Gas solid techniques for preparation of pure lanthanum hexaboride

The processes reported for the preparation of lanthanum hexaboride (LaB6) from lanthanum oxide involve the use of carbon either elemental or in the form of boron carbide or elemental boron itself as reducing agents, fused salts at high temperatures or reactions which require the product boride to be leached out. Each of these techniques either increases the process costs and/or increases chances of contamination in fi-nal product. Pure LaB6 can best be prepared by a reaction which produces a gaseous byproduct. In the present study, such a reaction was successfully used to yield pure lanthanum hexaboride. The process involved mixing of anhydrous lanthanum chloride with aluminium and boron and heating the charges under dynamic argon flow. Lanthanum chloride is known to be highly hygroscopic; hence the process using improperly dehydrated LaCl3 led to the formation of lanthanum oxychloride which does not convert to LaB6 under conditions wherein LaCl3 converts. Not only the formation of AlCl3 but also its continuous removal from the reaction zone is necessary for the success of the process.     

Efects of Washing and Drying on Crystal Structure and Pore Size Distribution（PSD） of Zn4O13C24H12 Framework（IRMOF-1）

In this study,the efects of various methods of washing and drying of MOF-5 nanocrystals on structure formation were investigated.Eight samples of MOF-5 were synthesized under diferent conditions.TGA,XRD and PSD analysis were applied to characterize of the samples.The methods of washing and drying were found to be important in determining the final structure of MOF-5s.MOF-5 with high BET surface area can be obtained by choosing a suitable method of washing and drying.According to the results obtained in this work,it was found that vacuum drying at 425℃ is sufcient to dissolve the MOF-5-DMF.Similar results were obtained by washing method(with℃H2Cl2and℃HCl3),when compared with vacuum drying at 425℃ according to XRD test.The pore size distribution of samples 1-5 and 8 were calculated by SHN1 method and results showed that the samples in which solvent vacuum was DMF,have lower pore volume,uniform pore size distribution and the pore size are smaller than samples 3,4 and 8.It was also found that activated MOF-5can be converted to its deactivated form prior to drying of the samples.     

Erosion Resistance Behaviours of H13 Steel to Molten ADC12 Alloy

H13 hot work steel samples and surface water vapor oxidized H13 samples were immersed into molten ADC12 alloy under static resting or dynamic rotating conditions. Weigh-losing method was used to discover the influences of temperature, time and surface conditions on the erosion resistance of H13 steel. The interfaces between the steel and the molten alloy were studied with optical microscopy to compare the different erosion resistance behaviours. The results show that the composite layer outside of the compounds layers changes obviously with increasing temperature, lasting time or sample movement. The better erosion resistance of H13 steel can be endowed with the oxide films, which would gradually decrease along with the dissolve of the films.     

Characteristics of oxide pegs in Ti-and Y-doped CoNiCrAl alloys at 1150 °C

Oxide pegging is a widely accepted mechanistic model explaining the reactive element effect on the improved adherence of scale. However, previous models for the oxide peg formation process have not considered the effects of more than one active element added into the alloy during the peg formation. This study proposes a new model of oxide peg formation and growth for the doping of two reactive elements in an alloy(the precipitated Y and solid solute Ti). Different amounts of Ti and Y were added to a Co Ni Cr Al alloy, and the characteristics of the resulting oxide pegs, such as their linear density, size, and forming process, are obtained by examining alloy samples subjected to an isothermal oxidation operation at a temperature of 1150 °C. It is found that the amount of Y determines the density of the oxide pegs, and Ti does not form a Ti-rich oxide core if a Y-rich oxide exists in the sample. In samples with the same Y content, the oxide pegs primarily grow in length, and with increased Ti content, they grow along the b-phase boundary and into the alloy. Based on these results, a three-step model for oxide peg formation and growth is conceived.     

A COMPUTERIZED SYSTEM ON KINETIC ANALYSIS AND EVALUATION OF GAS／SOLID REACTIONS

The present paper presents the structure, features and functions of a computerized system on kinetic analysis and evaluation of gas/solid reactions, KinPreGSR. Kin-PreGSR is a menu driven system, can be operated with MS Windows as workbench in a PC computer. It has been developed using visual C++ with FoxPro hybrid coding technique.KinPreGSR combines the characteristics of gas/solid reactions with the kinetic models as well as mass and heat transfer equations. The database files were established for the apparent activation energies of some reduction and decomposition reactions to allow the prediction of the reaction kinetics to some extents. Outputs can be displayed using graphical or numerical forms. Examples regarding the oxide reduction and carbonate decomposition under isothermal conditions are given to show those functions.     

