Phase diagrams of nanometer-sized particles in binary systems

A study on alloy phase formation in nanometer-sized particles by insitu transmission-electron microscopy revealed that the phase equilibrium of these particles is significantly different from that of the corresponding bulk materials. A theoretical study was conducted based on thermodynamics modified so that Gibbs free energies for bulk materials available in the CALPHAD database were modified by taking into consideration factors affecting the phase equilibrium of nanometer-sized alloy particles. The study proved useful to evaluate the results obtained from experiments. For more information, contact Junggoo Lee, Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871, Japan; +81-6-6879-7941; fax +81-6-6879-7942; e-mail; jg-lee@uhvem.osakau.ac.jp.     

Synthesis of NaAlH4-based hydrogen storage material using milling under low pressure hydrogen atmosphere

The present study highlights the advantages of milling NaH/Al under moderate hydrogen pressure as a favourable production step for NaAlH₄-based hydrogen storage materials. Firstly, it is demonstrated that NaAlH₄ can be obtained by applying a moderate hydrogen pressure (6–12 bar) during milling of NaH and Al with and without the presence of an inexpensive catalyst (TiCl₄). The yield of NaAlH₄ depends critically on process parameters, such as hydrogen pressure and milling time. A fully converted product is capable of reversible hydrogen storage without any activation procedure. Under optimized conditions, a capacity of 4.2 wt.% was achieved and kinetics in the first desorption are comparable to NaAlH₄ doped with TiCl₃. Secondly, the synthesis has been optimized towards shorter milling times. By applying a few absorption/desorption cycles to material that was partially converted during milling, almost full reversible storage capacity can be reached. In addition, kinetics is extremely enhanced. For example, such material exhibits an optimum capacity already after two sorption cycles at 100 bar and 125 °C and allows to absorb 80% of the reversible hydrogen content within a few minutes.     

Formation of titanium nitride produced from nanocrystalline titanium powder under nitrogen atmosphere

The initially globular-shaped Ti powder particles were flattened to ‘pan-cake’ like shape after 12, 16, and thin flakes after 20 h of mechanical milling. Although no change peak positions of HCP Ti crystal structure, the increase in peak intensity with milling time was evident. It is found that the greater surface to volume ratio of the milled Ti powders accelerated the N₂ uptake and subsequent formation of TiN at lower temperatures (884, 856 and 833 °C for 12, 16 and 20 h, respectively) than in the unmilled powder (∼ 1100 °C). Higher nitrogen content of 41–44 at.% by EDS analysis confirmed the high rate of dissolution on the milled powders.     

湿H2气氛下CGO硅钢初次再结晶织构演变行为

通过对湿H2气氛下,相同退火温度、不同退火时间的CGO硅钢初次再结晶样品进行金相组织观察,并进行了EBSD微观织构分析,研究了CGO硅钢初次再结晶过程中的组织及再结晶织构演变行为。结果表明,在湿H2气氛下,820℃保温,CGO硅钢初次再结晶过程约在120 s时完成。随着退火时间的延长,γ面上{111}<112>织构含量逐渐减少,{111}<110>织构先减少后增多,随着再结晶的完成,部分{111}<112>取向晶粒向高斯{110}<001>取向转化的同时,也向{111}<110>取向转化,高斯{110}<001>织构含量逐渐增多。高斯取向晶粒较多是由{111}<112>取向晶粒转化而来,同时也证明了CGO硅钢高斯取向晶粒的二次再结晶异常长大生长机制为择优形核。     

Wetting of Au and Ag particles on monocrystalline graphite substrates

1. Introduction Carbon is widely used in areas such as the proc- essing of graphite-metal compacts, brazing of graph- itic materials and carbon nanotubes [1]. The most common carbon material is graphite. Recently, monocrystalline graphite is used as substrates for the fabrication and observation of metallic nanoparticles [2-4]. With decreasing particle size, the effects of the surface and substrate on the physical and chemical stabilities of the particles cannot be ignored due to the large sur…     

Fracture of welded joints exposed to hydrogen atmosphere

Soldering of aluminium with copper becomes more significant, because of relatively low process temperature of about 400–450°C. It is applied not only in electrotechnical industry, in joining Al–Cu conductors, but also in cooling and air-conditioning equipment and in solar construction of collectors (Winiowski A. Lutowanie twarde aluminium i jegostopów – nowe trendy technologiczne, Biuletyn Instytutu Spawalnictwa, nr 6/2000, Fontargen GmbH. Löten in der Kälte- und Klimatechnik, Eisenberg. 2001 and Fontargen GmbH. Aluminium-Löten. Eisenberg 2003). In this paper, problems concerning Al–Cu soldering are presented. For soldering, zinc solders with the addition of 2, 4, and 15 wt% Al have been used. Results of wettability and spread factor measurements of zinc solders on aluminium and copper surface, as well as metallography, microhardness, and shearing tests of Al–Cu joints are presented. Effects of copper pipes with aluminium plate soldering with application of flux coating solders are also described.     

