Showing papers on "Atmospheric pressure published in 2009"

Atmospheric Pressure Plasma Jet for Medical Therapy: Plasma Parameters and Risk Estimation

Abstract: A set of minimum standards which have to be adjusted if a plasma source is intended for therapeutic applications has been defined. The main performance parameters of an optimized low-temperature atmospheric pressure plasma source were investigated and controlled. This has been done to discuss global risk factors that have to be avoided during application. By using this minimum standard set of parameters it should become possible to directly compare different atmospheric plasma sources for special biomedical applications and to derive optimum treatment parameters found on different sources and locations. Up to now a strict comparison is mainly done indirectly by investigating the effect of the plasma treatment on the surface. Temperature, thermal load, UV radiation, production of radicals and toxic gases and the resulting biological effects have been investigated to minimize risk factors and to indicate first meaningful parameter ranges (dosages) for therapeutic applications. The mix of these parameters (like mixing a cocktail) has to be adapted individually for each application. For practical use constant energetic conditions at the visible tip of the investigated jet could be observed, therefore it could be recommended to adjust the visible tip of the pen in such a way that it just touches the surface.

Nanosecond repetitively pulsed discharges in air at atmospheric pressure—the glow regime

Abstract: In atmospheric-pressure air preheated to 1000 K, nanosecond repetitively pulsed (NRP) discharges are shown to generate three plasma discharge regimes. In addition to the well-known corona and spark regimes, there exists a glow-like regime that develops through an initial cathode-directed streamer, followed by a return wave of potential redistribution. The applied electric field is then switched off before the formation of the cathode fall, resulting in an 'imminent' glow discharge. Previously, this regime had been observed only at 2000 K in air at atmospheric pressure. Measurements of the plasma dynamics, current–voltage characteristics, gas temperature and plasma chemistry of the excited species N2(B), N2(C), , NO(A) and O(3p 5P) in the pulsed glow regime are presented. Using 10 ns pulses applied repetitively at 30 kHz, we find that this glow regime generates an estimated electron number density of 1013 cm−3, while consuming only 1–10 µJ per pulse and heating the gas by less than 200 K.

Characterization of MgSO4 Hydrate for Thermochemical Seasonal Heat Storage

Abstract: Water vapor sorption in salt hydrates is one of the most promising means for compact, low loss, and long-term storage of solar heat in the built environment. One of the most interesting salt hydrates for compact seasonal heat storage is magnesium sulfate heptahydrate MgSO4 ·7H 2O. This paper describes the characterization of MgSO4 ·7H 2 Ot o examine its suitability for application in a seasonal heat storage system for the built environment. Both charging (dehydration) and discharging (hydration) behaviors of the material were studied using thermogravimetric differential scanning calorimetry, X-ray diffraction, particle distribution measurements, and scanning electron microscope. The experimental results show that MgSO4 ·7H 2O can be dehydrated at temperatures below 150° C, which can be reached by a medium temperature (vacuum tube) collector. Additionally, the material was able to store 2.2 GJ/ m 3 , almost nine times more energy than can be stored in water as sensible heat. On the other hand, the experimental results indicate that the release of the stored heat is more difficult. The amount of water taken up and the energy released by the material turned out to be strongly dependent on the water vapor pressure, temperature, and the total system pressure. The results of this study indicate that the application of MgSO4 ·7H 2O at atmospheric pressure is problematic for a heat storage system where heat is released above 40° C using a water vapor pressure of 1.3 kPa. However, first experiments performed in a closed system at low pressure indicate that a small amount of heat can be released at 50° C and a water vapor pressure of 1.3 kPa. If a heat storage system has to operate at atmospheric pressure, then the application of MgSO4 ·7H 2O for seasonal heat storage is possible for space heating operating at 25° C and a water vapor pressure of 2.1 kPa. DOI: 10.1115/1.4000275

Anomalies in water as obtained from computer simulations of the TIP4P/2005 model: density maxima, and density, isothermal compressibility and heat capacity minima

Abstract: The so-called thermodynamic anomalies of water form an integral part of the peculiar behaviour of this both important and ubiquitous molecule. In this paper our aim is to establish whether the recently proposed TIP4P/2005 model is capable of reproducing a number of these anomalies. Using molecular dynamics simulations we investigate both the maximum in density and the minimum in the isothermal compressibility along a number of isobars. It is shown that the model correctly describes the decrease in the temperature of the density maximum with increasing pressure. At atmospheric pressure the model exhibits an additional minimum in density at a temperature of about 200K, in good agreement with recent experimental work on super-cooled confined water. The model also presents a minimum in the isothermal compressibility close to 310K. We have also investigated the atmospheric pressure isobar for three other water models; the SPC/E and TIP4P models also present a minimum in the isothermal compressibility, although...

