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Abstract: The study reports the successful deposition of 15–5 precipitation-hardened (PH) martensitic steel on SAF 2507 duplex stainless steel (and vice versa) to form functionally graded materials (FGMs) using powder-based, directed-energy-deposition (DED) technology. The evolution of the microstructure and the mechanical properties of the 15–5 PH/SAF 2507 functionally graded material in the as-built state were investigated systematically. The results proved that the microstructural transition zone (MTZ) is formed above the fusion line due to the dilution effect of both steels. The phase composition of the MTZ consists of ferrite and, in comparison to the base materials, an increased amount of austenite. The interface has the lowest hardness owing to the formation of a significant proportion of the austenitic phase. However, the tensile mechanical properties were not affected by the interface as failure occurred in both SAF 2507 and at the interface regions. The research presents a promising application of FGMs in a horizontal configuration to form a high - quality, metallurgical joint between heterogeneous materials. This study introduces a novel approach by additive manufacturing (AM) of heterogeneous multi-materials, merging the favorable properties of duplex SAF 2507 and martensitic 15-5 PH stainless steels through superior metallurgical bonding. The combination of SAF 2507 and 15-5 PH in a functionally graded material has not been previously explored, as the existing studies deal with the duplex stainless steels SAF 2507 and either martensitic stainless-steel 15-5 PH deposited separately by laser powder-bed-fusion (L-PBF) or DED methods. This research pioneers the investigation of these materials in tandem, paving the way for the development of novel FGMs with optimized properties for specific applications. The resulting FGM exhibits exceptional corrosion resistance and high strength, making it highly versatile for applications in diverse industries such as offshore oil and gas production, aerospace, aviation, and chemical processing equipment.
Keywords: directed energy deposition, functionally graded materials, miniaturized specimen testing methods, SAF 2507, 15-5 PH
Published in DiRROS: 04.04.2024; Views: 60; Downloads: 27
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Abstract: Alkali activated materials (AAM) are, in their broadest classification, any binder systems derived by the reaction of an alkali metal source (silicates, alkali hydroxides, carbonates , sulphates) with a solid, amorphous alumosilicate powder (found in precursors such as slag, fly ash and bottom ash). A wide variety of products can be obtained by the alkali activation process and could replace traditional construction products. Among the se, alkali activated foams (AAF) represent one of the most promising materials, owing to their economically accessible alumosilicate rich source materials, including industrial waste materials, clean processing, higher added value and most importantly, pro ducts with competitive properties. In the present study, the properties of alkali activated fly ash - based foam materials were studied at room temperature as well as at elevated temperatures (up to 1200 °C ) in order to develop a durable material in terms o f mechanical properties and suitability for high temperature applications.
Keywords: lightweight porous insulating material, alkali activated materials, microstructural analysis
Published in DiRROS: 05.03.2024; Views: 103; Downloads: 42
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Abstract: Alkali activation is a chemical process whereby materials rich in aluminosilicate, which dissolves in basic media at room temperature, form binding phases by polycondensation. The alkali- activated materials (AAM) are a promising alternative to binding materials such as cement or other products in civil engineering (van Deventer et al., 2012). This study investigates the early age shrinkage behavior of Slovenian ladle and electric arc furnace slag - based alkali activated materials at different curing temperatures. The dimensions of specimens cured at room temperature and elevated temperatures up to 90 °C were measured over the first 7 hours (every 10 min). The results show that the most shrinkage occurred at the highest temperature, owing to the highest rate of evaporation of liquid content. Loss of mass follows from the drying shrinkage.
Keywords: alkali activated materials, shrinkage, compressive strength
Published in DiRROS: 01.03.2024; Views: 113; Downloads: 75
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Abstract: The main objective of this manuscript is to collect, classify, and compile all available data about secondary mineral sources of REEs in the South-Eastern Europe (SEE). The material is generated from the extracting and processing sector, that might be possibly transformed in the business process becoming an important raw material for another industry. The management inventory guide will strengthen communication and dissemination efforts and simultaneously contribute to Europe’s self-sufficiency and support transitioning to green and digital technology. Identification of the knowledge gaps associated with secondary sources of REEs in SEE will contribute to connections between all partners being involved at the beginning, during the lifetime of products and at the end of the life cycle, represented with deposit owners, technology developers and potential processors, producers, and potential users. At the investigated area it was found 1835 individual landfills, most of them belonging to waste rocks. The total quantity of all material in SRM is about 3.2 billion tons on an area of about 100 km2. The largest 95 individual landfills were selected as potential prospective landfills, containing about 1600 million tons of material. The estimated total potential of REEs (ΣREE) is more than 200 Kt. The largest quantities are found in landfills for coal fly ash and Cu flotation, which correspond to more than 80% of the ΣREE. Most of the promising sites are located in Serbia and North Macedonia. It has been calculated that the valorisation potential and perspectivity of REE2O3 is about 32.5 billion USD (prices from December 2022). According to the average concentrations of REEs, the most prospective are the red mud dams but their total volume is limited compared to massive amounts of coal fly ash landfills. The REEs content in all type of investigated materials, especially in coal fly ash in North Macedonia is twice as high as in other countries.
Keywords: secondary raw materials, ESEE, rare elements, economic prospective
Published in DiRROS: 06.02.2024; Views: 146; Downloads: 39
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Abstract: Alkali-activated binders are an environmentally friendly alternative to Portland cement, particularly when locally-available raw materials are used. It is well known that alkali activation with a sodium silicate activator generates a hardened binder with higher compressive strength than a binder hardened with sodium hydroxide. As the alkali-silicate activators are produced through energy extensive processes, and their use can significantly increase the carbon footprint of the final products, it is of great significance to develop alternative alkaline activators based on locally-available waste materials. This article assesses the potential to apply waste bottle glass and waste cathode-ray tube (CRT) glass to synthesise alternative alkali activators by the hydrothermal method. Inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to determine silicon and aluminium content in the alternative activators. The influence of dissolution process parameters (time, temperature, particle size) on the concentrations of silicon and aluminium in the alternative activators was investigated. The alternative activators with silicon concentration up to 19 g/L and aluminium concentration up to 0.9 g/L were prepared at T = 120 °C and boiling time 24 h. The alternative alkali activators and, for comparison, also commercial sodium silicate were used in the alkali activation of fly ash powder. The formed pastes were cured at 70 °C for 72 h. Mechanical strength measurements indicated that alkali activation of fly ash with the optimal alternative activator yielded hardened paste with compressive strength of 33 MPa. However, the compressive strength of hardened paste prepared from fly ash and commercial sodium silicate reached 70 MPa. Part of this difference can be ascribed to the lower density of hardened pastes prepared with alternative activators.
Keywords: alkali -activated materials, alternative alkali activators, waste bottle glass, waste cathode -ray tube glass, fly ash, hydrothermal method
Published in DiRROS: 25.01.2024; Views: 154; Downloads: 104
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