固体生物质燃烧中氮氧化物产生机理综述

在生物质燃料燃烧过程中燃料氮会转化为氮氧化物(NOx)释放,造成环境污染。为揭示NOx的转化机理,本文对相关文献的研究结果进行了汇总。文献表明:固体生物质中燃料氮的主要成分是蛋白质,构成蛋白质的不同氨基酸分布呈现较高的一致性;燃料氮在燃烧过程中首先进行热解,其产物分布在挥发分、焦油和焦炭中,挥发分氮、焦油氮进一步裂解生成NOx前驱物等气相氮物质,焦炭氮、气相氮燃烧生成NOx;NOx的生成与生物质种类、热力因素(温度、升温速率)、反应气氛、和其他条件(添加物)等因素有关。目前,研究只发现了一些实验规律,并未掌握燃料氮向NOx转化的详细机理,采用模型化合物结合计算化学的方法成为研究燃料氮转化机理的新趋势。

生物质热解过程中氮迁移转化机理研究进展

生物质热解产物中热解气和热解油具有较高能源利用价值,可作为替代燃料或化工原料,但伴随热解过程迁移至热解气/油中的氮元素不仅会影响其品质,热解气/油进一步利用后也会污染大气环境。该研究围绕生物质资源制备清洁能源的总目标,系统分析生物质热解过程中氮迁移转化机理,重点论述气相氮、液相氮和焦炭氮的生成与转化机理。通过总结前人研究,得出生物质热解气中的含氮物质主要为HCN、NH3等,其中NH3主要来源于氨基酸热解释放的氨基以及HCN在焦炭表面的水解转化;HCN主要来源于腈、含氮杂环等一次热解产物的二次裂解;热解油中的含氮物质主要为含氮杂环、腈与酰胺,其中含氮杂环主要由部分氨基酸片段或氨基酸间的脱水缩合反应产生;腈主要来源于氨基酸分子脱H2反应以及酰胺脱H2O反应;酰胺主要来源于NH3与羧基的置换反应。不同生物质种类与热解工况下氮的迁移转化特性复杂多样,生物质种类以及热解过程中的压力、停留时间、升温速率、温度、热解气氛、粒径、催化剂等因素均会影响热解过程中氮的迁移转化路径,最终影响生物质热解气/油中含氮物质的组成及分布。进一步提出生物质热解过程中氮排放控制未来研究方向,以期为实现农村生物质资源高效清洁利用提供参考。

Twinning in Low-Temperature MOCVD Grown GaN on (001) GaAs Substrate

GaN buffer layers (thickness ～60nm) grown on GaAs(001) by low-temperature MOCVD are investigated by X-ray diffraction pole figure measurements using synchrotron radiation in order to understand the heteroepitaxial growth features of GaN on GaAs(001) substrates.In addition to the epitaxially aligned crystallites,their corresponding twins of the first and the second order are found in the X-ray diffraction pole figures.Moreover,{111} φ scans with χ at 55° reveal the abnormal distribution of Bragg diffractions.The extra intensity maxima in the pole figures shows that the process of twinning plays a dominating role during the growth process.It is suggested that the polarity of {111} facets emerged on (001) surface will affect the growth-twin nucleation at the initial stages of GaN growth on GaAs(001) substrates.It is proposed that twinning is prone to occurring on {111}B,N-terminated facets.

Structural and Optical Performance of GaN Thick Film Grown by HVPE

Thick GaN films were grown on GaN/sapphire template in a vertical HVPE reactor. Various material characterization techniques,including AFM, SEM, XRD, RBS/Channeling, CL, PL, and XPS, were used to characterize these GaN epitaxial films. It was found that stepped/terraced structures appeared on the film surface,which were indicative of a nearly step-flow mode of growth for the HVPE GaN despite the high growth rate. A few hexagonal pits appeared on the surface, which have strong light emission. After being etched in molten KOH, the wavy steps disappeared and hexagonal pits with {1010} facets appeared on the surface. An EPD of only 8 ×10^6cm^-2 shows that the GaN film has few dislocations. Both XRD and RBS channeling indicate the high quality of the GaN thick films. Sharp band-edge emission with a full width at half maximum（FWHM）of 67meV was observed, while the yellow and infrared emissions were also found. These emissions are likely caused by native defects and C and O impurities.

