Numerical Study of Air Compressibility During Horizontal Pneumatic Transport

Using numerical simulations, the effect of the compressibility of air on the flow pattern of particles and pressure drop in the presence of particles during horizontal pneumatic transport operating under negative pressure was examined. The length and inside diameter of the pipeline were 30 m and 40 mm, respectively, and the chosen particles (4 mm in diameter) had densities of ρ_p = 1000 and 2000 kg/m³. The mean air velocities at pipe the inlet were U_inlet = 19, 22, and 28 m/s, and the range of the mass flow rate ratios of particle to air, μ, was varied up to 2.0. For a given inlet air velocity, the difference in the flow pattern between compressible and incompressible flow calculation is generally small. For ρ_p = 1000 kg/m³ particles the additional pressure drop in compressible flow increases when μ is above 0.5 and U_inlet is 28 m/s, μ is above 1.3 and U_inlet is 22 m/s, and μ is above 1.5 and U_inlet is 19 m/s. In these cases, the particle flow pattern is homogeneous. For ρ_p = 2000 kg/m³ particles, the pressure drop increases only when μ is above 1.5 and U_inlet is 28 m/s. The difference is not noticeable when the particle flow pattern is heterogeneous. Also, the difference in the additional pressure drop is much larger during homogeneous flow than heterogeneous flow.     

Aluminum Dross Particles as Cost Effective Reinforcement for Aluminum Composites

In this work, the potential of Finely powdered aluminum dross by-product (d₅₀ = 67 (μm) as a cost effective reinforcement in discontinuously reinforced aluminum matrix composites (A356) was investigated on the basis of quality-cost modeling. Using a standard rheocasting procedure, samples of composite material were obtained consisting of 20 vol.% of as-received and laboratory processed grades of dross particles which differed mainly in particle size and level of impurities.

Inspection of the tensile properties of these different composite materials showed that a slight improvement in strength over the unreinforced matrix is achievable only by the introduction of fine dross particles with an average particle size less than 10 μm. In composites with larger dross particles the strengthening effect was not observed. In contrast, evaluation of the wear properties demonstrated that the introduction of coarse and as-received dross particles in an aluminum matrix results in a significant improvement in the wear resistance of the composite material. However, in that case, there is a sacrifice in strength. Quality-cost modeling of these two grades of dross reinforced aluminum based composites indicates that both may be applicable for some less critical engineered and wear resistant components, with possible widespread application in the transportation industry.     

MASS TRANSFER OF SULFUR DIOXIDE TO CONDENSING AQUEOUS AEROSOLS

Sodium chloride aerosols were generated from a 1.0 percent solution and passed through a tubular furnace, then recondensed at 29°C in a cooling section in the presence of SO₂. The dry particles ranged from 0.711 to 0.843 µm and the condensed droplets were in the 1.66 to 2.88 µm range. Final droplet size was varied by controlling the temperature of the nebulizer solution between 17 and 50°C. The SO₂ concentration in the gas phase of the condensing cloud was varied between 0.5x10 - ³ and 2.5 xl0 - ³ atm.

Cloud droplets were separated from the gas stream in a point-to-plane electrostatic precipitator and the droplets analyzed colorimetrically for total sulfur content.

Concentrations of SO₂ in the aqueous phase were about one order of magnitude greater than values obtained from equilibrium constants. The collection rate of SO₂ at 29°C appeared to be first order in SO₂ gas phase concentrations.

A model for this process was constructed, based on the hydrate formation in the gas-water interface[SO₂]_g + n[H₂O]ℓ ⇋ [SO₂ · n(H₂O)]ℓ

The order of the hydrate n was estimated to be 4.0.     