Atmospheric Circulation Trends, 1950–2000: The Relative Roles of Sea Surface Temperature Forcing and Direct Atmospheric Radiative Forcing

Abstract: The relative roles of direct atmospheric radiative forcing (due to observed changes in well-mixed greenhouse gases, tropospheric and stratospheric ozone, sulfate and volcanic aerosols, and solar output) and observed sea surface temperature (SST) forcing of global December–February atmospheric circulation trends during the second half of the twentieth century are investigated by means of experiments with an atmospheric general circulation model, Community Atmospheric Model, version 3 (CAM3). The model experiments are conducted by specifying the observed time-varying SSTs and atmospheric radiative quantities individually and in combination. This approach allows the authors to isolate the direct impact of each type of forcing agent as well as to evaluate their combined effect and the degree to which their impacts are additive. CAM3 realistically simulates the global patterns of sea level pressure and 500-hPa geopotential height trends when both forcings are specified. SST forcing and direct atmosphe...

On the effect of the atmosphere on the evaporation of sessile droplets of water

Abstract: An experimental and theoretical study of the effect of the atmosphere on the evaporation of pinned sessile droplets of water is described. The experimental work investigated the evaporation rates of sessile droplets in atmospheres of three different ambient gases (namely, helium, nitrogen, and carbon dioxide) at reduced pressure (from 40 to 1000 mbars) using four different substrates (namely, aluminum, titanium, Macor, and polytetrafluoroethylene) with a wide range of thermal conductivities. Reducing the atmospheric pressure increases the diffusion coefficient of water vapor in the atmosphere and hence increases the evaporation rate. Changing the ambient gas also alters the diffusion coefficient and hence also affects the evaporation rate. A mathematical model that takes into account the effect of the atmospheric pressure and the nature of the ambient gas on the diffusion of water vapor in the atmosphere and the thermal conductivity of the substrate is developed, and its predictions are found to be in encouraging agreement with the experimental results.

Generation of atomic oxygen in the effluent of an atmospheric pressure plasma jet

Abstract: The planar 13.56 MHz RF-excited low temperature atmospheric pressure plasma jet (APPJ) investigated in this study is operated with helium feed gas and a small molecular oxygen admixture. The effluent leaving the discharge through the jet's nozzle contains very few charged particles and a high reactive oxygen species' density. As its main reactive radical, essential for numerous applications, the ground state atomic oxygen density in the APPJ's effluent is measured spatially resolved with two-photon absorption laser induced fluorescence spectroscopy. The atomic oxygen density at the nozzle reaches a value of ~1016 cm−3. Even at several centimetres distance still 1% of this initial atomic oxygen density can be detected. Optical emission spectroscopy (OES) reveals the presence of short living excited oxygen atoms up to 10 cm distance from the jet's nozzle. The measured high ground state atomic oxygen density and the unaccounted for presence of excited atomic oxygen require further investigations on a possible energy transfer from the APPJ's discharge region into the effluent: energetic vacuum ultraviolet radiation, measured by OES down to 110 nm, reaches far into the effluent where it is presumed to be responsible for the generation of atomic oxygen.

Microwave-excited atmospheric-pressure microplasmas based on a coaxial transmission line resonator

Abstract: We report the design, fabrication and characterization of two microwave-excited microplasma sources based on coaxial transmission line resonators (CTLR). The sources are capable of generating electric fields of ~106 V m−1 at 900 MHz and 2.45 GHz. These devices can self-ignite helium or argon discharges in a wide pressure range including atmospheric pressure. The gas temperature in an argon discharge open to atmospheric air is ~400 K. Using air as a dielectric, the working gases can be passed through the CTLR, resulting in the formation of plasma jets suitable for surface treatments. The device efficiency on transferring the input power into the plasma is 50–85% depending on the gas used. No thermal damage or electrode erosion has been observed in the devices.

