ZrN–Si_3N_4–Y_2O_3复合材料的相组成（英文）

采用不同组分的Zr N、Si_3N_4和Y_2O_3混合粉末,在1 750℃高温固相反应合成Zr N–Si_3N_4–Y_2O_3复合材料,借助于X射线衍射仪表征6种按不同比例混合样品的物相组成。结果表明:在Zr N–Si_3N_4–Y_2O_3三元系统中,Zr N分别与Si_3N_4、Y_2O_3和Y2Si3O3N4(M相,黄长石结构)共存;M相为Si_3N_4和Y_2O_3在摩尔比为1:1时的产物,Zr N–Si_3N_4–Y_2O_3三元系统扩展为Zr N–Si_3N_4–Y_2O_3–Si O2四元系统,在该四元系统中,Zr N分别与M相、Y4Si2N2O7(J相,单斜Y4Al2O9结构)及Y5(Si O4)3N(H相,磷灰石结构)3种含钇硅酸盐及Si_3N_4、Y_2O_3共存。其中,J相和H相分别是Si2N2O(Si_3N_4和Si O2在摩尔比为1:1时的产物)和Y_2O_3在摩尔比分别为2:1和9:5时的产物。用Zr N–Si_3N_4–Y_2O_3体系相图可解析制备Zr N陶瓷和Zr N/Si_3N_4复合陶瓷的相组成。     

Ca~(2+)、Mg~(2+)固溶Ba_2Si O_4:Eu~(2+)荧光增强机理

采用高温固相法在还原气氛得到(Ba_(1-x)Me_x)_(1.95)Si O_4:0.05Eu(Me=Ca,Mg)荧光粉。采用X射线衍射仪、场发射扫描电镜、元素分析仪、荧光光谱仪对样品进行分析,结果表明:Ca~(2+)、Mg~(2+)在Ba_2Si O_4相的固溶度分别为10%(摩尔分数,下同)和30%,其对应荧光粉比Ba_2Si O_4:Eu在紫外激发绿色荧光亮度有明显提高(365 nm激发下亮度为Ba_2Si O_4:Eu的110%、140%,254 nm激发下则为105%、125%)。(Ba_(1-x)Ca_x)_(1.95)Si O_4(0.1x≤0.3)为T相而非Ba_2Si O_4相,故离子半径与Ba~(2+)更接近的Ca~(2+)反而比Mg~(2+)在Ba_2Si O_4相的固溶度更低;Ca~(2+)、Mg~(2+)在Ba_2Si O_4中固溶,使得晶格参数略微减小,且b比c减小更快,即Ca~(2+)、Mg~(2+)更倾向取代9配位Ba~(2+)(II)而非10配位Ba~(2+)(I);固溶有利于粉末结晶状况提高(衍射峰增强、半峰宽变窄)。Eu~(2+)(I)比Eu~(2+)(II)对绿光贡献更大,Ca~(2+)、Mg~(2+)可促进Eu~(2+)(I)/Eu~(2+)(II)比值提高。Eu4d高分辨光电子谱表明,Ca~(2+)、Mg~(2+)对Eu离子的价态无明显影响。由此可见,Ca~(2+)、Mg~(2+)固溶可提高Ba_2Si O_4相粉末结晶程度、促进Eu~(2+)进入发光效率更高Ba~(2+)(I)位置,同时不影响Eu~(2+)的价态稳定性,是固溶提升Ba_2Si O_4:Eu荧光粉发光性能原因所在。     

(Sr_(0.1)Ca_(0.9))_(0.97)TiO_3∶Eu_(0.03)~(3+)荧光粉掺杂复合发光玻璃的制备与研究

玻璃具有透明、耐腐蚀等优点,是一种良好的基质材料。本文选用了TeO_2-ZnO、Bi_2O_3-ZnO-B_2O_3两种低熔点玻璃基体,掺杂(Sr_(0.1)Ca_(0.9))_(0.97)TiO_3∶Eu_(0.03)~(3+)荧光粉制备复合发光玻璃。研究表明,荧光粉在玻璃基体中的分散均匀性也受多种因素限制;荧光粉掺入玻璃基体中,受玻璃本身光散射的影响,发光性能受到了较大的限制。复合玻璃发光强度随着荧光粉掺杂量的增加而升高,但掺杂量超过一定值后,发光性能反而降低。掺杂量增加到一定程度时,得到的产物是烧结态陶瓷结构,其结构的变化降低了发光性能。对比TeO_2-ZnO、Bi_2O_3-ZnO-B_2O_3两种玻璃基体,TeO_2-ZnO玻璃与(Sr_(0.1)Ca_(0.9))_(0.97)TiO_3∶Eu_(0.03)~(3+)荧光粉有更好的匹配性。     

