Effect of Ti (Macro-) Alloying on the High-Temperature Oxidation Behavior of Ternary Mo–Si–B Alloys at 820–1,300 °C

The aim of the present investigation was to gain an initial understanding of the effect of (macro-) alloying with Ti on the oxidation behavior of Mo–Si–B alloys in the ternary phase region of Mo_ss–Mo₃Si–Mo₅SiB₂ at 820–1,300 °C. Motivated by recent studies and thermodynamic calculations, the alloy compositions Mo–9Si–8B–29Ti (at.%) and Mo–12.5Si–8.5B–27.5Ti (at.%) were selected and synthesized by arc-melting. Compared to the reference alloy Mo–9Si–8B, superior initial oxidation rates at 1,100–1,300 °C as well as a significant density reduction by nearly 18 % were observed. Due to enhanced initial evaporation of MoO₃ and mainly inward diffusion of oxygen, a borosilicate-rutile duplex scale with a continuous TiO₂ phase had formed. Detailed investigations of the oxidation mechanism by SEM, EDX, XRD and confocal micro-Raman spectroscopy indicated that Ti alloying is promising with regard to further improvement of the oxidation resistance as well as the strength-to-weight ratio of Mo–Si–B alloys.     

Radioactivity levels in aerosol particles surrounding a large TENORM waste repository after application of preliminary restoration work

In this paper, (238)U-series radionuclides have been analysed in particulate matter samples collected at a phosphogypsum stack system located near the city of Huelva (SW Spain) during the course of 1 year. The results have been compared to those collected at a reference (background) site located a few km away, in order to establish if the stack system provokes an increase in radionuclide exposure due to inhalation with particulate matter. The (222)Rn progeny, which is considered a very important contributor to the internal dose rate received by the population, was collected for 6 months. The results indicate that for several types of radionuclides there is a significant increase in the radioactivity adsorbed by the aerosol particles collected at phosphogypsum stacks. The isotope analysis indicates that this increment could be affected by the water vapour emissions from the factory, which contain high concentrations of these radionuclides. However, the majority of these radionuclides could not be detected at the background location. The corresponding dose increment estimated at the sampling point is, however, negligible. This fact is a consequence of the very small radionuclide concentration increment, together with relatively conservative nature of the occupational factor applied. Regarding the Rn progeny, no significant differences between either the collecting sites has been registered due to of the dominant wind regime at the sampling locations.     

Applicability of Zel’dovich’s theory of chain propagation of flames to combustion of hydrogen-oxygen mixtures

The applicability of Zel’dovich’s theory to the propagation velocity of flames with chain-branching reactions was tested by calculations based on a detailed mechanism and using Zel’dovich’s approximate formulas with a refined mechanism of hydrogen atom recombination for stoichiometric hydrogen-oxygen and hydrogen-air mixtures at pressures of 47.5–760 torr. Good agreement of the results was obtained. Zel’dovich’s approximate theory for a flame with chain-branching reactions dominated by recombination processes gives a reasonable physical picture and provides approximate formulas for flame propagation velocity.     

Diamond Diode Structures Based on Homoepitaxial Films

(m–i–p)-Structures with high-resistance epitaxial i-layers are fabricated on heavily doped p⁺-type substrates with platinum contacts. The structures are studied using several methods: optical and electron microscopy and luminescence, and electrophysical (C–V and I–V characteristics) methods and tested as detectors of ionizing radiation. It is shown that the (m–i–p)-structures are promising for development of several electronic devices (high-voltage diodes, detectors of ionizing radiation, and photovoltaic devices).     

Theory of Intermittent Cutting. 5. Description of Tool Entry in the Blank

Vorontsov’s plastic-flow method permits the derivation of a model of cutting for the region where the tool enters the blank. The stress–strain state of the blank is determined, and the dimensions of the plasticdeformation zone are calculated. The main cutting parameters are shown to be variable.     

Theory of Intermittent Cutting. 4. Interpretation of Empirical Data Regarding Tool Exit from the Blank

Empirical observations of tool exit from the blank are interpreted on the basis of the model developed.     

The Theory of Discontinuous Cutting

Cutter entry and exit at the workpiece considerably influence the tool life. It is established that an adequate model of the cutting process during tool entry and exit remains to be developed.     

Theory of Intermittent Cutting. 2. Existing Approaches

Existing approaches to cutting are analyzed. The advantages and disadvantages of each model are considered in detail.     

Acoustic-Emission Testing of Vertical Steel Tanks in Hard-To-Reach Areas of the Far North

The long-term safe operation of vertical steel storage tanks (VSSTs) for petroleum products in remote regions of the Far North implies objective timely detection of various types of emerging and existing defects with further provision for the monitoring of their development. The poor infrastructure and climatic features of the northern regions, as well as the time and material resources spent on preparing the standard scope of VSST testing adversely affect the performance and quality of its implementation. Therefore, taking these circumstances into account, a different approach is needed to inspect VSSTs operating in the hard-to-reach regions of the Far North. Taking the peculiarities of operating VSSTs at low temperatures in the Far North into account and based on the analysis of emergencies and accidents resulting from the degradation of VSST metal structures, the sources of damage are identified, the main problems of detecting planar flaws leading to catastrophic failures of VSSTs are shown, and a modified method is proposed for the local loading of bearing VSST members when conducting their acoustic-emission (AE) testing.