RE-ENTRAINMENT OF DUSTS FROM THE DUST LAYER ON THE THE DEPOSITED DUSTS IN THE CYCLONE DUST COLLECTORS

There were many papers concerning the experimental results of the collection efficiency, but up to this time there are a few papers concerning the experimental results of the re-entrainment or dispersion of the dust particles from the dust layer by the turbulent rotational air flow in the dust bunker for the cyclone dust collector. Then in this paper, the author described the experimental results of the re-entrainment of the test dust ( talc X_R50 = 8.O µm ) for the four kinds of the throat diameter D₃ = 50, 80, 100 and 150 mm. Especially it is very importance to take into consideration of flow rate Qb into the dust bunker which is a function of D₃ and cyclone diameter D₁ and the maximum tangential velocity Vet in the dust bunker which depends on D₁,D₃ and Qb.     

Influence of a Weak Magnetic Field on Photoconductivity Spectrum of C60 Single Crystal

Comparative research of the excitation photoconductivity spectra (quantum light energy 2-5 eV) of C₆₀ single crystal in and out of magnetic field at the temperature T = 250-350 K has been carried. The spectral evolution at this temperature range is described. It is shown that the spectra changes abrupt at temperature T₁ ∼ 260 K and T₂ ∼ 315 K. An increase in the photoconductivity up to 15% was observed in the magnetic field (B = 0.4 T) within the photon energy range 2.5-4.5 eV. Local photoconductivity peak's appearances in the magnetic field have been proven that the charge transfer excitons take part in a photoconductivity.     

Deposition of HfO2 thin films on ZnS substrates

HfO₂ thin films with columnar microstructure were deposited directly on ZnS substrates by electron beam evaporation process. SiO₂ thin films, deposited by reactive magnetron sputtering, were used as buffer layers, HfO₂ thin films of granular microstructure were obtained on SiO₂ interlayer by this process. X-ray diffraction patterns demonstrate that the as-deposited HfO₂ films are in an amorphous-like state with small amount of crystalline phase while the HfO₂ films annealed at 450 °C in O₂ for 30 min and in Ar for 150 min underwent a phase transformation from amorphous-like to monoclinic phase. Antireflection effect in certain infrared wave band, such as 3–6 μm, 4–12 μm, 4–8 μm and 3–10 μm, can be observed, which was dependent on the thickness of thin films. The cross-sectional images of HfO₂ films, obtained by field emission scanning electron microscopy, revealed that there was no distinct morphological change upon annealing.     

DUST STRANDS IN CYCLONE SEPARATORS AT LOW DUST CONCENTRATION

State of the art in calculating a cyclone separator is the application of the equilibrium theory and taking the formation of dust strands into account as well. The latter process does not depend on particle size mainly. An ideal flow pattern for the formation of dust strands is the so called Dean-vortex: it is being realized favorably in the axial flow cyclone. A dust strand can be produced down to a raw gas concentration C₀ ≈ 10^-5. Then, it is being exhausted through one or few holes in the mantle of the axial cyclone applying bleeding of about 10 % of the volume flow Separating its dust in a bin cyclone and recirculating the binflow gas to the main, axial cyclone completes this high performance cyclone separator. Dimensional analysis shows that the clean gas concentration c₁ mainly depends on the swirl W_tan/w_ax, the raw gas concentration c₀and on Reynolds number. For usual dust conditions a clean gas concentration c₁ ≤ 50 mg/m³ is feasible.     

