Functional Bi2O3/Gd2O3 Silica-Coated Structures for Improvement of Early Age and Radiation Shielding Performance of Cement Pastes

Data Availability Statement: The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.Copyright © 2024 by the authors. This study presents a new approach towards the production of sol-gel silica-coated Bi2O3/Gd2O3 cement additives towards the improvement of early mechanical performance and radiation attenuation. Two types of silica coatings, which varied in synthesis method and morphology, were used to coat Bi2O3/Gd2O3 structures and evaluated as a cement filler in Portland cement pastes. Isothermal calorimetry studies and early strength evaluations confirmed that both proposed coating types can overcome retarded cement hydration process, attributed to Bi2O3 presence, resulting in improved one day compressive strength by 300% and 251% (depending on coating method) when compared to paste containing pristine Bi2O3 and Gd2O3 particles. Moreover, depending on the type of chosen coating type, various rheological performances of cement pastes can be achieved. Thanks to the proposed combination of materials, both gamma-rays and slow neutron attenuation in cement pastes can be simultaneously improved. The introduction of silica coating resulted in an increment of the gamma-ray and neutron shielding thanks to the increased probability of radiation interaction. Along with the positive early age effects of the synthesized structures, the 28 day mechanical performance of cement pastes was not suppressed, and was found to be comparable to that of the control specimen. As an outcome, silica-coated structures can be successfully used in radiation-shielding cement-based composites, e.g. with demanding early age performances.National Science Centre of Poland within Project no. 2020/39/D/ST8/00975 (SONATA-16)

Recycled brick aggregates in one-part alkali-activated materials: Impact on 3D printing performance and material properties

Data availability: Data will be made available on request.This study investigates the printability of one-part brick powder-based alkali-activated materials (AAMs) containing end-of-life brick particles as aggregate. The novel formulation showcases promise for 3D printing of small to medium-sized building blocks, reminiscent of a Lego-type system, capitalising on the rapid setting time inherent to one-part AAMs. The effect of replacing up to 50% by weight of natural aggregate with brick aggregate on the fresh properties of brick powder-based alkali-activated materials, including slump measurements, flowability, setting time, open time and green strength were investigated. In addition, the flexural and compressive strength of the 3D printed mixtures were determined and compared to those of cast specimens. The buildability and microstructure were also examined. The results showed that incorporating high porous and rough brick aggregate to replace natural aggregate is beneficial in improving the mixtures’ slump, which is essential for retaining the shape of the printed layers. However, it decreased the flowability, setting time and open time when incorporating up to 50% brick aggregate. The green, flexural and compressive strengths were increased with increasing brick aggregate content up to 50% due to enhancing interlock between the binder and brick aggregate, and the better compaction because of the absorption properties of brick aggregate. The mechanical results revealed the better performance of 3D printed specimens than the cast specimens. Moreover, the incorporation of brick aggregate enhanced the buildability of the mixtures showcasing their potential in advancing 3D printing capabilities.This work was funded as part of the DigiMat project, which has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement ID: 101029471. This research was funded in part by the National Center for Research and Development (NCBR), Poland within Project no. ERA-MIN3/140/Recycl3D/2022 (ERA-NET Cofund ERA-MIN3 (Joint Call 2021)). The funding provided by FCT - the Portuguese Foundation for Science and Technology, is acknowledged: references UIDB/04625/2020 (CERIS research centre) and ERA-MIN3/0001/2021 (ERA-NET Cofund ERA-MIN3)

The preparation and EPR study of nanocrystalline ZnFe2O4

Nanocrystalline zinc oxide doped with different concentrations of Fe2O3 (from 5 to 50 wt.%) has been prepared by means of coprecipitation and calcination processes. Depending on the chemical composition, phases of hexagonal ZnO, and/or cubic ZnFe2O4 were identified. The mean crystallite size of the latter phase, determined using the Scherrer’s formula, varied from 8 to 12 nm. The EPR spectra for six different concentrations of Fe2O3 were recorded. A symmetrical, very intense and broad EPR resonance line has been obtained for the all the samples where the intensity strongly depended on the ratio of ZnO/Fe2O3 in the samples. The resonance field slightly shifted in the direction of lower magnetic field and the integrated intensities increased with increasing concentration of magnetic nanoparticles of ZnFe2O4, where the linewidth showed an extraordinary behaviour. The dipole-dipole interaction depended essentially on the concentration of magnetic nanoparticles

Effect of synthesis parameters of graphene/Fe₂O₃ nanocomposites on their structural and electrical conductivity properties

Due to its fascinating properties such as high surface area, very good electrical and thermal conductivity, excellent mechanical properties, optical and electrochemical properties, graphene may be the ideal material as a substrate of nanocomposites for applications in electronics. Graphene layer can be used as a conductive matrix allowing good contact between crystallites of nanomaterials. Despite pure graphene, its composites with other species can be of interest. In this paper the results of studies on the effect of methods and parameters of synthesis, for obtaining composites graphene/Fe₂O₃ on their structural properties and electrical properties are presented. A series of experiments was conducted using a commercially available graphene (Graphene Nanopowder AO-3) and iron nitrate. The materials were obtained using two pressure methods: pressure synthesis in the autoclave and synthesis in the microwave solvothermal reactor. The syntheses were carried out in a solution of ethanol. The specific surface area, helium density, morphology, phase composition, thermal properties and electric conductivity of the obtained composites were investigated

