High quality sapphire crystal by advanced chemical transport process

Single crystal sapphire was synthesized by chemical transport of Al-O generated by the reaction of polycrystalline Al₂O₃ ceramic and carbon. Using C-axis oriented polycrystalline Al₂O₃ ceramics as a seed crystal in the deposition temperature range, a C-axis sapphire crystal (Φ5xL35 mm) was grown at a temperature range of 700–1000 °C, and the growth rate in the C-axis direction was about 3.5 mm/h. The transmittance in the visible to infrared region of the synthesized sapphire is a theoretical value (transmission loss is lower than 0.1 %/cm), and the absorption edge was less than 200 nm (the band gap is 6.2 eV), which is shorter than the absorption edge (240 nm) of the commercially available single crystal (band gap 5.2 eV) synthesized by the Czochralski method. The dislocation density in this material was extremely low, and it was confirmed by lattice image observation that it was a high-quality single crystal with very few defects.     

Iron doped thin TiO2 films synthesized with the RF PECVD method

Iron doped titanium dioxide coatings were synthesized with the help of RF plasma enhanced CVD technique. As a source of titanium, titanium chloride (IV) TiCl₄ was used while iron pentacarbonyl (0) Fe(CO)₅ served as iron supply. The coatings were diagnosed using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Their elemental and chemical composition was studied with the help of X-ray energy dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy, respectively. For the determination of their optical properties, variable angle spectroscopic ellipsometry (VASE) and ultraviolet-visible (UV-Vis) spectroscopy techniques were used. Iron content in the range of 0.07–11.5 at% was found in the films. Apart from oxygen, titanium and iron, a presence of trace amounts of chlorine, very likely originating from the titanium precursor, was recorded. FTIR studies showed that iron was built-in in the structure of TiO₂ matrix. Surface roughness, assessed using SEM and AFM techniques, increases with an increasing content of this element. VASE measurements revealed an increase of the coatings refractive index with a growing iron concentration, with the extinction coefficient remaining low and independent of that parameter. Trace amounts of iron resulted in a lowering of an absorption threshold of the films as well as their optical gap, but the tendency was reversed for high concentrations of that element.     

Study of aging behavior of 9/70/30 and 9/65/35 PLZT by optical interferometric technique

In this work Pb_0.91La_0.09(Zr_0.70Ti_0.30)_0.9775O₃ PLZT (9/70/30) and Pb_0.91La_0.09(Zr_0.65Ti_0.35)_0.9775O₃ PLZT (9/65/35) ceramics were prepared at four different sintering temperatures by solid solution method. The samples were aged by keeping at room temperature for 19 days. After the aging process, structural and electrical properties of the samples were studied using Modified Michelson Interferometer, LCR meter and X-ray diffraction. The effect of the Zr/Ti ratios on the dielectric and ferroelectric properties was also investigated. The aged PLZT (9/70/30) showed pinched P–E loop and remnant strain in rhombohedral phase, while PLZT (9/65/35) showed distort s–E shape implying non-180° domain in tetragonal phase.     

High-resolution FIB-TEM-STEM structural characterization of grain boundaries in the high dielectric constant perovskite CaCu3Ti4O12

In this work, the grain boundaries composition of the polycrystalline CaCu₃Ti₄O₁₂ (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu₂O and the metastable phase Cu₃TiO_4.     

In2O3:Ga and In2O3:P-based one-electrode gas sensors: Comparative study

Gas sensing characteristics of one-electrode sensors based on the In₂O₃ ceramics doped by gallium and phosphorus have been discussed. In₂O₃-based ceramic was prepared by sol–gel technology. Ozone, CO, CH₄ and H₂ were used as tested gases. The doping concentration effect on the sensor parameters such as magnitude of response, operating temperature, response and recovery times, sensitivity to the air humidity, and selectivity have been analyzed. It was shown that In₂O₃ doping by Ga and P could be used for the sensor performance optimization. It was assumed that the appearance of the second phase (InPO₄ and Ga₂O₃) and the change of structural parameters, taking place during doping process, were the main factors controlling the change of operating characteristics in In₂O₃:P and In₂O₃:Ga-based sensors.     

Mullitization kinetics from kaolinite incorporating nanometric Ba and Ca fluorides

The work presents the kinetic effect of nanometric BaF₂ and CaF₂ particles on kaolinite to mullite transformation. The kinetics were evaluated from dilatometric data using two different non-isothermal procedures: conversional model-fitting method and diffusional sintering analysis. From experimental data, the activation energy of mullite formation calculated from sintering (942 kJ/mol) and from conversional method (910 kJ/mol) were in good agreement with those values reported by other authors (mean value 1030 kJ/mol). After incorporation of 3 mol% of nanometric BaF₂ and CaF₂ in kaolinite and applying both analytical procedures, lower activation energies for mullite formation were obtained, assigning to the transformation the value of 635 kJ/mol for kaolinite/BaF₂ and 428 kJ/mol for kaolinite/CaF₂ composites.     

