MICROFABRICATION OF CYLINDRICAL ION TRAP MASS SPECTROMETER ARRAYS FOR HANDHELD CHEMICAL ANALYZERS

A new microfabrication method for micro-cylindrical ion trap (μ-CIT) mass spectrometer arrays (r _o , z _o  ? 360 μm) is presented along with a strategy for incorporating integrated high-field emission electron sources for ionization. Simulations of the performance of μ-CITs were used to guide the geometrical design of the array, and process flows for microfabrication in silicon were developed and optimized for reduced capacitance. The microfabrication process is described in detail along with initial test results. Field emission sources were also fabricated in silicon using an edge-to-edge emission strategy to improve robustness in moderate vacuum environments. Simulations were also used to guide the design of the field emitter arrays. The microfabrication process is described and initial field emission data are presented. Strategies for further optimization and integration are also briefly discussed.     

DRYING OF CARROTS IN A FLUIDIZED BED. I. EFFECTS OF DRYING CONDITIONS AND MODELLING

Drying curves were determined in a mechanically agitated fluidized bed dryer, at temperatures between 70°C and 160°C, air velocities between 1.1 m/s and 2.2 m/s and stirring rates between 30 rpm and 70 rpm for batch drying of 3 kg lots of carrot slices, measuring the moisture content and shrinking of the particles in time. This was complemented by a study of the rate and degree of swelling of dried carrot particles in water between 20 and 75°C. Drying kinetics were modeled by Fick's second law, for which an optimal agreement with the experimental data was obtained when the effective diffusivity (D_e) was determined by a correlation based on the air velocity (v), the air temperature (T) and the dimensional moisture content of the carrot particles (X/X_o). Loss of carotenes is minimized when dehydration is carried out at about 130°C with a drying time below 12 min.     

Electrical resistivity and thermopower of (La1−xSrx)MnO3 and (La1−xSrx)CoO3 at elevated temperatures

Electrical resistivity and Seebeck (S) measurements were performed on (La_1−xSr_x)MnO₃ (0.02x0.50) and (La_1−xSr_x)CoO₃ (0x0.15) in air up to 1073 K. (La_1−xSr_x)MnO₃ (x0.35) showed a metal-to-semiconductor transition; the transition temperature almost linearly increased from 250 to 390 K with increasing Sr content. The semiconductor phase above the transition temperature showed negative values of S. (La_1−xSr_x)CoO₃ (0x0.10) showed a semiconductor-to-metal transition at 500 K. Dominant carriers were holes for the samples of x0.02 above room temperature. LaCoO₃ showed large negative values of S below ca. 400 K, indicative of the electron conduction in the semiconductor phase.     

Electrical ageing of carbon nanotube composite cathode layers

Effect of electrical ageing (EA) on the field emission parameters of thin multiwall carbon nanotube composite (t-MWCNTs-composite) was studied. Initially, t-MWCNTs were mixed with -terpineol and ethyl cellulose and subjected to three roll milling process to obtain t-MWCNTs-composite. Following this, the composite was screen printed on a conducting substrate, annealed for 10 min and employed to the electrical ageing process for a period of 6 h. The ageing, on each cathode layer, was repeated for five times and J–E characteristics have been collected before and after each ageing attempt. The analysis revealed that, the magnitude of threshold turn-on-field gradually increased from its virgin value of 1.223 to 1.968 V µm^− 1 and corresponding mean field enhancement factor, γ_m, gradually decreased from 2700 ± 210 to 1940 ± 30 with a sequential increase in the ageing attempts. The degradation rate, δJ/δt, estimated for untreated and EA samples, indicated that the magnitude of δJ/δt reached to an equilibrium value of ~ 0.785 μA cm^− 2 min^− 1, which shows a stable emission state of the emitters. To investigate the effect of EA on the physical state of the emitters, a few virgin and all EA samples were subjected to scanning electron microscopy, micro Raman spectroscopy and X-ray photoelectron spectroscopy. The details of the analysis are presented.     