Effect of the surface properties of an activated coke on its desulphurization performance

Commercial coke was modified by H2O2 and/or NH3.H2O to obtain an activated coke containing additional oxygen functional groups and/or nitrogen functional groups. The aim of the modification was to enhance the SO2 adsorption capacity of the activated coke. Several techniques, including total nitrogen content measurements, SO2 adsorption, XPS and FTIR analysis, were used to characterize the coke samples. The XPS and FTIR spectra suggest the existence of -CONH2 groups in the H2O2 plus ammonia modified coke. The SO2 adsorption capacity of an activated coke increases slightly with an increase in H2O2 concentration during the modification process. The desulphurization performance of a modified coke is considerably enhanced by increasing the treatment temperature during ammonia modification. The amount of nitrogen in a coke modified by H2O2 plus NH3.H2O is the highest, and the SO2 adsorption capacity of the coke is also the highest (89.9 mg/gC). The NH3.H2O (only) modified sample has lower nitrogen content and lower desulphurization capacity (79.9 mg/gC). H2O modification gives the lowest SO2 adsorption capacity (28.9 mg/gC). The H2O2 pre-treatment is beneficial for the introduction of nitrogen onto the surface of a sample during the following ammonia treatment process.

Growth of Free-Standing AlN Nanocrystals on Nanorod ZnO Template

AlN film is deposited on a nanorod ZnO template by metalorganic chemical vapor deposition. Scanning electron microscopy measurements reveal that this film forms a lying nanorod surface. The grazing incidence X- ray diffraction further proves that it is entirely a wurtzite AIN structure, and the average size of the crystallite grains is about 12nm,which is near the ZnO nanorod diameter （30nm）. This means that the nanorod ZnO template can restrict the AlN lateral overgrowth. Additionally, by etching the ZnO template with H2 at high temperatures,we directly achieve epitaxial lift-off during the growth process. Eventually, free-standing AlN nanocrystals are achieved,and the undamaged area is near 1cm × 1cm. We define the growth mechanism as a ＂grow-etch- merge＂ process.

Promotion of activation ability of N vacancies to N2 molecules on sulfur-doped graphitic carbon nitride with outstanding photocatalytic nitrogen fixation ability

Nitrogen vacancies and sulfur co-doped g-C3N4 with outstanding N2 photofixation ability was synthesized via dielectric barrier discharge plasma treatment. X-ray diffraction, ultraviolet–visible spectroscopy, N2 adsorption, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and temperature-programmed desorption were used to characterize the as-prepared catalyst. The results showed that plasma treatment cannot change the morphology of the as-prepared catalyst but introduces nitrogen vacancies and sulfur into g-C3N4 lattice simultaneously. The as-prepared co-doped g-C3N4 displays an ammonium ion production rate as high as 6.2 mg·L^-1·h^-1·gcat^-1, which is 2.3 and 25.8 times higher than that of individual N-vacancy-doped g-C3N4 and neat g-C3N4, respectively, as well as showing good catalytic stability. Experimental and density functional theory calculation results indicate that, compared with individual N vacancy doping, the introduction of sulfur can promote the activation ability of N vacancies to N2 molecules, leading to promoted N2 photofixation performance.

Deposition of Silicon Nitride Films by Silane Hydrazine Process

A new catalytic chemical vapor process for depositing silicon nitride films using silane hydrazine gaseous mixture is described. This system can be useful at a temperature of lower than 400 ℃. The catalytic process gives more rapid deposition rate than 10 nm/min. The atomic composition ratio, N/Si, which is evaluated by Rutherfold backscattering method is about 1.4 under a given experimental conditions more than the stoichiometric value of 1.33 in Si 3N 4. The infrared transmission spectra show a large dip at 850 cm -1 due to Si-N bonds and no clear dip due to Si-O bonds. High N-H bond density is the evidence that the deposition mechanism is limited by N-N bond breaking of the hydrazine. The H contents, evaluated from Si-H and N-H bonds in the infrared absorption spectra, and the deposition rate are measured as a function of the substrate temperature. In addition some film properties such as the resistivity and the breakdown electric field are presented.

