Cu_(70)Ni_(30)过冷熔体凝固组织的粒化机制

在高真空下，采用熔融玻璃净化与循环过热相结合的方法，在２２￣２７０Ｋ过冷度范围内，研究了Ｃｕ７０Ｎｉ３０合金凝固组织形态演化过程。

偏晶合金Ni-31.44%Pb过冷组织粒化机制

利用熔融玻璃净化、循环过热相结合的方法对 Ni- 31.44 % Pb(质量分数 )偏晶合金宽过冷区间组织演化规律进行研究。结果表明 :随过冷度的增大 ,凝固组织发生三次转变。其中当 ΔT>2 42 K时 ,合金组织发生第三次转变 ,由细密枝晶骤然粒化为过冷粒状晶。通过组织观察和过冷熔体枝晶生长过程的理论计算发现 ,快速凝固过程中固液相变速率骤然增加 ,引起枝晶全面碎断 ,然后在枝晶块表面能和应变能的驱动下 ,晶界移动 。

液态钢渣离心粒化机水淬新方法构思

论述了液态钢渣离心粒化机水淬新方法的基本原理、性能特点及其可行性模拟试验。结果表明:该方法具有工艺简单、操作安全、粒化效果好及粒度控制方便等优点。

首饰合金粒化机的研制

金属的粒化有利于保证首饰的铸造质量,粒化效果主要取决于粒化装置的结构设计和粒化工艺参数,在设计粒化机时充分考虑了温度控制方式、坩埚结构、金属液保护方式、冷却水缸的结构等因素。研制的首饰合金粒化机可应用于金、银、铜等多种首饰合金的粒化,设备操作简便,安全性能好;形成的颗粒圆整致密,粒度均匀,表面光洁,气孔和氧化夹杂少;熔炼及粒化速度快,金属液烧损少,化学成分稳定,并降低了贵金属的损耗。

低过冷Cu70Ni30合金熔体凝固组织粒化机制

采用熔融玻璃净化技术 ,使大体积Cu70Ni30合金获得 2 70K深过冷 ,在宽过冷范围内合金不同过冷度区间的凝固组织演化表明 ,存在 2类晶粒细化和 2类不同的枝晶花样。其中 ,介于 38K～ 12 0K过冷区间 ,由于再辉过程中的化学过热 ,首先发生了枝晶熔断 ,熔断后的枝晶段在界面能驱动下 。

好氧活性污泥的厌氧颗粒化机制

升流式厌氧污泥床（UASB）反应器被广泛应用于有机废水厌氧生物处理。在系统内培育出沉降性能良好、产甲烷活性高的颗粒污泥是其高效稳定运行的关键。用于启动UASB的接种污泥，一般采用厌氧活性污泥，

过冷Ni-2Pb单相偏晶合金的组织粒化

采用熔融玻璃净化与循环过热相结合的方法研究了过冷Ni 2Pb单相偏晶合金的组织粒化机制。在 2 2～ 2 80K过冷度范围内 ,Ni 2Pb合金组织发生两次粒化。当 2 2K <ΔT <6 6K时 ,合金组织由普通树枝晶渐变为第一类粒状晶 ;当ΔT >88K时 ,合金组织由第一类粒状晶转变为深过冷树枝晶 ;当ΔT >187K时 ,合金组织骤然粒化为第二类粒状晶。BCT模型分析表明 :第一类粒状晶的粒化机制为枝晶熔断再结晶机制 ;第二类为枝晶碎断再结晶机制。

深过冷技术制备均质过偏晶合金及其形成机制的研究

采用熔融玻璃净化和循环过热相结合的方法使Ni 40 % (质量分数 )Pb合金获得 2 92K大过冷度 ,成功制备出大体积均质过偏晶合金。根据BCT模型和组织演化结果分析表明 :过冷粒状晶是在内应力的作用下 ,枝晶发生全面碎断 ,随后在枝晶段表面和应变能的驱动下使晶界移动发生再结晶的结果 ,即枝晶碎断 再结晶机制 ;试样基体上弥散分布的细密铅颗粒是由于快速凝固阶段溶质截留效应而形成的 ,少量较大尺寸铅颗粒的形成主要与慢速凝固阶段分布于枝晶骨架间残余富铅液相的聚合有关。

过冷Ni-31.44%Pb偏晶合金凝固行为

采用熔融玻璃净化和循环过热相结合的方法研究Ni 3 1.44%Pb偏晶合金宽过冷区间凝固组织演化规律 ;结果表明 ,过冷偏晶合金在快速凝固阶段首先形成枝晶α骨架 ,再辉重熔后分布于枝晶间的残余液相按照平衡凝固模式进行后续反应 ;在0～ 2 86K过冷范围内 ,当ΔΤ <5 0K时 ,合金凝固组织为粗大枝晶α +枝晶间Pb相 ;当 70 <ΔT <2 3 2K时 ,凝固组织为细密枝晶α +枝晶臂上细小的Pb颗粒 +枝晶间Pb相 ;当ΔT >2 42K时 ,凝固组织为过冷粒状晶 +均匀细小的Pb颗粒 +少量尺寸较大的枝晶间Pb颗粒 。

