Nonionic surfactant-assisted hydrothermal synthesis of YVO4:Eu3+ powders in a wide pH range and their luminescent properties

YVO₄:Eu³⁺ powders with different morphologies were fabricated by a simple hydrothermal method at 180 °C for 24 h in a wide pH range with the assistance of polyvinylpyrrolidone (PVP) as a nonionic surfactant. The as-synthesized samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The obtained results showed that the pH value of synthesis solution played a key role in the formation of final products with different morphologies, such as, microspheres, irregular microspheres with grain-like nanoparticles, stone-like structures with regular short nanorods, and smooth rhombohedrons. The PL measurements revealed that the emission intensity of the samples was first decreased, and then increased with increasing the pH value due mainly to the increase in crystallinity and decrease in surface defects.     

Hydrothermally-induced morphological transformation of GdVO4:Eu

The aim of the present study is to investigate the effect of a wide pH range on morphology and luminescence properties of europium-doped gadolinium vanadate (GdVO₄:Eu³⁺). GdVO₄:Eu³⁺ powders were hydrothermally synthesized at 180 °C for 24 h in a wide pH range. The as-synthesized powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. The XRD results showed that GdVO₄:Eu³⁺ with the tetragonal structure formed at pH < 13 as a single phase and Gd(OH)₃ formed at pH ≥ 13 as a secondary phase. The SEM and TEM observations demonstrated the hydrothermally-induced morphological transformation of GdVO₄:Eu³⁺ powders by altering the pH of the synthesis solution. The possible mechanism for the morphological transformation was proposed. The intensities of the prominent peaks at 618 nm in the PL emission spectra of GdVO₄:Eu³⁺ powders considerably shift according to the specific morphology. The luminescence intensity of the octahedron- and rod-like GdVO₄:Eu³⁺ powders hydrothermally obtained at pH = 3 was the strongest one due to high packing density and high crystallinity as well as the extended reduction of the concentration of inherent defect states or adsorbed species.     

Environment-dependent indentation recovery of select soda-lime silicate glasses

Indentations made on silicate glasses can easily be affected by the environment. In the present work, indentations were made on select commercial float glasses as well as on experimental soda-lime silicate glasses using a 1 mm diameter spherical tungsten carbide ball-mounted Brinell indenter. Recovery of indentations made on the glass samples was measured in different environments, namely, 100 °C, room temperature/room humidity and 100% relative humidity, as a function of time by using a Zygo laser non-contact profiliometer. Elastic (Young's modulus, bulk modulus, shear modulus and Poisson's ratio) and indentation (Vickers hardness, fracture toughness, brittleness and fracture surface energy) properties of the glasses were also determined by a pulse-echo and Vickers indentation methods, respectively, to correlate with the recovery of indentations. The elastic properties and Vickers hardness are directly proportional to the packing ions present in the glass structure and the strength of an individual bond, whereas the brittleness and fracture toughness more likely depend on molar volume of the glasses. According to the applied environment, a recovery rate of indentations follows the order: room temperature/room humidity <100% relative humidity <100 °C, regardless of glass composition. The reason for higher recovery rate of indentations is attributed to the structural relaxation, which is promoted by a thermodynamic driving force at 100 °C, and stored strain energy in deformation zone, allowing the indentations to regain their original configurations at certain points.     

Cellular Anorthite Glass–Ceramics: Synthesis, Microstructure and Properties

Highly permeable cellular anorthite glass ceramics with porosity of ∼95% were obtained by a simple replication technique using near-stoichiometric glass powders and a polymeric foam as sacrificial template material. Impacts of sintering conditions and additions of minor constituents, respectively, on microstructural evolution and resulting macroscopic properties of the derived foams were investigated by X-ray diffraction, scanning electron microscopy (SEM), differential thermal analysis and X-ray microcomputer tomography. Apparent activation energies of crystallization and the Avrami coefficient were estimated from nonisothermal crystallization experiments to evaluate the impact of titania and zirconia, respectively, as potential nucleation agents. Consistent with SEM analyses, it was found that crystal growth occurs in two dimensions. While TiO₂ primarily acts on the viscosity of the precursor glass and, thus, on the process of sintering by viscous flow, ZrO₂ is found to exhibit at least some nucleation efficiency. As compared with sintering of ceramic powders and solid-state reactions in general, the glass ceramic route enables significant reduction in sintering time and temperature.     