Definition and experimental evaluation of the smoke “confinement velocity” in tunnel fires

An experimental study is carried out on a reduced scale tunnel model (scale reduction is 1:20). The main objective is to evaluate the longitudinal velocity induced into a tunnel when a fire plume continuously released is confined and extracted between two exhaust vents located on both sides of the fire source. For the experimental simulations, fire-induced smoke is simulated by an air and helium mix release. Smoke flow is symmetrical as regards the fire location and experiments are realized for an half tunnel with only one vent activated downstream the source. The vent extraction flow rate is step by step increased and the length of the stratified smoke layer downstream the vent as well as the longitudinal fresh air flow induced, are measured. A confinement velocity is then associated to the minimum value of the longitudinal air flow needed to prevent the smoke layer propagation downstream the vent. This velocity is evaluated for several values of the fire heat release rate and finally compared with the corresponding critical velocity obtained for a longitudinal ventilation system.     

Synthesis and characterization of sol–gel derived calcium hydroxyapatite thin films spin-coated on silicon substrate

The goal of this study was to demonstrate that sol–gel processing route is suitable for the fabrication of calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, CHA) thin films on Si substrate by spin-coating technique. The substrate was spin-coated by precursor sol solution 1, 5, 15 and 30 times. The samples were annealed after each spin-coating procedure at 1000 °C for 5 h in air. In the sol–gel process ethylendiamintetraacetic acid and 1,2-ethandiol, and triethanolamine and polyvinyl alcohol were used as complexing agents and as gel network forming agents, respectively. The coatings were characterized using X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) and Raman spectroscopies, profilometry and the contact angle measurements (CAM). It was demonstrated, that properties of calcium hydroxyapatite thin films depend on spinning and annealing times.     

Preparation of ZnFe2O4–chitosan-doxorubicin hydrochloride nanoparticles and investigation of their hyperthermic heat-generating characteristics

In this study, the structural morphology and magnetic effects of magnetic ZnFe₂O₄ nanoparticles loaded with the cancer-fighting drug doxorubicin hydrochloride (DOX-HCl) were investigated. These nanoparticles have been found to have potential biomedical applications in targeted drug-delivery systems. The zinc ferrite nanoparticles were prepared by a chemical coprecipitation method and coated with chitosan. The nanoparticles were loaded with DOX-HCl and their surfaces improved by folic acid, which can be activated to target specific cancer cells. The specific absorption rate (SAR) values of the ZnFe₂O₄–chitosan–DOX-HCl nanoparticles were investigated at a frequency of 200 kHz and 1.5 kA/m amplitude in order to obtain Brownian relaxation time parameters. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and ultraviolet–visible spectrophotometry (UV–vis) were used to characterize the bulk properties of these nanoparticles. In addition, the impact of the nanoparticles under an alternating current (AC) magnetic field and their heat-generation ability were investigated using an experimental setup. The average nanoparticle size was found to be 8.5 nm. Magnetic hysteresis loops confirmed the superparamagnetism of the nanoparticles. The saturation magnetization was 6 emu/g. UV–vis was used to measure the amount of drug loaded onto the nanoparticles. The amount of drug absorption was significantly higher after 12 h, totaling 75%. The specific absorption rate parameter was 80.66 W/g, and the Brownian relaxation time was 188×10⁻⁹ s.     

Effects of europium content on structures and luminescence properties of tunable light-emitting silicon oxynitride phosphors

A series of europium (Eu)-activated silicon oxynitride samples with various atomic ratios x of Eu/Si from 0.001 to 0.057 was prepared by employing the polymer-derived method with polycarbosilane and Eu acetylacetonate as starting materials. Chemical compositions, phase structures, morphologies, and luminescence properties of the samples were investigated. It was found that all samples contained a dominated β-Si₃N₄-like phase, and had emission spectra with two peaks. The emission colors of the samples under near-UV excitation were tunable from blue to white, and then to yellow as x in the samples increased from 0.009 to 0.030, and then to 0.057. The white emitting sample with x = 0.030 was in the β-Si₃N₄-like single phase with its particles being single-crystallized in two space groups P6₃ and P6₃/m. Eu²⁺ ions located at interstitial sites of lattices and were coordinated by nine N/O atoms with different average bond lengths for the two space groups. A discussion was given to attribute the difference in the lattice environments for Eu²⁺ ions in two space groups P6₃ and P6₃/m to the appearance of two emission peaks at the lower (597 nm) and higher (454 nm) energy levels for the sample with x = 0.030.