Corrosion of Ceramic-Metal Composites in Artificial Acid Rain

In this work, the basalt deposits site from southern Serbia was used as a matrix for the composite materials. The corrosion behavior of basalt matrix composites with various ratios of commercial stainless steel 316L (5, 10, 15, and 20 wt.%) and bulk basalt produced by sintering in the air (t=1060ºC and τ=60 min) were studied by immersion corrosion technique. The samples were immersed in a solution of artificial acid rain H2SO4:HNO3 = 9:1 at ≈ pH 3 to measure the concentration of released metal ions using inductively coupled plasma-optical emission spectrometry (ICP-OES). The elements Fe, Cr, Mn, and Ni were monitored, while the others were below the limit of quantification. The concentrations of the metal ions in the solution were studied over 15 weeks. The ions release rate from all the sintered samples was found to follow the Weibull cumulative distribution function (CDF). This means that the release rate changes over time and allows us to calculate the characteristic times of ion release. The changes in the samples were monitored by light microscopy (LM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and weight loss. Sintered basalt shows high resistance to corrosion with a characteristic time of about 18 years for Fe and more than 25 years for Cr and Mn. The weight difference between the initial and after 15 weeks of exposure to the solution (sintered basalt) was not observed. On the other hand, the presence of 5 wt.% steel powder in the sintered basalt accelerates the release of metal ions by about six times. When the steel powder content in the composite materials increases, the metal release rate does not change further, but a weight loss is observed. The characteristic times for Fe, Cr, Ni, and Mn in composite materials are about 5 years. These composite materials can be investigated as materials for using in an acid environment.5th Metallurgical & Materials Engineering Congress of South-East Europe (MME SEE 2023) : book of abstracts; June 7-10, Trebinje, Bosnia and Herzegovin

Hydrogen Adsorption Process In Nanocrystalline Nuclear Graphite

Kinetics and mechanism of hydrogen adsorption in as-obtained and ground nuclear graphite Wendelstein 7-X are examined. In the first time interval the adsorption process is determined by dissociation of the hydrogen molecule, occurring at the outer surface and in open micropores of nuclear graphite particles. However, in the second time interval, the slowest step in the hydrogen adsorption is inter-granular and inter-crystallite diffusion in nanopores of graphite. The X-ray analysis shows, that grinding of as-obtained nuclear graphite results in finer particles with finer nanocrystals and larger density of opened pores and carbon reactive sites. The capacity and rate of adsorption increase with comminution of nuclear graphite particles and adsorbed hydrogen does not sub stantially alter the microstructure of nuclear graphite

Synthesis and characterization of high-entropy A2B2O7 pyrochlore with multiple elements at A and B sites

Single nano high-entropy pyrochlore-type compound (A2B2O7) with 7 different rare-earth cations at site A and 3 different metal cations at site B with equiatomic amounts (7A1/7)2(3B1/3)2O7 is successfully obtained. The powder with nominal composition (La1/7Sm1/7Nd1/7Pr1/7Y1/7Gd1/7Yb1/7)2(Sn1/3Hf1/3Zr1/3)2O7 was fabricated by reacting metal nitrates (site A) and metal chlorides (site B) with glycine during the combustion reaction. The XRD analysis revealed that the powder attained during synthesis is in an amorphous state. To induce crystallization of the obtained pyrochlore structure, the post-calcination process at 600-1500 °C was conducted and studied. Results of this study showed that the monophase pyrochlore (A2B2O7) structure is obtained during the calcination at 900 °C. The high-density ceramic pellet with 97% of theoretical density and free of any additives was obtained through pressureless sintering at 1650 °C for 4 h in the air using the powder calcined at 900 °C

Basalt-based glass-ceramic composites

Two series of glass-ceramic composites (basalt/mine tailings, basalt/basalt fibers) as well as one pure glass-ceramic were prepared from basalt rocks located in the SE part of Serbia (Lukovska Banja). Both composites contained 85, 90 and 95 wt.% basalt glass respectively. The basalt glass was obtained from initial melting of basalt at 1300 °C. In the present study, the crystallization process of basalt glass contained in the glass-ceramic composite, achieved by thermal treatment, was observed, and analyzed. The thermal treatment was done at 900 °C, 950 °C, 1000 °C and 1050 °C respectively, with the retention times of 1, 3, 6, 8 and 16 hours. It was found that the addition of mine tailings and basalt fibers caused a change in the density and microstructure. The study also showed that the best mechanical and structural characteristics of the examined glassceramics were attained at the temperature of 1050 °C, with the retention time of 1 hour. Additionally, structural and optical characteristics of the glass-ceramics were assessed

