Removal of dilute benzene using a zeolite-hybrid plasma reactor

The decomposition of benzene was carried out using a plasma reactor packed with a mixture of BaTiO₃ and zeolite pellets, the zeolite-hybrid reactor. The reactor performance was characterized by measuring CO_x formed during plasma discharge and CO_x adsorbed on the solid surface, The decomposition efficiency of benzene in the hybrid reactor was 1.4-2.1× higher than that in a conventional plasma reactor packed with BaTiO₃ alone. Benzene existing outside a zeolite crystalline pore was found to decompose more easily than that inside a zeolite pore. In addition, the presence of zeolites suppressed the formation of NO_x     

Catalysis-assisted plasma technology for carbon tetrachloridedestruction

Single-stage, catalysis-assisted plasma technology is a new concept developed to decompose carbon tetrachloride (CCl₄), one of the greenhouse gases, and to reduce the reaction by-products at the same time. A laboratory-scale plasma reactor used a packed-bed reactor with 1-mm spherical BaTiO₃ pellets. The configuration employed a unique one-stage catalysis/plasma process in which the BaTiO ₃ pellets were coated or impregnated by active catalysts such as Co, Cu, Cr, Ni, and V. The power supply used for these experiments was either a 50-Hz neon transformer or an 18-kHz inverter neon transformer. Enhancement of the CCl₄ destruction and the conversion of by-product CO to CO₂ were demonstrated using Ni catalyst in the one-stage plasma reactor     

A novel plasma reactor for NOx control usingphotocatalyst and hydrogen peroxide injection

The authors have developed a new type of plasma reactor combining discharge plasma with a photocatalyst (TiO₂) which improves the performance of NO_x removal. This reactor is designated as a plasma-driven catalyst (PDC) reactor. The authors found that hydrogen peroxide (H₂O₂) is a very effective additive in this PDC reactor and the formation of undesirable by-product (such as O ₃, N₂O) was reduced significantly. Comparative test results showed that the combination of discharge plasma with TiO ₂ catalyst is a very effective method in NO_x, removal over a conventional wire-cylinder reactor. NO_x was effectively oxidized to HNO₃ on the TiO₂ catalyst and trapped on the catalyst surface. Specific energy consumption of this de-NO_x process is significantly reduced, in particular, with the injection of H₂O₂     

Mechanisms for formation of inorganic byproducts in plasma chemicalprocessing of hazardous air pollutants

Plasma chemical behavior of hazardous air pollutants (HAPs) (Cl ₂C=CCl₂, Cl₂C=CHCl, Cl₃C-CH ₃, Cl₂CH-CH₂Cl, CH₃Cl, CH ₃Br and benzene), their molecular probes (CH₄, CH ₃-CH₃, and CH₂=CH₂), and carbon oxides (CO_x) was investigated with a ferroelectric packed-bed plasma reactor to obtain information on the formation of CO _x and N₂O. It has been shown that the oxidation of CO to CO₂ is a slow reaction in plasma, and that CO and CO ₂ mainly result from different precursors. Simultaneous achievement of complete oxidative decomposition of HAPs in plasma and recovery of CO as a chemical feedstock could be favorable. The process of N₂O formation is affected by HAP structures and oxygen concentration. In the decomposition of olefinic HAPs, such as Cl₂ C=CCl₂ and Cl₂C=CHCl, high-power short-residence-time operations are effective in suppressing N₂ O formation. In the cases of CH₃Cl and CH₃Br, low specific energy density operations could be necessary to reduce N₂O concentrations. The yields and selectivities of CO, CO₂ and N₂O change drastically by adding only 2% of oxygen to N₂, and oxygen concentration is not a good factor to control these inorganic oxides     

Removal of NF3 from semiconductor-process flue gases bytandem packed-bed plasma and adsorbent hybrid systems

A tandem hybrid gas cleanup system, consisting of a BaTiO₃ packed-bed plasma reactor and a CaCO₃ adsorbent filter, was used to study the removal of NF₃ from semiconductor-process flue gases. Plasma-chemical kinetics of N₂ -NF₃-O₂-H₂ gas mixtures suggested byproducts observed in the experiments. The laboratory-scale system showed NF₃ removal at atmospheric pressure. Typically, 100% NF₃ abatement was achieved with an inlet concentration of 5000 ppm and a gas residence time in the reactor less than 10 s     