Improved analytic methods for coal surface area and pore size distribution determination using 77 K nitrogen adsorption experiment

77 K nitrogen adsorption was the most widely used technique for determining surface area and pore size distribution of coal. Brunauer–Emmett–Teller(BET) and Barrett–Joyner–Halenda(BJH) model are commonly used analytic methods for adsorption/desorption isotherm. A Chinese anthracite coal is tested in this study using an improved experimental method and adsorption isotherm analyzed by three adsorption mechanisms at different relative pressure stages. The result shows that the micropore filling adsorption predominates at the relative pressure stage from 6.8E 7 to 9E 3. Theoretically, BET and BJH model are not appropriate for analyzing coal samples which contain micropores. Two new analytic procedures for coal surface area and pore size distribution calculation are developed in this work. The results show that BET model underestimates surface area, and micropores smaller than 1.751 nm account for 35.5% of the total pore volume and 74.2% of the total surface area. The investigation of surface area and pore size distribution by incorporating the influence of micropore is significant for understanding adsorption mechanism of methane and carbon dioxide in coal.

Effect of BaO addition on relative density and electric conductivity of xNi/10NiO-NiFe_2O_4 cermets

xNi/10NiO-NiFe2O4 （x=5, 10, 17） cermets and those doped with 1% BaO （mass fraction） were prepared by cold isostatic pressing at 200 MPa and sintering in nitrogen atmosphere at 1 473 K. The effects of BaO addition on relative density, microstructure and electric conductivity of cermets were investigated. The results show that relative densities ofxNi/10NiO-NiFe2O4 cermets （x=5, 10, 17） doped with 1% BaO at 1 473 K in nitrogen atmosphere are increased by 0.49%, 1.45% and 2.99% compared with those of the undoped BaO cermets, respectively. Moreover, the electric conductivities （21.98, 28.37 and 50.10 S/cm） of xNi/10NiO-NiFe2O4 cermets （x=5, 10, 17） doped with 1% BaO at 1 233 K are improved compared with those （18.70, 22.79 and 39.58 S/cm） of xNi/lONiO-NiFe2O4 cermets （x=5, 10, 17）, respectively. This indicates that perhaps the addition of BaO or formation of BaFe204 and Ba2Fe2O5 has an active effect on electric conductivities ofxNi/10NiO-NiFe2O4 （x=5, 10, 17） cermets.

Study on the basic nitrogen compounds from coal-derived oil

The distillation range analysis and elemental analysis of fractioned direct liquefied oil were conducted. Each fraction of liquefied oil contains some nitrogen compounds. Using the acid extraction method and gas chromatography/mass spectrometry （GC-MS）, the basic nitrogen compounds have been separated and identified. Compared with the nitrogen content of the liquefied oil before and after separation, the basic nitrogen compounds account for more than half of all nitrogen compounds. The basic nitrogen compounds in the light liquefied oil are easily separated, and contain more types of basic nitrogen compounds. The results also show that there are many basic nitrogen compounds in liquefied oil, such as pyrrole, aniline, pyridine, quinoline and so on. However, there are fewer other types of basic nitrogen compounds.

Gas-phase Thermolysis of 1,2,3-triazole and 1,2,3-triazine Derivatives

Gas-phase thermolysis of 1-ethoxycarbonyl-benzotriazole under static, FVP and microwaves condition yielded N^1 and NZ-ethylbenzotriazole, 2-ethoxy-1,3-benzooxazole, biphenylene and oxazolidin-2-one. On the other hand, direct condensation and pyrolysis of naphtho[1,8-de][1,2,3]triazine with ethylisocyanate, phenylisocyanate and their isothiocayanates, benzoylisothiocyanate and thiourea at 150-160 ℃ or under microwaves irradiation produced the corresponding naphthopyrimidin-2-one derivatives.

Analysis of the Mechanical Properties of the Sintered Composite FeCuC in Two Different Atmospheres

This study aimed to analyze the mechanical properties of the compound FeCuC when compacted at varying pressures and sintered in two different types of furnaces. Besides the different models of furnace, the working atmospheres were varied： one is being composed with argon gas and another constituted with a balancing nitrogen and hydrogen. Atmospheres vary with the amount of production and the type of equipment used. The compound generated is used in the manufacture of rings for mechanical seals and is currently manufactured by the sintering process in passing furnace. The sintering was performed in a static furnace with argon atmosphere and compared with the same compound sintered in passage furnace with hydrogen and nitrogen atmosphere. The analysis of the properties of the tested material was performed with the aid of metallography using a scanning electron microscope, which verified the particle size distribution, chemical elements and pores present. Brinell hardness and Vickers micro hardness tests were also used to analyze the properties of this material after completion of the two processes. Thus, the research carried out has shown that variations may occur in the mechanical properties when processed in different furnace types and different sintering atmospheres.

