Crystallization and spectroscopic properties investigations of Er3+ doped transparent glass ceramics containing CaF2

Transparent oxyfluoride glass ceramics with composition of 45SiO₂–25Al₂O₃–5CaCO₃–10NaF–15CaF₂–0.5ErF₃ (in mol%) were developed through controlled crystallization of melt-quenched glass. Non-isothermal crystallization kinetics investigation showed that the average apparent activation energy E_a and Avrami exponent n are about 283 kJ/mol and 2.22, respectively, indicating the crystallization a three dimensional crystal growth process controlled by the diffusion with a decreasing nucleation rate. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) observation revealed the precipitation of CaF₂ crystallites sized about 15 nm among the glass matrix after heat-treatment at 650 °C for 2 h. For as-made glass, no upconversion signals were detected when excited with a 30 mW diode laser at 980 nm, while strong upconversion emissions at 545, 660 and 800 nm were obtained for transparent glass ceramic under similar excitation condition.     

Crystallization of aragonite CaCO3 with complex structures

In this work, aragonite CaCO₃ with complex morphologies was synthesized through homogeneous precipitation, in which calcium acetate and urea precipitated at 90 °C in the presence of PVP. The effect of the concentration of urea and PVP on the CaCO₃ crystalline was investigated. The morphology and structure of the CaCO₃ particles were characterized by SEM, XRD, and FT-IR. It was found that the concentrations of urea and PVP in the mixed aqueous solution were turned out to be important parameters for the morphology of CaCO₃ particles. All CaCO₃ particles were mainly aragonite with morphology from bundles of rods, bouquet-like and dumbbell-like. And there was no phase transition under the research conditions. Moreover, the possible process for the formation of the morphology of aragonite was discussed.     

PUA/PSS multilayer coated CaCO3 microparticles as smart drug delivery vehicles

Hybrid CaCO₃ microparticles coated by sodium poly(styrene sulfonate) (PSS) and aliphatic poly(urethane-amine) (PUA) were developed as thermal-/pH-responsive drug delivery vehicles via LbL self-assembly technique. The DOX release from the CaCO₃ microparticles was higher than 60% within 36 h, whereas the value of PUA/PSS-coated microparticles was only 20%. The results demonstrated that the PUA/PSS multilayer coating could reduce the drug release rate and significantly assuage the initial burst release of DOX. In addition, the drug release of the hybrid microparticles was found to be thermal-/pH-dual responsive. More interestingly, more than 90% of DOX was released in 36 h at pH 2.1 and 55 °C owing to the combined action of the dissolution of the CaCO₃ core and the shrinkage of aliphatic PUA.     

Growth of calcium carbonate crystal imitating stalagmite growth in nature

Calcite crystals were prepared by dropping a saturated calcium carbonate aqueous solution on a substrate. The calcite crystals were grown with a growth rate of approximately 0.7 μm/day under the condition of aqueous temperature of 2 °C, aqueous concentration of 0.006 mol/l, and substrate temperature of 40 °C. When the calcite substrate was used, calcite crystals were grown epitaxially. Na₂CO₃ and CaCl₂ aqueous solutions were dropped and reacted on the calcite crystal substrate with a CaCO₃ concentration of 0.06 mol/l, which is 10 times the saturated concentration at an aqueous temperature of 40 °C. Rhombohedral calcite was also deposited epitaxially with a growth rate of about 6.3 μm/day under this condition.     

Interplay between random laser performance and self-frequency conversions in NdxY1.00−xAl3(BO3)4 nanocrystals powders

Random Laser emission at 1.06 μm, self-second-harmonic generation at 0.53 μm and self-sum-frequency generation at 0.46 μm were investigated in Nd_xY_1.00−xAl₃(BO₃)₄ nanocrystalline powders, for 0.05 ⩽ x ⩽ 1.00, excited by a pulsed laser operating at 808 nm, focusing on the interplay between the RL performance and the second-order nonlinear processes. The RL performance, characterized by a figure-of-merit relating the laser slope efficiency and the excitation pulse energy threshold, improved as x increased up to 1.00 while the efficiency of the self-frequency conversion processes reduced for increasing x because of distortions introduced in the crystalline structure of the grains. The RL wavelength was also dependent on the Nd³⁺ concentration and presented a redshift from 1061.9 nm to 1063.5 nm for increasing values of x.     