Traps identification in silicon nanocrystals memories by low noise technique

This work reports the extraction of oxide traps properties of n-metal–oxide–semiconductor field-effect transistors with W × L = 0.5 × 0.1 μm² using random telegraph signals (RTS) techniques. RTS study of nc-Si has been performed on thin tunnel oxides from 0.8 to 2.0 nm. RTS signals were two or more levels switching events observed on the drain current of transistors with and without nc-Si. The simple two levels RTS₁ noise was observed on samples without nc-Si. On transistors with nc-Si we distinguish two different RTSs (RTS₂ and RTS₃). RTS signal variations with temperature have shown that there's three slow interfacial traps located at E_c — 0.26 eV (trap1), E_c — 0.23 eV (trap2) and E_c — 0.2 eV (trap3). The spatial localization of traps 1, 2 and 3 from the Si–SiO₂ interface are determined using numerical simulations (x_Trap1 ≈ 0.6 nm, x_Trap2 ≈ 0.8 nm and x_Trap3 ≈ 0.4 nm). RTS noise observed on these devices is attributed to traps localized precisely at the interface thermal oxide/deposited control oxide. (RTS₁) noise is attributed to trap1 and (RTS₂, RTS₃) to traps 2 and 3. From RTS analysis in frequency domain, we extract the power spectrum density of the drain current noise (PSD). From these PSDs we have measured the cut-off frequencies of a single trap even at very low frequencies (for RTS₁ noise f_c = 5 Hz (trap1) and for RTS₂ noise f_c1 = 2 Hz (trap2), f_c2 = 130 Hz (trap3)). These results are in good agreement with those obtained by analysis in time domain and confirm the localization of each trap from the Si–SiO₂ interface.     

Effect of Particle Size on Deformation and Compaction Characteristics of Ascorbic acid and Potassium Chloride: Neat and Granulated Drug

Deformation and compaction characteristics of two soluble drugs, ascorbic acid and potassium chloride, were investigated. Five different particle size fractions of ascorbic acid with mean particle size (d₅₀) ranging from 30-300μm and four different particle size fractions of potassium chloride with d₅₀ ranging from 20-400 μm were selected in the study. The compaction behavior of the drug substances as neat drugs or as granulated drugs were evaluated on both a Carver press and an instrumented single-punch tablet press. The results clearly show that mean particle size of the drug substances plays an important role in their compactibility. Intrinsic compactibility of both drug substances was slightly improved with increased particle size. Granulations of the drugs with polyvinyl pyrrolidone significantly improved their compactibility. However, this effect was more pronounced in the drug substance with finer particle size. The Heckel plots indicate that deformation characteristics of both granulated drugs were related to their original mean particle sizes. The granulations prepared from the coarser particle size (d₅₀ 250 μm to 400 μm) underwent two stages of deformation, so-called “brittle fracture” and “plastic deformation”. While the granulations prepared from the finer particle size predoninantly underwent “plastic deformation”. The results indicated that the plastic deformation of both granulated drugs was progressively enhanced whilst fragmentation of particles was correspondingly reduced as the particle size of the drugs was decreased. Scanning electron photomicrographs indicated that the granulation process changed the surface morphology of the drug particles imparting more “microirregularities” or “defects”, thereby providing greater “interparticulate bonding” as compared with the neat drugs. Optimum particle size range of ascorbic acid and potassium chloride for satisfactory compactibility was found to be 30-40 μm and 20-40 μm, respectively. The present study demonstrates the importance of selecting the appropriate particle size of drug for the development of tablet dosage forms.     

DISTRIBUTIONS OF THE TANGENTIAL VELOCITIES ON THE DUST LADEN GAS FLOW IN THE CYLINDRICAL CYCLONE DUST COLLECTOR

The authors measured the distributions of the tangential velocities of the feed dust concentration C_o = 0. 6 ~15. 0 g/ m³ by the hot wire anemometers. The test dust was fly-ash which had the mean diameter Xpn = 2.03 μm. The used cylindrical cyclone had the diameter D1 = 140 mm, the diameter of the exit pipe D2 = 50 mn and the total length HT = 382 mm. In order to measure the fluctuating velocities and the time mean velocity on the dust Iaden gas flow and on the pure air flow, we had applied two kinds of the hot-wires. The flow Reynolds number Rec was Rec = Qo/HiV = 797~5582. The expert mental results sho-ed that there were no distinct differences of the time mean and fl uctuating velocities between the pure air flow and the dust laden gas flow. Then the authors have tried to explain those expert mental results by the response time of the fine solid particles and that of the scale of the nixing length in the turbulent rotational air flow.     

