Gas Mixture Of NH3 Research Articles

Selective Detection of Formaldehyde By a Flame-Made Sensor Array for Environmental Monitoring

Introduction Formaldehyde is a carcinogenic pollutant omnipresent in indoor air due to emission from wood-based furniture, textiles, and paints [1]. But it is formed also outdoors from biofuel combustion, forest fires and photooxidation of smog [2]. Therefore, its exposure is strictly regulated worldwide (e.g., World Health Organization < 80 ppb for short-term exposure). However, reliable and portable devices for on-site monitoring do not exist. Currently, formaldehyde emission testing is carried out by sampling via sorption tubes and subsequent off-site laboratory analysis by gas chromatography. This is expensive, time-consuming, and thus not applicable for distributed indoor air quality monitoring or personal exposure assessment. Chemical sensors are promising for these applications as they are compact, low-cost and simple-in-use. Current sensors, however, typically fail to fulfill the necessary sensitivity and selectivity requirements to detect relevant formaldehyde concentrations below 100 parts per billion (ppb) in ambient air, which contains hundreds of interfering compounds. Here, we present a highly sensitive, selective and compact sensor array of flame-made metal-oxide sensors for real-time quantification of formaldehyde at 90% relative humidity (RH) in gas mixtures. Method Sensing nanoparticles of Pt-, Si-, Pd- and Ti-doped SnO2 are produced by flame-spray pyrolysis and directly deposited onto microsensor substrates by thermophoresis. The individual sensors are assembled to an array (E-nose) by wire-bonding them on a leadless chip carrier, which is placed inside a Teflon sensor chamber. Sensing films are heated to 400 °C with a Pt back heater and the E-nose is characterized in synthetic gas mixtures with a gas mixing setup at 90% RH [3]. The E-nose is tested in gas mixtures containing formaldehyde, acetone, ammonia and ethanol and a multilinear linear regression model is applied to obtain individual analyte concentrations [4]. Results and Conclusions The E-nose consists of four nanostructured and highly porous Pt-, Si-, Pd- and Ti-doped SnO2 sensing films precisely deposited onto silicon wafer-based microsubstrates by flame spray pyrolysis (Figure 1a, b). Flame-made sensing particles are deposited (black patterns) within the designated area of the interdigitated electrodes, while the heater and electrode pads are shielded by the shadow mask and not contaminated by particles. This technique is scalable and be readily applied to wafer-level processing (69 sensors in a single step [5]).The individual sensors offer a sensing film consisting of a highly porous and nanostructured network of nanoparticles (Figure 1b). As a result, they are highly sensitive for formaldehyde concentrations <10 ppb even at 90% RH with fast response dynamics (response time 140 s) as shown in Figure 2. Even concentrations as low as 5 ppb are detected with high signal-to-noise ratio >25. Each dopant induces different analyte selectivity, enabling selective detection of formaldehyde in gas mixtures by multivariate linear regression. We apply this for formaldehyde detection in complex gas mixtures of formaldehyde, acetone, NH3, and ethanol at realistic concentrations and humidity. Formaldehyde is thereby detected with an average error of ≤9 pbb at concentrations 30–180 ppb despite the much higher concentrated interferants.As a result, based on its compact size and low price, this device is promising for monitoring of formaldehyde in indoor and outdoor air. When interconnected, such next-generation low-cost detectors could enable distributed chemical recognition [6] for air quality in “smart” buildings and “future” cities.

Boron and nitrogen doping in graphene: an experimental and density functional theory (DFT) study

Boron (B) and Nitrogen (N) doped few layer graphene (BNG) is directly synthesized via electric arc discharge (EAD) method. NH3 and BCl3 gas mixtures are used in the synthesis atmosphere. Raman spectroscopy is used to determine graphene’s purity and number of layers. The investigation of structure and morphology of pristine graphene and BNG are carried out via Transmission Electron Microscopy (TEM). The presence of B and N in the structure of graphene is detected by Energy Dispersive X-ray Spectroscopy (EDS) analysis. Elemental mapping show that N and B are distributed homogeneously in the graphene structure. It is observed that doping process did not affect the positions of the D, G and 2D bands in the Raman spectroscopy. The effect of doping on the number of layers of graphene is found negligible. TEM results exhibit that pristine graphene and BNG have 5 to 6 layers. Besides, the theoretical calculations based on Density Functional Theory (DFT) are employed to support experimental studies. Theoretical results based on DFT showed that bonding of B and N is favorable.