From ultratough artificial nacre to elastomer: Poly(n-butyl acrylate) grafted graphene oxide nanocomposites

A biologically inspired, multilayer laminate structural design is deployed into composite films of poly(n-butyl acrylate) (PBA) graft graphene oxide (GO) synthesized by Ce(IV)/HNO₃ redox system in aqueous solution. Artificial hybrid films are fabricated by vacuum-assisted filtration macroscopic assembly method. Using nacre as the brick-and-mortar model construct free-standing membranes, here GO is similar to brick and PBA acts as mortar revealing the similar function of biopolymers in the natural nacre. Owing to the low T_g of PBA, the polymer chains could move freely at room temperature, enhancing the extensibility and flexibility. Meanwhile, the chemical structure of free-standing membranes was studied by Raman spectrum and XPS. The morphologies were charactered by XRD, SEM and TEM which are compact with the mechanical properties of the films. Interestingly, by tuning grafted PBA contents from 3.5 wt% to 77 wt%, quite wide range of mechanical properties (tensile strength from 20 to 180 MPa, Young’s modulus from 0.1 to 7 GPa, toughness from 0.8 to 4.3 MJ/m³, elongation from 1.2 to 24.5%) were obtained. At the same time, we found that the nanocomposite membranes can be adjusted from mimic nacre-liked film with high strength to a homogenous dispersed elastomer.     

Synthesis of vaterite CaCO3 by direct precipitation using glycine and l-alanine as directing agents

We report room temperature synthesis of calcium carbonate (CaCO₃) vaterite phase by the reaction of calcium chloride and sodium carbonate with glycine or l-alanine as directing agents. The compound crystallize in the hexagonal symmetry, P6₃/mmc with a = 4.1304(8) Å and c = 8.4770(2) Å.     

The influence of dissolved organic carbon on sorption of heavy metals on urea-treated pine bark

A previous study showed considerably higher metal adsorption by urea-treated pine bark (UTB) compared to non-treated bark (NTB) at metal adsorption from their individual relatively concentrated solutions. Comparison of the sorption characteristics of the two pine barks at low but environmentally relevant metal concentrations, and investigation of the influence of pH and dissolved organic carbon (DOC) on the sorption process are the aims of the present study. Sorption of Cu²⁺, Ni²⁺, Zn²⁺ and Pb²⁺ on pine bark of the species Pinus sylvestris was measured in multi-metal solutions in the presence and absence of DOC. In the absence of DOC, UTB gave lower residual metal concentrations (2–7 μg/l for copper, 1–5 μg/l for nickel, <0.05 μg/l for zinc and lead) in the range of initial concentrations up to 0.7 mg/l, compared to NTB (6–15 μg/l for copper, 2–24 μg/l for nickel, 2–9 μg/l for zinc, 2–3 μg/l for lead). In the presence of DOC, sorption of Zn, Ni and Pb decreased by up to 75% depending on the DOC concentration. Metal sorption on UTB is less sensitive to pH and more adsorbed metal ions are retained compared to NTB. The potential use of urea-treated bark for treatment of waste water containing DOC and low concentrations of metals is discussed.     

Influence of manganese on magnetic and electronic properties of ZnCr2Se4

The Zn_1?xMn_xCr₂Se₄ crystals were prepared by chemical vapor transport in closed silica tubes using ZnSe and MnSe with CrCl₃ as the transport agent. Four crystals with different Mn content (x = 0.12, 0.13, 0.18 and 0.24) were studied by X-ray photoelectron spectroscopy (XPS) and magnetic measurements in order to determine influence of manganese on their magnetic and electronic properties. The XPS revealed no change of chemical shifts of Cr core lines indicating a Cr³⁺ (3d³) electronic configuration. Magnetization measurements revealed a systematic increase in saturation magnetic moments from 6.32 μ_B/mol for x = 0.12 to 7.63 μ_B/mol for x = 0.24, as well as effective paramagnetic Bohr magneton numbers from 4.87 μ_B/mol for x = 0.12 to 6.91 μ_B/mol for x = 0.24.     

