Selenium Status of Cattle in the Czech Republic

Selenium status was assessed directly by determination of selenium concentration, or indirectly by measurement of glutathione peroxidase activity in whole blood samples collected from 879 cattle (733 cows, 63 calves, 42 heifers, 41 finishing bulls) reared on 93 farms in 12 of the 14 regions of the Czech Republic. Selenium deficiency or marginal values were found in 50 % of the tested animals and on 54 % of the farms. In terms of animal categories, deficient or marginal selenium status was found in 42 % of cows, 80 % of calves, 100 % of heifers, and 90 % of bulls. Selenium-deficient herds were detected in almost all regions of the Czech Republic. The lowest selenium concentrations (< 20 µg.l-1 whole blood) were found in western, northern, and north-eastern Bohemia and in northern Moravia. It is evident that selenium deficiency in cattle is a topical problem in the Czech Republic and that selenium status must be monitored within preventive diagnostics in all age groups of cattle to decide correctly on the most effective way of supplementation. Glutathione peroxidase, preventive diagnostics, blood, dairy cows, heifers Like with most minerals, satisfactory intake of selenium by ruminants depends on the presence of this element in soil and on the potential of plants to utilise it. The occurrence of selenium in soil varies considerably worldwide. Oldfield (2000) denoted as selenium deficient the west coastal and eastern areas of the United States and Canada, extensive area

Overview of processing technologies for tungsten-steel composites and FGMs for fusion applications

Tungsten is a prime candidate material for the plasma-facing components in future fusion devices, e.g. ITER and DEMO. Because of the harsh and complex loading conditions and the differences in material properties, joining of the tungsten armor to the underlying construction and/or cooling parts is a complicated issue. To alleviate the thermal stresses at the joint, a sharp interface may be replaced by a gradual one with a smoothly varying composition. In this paper, several techniques for the formation of tungsten-steel composites and graded layers are reviewed. These include plasma spraying, laser cladding, hot pressing and spark plasma sintering. Structure, composition and selected thermal and mechanical properties of representative layers produced by each of these techniques are presented. A summary of advantages and disadvantages of the techniques and an assessment of their suitability for the production of plasma-facing components is provided

Mechanical and Thermal Properties of Individual Phases Formed in Sintered Tungsten-Steel Composites

Tungsten is a prime candidate material for plasma facing components in fusion devices, thanks to its advantageous properties with respect to interaction with hot plasma. For its bonding to the supporting structure, composites and graded layers can be used for the reduction of stress concentration at the interface. When tungsten and steel are processed at elevated temperatures, e.g. hot pressing or spark plasma sintering, intermetallic phases may form and their presence and properties will affect the properties of the composite. In this work, mechanical and thermal properties of the individual phases, i.e. steel, tungsten and Fe-W intermetallics are investigated. Mechanical properties were determined by instrumented indentation. Thermal conductivity was determined by the xenon flash method on a range of samples with varying composition, from which the conductivities of each constituent were estimated. The results can be used for the optimization of compositional profiles and processing conditions for manufacturing of plasma facing components

Heat load and deuterium plasma effects on SPS and WSP tungsten

Tungsten is a prime choice for armor material in future nuclear fusion devices. For the realization of fusion, it is necessary to address issues related to the plasma–armor interactions. In this work, several types of tungsten material were studied, i.e. tungsten prepared by spark plasma sintering (SPS) and by water stabilized plasma spraying (WSP) technique. An intended surface porosity was created in the samples to model hydrogen/ helium bubbles. The samples were subjected to a laser heat loading and a radiation loading of deuterium plasma to simulate edge plasma conditions of a nuclear fusion device (power density of 108 W/cm2 and 107 W/cm2, respectively, in the pulse intervals up to 200 ns). Thermally induced changes in the morphology and the damage to the studied surfaces are described. Possible consequences for the fusion device operation are pointed out