Effect of Al_2Ca intermetallic compound addition on grain refinement of AZ31 magnesium alloy

The Al2Ca intermetallic compound was prepared by melting process in a vacuum induction furnace. And the A12Ca compound was added in as-cast AZ31 alloys for grain refinement. The effect of its additional levels on grain refinement of as-cast AZ31 alloy was investigated and the mechanism of the grain refinement was discussed. The results reveal that the addition of 1.1% Al2Ca （mass fraction） decreases the average grain size of as-cast AZ31 alloy from 354 to 198 μm. And the thermal stability of the grains refined by Al2Ca is superior. The grain refining mechanism is attributed to the combined effects of solute and heterogeneous nucleation from the Al2Ca.

Grain refinement of Al-5%Cu aluminum alloy under mechanical vibration using meltable vibrating probe

A mechanical vibration technique to refine solidified microstructure was reported. Vibration energy was directly introduced into a molten alloy by a vibrating horn, and the vibrating horn was melted during vibration. Effects of vibration acceleration and mass ratio on the microstructure of Al-5% Cu alloy were investigated. Results show that the present mechanical vibration could provide localized cooling by extracting heat from the interior of molten alloy, and the cooling rate is strongly dependent on vibration acceleration. It is difficult to refine the solidified microstructure when the treated alloy keeps full liquid state within the entire vibrating duration. Significantly refined microstructure was obtained by applying mechanical vibration during the initial stage of solidification. Moreover, mechanisms of grain refinement were discussed.

Grain size effect on cyclic oxidation of(TiB_2+TiC)/Ni_3Al composites

（TiB2＋TiC）/Ni3Al composites were prepared by mechanical alloying of elemental powders and subsequently spark plasma sintering.Microstructure of（TiB2＋TiC）/Ni3Al composite sintered at 950°C was finer than that of composite sintered at 1050°C.The influence of grain size on cyclic oxidation behavior was investigated.Cyclic oxidation results showed that the composite sintered at 950°C had smaller mass gains than the composite sintered at 1050°C.XRD and EDS results indicate that finer grain size is beneficial for increasing the oxidation resistance by improving the formation of a continuous TiO2 outer layer and a continuous Al2O3 inner layer on the surface of the composites sintered at 950°C.

Microstructure evolution and dislocation configurations in nanostructured Al-Mg alloys processed by high pressure torsion

Microstructure evolution and dislocation configurations in nanostructured Al–Mg alloys processed by high pressure torsion （HPT） were analyzed by transmission electron microscopy （TEM） and high-resolution TEM （HRTEM）. The results show that the grains less than 100 nm have sharp grain boundaries （GBs） and are completely free of dislocations. In contrast, a high density of dislocation as high as 1017 m^-2 exists within the grains larger than 200 nm and these larger grains are usually separated into subgrains and dislocation cells. The dislocations are 60° full dislocations with Burgers vectors of 1/2〈110〉and most of them appear as dipoles and loops. The microtwins and stacking faults （SFs） formed by the Shockley partials from the dissociation of both the 60° mixed dislocation and 0° screw dislocation in ultrafine grains were simultaneously observed by HRTEM in the HPT Al–Mg alloys. These results suggest that partial dislocation emissions, as well as the activation of partial dislocations could also become a deformation mechanism in ultrafine-grained aluminum during severe plastic deformation. The grain refinement mechanism associated with the very high local dislocation density, the dislocation cells and the non-equilibrium GBs, as well as the SFs and microtwins in the HPT Al-Mg alloys were proposed.

Non-equilibrium solidification of undercooled Ni-31.44%Pb monotectic alloy melts

By using the method of molten glass denucleating combined with superheating cycling, solidification behavior of the bulk undercooled Ni 31.44% Pb monotectic alloy melts was systematically investigated. The results indicated that the undercooled monotectic alloy solidifies in form of dendrite essentially during the stage of rapid solidification and after recalescence, the residual melts between the dendrites solidify in the equilibrium mode. Within the achieved undercooling range, the solidification structures are classified into three categories. When the undercooling is less than 50?K, the structures are composed of coarse dendrites and interdendritic lead phase. With the undercooling increasing into the range of 70 ～ 232?K, the dendrite clusters are refined and fine lead particles separate out from the supersaturated primary dendrite arms because of solute trapping. When the undercooling exceeds 242?K, the granular grains form and fine lead particles homogeneously distribute in the whole sample. Based on the observation of the solidification structures and the calculated results with BCT model, it is found that the granulation mechanism of the granular grains is owing to the primary dendrite disintegration and recrystallization.

Grain refining mechanism of Al-3B master alloy on hypoeutectic Al-Si alloys

Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ＇Al-AlB2＇ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α（Al） phase.

