Effect of Ce addition on hot corrosion behaviours of a cast γ′-strengthened Co–Al–W–Mo–Ta–B alloy at 800 ​°C

Hot corrosion behaviours of a novel Co–9Al-4.5W-4.5Mo–2Ta-0.02B alloy doped with 0.01, 0.05, 0.1 and 0.2 ?at% Ce exposed at 800 ?°C in a solution of 75%Na₂SO₄/25%NaCl were investigated. The alloys comprised a coherent γ-Co_SS/γ′-Co₃(Al, W) microstructure (0.01Ce and 0.05Ce alloys) and κ-Co₃(W, Mo) precipitates (0.1Ce and 0.2Ce alloys) at grain boundaries. Hot corrosion kinetics curves demonstrated the parabolic time dependency profile with two stages: the first parabolic stage is within the beginning ～50 ?h corrosion and follows by the second parabolic stage. With an increasing nominal Ce content the weight gain of the alloy significantly decreased from approximately 70.1 ?mg ?cm^?2 (0.01Ce) to 40.8 ?mg ?cm^?2 (0.2Ce) when exposed for 100 ?h. A two-layer corrosion scale formed, and the scale was composed of an outer layer of Co₃O₄ oxide with spinel compounds of CoAl₂O₄, CoWO₄and CoSO₄, and an inner γ/needle-like Co₃W/sulphide layer adhered to the substrate. Heavy spallation of the corrosion scale occurred in the 0.01Ce～0.1Ce alloys, however, spallation was slight in the 0.2Ce alloy. The excellent corrosion resistance of the 0.2Ce alloy could be attributed mainly to the formation of continuous Al₂O₃ lines in the corrosion scale, as well as the prolongation of the incubation period of the corrosion product spallation.     

Significantly enhanced hydrogen desorption properties of Mg(AlH4)2 nanoparticles synthesized using solvent free strategy

Mg(AlH_4)_2 nanoparticles with a particle size less than 10 nm have been successfully synthesized by mechanochemical method using LiAlH_4 and MgCl_2 as raw materials together with Li Cl buffering additive. In comparison to Mg(AlH_4)_2 microparticles, Mg(AlH_4)_2 nanoparticles exhibit a faster hydrogen desorption kinetics and lower desorption temperature. The hydrogen desorption temperatures of the first and second dehydrogenation steps are 80 and 220 °C for the Mg(AlH_4)_2 nanoparticles, which are about 65 and 60 °C, respectively, lower than those of Mg(AlH_4)_2 microparticles. The decomposition activation energy is reduced from 135 k J/mol for Mg(AlH_4)_2 microparticles to 105.3 k J/mol for Mg(AlH_4)_2 nanoparticles. It is proposed that the shortened diffusion distance and enhanced diffusivity of Mg(AlH_4)_2/MgH_2 nanoparticles provide an energy destabilization for lowering the dehydrogenation temperature, and thus being the key factor for promoting the hydrogen desorption kinetics. More importantly, it is demonstrated that the dehydrided nano MgH_2 hydride with a particle size below 10 nm can be formed after rehydrogenation process, resulting in the good cycling hydrogen desorption performance of nano MgH_2.     

机器人动力学分析新方法──Kane方法

本文比较了闭链机器人动力分析的各种方法，提出使用Ｋａｎｅ方法求解机器人的动力学问题，并利用Ｋａｎｅ方法求解了一个五杆二自由度机械手的动力学问题。     

Kinetics of non-catalyzed hydrolysis of tannin in high temperature liquid water

High temperature liquid water （HTLW） has drawn increasing attention as an environmentally benign medium for organic chemical reactions, especially acid-/base-catalyzed reactions. Non-catalyzed hydrolyses of gallotannin and tara tannin in HTLW for the simultaneous preparation of gallic acid （GA） and pyrogallol （PY） are under investigation in our laboratory. In this study, the hydrolysis kinetics of gallotannin and tara tannin were determined. The reaction is indicated to be a typical consecutive first-order one in which GA has formed as a main intermediate and PY as the final product. Selective decomposition of tannin in HTLW was proved to be possible by adjusting reaction temperature and time. The present results provide an important basic data and reference for the green preparation of GA and PY.     

枞酸型树脂酸与顺丁烯二酸酐催化DIELS-ALDER反应动力学研究

本文研究了在二氧化碳气体保护下，以氯化辞为催化剂，一缩二乙二醇二甲醚为溶剂时，松香中的枞酸型树脂酸与顺丁烯二酸酐催化Diels-Alder反应的动力学，研究了反应温度、反应物浓度和催化剂浓度对反应的影响。结果表明，生成马来海松酸的速度对枞酸型树脂酸的总浓度表现为一级反应，而与顺丁烯二酸酐的浓度无关．其反应的动力学方程为：-d[∑CA]／dt=kc[∑ECA]其中kc为催化反应的速度常数，只与反应条件和氯化锌的浓度有关，[∑CA]为枞酸型树脂酸的总浓度。     

两段提升管催化裂化技术研究

提出了两段提升管催化裂化概念，并从理论上分析了两段催化裂化的优点，推导出了适合于两段催化裂化的Ｗｅｋｍａｎ三集总动力学模型的拓展式，进一步充实了两段催化裂化的理论依据．两段催化裂化的模拟实验结果表明，前期反应使催化剂结焦，使后期反应的汽油选择性明显变差，催化剂上的结焦属选择性失活．     

协同萃取动力学研究

本文采用上升液滴法研究HPMBP-φ_2SO-甲苯溶液协同萃取钕的动力学过程。考察了Nd~(3+),HPMBP,H~+,φ_2SO和温度对萃取速率的影响,观察到在协同萃取体系中,不仅具有热力学的协同效应,同时也还有动力学的协同效应。在同样条件下,加入协萃剂φ_2SO,可使萃取反应速度加快,并根据实验结果推测了萃取反应的过程机制。     

裂化催化剂再生动力学简单反应模型与串连反应模型的关系及其误差

微球裂化催化剂的再生(烧碳)反应可用简单反应和串连反应两种模型描述。本文分析了两种模型的内在联系,讨论了简单反应模型的适用条件及其引入的误差。对CRC-1催化剂的再生反应,低于700℃时,使用简单反应模型误差较小(与串连反应模型结果较好地吻合);高于700℃时,误差较大。     

分光光度法研究二过碲酸合铜(Ⅲ)氧化四氢糠醇的动力学

采用分光光度法研究了碱性介质中二过碲酸合铜（Ⅲ）配离子氧化四氢糠醇的动力学及机理。实验结果表明，反应对［Ｃｕ（Ⅲ）］是一级，对四氢糠醇为１．２７～１．４９级（２９４．２～３０２．２Ｋ）。表观速率常数随体系中［ＯＨ－］的增大而降低，随碲酸根浓度的增加而降低。根据实验事实，提出了一种含有前期平衡的反应机理，据此导出了一个能够解释实验事实的速率方程，求得了速控步的速率常数，并给出了２９８．２Ｋ时的活化参数。