Pure Synthetic Air Research Articles

Induced nucleation by gassing and its monitoring for the design and operation of an MSMPR cascade

Control of the nucleation step – the first and most important step in the crystallization process – is crucial for obtaining a desired crystalline product with defined properties such as shape, size and size distribution.For batch crystallization, much effort has been made to identify and investigate the various parameters that affect the conditions under which nucleation takes place. In this context, a promising approach to control the events at the beginning of crystallization can be seen in the use of bottled pure synthetic air to induce nucleation. This process is called gassing crystallization. In this paper, for the first time gassing with synthetic air was applied to induce nucleation in a continuously operated single-stage MSMPR crystallizer. To determine the operating boundaries of an MSMPR cascade and to monitor the process, a self-constructed conductivity probe was used, which represents an inexpensive process analytical technology tool. The experimental results for the binary model system l-alanine/water demonstrate that gassing shows a great potential to carry out the nucleation step in a controlled manner, thus enabling the production of crystals with a constant product quality.

A Semiconductor Gas System of Healthcare for Liver Disease Detection Using Ultrathin InN-Based Sensor

The gas sensor based on platinum-catalyzed ultrathin indium nitride (Pt-InN) was used to detect liver disease by sub-ppm ammonia (NH3) concentration variation in an ambient environment simulating exhaled human breath. Because the InN with strong surface electron accumulation extensively enhanced sensitivity, the NH3 gas sensor minimum detection limit is 0.2 ppm. Meanwhile, the sensor enables to distinguish slight deviation in NH3 concentration between 0.2 and 0.8 ppm that brings simple diagnosis of liver disease for portable and homecare clinical applications. Liver cancer is first of the top ten causes of death in Asia. Abnormal concentrations of the breath volatile organic compounds (VOCs) are reported to correlate with unhealthy/injurious body/organ conditions; for instance, ammonia (NH3) gas for renal and liver disease. Therefore, the detection of ammonia concentration in exhaled breath more important. In this study, an indium nitride (InN) gas sensor of 10 nm in thickness has achieved detection limit of 0.2 ppm ammonia. The sensor has a size of 1 mm by 2.5 mm, while its sensing area is 0.25 mm by 2 mm and deposited with a 10 nm thick Pt film on the sensing window to investigate the effect of catalyst on ammonia gas detection, shown in Fig 1. The ultrathin InN epilayer extensively enhances sensing sensitivity due to its strong electron accumulation on roughly 5–10 nm deep layers from the surface. Sensitivity is expected to be much better due to the natural electronic characteristics of as-grown InN films, including a narrow band gap, excellent electron transport characteristics (mobility > 1,000 cm2·V·s), a background high electron density (typically in excess of 1 × 1018 cm-3), and the unusual phenomenon of strong surface electron (charge) accumulation (1.57 × 1013 cm- 2) for the InN films grown on AlN film on a buffer layer . We proposing the miniaturized prototype, and packaging the ammonia gas sensor system (Including: Pt-InN sensor chip, heater, K-type thermocouple) on the 8 pin dual in-line package (DIP) for the portable human breath liver disease physiological detection application, shown in Fig 2. The current variation (DI) of a Pt-InN ammonia sensor under exposure to various ammonia concentrations from 0.2 ppm to 0.8 ppm in synthetic air at 200 °C is depicted in Fig 3. The experiments were repeatedly performed while the ammonia gas was turned on for 5 minute and off (i.e., in pure synthetic air) for another 5 minute at various ammonia concentrations. The current went up as ammonia concentration increased; such current increment was induced by the reduction of pre-adsorbed oxygen atoms. When ammonia molecules are introduced to the sensing system, the hydrogen atoms on dissociated ammonia molecules react with pre-adsorbed oxygen atoms, reducing the effects of surface depletion. Platinum as catalyst can increase output current signals as well as reduce response in comparison with Pt-InN, indicating that such an ammonia concentration can be analyzed in air. The dynamic responses of the Pt-InN sensor indeed demonstrate the great ability to sense ammonia gas at the sub-ppm level, and promising device for the realization of non-invasive ammonia sensing to detect ammonia in exhaled breath as a marker for liver disease. Figure 1

High-Resolution Mobility and Mass Spectrometry of Negative Ions Produced in a 241Am Aerosol Charger

This work concentrates on the simultaneous mobility and mass measurement of negative ions generated by the ionizing radiation in a 241Am aerosol charger in N2 (5.0), a 1:1-mixture of N2 and synthetic air, pure synthetic air (5.0), and filtered laboratory air at ∼30% relative humidity. Therefore, a high-resolution mobility analyzer (UDMA) and an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF) were operated in series. Experiments with N2 as carrier gas showed a dominating signal at an electrical mobility of 2.09 cm2/Vs with 90% of the ions being nitrate based. The ion composition was altered after a baking-out to a spectrum with three strong mobility-peaks at Z1 = 2.34 cm2/Vs, Z2 = 1.42 cm2/Vs, Z3 = 1.08 cm2/Vs and a higher diversity of ions in the corresponding mass spectra. The carrier gas was gradually changed from N2 (5.0) to a 1:1-mixture of N2 with synthetic air and pure synthetic air (5.0), having only a minor effect on the overall pattern of the ion spectrum. Using room air...

