Crystallization of micro particles of sulindac using rapid expansion of supercritical solution

In pharmaceutical industry, many drugs exhibit poor solubility in biological fluid. Solubility of drugs affects on the rate of dissolution and bioavailability in biological fluids. The bioavailability of drugs can be enhanced by decreasing the drug particle size. In this study, sulindac was micronized via rapid expansion of supercritical solution (RESS) where CO2 was used as a solvent. The experiments were conducted to investigate the effect of the extraction pressure and temperature (140–230 bar and 40–60 °C), collection distance (1–10 cm), effective nozzle diameter (450–1700 μm) and nozzle length (2–15 mm) on the size and morphology of the sulindac particles. The size and morphology of the precipitated particles were monitored by scanning electron microscopy (SEM). The particle size of intact sulindac particles was about 33.03 μm, while the average particle size of the micronized sulindac particles was between 0.76 and 8.02 μm based on different experimental conditions. Additionally, the different morphology of the micronized particles was observed like needle, rectangular, quasi spherical and irregular form while the morphology of the intact particles of sulindac was rectangular and irregular.     

GHz microwave properties of melt spun Fe-Si alloys

The structural and microwave properties of melt spun Fe_100−xSi_x (x = 10, 20, 30) nanocomposites were investigated. The phases varied with Si content in FeSi alloys. It is found that the Fe₃Si and FeSi phases could be obtained with Si content up to 20 at.%. The X-ray absorption fine structure (XAFS) spectra of Fe K-edges show that the local structures around Fe atoms in melt spun Fe-Si alloys become more disordered with increasing Si content when compared with that of α-Fe. The complex permittivity-frequency and permeability-frequency properties were determined in the microwave frequency regime of 2-18 GHz by vector network analysis. It is found that flake-like FeSi powder composite has the largest values of μ′ and μ″ at 2 GHz. The reflection loss shifts to the higher frequency with the Si content increasing for melt spun FeSi alloys. A minimum reflection loss of −16.5 dB is obtained at 13.9 GHz for composition Fe₇₀Si₃₀ with the thickness of 1.5 mm. However, for composition Fe₇₀Si₃₀, the minimum reflection loss shifts to lower frequency and larger value with the thickness increasing. The results suggest a new design for microwave absorbers based on electromagnetic wave-absorbing materials.     

Effect of rogue particles on the sub-surface damage of fused silica during grinding/polishing

The distribution and characteristics of surface cracks (i.e., sub-surface damage or scratching) on fused silica formed during grinding/polishing resulting from the addition of rogue particles in the base slurry has been investigated. Fused silica samples (10 cm diameter × 1 cm thick) were: (1) ground by loose abrasive grinding (alumina particles 9-30 μm) on a glass lap with the addition of larger alumina particles at various concentrations with mean sizes ranging from 15 to 30 μm, or (2) polished (using 0.5 μm cerium oxide slurry) on various laps (polyurethane pads or pitch) with the addition of larger rogue particles (diamond (4-45 μm), pitch, dust, or dried Ceria slurry agglomerates) at various concentrations. For the resulting ground samples, the crack distributions of the as-prepared surfaces were determined using a polished taper technique. The crack depth was observed to: (1) increase at small concentrations (>10⁻⁴ fraction) of rogue particles; and (2) increase with rogue particle concentration to crack depths consistent with that observed when grinding with particles the size of the rogue particles alone. For the polished samples, which were subsequently etched in HF:NH₄F to expose the surface damage, the resulting scratch properties (type, number density, width, and length) were characterized. The number density of scratches increased exponentially with the size of the rogue diamond at a fixed rogue diamond concentration suggesting that larger particles are more likely to lead to scratching. The length of the scratch was found to increase with rogue particle size, increase with lap viscosity, and decrease with applied load. At high diamond concentrations, the type of scratch transitioned from brittle to ductile and the length of the scratches dramatically increased and extended to the edge of the optic. The observed trends can be explained semi-quantitatively in terms of the time needed for a rogue particle to penetrate into a viscoelastic lap. The results of this study provide useful insights and ‘rules-of-thumb’ relating scratch characteristics observed on surfaces during optical glass fabrication to the characteristics of the rogue particles causing them and their possible source.     