Alteration and Stability of Complex Macromolecular Amino Acid Precursors in Hydrothermal Environments.

The early Solar System comprised a broad area of abiotically created organic compounds, including interstellar organics which were integrated into planetesimals and parent bodies of meteorites, and eventually delivered to the early Earth. In this study, we simulated interstellar complex organic compounds synthesized by proton irradiation of a gas mixture of CO, NH3, and H2O, which are known to release amino acids after acid hydrolysis on the basis of Kobayashi et al. (1999) who reported that at the first stage of chemical evolution, the main compounds formed abiotically are complex organic compounds with high molecular weights. We examined their possible hydrothermal alteration and stabilities as amino acid precursors under high temperature and pressure conditions simulating parent bodies of meteorites by using an autoclave. We reported that all samples treated at 200-300°C predominantly released glycine and alanine, followed by α-aminobutyric acid, and serine. After heating, amino acid concentrations decreased in general; however, the recovery ratios of γ-aminobutyric acid increased with temperature. The interstellar complex organic analog could maintain as amino acid precursors after being treated at high temperature (200-300°C) and pressure (8-14MPa). However, the molecular structures were altered during heating to form organic compounds that are more stable and can survive in elevated hydrothermal conditions.

Hexagonal boron nitride grown using high atomic boron emission during microwave plasma chemical vapor deposition

Boron nitride (BN) is a member of Group III nitrides and continues to spark interest among the scientific community for its mechanical properties, chemical inertness, thermal conductivity, and electrical insulating properties. In this study, microwave plasma chemical vapor deposition is used to synthesize BN on silicon substrates. Feed gas mixtures of H2, NH3, and B2H6 are used for a range of systematically varied power, pressure, and flow rate conditions. Plasma optical emission from atomic boron is shown to increase nonlinearly by nearly a factor of five with decreasing chamber pressure in the range from 100 to 10 Torr. Copious amounts of atomic boron in the plasma may be beneficial under some growth conditions for producing high hardness boron-rich nitrides, such as B13N2, B50N2, or B6N, which, to date, have only been synthesized under high pressure/high temperature conditions. Despite the higher atomic boron emission in the plasma at low pressure, BN coatings grown at 15 Torr result in hexagonal BN (B/N ratio of 1), regardless of the B2H6 flow rate used in the range of 0.6–3.0 sccm.

Influence of temperature and duration on the nitriding behavior of 40Cr low alloy steel in mixture of NH3 and N2

40Cr low alloy steel samples was nitrided by plasma nitriding with hollow cathode discharge assistance in a gas mixture of N2 and NH3 with different ratios at temperatures ranging from 520 °C to 560 °C for processing time from 2 to 6 h. The influences of processing temperature and time on the thickness and phase composition of nitrided layer were researched. Nitrided layers were evaluated using scanning electron microscope (SEM), X-ray diffraction and microhardness tester. The thickness of white layer increased with the processing temperature and time increasing. For samples nitrided at 540 for 4 h, the white layer is 5.6 μm in ammonia and 10.2 μm in mixture gas respectively. The maximum thickness of white layer about 15 μm thick is obtained after nitrided at 560 °C for 6 h in this study. The phases of nitrided layer are mainly composed of ε-Fe2-3N with a small amount of Fe4N. Such nitrided layer was beneficial to reducing the friction coefficient. The corrosion resistance of the nitrided sample was improved with the increasing thickness of the white layer.

