Reanalysis of Microgravity Heat Capacity Measurements Near the SF<Subscript>6</Subscript> Liquid–Gas Critical Point

The earlier microgravity heat capacity measurements in SF₆ by Haupt and Straub have been reanalyzed in this study. A simple power law as well as the minimal-subtraction renormalization (MSR) scheme were used to fit the measurements. In this paper the unexpected result that the SF₆ heat capacity measurements appear to be within the asymptotic critical region all the way out to a reduced temperature |t| 10^–2 is presented. This conclusion is in contradiction with the smaller asymptotic region |t| < 1.6× 10^–4 found in the original investigation. These heat capacity measurements were found to be inconsistent with renormalization group predictions using SF₆ compressibility measurements.     

Phase equilibria in the Tl<Subscript>5</Subscript>Te<Subscript>3</Subscript>–Tl<Subscript>9</Subscript>BiTe<Subscript>6</Subscript>–Tl<Subscript>9</Subscript>TbTe<Subscript>6</Subscript> system

Phase equilibria in the Tl₅Te₃–Tl₉BiTe₆–Tl₉TbTe₆ system have been studied using differential thermal analysis, X-ray diffraction, and microhardness measurements. We have mapped out a number of vertical sections, the 760-K isothermal section of its phase diagram, and projections of its liquidus and solidus surfaces. The composition dependences of lattice parameters and microhardness have been obtained. The system has been shown to contain a continuous series of solid solutions, which crystallize in a tetragonal structure (Tl₅Te₃ type, sp. gr. I4/mcm).     

In vitro dissolution behavior of SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–F glass–ceramic system

Herein, we report the results of the in vitro dissolution tests, which were carried out by immersing the selected glass-ceramic samples in artificial saliva (AS) for various time periods of up to 42 days. In our experiments, the SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass ceramics with different crystal morphology and crystal content were used and a comparison is also made with the baseline glass samples (without any crystals). The bioactivity of the samples was probed by measuring the changes in pH, ionic conductivity and ionic concentration of AS following in vitro dissolution experiments. High resistance of the selected glass-ceramic samples against in vitro leaching has been demonstrated by minimal weight loss (<1%) and insignificant density change, even after 6 weeks of dissolution in artificial saliva. While XRD analysis reveals the change in surface texture of the crystalline phase, FT-IR analysis weakly indicated the Ca-P compound formation on the leached surface. The experimental measurements further indicate that the leaching of F(-), Mg(2+) ions from the sample surface commonly causes the change in the surface chemistry. Furthermore, the presence of (Ca, P, O)-rich mineralized deposits on the leached glass-ceramic surface as well as the decrease in Ca(2+) ion concentrations in the leaching solutions (compared to that in the initial AS solution) provide evidences of the moderate bioactive or mild biomineralisation behaviour of investigated glass-ceramics.     

Evaluation of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Na<Subscript>2</Subscript>O–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> bioglass-ceramics for hyperthermia application

Magnetic bioglass ceramics (MBC) are being considered for use as thermoseeds in hyperthermia treatment of cancer. While the bioactivity in MBCs is attributed to the formation of the bone minerals such as crystalline apatite, wollastonite, etc. in a physiological environment, the magnetic property arises from the magnetite [Fe₃O₄] present in these implant materials. A new set of bioglasses with compositions 41CaO · (52 ? x)SiO₂ · 4P₂O₅  · xFe₂O₃ · 3Na₂O (2 ≤ x ≤ 10 mol% Fe₂O₃) have been prepared by melt quenching method. The as-quenched glasses were then heat treated at 1050°C for 3 h to obtain the glass-ceramics. The structure and microstructure of the samples were characterized using X-ray diffraction and microscopy techniques. X-ray diffraction data revealed the presence of magnetite in the heat treated samples with x ≥ 2 mol% Fe₂O₃. Room temperature magnetic property of the heat treated samples was investigated using a Vibrating Sample Magnetometer. Field scans up to 20 kOe revealed that the glass ceramic samples had a high saturation magnetization and low coercivity. Room temperature hysteresis cycles were also recorded at 500 Oe to ascertain the magnetic properties at clinically amenable field strengths. The area under the magnetic hysteresis loop is a measure of the heat generated by the MBC. The coercivity of the samples is another important factor for hyperthermia applications. The area under the loop increases with an increase in Fe₂O₃ molar concentration and the. coercivity decreases with an increase in Fe₂O₃ molar concentration The evolution of magnetic properties in these MBCs as a function of Fe₂O₃ molar concentration is discussed and correlated with the amount of magnetite present in them.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.     