EFFECT OF TOOL WEAR ON MICROSTRUCTURE, MECHANICAL PROPERTIES AND ACOUSTIC EMISSION OF FRICTION STIR WELDED 6061 Al ALLOY

Tool condition is one of the main concerns in friction stir welding （FSW）, because the geometrical condition of the tool pin including size and shape is strongly connected to the microstrueture and mechanical performance of the weld. Tool wear occurs during FSW, especially for welding metal matrix composites with large amounts of abrasive particles, and high melting point materials, which significantly expedite tool wear and deteriorate the mechanical performance of welds. Tools with different pin-wear levels are used to weld 6061 Al alloy, while acoustic emission （AE） sensing, metallographic sectioning, and tensile testing are employed to evaluate the weld quality in various tool wear conditions. Structural characterization shows that the tool wear interferes with the weld quality and accounts for the formation of voids in the nugget zone. Tensile test analysis of samples verifies that both the ultimate tensile strength and the yield strength are adversely affected by the formation of voids in the nugget due to the tool wear. The failure location during tensile test clearly depends on the state of the tool wear, which led to the analysis of the relationships between the structure of the nugget and tool wear. AE signatures recorded during welding reveal that the AE hits concentrate on the higher amplitudes with increasing tool wear. The results show that the AE sensing provides a potentially effective method for the on-line manitoring of tool wear.     

Oxidation-induced damage of an uncoated and coated nickel-based superalloy under simulated gas environment

Turbine blades and vans operated in an aggressive gas environment usually suffer from combined oxidation and cycle loading effects. The surface oxide layer will result in premature failure and lead to a significant reduction in the service lifetime. The effects of prior oxidation-induced damage under a simulated combustion-gas environment on the fatigue lifetime of the directionally solidified(DS) nickel-based superalloy DZ125 with and without an oxidation-resistant coating were presented. The fatigue lifetime of uncoated samples is adversely affected by prior oxidation exposure. The deterioration of fatigue lifetime in uncoated samples is associated with surface microstructural degradation, which occurs during prior exposure. However,the presence of MCrAlY coating is beneficial for the sample's lifetime under high stress. Further scanning electron microscopy(SEM) analysis demonstrates that the coating does not contribute to the initiation mode of fatigue cracks.     

Electrochemical behaviour of commercially pure titanium and Co—Cr alloy in Ringer‘s solution

The electrochemical behaviors of commercially pure titanium(CP Ti) and Co-Cr alloy in Ringer‘s solution have been investigated.The results indicate that the electric potential of passive region for CP Ti is up to 3000mV,and its passive current density is 3.078 μA/cm^2,The excellent corrosion resistance of CP Ti can be attributed to the formation of TiO2 oxide film.The passive region of Co-Cr alloy is 770mV,which is narrower than that of CP Ti.However,no hystersis loops are found in the reverse scanning curves of Cu-Cr alloy.A complex oxide film of Co3O4,Co2O3,and Cr2O3 formed on the surface provides Co-Cr alloy with a stable electrochemistry property.The corrosion rates of the crevice samples increase with the pH value of medium decreasing.The electron probe microanalyzer(EPMA) analysis indicates that Ti in CP Ti and Co,Cr in Co-Cr alloy dissolve in crevice area due to the Sealed-Cell effect.     

Hydrothermal synthesis and characterization of nano-petal nickel hydroxide

The current article reports a preparation method of nano-petal nickel hydroxide, which was synthesized using urea as a precipitator by hydrothermal method. Nickel hydroxide samples with different microstructural characteristics were prepared by changing molar ratio of nickel/urea and reaction time. The prepared nickel hydroxide samples were characterized using X-ray diffraction(XRD) and scanning electron micrography(SEM).Electrochemical performances of the samples were then determined under charging–discharging rate of 0.2C. The influences of different conditions of the hydrothermal synthesis method on microstructure parameters of nickel hydroxide were analyzed, while relationships between microstructural characteristics parameters of nickel hydroxide and the electrochemical performances of nickel electrode were also explored.     

Insertion/removal kinetics of lithium ion in spinel LiCuxMn2-xO4

The insertion/removal processes of lithium ion in spinel lithium manganese oxide（LiMn204） and copper doped spinel lithium manganese oxide （LiCuxMn2-xO4） on a powder microelectrode were studied by electrochemical impedance spectroscopy（EIS）, cyclic voltammetry（CV） and X-ray diffractometry（XRD）. The insertion/removal process of lithium ion in the spinel oxides consists of three steps： charge transfer of lithium ion on the surface of the spinel oxides, diffusion and occupation of lithium ion in the lattice of the spinel oxide. Similar to chromium, the doping of copper in spinel lithium manganese oxide results in the increase of the charge transfer resistance and the double layer capacitance for lithium insertion or removal, and the decrease of the diffusion coefficient of lithium ion in the lattice of spinel oxide. However, the insertion capacitance, a parameter reflecting the occupation of lithium ion in the lattice of the spinel oxide, is hardly influenced by the doping of copper. The influence of the doped copper on the kinetic process of lithium insertion/removal in spinel lithium manganese oxide is related to the contraction of spinel lattice.     

