PROSPECTS FOR IMPROVING THE PROPERTIES OF SECONDARY FOUNDRY ALLOYS OF THE AL-SI SYSTEM USING THE MODIFICATION PROCESS

The results of analytical studies of the use of modern modifiers for secondary aluminum alloys, which affect the structure of the metal of castings and allow to obtain the necessary physical and mechanical characteristics. It is shown that modifiers influencing the size of the primary grain and the shape of eutectic silicon inclusions are of the greatest interest for the production of castings from secondary silumins. It is shown that according to modern ideas the structure of the metal melt is not homogeneous. In some temperature range, complete mixing of atoms does not occur, and microregions with a short-range structure characteristic of the crystalline phase appear. These formations are called differently: atomic groups, clusters, clots, islands, complexes of atoms, clusters, etc. In the last decade, ultrafine powders of chemical compounds (nanopowders), which act as additional crystallization centers during primary crystallization, have become increasingly used as modifiers of cast alloys.

Short-range structure, the role of bismuth and property-structure correlations in bismuth borate glasses

Bismuth-containing borate glasses, xBi2O3-(1-x)B2O3, were synthesized in the broad composition range 0.20≤x≤0.80 by melting in Pt crucibles and splat-quenching between two metal blocks. Infrared reflectance spectra, measured in the range...

Examination of the short-range structure of molten salts: ThF4, UF4, and related alkali actinide fluoride systems

The short-range structures of LiF-ThF4, NaF-AnF4, KF-AnF4, and Cs-AnF4 (An = Th, U), were probed using in situ high temperature Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Signally, the EXAFS...

In situ high pressure neutron diffraction and Raman spectroscopy of 20BaO–80TeO2 glass

The short-range structure of 20BaO–80TeO2 glass was studied in situ by high pressure neutron diffraction and high pressure Raman spectroscopy.

Influence of Se on Properties of As-S-Se-I Glass for Immersion Mid-IR Leds Lenses

The study of glass components influence on the physical and chemical properties of As–S–Se–I glasses has the potential to help design glasses with the required properties. A change of certain glass properties upon the introduction of selenium into AsSI glass was demonstrated. Non-stoichiometric compounds along the As2S3-AsI3-Se diagram section were investigated by differential thermal analysis, ultrasonic measurements, dilatometric measurements. It has been shown that the introduction of selenium decreases the glass solubility in water. Change in the glass properties with the change in the short-range structure studied by Raman spectroscopy was shown. These glasses can be used for creation of immersion lenses and optical adhesives which change radiation characteristics of mid-IR LEDs.

Structure and dynamics of glass-forming alloy melts investigated by application of levitation techniques

In this work results of studies on the short-range order and on the atomic dynamics in different stable and undercooled glass-forming metallic melts are reviewed. In order to undercool the melts deeply below the melting temperature and to avoid chemical reactions of the melts with crucible materials, the samples are containerlessly processed utilizing the electromagnetic or the electrostatic levitation technique. The short-range structure of the melts is studied by neutron diffraction, while the atomic dynamics are investigated by quasielastic neutron scattering. The relationship between short-range structure and atomic dynamics is discussed within the mode coupling theory of the glass transition. We will show that taking the time- and space-averaged structural information provided by measured partial structure factors as an input, mode coupling theory is able to explain the experimental results concerning the activation energies for self-diffusion and the coupling/decoupling behavior of the self-diffusion coefficients of the different alloy components.