Search Results (10)

Ferrospheres (FSs) are a microspherical component of fly ash from pulverized coal combustion. The wide variations in chemical and phase composition, morphology, and the spherical design of FSs suggest their use as functional materials capable of replacing expensive synthesized materials. A general understanding of the formation of FSs from thermochemical transformations of the mineral components of the original coal is important for identifying the most promising sources of FSs with a high content of a certain morphological type active in a specific process. A systematic SEM-EDS study of the composition–structure relationship of the skeletal-dendritic FSs isolated from fly ash has revealed common routes of their formation. These FSs are formed as a result of thermochemical transformations of iron-containing minerals with the participation of aluminosilicates of the original coals. The aluminosilicate precursor that determines the skeletal-dendritic structure is illite. The crystallization of skeletal-dendritic globules occurs due to the “seed” of Al, Mg-ferrospinel formed from the thermochemical transformation of illite. The general trend of change in the structure of globules from a coarse skeletal to a fine dendritic structure is associated with a decrease in the main spinel-forming oxides content and an increase in the silicate melt viscosity. Full article

This study investigates the potential of utilizing industrial by-products—mill scale (MS) and aluminum dross (AD)—as sources of Fe₂O₃ and Al₂O₃, respectively, for hercynite (FeAl₂O₄) production. Through combustion of MS-AD-graphite systems at 1550 °C under air atmosphere, hercynite-based refractory materials were synthesized. Results confirm the viability of this upcycling approach for hercynite synthesis. During the formation of hercynite, the development of a dendritic structure can be observed, which subsequently fuses into a grain shape. XRD phase analysis using the Rietveld method revealed that the major components of the product with a C/O ratio of 1 were 85.11% FeAl₂O₄, 10.99% Al₂O₃, and 3.9% C. For the product with a C/O ratio of 2, the composition was 82.4% FeAl₂O₄, 13.0% Al₂O₃, and 4.6% C. The combustion of raw pellets with a C/O ratio of 1 at 1550 °C for 1 h in a normal air atmosphere is economically viable for producing hercynite, yielding 85.11 wt%. This approach presents a sustainable and eco-friendly alternative to using commercial raw materials, potentially eliminating the need for virgin alumina and iron ore. By repurposing waste materials from the steel and aluminum industries, this study contributes to the circular economy and aligns with the goal of zero waste. Full article

Since solid electrolytes have a broad electrochemical stability window, are exceptionally electrochemically stable against Li metal, and function as a physical separator to prevent dendrite growth, they are at the forefront of alternate possibilities, further increasing the stability and energy density of Li-ion batteries. NASICON-type electrolytes are a promising candidate due to their negligible moisture sensitivity, which results in outstanding stability and a lower probability of Li₂CO₃ passivity under the ambient atmosphere. However, one of the most promising representatives, Li_1+xY_xZr_2−x(PO₄)₃ (LYZP), has multiple stable phases with significant variation in their corresponding Li-ion conductivity. In this paper, we have successfully synthesized the highly ionically conductive rhombohedral phase of LYZP via spray-flame synthesis. Two different solvent mixtures (e.g., 2-ethyl hexanoic acid/ethanol, propanol/propanoic acid) were chosen to explore the effect of precursor composition and combustion enthalpy on the phase composition of the nanoparticle. The as-synthesized nanoparticles from spray-flame synthesis consisted of the crystalline tetragonal zirconia (t-ZrO₂) phase, while lithium, yttrium, and phosphate were present on the nanoparticles’ surface as amorphous phases. However, a short annealing step (1 h) was sufficient to obtain the NASICON phase. Moreover, we have shown the gradual phase conversion from orthorhombic β phase to rhombohedral α phase as the annealing temperature increased from 700 °C to 1300 °C (complete removal of β phase). In this context, Y³⁺ doping was also crucial, along with the appropriate solvent mixture and annealing temperature, for obtaining the much-desired rhombohedral α phase. Further, 0.2 at% Y³+ doping was added to the solvent mixture of 2-ethyl hexanoic acid/ethanol, and annealing at 1300 °C for 1 h resulted in a high ionic conductivity of 1.14∙10⁻⁵ S cm⁻¹. Full article

Cu–Cr–Zr alloys reinforced in situ with TiC_x nanoparticles were prepared via combustion synthesis and electromagnetic stirring casting. The microstructure of TiC_x/Cu-Cr-Zr composites with various contents was analyzed. The microhardness and Brinell hardness of the composites were determined; the average volumetric abrasive wear rate and worn surface of the composites were investigated; and the electrical, thermal conductivity and thermal expansion coefficients of the materials were discussed. The results indicated that the addition of TiC_x particles transformed the Cu–Cr–Zr matrix alloy microstructure from a dendritic to an equiaxed crystal, and the grain size was significantly refined as the amount added was increased. The composites with high TiCx content possessed higher hardness and abrasive wear resistance. The addition of TiC_x particles reduced the electrical and thermal conductivity and thermal expansion coefficients of the materials. Full article

The Hastelloy X superalloy is a widely used solid-solution Ni-based sheet alloy for gas turbines, aero-engine combustion chambers, and other hot-end components. To investigate the effect of microstructure, especially grain size, on its weldability, Hastelloy X alloy bars are homogenized, cold-rolled to thin sheets, and recrystallized under different conditions to obtain equiaxed grain microstructures with average grain sizes of ~5 μm, ~12 μm, and ~90 μm. The laser welding process is used for joining the alloy sheets, and then the alloy’s weldability is investigated through microstructural and mechanical property characterizations. The microstructures in weld consist of coarse columnar grains with dendrite, and grain sizes of these columnar grains are almost the same when grain size of Hastelloy X base metal increases from ~5 μm to ~90 μm. Moreover, although all welds exhibit lower yield strengths (YS), ultimate tensile strengths (UTS), and elongations to fracture (EF) than the base metal, the degrees of reduction in them become slight when the grain size of base metal increases from ~5 μm to ~90 μm. Full article