白光LED用Ca_6Sr_4(Si_2O_7)_3Cl_2:Ce~(3+),Eu~(2+),Sm~(3+)荧光粉的合成及其发光性质

采用传统的高温固相法合成了Ce3+,Eu2+,Sm3+离子分别单激活和三种稀土离子共激活的Ca6Sr4(Si2O7)3Cl2荧光粉,并通过X射线粉末衍射、荧光光谱和CIE色坐标对其结构和发光性质进行了研究。荧光粉Ca5.91Sr3.96(Si2O7)3Cl2:0.02Ce3+,0.04Eu2+,0.04Sm3+在365 nm激发下能发射高强度白光,其色坐标为x=0.2183,y=0.2187,有望成为一种新型白光LED灯用荧光粉。     

Ba-La-Cu-O、Ba_(2-x)Sr_xLaCu_3O_(7-δ)、Ba_2La_(1-x)Ce_xCu_3O_(7-δ)体系的物相及电性研究

本文对Ba-La-Cu-O中Ba_3La_3Cu_6O_(14+δ)相(336相),Ba_2La(LaCe)_(31-x)Ce_xCu_3O_(7-δ)中Ba_3(LaCe)_3Cu_6O_(14+δ)相(336相)进行了研究,用Sr部分取代Ba-La-Cu-O中的Ba,当Sr/Ba<80%时,体系发生336相到123相的转变.     

SrO对Si_3N_4–ZrO_2–SrO系统反应合成ZrN的影响

通过引入SrO,利用Si_3N_4–ZrO_2–SrO三元系统反应合成ZrN,使得SiO_2–Si_3N_4–ZrO_2–ZrN四元系统形成互易关系,并结合热力学计算,对在N2气氛无压条件下Si_3N_4–ZrO_2–SrO三元系统分别在1 500和1 700℃时的反应途径进行了研究,并采用XRD进行物相分析。结果表明:当烧结温度为1 500℃时,Si_3N_4–ZrO_2–SrO系统可生成ZrN+SrSi_2O_2N_2和ZrN+Sr_3SiO_5+SrZrO_3的复合相;当烧结温度提高到1 700℃时,反应产物中与ZrN复合的物相不仅有SrSi_2O_2N_2和Sr_3SiO_5+SrZrO_3,还生成了Sr_2SiO_4+SrZrO_3和Sr7_ZrSi_6O_(21)+SrZrO_3,其中,SrZrO_3为ZrO_2–SrO二元系统反应的结果。在1 500和1 700℃时,Si_3N_4–ZrO_2–SrO三元系统中可生成ZrN+X(+SrZrO_3)复合相,且ZrN–X共存关系在扩展的SiO_2–Si_3N_4–SrO–ZrO_2–ZrN五元系统中给出。Si_3N_4–ZrO_2–SrO三元系统的数个反应可被用于在较低温度下一步反应制备ZrN复相陶瓷。     

纳米SiO_2对Sr_(0.98)BaSiO_4:0.02Eu绿色荧光粉性能的影响

以纳米和微米Si O_2为原料,采用高温固相法合成了Sr_(0.98)Ba Si_xSi-(1-x)O_4:0.02Eu(其中,x表示纳米Si O_2的含量,x=0-1.0)一系列绿色荧光粉。结果表明:原料中掺入纳米Si O_2后,可以有效改善荧光粉的发光强度、晶体形貌和尺寸,增强粉体稳定性,降低用粉量等。值得注意的是,当纳米Si O_2的掺杂比例为0.6时,所得粉体质量较佳。本研究为后期进一步改进绿色荧光粉的性能奠定了一定的实验基础。     

白光LED用红色发光粉La_(9.33)(SiO_4)_6O_2:Eu~(3+)的制备和发光特性

采用高温固相法合成具有磷灰石结构的La9.33(Si O4)6O2:Eu3+红色荧光粉。该荧光粉的性质通过X射线粉末衍射、荧光光谱来表征。La9.33(Si O4)6O2:Eu3+的激发光谱主要由以285 nm为中心的宽谱峰以及一系列由Eu3+离子f-f跃迁的锐线峰组成,在近紫外区有一个最强的激发峰在393 nm。在393 nm激发下,可以观察到La9.33(Si O4)6O2:Eu3+在612 nm处产生强烈的红光。发光特性表明,La9.33(Si O4)6O2:Eu3+荧光粉可能成为潜在近紫外芯片用红色荧光粉。     