Nonthermal plasma approach in direct methanol synthesis fromCH4

Direct methanol synthesis from CH₄ and O₂ has been experimentally studied using pulsed discharge plasma in concentric-cylinder-type reactors. The methanol production becomes efficient with an increase in the average electric field strength of the reactor. A combination of the pulsed discharge and catalysts was tested and was proved to be effective in increasing both the production and selectivity of methanol. In the present stage, about 2% of CH₄ can be converted into other hydrocarbons, and a methanol yield of around 0.5% and selectivity of 38% can be obtained when a catalyst of V₂O₅+SiO₂ is combined with the pulsed discharge plasma     

Decomposition of benzene using a nonthermal plasma reactor packedwith ferroelectric pellets

The decomposition of benzene in air was carried out using a nonthermal plasma discharge reactor packed with ferroelectric materials. It was found that ferroelectric materials of 1-2 mm in diameter with a relative dielectric constant of ϵ_r>1100 decomposed benzene with greatest energy efficiency. Benzene at low concentrations (below 50 ppm) was completely decomposed to CO and CO₂ with no formation of other hydrocarbons. The ratio of CO to CO₂ produced from benzene was minimized under an atmosphere containing more than 5% O₂     

Energy and Spatial Distribution of Traps in SiO2/Al2O3 nMOSFETs

The energy and spatial profiling of the interface and near-interface traps in n-channel MOSFETs with SiO₂/Al₂ O₃ gate dielectrics is investigated by charge-pumping (CP) measurements. By increasing the amplitude as well as lowering the frequency of the gate pulse, an increase of the charge recombined per cycle was observed, and it was explained by the contributions of additional traps located higher in energy and deeper in position at the SiO₂/Al₂O₃ interface. In addition, CP currents, acquired after different constant voltage stress, have been used to investigate the trap generation in this dielectric stack     

The influence of reaction conditions on SO2 oxidation ina discharge plasma reactor

In this paper, experimental approaches have been carried out to investigate the removal of sulfur dioxide (SO₂) using pulsed discharge nonthermal plasma in the absence of ammonia (NH₃). The gas-phase reaction was found to be less attractive due to its large energy cost. The increase in temperature decreased the SO₂ removal rate, resulting in large energy cost. SO₂ removal was increased as the concentration of water vapor increased. The presence of SO₂ did not influence the gas-phase removal of NO in an NO-SO ₂-O₂-H₂O-N₂ system. In the case of the wet-type plasma reactor, gas-phase discharge plasma directed to the surface of water film greatly enhanced the liquid-phase oxidation of HSO₃^- to SO₄^2-. Comparing the results with different absorbents indicated that the hydroxyl (OH) radical plays a key role in the plasma induced liquid-phase reactions     

Low-Threshold Stimulated Emission in ZnO Thin Films Grown by Atomic Layer Deposition

In this study, high-quality ZnO thin films were grown on sapphire substrates by atomic layer deposition (ALD), followed by high-temperature postdeposition annealing. A thin Al₂O₃ layer was subsequently deposited by ALD on the ZnO surface to reduce detrimental surface states. Photoluminescence measurements conducted in a backscattering configuration at room temperature show that the ZnO film exhibited stimulated emission with a low threshold intensity of 35.1 kW/ cm². This may be attributed to the high-quality ZnO film and Al₂O₃ surface passivation layer grown by ALD, as well as the Al doping effect caused by the thermal diffusion of Al from the sapphire into the ZnO. Results show that ZnO films grown by the ALD technique are applicable to next-generation short-wavelength photonic devices.     

Gas cleaning with semi-wet type plasma reactor

An experimental study on the removal of NH₃, NO, NO_x in concentration of 10-40 ppm in air has been carried out using plasma chemical reactions in a streamer corona discharge. The results of the performance of dry type and semi-wet type reactors are compared. The effects of different type of applied voltages such as rectangular pulse, 60-Hz sinusoidal, and 18-kHz alternating voltages are investigated. During NO removal, O₃ and NO₂ are produced. NO₂ can, partially, be removed with higher power input into the discharge. Another undesirable pollutant, namely N₂ O, is also produced, especially, in case of dry reactors having long residence time (~2.4 s). N₂O production decreases, essentially, to zero at 0.6-s residence time while using a semi-wet reactor. In general, higher removal efficiency has been obtained with pulse voltage in a semi-wet reactor. NH₃ in air appears to produce ozone and ammonium nitrate in a discharge. The performance of semi-wet reactors an the removal of submicron dust particles has also been investigated and very high removal efficiency (~93% at 0.6-s residence time) has been obtained     

Permittivity and tan delta characteristics of epoxy nanocomposites in the frequency range of 1 MHz-1 GHz

