CO、CO2和O2对铀氢初始反应的影响

利用静态容量法测定了288 K下CO、CO2和O2在UO2表面的吸附等温线,利用压降法结合原位显微观测研究了CO、CO2和O2对铀氢初始反应的影响.结果表明,3种气体在U02表面的吸附强弱关系为O2＞CO2 ＞CO,Langmuir和Freundlich方程分别较好描述了CO、CO2的等温吸附行为.含氧气体对孕育期的影响与其吸附特性密切相关,3种气体阻抑效应的强弱关系为CO2＞CO＞O2.CO和O2对孕育期的影响近呈线性关系,CO2对孕育期的影响则与CO2含量有关.CO和CO2的阻抑机制主要是气体分子对铀表面活性位的优先占据,而O2的阻抑机制相对复杂,可能涉及水分子前驱态的形成和吸附O粒子扩散两种表面化学过程.根据阻抑机制和吸附特性导出的数学模型较好描述了CO和CO2对孕育期的影响规律.     

纳米金催化NO+CO反应机理的密度泛函理论研究（英文）

采用密度泛函理论对NO+CO反应机理在Au(111)面上的反应历程进行详细讨论。通过对表面吸附物种(N、O、NO、CO、N_2、N_2O、CO_2)的吸附行为进行研究,得到最佳活性吸附中心。对三种机理中的基元反应的活化能进行计算分析,结果发现由于NO在Au(111)面上直接分解为N和O需要很高的能垒(599.4 kJ·mol~(-1)),NO+CO反应按照直接分解机理的可能性很小,按照二聚体机理的可能性更大。最佳反应途径是2NO→(NO)2→N2O+O→N2+2O,其中通过O端吸附在Au(111)面上的二聚体(NO)_2是不可避免的中问体。该反应的决速步骤是N_2O~*→N_2~*+O~*,活化能为49.5 kJ·mol~(-1)。     

气体渗碳、真空渗碳表面硬化热处理缺陷及其纠正办法 3.发生炉煤气气体渗碳

气体渗碳量的调节: CaHm (n/2)O 1.83n·N2→nCo (m/2)H2 1.88n·N2…………(1) 2CO=〔C〕 CO_2…………(2) H_2 CO_2=CO H_2O…………(3) CH_4=〔C〕 2H_2…………(4) CH_4 CO_2=2CO 2H_2………(5) CH_4 H_2O=CO 3H_2………(6) 式(1)表示做为气体渗碳基本气体的生成反应:通常用丁烷丙烷甲烷等饱和碳氢化合物。在1000℃以上高温下,通过Ni触煤进行的反应。该反应初期是放热反应,但后期是吸热反应,总的来说是吸热反应。反应生成气体中,含有微量的H_2O·CO_2·CH_4     

TiO_2可见光催化H_2O_2降解水中的有机污染物

以活性艳红X-3B及苯酚作模型污染物,研究催化剂晶型(锐钛矿和金红石)及H2O2对TiO2可见光催化性能的影响,并研究Fe3+在这一反应体系中的协同效应。结果表明:在H2O2存在条件下,锐钛矿和金红石TiO2均能可见光催化降解活性艳红X-3B,且TOC的去除率达65%,反应并不限于发色基团的破坏,但当TiO2的吸附点位吸附CO32?达到饱和后,则对活性艳红X-3B基本无降解效果;TiO2能可见光催化H2O2降解苯酚,金红石TiO2显示出较锐钛矿TiO2更高的催化活性,反应120 min后,对苯酚的降解率达80%,且反应体系生成的环状中间产物的浓度明显较锐钛矿TiO2的高;以Fe3+协同TiO2可见光催化H2O2降解苯酚时,反应效率显著加快,经20 min反应,对苯酚的降解率可达100%,而金红石TiO2显示更为明显的协同效应。     

纳米Fe3O4负载啤酒酵母菌对铀的吸附性能与机理

以纳米Fe3O4磁性微粒负载啤酒酵母菌,制备一种新型铀吸附剂,考察其吸附铀的主要影响因素,即溶液pH值、铀初始浓度、吸附剂投加量及其粒度,分析吸附过程的反应动力学和等温吸附规律,并用扫描电镜和能谱仪分析吸附机理。结果表明:纳米Fe3O4负载啤酒酵母菌(NFSC)吸附铀的最佳条件是pH值为7.0,铀初始浓度为60 mg/L,NFSC加入量为50 mg,NFSC的最佳粒径为12 nm。NFSC对铀的吸附动力学较好地符合准二级动力学模型,相关系数为0.999 6;吸附等温线均能符合Langmuir和Freundlich等温线模型,说明该吸附体系是一个单层覆盖与多层吸附相结合的模式。扫描电镜和能谱图表明:NFSC吸附铀后表面形态发生变化,且吸附过程中共存物理吸附和化学吸附,属于混合吸附类型。     