Interactive effect of climate warming and nitrogen deposition may shift the dynamics of native and invasive species

Aims Projections of invasive species expansion under a warmer world often do not explicitly consider the concurring nitrogen(N)deposition.It remains largely unknown how the convoluted effect of climate warming and N deposition will shift the native and invasive species dynamics.Here,we hypothesize that the concurring in creases in N and temperature would promote growth of invasive species greater than that of native species.Methods A controlled greenhouse experiment was conducted to quantify the growth response of an invasive species(Solidago canadensis L.)and a co-existing native species(Artemisia argyi Levi,et Van)under the effects of climate warming,N deposition and their interactions.Important Findings Due to the strong positive effect of N addition,the interactive effect of temperature increase and N addition resulted in an overall significant increase in growth of both in vasive and native species,demonstrating that these manipulations may make microhabitats more favorable to plant growth.However,the relative increases in biomass,height and diameter of invasive S.canadensis were signifiesntly lower than those of native A.argyi.This suggests that the vegetative growth superiority of invasive S.canadensis over the native species A.argyi is reduced by the enhanced N availability in the warmer world.Therefore,the inclusion of N deposition may mitigate the projection of invasive species S.canadensis expansion under climate warming.

Characterization of a-Si:H/SiN multilayer waveguide polarization using an optical pumping application—LED

This paper describes the fabrication of a waveguide and the analysis of its polarization characteristics by applying light-emitting diode(LED) pumping lights to its surface.By using double tubed coaxial line(DTCL) microwave plasma chemical vapor deposition(MPCVD) equipment,an a-Si:H/SiN multilayer waveguide was fabricated whose thickness could be controlled at nanometer order.The main structural material of the waveguide sample consisted of a combination of layers of amorphous silicon hydrogen and silicon nitrate.Once the sample was ready,another major objective of the experiment was to analyze the polarization characteristics of the fabricated waveguide.The idea of the experiment was to analyze how the waveguide reacts when three types of LED(blue,yellow,and red) are radiated onto its surface.The results showed that the fabrication of the a-Si:H/SiN sample is successful.Most effective transmission results,which accord with the polarization characteristics analysis,were obtained.

High Nitrogen Pressure Solution (HNPS) growth of GaN on 2 inch free standing GaN substrates

Recent results of High Nitrogen Pressure Solution (HNPS) growth of GaN crystals deposited on and separated from 2 inch,and smaller,GaN substrates grown by Hydride Vapor Phase Epitaxy (HVPE) have been presented. The influence of the c-plane bowing in the initial substrate on quality,rate and mode of growth by HNPS method has been analyzed in details.

Stress control of silicon nitride films deposited by plasma enhanced chemical vapor deposition

Stress controllable silicon nitride(Si Nx) films deposited by plasma enhanced chemical vapor deposition(PECVD) are reported. Low stress Si Nx films were deposited in both high frequency(HF) mode and dual frequency(HF/LF) mode. By optimizing process parameters, stress free(-0.27 MPa) Si Nx films were obtained with the deposition rate of 45.5 nm/min and the refractive index of 2.06. Furthermore, at HF/LF mode, the stress is significantly influenced by LF ratio and LF power, and can be controlled to be 10 MPa with the LF ratio of 17% and LF power of 150 W. However, LF power has a little effect on the deposition rate due to the interaction between HF power and LF power. The deposited Si Nx films have good mechanical and optical properties, low deposition temperature and controllable stress, and can be widely used in integrated circuit(IC), micro-electro-mechanical systems(MEMS) and bio-MEMS.

Boron nitride nanotube growth via boron oxide assisted chemical vapor transport-deposition process using LiNO3 as a promoter

High-purity straight and discrete multiwalled boron nitride nanotubes （BNNTs） were grown via a boron oxide vapor reaction with ammonia using LiNO3 as a promoter. Only a trace amount of boron oxide was detected as an impurity in the BNNTs by energy-dispersive X-ray （EDX） and Raman spectroscopies. Boron oxide vapor was generated from a mixture of B, FeO, and MgO powders heated to 1,150 ℃, and it was transported to the reaction zone by flowing ammonia. Lithium nitrate was applied to the upper side of a BN bar from a water solution. The bar was placed along a temperature gradient zone in a horizontal tubular furnace. BNNTs with average diameters of 30-50 nm were mostly observed in a temperature range of 1,280-1,320 ℃. At higher temperatures, curled polycrystalline BN fibers appeared. Above 1,320 ℃, the number of BNNTs drastically decreased, whereas the quantity and diameter of the fibers increased. The mechanism of BNNT and fiber growth is proposed and discussed.