Pressure and preheat dependence of laminar flame speeds of H2/CO/CO2/O2/He mixtures

Abstract: Laminar flame speeds of lean H2/CO/CO2 (syngas) fuel mixtures have been measured for a range of H2 levels (20–90% of the fuel) at pressures and reactant preheat temperatures relevant to gas turbine combustors (15 atm and up to 600 K) A conical flame stabilized on a contoured nozzle is used for the flame speed measurement, which is based on the reaction zone area calculated from chemiluminescence imaging of the flame An O2:He mixture (1:9 by volume) is used as the oxidizer in order to suppress the hydrodynamic and thermo-diffusive instabilities that become prominent at elevated pressure conditions for lean H2/CO fuel mixtures All the measurements are compared with numerical predictions based on two leading kinetic mechanisms: a H2/CO mechanism from Davis et al and a C1 mechanism from Li et al The results generally agree with the findings of an earlier study at atmospheric pressure: (1) for low H2 content ( 60%) H2 content fuels, especially at very lean conditions At elevated pressure, however, the effect is less pronounced than at atmospheric conditions The exaggerated temperature dependence of the current models may be due to errors in the temperature dependence used for so-called “low temperature” reactions that become more important as the preheat temperature is increased There is also evidence of slight radiative heat transfer effects on the laminar flame speed for lean syngas mixtures associated with CO2 addition to the fuel (up to 40%) at elevated pressure and preheat temperature

Visualization of volatile substances in different organelles with an atmospheric-pressure mass microscope

Abstract: We have developed a mass microscope (mass spectrometry imager with spatial resolution higher than the naked eye) equipped with an atmospheric pressure ion-source chamber for laser desorption/ionization (AP-LDI) and a quadrupole ion trap time-of-flight (QIT-TOF) analyzer. The optical microscope combined with the mass spectrometer permitted us to precisely determine the relevant tissue region prior to performing imaging mass spectrometry (IMS). An ultraviolet laser tightly focused with a triplet lens was used to achieve high spatial resolution. An atmospheric pressure ion-source chamber enables us to analyze fresh samples with minimal loss of intrinsic water or volatile compounds. Mass-microscopic AP-LDI imaging of freshly cut ginger rhizome sections revealed that 6-gingerol ([M + K](+)at m/z 333.15, positive mode; [M - H](-) at m/z 293.17, negative mode) and the monoterpene ([M + K](+) at m/z 191.09), which are the compounds related to pungency and flavor, respectively, were localized in oil drop-containing organelles. AP-LDI-tandem MS/MS analyses were applied to compare authentic signals from freshly cut ginger directly with the standard reagent. Thus, our atmosphere-imaging mass spectrometer enabled us to monitor a quality of plants at the organelle level.

Effects of gas flow rate on the length of atmospheric pressure nonequilibrium plasma jets

Abstract: Effects of gas flow rate on the length of atmospheric pressure plasma jets have been investigated using a capillary dielectric barrier discharge configuration. For the discharge in only downstream region, three distinguishable modes of plasma jet length versus argon gas flow rate, namely, laminar, transition, and turbulent jet mode, have been identified. For the case of discharge in both downstream and upstream regions, the curve of length versus flow rate has significant “dent” in the laminar jet mode for pure helium, neon, and argon flow gas spraying into air ambient.

Time dependent optical emission spectroscopy of sub-microsecond pulsed plasmas in air with water cathode

Abstract: This paper reports an experimental study of sub-microsecond pulsed discharges between a metal pin electrode and a tap water cathode in atmospheric pressure air. The dynamics of excited molecular and atomic species produced in the discharge is investigated by time resolved optical emission spectroscopy. The initial diffuse plasma constricts around 300 ns after the start of the voltage pulse. This constriction is correlated with an increase in gas temperature from 1000 to 5000 K and a strong increase in emission from O (777 nm), Hα and NH(A–X). The formation of OH(A–X) is discussed in the framework of OH (and thus H2O2 production) in plasmas in and in contact with liquids. It is argued that electron dissociative recombination of the water ion plays an important role in the production of OH(A) and that the relative intensity of the OH(A) emission may not provide a good estimate of the OH concentration without correction for electronic quenching of OH(A).