(Ba,Sr)_2SiO_4∶Eu~(2+)的低温合成与荧光性能研究

以MCM-41为硅源,采用共沉淀法在900℃合成了BaxSr1.99-xSi O4∶0.01Eu2+荧光粉,研究了其结构和发光性能随Ba掺量x的变化。结果表明,Sr1.99Si O4:0.01Eu2+为α'-Sr2Si O4相和β-Sr2Si O4相的混合相,随着Ba2+的掺入,β相转变为α'相,同时各XRD衍射峰向低角度移动。在365 nm紫外光激发下,所有样品均在450~600 nm区域出现一个宽发射带。当x由0增加到0.8时,最大发射峰位由475 nm红移到516 nm,当x由0.8增加到1.99时,最大发射峰位由516 nm蓝移到502 nm。Ba1.99Si O4∶0.01Eu2+样品具有最高的发射强度。     

稀土Sm_2O_3对多孔Si_2N_2O陶瓷显微结构和性能的影响

以Si_3N_4与Si O2为初始原料、Sm_2O_3为烧结助剂,通过无压烧结制备了气孔率不同的多孔Si_2N_2O陶瓷。研究了烧结温度、助剂含量对烧结后的产物的影响;测试了多孔Si_2N_2O陶瓷的力学性能、介电性能和抗氧化性能。结果表明:烧结温度过高或助剂含量过高都会导致Si_2N_2O相的分解;助剂含量对Si_2N_2O陶瓷微观组织产生明显的影响,随着助剂含量的增多,其显微结构由细小层片状过渡到板状晶粒再到短纤维搭接的板状晶粒结构,所制备的Si_2N_2O陶瓷比Si_3N_4陶瓷具有更优异的性能,抗弯强度为220 MPa,介电常数ε为4.1,介电损耗tanδ0.005。1 400℃氧化10 h,Si_2N_2O与Si_3N_4的质量增量分别为0.6%与2.1%。     

Fertilizers, agronomy and N2O

N₂O is emitted from agricultural soils due to microbial transformation of N from fertilizers, manures and soil N reserves. N₂O also derives from N lost from agriculture to other ecosystems: as NH₃ or through NO ₃ ^- leaching. Increased efficiency in crop N uptake and reduction of N losses should in principle diminish the amount of N₂O from agricultural sources. Precision in crop nutrient management is developing rapidly and should increase this efficiency. It should be possible to design guidelines on good agricultural practices for low N₂O emissions in special situations, e.g. irrigated agriculture, and for special operations, e.g. deep placement of fertilizers and manures. However, current information is insufficient for such guidelines. Slow-release fertilizers and fertilizers with inhibitors of soil enzymatic processes show promise as products which give reduced N₂O emissions, but they are expensive and have had little market penetration. Benefits and possible problems with their use needs further clarification.     

电氧化N_2O_4制备N_2O_5工艺研究

以N2O4和HNO3为原料,通过电氧化法制备了新型绿色硝化剂N2O5,并研究了电解氧化法制备N2O5工艺的影响因素,主要讨论了电解反应时间、电流密度和反应温度对该工艺的影响。在反应时间为4～5h,电流密度为0.09～0.10A/cm2,反应温度为5～10℃时,可得到质量分数较高的N2O5阳极液。     

Subsoils: chemo-and biological denitrification, N2O and N2 emissions

Agricultural practices, soil characteristics and meteorological conditions are responsible for eventual nitrate accumulation in the subsoil. There is a lot of evidence that denitrification occurs in the subsoil and rates up to 60–70 kg ha^-1 yr^-1 might be possible. It has also been shown that in the presence of Fe²⁺ (formed through weathering of minerals) and an alkaline pH, nitrate can be chemically reduced. Another possible pathway of disappearance is through the formation of nitrite, which is unstable in acid conditions. With regard to the emission of N₂O and N₂, it can be stated that all conditions whereby the denitrification process becomes marginal are favourable for N₂O formation rather than for N₂. Because of its high solubility, however, an important amount of N₂O might be transported with drainage water.     