Effects of Different Variants of Plasma Nitriding on the Properties of the Nitrided Layer

Several process variants of plasma nitriding can be distinguished depending on the location of the voltage introduction. The aim of this study is to compare three different variants of plasma nitriding (DC plasma nitriding, active screen plasma nitriding, and active screening process with bias voltage application) extended by the study of the coverage of active screen on C45E unalloyed steel, using two different N2-H2 gas mixtures. The thickness of the compound layer was measured using a scanning electron microscope, the phase analysis was performed by an x-ray diffractometer, and the nitrogen contents were analyzed by glow discharge optical electron spectroscopy. The results showed that the layer thickness and the surface hardness were higher by using active screen-biased plasma nitriding with high N2 content gas mixture. Besides, the lid of the active screen did not influence significantly the chemical composition of the compound layer.

A Numerical Study of the V/III Ratio in the MOCVD Process with Pulsed Injection Method

AlN layer grabs lots of attention as a great super lattice layer between Si or sapphire substrate and GaN-based material. V/III ratio in the AlN MOCVD process is regard as an important parameter which causes different AlN growth modes on the substrate surface. The growth mode changes from 3D nucleation to 2D growth while the V/III ratio decreases. On the other hand, the pulsed injection method is applied in the MOCVD process to depress parasitic reaction and improve the quality of the AlN film. However, the growth conditions at the wafer surface are strongly affected by the mass transport in the reactor chamber which depends on the flow pattern and gas phase reaction. The momentum, heat and mass transfers are complicated by the pulse action. Different types of pulse sequences and pulse times are reported for finding a better process condition. Until now, it still depends on the empirical data very much and induces enormous time consumption and financial cost in the chamber design process. A suitable numerical simulation is needed to be developed for overcoming this difficulty. In this study, a time-dependent numerical model is developed to analysis the flow motion and the heat and mass transfer caused by different pulse conditions. For the case with the TMAl gas mixture maintained a constant and a pulsed NH3 gas mixture, the V/III ratio at the surface of substrate increases with the process time after the pulse of NH3 mixture ejected into the chamber. It approaches to a constant when the time is greater than a certain value. The V/III ratio decreases to zero after the pulse of NH3 mixture ends. The V/III changes quickly in a little time when the pulse of NH3 mixture is turned on or off. When the NH3 and TMAl are pulsed into the chamber alternatively, the V/III ratio at the surface of the substrate keeps increasing after the pulse of NH3 mixture turned on. The V/III ratio decreases to zero after the pulse of NH3 mixture turned off. The V/III ratio does not stay at a certain value like the cases which has the constant supply of TMAl mixture. Based on the variation of V/III ratio at the surface of the substrate, we can predict the history of the growth mode at the surface of the substrate during the process.

Oxide layer formed on AISI 5140 steel by plasma nitriding and post-oxidation in a mixture of air and ammonia

AISI 5140 low alloy steel has been treated by plasma nitriding at 540 °C for 4 h, followed by post-oxidation at 450 °C in plain air and a mixture containing air and ammonia with various ratios for 1 h respectively. The microstructure, phase composition, corrosion resistance and tribological characteristics of the nitrided and nitrided + post-oxidation samples are examined. The results show a thin, continuous and dense oxide layer with the thickness ranging from 1.6 to 1.8 μm was formed on the top of nitride layer after plasma post-oxidation. The oxide layer is mainly composed of Fe3O4 phase accompanied by a small amount of Fe2O3 phase for post-oxidation in plain air. Only Fe3O4 phase appears in oxide layer after post-oxidation in 25% air – 75% NH3, 50% air – 50% NH3 gas mixture. Addition of ammonia into air favors the formation of Fe3O4 which is responsible for the excellent corrosion resistance of treated samples. The friction coefficients of the nitrided samples are significantly decreased due to oxide layer formation by plasma post-oxidation in plain air and mixture of air and ammonia.

Comparable investigation of polyaniline behavior towards gaseous ammonia and toluene adsorption.