O2在U和U—Nb合金表面吸附的XPS研究

采用X射线光电子能谱（XPS）分析研究了298K时O2在金属U和U－Nb合金清洁表面的原位吸附过程,作为对照还研究了经纯Nb表面的吸附,吸附各阶段XPS图谱的变化揭示了O2在U,Nb和N－Nb合金表面的吸附将导至UO2,NbO和Nb2O5等多种产物形成,定量分析表明,O2在U和U－Nb合金表面的饱和吸附量大约分别为45L和40L（1L＝1．33x10^-4Pa.s）,而O2在金属Nb上的饱和吸附量仅约为10L。     

海绵钯表面CO、O2、CH4的吸附特性

在300K和0～13.3 kPa压力范围内,测量了海绵钯表面对CO、o2、CH4的吸附等温线.结果表明:钯表面对CO的吸附量先随压力的升高而增加,之后呈现饱和吸附状态;对O2的吸附至少可以分3个区间,在0～100 Pa压力区间,吸附量随压力升高快速增加,此后直至4kPa的区间内,吸附量随压力升高较缓慢增加,但当压力高于4kPa时,吸附量随压力的升高而增加又变得较为显著:CH4的吸附量相对较小,并持续随压力升高而缓慢增加.在整个压力测量区间,CO、CH4的吸附等温线符合兰缪尔模型,而O2的吸附等温线只在压力小于1.33 kPa的区间才符合.     

CO2毒化对Pd膜表面状态与氢同位素渗透性能的影响

在不同温度的CO2气氛中对Pd膜进行了毒化,将毒化后的Pd膜与氢气反应并测试其氢同位素渗透性能。采用XPS、SEM等检测了CO2在不同温度下对Pd膜毒化后的表面成分与形貌,并对比分析了吸氢前、后的Pd膜表面状态的变化,得出了CO2对Pd膜表面状态的影响规律,探讨了CO2气体的毒化机理。结果表明,CO2分子在Pd表面会解离成为C=O,C-O与O原子,随着温度升高,C=O减少,而C-O与O原子含量增加。当CO2毒化温度达到500℃时,Pd表面会生成PdO并伴有微孔出现,而C-O随温度升高能够稳定吸附于Pd表面。毒化后的试样在常温下进行吸氢反应后表面PdO消失,吸附O含量减少,多孔形貌得到改变。CO2毒化后,由于C-O与O原子在Pd表面吸附并占据了Pd膜表面的氢解离位,从而导致Pd膜透氘能力下降。     

CO，O2，CH4，CO2对钯柱氢氘排代性能的影响

为了解杂质气体对钯柱氢氘排代性能的影响程度，利用快排代法考察了排代氢中添加CO，O2，CH4，CO2等气体后室温下钯柱氢氘排代效率的变化情况，并测量了钯表面O2，CO，CH4的等温吸附曲线。结果表明：H2中仅加入10μL／L的CO，排代性能已显著下降，随CO含量的增加，排代性能随之显著降低，当CO含量增至3000μL／L时将几乎没有排代效果；O2的影响比CO弱，H2中含3000μL/L的O2时排代性能约下降20％；然而当H2中含3000μL／L的CO2时排代性能约下降3．2％；CH4的影响则相对可忽略。     

不锈钢电弧辅助活性TIG焊

针对不锈钢,提出了一种新型活性YIG焊方法--电弧辅助活性TIG焊,即AA-TIG焊(arc assisted activating TIG welding).该焊接方法通过在正常TIG焊前以活性混合气体作为保护气体,采用小电流钨极电弧预熔待焊焊道表面,可使熔深显著增加,焊接效率大大提高,而且具有可全自动化焊接和工艺可重复性好等优点.分别采用O2+Ar,CO2+Ar,空气作为小电流钨极电弧的保护气体进行了单弧AA-TIG焊.与传统TIG焊比较,发现O2+Ar,CO2+Ar和空气都可显著增加熔深,减小熔宽,焊缝表面成形良好.采用CO2+Ar作为活性混合保护气体进行双弧AA-TIG焊,焊缝成形良好,熔深显著增加.熔深随着焊枪间距减小而增大.     