Crystallization and microstructural evolution of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–La<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-ceramics

Crystallization and microstructure of glasses with the molar compositions 1MgO·1.2Al₂O₃·2.8SiO₂·1.2TiO₂·xLa₂O₃ (x = 0.1 and 0.4) were thermally treated at different temperatures in the range from 950 to 1250 °C and then analyzed by X-ray diffraction and scanning electron microscopy, in combination with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was found that the microstructure is first homogeneous with the precipitation of randomly distributed crystals and then indialite domains with embedded perrierite and rutile crystals are formed. For higher temperatures or prolonged times, more domains appear and expand into the bulk of the sample. Finally, the entire sample consists of the indialite domains and the boundaries that are enriched in rutile, perrierite, and magnesium aluminotitanate. Nevertheless, very distinct differences are observed between the samples with different La₂O₃ concentrations. For the sample with x = 0.4, the domains were detected at lower temperatures, while the quantity and size of the domains increase faster due to the promoted precipitation of indialite. For the sample with x = 0.1, in addition to the domain boundaries, secondary boundaries between the “regions” (assemblages of the domains) are observed in a larger length scale. The average size of the crystalline phases found between the “regions” is larger than that typically observed at the domain boundaries. The sizes of the crystals at the boundaries decrease with higher concentrations of La₂O₃, and the crystals (especially perrierite) within the domains become larger, resulting in a more homogeneous microstructure. This results in better dielectric properties, i.e., much higher quality factor for the sample with x = 0.4 in comparison to that with x = 0.1 after heat-treatment at 1150 or 1250 °C.     

Compositional dependence of the structural and dielectric properties of Li<Subscript>2</Subscript>O–GeO<Subscript>2</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

(10Li₂O–20GeO₂–30ZnO–(40-x)Bi₂O₃–xFe₂O₃ where x = 0.0, 3, 6, and 9 mol%) glasses were prepared. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, DC and AC conductivities, and dielectric properties (constant ε′, loss tan δ, AC conductivity, σ _ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of iron ion concentration. The analysis of the results indicate that, the density and molar volume decrease with an increasing of iron content indicates structural changes of the glass matrix. The glass transition temperature T _g and onset of crystallization temperature T _x increase with the variation of concentration of Fe₂O₃ referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter ΔT decrease with increase Fe₂O₃ content, indicates an increasing concentration of iron ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BiO₃, BiO₆, ZnO₄, GeO₄, and GeO₆. The structural changes observed by varying the Fe₂O₃ content in these glasses and evidenced by FTIR investigation suggest that the iron ions play a network modifier role in these glasses while Bi₂O₃, GeO₂, and ZnO play the role of network formers. The temperature dependence of DC and AC conductivities at different frequencies was analyzed using Mott’s small polaron hopping model and, the high temperature activation energies have been estimated and discussed. The dielectric constant and dielectric loss increased with increase in temperature and Fe₂O₃ content.     

Phase equilibria in the Tl<Subscript>2</Subscript>Te–Tl<Subscript>5</Subscript>Te<Subscript>3</Subscript>–Tl<Subscript>9</Subscript>TbTe<Subscript>6</Subscript> system

The Tl₂Te–Tl₅Te₃–Tl₉TbTe₆ system has been studied using differential thermal analysis, X-ray diffraction, and microhardness measurements. We have mapped out a number of vertical sections, the 680 K isothermal section of its phase diagram, and projections of its polythermal projections of its liquidus and solidus surfaces. The field of solid solutions with the Tl₅Te₃ structure (δ-phase) has been shown to account for more than 90% of the area of the composition triangle. Tl₂Te-based solid solutions (α-phase) exist in a narrow composition region.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Local investigation of the emissive properties of LaB<Subscript>6</Subscript>–ZrB<Subscript>2</Subscript> eutectics

LaB₆–ZrB₂ composites obtained by directional solidification at eutectic composition have been investigated by low-energy electron microscopy (LEEM) and thermal emission electron microscopy (ThEEM). The transitions from the mirror electron microscopy mode to the LEEM mode for the hexa- and diborides indicate lower work functions of the two phases when embedded in the composite compared to the corresponding single phases. In the composite, the work function of the ZrB₂ fibers is similar to that of the matrix and ThEEM images display a brighter contrast for the fibers. This is explained by the thermally activated diffusion of La on the fiber surface.     