With raising awareness of gaseous air pollutants and their harmful impact, adsorption is considered one of the most prominent techniques for gaseous emissions control. The usage of polyaniline as a gas adsorbent is an innovative idea. This work aims to compare the efficacy of synthesized polyaniline nanotubes (PANT) as a novel adsorbent towards inorganic gases (ammonia NH3) and volatile organic compounds (toluene vapor). PANT was prepared via a sol-gel preparation technique. The molecular structure of prepared PANT was characterized by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The morphological structure was confirmed using transmission electron microscopy (TEM) and scanning electron microscope (SEM). The PANT adsorbent surface area was determined using Brunner Emmett Teller (BET). Dynamic behavior of simulated feed gas mixture of NH3 and toluene in air were examined using a fixed bed adsorption arrangement. The same adsorption conditions (inlet concentration, gas mixture feed flow rate, and a fixed amount of adsorbent) were applied for both NH3 and toluene adsorption test. The NH3 and toluene removal efficiencies were 100% and 96% respectively. Consequently, PANT is an auspicious adsorbent that can be utilized to control the indoor and outdoor gaseous air emissions. Graphical Abstracts ᅟ.

Solid carbon active screen plasma nitrocarburizing of AISI 316L stainless steel: Influence of N2-H2 gas composition on structure and properties of expanded austenite

Plasma nitrocarburizing based on active screen technology using a carbon-fiber reinforced carbon active screen was applied in an industrial-scale unit for thermochemical surface treatment of austenitic stainless steel. This concept is based on the use of a solid-carbon-source for the generation of highly reactive process gases directly in the active screen plasma. In this work, plasma nitrocarburizing of AISI 316L stainless steel was performed by means of the variation of the precursor gases H2 and N2 in the range of 0% N2 up to 100% N2 without the use of any additional carbon bearing gas. For a set of H2-N2 gas mixtures, the resulting reaction gas was monitored using infrared laser absorption spectroscopy (IRLAS). The four main stable species HCN, CH4, NH3 and C2H2 were detected. A detailed analysis of the surface microstructure resulting for each specific H2-N2 precursor gas mixture was performed. This included glow discharge optical emission spectroscopy (GDOES), optical microscopy, micro hardness measurements, as well as X-ray diffraction analysis.The concentrations of hydrocarbons CH4 and C2H2 were most abundant in case of pure hydrogen plasma, and a carbon-expanded austenite layer with hardness values up to 600 HK0.01 and smooth hardness gradient resulted. The admixture of N2 to the precursor gas significantly increased the concentrations of HCN and NH3. Due to this, a duplex structure of nitrogen-expanded austenite γN and carbon-expanded austenite γC formed. With increasing content of N2 up to 50% in the precursor gas, the resulting layer thickness increased and the hardness reached values up to 1300 HK0.01. At strong nitrogen excess in the precursor gas, the nitrogen concentration in the expanded austenite significantly increased, the Fe2–3(N, C) phase was formed, and simultaneously the layer thickness decreased. Structure and properties of the expanded austenite layer significantly changed by only varying the H2-N2 ratio of the precursor gas mixture.

Grain boundary dominated electrical conductivity in ultrananocrystalline diamond

N-type electrically conductive ultrananocrystalline diamond (UNCD) films were deposited using the hot filament chemical vapor deposition technique with a gas mixture of H2, CH4 and NH3. Depending on the deposition temperature and ammonia feed gas concentration, which serves as a nitrogen source, room temperature electrical conductivities in the order of 10−2 to 5 × 101 S/cm and activation energies in the meV range were achieved. In order to understand the origin of the enhanced electrical conductivity and clarify the role of ammonia addition to the process gas, a set of UNCD films was grown by systematically varying the ammonia gas phase concentration. These samples were analyzed with respect to their morphology and electrical properties as well as their carbon and nitrogen bonding environments. Temperature dependent electrical conductivity measurements (300–1200 K) show that the electrical conductivity of the samples increases with temperature. The near edge x-ray absorption fine structure measurements reveal that the electrical conductivity of the UNCD films does not correlate directly with ammonia addition, but depends on the total amount of sp2 bonded carbon in the deposited films.