空气主要组分在Ag表面的吸附行为研究

空气中熔融的Ag能够溶解自身体积的22倍氧气,冷却固化过程中其他气体(N₂、CO₂等)几乎为零。吸附是气体溶解的第一步,本文基于量子化学和簇模型的方法建立空气主要组分N₂、O₂、CO₂于Ag表面的吸附模型,研究Ag表面对空气主要组分的吸附行为。结果显示,O₂在Ag(100)、Ag(110)、Ag(111)上的吸附能都为最大,空气中Ag的周围主要吸附O₂,且几乎不产生与其他非氧组分的直接接触;Ag表面上N₂、O₂、CO₂的解离都需要一定的热激活条件,O₂在Ag表面的解离能垒低于N₂和CO₂,更容易解离成O吸附在表面。因此,Ag对空气中的O₂具有选择性吸附的功能。     

SiO2包覆对含微量CO氢环境中LaNi4.25Al0.75吸氢动力学性能的影响

采用气相二氧化硅法制备了LaNi4.25Al0.75/SiO2复合材料,研究了该复合材料表面形貌以及氢中微量CO对LaNi4.25Al0.75合金及LaNi4.25Al0.75/SiO2复合材料吸氢动力学性能的影响。结果表明：合金被毒化后,在表面生成含NiO、La(OH)3、La2O3、Al(OH)3的氧化层,并且吸附大量CO,导致合金的吸氢量减少,动力学变慢。表面包覆SiO2可显著改善合金抗毒化性能     

High-temperature linear kinetics of FeS formation and reduction in COS-CO-CO2 gas mixtures

The linear kinetics of the monosulfide scale formation and reduction according to the overall reaction Fe_(s) + COS_(g) = FeS_(s) + CO_(g) in COS-CO-CO₂ gas mixtures was studied in the temperature range 750–910 C by a thermogravimetric technique. The validity of the linear rate law is limited to short times of exposure and relatively low partial pressures of COS. A proposed model for the sulfidation reaction implies that both adsorption of COS and dissociation of adsorbed COS are involved in the rate-limiting steps. For the reverse reaction it is suggested that both adsorption of CO and recombination of adsorbed CO with sulfur either in an adsorbed state or incorporated in the sulfide lattice are the rate-controlling steps. The theory of absolute reaction rates was applied to the proposed reaction model. Activation enthalpies and entropies for both the sulfidation and the reduction process were derived. From these data standard enthalpy and entropy changes for the overall reaction were evaluated and found to be in close agreement with thermochemical data from the literature.     

Effect of aluminum-containing additives on the reactivity in air and CO2 of carbon anode for aluminum electrolysis

Airbum reaction and carboxy reaction result in the excess consumption of carbon anode in aluminum electrolysis.To reduce the excess carbon consumption, carbon anode was doped with aluminum-containing additives, such as A1, Al4C3,AlF3 and Al2O3. Their reactivity in air and CO2 was determined with an isothermal-gravimetric method to study the effect of aluminum-containing additives on the reactivity in air and CO2 of carbon anode. Results shown that the airbum reactivity at 450℃ and carboxy reactivity at 970℃ of carbon anode both decreased with Al-containing additives adding, while shown a minimum with the amount of Al4C3, AlF3 and Al2O3 increasing. However, all Al-containing additives increase the alrbum reactivity at 550℃ of carbon anodes. Coke yield measurement and XRD examination with aluminum containing additives doped pitch cokes revealed that the effect of Al-containing additives on the airburn reactivity and carboxy reactivity of carbon anode would result from chemical factors and structural factors.     

Au/ZrO2 catalysts for low-temperature water gas shift reaction: Influence of particle sizes

The size effects of Au and ZrO₂ particles on the structural property and the catalytic performance of Au/ZrO₂ catalysts for the water gas shift reaction were extensively investigated. It was found that the Au-ZrO₂ contact boundaries played essential roles in determining the catalytic reactivity. By keeping the size of Au particle to be ∼3 nm, the increase in the particle size of ZrO₂ from ∼7 nm to ∼55 nm caused significant decrease in the reaction rate. When the particle size of ZrO₂ was fixed at ∼20 nm, the conversion of CO decreased greatly with increasing the size of gold particle from 2.9 to 6.2 nm. IR spectroscopy and kinetic study revealed that the water gas shift reaction occurred at the Au-ZrO₂ contact boundaries, where CO is adsorbed on the Au species and H₂O is activated on the surface of ZrO₂ through the formation of formate species, acting as key reaction intermediates.     