Magnetic resonance study of nanocrystalline 0.10MnO/0.90ZnO

Magnetic properties of nanosize ZnO powders doped with MnO magnetic dopand have been studied. Sample designated as 0. 10MnO/0. 90ZnO was characterized by XRD that revealed the presence of ZnO and ZnMnO3 phases. An average size of magnetic ZnMnO3 nanocrystallites was 9 nm. Magnetic resonance study has been carried out in the 4-290 K temperature range. The spectrum at each temperature was analyzed in terms of three components. The temperature dependences of resonance field, linewidth and integrated intensity of these components have been determined. Magnetic centers responsible for producing the observed spectra have been proposed. © 2013 Versita Warsaw and Springer-Verlag Wien

FMR and magnetization study of ZnFe2O4 nanoparticles in 0.40Fe2O3/0.60ZnO nanocomposite

Zinc oxide (ZnO) nanocrystals containing Fe2O3 have been synthesized by the calcination method. Ferromagnetic resonance (FMR) and dc magnetization measurements of 0.40(Fe2O3)/0.60(ZnO) nanocomposite have been carried out in the 4-300 K range to study the magnetic properties of agglomerated magnetic zinc ferrite ZnFe2O4 (ZFO) nanoparticles with an average crystallite size of 12 nm. Temperature dependence of the resonance field, linewidth, and the integrated intensity calculated from FMR spectra have been determined to obtain the value of the uniaxial anisotropy field and to establish the ranges of different relaxation types. Magnetization measurements in ZFC and FC modes as well as the study of hysteresis loops allowed calculating different magnetic characteristics-blocking/freezing temperature, magnetic moment, anisotropy constant, and anisotropy field. The observed magnetic properties of 0.40(Fe2O3)/0.60(ZnO) nanocomposite were explained based on the core-shell model of ZFO nanoparticles. From comparison of FMR and dc magnetization measurements, the temperature ranges of magnetic phases existing in ZFO nanoparticles in 0.40Fe2O3/0.60ZnO nanocomposite are proposed. © 2014 IEEE

Nanocomposites graphene/CoFe2O4 and graphene/NiFe2O4 – preparation and characterization

A series of nanocomposite graphene/CoFe2 O4 and graphene/NiFe2 O4 hybrid materials was synthesized via facile, one-pot solvothermal route. The materials were obtained using two pressure methods: synthesis in the autoclave and synthesis in the microwave solvothermal reactor. The use of a microwave reactor enabled to significantly shorten the synthesis time up to 15 min. All the syntheses were carried out in a solution of ethanol. The effect of processing conditions and composite composition on the physicochemical properties and electric conductivity was studied. The specific surface area, density, morphology, phase composition, thermal properties and electric conductivity of the obtained composites were investigated. The results of studies of composites obtained in an autoclave and in a microwave reactor were compared

Carbon Spheres as CO2 Sorbents

Microporous nanocarbon spheres were prepared by using a microwave assisted solvothermal method. To improve the carbon dioxide adsorption properties, potassium oxalate monohydrate and ethylene diamine (EDA) were employed, and the influence of carbonization temperature on adsorption properties was investigated. For nanocarbon spheres containing not only activator, but also EDA, an increase in the carbonization temperature from 600 °C to 800 °C resulted in an increase of the specific surface area of nearly 300% (from 439 to 1614 m2/g) and an increase of the CO2 adsorption at 0 °C and 1 bar (from 3.51 to 6.21 mmol/g)

Synthesis and Characterization of ZnO Doped with Fe2O3Fe_{2}O_{3} - Hydrothermal Synthesis and Calcination Process

The aim of the present work is to compare two methods of synthesis of nanocrystallline zinc oxide doped with iron oxide. The synthesis was carried out using microwave asssisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The phase composition of the samples was determined using X-ray diffraction measurements. Depending on the chemical composition of the samples, hexagonal ZnO, and/or cubic $ZnFe_{2}O_{4}$ were identified. The morphology of the received materials was characterized using scanning electron microscopy. Two different structures of agglomerates were observed: a hexagonal structure (corresponding to zinc oxide) and spherical (corresponding to spinel phase). The effect of the iron oxide concentration on specific surface area and density of the samples was determined

Magnetic Resonance Study of MnO/ZnO Nanopowders

Fine particles n(MnO)/-(1-n)ZnO (n = 0.05 to 0.95) were prepared by wet chemistry method. According to X-ray diffraction analysis the obtained samples with n = 0.95, 0.90, 0.80, 0.70, 0.60 contained $Mn_3O_4$ and $ZnMn_2O_4$ phases, while samples with n = 0.05, 0.10, 0.20, 0.30, 0.40 and 0.50 contained $ZnMnO_3$ and ZnO phases. The mean crystalline size of $ZnMnO_3$ varied from 8 to 13 nm. The magnetic resonance investigations have been carried out at room temperature. Slightly asymmetric, broad and intense magnetic resonance line is recorded for all samples. The magnetic resonance spectra parameters showed marked differences depending on the composition index n. This could be explained by the variation of the magnetic susceptibility and a much slower evolution of spin relaxation, associated with the interaction of crystal field and superexchange interactions. Taking into account the values of magnetic resonance parameters, the investigated samples could be divided into two groups: these with the composition index n0.50. A detailed discussion of the magnetic properties of different phases in the n(MnO)/-(1-n)ZnO system is presented