This paper focuses on a study of fine (less than 2.5 µm) airborne particles collected inside seven primary schools located on a coastal Mediterranean area which has a significant industrial hub for the processing of clays and other minerals as raw materials. Of the seven schools, three are located in an urban area 20 km away from the main industrial hub, three are in a town located next to the industrial estate, and one is in a rural location, 30 km from the industrial area. The objective of this study is to identify the main types of particles found in the three examined environments. The particle matter identified in the fine particle samples is grouped into three main groups: mineral compounds, particles from combustion processes and phases emitted in high-temperature industrial processes. The mineral particles, which can come from natural or anthropogenic emissions, have been classified depending on their morphology as isometric allotriomorphs or subidiomorphs, with a tabular habit; acicular forms; or pure crystalline forms. Compounds from combustion processes have two types of morphologies: spheroid and dendritic soot particles. Additionally, in smaller quantities, spherical particles associated with high-temperature industrial processes, such as the emissions of ceramic tile-firing and frit-melting processes, are identified. A summary table is shown, which lists the characteristics, as well as the most significant origin of the main particles identified in the fine (<2.5 μm) airborne particles collected inside primary schools located in three different environments (urban, industrial and rural). A visual scale has been established based on the number of particles observed in the samples of the atmospheric particulate fraction between the sizes of 2.5 and 10 µm collected inside the schools. The ratios Ca/Si, S/Si, S/Ca and (Si+Ca)/S have been established. Results obtained may be useful in epidemiological studies in the ceramic cluster area in order to estimate children’s exposure to different indoor primary school microenvironments. Effective policies and mitigation measurements for the protection of children’s health should be carried out in this highly industrialized area. Full article

The purpose of this paper is to assess the content and distribution of some elements in coal from two bituminous coal basins and in fly ash and slag derived from combustion of the coals in six power plants in Poland. The petrographic composition and distribution of elements were characterized in the tested samples, using reflected light microscope, X-ray powder diffractometer, inductively coupled plasma atomic emission spectroscopy, and scanning electron microscope with energy dispersive X-ray. The highest content of elements in coal occurs in siderite. In Al-Si particles, as well as in magnetite with skeletal and dendritic structure crystallized on the surface of Al-Si microspheres or cenospheres included in fly ash size < 0.05 mm and in the magnetic fraction of slag, the highest content of elements was noted. Due to the content of elements, fly ash and slag were considered to be neutral for the soil environment. Correlations, which have not been described before, have been observed between the likely mode of binding of some elements in coal and their distribution in fly ash and slag. These correlations could be of particular value when predicting the content and distribution of elements in combustion residues and in the assessment of their environmental toxicity. Full article

The morphology and surface characteristics of SCS (Solution Combustion Synthesis)-derived Ni–NiO nanocatalysts were studied. The ΤΕΜ results highlighted that the nanomaterial’s microstructure was modified by changing the reactants’ concentrations. The dendrites’ growth conditions were the main factors responsible for the observed changes in the nanomaterials’ crystallite size. Infrared camera measurements demonstrated a new type of combustion through dendrites. The XPS analysis revealed that the NiO structure resulted in the bridging of the oxygen structure that acted as an inhibitor of hydrogen adsorption on the catalytic surface and, consequently, the activity reduction. The RF-IGC indicated three different kinds of active sites with different energies of adsorption on the fresh catalyst and only one type on the aged catalyst. Aging of the nanomaterial was associated with changes in the microstructure of its surface by a gradual change in the chemical composition of the active centers. Full article

This study was carried out using a scanning electron microscope (SEM) analysis of airborne fine particles and indoor samples, obtained in the interiors of seven primary schools located along the Mediterranean coast in an area with an important industrial nucleus. The objectives of this study are to create a catalogue that gathers the principle particles found in the three environments examined and to assess the influence of outside sources of particulate matter on particles found indoors. The particles identified in the fine particle samples have been grouped into two main groups: mineral compounds and particles originating from combustion processes. The mineral particles emanating from natural emissions and anthropogenics were classified according to their morphology into: isometric alotriomorphs or subidiomorphs, with tabular, acicular, and pure crystalline forms. The compounds originating from combustion processes present two types of morphology: spheric-like particles and dendritic soot ones. On the other hand, in lesser proportion, spherical particles were also identified as being associated with industrial processes at high temperatures. To conclude a summary table is presented, that gathers the characteristics (morphology, type and size) along with the origins of the principle particles identified in the interior airborne fine particle samples obtained from primary schools located in three different environments. Full article

Nanostructured nickel-based catalysts were produced by solution combustion synthesis and it was found that their properties and structure depended on the pretreatment of the precursor solution. X-ray diffraction, N₂ adsorption, and an infrared high-speed camera were used to follow the various synthesis steps and to characterize the obtained catalysts, while their catalytic activity was determined in the hydrogenation of maleic acid. It was determined that the amount of water used and the heating of the precursor solution under mild stirring up to 70 °C influenced the nickel nitrate–glycine–water complexes that were formed in the precursor solution in the form of dendrites. These play a key role in the solution combustion synthesis (SCS) reaction mechanism and in particular in the formation of nickel-based catalysts. Understanding the interrelationships between the processing parameters and the ensuing powder properties allowed an efficient optimization of the catalytic performance. Full article