In-situ Raman spectroscopy analysis of the interfaces between Ni-based SOFC anodes and stabilized zirconia electrolyte

A novel experimental approach for in-situ Raman spectroscopy of the electrode | solid electrolyte interfaces in controlled atmospheres, based on use of the optically transparent single-crystal membranes of stabilized cubic zirconia, was proposed and validated. This technique makes it possible to directly access the electrochemical reaction zone in SOFCs by passing laser beam through the single-crystal electrolyte onto the interface, in combination with simultaneous electrochemical measurements. The case study centered on the analysis of NiO reduction in standard cermet anodes under open-circuit conditions, demonstrated an excellent agreement between the observed kinetic parameters and literature data on nickel oxide. The porous cermet reduction kinetics at 400–600°C in flowing H2-N2 gas mixture can be described by the classical Avrami model, suggesting that the reaction rate is determined by metal nuclei growth limited by Ni diffusion. The advantages and limitations of the technique are briefly addressed.

Metal-catalyst-free growth of graphene on insulating substrates by ammonia-assisted microwave plasma-enhanced chemical vapor deposition

We study the metal-catalyst-free growth of uniform and continuous graphene on different insulating substrates by microwave plasma-enhanced chemical vapor deposition (PECVD) with a gas mixture of C2H2, NH3, and H2 at a temperature of 700–750 °C.

Plasmochemical modification of aluminum-zinc alloys using NH3-Ar atmosphere with anti-wear coatings deposition

This paper constitutes a continuation of studies on modification technologies for 7075 series aluminum alloys (Al-Zn) in plasmochemical conditions using the RF CVD (Radio-Frequency Chemical Vapor Deposition) method. This technique is simultaneously the second stage of alloy ageing. The presented results concern optimization of alloy surface modification using N+ ions (in NH3 or NH3/Ar atmosphere) before obtaining a DLC (Diamond-Like Carbon) layer doped with Si and N.From the results it can be concluded that the most profitable mechanical properties (H, ca. 12 GPa and E, ca. 115 GPa) are obtained when the SiCNH coating process is preceded by Al-Zn alloy surface modification with nitrogen ions. These ions are provided by a flowing NH3 and Ar gas mixture (1:1 ratio). In these process conditions, the lowest tribological wear of the surface is also observed. Furthermore, the obtained coating exhibits a fine-grained structure.

Piezoresistivity of n-type conductive ultrananocrystalline diamond

Recent developments of a piezoresistive sensor prototype based on n-type conductive ultrananocrystalline diamond (UNCD) are presented. Samples were deposited using hot filament chemical vapor deposition (HFCVD) technique, with a gas mixture of H2, CH4 and NH3, and were structured using multiple photolithographic and etching processes. Under controlled deposition parameters, UNCD thin films with n-type electrical conductivity at room temperature (5×10−3–5×101S/cm) could be grown. Respective piezoresistive response of such films was analyzed and the gauge factor was evaluated in both transverse and longitudinal arrangements, also as a function of temperature from 25°C up to 300°C. Moreover, the gauge factor of piezoresistors with various sheet resistance values and test structure geometries was evaluated. The highest measured gauge factor was 9.54±0.32 at room temperature for a longitudinally arranged piezoresistor with a sheet resistance of about 30kΩ/square. This gauge factor is well comparable to that of p-type boron doped diamond; however, with a much better temperature independency at elevated temperatures compared to the boron-doped diamond and silicon. To our best knowledge, this is the first report on piezoresistive characteristics of n-type UNCD films.

Selectivity of Catalytically Modified Tin Dioxide to CO and NH3 Gas Mixtures

This paper is aimed at selectivity investigation of gas sensors, based on chemically modified nanocrystalline tin dioxide in the detection of CO and ammonia mixtures in air. Sol-gel prepared tin dioxide was modified by palladium and ruthenium oxides clusters via an impregnation technique. Sensing behavior to CO, NH3 and their mixtures in air was studied by in situ resistance measurements. Using the appropriate match of operating temperatures, it was shown that the reducing gases mixed in a ppm-level with air could be discriminated by the noble metal oxide-modified SnO2. Introducing palladium oxide provided high CO-sensitivity at 25–50 °C. Tin dioxide modified by ruthenium oxide demonstrated increased sensor signals to ammonia at 150–200 °C, and selectivity to NH3 in presence of higher CO concentrations.