Self-ignition combustion synthesis of TiFe in hydrogen atmosphere

This paper describes the self-ignition combustion synthesis (SICS) of highly active titanium iron (TiFe) in a high-pressure hydrogen atmosphere without employing an activation process. In the experiments, well-mixed powders of Ti and Fe in the molar ratio of 1:1 were uniformly heated up to 1085 °C, the eutectic temperature of Ti–Fe binary system, in pressurized hydrogen at 0.9 MPa. The electric source was disconnected immediately after the ignition between Ti and Fe, and the mixture was cooled naturally. In this study, the exothermic reaction Ti + Fe = TiFe + 40 kJ occurred at around 1085 °C after the hydrogenation and decomposition of Ti. X-ray diffraction analysis showed that the final product had only one phase—TiFeH_0.06—which can store hydrogen of 1.55 mass% under hydrogen pressure of 4 MPa. The product obtained by SICS contained considerably more hydrogen quickly as compared to the commercially available product; this fact can be explained by the porous structure of the obtained product, which was observed using a scanning electron microscope. In conclusion, the SICS of TiFe saved time and energy, yields products with high porosity and small crystals, enabled easy hydrogenation, and did not require activation processes.     

全氢罩式炉安全控制分析

采用罩式炉机组进行退火,钢卷以堆垛方式置于保护罩内,在保护罩空间中充入强还原性气体棗氢气.在保护罩外是加热罩,通过保护罩间接对钢卷进行加热.加热使用煤气,煤气在保护罩与加热罩形成的相对封闭空间内燃烧.     

过冷熔体中球晶组织的形成规律

研究LSPSF工艺条件下Al-20％（质量分数）Cu合金的初生α（Al）的形貌演变,结合微观组织模拟技术和M-S界面形态稳定性理论,分析过冷熔体中球晶组织快速形成的基本规律。结果表明：合金熔体中自由晶数目和浆料冷却速度共同决定初生固相的尺寸和形态;最早（凝固发生3s内）观察到的初生α（A1）呈细小球形,并在整个演变过程中始终保持球形不变,没有枝晶组织出现;晶粒周围溶质扩散层的叠加可明显降低固-液界面前沿的浓度梯度,提高固-液界面的稳定性;均匀化晶粒周围溶质分布,抑制晶粒的择优生长,促进初生α（A1）保持球形;由溶质扩散层的叠加和界面能引起的抑制和粗化效应可促使失稳的等轴晶粗化成球晶。     

石墨纤维在不同气氛下的高温热稳定性研究

将石墨纤维分别在氢气和氩气气氛下加热到900、1200、1500和1800℃保温4 h,测试石墨纤维在两种气氛下高温处理后的性能,用SEM和XRD观察和分析石墨纤维高温处理后的组织与形态。通过对比石墨纤维与钛锆钼(TZM)合金相应的性能,分析石墨纤维作为TZM合金增强体的可行性。结果表明,石墨纤维在氢气气氛下会被烧蚀而形成甲烷气体,在氩气气氛下则具有优良的热稳定性,即使长时间高温处理也不会使纤维微晶尺寸及组织发生较大变化,因此,石墨纤维可以用作TZM合金增强体。     

Characterization of borided pure molybdenum under controlled atmosphere

In this study, the structural characterization and boriding kinetics of the molybdenum borides formed on the surface of borided pure molybdenum (Mo) have been investigated. Boronizing was carried out in solid medium with boron component forming Ekabor ® 2 (90% SiC, 5% KBF₄, 5%B₄C) powders at 1273 K, 1373 K for 2, 4, 6, 8 hours under a controlled atmosphere containing argon gas flow. The boride layer was characterized by the scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Energy dispersive spectroscopy (EDS) and Vickers microhardness tester. X-ray diffraction analysis showed that the boride layers on molybdenum consisted of MoB and Mo₂B phases. However, the MoB phase was observed at certain boriding temperature and boriding times. The thickness of boronized layers almost ranged from 12 to 42.5 μm with boriding time. A parabolic relationship was observed between boride layer thickness and boriding time. The growth rate constant and activation energy for the boride layer were calculated. The hardness of borides compounds formed on the surface of molybdenum ranged from 925 to 1150 HV_0.05, whereas the hardness of the untreated molybdenum sample was 258 HV_0.05.     