Synthesis of nano-MoS_2/bentonite composite and its application for removal of organic dye

A nano-MoS2/bentonite composite was synthesized by calcinating MoS3 deposited on bentonite in H2. The obtained composite was characterized using thermogravimetric analysis, X-ray diffractometer, scanning electron microscope and transmission electron microscope. The results show that nano-MoS2 particles are distributed on the surface of bentonite and form layered structures with layer distance of about 0.64 nm. The composite presents an excellent performance for the removal of methyl orange. Some operation conditions affect the removal efficiency of methyl orange, such as dosage of composite, initial concentration of methyl orange, temperature and pH value. However, light source does not influence the removal efficiency. The removal mechanism is attributed to the adsorption of methyl orange on the nano-MoS2/bentonite composite. The adsorption of methyl orange on the composite is in accordance with the pseudo-second-order kinetic model.

Catalytic performance of cobalt oxide-supported gold-palladium nanocatalysts for the removal of toluene and o-xylene

Using the molten salt and polyvinyl alcohol-protected reduction method,we fabricated Co3O4 octahedron-supported Au-Pd（x（AuPdy）/Co3O4;x =（0.18,0.47,and 0.96） wt%;y（Pd/Au molar ratio） =1.85-1.97） nanocatalysts.The molten salt-derived Co3O4 sample possessed well-defined octahedral morphology,with an edge length of 300 nm.The Au-Pd nanoparticles,with sizes of 2.7-3.2 nm,were uniformly dispersed on the surface of Co3O4.The 0.96（AuPd1.92）/Co3O4 sample showed the highest catalytic activity for toluene and o-xylene oxidation,and the temperature required for achieving 90%conversion of toluene and o-xylene was 180 and 187 ℃,respectively,at a space velocity of 40000 mL/（g·h）.The high catalytic performance of Co3O4 octahedron-supported Au-Pd nanocatalysts was associated with the interaction between Au-Pd nanoparticles and Co3O4 and high concentration of adsorbed oxygen species.

AC-PSO ALGORITHM FOR UAV MISSION PLANNING

Choosing the best path during unmanned air vehicle （UAV） flying is the target of the UAV mission planning problem. Because of its nearly constant flight height, the UAV mission planning problem can be treated as a 2-D （horizontal） path arrangement problem. By modeling the antiaircraft threat, the UAV mission planning can be mapped to the traveling seaman problem （TSP）. A new algorithm is presented to solve the TSP. The algorithm combines the traditional ant colony system （ACS） with particle swarm optimization （PSO）, thus being called the AC-PSO algorithm. It uses one by one tour building strategy like ACS to determine that the target point can be chosen like PSO. Experiments show that AC-PSO synthesizes both ACS and PSO and obtains excellent solution of the UAV mission planning with a higher accuracy.

Theoretical investigations on CO oxidation reaction catalyzed by gold nanoparticles

It is crucial to understand the mechanism of low temperature CO oxidation reaction catalyzed by gold nanoparticles so as to find out the origin of the high catalytic reactivity and extend the indus‐trialization applications of nano gold catalysts. In this work, some theoretical works on CO adsorp‐tion, O2 adsorption, atomic oxygen adsorption, formation of surface gold oxide films, reaction mechanisms of CO oxidation involving O2 reaction with CO and O2 dissociation before reacting with CO on gold surfaces and Au/metal oxide were summarized, and the influences of coordination number, charge transfer and relativity of gold on CO oxidation reaction were briefly reviewed. It was found that CO reaction mechanism depended on the systems with or without oxide and the strong relativistic effects might play an important role in CO oxidation reaction on gold catalysts. In particular, the relativistic effects are related to the unique behaviors of CO adsorption, O adsorption, O2 activation on gold surfaces, effects of coordination number and the wide gap between the chem‐ical inertness of bulk gold and high catalytic activity of nano gold. The present work helps us to understand the CO oxidation reaction mechanism on gold catalysts and the influence of relativistic effects on gold catalysis.

Mn nanoparticles enhanced dehydrogenation and hydrogenation kinetics of MgH_(2) for hydrogen storage

Mn nanoparticles(nano-Mn)were successfully synthesized and doped into MgH_(2) to improve its de/hydrogenation properties.Compared with MgH_(2),the onset desorption temperature of 10 wt.%nano-Mn modified MgH_(2) was decreased to 175℃ and 6.7,6.5 and 6.1 wt.%hydrogen could be released within 5,10 and 25 min at 300,275 and 250℃,respectively.Besides,the composite started to take up hydrogen at room temperature and absorbed 2.0 wt.%hydrogen within 30 min at low temperature of 50℃.The hydrogenation activation energy of MgH_(2) was reduced from(72.5±2.7)to(18.8±0.2)kJ/mol after doping with 10 wt.%nano-Mn.In addition,the MgH_(2)+10 wt.%nano-Mn composite exhibited superior cyclic property,maintaining 92%initial capacity after 20 cycles.