烧结作用对CVD法超细铼粉性能的影响

研究了一种化学气相沉积(CVD)制备超细铼粉的新方法,即以NH4ReO7为原料,通过将其分解为Re2O7后气相输运至还原区,经氢气还原生成超细铼粉.对不同还原温度下制备的超细铼粉样品,采用XRD、SEM、激光粒度分析进行表征,实验揭示了烧结作用对晶粒尺寸、形貌、表面状态及粒度等粉末性能的影响规律.结果表明,随还原温度升高,烧结作用增强,制备的超细铼粉晶粒尺寸增大,具有更好的球形度,表面趋于光洁,平均粒径增大.     

The Effect of Sintering on the Properties of Ultrafine

研究了一种化学气相沉积(CVD)制备超细铼粉的新方法,即以NH4ReO7为原料,通过将其分解为Re2O7后气相输运至还原区,经氢气还原生成超细铼粉。对不同还原温度下制备的超细铼粉样品,采用XRD、SEM、激光粒度分析进行表征,实验揭示了烧结作用对晶粒尺寸、形貌、表面状态及粒度等粉末性能的影响规律。结果表明,随还原温度升高,烧结作用增强,制备的超细铼粉晶粒尺寸增大,具有更好的球形度,表面趋于光洁,平均粒径增大。     

活性炭吸附高铼酸铵性质的研究

研究了活性炭吸附高铼酸铵的性质,在15℃时,测得高铼酸铵(NH4ReO4)的溶解吸热量为-44.34kJ/mol;15.5℃时,高铼酸铵的吸附放热量为53.31kJ/mol.两个数值比较,说明活性炭吸附高铼酸铵在常温下属于物理吸附.     

从不同形式钨铼合金废料中回收铼的研究

铼作为一种稀有难熔金属,因具有独特的性能使其应用受到重视。在铼资源不足的情况下,从含铼废料中回收铼被认为是获取铼的重要途径之一。本工作选取粉末状、块状以及丝状3种不同形式的钨铼合金废料,进行火法回收铼的研究,对不同工艺参数下氧化焙烧、氨水浸出和蒸发结晶所得回收中间产物NH₄ReO₄和最终氢还原所得铼粉的性能进行表征。结果表明,钨铼合金废料的形式对铼的回收工艺条件和回收率有明显的影响,未合金化的钨铼合金粉末状废料及合金化后的块状和丝状废料回收时需采用不同的氧化温度,且在不同的温度下Re₂O₇有不同的挥发率,粉末状、块状以及丝状3种不同形式的钨铼合金废料回收所得铼粉的纯度分别为99.952%、99.939%和99.915%,铼的回收率分别为95.62%,94.57%和91.59%。     

铼(Re)的性质及应用研究现状

综述了稀散金属元素铼(Re)的物理性质、机械性能、资源及制备技术,特别介绍了铼在超耐热合金领域的应用研究现状和发展趋势。     

酸性溶液中铼的电沉积行为

采用电化学循环伏安法、恒电位沉积法和电化学石英微晶天平(EQCM)研究铼在酸性溶液中的电沉积行为.结果表明:当溶液接近中性(pH=6)时,金属铼难以被还原出来;当溶液酸度较低(pH=3)时,电沉积产物含有铼的氧化物(ReO3);当溶液酸度较高时(pH=1),电沉积产物为金属铼,所得产物的微观形貌中存在明显的裂纹;且随着...     

铼粉末冶金件的应用

铼的特殊性能包括：熔点高达3180℃，其弹性模量是难熔金属中最大的。即使在非常高的温度下，铼也不形成碳化物，另外，不论在室温下还是高温下，铼都具有很高的拉伸强度，它还具有优异的塑性、蠕变性和低周疲劳性能。 铼能够做成细条、棒材、薄板和中厚板材；但是，目前铼零件生产采用湿包套冷等静压，然后进行1400℃下的预烧结和2300℃下的最终烧结。这种方法为生产大型零件奠定了基础，例如美国航空与航天局(NASA)制造高效率的液体燃料推进器或者火箭燃烧室。 Re/Ir推进器 作为与美国航空与航天局所签订合同的一部分，美国铼合金公司…     