Spectroscopic diagnostics of active screen plasma nitriding processes: on the interplay of active screen and model probe plasmas

In a reactor used for active screen plasma nitriding (ASPN) the interplay of two plasma types, (i) the plasma of the cylindrical active screen driven in a pulsed dc mode (f = 1 kHz, 60% duty cycle) and (ii) the plasma at an internal model probe driven in a cw dc mode, ignited in a low pressure H2–N2 gas mixture (p = 3 mbar) containing small amounts of CH4 and CO2 have been studied by tunable diode laser infrared absorption (TDLAS) and optical emission spectroscopy (OES) techniques. Applying in situ TDLAS the evolution of the carbon containing precursors, CH4 and CO2, and of the reaction products, NH3, HCN, CO and H2O, has been monitored. The degree of dissociation of the carbon containing precursor molecules varied between 70% and 92%. The concentrations of the reaction products were found to be in the range 1012…1015 molecules cm−3. By analyzing the development of the molecular concentrations at changes of gas mixtures and plasma power values, it was found that (i) HCN and NH3 are the main products of plasma conversion in the case of methane admixture and (ii) CO, HCN and NH3 in the carbon dioxide case. The fragmentation efficiencies of methane and carbon dioxide (RF(CH4) ≈ 1…2 × 1015 molecules J−1, RF(CO2) ≈ 0.5…1.0 × 1016 molecules J−1) and the respective conversion efficiencies to the product molecules (RC(product) ≈ 1013–1015 molecules J−1) have been determined for different gas mixtures and plasma power values, while the influence of probe and screen plasmas, i.e. the phenomena caused by the interplay of both plasma sources, was analyzed. The additional usage of the plasma at the model probe has a sensitive influence on the generation of the reaction products, in particular that of NH3 and HCN. With the help of OES the rotational temperature of the screen plasma could be determined, which increases with power from 770 K to 950 K. Also with power the ionic component of nitrogen molecules, i.e. the intensity of the -(0-0) band of the first negative system, increases strongly in relation to the intensity of the neutral component, represented by the N2-(0-0) band of the second positive system. In addition, the behavior of the emission of the plasma at the model probe has been studied during the off phase of the plasma of the active screen leading to a direct comparison of the emission characteristics of both plasma sources.

Proximity Gettering of Copper via Oxygen Precipitates for Silicon-on-Insulator Wafer

Silicon-on-insulator (SOI) technology has attributed attention because it enables device to operate in high speed with reducing parasitic capacitance and body effect. However, in the conventional SOI wafer without any gettering site, a very small amount of metallic contaminants degrades the transistor. During fabrication of copper through-silicon-via (TSV) for 3D device structure, copper contaminants after copper damascene chemical-mechanical-polishing (CMP) are accumulated at top silicon layer, BOX layer and silicon substrate resulting in gate oxide leakage, junction leakage current, and threshold voltage shift, etc. Particularly, since the copper solubility in oxide layer is higher than that in silicon, the implementation of gettering sites for copper contaminants in SOI wafers is fundamentally difficult. Thus, a design of gettering for copper contaminants in SOI wafers has been a key engineering to improve device characteristics. In this study, we investigated the effect of oxygen precipitates, produced by rapid-thermal annealing (RTA), on gettering efficiency of copper for SOI wafers after a dynamic-random-access-memory (DRAM) heat-treatment. To design a desirable distribution of oxygen precipitates for the gettering sites, the wafers were subjected to a RTA at 1150, 1175 and 1200 ºC for 10 s in an NH3 and Ar gas mixture. In addition, the substrate wafers were annealed at 800 ºC for 4 h in a nitrogen ambient to grow the oxygen precipitates and then followed at 1000 ºC for 16 h. Then, the bonded SOI wafers with proximity gettering sites and conventional SOI wafer were intentionally contaminated with copper of 1 × 1012 atoms/cm2 on the wafer surface, and then all SOI wafers were subjected to a typical DRAM heat-treatment. We correlated concentration of the oxygen precipitate with gettering efficiency of copper contaminants. Figure. 1 shows the distribution of bulk micro defects (BMDs) in the substrate wafer with a different heat-treatment condition. It shows that the substrate wafer subjected to a RTA and two-step heat-treatment has the highest density of BMDs. A SOI wafer was conventionally fabricated and subjected to a DRAM heat-treatment after copper contamination intentionally. In this wafer, concentration of copper contaminants was measured via dynamic secondary ion mass spectroscopy (D-SIMS). As shown in Fig. 2, concentration of copper on top silicon, BOX layer and bulk silicon is high because there is no gettering site. In Fig. 3, a substrate wafer was subjected to a RTA at 1175 ºC for 10 s and then followed two-step heat-treatment. The concentration of copper contaminants was relatively lower than that of Fig 2. This means that coppers were well gathered at oxygen precipitates located at underneath buried oxide after DRAM heat-treatment, verifying an excellent gettering efficiency for copper contaminants. In our presentation, we will discuss the detailed gettering mechanism for copper contaminants in SOI wafers and report proximity gettering of copper via oxygen precipitates for SOI wafer.* This work was financially supported by the Brain Korea 21 Plus Program in 2013 and SiWEDS (Silicon Wafer Engineering and Defect Science).Reference[1] S.M. Myers et al., J. Appl. Phys. 88 (2000) 3795[2] Lixia Lin et al., Solid-State and Integrated Circuit Technology (2010) 1563