Thermoelectric characterization of NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe) polycrystalline materials

Layered -titanate materials, Na_xM_x/2Ti_1−x/2O₂ (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na_0.4Ni_0.2Ti_0.8O₂ were ca. 7×10³ S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm⁻¹ K⁻¹ at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na_0.4Ni_0.2Ti_0.8O₂ and Na_0.4Co_0.2Ti_0.8O₂ was about 1.9×10⁻⁴ and 1.2×10⁻⁴ K⁻¹ around 700 °C, respectively.     

Study of the impedance of a platinum electrode in the system Br2/Br (HClO4, aq.)—II. Mechanism of the electrode reaction

The Randles circuit well represents impedance measurements carried out with activated Pt electrodes. This enables us to study the variation of j_o for redox reactions with concentration of the reactants, at constant potential, and also the variation of j_o with potential, keeping constant the concentration of one of the reactants. The results thus obtained indicate that the step Br₂ + e Br₂⁻ is rate-determining; it is followed or preceded by the rapid equilibria Br₂⁻ Br⁻ + Br 2Br Br₂. The mechanisms proposed hitherto for the electrochemical behaviour of the halogen/halide systems at inert electrodes are discussed, and it is reasoned that the ‘reversibility’ of these systems increases in the order Cl₂/Cl⁻ < Br₂/Br⁻ < I₂/I.     

Effect of Cryoprotectant and Freeze-Drying Process on the Stability of W/O/W Emulsions

In order to protect a hydrophilic drug and to prolong its further delivery, the formulation of multiple emulsions could be worthy. However, the double emulsions are not stable, their structure can change, leading to the formation of a single emulsion as the destruction of the system, and the drug can release easily from the globules in liquid state. The freeze-drying technology could be used to produce dry emulsion, the powder form being much more stable. The aim of this work was to study the influence of a cryoprotectant and a freeze-drying process on the stability of W/O/W emulsions. Samples were frozen at two different freezing rate (ν_f = 0.55°C/min and 1.25°C/min) and successively dried at two different sublimation temperature (T_s = - 10°C and - 20°C). The particle size distributions were measured by granulometer and UV spectrophotometer was performed to investigate the leakage of internal constituent. The glass transition temperature (T_g) of the double emulsions was analyzed by DSC. The particle sizes became even smaller after freeze drying, except when κ-carrageenan is used as a cryoprotectant. In that case, the particles became aggregated after freeze drying, whatever the process conditions. The mean size is considerably reduced when the globules are diluted at low concentration in glucose and trehalose solution. When the concentration is increased, the size distribution is not significantly affected. The leakage of the internal aqueous phase to the external one during freeze drying was measured as an indicator of the structure stability. It is affected by the nature of the cryoprotectant and the conditions of the freeze-drying process. The leakage of the internal phase was smaller when cycle III (ν_f = 1.25°C/min, T_s = - 10°C) was processed. From our experiments, we suppose that the water transfer from the inner phase to the outer aqueous phase results in the diminution of the globules size in double emulsion. The T_g of the double emulsions diluted with trehalose and glucose were determined at - 33.8°C and - 47.1°C. In contrast, the T_g of double emulsion with κ-carrageenan and HES did not appear.     

PRODUCTION OF HYDROCORTISONE MICRO- AND NANO-PARTICLES USING SUPERCRITICAL ANTI-SOLVENT WITH ENHANCED MASS TRANSFER

Supercritical anti-solvent precipitation with enhanced mass transfer (SAS-EM) is used for the formation of particles of hydrocortisone (HC), an anti-inflammatory drug. This technique is similar to the supercritical anti-solvent process but uses a reflecting horn surface that vibrates at 20 kHz frequency, which enhances the mass transfer of the solvent to supercritical fluid anti-solvent, reducing the growth of the particles. Controllable sizes and morphologies of HC particles are obtained using the SAS-EM process. At a power supply of 0 watts (to ultrasonic transducer), HC fibers of an average length of ∼81 μm and an average diameter of ∼6 μm are obtained. Upon increasing the power supply to 120 watts, which enhances mass transfer, particles of average size as low as 180 nm are obtained. Intermediate particle size and morphology are easily obtained by adjusting the power supply to the desired intermediate value. The obtained powder is free of impurities and is mostly amorphous.     