美国铼合金公司简介

美国铼合金公司成立于1966年,当时,只是粉末冶金铼精细丝生产商,目前已发展成为具有多种产品的公司,包括铼粉、钨铼和钼铼合金产品,参见下表。     

新型钨铼混合基阴极的热电子发射性能

采用喷雾干燥结合两步氢还原法制备出W-Re混合粉末,并在此基础上通过压制、烧结和浸渍工艺制备出W-Re混合基浸渍型阴极。采用SEM、XRD、AES对W-Re混合基阴极的微观形貌、物相、表面活性元素进行表征分析,并用电子发射测试系统测试阴极在950~1050℃的脉冲电子发射性能。结果表明,铼的含量决定了阴极基体的物相,铼含量为75%(原子分数)的W-75Re阴极由Re3W单一物相组成,该阴极由于铼含量较高使得基体晶粒尺寸更细小,有利于活性自由钡的生成及其在阴极表面的扩散,从而W-75Re阴极具有相对较低的逸出功和较高的发射电流密度,其在1000℃b时的零场脉冲发射电流密度为14.03 A·cm~(-2),有效逸出功为1.902 e V。     

从沉钨钼后液中制备高纯铼酸铵

利用沉钨钼后液首先经氯化钾沉淀反应得到铼酸钾,其次采用离子交换法将铼酸钾溶液转为高铼酸溶液,最后经氨水中和-浓缩结晶-重结晶得到高纯铼酸铵。结果表明:向沉钨钼后液中加入KCl固体再浓缩析出KReO₄白色晶体,其主要杂质Na、Ca、Fe、Cl含量均小于1.00%,特别是W、Mo含量均小于0.10%,且Re结晶率可达94.92%～98.38%。采用动态法脱K,选用C160(H⁺型)树脂,当KReO₄溶液pH为中性,料液流速控制在2BVs·h^-1时,C160树脂对K⁺穿透容量和饱和容量分别为117.87和128.39g·L^-1,且树脂利用率达到91.81%;所得纯HReO₄溶液中K、Na、Ca、Fe、W、Mo、Mg浓度均降至0.50 mg·L^-1以下。通过添加优级纯氨水中和HReO₄溶液,控制终点pH为7～8,再经浓缩结晶+1次重结晶,所得铼酸铵纯度达到99.99%以上,其SEM形貌为树枝状。     

Recycling of rhenium-containing wire scrap

Rhenium is a refractory metal and is one of the rarest elements. Due to its high cost, recycling of rhenium-containing scraps is of economic interest. This paper pertains to the recycling of rhenium from tungsten–rhenium wire scrap generated in the manufacturing of W₉₇Re₃ wire. Rhenium from wire scrap, which contained 3.1–3.4% Re, was volatilized at 900 °C in the presence of air at 2 L/min in a tube furnace according to the following equation: 4Re + 7O₂ → 2Re₂O₇ (g). Volatilized Re was solidified on the inner surface of the tube and was recovered as ammonium perrhenate (NH₄ReO₄) solution after washing the tube with dilute ammonium hydroxide solution (Re₂O₇ + 2NH₄OH → 2NH₄ReO₄ + H₂O). Ammonium perrhenate solution was crystallized to obtain ammonium perrhenate crystals which were free of tungsten and other metal impurities. First pass yield of rhenium recovery was 65.1%. Ammonium perrhenate crystals were reduced in hydrogen at 400–700 °C to obtain Re-metal powder: (2NH₄ReO₄ + 7H₂ = 2Re + 8H₂O + 2NH₃₎. Rhenium metal powder obtained from the W–Re wire scrap was blended with non-sag tungsten powder to make a 6 kg W₉₇Re₃-alloy ingot which was rolled to make tungsten–rhenium wire. Results presented in this paper were intended for developing a commercial process for the recycling of a large inventory of W–Re wire scrap.     

Recovery of rhenium from molybdenum and copper concentrates during the Looping Sulfide Oxidation process

Rhenium is recovered during pyrometallurgical processing of molybdenum sulfide and copper sulfide ores; the traditional technology involves removing rhenium(VII) oxide, Re₂O₇, from the sulfurous gas phase generated during multiple hearth roasting (in molybdenum processing) and smelting (in copper processing). A new technology platform called Looping Sulfide Oxidation (LSO) has been proposed to produce molybdenum and copper using alternative process chemistries. A detailed thermodynamic study of the reaction conditions used in LSO process indicates that rhenium recovery is possible at higher rates than currently realized in the industry. Conditions at which Re₂O₇ is reduced to rhenium metal by S₂ have been identified and key process conditions are outlined to maximize performance of the LSO scheme and rhenium recovery.     

Mechanosynthesis of rhenium carbide at ambient pressure and temperature

We report the synthesis of Re₂C at ambient pressure and temperature. The formation of rhenium carbide (Re₂C) from the elements was obtained by mechanochemical treatment after 640 min of milling. The microscopy analysis shows polyhedral particle agglomerates with diameters of less than 600 nm. Thermogravimetric analysis results revealed the stability of material at up to 800 °C as well as chemical and surface analysis of polyhedral particles which show oxidative properties and a surface area of 2.0 m² g^− 1, respectively.     