Use of natural and thermally activated porphyrite in cement production

The aim of the present study was to investigate the use of porphyrite in the production of Portland cement. Natural and thermally activated porphyrites were used as a clay raw material and an activator, respectively, at 0, 10, 20, 30, 40 and 50 wt% in order to assess their effects on the cement properties. According to the test results, the compressive strength of the specimens decreased with increasing natural porphyrite content in various curing periods. However, the compressive strength of cement produced with 10 wt% porphyrite (activator) activated at 650 °C for 30 min showed a higher value (56 MPa in TPC-6) than cement without activator (51 MPa in RPC-2). Due to thermal activation, porphyrite activator containing a glass phase possesses an enhanced reactivity during clinker hydration that intensifies the synthesis of hydrosilicates and improves compressive strength accordingly. The X-ray diffraction analysis confirmed an intensive formation of Portland cement minerals such as C₃S, β-C₂S, C₃A and C₄AF. The addition of thermally activated porphyrite has also led to an improvement of the rheological behavior, stability to expansion, increase in setting time and decrease in specific surface area of cement. As prepared cement composites and concretes with improved properties meet the requirements of State Standards 310-86 and 10181-81 for Portland cement and concrete, respectively. The findings in this report indicate that porphyrite can be utilized both as a raw material and an activator in the production of cement.     

Utilization of muscovite granite waste in the manufacture of ceramic tiles

Granite waste is by-product from a decorative rock industry. The present study aims to investigate the effect of muscovite granite waste on the physico-mechanical properties of ceramic tiles to demonstrate its suitability for industrial production. A series of flooring- and facing ceramic tiles were prepared by adding 20, 25, and 30 wt% muscovite granite waste into the batch compositions. The sintering behavior and degrees of densification of two kinds of ceramic tiles were evaluated by determining their physico-mechanical properties and characterizing them by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. As expected, the facing ceramic tile (FacCT1) sample, containing wollastonite, hematite, anorthite, quartz, and cristobalite, with 20 wt% muscovite granite waste showed lower physico-mechanical properties than those of the flooring ceramic tile (FloCT3) sample, containing mullite, calcium aluminosilicate, quartz, and cristobalite, with 30 wt% muscovite granite waste. The reason is that lower firing temperatures cannot accelerate a complete fusion of the granite waste which behaves like an inert non-plastic material similar to quartz. These results illustrate the prospects of utilizing muscovite granite waste in ceramic tile production.     

Synthesis of orthorhombic and cubic PbF<Subscript>2</Subscript> by hydrothermal method

Orthorhombic (α-) and cubic (β-) PbF₂ have been successfully synthesized via a simple hydrothermal process at 200 °C for 8 h using Pb(C₂H₃O)₂ and NH₄F as the raw reaction materials. The crystal structure, morphology, and optical properties of the as-synthesized samples were characterized by X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectroscopy. XRD and SEM results show that the uniform β-PbF₂ microspheres and porous-microspheres with the average diameter about 3 and 5 μm, respectively, were synthesized assisting with citric acid and α-PbF₂ microrods and microtubes with a diameter about 15 and 10 μm, respectively, were synthesized assisting with acetic acid. The reaction conditions influencing the synthesis of these PbF₂ microstructures, such as reaction time, the amount of CTAB, and the molar ratio of F/Pb were investigated. On the basis of a series of observations, phenomenological elucidation of a mechanism for the growth of the β-PbF₂ microspheres and multispheres has been presented. Room-temperature photoluminescence measurements indicated that the as-prepared α-PbF₂ microrods exhibit a strong green emission.     

Synthesis RMn2O5 (R = Gd and Sm) nano- and microstructures by a simple hydrothermal method

Single-phase RMn₂O₅ (R = Gd and Sm) nano- and microstructures have been successfully synthesized via a simple hydrothermal process at 250 °C for 24 h using NaOH as mineralizer. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selective area electron diffraction patterns (SAED) were used to characterize the as-synthesized GdMn₂O₅ and SmMn₂O₅ samples. The effect of NaOH concentration and the molar ratio of Mn²⁺/Mn⁷⁺ on the morphology and size of the final products was studied, and a possible formation mechanism of RMn₂O₅ (R = Gd and Sm) nanoplates and nanorods under hydrothermal conditions was proposed.     

La-modification of multiferroic BiFeO<Subscript>3</Subscript> by hydrothermal method at low temperature

This study reports the effect of La doping on structural, morphological and magnetic characteristics of BiFeO₃ synthesized under mild hydrothermal conditions at 200°C for 16 h using the KOH concentration of 4 M. The as-synthesized powders of Bi_1−x La _x FeO₃ for x = 0.05, 0.10, and 0.15 were characterized by X-ray powder diffraction scanning electron microscope and the vibrating sample magnetometer. The formation mechanism of Bi_1−x La _x FeO₃ powders can be expressed by “dissolution-nucleation-crystallization” process. The magnetism of Bi_1−x La _x FeO₃ increased with increase of La content due mainly to increscent suppressing spiral magnetic structure and magnetic contribution of La.