The sensitivity of sensor structures with oxide graphene exposed to selected gaseous atmospheres

Abstract The paper presents the results of investigations on the resistive structure with a graphene oxide (GO) sensing layer. The effects of dangerous gases (hydrogen and nitrogen dioxide) on the structure were studied; the resistance changes were examined during the flow of the selected gas in the atmosphere of synthetic air. Measurements were performed with a special emphasis on the detection of low concentrations of the analyzed gases. The reactions of the sensing structure to the effect of nitrogen and synthetic air at different humidity were also tested. Much attention was also paid to the fast response of the sensor to the changes in the gas atmosphere. The thin palladium layer (~2 nm) has been applied in order to improve the sensing properties of the structure. The investigations were performed in the temperature range from RT to 120°C and the analyzed gases in synthetic air were batched alternately with pure synthetic air.

High Temperature Oxidation of TiAl Alloys Treated by Fluorine Resin

Surface treatment of γ-TiAl based alloys by the small amounts of halogens leads to the formation the protective Al2O3 scale instead of the fast growing mixed TiO2/(TiO2+Al2O3) scale. The halogens can be applied by ion techniques as well as by spraying or dipping with halogen-containing inorganic and organic compounds. Deposition of the fluorine-containing resin on the surface of TiAl alloys is the easiest way to achieve the best results. This work presents the results of microscopic studies of the oxidation behavior of a Ti-48Al-2Cr and Ti-47Al-6Nb (at.%) alloys non-treated and treated with resin containing amino-fluoride. The oxidation runs were carried out in the temperature range 900-1000°C in pure synthetic air.

Infrared absorption cross-sections for acetaldehyde (CH 3CHO) in the 3 μm region

A series of infrared absorption cross-sections for acetaldehyde has been measured in the 3 μm region from spectra obtained using a high-resolution Fourier transform spectrometer (Bruker IFS 125/HR). Results presented are for mixtures of acetaldehyde vapor combined with pure synthetic air taken at various temperatures and pressure to simulate atmospheric conditions found principally in the Earth's troposphere and lower stratosphere. Spectra were recorded at a resolution of 0.005 cm −1 and intensities were calibrated using three acetaldehyde spectra (measured at 278, 298 and 323 K) provided by the Pacific Northwest National Laboratory (PNNL) IR database.

Exposure of Human Lung Cells to Inhalable Substances: A Novel Test Strategy Involving Clean Air Exposure Periods Using Whole Diluted Cigarette Mainstream Smoke

An experimental approach was established for the validation of an in vitro test system for complex environmental test atmospheres consisting of both gaseous substances and particulates. Smoke from two different cigarette types (generated by an automatic cigarette-smoking machine) was employed to assess both the sensitivity and the specificity of the system. The smoke was diluted with synthetic air and used to expose human lung cells grown on microporous membranes. Cells were exposed alternately to diluted cigarette smoke and pure synthetic air. The effect of diluted smoke was assessed without humidification, addition of CO 2, or any other physical or chemical modification of the smoke. The experimental setup included online monitoring of the gas phase (by analysis of CO concentration) and particulate phase (by light-scattering photometry). Replicate experiments confirmed a reproducible generation and dilution of the smoke and a smoke age of about 7 s at the time it came into contact with the cells. Experiments using human lung cells revealed that smoke from the two different cigarette types induced different levels of dose-dependent toxicity. A cell exposure of 6 min using 6 alternating smoke and synthetic air periods was sufficient to cause different effects as measured by intracellular glutathione content. The fact that the system could differentiate between two different types of cigarette smoke demonstrated its high sensitivity and specificity. The system offers new ways to test native complex gaseous and aerosol mixtures in vitro using short exposure times and very small amounts of test substances.

Electric-field-induced migration of chemisorbed gas molecules on a sensitive film—a new chemical sensor

Thin films of sputtered In 2O 3 were exposed to a continuous flow of N 2, pure synthetic air and synthetic air contaminated with NO 2, NH 3 and H 2 while an electric field step function of 76 V/cm was applied. After the field parallel to the surface was switched on, large changes in the ratio between the film resistance close to the negative contact and the overall film resistance were observed. During the electric pulse different time-dependent behaviors were observed depending on the film ambient. This effect is attributed to migration phenomena on the surface and allows to build a new class of chemical sensors. It might, with this technology, be possible to distinguish different gases by means of the same sensitive film.

Dipole- and charge transfer contributions to the work function change of semiconducting thin films: experiment and theory

In the present paper the temperature dependence of the work function change is investigated for Ga 2O 3-thin films ( D = 1, 10, 100, 1000 nm) in a temperature region between 80°C and 180°C. Testing gases are 100 ppm NO 2 and 100 ppm NH 3 in synthetic air. Furthermore, measurements in pure nitrogen and pure synthetic air for Ga 2O 3-thin films are presented. The temperature coefficient of the nitrogen measurements exhibits an inverse behaviour compared to synthetic air. The experimental data are discussed in terms of the Volkenstein model, which takes into account both dipole contribution of weak and strong-chemisorbed species and charge transfer contributions.