All-chalcogenide middle infrared dielectric reflector and filter

We have fabricated a dielectric reflector and a passband filter, both with first order photonic bandgaps in the middle-infrared region around λ = 4 μm. The devices were made from alternating amorphous Ge₂₅S₇₅ and Ge₁₅Te₈₅ chalcogenide films with high transparency in the middle infrared region stacked in multilayers. Due to high thickness accuracy and periodicity of prepared multilayers we also observed second order photonic bandgaps at λ ~ 1.4 μm. The experimental data were in good agreement with theoretical predictions. The work focused on investigation of compositional homogeneity, surface roughness, thermal and optical properties of individual amorphous Ge₂₅S₇₅ and Ge₁₅Te₈₅ films. We confirmed chalcogenide materials as being of suitable choice for designing middle-infrared quarter wave stack devices. FT-IR reflectance spectra confirmed occurrence of 99.4% stopband near λ = 4 μm for fabricated reflector and narrow ~ 50% passband of prepared filter near λ = 3.934 μm.     

Grain size dependence of physico-optical properties of nanometallic silver in silica aerogel matrix

Synthesis of silver nanoparticles in silica aerogel matrix by sub-critical drying technique is reported in the present article. Physical characterization of silver/silica aerogel nanocomposites with 1, 5 and 25 wt% of silver has been discussed. Physico-optical properties of the composites have been evaluated as a function of the silver particle size crystallized within the silica matrix. The maximum size of the silver grains that could be accommodated in the amorphous matrix was observed to be 25 nm. Silver particles of diameter larger than 25 nm were found segregated out of the silica matrix; such silver particles were single crystalline with dendritic morphology. Optical absorption analysis confirmed the presence of both the oligomeric and nanometallic silver in the samples heat-treated up to 500 °C. With decreasing silver particle size, the surface plasmon resonance was found first to shift towards blue followed then by a red shift. The blue shift is attributed to the chemisorption occurring between the metallic core and the silica matrix. With larger grain size of 25-80 nm in 25 wt% Ag-silica aerogel sample, the diffuseness of electron cloud outside the potential well was observed to cause a red shift in the surface plasmon resonance.     

Effect of frit size on sintering, crystallization and electrical properties of wollastonite glass-ceramics

Wollastonite glass-ceramics were prepared through pressureless sintering. The sinterability of the prepared samples of the glassy powder in the system (SiO₂-CaO-Na₂O-Fe₂O₃-WO₃) was investigated in the temperature range 720-900 °C and soaking time of 180 min. The influence of the increase in the glass powder particle size on the sinterability and dielectric properties of the glass-ceramic samples was studied.The sintered specimens were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. XRD analysis revealed that wollastonite was the main crystalline phase in the sintered glass-ceramics. Dielectric properties such as dielectric constant and dielectric loss were measured via a network analyzer at 10 GHz.It was observed that the increase of the glassy powder particle size improved the sinterability and dielectric properties of the glass-ceramic specimens. Wollastonite glass-ceramics with 16 μm particle size had maximum constant and minimum loss (ε_r = 10.10 and tan δ = 0.005) compared with the other glass-ceramics.     

Electromagnetic reflection, shielding and conductivity of polypyrrole thin film electropolymerized in P-Tulensulfonic acid

The electrosynthesis of polypyrrole (PPy) thin film on stainless steel electrode was performed in P- Tulensulfonic acid. The electromagnetic reflection, shielding effectiveness, permittivity and conductivity in the frequency range 8.2 to 18 GHz were studied. The effect of change in the acid concentration on the properties is reported. The microwave conductivity varies from 16 S/cm to 415 S/cm with frequency. The dielectric constant and dielectric loss factor decreases with increase in frequency.     

The application of differential thermal analysis to the study of isothermal and non-isothermal crystallization kinetics of coal fly ash based glasses

The crystallization kinetics of glasses obtained from coal fly ash was investigated by both isothermal and non-isothermal methods using differential thermal analysis (DTA) data. In DTA experiments, glass samples having coarse (800-1000 μm) and fine (<180 μm) particle sizes were used and the results were compared. The Avrami exponent (n) was calculated by means of Johnson-Mehl-Avrami (JMA) and Ozawa equations. Calculated kinetic parameters indicated that the appropriate crystallization mechanisms were bulk and surface crystallization for coarse and fine particles, respectively. Isothermal and non-isothermal DTA experiments showed that the crystallization activation energies of coarse glasses are changed in the range of 444-578 kJ/mol, while the crystallization activation energies of fine glasses are changed in the range of 610-662 kJ/mol. It was found that crystallization activation energies of fine glasses are higher than those of the coarse glasses. Results showed that isothermal and non-isothermal crystallization kinetics of glasses produced from coal fly ash is in agreement within the experimental error.     