纳米WC粉氢处理脱除游离碳的研究

将高碳含量的纳米WC粉末在氢气流中进行热处理脱除游离碳,研究处理温度、保温时间和H2流量等工艺参数对WC粉碳含量及粒度的影响.结果表明,在温度为940℃,H2流量为3.5L/min,保温时间为100min的工艺条件下,可以将碳含量由9.74%降低至6.20%,处理后纳米WC颗粒无明显长大.当处理温度高于970℃会导致WC化合碳损失而生成W2C相,并造成WC颗粒长大.     

Photocatalytic methanol reforming on Au/TiO2 for hydrogen production

Methanol can be reformed with water, at ambient temperature, using photocatalysis, and this reaction represents a possible low energy, more sustainable pathway to hydrogen production than (for instance) steam reforming. The requirements for the catalysts are rather strict since titania itself is almost inactive for anaerobic photocatalysis, whereas the addition of a very limited range of metals to the surface renders it active. Surprisingly, this includes gold, which shows one of the highest reactivities for hydrogen production. The mechanism is proposed to involve the methoxy and formate intermediates, the latter being implicated in the route to CO₂ and hydrogen production. One oxygen atom is supplied from the titania support, which is replaced in the catalytic cycle by oxygen from water. The threshold for the excitation is that for bandgap excitation into the titania conduction band, which stores the energy for reactivation, and this is mediated by electrophilic oxygen.     

湿度对热镀锌钢材在海洋大气环境中氢脆敏感性的影响

采用改进的双面电解池检测热镀锌钢材在恒温30℃、不同湿度条件下的氢渗透电流,并结合慢应变速率拉伸和断口形貌分析,研究其在海洋大气环境中的氢脆敏感性。结果表明:在相对湿度小于70%时,热镀锌钢材未检测到明显的氢渗透电流,但随着湿度的增加,氢渗透电流密度逐渐增大;当镀层存在缺陷时,镀锌层在为钢材基体提供阴极保护的同时也会促进氢向钢材基体中渗透,且氢渗透电流密度的最大值随镀层缺陷面积的增加而降低;氢吸收和氢渗透降低了热镀锌钢材的断后伸长率,导致其断口切边处出现少量撕裂棱,表明热镀锌钢材在高温、潮湿的海洋大气中使用时,其氢脆敏感性将有所提高。     

The influence of carbon particles on the corrosion of iron in a humid,sulphur dioxide-containing atmosphere

Iron samples covered with a thin layer of activated carbon have been exposed to humid atmospheres at various relative humidities and with a various sulfur dioxide contents. Contrary to expectation the corrosion is initially faster at 55 and 65% relative humidity that at higher humidities. This phenomenon is attributed to adsorption of water vapour on activated charcoal, so that liquid films giving rise to corrosion can be formed at an earlier stage. After extended exposure, however, no accelerating effect can be attributed to the carbon particles.     

On ignition point of Mg-Ca alloy under nitrogen atmosphere

The production cost will be greatly reduced if nitrogen can be used instead of inert gas in the spray forming process of magnesium alloys,but the heat from the reaction between magnesium alloys and nitrogen makes magnesium alloy burn easily.To solve the problem above,the ignition point of Mg-Ca alloy under nitrogen atmosphere was studied using a home-made experimental device and DSC-DTA.Results show that under nitrogen atmosphere,Ca addition has a great effect on the ignition point of Mg alloy.The ignition point of the Mg-5Ca bulk even exceeds 1,030 ℃,and the alloy can be held for 30 min at 900℃ without burning; while the average ignition point of Mg-5Ca powders is lower than 700℃,and it increases with the increasing particle size.Moreover,the purity of nitrogen must be in a certain scope; Mg-Ca alloy shows a higher ignition point under nitrogen with a purity of 99.5％.Based on the experimental results,the best adding content of Ca and the purity of nitrogen were determined,and the security and economic performance of preparing magnesium alloys by spray deposition were improved with nitrogen as atomizing gas.     

Formation of hydrogen blister on AZ91 magnesium alloy during cathodic charging

The process of hydrogen blister formation on as-cast AZ91 magnesium alloy was investigated in 0.1 M NaOH solution using galvanostatic test. The results showed that cathodic charging of AZ91 alloy resulted in hydrogen blister formation, and blister rupture caused the nucleation and propagation of transgranular micro-cracks around the ruptured blister.     

Accumulation of hydrogen peroxide at the long-term effect of an atmosphere pressure glow discharge on electrolyte solutions

The kinetic characteristics of the hydrogen peroxide accumulation at the long-term effect of an atmospheric pressure glow discharge on aqueous solutions of electrolytes have been obtained. The initial rates of the H₂O₂ generation and the primary yields are calculated using the straight line portions of the kinetic characteristics. It is found that the times of reaching a steady hydrogen peroxide concentration (or its maximum) are rather long (about several hours). The OH^· yield has been estimated, and the initial yield of hydrogen peroxide and its effective lifetime have been calculated using the kinetic relationship obtained for a glow discharge-water system.