Simultaneous Deposition of Powder in Three Parallel-Oriented Cylindrical Dies

The inhomogeneity of bulk density distribution created during the die filling process might cause quality problems for powder compacts, such as distortion, lamination, and cracking. To avoid these problems, understanding the die filling process and ensuring a uniform pre-compaction powder deposition are necessary. The second-generation pressure deposition tester (PDT-II) was developed to investigate simultaneous deposition of powder into multiple dies. Its design requirements and new features were proposed through evaluating the main strength and limitations of the mass deposition tester (MDT). The operation of the PDT-II and analysis of its data showed that it generates real-time deposition profiles of the entire process for multiple locations. PDT-II data can be used to study the effects of various filling-related parameters (such as die shape, powder flowability, and feed shoe speed) on the deposition process and final pressure distribution. For cylindrical dies filled with a granulated powder with d₅₀ = 600 μm (1) at low feed shoe speeds (20 and 100 mm/s), the half circle close to the leeward end had higher final pressure values than the forward half circle; (2) at high feed shoe speed (500 mm/s), the final pressure distribution was more uniform than at lower feed shoe speed; (3) the final within-die pressure distribution at the bottom of the dies was not always symmetrical about the center line of the feed shoe movement direction, even though sometimes it was quite symmetrical; (4) the overall trend was that pressure decreases with increasing radial distance for lower feed shoe speeds; and (5) higher feed shoe speed (500 mm/s) resulted in higher final pressure values (774.5 to 1424.5 Pa) than lower feed shoe speeds (20 and 100 mm/s) (235.2 to 1136.0 Pa) at most of the locations. The results proved that feed shoe speed does have an effect on pressure distribution and its uniformity.     

Synthesizing and Physical Properties of GdPr-123 High-Tc Superconductor

Ceramic Gd_1-xPr_xBa₂Cu₃O_7-y (GdPr-123) high-T_c superconductors have been synthesized by the standard solid state reaction method and characterized by XRD, SEM, TGA, and DT techniques in the range of x, 0.0 ≤ x ≤ 1.0 Samples have orthorhombic structure with Pmmm symmetry and there is a small percentage (less than 1%) of the Ba sites occupied by Pr ions in some Pr-rich samples. In these samples a small trace of BaCuO₂ and Pr BaO₃ secondary phases persist with the main peaks at 2θ = 29.3° and 28.9° respectively. Microstructure analysis indicates a uniform grain size distribution with a mean size of 5 μm. No significant change of grain size is shown throughout the range of x studied. The valence of Pr and Cu were determined by magnetization measurements in the temperature range 100 to 250°K. These data reveal a valence of 3.86+ for Pr in all samples independant of x. The similarity of the superconducting and insulating properties in this system to those of the oxygen deficient RBa₂Cu₃O₇ (R-123) (R: Y or rare earth) system implies that the mechanism of superconductivity in high-T_c. superconductors cannot be two-dimensional, even though the superconductive current occurs in two dimensions.     

Elaboration, microstructure and reactivity of Cr3C2 powders of different morphology

Cr₃C₂ powders have been prepared by heat-treatment of metastable chromium oxides of controlled morphology in H₂---CH₄ atmosphere. Starting with these highly reactive oxides allows formation of Cr₃C₂ at 700 °C. The reaction is pseudomorphic and different grain shapes (needles, rods, spheres and polyhedra) have been obtained. The size distribution is narrow and the grain size is generally of the order of a few tens of micrometers, but the “spheres” are in fact made up of aggregates of small platelets about 1.5 μm wide and 0.7 μm thick. The oxidation in air of the carbides was studied by thermal analyses (TGA, DTG and DSC) and was found to proceed in four steps in the 250–700 °C range. The differences observed between the carbides are related to their morphology and texture.     

