Studying the process of modification of lithium aluminum alloys

The effect of modification with dispersed compositions on the grain structure and mechanical properties of industrial aluminum alloys has been studied. Aluminum alloys of the Al-Si, Al-Mg-Sc, Al-Cu-Mn systems were modified with dispersed Mg2Si powder with a particle size of up to 200 nm. The amount of modifier to be added to the melt is calculated. The physicochemical properties of dispersed Mg2Si have been studied. Melting of the AMg6, 1570, 2219, AK9ch alloys in the initial state and with the treatment of Mg2Si melts have been carried out. The action of insoluble applications, isomorphic to aluminum, the similarity of the influence of soluble elements holds only when the amount of insoluble addition exceeds the number of crystals formed arbitrarily under the same conditions. Thus, with an increase in the amount of insoluble addition, in particular silicon carbide particles, the grain size first decreases and then remains constant. The mechanism of the influence of dispersed particles of magnesium silicide on the formation of the structure of hypoeutectic aluminum alloys during crystallization is that their bulk is pushed out by the crystallization front into the liquid phase and participates in the refinement of the structural components of the alloy. To determine the optimal amount of silicon carbide modifier, industrial melting and testing were performed on specimens that underwent heat treatment according to the T6 mode (quenching and artificial aging). The quality of cast aluminum alloys during modification depends on many factors: the nature of the dispersed phase, the temperature of the melt, and the modes of its mixing with the introduction of particles. Dependences of the particle size and the amount of the modifier on the mechanical properties of the alloys have been established. The mechanism of interaction of the modifier with aluminum melt during crystallization has been established. In industrial experiments, the most effective size of SiC particles for increasing the σm of the AK9ch alloy from 115 to 260 MPa in the as-cast state has been established. The optimal content of Mg2Si (0.10 %) for increasing the σm of aluminum alloys has been determined.

Nickel Silicide Catalyst from Photovoltaic Waste for the Methanation Reaction

A technology designed for recycling photovoltaic (PV) cells at the end of their life was successfully used for the preparation of a nickel silicide catalyst. PV cells were mixed with magnesium scrap to produce magnesium silicide (Mg2Si), with almost total conversion under optimized conditions (400 °C, 5 Pa, 25 min), in a constructed semi-open tubular reactor. Subsequently, magnesium silicide was hydrolyzed by 25% phosphoric acid to produce a mixture of silicon hydrides, which were utilized as chemical vapor deposition (CVD) precursors for the preparation of a nickel silicide catalyst. The activity and stability of the prepared catalyst was repeatedly tested for methanation reactions. It was verified that the nickel silicide catalyst showed an approximately 20% higher activity for the methanation reactions compared to the commonly used nickel catalyst.

Analysis and Design of a Silicide-Tetrahedrite Thermoelectric Generator Concept Suitable for Large-Scale Industrial Waste Heat Recovery

Industrial Waste Heat Recovery (IWHR) is one of the areas with strong potential for energy efficiency and emissions reductions in industry. Thermoelectric (TE) generators (TEGs) are among the few technologies that are intrinsically modular and can convert heat directly into electricity without moving parts, so they are nearly maintenance-free and can work unattended for long periods of time. However, most existing TEGs are only suitable for small-scale niche applications because they typically display a cost per unit power and a conversion efficiency that is not competitive with competing technologies, and they also tend to rely on rare and/or toxic materials. Moreover, their geometric configuration, manufacturing methods and heat exchangers are often not suitable for large-scale applications. The present analysis aims to tackle several of these challenges. A module incorporating constructive solutions suitable for upscaling, namely, using larger than usual TE elements (up to 24 mm in diameter) made from affordable p-tetrahedrite and n-magnesium silicide materials, was assessed with a multiphysics tool for conditions typical of IWHR. Geometric configurations optimized for efficiency, power per pair and power density, as well as an efficiency/power balanced solution, were extracted from these simulations. A balanced solution provided 0.62 kWe/m2 with a 3.9% efficiency. Good prospects for large-scale IWHR with TEGs are anticipated if these figures could be replicated in a real-world application and implemented with constructive solutions suitable for large-scale systems.