Utilization of a ZnS(en)0.5 photocatalyst hybridized with a CdS component for solar energy conversion to hydrogen

Photocatalytic solar energy conversion to chemical energy attracts great attention due to its high potential in harvesting renewable energy for the future. A ZnS(en)_0.5 photocatalyst hybridized with a CdS component was synthesized by solvothermal and precipitation methods to compare the effect of preparation methods on photocatalytic performance. The highest hydrogen production rate (559 μmol g^?1 h^?1) was achieved from a solvothermally synthesized ZnS(en)_0.5?CdS composite at 80 wt% of CdS content under standard 1-sun-irradiation condition (1000 W/m²). Photocatalytic hydrogen production rates from ZnS(en)_0.5?CdS photocatalysts were highly associated with degrees of charge separation, crystallinity, reduction power, and light absorption. By comparing two different routes for the synthesis of ZnS(en)_0.5?CdS photocatalysts, solvothermally-fabricated material was shown to have a higher photocatalytic activity compared with material fabricated by a precipitation method. This improvement may be due to its excellent crystalline and charge-separation characteristics.     

Mechanical properties of a degradable phosphate glass fibre reinforced polymer composite for internal fracture fixation

This paper reports on the mechanical properties and pH upon degradation of phosphate glass fibre reinforced methacrylate-modified oligolactide. Phosphate glass fibres of the composition 51.04 P₂O₅–21.42 CaO–25.51 Na₂O–2.03 SiO₂ (mol%) were produced by a crucible spinning technique. Fibres were embedded into a matrix of a degradable organic polymer network based on methacrylate-modified oligolactide; samples with and without addition of CaCO₃ for pH control were produced. pH during degradation in physiological NaCl solution could be increased to up to 6.5 by addition of 20 wt.% calcium carbonate to the fibre composites. pH in Tris buffer solution was about 7.11. Mechanical properties of dry specimens were investigated during 3-point bending tests and gave elastic moduli in the range of cortical bone (15 to 20 GPa). However, addition of calcium carbonate decreased tensile strength of the fibre composites and resulted in brittle fracture behaviour, while CaCO₃-free composites showed a fibrous fracture mode. Control of pH and degradation is a requirement for obtaining a fracture fixation device with degradation properties matching in vivo requirements. Results show that addition of CaCO₃ is suitable for controlling the pH during degradation of metaphosphate glass polymer composites.     

Unidirectional solidification of a Zn-rich Zn–2.17 wt%Cu hypo-peritectic alloy

Unidirectional solidification of a Zn-rich Zn–2.17 wt%Cu hypo-peritectic alloy has been carried out to investigate the microstructure evolution over the growth velocity range 0.02–4.82 mm/s at a temperature gradient of 15 K/mm by means of the Bridgman technique. Regular and plate-like two-phase cellular structures were observed in samples grown at growth velocities V above 0.48 and 2.64 mm/s, respectively. The dominant microstructure in samples grown below 0.22 mm/s was dendrites of primary ε in a matrix of secondary η. Intercellular spacing Λ decreased with increasing growth velocity V such that ΛV^1/2 is a constant of 316±55 μm^3/2/s^1/2. Secondary dendrite arm spacing λ₂ of primary ε decreased with increasing V such that λ₂V^1/3 is a constant of 14.9±0.9 μm^4/3/s^1/3. The observed transition from regular cells to plate-like cells of η is discussed on the basis of competitive growth and crystallographic effect.     

Growth and characterization of (Pb,La)TiO3 films with and without a special buffer layer prepared by RF magnetron sputtering

The (Pb, La)TiO₃ (PLT) ferroelectric thin films with and without a special buffer layer of PbO_x have been deposited on Pt/Ti/SiO₂/Si(100) substrates by RF magnetron sputtering technique at room temperature. The microstructure and the surface morphology of the films annealed at 600 °C for 1 h have been investigated by X-ray diffraction (XRD) and atomic force microscope (AFM). The surface roughness of the PLT thin film with a special buffer layer was 4.45 nm (5 μm × 5 μm) in comparison to that of 31.6 nm (5 μm × 5 μm) of the PLT thin film without a special buffer layer. Ferroelectric properties such as polarization hysteresis loop (P–V loop) and capacitance–voltage curve (C–V curve) of the films were investigated. The remanent polarization (P_r) and the coercive field (E_c) are 21 μC/cm² and 130 kV/cm respectively, and the pyroelectric coefficient is 2.75 × 10^− 8 C/cm² K for the PLT film with a special buffer layer. The results indicate that the (Pb, La)TiO₃ ferroelectric thin films with excellent ferroelectric properties can be deposited by RF magnetron sputtering with a special buffer layer.     