Synthesis and characterization of reinforced alumina composites

Alumina composite was prepared via simple route. Alumina ceramics that resembels seashells are made of aligned micron-sized monocrystalline platelets joined together by silica secondary phase. SiO2 was added to improve mechanical properties of composite. The evolution of the phase composition during thermal treatment was investigated by X-ray powder diffraction (XRPD) and thermal analyses. Effect of sintering temperature on mechanical properties, due to the increase of sintering temperature that can produce a higher strength and higher density, was also investigated. SEM observation of composite was also included. Ceramics composites such as this are good candidates for high temperature oxidation atmosphere applications, as they have excellent mechanical and other performance requirements.VII Conference of The Serbian Society for Ceramic Materials, 7CSCS-2023, June 14-16, 2023, Belgrade, Serbi

High-entropy stabilized Zr0.2Hf0.2Ce0.2Yb0.2Gd0.2O2-δ with fluorite structure

Program and book of abstracts / 2nd International Conference on Innovative Materials in Extreme Conditions i. e. (IMEC2024), 20-22 March 2024 Belgrade, Serbia

Entropy-stabilized oxides owning fluorite structure: preparation and sintering

Entropy-Stabilized Oxides are advanced ceramic materials that possess highly desirable functional properties. Through a five-component oxide formulation, these materials utilize configurational entropy to achieve phase stabilization. In this study we have successfully synthesized a novel type of high-entropy fluorite oxide, specifically Zr0.2Hf0.2Ce0.2Yb0.2Gd0.2O2-δ, through the Self Propagation Room Temperature reaction (SPRT) method. Through heat treatment experiments, it was observed that the phase composition of all samples remained a single phase after high-temperature heating. Furthermore, a thermal treatment at 1500°C resulted in a fully crystallised single-phase fluorite structure. The powders also demonstrated a lack of agglomeration, which allowed for the sintered specimen to exhibit sufficient densification with a small porosity that was uniformly distributed throughout the samples.VII Conference of The Serbian Society for Ceramic Materials, 7CSCS-2023, June 14-16, 2023, Belgrade, Serbi

Basaltic Glass-Ceramic Composites: Exploring Structural, Morphological, and Thermal Insights for Ballistic Protection and Radiation Shielding Applications

Program and book of abstracts / 2nd International Conference on Innovative Materials in Extreme Conditions i. e. (IMEC2024), 20-22 March 2024 Belgrade, Serbia

Heavily doped high-entropy A2B2O7 pyrochlore

A novel class of high-entropy pyrochlore compounds with multiple elements at the A and B site positions (A2B2O7) was successfully obtained. Powders with (La1/7Sm1/7Nd1/7Pr1/7Y1/7Gd1/7Yb1/7)2(Sn1/3Hf1/3Zr1/3)2O7 nominal composition were fabricated from pure metal oxides obtained through a reaction of metal nitrates (for site A) and metal chlorides (for site B) with sodium hydroxide during the solid-state displacement reaction (SSDR). The phase evolution was analyzed using XRD method. During the thermal treatment of ten individual metal oxides, the single pyrochlore phase was created. The present study showed that the highdensity (98%TD) ceramics with a hardness of 8.1GPa was successfully obtained after pressureless sintering at 1650 °C for 4 h. Results of the Raman study and the Rietveld structural refinement showed that sintered highentropy ceramics is characterized by a single-phase pyrochlore structure, which was investigated in detail

Tectonic evolution of the Vršac Mts. (NE Serbia): Inferences from field kinematic and microstructural investigations

The Vršac Mts. in NE Serbia represent the key area to investigate structural relations between the Northern Serbo-Macedonian Subunit and Supragetic Unit of the Dacia Mega-Unit. The geodynamic events during the Variscan orogeny in the Late Paleozoic colligated the two units and led to their metamorphic differentiation. The Late Cretaceous extension exhumed the medium-grade Serbo-Macedonian metamorphic rocks and structurally juxtaposed them against the low-grade metamorphosed basement of the Supragetic Unit along an E-dipping shear zone, which outcrops in the crystalline basement of the Vršac Mts. The subsequent Oligocene–Miocene extension, which led to the formation of the Pannonian Basin, overprinted the effects of earlier tectonic phases to a large extent. Hence, large segments of the Northern Serbo-Macedonian Subunit and the Supragetic Unit, including their contact, were buried beneath the Neogene deposits of the southern part of Pannonian Basin. The tectonic uplift of the Vršac Mts. occurred in middle to late Miocene times along the SW-dipping normal faults that controlled deposition in the adjacent Zagajica Depression. The Miocene extension, triggered by the retreat of Carpathian slab, exhumed the crystalline basement of the mountains, and exposed the Late Cretaceous Serbo-Macedonian/Supragetic extensional contact