Investigation of CdTex and Cd1-xZnxTe Schottky Barrier Diode Structure Based γ-Ray Detectors

Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) based detectors have been developed for hard X-ray and γ -ray detection. These semiconducting materials have high resistivity because of the wide bandgap and also have high photon absorption efficiency because of the large atomic number (Z_Cd = 48, Z_Te = 52). CdTe and CdZnTe substrates (7 mm × 9 mm × 0.5 mm) with different stoichiometry were taken for the fabrication of γ-ray detectors. The substrate was prepared by polishing the bulk crystals grown by the rotational Bridgman method. Crystals with maximum electrical resistivity were grown in this way. For fabrication of Schottky barrier diode structures, the Schottky contacts were made by electroless deposition for gold (Au) and thermal evaporation for Indium (In). The Au/CdTe/In and Au/CdZnTe/In Schottky barrier diodes were linked to the charge sensitive preamplifier by gold wires. Then, I-V measurement and detector efficiency like charge collection performance with energy resolutions were analyzed at room temperature by using ⁵⁷Co and ¹³⁷Cs gamma sources. The good energy resolutions of ⁵⁷Co (122 KeV) and ¹³⁷Cs (662 KeV) sources are obtained for both CdTe and CdZnTe diode detectors.     

Chemical vapour deposition of praseodymium oxide films on silicon: influence of temperature and oxygen pressure

Metal-organic chemical vapour deposition (MOCVD) of various phases in PrO_x system has been studied in relation with deposition temperature (450–750 °C) and oxygen partial pressure (0.027–100 Pa or 0.2–750 mTorr). Depositions were carried out by pulsed liquid injection MOCVD using Pr(thd)₃ (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) precursor dissolved in toluene or monoglyme. By varying deposition temperature and oxygen partial pressure amorphous films or various crystalline PrO_x phases (Pr₂O₃, Pr₇O₁₂, Pr₆O₁₁) and their mixtures can be grown. The pure crystalline Pr₂O₃ phase grows only in a narrow range of partial oxygen pressure and temperature, while high oxygen pressure (40–100 Pa) always leads to the most stable Pr₆O₁₁ phase. The influence of annealing under vacuum at 750 °C on film phase composition was also studied. Near 90% step coverage conformity was achieved for PrO_x films on structured silicon substrates with aspect ratio 1:10. In air degradation of Pr₂O₃ films with transformation to Pr(OH)₃ was observed in contrast to Pr₆O₁₁ films.     

LED Lighting Configurations for Visual Inspection of IC Packages

This article discusses configurations of light-emitting diode (LED) light sources for visual inspection of integrated circuit (IC) packages. A package visual inspection (PVI) system with multiple LED light sources used for inspection of IC packages was designed. The image contrast changes of the sample IC packages are explained using the Torrance-Sparrow (TS) model. A few conclusions on appropriate lighting configurations for inspection of various IC packages are achieved. The TS model can be used to represent the specular lobe component. The contrast between two surfaces with different surface roughness values increases with increasing θ_i (incident light angle). Lighting C (θ_i = 75°) is recommended for packages with high surface roughness heights and resin materials. Lighting B (θ_i = 60°) is recommended for packages with moderate surface roughness heights and metal materials. If the background is white, the use of light sources A (θ_i = 15°) and B simultaneously is recommended. Light sources A and C are recommended to be chosen for packages with low surface roughness values and transparent materials. The experimental results with the actual gray-level values of the images are compared to support the conclusions. The PVI system is part of an inspection machine. All images of the sample IC packages reported in this article were obtained from an actual production line. Therefore, the results are close to those of the actual inspection situation in the manufacturing industry.     

Optical gain calculation of mid-infrared InAsN/GaSb quantum-well laser for tunable absorption spectroscopy applications

We report on optical gain calculations of a dilute-nitride mid-infrared laser structure designed to be grown on InAs substrate. The active region is composed of several strain-compensated type-II “W”-like InAsN/GaSb/InAsN quantum wells adapted to operate near 3.3 μm at room temperature. For typical injected carrier density σ = 1.1012 cm^− 2, the theoretical laser structure performances reveal a gain value at around 1000 cm^− 1 at 300 K, inducing a modal gain value equal to 50 cm^− 1. Low radiative current densities lower than 100 A/cm² are predicted, indicating that this dilute-nitride structure could operate at 300 K with small threshold current density.     

