19 research outputs found
Synthesis of High-Performance CSA Cements as Low Carbon OPC Alternative
No full textStarting from natural raw materials, cements based calcium sulphoaluminate (CSA) clinkers have been successfully obtained as an eco-friendly alternative to ordinary Portland cement. CSA-based cements with ye’elimite as the main phase have been produced over the years and are widely used today. In this regard, the present paper considers the study of hydration processes for CSA pastes prepared with a water/cement ratio of 0.5 according to the EN-197 standard and their characterization by thermal analysis (DTA-TG), X-ray diffraction analysis (XRD), and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX). A mechanical strength of 60.9 MPa was the greatest achieved for mortars hardened for 28 days
JSCS–3779 Original scientific paper Synthesis of lithium ferrites from polymetallic carboxylates
No full textAbstract: Lithium ferrite was prepared by the thermal decomposition of three polynuclear complex compounds containing as ligands the anions of malic, tartaric and gluconic acid: (NH4) 2[Fe2.5Li0.5(C4H4O5) 3(OH) 4(H2O) 2]�4H2O (I), (NH4) 6[Fe2.5Li0.5(C4H4O6) 3(OH) 8]�2H2O (II) and (NH4) 2[Fe2.5Li0.5(C6H11O7) 3(OH) 7] (III). The polynuclear complex precursors were characterized by chemical analysis, IR and UV–Vis spectra, magnetic measurements and thermal analysis. The obtained lithium ferrites were characterized by XRD, scanning electron microscopy, IR spectra and magnetic measurements. The single �-Li0.5Fe2.5O4 phase was obtained by thermal decomposition of the tartarate complex annealed at 700 °C for 1 h. The magnetization value ≈ 50 emu g-1 is lower than that obtained for the bulk lithium ferrite due to the nanostructural character of the ferrite. The particle size was smaller than 100 nm
Synthesis of lithium ferrites from polymetallic carboxylates
No full textLithium ferrite was prepared by the thermal decomposition of three polynuclear complex compounds containing as ligands the anions of malic, tartaric and gluconic acid: (NH4)2[Fe2.5Li0.5(C4H4O5)3(OH)4(H2O)2]×4H2O (I), (NH4)6[Fe2.5Li0.5(C4H4O6)3(OH)8]×2H2O (II) and (NH4)2[Fe2.5Li0.5(C6H11O7)3(OH)7] (III). The polynuclear complex precursors were characterized by chemical analysis, IR and UV–Vis spectra, magnetic measurements and thermal analysis. The obtained lithium ferrites were characterized by XRD, scanning electron microscopy, IR spectra and magnetic measurements. The single α-Li0.5Fe2.5O4 phase was obtained by thermal decomposition of the tartarate complex annealed at 700 °C for 1 h. The magnetization value ≈ 50 emu g-1 is lower than that obtained for the bulk lithium ferrite due to the nanostructural character of the ferrite. The particle size was smaller than 100 nm
Investigation of Physical-Mechanical Properties and Microstructure of Mortars with Perlite and Thermal-Treated Materials
No full textThis study aimed to obtain and characterize a mortar with perlite aggregate and thermal-treated materials that could substitute for Portland cement. First, the thermally treated materials were obtained by calcinating old Portland cement (OC-tt) and concrete demolition waste (CC-tt) at 550 °C, for 3 h. Second, plastic mortars with a perlite: cement volume ratio of 3:1 were prepared and tested for water absorption, mechanical strength, and thermal conductivity. The microstructure was also analyzed. Portland cement (R) was partially substituted with 10%, 30%, and 50% OC-tt. Thermal-treated materials negatively influenced the compressive and flexural strengths at 7 and 28 days. With an increase in the substitution percentage to 50%, the decrease in the compressive strength was 40% for OC-tt and 62.5% for CC-tt. The presence of 10% OC-tt/CC-tt positively influenced the water absorption. The thermal conductivity of the tested mortars was in the range of 0.37–0.48 W/m·K. SEM analysis shows the expanded perlite pores remained unbroken
Nanocomposite Hydrogels Based on Poly(<i>N</i>-vinyl pyrrolidone)