含硫油品储罐腐蚀产物硫化亚铁自燃性的研究

模拟油品储罐中硫化亚铁的生成方式，研究了H2S气体在没有氧气存在的条件下与油品储罐内壁腐蚀产物-Fe(OH)3、Fe2O3和Fe3O4发生反应及反应产物硫化亚铁的自燃性.结果表明：油品储罐中腐蚀产物Fe(OH)3、Fe2O3和Fe3O4与H2S在无氧条件下均可发生放热反应生成硫化亚铁，且生成的硫化亚铁与空气接触会发生氧化反应放出热量，热量聚集使油品温度上升是引起油品自燃并导致油品储罐发生火灾和爆炸事故的主要原因.但不同生成方式所生成的硫化亚铁的氧化速度不同，其自燃性也不同.     

电池级四氧化三钴生产工艺研究

为制备满足锂离子电池用四氧化三钴,对化学沉淀-热分解法制备四氧化三钴工艺进行了研究,重点研究了氢氧化钴前驱体的制备工艺及煅烧工艺对产品的影响,实验得到指标稳定的四氧化三钴:振实密度大(≥2.2g/cm3),激光粒度分布范围窄(5~10μm),纯度高(钴的质量分数为72.6%~73.6%,氧化钴项的质量分数为≤5%),形貌为类球形。结果表明:四氧化三钴产品指标主要由化学沉淀法合成的氢氧化钴决定,其次与煅烧工艺有关,通过工艺优化,得到的产品稳定,可满足锂离子电池生产需求。     

Kristallographische Modelltheorie des Passivierungsvorganges

A cristallographic model theory of the passivation process A crystallographic pattern theory of the passivating process has been investigated. Starting from the tridy mit-like structure of water the mechanism of formation of hydroxide- and oxidelayers is reported. The question will be discussed under which conditions a hydroxide, oxidhydrate or oxide is formed.     

钙添加剂对可充锌电极性能的影响

通过直接化学反应法,化学共沉淀法以及物理混合方法在可充锌电极活性物质一氧化锌中掺入钙添加剂,研究了锌电极的充放电特必,放电容量及循环寿命等电化学性能,SEM分析表明直接化学反应法制备的样品是基面为四角形的薄片,化学共沉积法制备的样品是基面为六角形的多面体。XRD分析表面两种化学反应方法制备的样品均为锌酸钙晶体,由于制备过程中晶体优先生长方向不同而具有不同的形状。电极充放电实验结果表明,掺钙锌电极的电化学性能明显优于无钙锌电极,化学掺钙对锌电极电化学性能的改善优于物理混合掺钙。X射线照片表明由锌酸钙组成锌电极的表面活性物质分布较均匀,不掺钙的锌电极经多次充放电循环后电极表面已基本上没有活性物质。     

Mortars for encapsulating sacrificial zinc anodes in reinforced concrete

Expansion measurements, chemical analysis and petrography have been undertaken to assess a possible side‐effect of using strongly alkaline additives (lithium hydroxide or sodium hydroxide) in encapsulating mortars used to promote the activity of sacrificial zinc anodes employed for galvanic cathodic protection of steel in concrete. Very high concentrations of lithium hydroxide in the encapsulating mortars were found to cause no deleterious expansion associated with alkali‐silica reaction (ASR) in surrounding “model” concrete specimens even when the latter contained aggregate of known susceptibility to ASR and a near‐threshold level of intrinsic alkalinity. Encapsulating mortars formulated with an equivalent molarity of sodium hydroxide, however, were found to induce significant expansion due to ASR in similar specimens.     

Characterization of alkaline-earth oxide additions to the MnO2 cathode in an aqueous secondary battery

The effect of alkaline-earth oxide additions on aqueous rechargeable battery is investigated using microscopic and spectroscopic techniques. The alkaline-earth oxide additions such as magnesium oxide (MgO) and barium oxide (BaO) were physically mixed to the manganese dioxide (MnO₂) cathode of a cell comprising zinc as an anode and aqueous lithium hydroxide as the electrolyte. The results showed that such additions greatly improved the discharge capacity of the battery (from 145 to 195 for MgO and 265 mAh/g for BaO). Capacity fade with subsequent cycling is reduced only for MgO but not for BaO. With an aim to understand the role of these additives and its improvement in cell performance, we have used microscopy, spectroscopy, ion beam analysis and diffraction based techniques to study the process. Transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy analysis (EDS) results showed evidence of crystalline MnO₂ particles for MgO as additive, whereas, MnO₂ particles with diffused structure leading to mixture of phases is observed for BaO additives which is in agreement with X-ray diffraction (XRD) data. This work relates to improvement in the electrochemical behaviour of the Zn-MnO₂ battery while the MgO additive helps to reduce the formation of manganese and zinc such as hetaerolite that hinders the lithium intercalation.     