Thermal conductivity of nanocomposites based on diamonds and nanodiamonds

The thermal conductivity of composites sintered from natural microdiamond (5–7 and 10–14 μm) and nanodiamond powders under pressure of  6.0 to 6.5 GPa at the temperature  1000 to 2000 °C for 6–20 s was measured in a steady heat flow in the temperature range of 50–200 °C. It was found that the thermal conductivity of nanodiamond composites produced in these conditions was less than 10 W/(mК) while that of natural microdiamonds was as high as 500 W/(mК).     

WATER MIST FLOW IN A SUPERCONDUCTING MAGNET INCLINED AT VARIOUS ANGLES

Water mist (diamagnetic) flow in a superconducting magnet of 10 T at various angles is studied experimentally and numerically. Water mist is produced by ultrasonic atomizers and fed into a cylindrical Plexiglas pipe (inner diameter, 90 mm) placed in a bore space of an inclined superconducting magnet. The water mist is found to stop at some locations in the magnet at inclined angles ψ ≤ π/6. At ψ ≥ π/4, the amount of mist flowing out of the other opening of the pipe increases with an increase in inclined angle. In the computation of this phenomenon, water mist is simulated with 1000 water droplets of 3 μm diameter. Brownian motion is considered and the Langevin equation is solved. The numerical results show that at ψ ≤ π/6, most of the water droplets accumulate above the magnetic coil. However, at ψ ≥ π/4, with an increase in inclined angle, the number of water droplets passing through the magnetic coil increases.     

Synthesis and properties of lanthanum hexaaluminate ceramic La1−xCaxAl11−y−zMgyTizO18

The aim of the present work is to obtain ceramic materials with a hexagonal structure and high density, hardness and mechanical strength at lower synthesis temperature. Ceramic samples with nominal composition La_1−xCa_xAl_11−y−zMg_yTi_zO₁₈ (x=0–1; y=0–3; z=0–3,5) are prepared. The samples are sintered at temperature 1500 °C by one-stage and two-stage ceramic technology. By X-ray diffraction and scanning electron microscopy, predominant phase LaAl₁₁O₁₈ and second phases LaAlO₃ and -Al₂O₃ are identified. Ceramic materials are characterized with high physico-mechanical properties and may be find application for production of mill bodies and materials for immobilization of nuclear waste.     

AN EXPERIMENTAL STUDY OF A TURBULENT ROUND TWO-PHASE JET

The effect of solid particles on the flow structure of an axisymmetric turbulent incompressible jet has been studied. A two-color laser anemometer was used to measure the mean and fluctuating velocity components along the axial and radial directions as well as the corresponding component of the shear stress. 50 μ and 200 μ glass beads were used. Results for the 200 μ case are presented for moderate mass loadings (mass ratio = 0.8, volumetric ratio = 3.5 × 10^-4)which indicates ignificant influence of the solid phase on the flow structure. Results for the 50 μ. case are reported elsewhere.1 When compared with the single-phase measurement, the spread rate of the two-phase jet was found to be smaller and a lower level of turbulence was observed.     

EFFECT OF SHEAR STRESS ON PLATELET-PMN LEUKOCYTE INTERACTIONS

A cone and plate viscometer, Coulter counter, and spectrophotometer were used to study platelet modulation of polymorphonuclear leukocyte (PMNL) function caused by controlled shear stress. Aggregation and release of the enzymes β-glucuronidase and lactate dehydrogenase (LDH) were observed. PMNL suspensions in buffer (1.0 × 10⁷ cells/ml, final concentration) did not show any aggregate formation or enzyme release at shear stresses below 150 dynes/cm² for an exposure time of 1 minute. However, supernatant plasma from sheared platelets initiated PMNL aggregation and β-glucuronidase release at moderate shear stresses (150 dynes/cm² for 1 minute). These stress-induced alterations were compared with chemotactic factor and calcium ionophore A23187 induced functional changes. LDH release was less than 3% in all the experiments indicating little overt lysis. The shear-induced enzyme release was enhanced by cytochalasin B and heparinized samples showed greater effects than citrated samples. The use of a cyclooxygenase inhibitor (acetylsalicyclic acid, 50 μM) did not suppress the aggregation of PMNLs after shear. However, preincubation with lipoxygenase inhibitors (nordihydroguaiaretic acid, 10 μM, and U-60257, 10 μM) suppressed aggregation and enzyme release. The formation of arachidonic acid metabolites activated by shear stress was documented by reversed phase-high pressure liquid chromatography. Thus, an interaction between C-12 and C-5 lipoxygenase enzymes can promote the formation of leukotriene B₄ and these data strongly support the possibility of a cooperation between platelet and PMNL arachidonic acid metabolites in shear-induced PMNL functional changes.     

Role of wollastonite additive on density, microstructure and mechanical properties of alumina

Wollastonite is a low fusing material and has a considerable effect on the densification of alumina bodies at sintering temperatures ranging from 1300 to 1450 °C. The wollastonite acts as a flux and accelerates the liquid forming process leading to lower temperature densification. The addition of 1.0 wt.% wollastonite alters the microstructure to form well-defined grains with an average grain size in the range of 3.0–5.0 μm. The grains are distributed uniformly and the fracture occurs along the grain boundaries and the microstructure reveals the presence of highly dense and sintered grains. The hardness and bend strength for 0–5.0 wt.% wollastonite increases from 8.5 to 14 GPa and from 119 to 249 MPa respectively at a sintering temperature of 1400 °C.     

Influence of purge gas on the characteristics of lead–zirconium–titanate thin films prepared by metalorganic chemical vapor deposition

In order to optimize the metalorganic chemical vapor deposition process for PbZr_xTi_1−xO₃ (PZT) thin films, the effect of purge gas species was investigated. Two steps of gas input process for stabilizing reaction chamber pressure, the gas flow prior to PbTiO₃ (PTO) seed layer deposition and PZT thin film deposition, were varied and their effect on structural and electrical properties were examined with regard to the memory device application. PZT film properties exhibited remarkable dependency on the gas species before PTO seed deposition, and insignificant dependency on the gas species before PZT film deposition. With the optimized pre-deposition gas flow, PZT thin film showed excellent properties such as high (1 1 1)-orientation (92.2%), high remnant polarization value of 71 μC/cm² at 3 V. Retention property also showed a heavy dependency on the pre-deposition gas flow that 91.1% of initial charge could be maintained after 100 h of baking at 150 °C.     

Surface engineering of diamond tips for improved field electron emission

Results are reported on the study of surface engineering of diamond microtips for improved field electron emission. Two-dimensional (2D) arrays of diamond pyramids were prepared using a molding technique. As-grown diamond pyramids of 3 and 9 μm in size with sharp apexes were insulating and showed a relatively poor field electron emission. Several ways are examined to provide an electrical conductivity of diamond in order to supply electrons for the emission: diamond boron doping, partial graphitization/amorphization by nitrogen ion implantation and/or high temperature annealing, formation of built-in conductive metal layers. A perceptible improvement of surface electrical conductivity and reduction of field electron emission thresholds down to 10 V/μm was observed. For explanation of the results it was enough to take into account only the geometric field enhancement on pyramids apexes.     

Synthesis, densification and electrical properties of strontium cerate ceramics

Powders of pure and 5% ytterbium substituted strontium cerate (SrCeO₃/SrCe_0.95Yb_0.05O_3−δ) were prepared by spray pyrolysis of nitrate salt solutions. The powders were single phase after calcination in nitrogen atmosphere at 1100 °C (SrCeO₃) and 1200 °C (SrCe_0.95Yb_0.05O_3−δ). Dense SrCeO₃ and SrCe_0.95Yb_0.05O_3−δ materials were obtained by sintering at 1350–1400 °C in air. Heat treatment at 850 and 1000 °C, respectively, was necessary prior to sintering to obtain high density. The dense materials had homogenous microstructures with grain size in the range 6–10 μm for SrCeO₃ and 1–2 μm for SrCe_0.95Yb_0.05O_3−δ. The electrical conductivity of SrCe_0.95Yb_0.05O_3−δ was in good agreement with reported data, showing mixed ionic–electronic conduction. The ionic contribution was dominated by protons below 1000 °C and the proton conductivity reached a maximum of 0.005 S/cm above 900 °C. In oxidizing atmosphere the p-type electronic conduction was dominating above 700 °C, while the contribution from n-type electronic conduction only was significant above 1000 °C in reducing atmosphere.     

Effect of macromolecular length on anisotropic scattering of light in an electric field

Light scattering by monodisperse solutions of rigid rod-like anisotropic macromolecules, with linear dimensions l of the order of incident wavelength λ, oriented in an external d.c. electric field, →E has been analysed. The relative variations δV^E_v, δH^E_v, δV^E_h, δH^E_h of the scattered light components are discussed for the three values [l/λ] = 1, 0·5, 2, and various reorientation parameters, p = [μE/kT] of the permanent dipole moment μ and q = [(₃ − ₁)E²/2kT] of the moment induced by the principal polarizabilities ₁ = ₂ ≠ ₃. The saturation orientation field strength has been calculated for certain macromolecules with the aim of determining their optical anisotropy numerically.     

Simple fabrication process of a screen-printed triode-CNT field emitter array

We introduced a simple fabrication process for field emission devices based on carbon nanotubes (CNTs) emitters. Instead of using the ITO material as a transparent electrode, a metal (Au) with thickness of 5–20 nm was used. Moreover, the ITO patterning process was eliminated by depositing metal layer, before the CNT printing process. In addition, the thin metal layer on a photoresist (PR) layer was used as UV block. We fabricated the CNT field emission arrays of triode structure with a simple process. And I–V characteristics of field emission arrays were measured. The maximum current density of 254 μA/cm² was achieved when the gate and the anode voltages were kept 150 and 3000 V, respectively. The distance between anode and cathode was kept constant.     

Top-spray fluid bed coating: Scale-up in terms of relative droplet size and drying force

Top-spray fluid bed coating scale-up experiments have been performed in three scales in order to test the validity of two parameters as possible scaling parameters: The drying force and the relative droplet size. The aim was to be able to reproduce the degree of agglomeration as well as the mechanical properties of the coated granules across scale. Two types of placebo enzyme granule cores were tested being non-porous glass ballotini cores (180–350 μm) and low porosity sodium sulphate cores (180–350 μm). Both types of core materials were coated with aqueous solutions of Na₂SO₄ using Dextrin as binder. Coating experiments were repeated for various drying force and relative droplet size values in three top-spray fluid bed scales being a small-scale (Type: GEA Aeromatic-Fielder Strea-1), medium-scale (Type: Niro MP-1) and large-scale (Type: GEA MP-2/3). The tendency of agglomeration was assessed in terms of particle size fractions larger than 425 μm determined by sieve analysis. Results indicated that the particle size distribution may be reproduced across scale with statistical valid precision by keeping the drying force and the relative droplet size constant across scale. It is also shown that none of the two parameters alone may be used for successful scaling. Morphology and microscope studies indicated that the coating layer is homogenous and has similar structures across scale only when both the drying force and the relative droplet size were fixed. Impact and attrition tests indicated that it is possible to produce granules with similar attrition and impact strength across scale and that the two types of mechanical properties are inversely related.