Flame spread over electric wire in sub-atmospheric pressure

Abstract: Flame spread along the single wire harness (thin-metal wire with coating of polyethylene film) in sub-atmospheric pressure has been examined experimentally to gain better understandings of the electric fire in the aircraft and space habitats. Two kinds of sample wires, made by nickel-chrome (NiCr) and iron (Fe) as core metal, are used in this study. Ambient gas is fixed as air and total pressure is varied from atmospheric to sub-atmospheric (100–20 kPa). As the pressure decreases, flame shape changes from typical “teardrop” to “oval” and flame becomes less-luminous irrespective of the materials of the wire. It turns out that the dependence of the spread rate on pressure varies with the materials of the wire; when the pressure decreases, the spread rate of NiCr-harness monotonically increases, whereas that of Fe-harness mostly remains as constant. From the simple thermal-length analysis, it is proposed that there are two modes in the spread depending on the controlling factor; one is “wire-driven mode” (the spread is mainly governed by the thermal input through the wire) and the other is “flame-driven mode” (the spread is mainly governed by the thermal input from the flame). Observed two cases (NiCr- and Fe-harness) would be categorized to the latter and former modes, respectively.

The transition between different modes of barrier discharges at atmospheric pressure

Abstract: Barrier discharges (BDs) can be operated in so-called diffuse modes. In contrast to the usual filamentary regime, which is characterized by a large number of individual microdischarges, the plasma of a diffuse BD covers the entire electrode area uniformly. Depending on the operation conditions (gas composition, amplitude and frequency of applied voltage), different diffuse modes can be investigated, namely, the atmospheric pressure Townsend discharge (APTD) and the atmospheric pressure glow discharge (APGD). The subject of the paper is the study of the transition between APTD and APGD as well as between diffuse and filamentary BD modes. Therefore, BDs were studied in the gas mixtures N2/H2, N2/He, N2/Ne and N2/Ar. It is shown that APGD in the noble gases helium and neon is formed due to high ionization rate at a comparatively low electric field, assisted by indirect ionization mechanisms involving metastable states of inert gases and nitrogen impurities, while the existence of APTD is coupled to the existence of metastable states of molecular nitrogen. Furthermore, a similar memory effect of residual surface charges on the dielectric barriers as described for filamentary BDs was observed in diffuse BDs.

Organic–inorganic behaviour of HMDSO films plasma-polymerized at atmospheric pressure

Abstract: Recently, plasma-polymerization at atmospheric pressure has become a promising technology due to its reduced equipment costs and its possibility of in-line processing. This paper focuses on plasma deposition by an atmospheric pressure dielectric barrier discharge (DBD) using hexamethyldisiloxane (HMDSO) as gaseous precursor. HMDSO plasma-polymerized films are deposited onto polyethylene terephthalate (PET) films using argon and different argon/air mixtures as carrier gases. The chemical and physical properties of the obtained coatings are discussed using contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Contact angle and FTIR results show that the composition of the gas phase and the chemical structure of the obtained coatings are clearly correlated. When pure argon is used as working gas, the film is polymeric with a structure close to [(CH3)2–Si–O]n. However, with increasing air content, a gradual change is observed from organic polydimethylsiloxane-like coatings to inorganic, quartz-like deposits. AFM results clearly indicate that with increasing air content, the deposition rate decreases, while the surface of the deposited films becomes rougher. From this point of view, the capability of controlling both chemical and physical properties of the plasma-polymerized films by varying operation conditions opens interesting perspectives.

A simple atmospheric pressure room-temperature air plasma needle device for biomedical applications

Abstract: Rather than using noble gas, room air is used as the working gas for an atmospheric pressure room-temperature plasma. The plasma is driven by submicrosecond pulsed directed current voltages. Several current spikes appear periodically for each voltage pulse. The first current spike has a peak value of more than 1.5 A with a pulse width of about 10 ns. Emission spectra show that besides excited OH, O, N2(C–B), and N2+(B–X) emission, excited NO, N2(B–A), H, and even N emission are also observed in the plasma, which indicates that the plasma may be more reactive than that generated by other plasma jet devices. Utilizing the room-temperature plasma, preliminary inactivation experiments show that Enterococcus faecalis can be killed with a treatment time of only several seconds.

The acidification of lipid film surfaces by non-thermal DBD at atmospheric pressure in air

Abstract: We studied the acidifying efficiency of a cold atmospheric pressure plasma treatment and ambient air as a working gas on lipid films. Acidification of a thin water film could be observed on plasma-treated surfaces of wool wax, pork sebum and human lipids. This pH shift was partly attributable to NOx species and to the formation of nitric acid in the upper layers of the substrates. The acidic compounds on the lipid surfaces resulted in pH shifts for up to 2 h after plasma exposure, which might be beneficial for pH-targeted therapies in dermatology.