Anti-amyloidogenic activity of glutathione-covered gold nanoparticles

This study is an investigation of the effect of biocompatible glutathione-covered gold nanoparticles (AuSG_7) with an average size of 3 nm on the amyloid fibrils of hen egg-white lysozyme. The anti-amyloid activity of AuSG_7 nanoparticles on this protein was monitored with thioflavin T assay, atomic force microscopy and transmission electron microscopy. The study found that AuSG_7 nanoparticles in vitro depolymerize the amyloid aggregates and inhibit lysozyme aggregate formation. The ability to inhibit amyloid formation and promote amyloid disassembly has concentration-dependent characteristics: the concentration of nanoparticles at which inhibition is half maximal (IC₅₀) was found to be 6.19 μg/mL, and the concentration at which depolymerization is half maximal (DC₅₀) was found to be 8.26 μg/mL.     

Exploration of structural,thermal, vibrational and spectroscopic properties of new noncentrosymmetric double borate Rb3NdB6O12

New noncentrosymmetric rare earth borate Rb₃NdB₆O₁₂ is found in the ternary system Rb₂O–Nd₂O₃–B₂O₃. The Rb₃NdB₆O₁₂ powder was fabricated by solid state synthesis at 1050 K for 72 h and the crystal structure was obtained by the Rietveld method. Rb₃NdB₆O₁₂ crystallized in space group R32 with unit cell parameters a = 13.5236(4), c = 31.162(1) Å, Z = 3. From DSC measurements, the reversible phase transition (I type) in Rb₃NdB₆O₁₂ is observed at 852–936 K. The 200 μm thick tablet is transparent over the spectral range of 0.3–6.5 μm and the band gap is found as E_g ～ 6.29 eV. Nonlinear optical response of Rb₃NdB₆O₁₂ tested via SHG is estimated to be higher than that of K₃YB₆O₁₂. Blue shift of Nd luminescent lines is found in comparison with other borates. The vibrational parameters of Rb₃NdB₆O₁₂ are evaluated by experimental methods.     

Critical current density and stability of Tube Type Nb3Sn conductors

The critical current densities (J_c) and stabilities of Tube Type Nb₃Sn conductors have been measured. The strands had superconducting subelement counts ranging from 192 to 744, and flat-to-flat filament sizes (for 0.7 mm OD wire) of from 35 μm down to 15 μm. These Tube Type conductors had a very simple structure: prior to heat treatment the filaments consist of a Sn core surrounded by a thin Cu tube, itself surrounded by a Nb or Nb alloy tube. Eight different strand types were investigated using various techniques including SEM, residual resistance ratio (RRR), transport J_c, and stability measurement. Most strands were studied at 0.7 mm OD, with one representative at 0.42 mm. The transport measurements were made at 4.2 K in fields up to 14 T. Numerous heat treatment schedules were investigated, with reaction temperatures ranging from 615 °C to 650 °C, and times ranging from 36–500 h. The highest J_cs were seen for the lowest reaction temperatures, with 12 T transport J_c values as high as 2450 A/mm² observed. The RRRs were lower for longer time and higher temperature reactions and ranged from 4 to 180. Strand stability was a strong function of the effective filament diameter, d_eff, and RRR. The most stable strands showed stability currents, J_s, of 8700 A/mm² and 15,300 A/mm² for 0.7 mm OD and 0.42 mm OD conductors, respectively.     

Effect of growth rate on microstructure parameters and microhardness in directionally solidified Ti–49Al alloy

Intermetallics Ti–49Al (at.%) alloy was directionally solidified with different growth rates (V = 5 μm/s–30 μm/s) at a constant temperature gradient (G = 12.1 K/mm) by using a Bridgman type directional solidification furnace. The primary dendritic spacing (λ), interlamellar spacing (λ_L), and microhardness (HV) were measured. Effect of V on HV, λ and λ_L was experimental investigated. The dependencies of λ, λ_L and HV on the growth rate were determined by using linear regressing analysis. According to the result, the values of λ and λ_L decrease with the increasing of V, and the values of HV increase with the increasing of V and with the decreasing of λ and λ_L. The results were compared with previous similar experimental results for TiAl-based alloys.     

