ABSTRACT
As part of extensive research on the properties of nickel-aluminum alloys, corrosion tests of sintered materials produced by the innovative HPHT/SPS (high pressure, high temperature/spark plasma sintering) method were performed in 0.1 molar H2SO4 acid. The hybrid, unique device used for this purpose (one of only two such devices operating in the world) is equipped with a Bridgman chamber, which allows heating with high-frequency pulsed current and sintering of powders under high pressure in the range of 4-8 GPa and at temperatures up to 2400 °C. Using this device for the production of materials contributes to the generation of new phases not obtainable by classical methods. In this article, the first test results obtained for the nickel-aluminum alloys never before produced by this method are discussed. Alloys containing 25 at.% Al, 37 at.% Al and 50 at.% Al were produced. The alloys were obtained by the combined effect of the pressure of 7 GPa and the temperature of 1200 °C generated by the pulsed current. The time of the sintering process was 60 s. The electrochemical tests, such as OCP (open circuit potential), polarization tests and EIS (electrochemical impedance spectroscopy), were carried out for the newly produced sinters and the results were compared with the reference materials, i.e., nickel and aluminum. The corrosion tests showed good corrosion resistance of the produced sinters, with corrosion rates of 0.091, 0.073 and 0.127 mm per year, respectively. It leaves no doubt that the good resistance of materials synthesized by powder metallurgy is due to the proper selection of the manufacturing process parameters, ensuring a high degree of material consolidation. This was further confirmed by the examinations of microstructure (optical microscopy and scanning electron microscopy) and the results of density tests (hydrostatic method). It has been shown that the obtained sinters were characterized by a compact, homogeneous and pore-free structure, though at the same time differentiated and multi-phase, while the densities of individual alloys reached a level close to the theoretical values. The Vickers hardness of the alloys was 334, 399 and 486 HV10, respectively.
ABSTRACT
Combining ellipsometric and EIS methods, the dielectric constant ε for the oxide Nb2O5 at room temperature was determined. At first, the linear dependence between anodization voltage and oxide thickness was established in the form d = 2.14 (± 0.05) · U + 12.2 (± 1.7) nm in the range of anodizing potentials 0-50 V. Next, assuming the equivalent circuit corresponds to one, the capacitance C of the dense oxide layer was measured. All results taken together gave the value of dielectric constant ε = 93 ± 5.
ABSTRACT
Materials were obtained from commercial zirconium powders. 1 mass%, 2.5 mass% and 16 mass% of niobium powders were used as the reinforcing phase. The SPS method and the extrusion method classified as the SPD method were used. Relative density materials of up to 98% were obtained. The microstructure of the sintered Zr-xNb materials differs from that of the extruded materials. Due to the flammability of zirconium powders, no mechanical alloying was used; only mixing of zirconium and niobium powders in water and isopropyl alcohol. Niobium was grouped in clusters with an average niobium particle size of about 10 µm up to 20 µm. According to the Zr-Nb phase equilibrium system, the stable phase at RT was the hexagonal α-phase. The tests were carried out for materials without the additional annealing process. The effect of niobium as a ß-Zr phase stabilizer is confirmed by XRD. Materials differed in their phase composition, and for both methods the ß-Zr phase was present in obtained materials. A very favorable effect of niobium on the increase in corrosion resistance was observed, compared to the material obtained from the powder without the addition of niobium.
ABSTRACT
INTRODUCTION: In the modern world, people gather more increasingly in large clusters such as shopping centres, markets, cinema centres, operas, ferries, liners, recreation areas and resorts. Such clusters predispose to intensified occurrences of states of rapid health worsening and health hazard. THE AIM: The main aim is to indicate that in trade space, especially in municipal markets, states of rapid health worsening and health hazard appear, as well as to characterize the individual incidents and types of medical interventions. MATERIAL AND METHODS: The empirical material originates from the sheets of records of first-aid concerning life-saving actions, the nurse work register, as well as the security agency reports. Records of first-aid of events taking place during one selected weekend day, for 6 hours of highest population density, underwent a retrospective analysis. The analysis of the material was carried out in terms of reasons of interventions, in states of rapid health worsening and health hazard, as well as the frequency of calls of medical first-aid service. RESULTS: During 2011, there were approximately 100 such states in the municipal markets which underwent the study. In shopping centres there were 95% of such states. In each of the three analysed areas, the internal factors responsible for rapid health worsening constitute over 60%. Among interventions caused by a disease, states related to circulatory system and nervous system occurred most frequently. Big municipal market themselves are potential areas of an increased occurrence of states of rapid health worsening and health hazard. They can be compared to religious ceremonies described in the subject bibliography. CONCLUSIONS: Large trade spaces, especially municipal markets in city centres, generate a high risk of occurrences of states of rapid health worsening and health hazard, in comparison to shopping malls. The risk increases with the age of customers. The incidences related to sicknesses are the majority of interventions in trade areas.