To achieve a compact and reliable design of electrical equipment for the present day requirements, there is an urgent need for better and smart insulating materials and in this respect, the reported enhancements in dielectric properties obtained for polymer nanocomposites seems to be very encouraging. To further understand the dielectric behavior of polymer nanocomposites, this experimental work reports the trends of dielectric permittivities and tan delta (loss tangent) of epoxy nanocomposites with single nano-fillers of Al₂O₃ and TiO₂at low filler concentrations (0.1%, 0.5%, 1% & 5%) over a frequency range of 1 MHz-1 GHz. Results show that the nanocomposites demonstrate some very different dielectric characteristics when compared to those for polymer microcomposites. Unlike the usual expectations of increasing permittivity with increasing filler concentration in polymer microcomposites, it has been seen that up to a certain nano-filler concentration and depending on the permittivity of the nano-filler, the permittivities of the epoxy nanocomposites are less than that of the unfilled epoxy at all the measured frequencies. This suggests that there is a very strong dependence of the filler concentration and nano-filler permittivity on the final permittivity of the nanocomposites at all these frequencies. But, in the case of tan delta behavior in nanocomposites, significant effects of filler concentrations were not observed with both Al₂O₃ and TiO₂ fillers. Tan delta values in nanocomposites with Al₂O₃ fillers are found to be marginally lower at all filler concentrations when compared with the value for unfilled epoxy. But, in TiO_2Oepoxy nanocomposites, although the variations in tan delta are not significant with respect to unfilled epoxy, some interesting trends are observed with respect to the frequencies of measurement.     

Electrical relaxation in iron-containing glasses

Glasses with composition 70 mol%(SiO₂, B₂O ₃, P₂O₅, TeO₂)-15 mol% Fe ₂O₃-15 mol%(BaO, CaO) were prepared by the conventional melt quenching technique. The electrical relaxation of these glasses has been studied in the frequency range 20 to 10⁵ Hz. The small polaron hopping between iron ions in a different valence state Fe²⁺ to Fe³⁺ is found to be the principal conduction mechanism. The ratio of Fe²⁺ ions to the total iron content, C=Fe²⁺/Fe_tot, is one of the factors determining the electrical conductivity. The glass former has a minor influence on dc conductivity, except of TeO₂ glass where conductivity is three order of magnitude higher than those of other glasses. The ac conductivity as a function frequency is divided into two domains, a dc plateau, followed by a power law in frequency. These two regions are well distinguished in the complex plot of electric modulus where all data points for different temperatures reside on the single plot. The results are discussed in the frame of the Hunt theory of dielectric relaxation in glasses containing mobile charge carriers     

Pulsed electrical breakdown from superconducting electrodes invacuum diodes

Results are presented of investigations of the pulsed electric strength and threshold current densities of YBa₂Cu₃O₇ and Nb cathodes at cryogenic temperatures. It has been shown that the cooling of a Nb cathode from 300 to 4.2 K leads to a 1.5 to 2.5× increase of pulsed electric strength and that the transition of the cathode from the normal to the superconducting state has no effect on either the breakdown delay time or the threshold current density of cathode micropoints. An analysis is made of the process of heating of cathode micropoints from cryogenic temperatures under the action of high-density field emission current. Experiments have shown that the atomic structure and electronic properties of Nb cathode micropoints and the dynamics of their heating are the same for Nb cathode tips having an atomically smooth and clean surface. We did not observe this effect for YBa₂Cu₃O_7-x single crystal cathodes. That is why the prebreakdown phenomena in diodes with YBa₂Cu ₃O_7-x electrodes are similar to those in diodes with metallic ones. Data are presented of the work function, limiting current densities, and tensile strength of YBa₂Cu₃O_7-x single crystal cathode tips     

高镍三元正极材料锂离子电池的热失控分析

研究使用3种高镍三元正极材料[Li(Ni0.8Co0.1Mn0.1)O2(NCM811)、Li(Ni0.5Co0.2Mn0.3)O2(NCM523)和 Li(Ni0.8Co0.15Al0.5)O2(NCA)]的锂离子电池在100％荷电状态(SOC)状态下的热失控特征参数.进行3组重复性实验,对比自产热起始温度θ1、热失...     