Carbonatbildung in inhibierten Chloridsolen

Carbonate formation in inhibited chloride brines If air is absorbed by chloride cooling brines, the carbon dioxide in the air gives rise to the formation of carbonates; in calcium chloride brines, calcium carbonate is formed. Upon precipitation of the latter, hydrochloric acid is liberated, the p_H decreases sharply and the cooling brine gains in corrosivity. In sodium chloride brines, the sodium carbonate or bicarbonate formed remains in solution and the p_H changes but slightly. Conditions are different in sodium chloride brines containing sodium nitrite as an inhibitor and being in contact with iron. With free access of air the amount of carbonates formed in addition to ferric hydroxide is sufficient to raise the p_H to dangerous values. In cooling installations involving ferrous metals and operating on a sodium chloride brine inhibited with sodium nitride, it is therefore important to prevent access of air as far as possible.     

Inhibition of molten droplet deposition by substrate surface hydroxides

Nickel or nickel-chrome molten droplets were plasma-sprayed onto aluminium substrates which were hydrothermally-treated to grow thick layers of hydroxide and oxide on the surface. The boiled samples were subsequently thermally-treated at different temperature conditions to test whether removal of water vapour released from the dehydration of the surface hydroxide affects the splat deposition. It was observed that there was a complete absence of splat deposition on substrates held at room temperature, regardless of the roughness of their surfaces. The absence of splat deposition on these surfaces was also independent of the spraying parameters and particle properties. In contrast, significant splat deposition was found on the substrates held at 350 °C during spraying. The obvious difference in splat deposition between non-heated and heated samples can be explained by their significant variation proportion of hydroxide in the substrate surface layers. It was also found that the oxide layers on the substrate surface remained intact across the entire interface between the splat and the substrate.     

空间用超轻LA141镁锂合金表面腐蚀产物及腐蚀机理研究

目的 明确空间用超轻LA141镁锂合金的腐蚀机理，为进一步设计防护涂层体系提供理论依据。方法 将未腐蚀和已在空气中放置一段时间表面形成灰黑色腐蚀膜的超轻LA141镁锂合金的一部分放置于水溶液中，一部分暴露在空气中，研究其随时间延长的腐蚀产物生成规律，并用SEM、偏光显微镜对其腐蚀产物的微观形貌进行观察，用EDS能谱分析、XRD、红外光谱手段对其成分进行鉴定。结果 超轻LA141镁锂合金放置于水溶液后，有细密的气泡(H2)逸出，并在表面迅速生成一层灰黑色腐蚀膜层。已生成腐蚀膜层的镁锂合金放入水中后，没有明显气泡逸出的现象，且腐蚀膜层厚度增加速度低于未生成腐蚀膜层的镁锂合金。通过在SEM、偏光显微镜下对腐蚀产物进行观察，并结合EDS、XRD和红外的分析结果，发现LA141镁锂合金放入水中后，锂金属优先腐蚀，生成大量氢气，同时也伴随着镁金属的腐蚀，生成氢氧化锂和氢氧化镁，氢氧化锂在空气中不稳定，接触空气后生成碳酸锂。结论 腐蚀产物主要为氢氧化镁及碳酸锂。另外，腐蚀膜层能在一定程度上减缓底部镁锂合金的进一步腐蚀。该研究结果对设计选用抑制镁锂合金腐蚀的材料具有一定的参考价值。     

Prevention of metal dusting on Ni-based alloys by MCrAlY coatings

The flame tubes from the domestic heating devices made of different Ni-based alloys (alloy 601/NiCr23Fe and even alloy 602/NiCr25FeAlY) showed after a short operation time severe attack by metal dusting. This phenomenon occurred only during combustion of the fuel oil with a new chemical composition. The german market offers such fuel oils with a reduced sulphur content due to more severe environment regulations. Sulphur is able to stabilize the cementite suppressing or retarding the appearance of metal dusting. Metallographical studies revealed that under this operation conditions the oxide scale on the Ni-based alloy forms only partially.In order to prevent the appearance of metal dusting, the flame tubes were coated by a high performance layer (MCrAlY-alloy) which shows a good stability under these corrosive conditions. Uncoated and MCrAlY-coated samples made of alloy 601 and alloy 602 were used for metal-dusting experiments. The specimens were tested using a computer-controlled special equipment which was developed and built in order to simulate the parameters in a flame tube of an oil heating device.Metallographical investigations of the tested samples revealed that the oxide scale present on the uncoated based alloy was formed only partially, whereas in the case of the MCrAlY coatings the oxide scale has an uniform distribution and a good stability due to the presence of the β-NiAl phase which is considered the Al-reservoir for its formation.