Atmospheric plasma discharge chemical vapor deposition of SnOx thin films using various tin precursors

A series of 0.2–0.6 μm thick SnO_x films were deposited onto borosilicate and sodalime silica glass substrates by atmospheric plasma discharge chemical vapor deposition at 80 °C. SnO_x films deposited from monobutyltin trichloride contained a large percentage of SnCl₂:2H₂O, and therefore were partially soluble in water. SnO_x coatings deposited from tetrabutyltin were not soluble in water or organic solvents, had good adhesion even at growth rates as high as 2.3 nm/s, had high transparency of  90% and electrical resistivity of 10⁷ Ω cm. As-grown tin oxide coatings were amorphous with a small concentration of SnO₂, SnO and Sn crystalline phases as determined by grazing angle X-ray diffraction and X-ray photoelectron spectroscopy measurements. Upon annealing in air at 600 °C the resistivity of SnO_x films decreased to 5–7 Ω cm. Furthermore, optical and X-ray measurements indicated that SnO_x was converted into SnO₂ (cassiterite) with a direct band gap of 3.66 eV. Annealing of as-grown SnO_x films in vacuum at 340 °C led to formation of the p-type conductor SnO/SnO_x. The indirect band gap of SnO was calculated from the optical spectra to be 0.3 eV.     

Spectroscopic Evidence for Anionic Coordination Complexes of the Transition Metals with C70 and the Higher Fullerenes C76, C78, C82, C84, C86, C90, and C92

The carbonylate anions [M(CO)₅]^- (M = Mn, Re), [Co(CO)₄]^-, [CpFe(CO)₂]^-, and [CpM(CO)₃]^- (M = Mo, W) react with C₇₀ via single electron transfer processes to give, respectively, the corresponding 17-electron, metal-centered radicals Co(CO)₄, M(CO)₅ (M = Mn, Re), CpFe(CO)₂, and CpM(CO)₃ (M = Mo, W) in addition to the radical anion C₇₀^-. In secondary thermal or photochemical processes, the metal-centered radicals Co(CO)₄ and M(CO)₅ (M = Mn, Re) combine with the C₇₀^- to form the new η²-C₇₀ complexes [Co(CO)₃(η²-C₇₀)]^- and [M(CO)₄(η²-C₇₀)]^-. However, the metal-centered radicals CpM(CO)₃ (M = Mo, W) require photolysis to react with C₇₀^- to form [CpM(CO)₂(η²-C₇₀)]^-, whereas neither thermolysis nor photolysis induces reaction between CpFe(CO)₂ and C₇₀^-. The photochemical reaction of [Mn(CO)₅]^- with a mixture of higher fullerenes known to contain at least C₇₆, C₇₈, C₈₄, C₈₆, and C₉₀ resulted similarly in the formation of the higher fullerene complexes [Mn(CO)₄(η²-C_n)]^- (n = 76, 78, 80, 82, 84, 86, 88, 90, 92, 96, and 98), all identified using electrospray mass spectrometry.     

Discharge Characteristics of Polydisperse Powders through Conical Hoppers. Part 2: Predictions for Coarse, Granular, Free Flowing Powders

Discharge characteristics of coarse polydisperse granular powders through a conical hopper are experimentally investigated. The average discharge rates of four different powder types are systematically measured for seven different diameters of hopper orifice under gravity flow conditions. Each powder type is a mixture of some sub-sizes (smaller than 3 mm) of same powder material. Effects of orifice diameter of hopper and size distribution of polydisperse powders on discharge characteristics are experimentally determined. The measured discharge data are compared with discharge values predicted by using modified forms of the well-known Beverloo correlation. The volume-moment-mean diameter, d_VM, and the 50% weight fraction diameter, d₅₀, cited in available literature are both checked to characterize the coarse polydisperse powders and used throughout the predictions. Comparisons implied that both d_VM and d₅₀ diameters can be successfully used to characterize polydisperse test powders, and discharge rate predictions are in good agreement with experimental data, with mean deviations lower than ±4.04%.