Neutral gas flow and ring-shaped emission profile in non-thermal RF-excited plasma needle discharge at atmospheric pressure

Abstract: We demonstrate that a balance between convective helium flow and ambient air diffusion creates a unique ring-shaped light emission profile by means of finite element analysis of the atmospheric pressure RF-excited plasma needle. The plasma needle has a point-to-plane geometry with a radius of 30 µm at the tip and an inter-electrode gap of 1 mm. We employ a coupled model between time-dependent plasma dynamics based on a fluid model and steady state neutral gas flow in two-dimensional cylindrical coordinates. When the mean inlet gas velocity is 1.5 m s−1 and the discharge is in high-power glow mode at 200 mW, the concentration of air drastically increases near a treated surface being away from the needle tip. As a result, Penning ionization by helium metastables and air (nitrogen) peaks at an off-axis position, corresponding to the ring-shaped emission profile in cylindrical coordinates. The off-axis ionization peak leads to an off-axis flux peak of nitrogen ions onto the treated surface. The 'ion wind' and gas heating have only minor effects on the discharge structure under the conditions considered here.

Is the rotational temperature of OH(A-X) for discharges in and in contact with liquids a good diagnostic for determining the gas temperature?

Abstract: In this paper the rotational temperature of OH(A-X) and rotational population distribution of OH(A) are investigated for streamer discharges in bubbles and glow discharges with liquid electrodes, both at atmospheric pressure. The influence of the filling gas is investigated in detail and the non-Boltzmann nature of the rotational population distributions is discussed. It is shown that the rotational population distribution of OH(A) is even at atmospheric pressure an image of the formation process or is at least influenced by it. As a consequence the rotational temperature is in this case not a good estimate of the gas temperature as the rotational population distribution is not an image of a kinetic temperature. In some cases rotational states with small rotational numbers offer a possibility to obtain the gas temperature. The influence of these results on the determination of gas temperatures in the field of liquid plasmas is discussed.

Plasma structures observed in gas breakdown using a 1.5 MW, 110 GHz pulsed gyrotron

Abstract: Regular two-dimensional plasma filamentary arrays have been observed in gas breakdown experiments using a pulsed 1.5 MW, 110 GHz gyrotron. The gyrotron Gaussian output beam is focused to an intensity of up to 4 MW/cm2. The plasma filaments develop in an array with a spacing of about one quarter wavelength, elongated in the electric field direction. The array was imaged using photodiodes, a slow camera, which captures the entire breakdown event, and a fast camera with a 6 ns window. These diagnostics demonstrate the sequential development of the array propagating back toward the source. Gases studied included air, nitrogen, SF6, and helium at various pressures. A discrete plasma array structure is observed at high pressure, while a diffuse plasma is observed at lower pressure. The propagation speed of the ionization front for air and nitrogen at atmospheric pressure for 3 MW/cm2 was found to be of the order of 10 km/s.

Characteristics of atmospheric pressure plasma jets emerging into ambient air and helium

Abstract: An investigation of atmospheric pressure helium plasma jets emerging into ambient air and helium was carried out with the aim of shedding light on the mechanism for the formation of extended plasma plumes. By electron multiplying charge coupled device imaging, it is shown that the geometrical shape of the jet in ambient helium is not an arrow-like shape as that in ambient air, but a diffusive one. In ambient helium, the jet length increased continuously with the applied voltage. For ambient air, the jet length was determined by both the helium flow rate and the applied voltage. In addition, the N2 (C–B) band and the lines dominate the emission spectra of the jet in ambient air. The Penning ionization between metastable He atoms and N2 molecular may be the main source of .

Diffuse mode and diffuse-to-filamentary transition in a high pressure nanosecond scale corona discharge under high voltage

Abstract: The dynamics of a point-to-plane corona discharge induced in high pressure air under nanosecond scale high overvoltage is investigated. The electrical and optical properties of the discharge can be described in space and time with fast and precise current measurements coupled to gated and intensified imaging. Under atmospheric pressure, the discharge exhibits a diffuse pattern like a multielectron avalanche propagating through a direct field ionization mechanism. The diffuse regime can exist since the voltage rise time is much shorter than the characteristic time of the field screening effects, and as long as the local field is higher than the critical ionization field in air. As one of these conditions is not fulfilled, the discharge turns into a multi-channel regime and the diffuse-to-filamentary transition strongly depends on the overvoltage, the point-to-plane gap length and the pressure. When pressure is increased above atmospheric pressure, the diffuse stage and its transition to streamers seem to satisfy similarity rules as the key parameter is the reduced critical ionization field only. However, above 3 bar, neither diffuse avalanche nor streamer filaments are observed but a kind of streamer–leader regime, due to the fact that mechanisms such as photoionization and heat diffusion are not similar to pressure.