Frequency dependence of dielectric properties of CaO–SrO–Li<Subscript>2</Subscript>O–Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

CaO–SrO–Li₂O–Ln₂O₃–TiO₂ ceramics were prepared by solid state reaction method, where Ln₂O₃ consists of equal proportions of Nd₂O₃ and Sm₂O₃. Dielectric properties and crystal structure were investigated with respect to the content of TiO₂. Single phase with an orthorhombic perovskites structure was formed within the composition range of investigation. The frequency dependence of dielectric properties of the present ceramics was extensively investigated. Dielectric constant was less sensitive to frequency. However, dielectric loss and temperature coefficients were both very sensitive to frequency and gradually decreased with increasing frequency, such as the variation was more than ten times between 1 MHz and several GHz. The relationship between the temperature coefficient and dielectric loss was also discussed at different frequencies. And the mechanism of the frequency dependence was discussed in term of the role of Li ions.     

Chemical interaction of InAs,InSb, GaAs,and GaSb with (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>–HBr–C<Subscript>4</Subscript>H<Subscript>6</Subscript>O<Subscript>6</Subscript> etching solutions

This paper presents results on the kinetics and mechanism of the physicochemical interaction of InAs, InSb, GaAs, and GaSb semiconductor surfaces with (NH₄)₂Cr₂O₇–HBr–C₄H₆O₆ etching solutions under reproducible hydrodynamic conditions in the case of laminar etchant flow over a substrate. We have identified regions of polishing and nonpolishing solutions and evaluated the apparent activation energy of the process. The surface morphology of the crystals has been examined by microstructural analysis after chemical etching. The results demonstrate that the presence of C₄H₆O₆ in etchants helps to reduce the overall reaction rate and extend the region of polishing solutions.     

Preparation and characterization of Li<Subscript>2</Subscript>O–CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> glasses as bioactive material

The aim of the present investigation was to study the role of Al₂O₃ in the Li₂O–CaO–P₂O₅–SiO₂ bioactive glass for improving the bioactivity and other physico-mechanical properties of glass. A comparative study on structural and physico-mechanical properties and bioactivity of glasses were reported. The structural properties of glasses were investigated by X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy and the bioactivity of the glasses was evaluated by in vitro test in simulated body fluid (SBF). Density, compressive strength, Vickers hardness and ultrasonic wave velocity of glass samples were measured to investigate physical and mechanical properties. Results indicated that partial molar replacement of Li₂O by Al₂O₃ resulted in a significant increase in mechanical properties of glasses. In vitro studies of samples in SBF had shown that the pH of the solution increased after immersion of samples during the initial stage and then after reaching maxima it decreased with the increase in the immersion time. In vitro test in SBF indicated that the addition of Al₂O₃ up to 1.5 mol% resulted in an increase in bioactivity where as further addition of Al₂O₃ caused a decrease in bioactivity of the samples. The biocompatibility of these bioactive glass samples was studied using human osteoblast (MG-63) cell lines. The results obtained suggested that Li₂O–CaO–Al₂O₃–P₂O₅–SiO₂-based bioactive glasses containing alumina would be potential materials for biomedical applications.     

Synthesis of LaB<Subscript>6</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite powders via ball milling-assisted annealing

In this study, LaB₆–Al₂O₃ nanocomposite powders were synthesized via ball milling-assisted annealing process starting from La₂O₃–B₂O₃–Al powder blends. High-energy ball milling was conducted at various durations (0, 3, 6 and 9 h). Then, the milled powders were annealed at 1200 °C for 3 h under Ar atmosphere in order to obtain LaB₆ and Al₂O₃ phases as reaction products. X-ray diffractometry (XRD), scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) and transmission electron microscopy (TEM) techniques were utilized to carry out microstructural characterization of the powders. No reaction between the reactants was observed in the XRD patterns of the milled powders, indicating that high-energy ball milling did not trigger any chemical reactions even after milling for 9 h. LaAlO₃ and LaBO₃ phases existed in the annealed powders which were milled for 0, 3 and 6 h. LaBO₃ phase was removed after HCl leaching. 9-h milled and annealed powders did not exhibit any undesired phases such as LaAlO₃ and LaBO₃ after leaching step, and pure nanocrystalline LaB₆–Al₂O₃ composite powders were successfully obtained. TEM analyses revealed that very fine LaB₆ particles (~?100 nm) were embedded in coarse Al₂O₃ (~?500 nm) particles.     