Nucleation kinetics in deionized charged colloidal suspension

A systematic experimental study on the nucleation, crystallization and crystal-growth of one-component charged colloidal particles (122 nm diluted in pure water with densities between 0.5 μm⁻³ < n_p < 5 μm⁻³) is present by means of time resolved static light scattering spectroscopy revealing the heterogeneous and homogenous nature of the crystallization. The interactions between the charged colloidal particles are sufficiently strong to cause crystallization which described in terms of Debye-Hückel approximation. Crystallization starts always with the formation of compressed structurally heterogeneous precursor domains. The results show that the heterogeneous nucleation at the cell walls starts simultaneously with the homogeneous bulk nucleation and the rate density of the heterogeneous nucleation appears slightly higher. It has been also found that the overall crystallization consists of at least a two-step nucleation process involving formation of early stage nuclei or crystal precursor then followed by the main crystallization. The induction time, the number density of nuclei and the growth rate of crystals, is strongly dependent on particle concentration and on whether the nucleation are homogeneous in cell center or heterogeneous on cell walls.     

Preparation of Sb2S3 nanomaterials with different morphologies via a refluxing approach

Single-crystalline antimony trisulfide (Sb₂S₃) nanomaterials with flower-like and rod-like morphologies were successfully synthesized under refluxing conditions by the reaction of antimony trichloride (SbCl₃) and thiourea with PEG400 and OP-10 as the surfactants. X-ray diffraction (XRD) indicates that the obtained sample is orthorhombic-phase Sb₂S₃ with calculated lattice parameters a=1.124 nm, b=1.134 nm and c=0.382 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the flower-like Sb₂S₃ is 9–10 μm in size, which is composed of thin leaves with thickness of 0.05–0.2 μm, width of 0.8–2.2 μm and length of 2.5–3 μm, and the rod-like Sb₂S₃ is 45–360 nm in diameter and 0.7–4 μm in length, respectively. UV–Vis analysis indicates that the band gap of Sb₂S₃ nanorods is 1.52 eV, suitable for photovoltaic conversion. A possible mechanism of formation was proposed. The effects of reaction time and surfactants on the growth of nanomaterials with different morphologies were also investigated.     

Thermodynamics of formation of aluminum-iron-germanium amorphous alloys

Thermodynamic properties of ternary liquid Al-Fe-Ge alloys were studied by electromotive force method at 1050-1250 K and by high-temperature isobasic calorimetry at 1740 ± 5 K. The heat capacity change at ternary alloy formation (Δ_mixC_p) was estimated using the temperature dependence of integral enthalpy of mixing. Thermodynamics of the formation of Al-Fe-Ge amorphous alloys was evaluated by extrapolation of thermodynamic functions of mixing to the temperature of amorphization. The process of glass forming is preferable by both enthalpy and entropy for compositions of (0.1<x_Fe<0.6, x_Ge<0.5). The area with most negative integral Gibbs free energy and enthalpy of amorphous alloy formation corresponds well to the area of amorphization estimated by a glass-forming tendency (GFT) criterion.     

Structure and thermomagnetic properties of powders produced from melt spun FeNbBCu ribbons

Amorphous ribbons of Fe₇₇Nb₇B₁₅Cu₁ prepared by melt-spinning and powders produced from them by ball-milling were characterized by means of calorimetry, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. Upon thermal treatment the amorphous alloy experiences a primary crystallization that leads to bcc-Fe nanocrystals dispersed in an amorphous matrix. Magnetic measurements indicate that this alloy in the amorphous and nanocrystalline state is a good soft magnetic material. Values of saturation magnetization and coercivity are 120 Am²/kg and 5 A/m respectively, for the alloy in the nanocrystalline state. Pre-annealing, post-relaxation and nanocrystallization as well as various milling parameters were explored and the structural and magnetic changes induced have been studied. The analysis of the particle size distribution and morphology of the powders show that the brittleness resulting from pre-annealing of the ribbons is very effective in reducing the particle’s size. Recovery of the high coercitive field induced by milling is achieved by post-annealing to an extent that depends mostly on the milling conditions.     