Investigation of simultaneous removal of ammonia and hydrogen sulphide from producer gas in biomass gasification by titanomagnetite

A novel hot gas cleaning process using titanomagnetite for the simultaneous removal of ammonia (NH3) and hydrogen sulphide (H2S) from a producer gas in biomass gasification has been developed. In a hot reactor operated at 500–800°C and under atmospheric pressure, NH3 is removed by a decomposition reaction to N2 and H2, whereas H2S is removed by an adsorption reaction. Titanomagnetite was tested using three different gas streams, namely 2000ppmv NH3 in Ar, 2000ppmv NH3 and 230ppmv H2S in Ar, and 2000ppmv NH3 and 230ppmv H2S in a simulated biomass producer gas. From the experimental results, it was discovered that ferrite (α-Fe) was readily formed by the H2 reduction of titanomagnetite and that almost complete decomposition of NH3 (100%) was achieved in Ar gas at 700 and 800°C. The presence of H2S in a gas mixture of NH3 and Ar slightly reduced the catalytic activity for NH3 decomposition at 700 and 800°C (>96%), and H2S adsorption of greater than 98% could be achieved in the same temperature range. Under the coexistence of a simulated biomass producer gas, the NH3 decomposition rate and H2S adsorption rate were decreased at 800°C, which could be due to the high content of H2 (45vol%) in the feed gas that favours the reverse reaction of NH3 decomposition and H2S adsorption, the increased surface coverage of the active α-Fe phase by adsorbed hydrogen, and the competition of α-Fe for the reverse water–gas shift reaction. Moreover, it was discovered that temperature significantly affected the removal of NH3 and H2S in the simulated biomass producer gas and thus the operation temperature needs to be optimised.

A Plausible Simultaneous Synthesis of Amino Acids and Simple Peptides on the Primordial Earth

AbstractFollowing his seminal work in 1953, Stanley Miller conducted an experiment in 1958 to study the polymerization of amino acids under simulated early Earth conditions. In the experiment, Miller sparked a gas mixture of CH4, NH3, and H2O, while intermittently adding the plausible prebiotic condensing reagent cyanamide. For unknown reasons, an analysis of the samples was not reported. We analyzed the archived samples for amino acids, dipeptides, and diketopiperazines by liquid chromatography, ion mobility spectrometry, and mass spectrometry. A dozen amino acids, 10 glycine‐containing dipeptides, and 3 glycine‐containing diketopiperazines were detected. Miller’s experiment was repeated and similar polymerization products were observed. Aqueous heating experiments indicate that Strecker synthesis intermediates play a key role in facilitating polymerization. These results highlight the potential importance of condensing reagents in generating diversity within the prebiotic chemical inventory.