich garnets, cordierite (Mg2A14Si5O18) and anorthite were identified as non-ferrous phases.

MöSsbauer Spectroscopy in Studying the Thermally Induced Oxidation of Fe2+ Cations in Iron-Bearing Silicate Minerals

The oxidation mechanisms of Fe2+ in different iron-bearing minerals depend strongly on the external conditions, including the heating temperature, mineral crystal unity, pressure conditions and oxidation atmosphere. However, slight differences in the internal features (the total content of iron, distribution of iron in non-equivalent sites, chemical environment and coordination of iron) can also significantly influence the oxidation mechanism. Thus, different oxidation routes can occur depending on the structural ordering and external conditions.

Attenuation of thermal radiation through water mist

This article focuses on the interaction of thermal radiation with water droplets and the creation of water mist for the purpose of evaluating the decrease of heat flux when positioning a water curtain of various parameters between a radiation source and a radiometer. The change of water curtain parameters, affecting the passing through of thermal radiation, was performed using five nozzles with a variable spray characteristics. For the respective nozzles the attenuation of thermal radiation was determined and the thermal radiation transmittance was calculated. Water mist was created using a high‐pressure pump and nozzles with a different size of the orifice. The measurement of droplet size was performed using the time‐shift technique. The Omegalux radiant panel was used as the radiation source and the Hukseflux SBG01 radiometer with a working range of 0–5 kW.m−2 was used as the detector.

Attenuation of Infrared Radiation When Passing Through a Water Curtain

Abstract This article focuses on the interaction of infrared (IR) radiation with water droplets. The main objective of the article is the production of water mist in order of evaluation the reduction in intensity of IR radiation. In the experiments described in this paper, a set of five different nozzles was used with various spray characteristics. The respective nozzles were gradually located between the IR radiation source and a detector and the attenuation of IR radiation was assessed. The reduction in IR radiation intensity was determined and IR radiation transmittance was calculated for the respective tested nozzles.

Analysis of Data Collected at Control Room Full Scope Simulator at Dukovany Nuclear Power Plant

Abstract This article describes a computer program that will be used by experts to analyze human factor reliability when analyzing data obtained during the training of operators on a nuclear power plants control room simulator. The program was applied to data collected during the training of a scenario called Rupture of the Hot Loop of the Primary Circuit (250 t/h). Based on the comparison of charts, temporal passage through the scenario, or by personal participation in the training, analysts evaluate the successful passing of the practice scenario and propose final recommendations. The article also describes the criteria for successfully passing the practiced scenario and its final evaluation.

The development of special sequentially-timed charges for breaking frozen waterways

Abstract This article documents the development of the noninvasive use of explosives during the destruction of ice mass in river flows. The system of special sequentially-timed charges utilizes the increase in efficiency of cutting charges by covering them with bags filled with water, while simultaneously increasing the effect of the entire system of timed charges. Timing, spatial combinations during placement, and the linking of these charges results in the loosening of ice barriers on a frozen waterway, while at the same time regulating the size of the ice fragments. The developed charges will increase the operability and safety of IRS units.

Possible IED threat to airport premises during security X-ray inspection

Abstract The premises of international airports in CR are major air transport hubs as well as key elements of critical infrastructure, belonging to the very high risk category. Any infringement leading to limitation or complete shutdown would cause considerable economic and psychological damage. The most important task is to ensure high quality and reliable physical and technical protection of the airport, because especially in the summer months these areas collect large numbers of people and a possible terrorist attack could be fatal. This paper focuses on assessing the possibilities of solving the problem of IEDs hidden in travel luggage, and their initiation by X-rays during security checks.

Vitreous Enamel Coating on Steel Substrates

Vitreous enamel is a glassy coating formed on a metal substrate by firing at temperatures above 800 °C. The quality of vitreous enamel coating depends on the pre-treatment of the steel substrate surface and the quality of enamel slip. The main aim of this study was to characterize the composition of the steel substrate surface after firing with double finish, to explain the effect of steel substrate surface pre-treatment (blasting, acid pickling) on forming the phase interface of the steel substrate – vitreous coating system, and on its final microhardness, fracture strength and the adhesive properties of the coating. To achieve these aims, the following experimental methods were used: Mössbauer spectroscopy, X-ray diffraction, electron analyzer, and EDAX. Based on the chemical composition of the initial enamel slip and the firing technology, the metal - enamel system interface exhibited various ratios of layers of magnetite, hematite, nonstoichiometric wüstite, and crystals of faylite. The measuring results indicate that the quality and age of enamel slip influences the brittle fracture properties of vitreous enamel coating.