Development of m-plane GaN anisotropic film properties during MOVPE growth on LiAlO2 substrates

The anisotropic film properties of m-plane GaN deposited by metal organic vapour phase epitaxy (MOVPE) on LiAlO₂ substrates are investigated. To study the development of layer properties during epitaxy, the total film thickness is varied between 0.2 and 1.7 μm. A surface roughening is observed caused by the increased size of hillock-like features. Additionally, small steps which are perfectly aligned in (1 1 −2 0) planes appear for samples with a thickness of ∼0.5 μm and above. Simultaneously, the X-ray rocking curve (XRC) full width at half maximum (FWHM) values become strongly dependent on incident X-ray beam direction beyond this critical thickness. Anisotropic in-plane compressive strain is initially present and gradually relaxes mainly in the [1 1 −2 0] direction when growing thicker films. Low-temperature photoluminescence (PL) spectra are dominated by the GaN near-band-edge peak and show only weak signal related to basal plane stacking faults (BSF). The measured background electron concentration is reduced from ∼10²⁰ to ∼10¹⁹ cm⁻³ for film thicknesses of 0.2 μm and ∼1 μm while the electron mobilities rise from ∼20 to ∼130 cm²/V s. The mobilities are significantly higher in [0 0 0 1] direction which we explain by the presence of extended planar defects in the prismatic plane. Such defects are assumed to be also the cause for the observed surface steps and anisotropic XRC broadening.     

Structure and properties of Ni60(Nb100−xTax)34Sn6 bulk metallic glass alloys

Refractory bulk metallic glasses and bulk metallic glass composites are formed in quaternary Ni-Nb-Ta-Sn alloy system. Alloys of composition Ni₆₀(Nb_100−xTa_x)₃₄Sn₆ (x = 20, 40, 60, 80) alloys were prepared by injection-casting the molten alloys into copper molds. Glassy alloys are formed in the thickness of half mm strips. With thicker strips (e.g., 1 mm), Nb₂O₅ and Ni₃Sn phases and the amorphous phase form an in situ composite. Glass transition temperatures, crystallization temperatures, and ΔT_x, defined as T_x1 − T_g (T_x1: first crystallization temperature, T_g: glass transition temperature) of the alloys increase dramatically with increasing Ta contents. These refractory bulk amorphous alloys exhibit high Young’s modulus (155-170 GPa), shear modulus (56-63 GPa), and estimated yield strength (3-3.6 GPa).     

Facile synthesis and size control of highly monodispersed hybrid silica spheres through a novel nuclei controlling method

Monodispersed hybrid silica spheres with particles sizes up to 4 μm were obtained by controlling the number of nuclei generated in the initiation phase of particle formation using a two-step sol-gel method. This method has two advantages: (i) the particle size can be tuned easily just by variation of the amount ammonia added in the step of precursor hydrolysis, and (ii) the amount of precursor used to prepare particles with the same diameter is at least ten times lower than with traditional methods. The effects of stirring speed and stirring time on the resulting particle size were also studied.     

Microstructure and optical properties of (Pb,Ca)TiO3 films grown on Si(1 0 0) substrates by a simple sol-gel process

Amorphous and polycrystalline (Pb_0.76Ca_0.24)TiO₃ (PCT) thin films deposited on an Si(1 0 0) substrate have been prepared by a simple sol-gel process. The microstructure and surface morphologies of the thin films have been studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The polycrystalline PCT film on the Si(1 0 0) substrate has a tetragonal perovskite structure with grain size from 60 to 110 nm. AFM reveals smooth surfaces and root mean square (rms) roughness of 0.17 and 4.4 nm for amorphous and polycrystalline films, respectively. The refractive index n and extinction coefficient k of the amorphous and polycrystalline thin films was obtained by spectroscopic ellipsometry as a function of the photon energy in the range from 2.0 to 5.4 eV. The maximum n and direct bandgap energies of amorphous and polycrystalline thin films were 2.66 and 4.11 eV, 2.64 and 3.84 eV, respectively.     