No full textPoly(N-vinyl pyrrolidone) (PNVP) is one of the most studied and recognized polymer for use in the pharmaceutical industry and medicine purposes due to its unique combination of highly essential properties such as nontoxicity, biocompatibility with human tissue, chemical stability, and good solubility in water and other solvents. Most of the PNVP-based hydrogels are characterized by low mechanical properties when handled in a swollen state. For this purpose, several methods have been reported to increase the mechanical properties of these gels by introducing an inorganic clay as a reinforcing agent. The present work deals with the preparation and detailed structural characterization of nanocomposite hydrogels based on amidic N-vinyl pyrrolidone (NVP) monomers with or without N,N-methylenbis(acrylamide) (MBA) as chemical crosslinker and different concentrations of Laponite XLG as reinforcing agent. The hydrogels were synthesized by the radical polymerization of the monomers using 2,2-azobisisobutyronitrile (AIBN) as the initiator. In this study, we evaluated the structure of PNVP-based nanocomposites by using FT-IR, their morphology through SEM–EDX, and the influence of different amounts of Laponite XLG on the final properties, by performing rheological measurements and swelling studies. The Laponite XLG, used as reinforcing agent, significantly contributed to the improvement in the mechanical properties of the nanocomposite hydrogels
Influence of Synthesis Route on Composition and Main Properties of Mullite Ceramics Based on Waste
No full textMullite, 3Al2O3·2SiO2, is a material with excellent thermal and mechanical properties. Two types of waste sand, rich in impurities, were employed as precursors for mullite ceramic synthesis. Two different synthesis routes were used: (i) solid-state reactions involving a sand and bauxite mixture, and (ii) precipitation synthesis, where alumina was deposited on sand particle surfaces; the sintering process was performed at temperatures ranging from 1300 °C to 1400 °C. Mullite was obtained as the main phase when the ceramics were obtained by solid-state reactions opposite to the second method, in which a composite ceramic with a specific microstructure, i.e., sand particles embedded in a matrix formed by alumina crystals, was assessed by electronic microscopy. The main properties, i.e., the apparent density, open porosity, compressive strength and thermal expansion coefficient (CTE) of the obtained materials were influenced by the composition and microstructure as well as the sintering temperature. The ceramics in which mullite was the main phase had slightly lower CTE’s and did not exhibit any phase transition in the 20–900 °C range. The results presented in this article highlight the importance of the synthesis route correlated with the nature of the precursors, the type and amount of impurities and the sintering temperature
Temperature dependence of tunability of Ba(Sn<sub>x</sub>Ti<sub>1−x</sub>)O<sub>3</sub> ceramics
No full textLightweight Gypsum Materials with Potential Use for Thermal Insulations
No full textThis article presents the influence of three additions i.e., hydroxyethyl methyl cellulose (HEMC), sodium bicarbonate and flue gas desulfurization (FGD) gypsum on the porosity of gypsum-based materials. The specific microstructure for a material with good thermal insulation properties i.e., numerous closed pores distributed in the binding matrix, was achieved using HEMC (0.3 wt.%) and sodium bicarbonate (0.5–2 wt.%). The addition of HEMC to the gypsum binder determines, as expected, an increase of the porosity due to its ability to stabilize entrained air. In the case of a sodium bicarbonate addition, the pores are formed in the binding matrix due to the entrapment of the gas (CO2) generated by its reaction. Sodium bicarbonate addition delays the setting of gypsum binder therefore in this study FGD gypsum (waste produced in the desulfurization process of combustion gases generated in power plants) was also added to the mixture to mitigate this negative effect. The decrease of geometrical density (up to 13%, in correlation with the additive nature and dosage) correlated with the increase of the porosity, determines, as expected, the decrease of flexural and compressive strengths (33–75%), but improves the thermal properties i.e., decreases the thermal conductivity (9–18%)