Recovery of groundwater N2O at the soil surface and its contribution to total N2O emissions

Production and accumulation of the major greenhouse gas nitrous oxide (N₂O) in surface groundwater might contribute to N₂O emissions to the atmosphere. We report on a ¹⁵N tracer study conducted in the Fuhrberger Feld aquifer in northern Germany. A K¹⁵NO₃ tracer solution (60 atom%) was applied to the surface groundwater on an 8 m² measuring plot using 45 injection points in order to stimulate production of ¹⁵N₂O by denitrification and to detect its contribution to emissions at the soil surface. Samples from the surface groundwater, from the unsaturated zone and at the soil surface were collected in regular intervals over a 72-days period. Total N₂O fluxes at the soil surface were low and in a range between ?7.6 and 29.1 μg N₂O-N m^?2 h^?1. ¹⁵N enrichment of N₂O decreased considerably upwards in the profile. In the surface groundwater, we found a ¹⁵N enrichment of N₂O between 13 and 42 atom%. In contrast, ¹⁵N enrichment of N₂O in flux chambers at the soil surface was very low, but a detectable ¹⁵N enrichment was found at all sampling events. Fluxes of groundwater-derived ¹⁵N-N₂O were very low and ranged between 0.0002 and 0.0018 kg N₂O-N ha^?1 year^?1, indicating that indirect N₂O emissions from the surface groundwater of the Fuhrberger Feld aquifer occurring via upward diffusion are hardly significant. Due to these observations we concluded that N₂O dynamics at the soil–atmosphere interface is predominantly governed by topsoil parameters. However, highest ¹⁵N enrichments of N₂O throughout the profile were obtained in the course of a rapid drawdown of the groundwater table. We assume that such fluctuations may enhance diffusive N₂O fluxes from the surface groundwater to the atmosphere for a short time.     

Solubility of N2O and CO2 in n-Dodecane

The solubility of CO₂ and N₂O in a physical solvent, n-dodecane [C.A. Registry N° 124–18–5], has been measured at 40, 80 and 120°C at pressures up to 9.6 MPa. The experimental results were correlated by the Peng-Robinson (1976) equation of state, and the interaction parameters, the Henry's constants and the N₂O analogy parameters were obtained.     

Effects of N management on N2O and CH4 fluxes and15N

Forage production in irrigated mountain meadows plays a vital role in the livestock industry in Colorado and Wyoming. Mountain meadows are areas of intensive fertilization and irrigation which may impact regional CH₄ and N₂O fluxes. Nitrogen fertilization typically increases yields, but N-use efficiency is generally low. Neither the amount of fertilizer-N recovered by the forage nor the effect on N₂O and CH₄ emissions were known. These trace gases are long-lived in the atmosphere and contribute to global warming potential and stratospheric ozone depletion. From 1991 through 1993 studies were conducted to determine the effect of N source, and timing of N-fertilization on forage yield, N-uptake, and trace gas fluxes at the CSU Beef Improvement Center near Saratoga, Wyoming. Plots were fertilized with 168 kg N ha^-1. Microplots labeled with¹⁵N-fertilizer were established to trace the fate of the added N. Weekly fluxes of N₂O and CH₄ were measured during the snow-free periods of the year. Although CH₄ was consumed when soils were drying, flood irrigation converted the meadow into a net source of CH₄. Nitrogen fertilization did not affect CH₄ flux but increased N₂O emissions. About 5% of the applied N was lost as N₂O from spring applied NH₄NO₃, far greater than the amount lost as N₂O from urea or fall applied NH₄NO₃. Fertilizer N additions increased forage biomass to a maximum of 14.6 Mg ha^-1 with spring applied NH₄NO₃. Plant uptake of N-fertilizer was greater with spring applications (42%), than with fall applications (22%).     

Preparation and Characterization of Copper Catalysts Supported on Mesoporous Al2O3 Nanofibers for N2O Reduction to N2

The gas-phase hydrogenation of benzene to cyclohexane over Ce_{1 - x} Pt _x O_{2 -} (x = 0.01, 0.02) catalyst was investigated in the temperature range 80-200 °C. A 42% conversion of benzene to cyclohexane with 100% specificity was observed at 100 °C over Ce_0.98Pt_0.02O_{2 -} with a catalyst residence time of 1.22 × 10⁴ g s/mol of benzene. The activity of the catalyst was compared with those of Pt metal, combustion-synthesized Pt/-Al₂O₃ and Pt/-Al₂O₃. The turnover frequency value of Ce_0.98Pt_0.02O_{2 -} is 0.292, which is an order of magnitude higher than those of the other Pt catalysts investigated. The kinetics of reaction and the deactivation behavior of the catalyst were studied and a regeneration methodology was suggested. The deactivation kinetics and structural evidence from XRD, XPS, TGA and H₂ uptake studies suggest that the oxidized Pt in Ce_0.98Pt_0.02O_{2 -} is responsible for the high catalytic activity towards benzene hydrogenation.     

Low-Temperature Catalytic Decomposition of N2O

Theoretical Foundations of Chemical Engineering - A series of oxide catalysts modified with potassium cations, 1–5% K2О/CoFe2O4, with a spinel structure were obtained via...