CVD自支撑金刚石厚膜的氧化动力学研究

为了了解直流等离子喷射CVD自支撑金刚石膜高温氧化机理,利用热失重的方法研究了金刚石膜在不同温度、不同氧浓度条件下的氧化反应.结果表明:CVD金刚石膜氧化反应中的反应指数大约为0.63,氧化反应的激活能为220kJ/mol.通过X-Ray和Raman分析可知,CVD金刚石膜的氧化经历3个过程:1)金刚石膜表面氢的解吸和氧的吸附;2)金刚石与氧发生化学反应;3)金刚石氧化产物(CO、CO2)的解吸.     

Corrosion of uranium and its low content Zr, Nb, and Ru alloys in aqueous solutions

Corrosion of uranium and its alloys with low content (0.5–5.0 at %) of Zr, Nb, and Ru in water and bicarbonate aqueous solutions is studied; the effect of hydrogen peroxide, the main product of radiation processes, on the corrosion rate is elucidated. The rate of the primary corrosion process U +(2 +n)H₂O=UO₂·nH₂O+ 2H₂↑ is measured by electrochemical methods in anaerobic and aerobic conditions for uranium metal and its alloys containing 0.5 to 5.0 at % of Zr, Nb, and Ru. It is shown that the corrosion rates for the alloys are lower than that of reactor-grade uranium; however, the difference is rather close to the measurement error. The corrosion mechanism is studied; U(III) is shown to be rather unstable in neutral solutions when uranium(III) hydroxide is precipitated and no significant amount of U(III) and UH₃ is present among the products of the metallic uranium corrosion in water. The kinetics of the second corrosion stage U(IV) + O₂→U(VI) is studied by spectrophotometric method. It is shown that the reaction of U(IV) oxidation by atmospheric oxygen is similar in weakly acid solutions (pH 1.5–4.0) and in bicarbonate media: in particular, it has an induction period for uranium (IV) accumulation, after which the reaction accelerates; it is formally a first-order reaction with respect to uranium. The reaction mechanisms differ in the two media: in weakly acid solutions, after the appearance of U(VI), the reproportionation reaction proceeds; thus formed U(V) interacts with O₂ faster than U(IV). In the bicarbonate medium, the acceleration of the reaction is due to the formation of a [U(IV)ΣU(VI)] complex whose reactivity is higher than that of uranium (IV). In the absence of bicarbonate, of great importance is the formation of a copolymer of U(IV) and U(VI), which at pH≥4 prevents formation of U(V). It is shown that on the introduction of hydrogen peroxide to aqueous solutions, the metallic uranium surface becomes transpassive, which increases the rate of corrosion process by at least an order of magnitude,. The introducing of oxidants and platinum mesh lowers the hydrogen accumulation at 120–150°C and, hence, the hydrogen-explosion danger of the uranium-water-corrosion-products system. Methods of deposition of metal oxide (Tc, Ru, Mo, W) films onto uranium surfaces by immersing uranium metal into Tc(VII), Ru(VI), or Mo and W heteropoly compound solutions are studied. Original Russian Text ? V.F. Peretrukhin, A.G. Maslennikov, A.Yu. Tsivadze, C.H. Delegard, A.B. Yusov, V.P. Shilov, A.A. Bessonov, K.E. German, A.M. Fedoseev, L.P. Kazanskii, N.Yu. Budanova, A.V. Kareta, A.V. Gogolev, K.N. Gedgovd, G.S. Bulato, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 3, pp. 229–251.     

P2O5对熔渣界面氧迁移反应的影响及机理

利用同位素交换法测定了熔渣表面CO2与氧化铁熔渣之间氧迁移反应的速度常数,并基于电化学反应机制,分析了添加P2O5对该过程的影响,建立了一个新的反应动力学模型．该模型认为P2O5作为易挥发组分参与对电子的竞争,抑制氧迁移(CO2 2e=CO O^2-)主反应的进行．对实验数据的分析和拟合表明了模型的可用性,也辅证了反应的电化学机制．