Length control of He atmospheric plasma jet plumes: Effects of discharge parameters and ambient air

Abstract: The effects of various discharge parameters and ambient gas on the length of He atmospheric plasma jet plumes expanding into the open air are studied. It is found that the voltage and width of the discharge-sustaining pulses exert significantly stronger effects on the plume length than the pulse frequency, gas flow rate, and nozzle diameter. This result is explained through detailed analysis of the I-V characteristics of the primary and secondary discharges which reveals the major role of the integrated total charges of the primary discharge in the plasma dynamics. The length of the jet plume can be significantly increased by guiding the propagating plume into a glass tube attached to the nozzle. This increase is attributed to elimination of the diffusion of surrounding air into the plasma plume, an absence which facilitates the propagation of the ionization front. These results are important for establishing a good level of understanding of the expansion dynamics and for enabling a high degree of control of atmospheric pressure plasmas in biomedical, materials synthesis and processing, environmental and other existing and emerging industrial applications.

Effect of relative humidity and sea level pressure on electrical conductivity of air over Indian Ocean

Abstract: [1] The electrical conductivity measured over the Indian Ocean (15°N, 77°E to 20°S, 58°E) during the Indian Ocean Experiment (INDOEX-1999) from 20 January to 12 March 1999 has been analyzed. The conductivity values over two oceanic regions, one with very low aerosol concentration and another with very high aerosol concentration, are studied in relation with meteorological parameters such as relative humidity and sea level pressure. The average conductivity is as low as 0.295 × 10−14 Sm−1 in the region of high aerosol concentration and it is 0.783 × 10−14 Sm−1 in the region of very low aerosol concentration. In both the regions, conductivity shows an inverse relation with relative humidity and this effect is more in the presence of high aerosol concentration. The hydrate growth of aerosol particles in high-humidity condition may be responsible for the inverse relation between conductivity and relative humidity. Size distributions of aerosol particles measured in the same cruise during high-humid conditions are also analyzed to show that sizes, rather than numbers, of aerosol particles increase with an increase in humidity. The relationship between conductivity and sea level pressure in these two regions is also studied and it shows good correlation in the region where the background aerosol concentration is low and no correlation in the region where aerosol concentration is high. The inverse relation between sea level pressure and electrical conductivity is attributed to the possible transportation of ultrafine particles from free troposphere, with subsiding motions associated with high pressure. The positive correlation between ultrafine particles and sea level pressure supports this idea.

A molecular dynamics simulation study of crystalline 1,3,5-triamino-2,4,6- trinitrobenzene as a function of pressure and temperature

Abstract: Quantum chemistry-based dipole polarizable and nonpolarizable force fields have been developed for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Molecular dynamics simulations of TATB crystals were performed for hydrostatic pressures up to 10 GPa at 300 K and for temperatures between 200 and 400 K at atmospheric pressure. The predicted heat of sublimation and room-temperature volumetric hydrostatic compression curve were found to be in good agreement with available experimental data. The hydrostatic compression curves for individual unit cell parameters were found to be in reasonable agreement with those data. The pressure- and temperature-dependent second-order isothermal elastic tensor was determined for temperatures between 200 and 400 K at normal pressure and for pressures up to 10 GPa on the 300 K isotherm. Simulations indicate considerable anisotropy in the mechanical response, with modest softening and significant stiffening of the crystal with increased temperature and pressure, respectively. For most properties the polarizable potential was found to yield better agreement with available experimental properties.

Atmospheric Pressure Process for Coating Particles Using Atomic Layer Deposition

Abstract: Atomic layer deposition (ALD) is a promising technique for coating micrometer- and nanometer-sized particles. Due to the self-terminating nature of the ALD half-reactions, the coating thickness can be controlled to the atomic level by choosing the number of cycles in which the half-reactions are repeated. This technique is performed in a fluidized bed reactor, under atmospheric pressure. LiMn2O4 particles (primary particles 200 − 500 nm in diameter) are coated with Al2O3 to various thicknesses, ranging from 5 ALD cycles to 28 ALD cycles. The resulting coatings are homogeneous, and the individual particles are coated, rather than the agglomerates as a whole; however there are indications of some build-up of water -mainly in pores- that may be related to the use of atmospheric pressure. Quantitative characterization of the coating is difficult due to the powdered substrate.