Precipitation in cold-rolled Al–Sc–Zr and Al–Mn–Sc–Zr alloys prepared by powder metallurgy

The effects of cold-rolling on thermal, mechanical and electrical properties, microstructure and recrystallization behaviour of the AlScZr and AlMnScZr alloys prepared by powder metallurgy were studied. The powder was produced by atomising in argon with 1% oxygen and then consolidated by hot extrusion at 350 °C. The electrical resistometry and microhardness together with differential scanning calorimetry measurements were compared with microstructure development observed by transmission and scanning electron microscopy, X-ray diffraction and electron backscatter diffraction. Fine (sub)grain structure developed and fine coherent Al₃Sc and/or Al₃(Sc,Zr) particles precipitated during extrusion at 350 °C in the alloys studied. Additional precipitation of the Al₃Sc and/or Al₃(Sc,Zr) particles and/or their coarsening was slightly facilitated by the previous cold rolling. The presence of Sc,Zr-containing particles has a significant antirecrystallization effect that prevents recrystallization at temperatures minimally up to 420 °C. The precipitation of the Al₆Mn- and/or Al₆(Mn,Fe) particles of a size ~ 1.0 μm at subgrain boundaries has also an essential antirecrystallization effect and totally suppresses recrystallization during 32 h long annealing at 550 °C. The texture development of the alloys seems to be affected by high solid solution strengthening by Mn. The precipitation of the Mn-containing alloy is highly enhanced by a cold rolling. The apparent activation energy of the Al₃Sc particles formation and/or coarsening and that of the Al₆Mn and/or Al₆(Mn,Fe) particle precipitation in the powder and in the compacted alloys were determined. The cold deformation has no effect on the apparent activation energy values of the Al₃Sc-phase and the Al₆Mn-phase precipitation.     

Biomimetic mineralization of calcium carbonate/carboxymethylcellulose microspheres for lysozyme immobilization

Porous calcium carbonate/carboxymethylcellulose (CaCO₃/CMC) microspheres were prepared by the biomimetic mineralization method for lysozyme immobilization via adsorption. The size and morphology of CaCO₃/CMC microspheres were characterized by transmitted electron microscopy (TEM) and zeta potential measurement. The lysozyme immobilization was verified by Fourier transform infrared (FTIR) spectroscopy. The effects of pHs and temperatures on lysozyme adsorption were investigated as well. It was revealed that CaCO₃/CMC microspheres could immobilize lysozyme efficiently via electrostatic interactions and a maximum adsorption capacity of 450 mg/g was achieved at pH 9.2 and 25 °C. Moreover, it was found that the adsorption process fitted well with the Langmuir isothermal model. In addition, UV, fluorescence, and circular dichroism (CD) spectroscopic studies showed that lysozyme maintained its original secondary structure during the adsorption/desorption process. Our study therefore demonstrated that CaCO₃/CMC microsphere can be used as a cost-effective and efficient support for lysozyme immobilization.     

Aluminum-free glass-ionomer bone cements with enhanced bioactivity and biodegradability

Al-free glasses of general composition 0.340SiO₂:0.300ZnO:(0.250-a-b)CaO:aSrO:bMgO:0.050Na₂O:0.060P₂O₅ (a, b = 0.000 or 0.125) were synthesized by melt quenching and their ability to form glass-ionomer cements was evaluated using poly(acrylic acid) and water. We evaluated the influence of the poly(acrylic acid) molecular weight and glass particle size in the cement mechanical performance. Higher compressive strength (25 ± 5 MPa) and higher compressive elastic modulus (492 ± 17 MPa) were achieved with a poly(acrylic acid) of 50 kDa and glass particle sizes between 63 and 125 μm. Cements prepared with glass formulation a = 0.125 and b = 0.000 were analyzed after immersion in simulated body fluid; they presented a surface morphology consistent with a calcium phosphate coating and a Ca/P ratio of 1.55 (similar to calcium-deficient hydroxyapatite). Addition of starch to the cement formulation induced partial degradability after 8 weeks of immersion in phosphate buffer saline containing α-amylase. Micro-computed tomography analysis revealed that the inclusion of starch increased the cement porosity from 35% to 42%. We were able to produce partially degradable Al-free glass-ionomer bone cements with mechanical performance, bioactivity and biodegradability suitable to be applied on non-load bearing sites and with the appropriate physical characteristics for osteointegration upon partial degradation. Zn release studies (concentrations between 413 μM and 887 μM) evidenced the necessity to tune the cement formulations to reduce the Zn concentration in the surrounding environment.