填充石英球对DBD等离子体转化NO的影响

放电等离子体辅助选择催化还原两段法脱除NOx是一项很有前景的氮氧化物治理技术.介质阻挡放电(DBD)是一种常见的等离子体产生方法,在DBD等离子体反应器中填入电介质小球可进一步增强放电.本文考察了有无石英填充球的DBD等离子体反应器对NO的转化和能量利用效率的影响,借助ANSOFT软件对DBD等离子体反应器内的电场进行了仿真分析.实验结果表明,在较低的放电电压下,填充石英球的DBD等离子体反应器虽然能耗略有提高,但在NO的转化和能量利用效率上都优于无填充情况,其原因归结为,填充石英球有利于反应器在更低电压下实现局部放电,同时促进反应器内的电场和气流在空间更均匀地分布,增加了反应气流与放电等离子体的接触机会.     

The effect of residence time on the CO2 reduction fromcombustion flue gases by an AC ferroelectric packed bed reactor

An experimental investigation was conducted to reduce CO₂ from combustion gases using an AC ferroelectric packed bed reactor. This ferroelectric packed bed reactor consists of two mesh electrodes packed with ferroelectric particles between them. An AC voltage is applied to the reactor to generate partial or spark discharges. The results show the following: the CO₂ gas reduction rate increases with increasing flue gas residence time and primary applied power; the CO₂ gas reduction rate increases with decreasing gas flow rate and dielectric constant of packed ferroelectric particles; and the CO₂ concentration is reduced by up to 18000 ppm, and 108 g of CO₂ are removed by 1 kWh of primary applied energy used in the packed-bed reactor     

Discharge plasma treatment for NO/sub x/ reduction from diesel engine exhaust: a laboratory investigation

A detailed study on the removal of oxides of nitrogen (NO_x ) with and without the presence of carbonaceous soot in a stationary diesel engine exhaust was carried out using pulsed electrical discharges/catalyst/adsorbent processes. The processes were separately studied first and then the cascaded processes namely plasma-catalyst and plasma-adsorbent were examined. To investigate the effect of carbonaceous soot on the plasma treatment process, the filtered and unfiltered exhaust was treated by plasma separately. In the cascaded plasma-catalyst process, the plasma treating filtered exhaust was cascaded with a reduction catalyst V₂O₅/TiO₂ using ammonia as reducing agent and in the cascaded plasma-adsorbent process, the plasma treating unfiltered (raw) exhaust was cascaded with adsorbents (MS-13X/activated alumina/activated charcoal). The enhanced NO_x removal efficiency of plasma process in the presence of soot is identified, possible pathways are summarized and the results of the cascaded processes are discussed in detail     

Comparison of reactor performance in the nonthermal plasma chemicalprocessing of hazardous air pollutants

The performance of three different types of plasma reactors such as ferroelectric packed-bed (FPR), pulsed corona (PCR), and silent discharge (SDR) were compared in the decomposition of trichloroethylene (Cl₂C=CHCl, TCE), bromomethane (CH₃Br), and tetrafluoromethane (CF₄). Irrespective of reactors, hazardous air pollutant (HAP) reactivity in dry N₂ decreased in the order: TCE>CH₃Br>CF₄. Similar byproducts were obtained with any of the above reactors, and similar trends were observed in the HAP decomposition rate-retarding effect by water. Only for SDR, TCE decomposition was accelerated by O₂ in the background gas. The most plausible active oxygen species is considered to be the triplet oxygen atom. In the reaction systems where chemically induced decomposition of HAPs can occur, as in the case of TCE, PCR is expected to exceed FPR and SDR in performance. In the cases of CH₃ Br and CF₄, residence time has been the most important factor governing their decomposition rates, and FPR and SDR have shown higher performance than PCR     

Aerosol generation and decomposition of CFC-113 by theferroelectric plasma reactor

Plasma chemical decomposition, aerosol generation and product distribution of trichlorotrifluoroethylene (CFC-113 [CCl₂F-CClF₂]) were investigated using a ferroelectric plasma reactor. CFC-113 decomposition was the highest with dry hydrogen, but was not significantly affected by background gases (N ₂ and air) and humidity. Most of the aerosols produced under plasma were of a particle size less than 0.1 μm. The aerosol generation rate increased with applied voltage and concentration, but was not affected by humidity and background gases, indicating that aerosol generation is associated with plasma energy per volume (plasma power density). Aerosolization of 1000-ppm CFC-113 was approximately 10 aerosols/cm³ for air, significantly greater than N₂. The greatest quantity of reaction gas phase byproducts was for dry H₂, followed by dry N₂, wet N₂ , wet air and dry air. Reaction gas phase byproducts were minimal with aerated condition. The plasma reaction starts out by breaking the C-C bond to form radicals, which react with background gas radicals. The formation of CHClF-CClF₂ during CFC-113 decomposition indicates that the C-F bond is much stronger than the C-Cl bond and the C-Cl bond with more P atoms is stronger than that with fewer F atoms