Structural characterization of Ni-based refractory glassy metals

X-ray scattering patterns of several Ni-based refractory alloy glasses indicated short range atomic order to at least four nearest neighbor shells. Comparisons between diffraction results from a synchrotron source vs. a standard laboratory source showed the necessity for low divergence and high intensity incident radiation in order to distinguish a low concentration of crystallites as small as ≈15 nm, which were present within an amorphous matrix. The divergence of both sources was examined by comparing the diffraction patterns of the same LaB₆ standard sample and using this as a reference standard to measure relative grain sizes. The crystallites in these glasses comprised between 0.0% and 7.5% by volume, and were relatively consistent amongst samples of the same composition. These crystalline peaks had potential matches with several metallic elements, compounds and oxides. It is seen that a very small composition range exists for near-perfect bulk metallic glass formers (as defined by a ≈0% crystallinity). Scattering electron microscopy was also performed to understand aspects of individual second phase particles such as size and distribution. Departure of radial distribution results from those predicted by hard sphere models indicated intermediate range order.     

Crystallization kinetics and magnetic properties of Fe63.5Co10Si13.5B9Cu1Nb3 nanocrystalline powder cores

Amorphous ribbons of the alloy Fe_63.5Co₁₀Si_13.5B₉Cu₁Nb₃ were prepared by the standard single copper wheel melt spinning technique in air and their crystallization kinetics was analyzed by non-isothermal differential scanning calorimetry (DSC) measurements. The crystallization activation energies (E_x, E_a1 and E_a2) of amorphous ribbons calculated from Kissinger model were 448, 385 and 396 kJ/mol for the first and the second crystallizations, respectively. The Avrami exponent n was calculated from the Johnson–Mehl–Avrami (JMA) equation and was used to identify the crystallization mechanism for the amorphous ribbons. The ribbons were milled into different sized flakes, which were molded subsequently to cores using 3 wt.% epoxy as a binder. The effective permeability of the cores showed high frequency stability and increased with the size of the flakes. For the cores made from small sized flakes (? 75 μm), the quality factor was increased at high frequencies, which was attributed to the reduction in the eddy current loss.     

Variation of crystallization mechanisms in flash-lamp-irradiated amorphous silicon films

Flash lamp annealing (FLA) can form polycrystalline silicon (poly-Si) films with various microstructures depending on the thickness of precursor amorphous Si (a-Si) films due to the variation of crystallization mechanisms. Intermittent explosive crystallization (EC) takes place in precursor a-Si films thicker than approximately 2 μm, and the periodicity of microstructure formed resulting from the intermittent EC is independent of the thickness of a-Si films if their thickness is 2 μm or greater. In addition to the intermittent EC, continuous EC and homogeneous solid-phase crystallization (SPC) also occur in thinner films. These crystallization mechanisms are governed by the ignition of EC at Si film edges and the homogeneous heating of interior a-Si. The results obtained in this study could be applied to control the microstructures of flash-lamp-crystallized poly-Si films.     

Electrical properties of AsxSe1−x (x ≤ 0.05) Mott-barriers

We have experimentally measured the current-voltage and capacitance-voltage characteristics of Au/amorphous As_xSe_1 − x (x ≤ 0.05)/Zr trilayer structures at temperatures from 4 to 295 K. The observed capacitance of structures with an amorphous As_xSe_1 − x (a-As_xSe_1 − x) thickness of ~ 0.4 to ~ 2.8 μm does not significantly change over the entire range of applied bias (− 5 V to 5 V), indicating that the a-As_xSe_1 − x films are fully depleted and thus the structures are Mott barriers. The current-voltage (I-V) characteristics of the a-As_0.03Se_0.97 device at low (< 3000 V/cm) to moderate fields (3000 V/cm-10000 V/cm) follow the predictions of trap limited space charge conduction theory, as they exhibit Ohmic behavior at low fields and trap limited space charge current at moderate fields. According to the trap limited space charge current model of Lampert, the a-As_0.03Se_0.97 film has an effective hole mobility, Θμ (with Θ < 1), of ~ 5 × 10^− 7 cm²/V-sec at 295 K. This value is similar to, but consistently lower than previously reported mobilities inferred from time of flight measurements. The current at high fields (> 10⁴ V/cm) increases rapidly with applied field as a result of carrier emission from localized states and is consistent with transport by the Poole-Frenkel mechanism. A permanent transition to a high conductance state (~ 10^− 3 S) is observed after exposure to very high electric fields (~ 4 × 10⁵V/cm).