Preparation and properties of Bi<Subscript>6</Subscript>Ti<Subscript>5</Subscript>WO<Subscript>22</Subscript>: a new phase in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> system

In a recent report, the evaluation of the phase relations in the Bi₂O₃–TiO₂–WO₃ ternary system has shown the existence of a new phase with nominal composition close to Bi₆Ti₅WO₂₂. In the present contribution we attempt to prepare this single phase by using a solid state route. Although XRD analyses also show traces of two minority Aurivillius-type phases in the synthesized materials, the crystal structure of the Bi₆Ti₅WO₂₂ phase has been determined by Rietveld analyses revealing a complex structure similar to that of Bi₃(AlSb₂)O₁₁ and PbHoAl₃O₈ related compounds. The electrical response of this new phase was characterized as well. Three peaks are observed in its dielectric response: two of them positioned around 0 °C and can be assigned to this Bi₆Ti₅WO₂₂ structure. The third one rises up to 665 °C and confirms the presence of the Aurivillius-type phases.     

Dielectric and piezoelectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xBaNb₂O₆ (BNT–BN100x), a new member of the BNT-based group, was prepared by conventional solid state reaction. X-ray diffraction showed that BaNb₂O₆ (BN) diffused into the lattice of Bi_0.5Na_0.5TiO₃ to form a solid solution with perovskite-type structure. The temperature dependence of dielectric constant ε_r revealed that the solid solution underwent two phase transitions from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric. Both the transition temperature T _d and T _m were shifted to lower with the increasing content of BaNb₂O₆. The temperature dependence of dielectric constant at different frequency revealed that the solid solution exhibited obviously dielectric relaxation characteristics. The sample with x = 0.6 mol% exhibited excellent electrical properties, piezoelectric constant d ₃₃ = 94 pC/N; electromechanical coupling factor k _p = 0.185. The results showed that BNT–BN100x ceramics were good candidates for use as lead-free piezoelectric ceramics.     

The effect of Fe contents on the local structure and crystallization behavior of SiO<Subscript>2</Subscript>–CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The glass and glass ceramics containing SiO₂–CaO–Fe₂O₃–P₂O₅ were prepared by sol–gel method. The influence of the Fe contents on the crystallization and local structure of the glass and glass ceramics was systematically investigated. The crystal structure of the glass ceramics was identified by XRD characterization. Hematite phase can be precipitated from the glass matrix in all glass ceramics with various Fe contents, and the crystallographic parameters of hematite were determined by XRD Rietveld refinement. The crystallization kinetics of the glasses was investigated in detail. Relative low activation energies were obtained at low Fe contents. The local structure evolution of the glass and glass ceramics has been studied in-depth by means of FTIR and Mössbauer spectroscopy. Fe element is present both as network former and network modifier which significantly influenced the crystallization activation energies of the glasses. The results of this work may be of great significance for the material design and practical applications of bioactive magnetic glass ceramics for hyperthermia.     

Catalytic combustion of methane over Pt and PdO-supported CeO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Catalytic combustion of methane was investigated on Pt and PdO-supported CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts prepared by a wet impregnation method in the presence of polyvinylpyrrolidone. The catalysts were characterized by X-ray fluorescence analysis, X-ray powder diffraction, X-ray photoelectron spectra, transmission electron microscopy, and BET specific surface area measurements. The Pt/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ and PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were selective for the total oxidation of methane into carbon dioxide and steam, and no by-products such as HCHO, CO, and H₂ were obtained. The catalytic activities of the PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were relatively higher than those of the Pt-supported catalysts, due to the facile re-oxidation of metallic Pd into PdO based on lattice oxygen supplied from the CeO₂–ZrO₂–Bi₂O₃ bulk. A decrease in the calcination temperature during the preparation process was found to be effective in enhancing the specific surface area of the catalysts, whereby particle agglomeration was inhibited. Optimization of the PdO amount and calcination temperature enabled complete oxidation of methane at temperatures as low as 320 °C on the 11.6 wt% PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalyst prepared at 400 °C.     

Fabrication of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> Optical Fibers with a Perfect Step-Index Profile by the MCVD Process

An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb₂O₃–Al₂O₃–P₂O₅–SiO₂ multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P₂O₅ losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated.