Headspace Analysis of Smokeless Powders: Development of Mass Calibration Methods using Microdrop Printing for Chromatographic and Ion Mobility Spectrometric Detection

Smokeless powder additives are usually detected by their extraction from post-blast residues or unburned powder particles followed by analysis using chromatographic techniques. This work presents the first comprehensive study of the detection of the volatile and semi-volatile additives of smokeless powders using solid phase microextraction (SPME) as a sampling and pre-concentration technique. Seventy smokeless powders were studied using laboratory based chromatography techniques and a field deployable ion mobility spectrometer (IMS). The detection of diphenylamine, ethyl and methyl centralite, 2,4-dinitrotoluene, diethyl and dibutyl phthalate by IMS to associate the presence of these compounds to smokeless powders is also reported for the first time. A previously reported SPME-IMS analytical approach facilitates rapid sub-nanogram detection of the vapor phase components of smokeless powders. A mass calibration procedure for the analytical techniques used in this study was developed. Precise and accurate mass delivery of analytes in picoliter volumes was achieved using a drop-on-demand inkjet printing method. Absolute mass detection limits determined using this method for the various analytes of interest ranged between 0.03 - 0.8 ng for the GC-MS and between 0.03 - 2 ng for the IMS. Mass response graphs generated for different detection techniques help in the determination of mass extracted from the headspace of each smokeless powder. The analyte mass present in the vapor phase was sufficient for a SPME fiber to extract most analytes at amounts above the detection limits of both chromatographic techniques and the ion mobility spectrometer. Analysis of the large number of smokeless powders revealed that diphenylamine was present in the headspace of 96% of the powders. Ethyl centralite was detected in 47% of the powders and 8% of the powders had methyl centralite available for detection from the headspace sampling of the powders by SPME. Nitroglycerin was the dominant peak present in the headspace of the double-based powders. 2,4-dinitrotoluene which is another important headspace component was detected in 44% of the powders. The powders therefore have more than one headspace component and the detection of a combination of these compounds is achievable by SPME-IMS leading to an association to the presence of smokeless powders.

MOVPE growth and characterization of Al(Ga)N and InAlN/AlGaN quantum wells for UV LED applications

The study of III-nitride materials (InN, GaN and AlN) gained huge research momentum after breakthroughs in the production light emitting diodes (LEDs) and laser diodes (LDs) over the past two decades. Last year, the Nobel Prize in Physics was awarded jointly to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for inventing a new energy efficient and environmental friendly light source: blue light-emitting diode (LED) from III-nitride semiconductors in the early 1990s. Nowadays, III-nitride materials not only play an increasingly important role in the lighting technology, but also become prospective candidates in other areas, for example, the high frequency (RF) high electron mobility transistor (HEMT) and photovoltaics. These devices require the growth of high quality III-nitride films, which can be prepared using metal organic vapour phase epitaxy (MOVPE). The main aim of my thesis is to study and develop the growth of III-nitride films, including AlN, u-AlGaN, Si-doped AlGaN, and InAlN, serving as sample wafers for fabrication of ultraviolet (UV) LEDs, in order to replace the conventional bulky, expensive and environmentally harmful mercury lamp as new UV light sources. For application to UV LEDs, reducing the threading dislocation density (TDD) in AlN epilayers on sapphire substrates is a key parameter for achieving high-efficiency AlGaNbased UV emitters. In Chapter 4, after careful and systematic optimisation， a working set of conditions, the screw and edge type dislocation density in the AlN were reduced to around 2.2×108 cm-2 and 1.3×109 cm-2 , respectively, using an optimized three-step process, as estimated by TEM. An atomically smooth surface with an RMS roughness of around 0.3 nm achieved over 5×5 µm 2 AFM scale. Furthermore, the motion of the steps in a one dimension model has been proposed to describe surface morphology evolution, especially the step bunching feature found under non-optimal conditions. In Chapter 5, control of alloy composition and the maintenance of compositional uniformity across a growing epilayer surface were demonstrated for the development of u-AlGaN epilayers. Optimized conditions (i.e. a high growth temperature of 1245 °C) produced uniform and smooth film with a low RMS roughness of around 2 nm achieved in 20×20 µm 2 AFM scan. The dopant that is most commonly used to obtain n-type conductivity in AlxGa1-xN is Si. However, the incorporation of Si has been found to increase the strain relaxation and promote unintentional incorporation of other impurities (O and C) during Si-doped AlGaN growth. In Chapter 6, reducing edge-type TDs is observed to be an effective appoach to improve the electric and optical properties of Si-doped AlGaN epilayers. In addition, the maximum electron concentration of 1.3×1019 cm-3 and 6.4×1018 cm-3 were achieved in Si-doped Al0.48Ga0.52N and Al0.6Ga0.4N epilayers as measured using Hall effect. Finally, in Chapter 7, studies on the growth of InAlN/AlGaN multiple quantum well (MQW) structures were performed, and exposing InAlN QW to a higher temperature during the ramp to the growth temperature of AlGaN barrier (around 1100 °C) will suffer a significant indium (In) desorption. To overcome this issue, quasi-two-tempeature (Q2T) technique was applied to protect InAlN QW. After optimization, an intense UV emission from MQWs has been observed in the UV spectral range from 320 to 350 nm measured by room temperature photoluminescence.

Mercury content and isotopic composition of frost flower, surface snow and brine samples near Barrow, Alaska

Frost flowers are ice crystals that grow on refreezing sea ice leads in Polar Regions by wicking brine from the sea ice surface and accumulating vapor phase condensate. These crystals contain high concentrations of mercury (Hg) and are believed to be a source of reactive halogens, but their role in Hg cycling and impact on the fate of Hg deposited during atmospheric mercury depletion events (AMDEs) are not well understood. We collected frost flowers growing on refreezing sea ice near Barrow, Alaska (U.S.A.) during an AMDE in March 2009 and measured Hg concentrations and Hg stable isotope ratios in these samples to determine the origin of Hg associated with the crystals. We observed decreasing Delta199Hg values in the crystals as they grew from new wet frost flowers (mean Delta199Hg = 0.77 ± 0.13 per mil, 1 s.d.) to older dry frost flowers (mean Delta199Hg = 0.10 ± 0.05 per mil, 1 s.d.). Over the same time period, mean Hg concentrations in these samples increased from 131 ± 6 ng/L (1 s.d.) to 180 ± 28 ng/L (1 s.d.). Coupled with a previous study of Hg isotopic fractionation during AMDEs, these results suggest that Hg initially deposited to the local snowpack was subsequently reemitted during photochemical reduction reactions and ultimately accumulated on the frost flowers. As a result of this process, frost flowers may lead to enhanced local retention of Hg deposited during AMDEs and may increase Hg loading to the Arctic Ocean.

Experimental and analytical investigation of refrigerant and lubricant migration

The off-cycle refrigerant mass migration has a direct influence on the on-cycle performance since compressor energy is necessary to redistribute the refrigerant mass. No studies, as of today, are available in the open literature which experimentally measured the lubricant migration within a refrigeration system during cycling or stop/start transients. Therefore, experimental procedures measuring the refrigerant and lubricant migration through the major components of a refrigeration system during stop/start transients were developed and implemented. Results identifying the underlying physics are presented. The refrigerant and lubricant migration of an R134a automotive A/C system-utilizing a fixed orifice tube, minichannel condenser, plate and fin evaporator, U-tube type accumulator and fixed displacement compressor-was measured across five sections divided by ball valves. Using the Quick-Closing Valve Technique (QCVT) combined with the Remove and Weigh Technique (RWT) using liquid nitrogen as the condensing agent resulted in a measurement uncertainty of 0.4 percent regarding the total refrigerant mass in the system. The determination of the lubricant mass distribution was achieved by employing three different techniques-Remove and Weigh, Mix and Sample, and Flushing. To employ the Mix and Sample Technique a device-called the Mix and Sample Device-was built. A method to separate the refrigerant and lubricant was developed with an accuracy-after separation-of 0.04 grams of refrigerant left in the lubricant. When applying the three techniques, the total amount of lubricant mass in the system was determined to within two percent. The combination of measurement results-infrared photography and high speed and real time videography-provide unprecedented insight into the mechanisms of refrigerant and lubricant migration during stop-start operation. During the compressor stop period, the primary refrigerant mass migration is caused by, and follows, the diminishing pressure difference across the expansion device. The secondary refrigerant migration is caused by a pressure gradient as a result of thermal nonequilibrium within the system and causes only vapor phase refrigerant migration. Lubricant migration is proportional to the refrigerant mass during the primary refrigerant mass migration. During the secondary refrigerant mass migration lubricant is not migrating. The start-up refrigerant mass migration is caused by an imbalance of the refrigerant mass flow rates across the compressor and expansion device. The higher compressor refrigerant mass flow rate was a result of the entrainment of foam into the U-tube of the accumulator. The lubricant mass migration during the start-up was not proportional to the refrigerant mass migration. The presence of water condensate on the evaporator affected the refrigerant mass migration during the compressor stop period. Caused by an evaporative cooling effect the evaporator held 56 percent of the total refrigerant mass in the system after three minutes of compressor stop time-compared to 25 percent when no water condensate was present on the evaporator coil. Foam entrainment led to a faster lubricant and refrigerant mass migration out of the accumulator than liquid entrainment through the hole at the bottom of the U-tube. The latter was observed for when water condensate was present on the evaporator coil because-as a result of the higher amount of refrigerant mass in the evaporator before start-up-the entrainment of foam into the U-tube of the accumulator ceased before the steady state refrigerant mass distribution was reached.

Vapor–liquid equilibrium of binary mixtures containing isopropyl acetate and alkanols at 101.32 kPa

Isobaric vapor-liquid equilibria of binary mixtures of isopropyl acetate plus an alkanol (1-propanol, 2-propanol, 1-butanol, or 2-butanol) were measured at 101.32 kPa, using a dynamic recirculating still. An azeotropic behavior was observed only in the mixtures of isopropyl acetate + 2-propanol and isopropyl acetate + 1-propanol. The application of four thermodynamic consistency tests (the Herington test, the Van Ness test, the infinite dilution test, and the pure component test) showed the high quality of the experimental data. Finally, both NRTL and UNIQUAC activity coefficient models were successfully applied in the correlation of the measured data, with the average absolute deviations in vapor phase composition and temperature of 0.01 and 0.16 K, respectively.

Impact of potassium and phosphorus in biomass on the properties of fast Pyrolysis bio-oil

This study investigates fast pyrolysis bio-oils produced from alkali-metal-impregnated biomass (beech wood). The impregnation aim is to study the catalytic cracking of the pyrolysis vapors as a result of potassium or phosphorus. It is recognized that potassium and phosphorus in biomass can have a major impact on the thermal conversion processes. When biomass is pyrolyzed in the presence of alkali metal cations, catalytic cracking of the pyrolysis liquids occurs in the vapor phase, reducing the organic liquids produced and increasing yields of water, char, and gas, resulting in a bio-oil that has a lower calorific value and an increased chance of phase separation. Beech wood was impregnated with potassium or phosphorus (K impregnation and P impregnation, respectively) in the range of 0.10-2.00 wt %. Analytical pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) was used to examine the pyrolysis products during thermal degradation, and thermogravimetric analysis (TGA) was used to examine the distribution of char and volatiles. Both potassium and phosphorus are seen to catalyze the pyrolytic decomposition of biomass and modify the yields of products. 3-Furaldehyde and levoglucosenone become more dominant products upon P impregnation, pointing to rearrangement and dehydration routes during the pyrolysis process. Potassium has a significant influence on cellulose and hemicellulose decomposition, not just on the formation of levoglucosan but also other species, such as 2(5H)-furanone or hydroxymethyl-cyclopentene derivatives. Fast pyrolysis processing has also been undertaken using a laboratory-scale continuously fed bubbling fluidized-bed reactor with a nominal capacity of 1 kg h-1 at the reaction temperature of 525 °C. An increase in the viscosity of the bio-oil during the stability assessment tests was observed with an increasing percentage of impregnation for both additives. This is because bio-oil undergoes polymerization while placed in storage as a result of the inorganic content. The majority of inorganics are concentrated in the char, but small amounts are entrained in the pyrolysis vapors and, therefore, end up in the bio-oil.

Acetic acid ketonization over Fe3O4/SiO2 for pyrolysis bio-oil upgrading

A family of silica supported, magnetite nanoparticle catalysts was synthesized and investigated for continuous flow acetic acid ketonization as a model pyrolysis bio-oil upgrading reaction. Physicochemical properties of Fe3O4/SiO2 catalysts were characterized by HRTEM, XAS, XPS, DRIFTS, TGA and porosimetry. Acid site densities were inversely proportional to Fe3O4 particle size, although acid strength and Lewis character were size invariant, and correlated with the specific activity for vapor phase acetic ketonization to acetone. A constant activation energy (~110 kJ.mol-1), turnover frequency (~13 h-1) and selectivity to acetone of 60 % were observed for ketonization across the catalyst series, implicating Fe3O4 as the principal active component of Red Mud waste.

Modeling of phase equilibrium and vapor adsorption on carbon black based on a combination of a lattice theory and equation of state

A thermodynamic approach is developed in this paper to describe the behavior of a subcritical fluid in the neighborhood of vapor-liquid interface and close to a graphite surface. The fluid is modeled as a system of parallel molecular layers. The Helmholtz free energy of the fluid is expressed as the sum of the intrinsic Helmholtz free energies of separate layers and the potential energy of their mutual interactions calculated by the 10-4 potential. This Helmholtz free energy is described by an equation of state (such as the Bender or Peng-Robinson equation), which allows us a convenient means to obtain the intrinsic Helmholtz free energy of each molecular layer as a function of its two-dimensional density. All molecular layers of the bulk fluid are in mechanical equilibrium corresponding to the minimum of the total potential energy. In the case of adsorption the external potential exerted by the graphite layers is added to the free energy. The state of the interface zone between the liquid and the vapor phases or the state of the adsorbed phase is determined by the minimum of the grand potential. In the case of phase equilibrium the approach leads to the distribution of density and pressure over the transition zone. The interrelation between the collision diameter and the potential well depth was determined by the surface tension. It was shown that the distance between neighboring molecular layers substantially changes in the vapor-liquid transition zone and in the adsorbed phase with loading. The approach is considered in this paper for the case of adsorption of argon and nitrogen on carbon black. In both cases an excellent agreement with the experimental data was achieved without additional assumptions and fitting parameters, except for the fluid-solid potential well depth. The approach has far-reaching consequences and can be readily extended to the model of adsorption in slit pores of carbonaceous materials and to the analysis of multicomponent adsorption systems. (C) 2002 Elsevier Science (USA).

The structural and piezoresponse properties of c-axis-oriented Aurivillius phase Bi5Ti3FeO15 thin films deposited by atomic vapor deposition

The deposition by atomic vapor deposition of highly c-axis-oriented Aurivillius phase Bi 5Ti 3FeO 15 (BTFO) thin films on (100) Si substrates is reported. Partially crystallized BTFO films with c-axis perpendicular to the substrate surface were first deposited at 610°C (8 excess Bi), and subsequently annealed at 820°C to get stoichiometric composition. After annealing, the films were highly c-axis-oriented, showing only (00l) peaks in x-ray diffraction (XRD), up to (0024). Transmission electron microscopy (TEM) confirms the BTFO film has a clear layered structure, and the bismuth oxide layer interleaves the four-block pseudoperovskite layer, indicating the n 4 Aurivillius phase structure. Piezoresponse force microscopy measurements indicate strong in-plane piezoelectric response, consistent with the c-axis layered structure, shown by XRD and TEM.

New prediction methods for CO2 evaporation inside tubes: Part I - A two-phase flow pattern map and a flow pattern based phenomenological model for two-phase flow frictional pressure drops

An updated flow pattern map was developed for CO2 on the basis of the previous Cheng-Ribatski-Wojtan-Thome CO2 flow pattern map [1,2] to extend the flow pattern map to a wider range of conditions. A new annular flow to dryout transition (A-D) and a new dryout to mist flow transition (D-M) were proposed here. In addition, a bubbly flow region which generally occurs at high mass velocities and low vapor qualities was added to the updated flow pattern map. The updated flow pattern map is applicable to a much wider range of conditions: tube diameters from 0.6 to 10 mm, mass velocities from 50 to 1500 kg/m(2) s, heat fluxes from 1.8 to 46 kW/m(2) and saturation temperatures from -28 to +25 degrees C (reduced pressures from 0.21 to 0.87). The updated flow pattern map was compared to independent experimental data of flow patterns for CO2 in the literature and it predicts the flow patterns well. Then, a database of CO2 two-phase flow pressure drop results from the literature was set up and the database was compared to the leading empirical pressure drop models: the correlations by Chisholm [3], Friedel [4], Gronnerud [5] and Muller-Steinhagen and Heck [6], a modified Chisholm correlation by Yoon et al. [7] and the flow pattern based model of Moreno Quiben and Thome [8-10]. None of these models was able to predict the CO2 pressure drop data well. Therefore, a new flow pattern based phenomenological model of two-phase flow frictional pressure drop for CO2 was developed by modifying the model of Moreno Quiben and Thome using the updated flow pattern map in this study and it predicts the CO2 pressure drop database quite well overall. (C) 2007 Elsevier Ltd. All rights reserved.

Effects of repetitive stress during the acute phase of Trypanosoma cruzi infection on chronic Chagas` disease in rats

The effect of repetitive stress during acute infection with Trypanosoma cruzi (T. cruzi) on the chronic phase of ensuing Chagas` disease was the focus of this investigation. The aim of this study was to evaluate in Wistar rats the influence of repetitive stress during the acute phase of infection (7 days) with the Y strain of T. cruzi on the chronic phase of the infection (at 180 days). Exposure to ether vapor for 1min twice a day was used as a stressor. Repetitive stress enhanced the number of circulating parasites and cardiac tissue disorganization, from a moderate to a severe diffuse mononuclear inflammatory process and the presence of amastigote burden in the cardiac fibers. Immunological parameters revealed that repetitive stress triggered a reduced concanavalin A induced splenocyte proliferation in vitro with major effects on the late chronic phase. Serum interleukin-12 concentration decreased in both stressed and infected rats in the early phase of infection although it was higher on 180 days post-infection. These results suggest that repetitive stress can markedly impair the host`s immune system and enhance the pathological process during the chronic phase of Chagas` disease.

Hysteresis and phase transitions in a single partially internally wetted catalyst pellet: Thermogravimetric studies

The hydrogenation of cyclohexene over palladium supported in a microporous gamma-alumina pellet is studied thermogravimetrically with a view to measuring the extent of partial internal wetting associated with the different steady state branches. As many as three steady state branches having significantly different degrees of internal wetting and reaction rates, with transitions between them, are confirmed from observations of catalyst weight change. It is seen that with reduction in catalyst activity the middle branch, obtained by condensation from a vapor filled pellet, is much more prominent without showing an evaporative transition for the range of hydrogen partial pressures used here. The catalyst activity is therefore an important parameter affecting the structure of the steady state branches. Hysteresis effects are found to occur, and the thermogravimetric results also confirm the importance of history in determining the catalyst state. The measured degree of wetting is in accordance with that estimated from a mathematical model incorporating capillary condensation effects in addition to reaction-diffusion phenomena. The same model also satisfactorily interprets the reaction rate variations and transitions seen in the present work.

A modified pore-filling isotherm for liquid-phase adsorption in activated carbon

This article modifies the usual form of the Dubinin-Radushkevich pore-filling model for application to liquid-phase adsorption data, where large molecules are often involved. In such cases it is necessary to include the repulsive part of the energy in the micropores, which is accomplished here by relating the pore potential to the fluid-solid interaction potential. The model also considers the nonideality of the bulk liquid phase through the UNIFAC activity coefficient model, as well as structural heterogeneity of the carbon. For the latter the generalized adsorption integral is used while incorporating the pore-size distribution obtained by density functional theory analysis of argon adsorption data. The model is applied here to the interpretation of aqueous phase adsorption isotherms of three different esters on three commercial activated carbons. Excellent agreement between the model and experimental data is observed, and the fitted Lennard-Jones size parameter for the adsorbate-adsorbate interactions compares well with that estimated from known critical properties, supporting the modified approach. On the other hand, the model without consideration of bulk nonideality, or when using classical models of the characteristic energy, gives much poorer bts of the data and unrealistic parameter values.

Finite, three-dimensional adsorbed phase growth in activated carbon mesopores

The role of PACs (primary adsorption centers) in the mesopore (i.e., transport) region of activated carbons during adsorption of polar species, such as water, is unclear. A classical model of three-dimensional adsorption on finite PACs is presented. The model is a preliminary, theoretical investigation into adsorption on mesopore PACs and is intended to give some insight into the energetic and physical processes at work. Work processes are developed to obtain isotherms and three-dimensional sorbate growth on PACs of varying size and energetic characteristics. The work processes allow two forms of adsorbed phase growth: densification at constant boundary and boundary growth at constant density. Relatively strong sorbate-sorbent interactions and strong surface tension favor adsorbed phase densification over boundary growth. Conversely, relatively weak sorbate-sorbent interactions and weak surface tension favor boundary growth over densification. If sorbate-sorbate interactions are strong compared to sorbate-sorbent interactions, condensation with hysteresis occurs. This can also give rise to delayed boundary growth, where all initial adsorption occurs in the monolayer only. The results indicate that adsorbed phase growth on PACs may be quite complex.