1,721,048 research outputs found
Tailoring optical properties of (Ce,Pr)O2-δ·(La,Sm,Y)2O3 high entropy oxides by substituting Pr with Gd or Dy for multi-wavelength emission applications
No full textHigh-entropy oxides (HEOs) has generated considerable research interest because of their novel inherent properties and tuneable functionality. In this study, reactive sintering method was used to synthesize HEOs with three different compositions (Ce,RE)O2-δ·(La,Sm,Y)2O3 [RE=Pr], and CeO2-δ·(RE,La,Sm,Y)2O3 [RE=Gd,Dy]. Replacement of Pr cation with Gd or Dy in the synthesized compositions significantly increased the band gap value from 1.8 eV to 3.13 eV and 3.18 eV respectively. The broader band gap improved luminescent properties of bulk ceramic samples. Strong emissions originating from Ce3+, Dy3+and Sm3+ in Dy-containing HEO and from Ce3+, Gd3+ and Sm3+in Gd- containing HEO were observed at multiple wavelengths through entire visible region. Under multi-wavelength excitation, effective regulation of the emission colour was achieved, resulting in enhanced photoluminescence performance. The prepared HEOs, CeO2-δ·(RE,La,Sm,Y)2O3 [RE=Gd,Dy] can be considered as a novel materials for white light application (WLED) with excitation at multiple wavelengths and tuneable emission
Hierarchically porous 3D-printed akermanite scaffolds from silicones and engineered fillers
Full text linkThe present investigation is dedicated to the manufacturing of reticulated three-dimensional akermanite scaffolds, developed by direct reaction between silica, from the oxidation of a commercial silicone resin and oxide fillers, forming pastes for direct ink writing. Crack-free scaffolds, with dense and regular struts, were due to the use of CaCO3 (micro) and MgO nano-particles as reactive fillers. An excellent phase purity was obtained, with the help of the liquid phase provided by anhydrous sodium borate (Na2B4O7), upon firing. The structure of the scaffolds, finally, was successfully modified by using Mg(OH)2 and hydrated sodium borate: besides macro-porosity from direct ink writing, the new scaffolds exhibited homogenous ‘spongy’ struts (owing to water vapor release in the heating step), with no crack. Both types of scaffolds (with dense or porous struts) exhibited remarkable strength-to-density ratios
Fabrication and environmental applications of glass microspheres: A review
Full text linkContinuous technological progress is required to improve production efficiency and environmental quality while maintaining economic competitiveness. A non-negligible contribution to some of these goals can be achieved through the production of glass microspheres for a wide range of applications. The fabrication techniques of glass microspheres including flame synthesis, liquid droplet method, dried gel process and electrical arc process are surveyed. The mechanisms of the recent syntheses of porous and hollow glass microspheres are also reviewed. Glass microspheres are a promising substrate for titania coatings which can be used in water purification and self-cleaning systems. Due to their high mechanical strength and low thermal conductivity, they can also be applied in cementitious and insulating products. Glass microspheres can carry hydrogen gas at pressures of up to 150 MPa. In addition, they can enhance the quality of lead-acid batteries by decreasing the critical volume fraction..
Waste-derived glass as a precursor for inorganic polymers: From foams to photocatalytic destructors for dye removal
Full text linkSynthetic alumino-silicate glasses may yield inorganic polymers, through activation with alkali hydroxide solutions. In this framework, we formulated a glass prepared by the melting of red mud from bauxite refinement, combined with coal combustion fly ash, discarded pharmaceutical glass and a minor addition of sodium carbonate. The activation with 6 M NaOH aqueous solution allowed for the manufacturing of highly porous foams, by gas generation at the early stages of gelation. These foams featured an extensive formation of zeolite at cell walls which, combined with the presence of magnetite formed upon cooling of the melt, favoured the application of the foams as sorbents for dye removal from contaminated water. The powders prepared by crushing the highly porous foams showed an excellent water purification ability documented by efficient removal of methylene blue used as a model contaminant. The specific iron oxide polymorph facilitated both magnetic recovery of dispersed powders and photocatalytic destruction of the dye under UV irradiation
Åkermanite glass microspheres: Preparation and perspectives of sinter-crystallization
Full text linkGlass microspheres with the exact stoichiometry of åkermanite (Ca2MgSi2O7), one of the most promising modern bioceramics, were produced by the flame synthesis method. The distinctive high cooling rate was found to prevent the crystallization; the size of amorphous microbeads could be correlated with the size of partially crystallized precursor powders, deriving from conventional melt quenching and milling. The glass microspheres were characterized in terms of crystallization and sintering behavior, in the perspective of applications in additive manufacturing of åkermanite-based scaffolds. The results showed that merwinite (Ca3MgSi2O8) is the primary product of glass devitrification; only in a second stage, merwinite reacts with the residual glass and yields åkermanite. The rapid crystallization, implying limited viscous flow sintering, was tested as an opportunity to create components with complex porosity distribution
Additive manufacturing of Ca–Mg silicate scaffolds supported by flame-synthesized glass microspheres
Full text linkNovel manufacturing techniques such as additive manufacturing also referred to as 3D printing hold a critical role in the preparation of novel bioactive three-dimensional glass-ceramic scaffolds. The present paper focuses on the use of Ca–Mg silicates microspheres (Ca2MgSi2O7, i.e. 40 mol% CaO, 20% MgO and 40% SiO2) for the fabrication of 3D structures by additive manufacturing. In the first step, the crystallization of the åkermanite system was avoided, by feeding nearly fully crystallized precursor powders prepared by conventional melt quenching into oxygen-methane (O2/CH4) torch, and solid glass microspheres (SGMs) with diameters bellow 63 μm were prepared. In the second step, the crystallization was utilized to control the viscous flow of SGMs during firing of reticulated scaffolds, obtained by digital light processing (DLP) of the SGMs suspended in a photocurable acrylate binder. The spheroidal shape facilitated a high solid content, up to 77 wt% of the SGMs in the suspension. After burn-out of the organic binder, a fast sintering treatment at 950 °C, for 30 min, led to scaffolds preserving the macro-porosity from 3D printing model (diamond cell lattice) but with well densified struts. The crystallization of 3D scaffolds during the sintering process led to 3D structures with adequate strength-to-density ratio
Polymorphic transitions and phase stability of CeO2-δ·(Dy,La,Sm,Y)2O3 high-entropy oxides consolidated by spark plasma sintering
No full textThe influence of spark plasma sintering (SPS) on the phase stability and bandgap of single-phase HEO ceramics with the composition CeO2-δ·(Dy,La,Sm,Y)2O3 was studied. Single phase HEO powders were prepared by combustion synthesis. The powders were consolidated by SPS at temperatures 1300° C, 1400° C, and 1600° C to prepare dense bulk ceramics. At 1600° C, a complete cubic-to-monoclinic phase transformation occurred, driven by Ce4 + to Ce3+ reduction under reducing SPS conditions. The change in the oxidation state of Ce resulted in an increase of the average ionic radius driving the cubic-to-monoclinic phase transition. Annealing the monoclinic samples at 1200° C in air led to a reversible transformation to the cubic structure. The phase transformations coupled with the presence of oxygen vacancies resulted in a bandgap energy reduction
Sustainable construction materials from alkali-activated waste fiberglass and waste refractory
Full text linkIn this work, waste fiberglass was up-cycled, alone, or mixed with used alumina-zirconia-silica (AZS) refractory from dismantled glass melting furnaces. Alkali activation was performed by suspending fiberglass and fiberglass/AZS powders in NaOH aqueous solution of various concentrations (8M, 6M, and 3M). The activation of waste fiberglass with 8M NaOH yields a gel with calcium and sodium-containing aluminosilicate hydrates. The addition of AZS refractory enabled the release of aluminates into the solution, which had beneficial effects on the mechanical properties. Low molarity activation yielded weaker materials which could be used as precursors for firing at moderate temperatures (800 °C and 1000 °C) to create cellular glass-ceramics, with a total porosity of up to 92 %. The firing of 8M activated samples resulted in glass ceramics with a 66–75 % porosity range and compressive strength of 10–23Mpa. The compressive strength-to-density ratio before and after firing was comparable to that of established commercial construction materials
Low cost structured photocatalysts from stereolithography of colorless pharmaceutical glass
Full text linkThe present study is dedicated to the manufacturing of highly porous triply periodic minimal surface (TPMS) constructs, fabricated from recycled end of life borosilicate pharmaceutical glass employing masked stereolithography. The structures were prepared from a simple blend of photocurable resin with glass powder (<38 μm). The gyroid model was selected with the porosity varying from 75 to 90%. Hot stage microscopy was applied to examine the glass sintering behaviour to improve the translucency of the 3D scaffolds. The obtained 3D scaffolds were dip-coated with TiO2 and further utilized for the photocatalytic degradation of dyes. The photocatalytic efficiency of the 3D scaffolds was evaluated by the degradation of methylene blue in water. It was found that 3D scaffolds coated with TiO2 showed a 40% higher degradation rate in comparison to bare 3D scaffolds under UV irradiation, which determines the significant role of TiO2 in the organic dye degradation. The better efficiency of 3D scaffolds coated with TiO2, compared with uncoated BSG 3D scaffolds is attributed to a better recombination rate, and the migration of electrons to the surface of the scaffold, where the charges participate in the photodecomposition of MB dye. The efficiency of the scaffolds was assessed for five consecutive cycles. The degradation efficiency after the fifth cycle was 75%, confirming the stability of the system
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