Characteristics of BaO-B2O3-SiO2 nano glass powders prepared by flame spray pyrolysis as the sintering agent of BaTiO3 ceramics

Nanosized BaO-B₂O₃-SiO₂ glass powders are directly prepared by flame spray pyrolysis. The mean size of the BaO-B₂O₃-SiO₂ glass powders with amorphous phase and spherical shape is 30 nm. The effects of glass powders on the sintering characteristics of the BaTiO₃ pellet formed from the nanosized BaTiO₃ powders are investigated. The mean size and BET surface area of the BaTiO₃ powders prepared by spray pyrolysis are 110 nm and 9.1 m²/g. The BaTiO₃ pellet with glass additive has large grain size with several microns, dense structure and pure tetragonal crystal structure at a sintering temperature of 1000 °C. The XRD pattern of the pellet has distinct split of (2 0 0) and (0 0 2) peaks at 2θ ≈ 44.95°. The dielectric constant of the pellet without glass additive is 2180. However, the dielectric constants of the pellets with 1, 3, 5 and 7 wt% glass additive with respect to BaTiO₃ are 2496, 2514, 2700 and 2225, respectively.     

Recovery of rhenium from tungsten‑rhenium wire by alkali fusion in KOH-K2CO3 binary molten salt

Tungsten‑rhenium wire is used in thermocouple and lamp filament manufacturing due to its good thermal sensitivity and high temperature plasticity, and many waste wires are generated in processing and after use. This work focuses on the efficient recovery of high value rhenium from tungsten‑rhenium wire waste with a mass composition represented by W95Re5. The main steps for recovery include alkali fusion, recrystallization, hydrogen reducing and washing. First, WRe wire was decomposed by KOH-K₂CO₃ molten salt to produce potassium perrhenate, where the decomposition ratios of W and Re reached 99.36% and 99.80% using a mass ratio of salt to wire of 3:1, m(KOH) of 80% (m representing the mass fraction of KOH in binary salt), a temperature of 800 °C and a reaction time of 60 min. Then, the decomposed product was leached by water, and from the resulting lixivium high purity KReO₄ crystals were obtained by segregation, which had a perfect rhombic dipyramid morphology and average size of 73.26 μm. Last, the material was reduced to Re powder at 350 °C with a H₂ flow rate of 10 L/min. Re powder, with a purity of higher than 99.5% and fine grain size of 19.37 μm, was obtained after washing with acid and water. This method provided a potential economic process for the recovery of waste WRe wire.     

New rhenium complexes containing 4,5-diazafluorene ligand for high-efficiency green electrophosphorescence

Two novel tricarbonyl rhenium complexes featuring 4,5-diazafluorene (DF)-based ligand, i.e., Re-DF and Re-EPDF (EPDF, 9,9-di-(4-ethoxyphenyl)-9-H-4,5-diazafluorene), were designed, synthesized and characterized by ¹H NMR and mass spectroscopy. The green organic light-emitting diodes (OLEDs) based on these complexes with the configuration of ITO/m-MTDATA (10 nm)/NPB (20 nm)/CBP: Re-complex (30 nm)/Bphen (10 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The devices based on Re-DF showed a maximum current efficiency of 20.7 cd/A and a peak luminance of 2506 cd/cm², respectively. And the Re-EPDF doped devices exhibited a maximum current efficiency of 13.5 cd/A and a luminance of 3208 cd/cm². Moreover, the 20 wt.% Re-EPDF doped device still provided a maximum current efficiency of 13.2 cd/A.     

Effect of Convection Gas on the Synthesis of Nanophase Tin Oxides During a Gas Condensation Method

Tin oxide powders of nanometer size have been synthesized by a gas condensation method using helium or a mixture of oxygen and helium as the convection gas. Changes in the average size, morphology, and crystal phases were investigated during heat treatment at temperatures between 350°C and 720°C in the air. Spherical tin oxide powders of 15 nm in average diameter were synthesized in a helium atmosphere, which was composed of Sn, SnO, and Sn₂O₃ phases. After annealing at 720°C, these multiphase particles transformed to a single SnO₂ phase and became an irregular shape of about 50 nm in diameter. This rapid coarsening was attributed to fast mass transfer among particles. The spherical SnO₂ powder of 7 nm in average diameter was directly synthesized using a gas mixture of oxygen and helium. Upon annealing up to 720°C, morphological changes were barely observed in the powder synthesized using a convection atmosphere containing oxygen.     

Diffusion of potassium atoms into rhenium covered with two-dimensional graphite film

The effective diffusion of K atoms into Re (1010) stimulated by a graphite monolayer on its surface is discovered. The activation energies of the diffusion of potassium into rhenium and from it, as well as the effectiveness of the diffusion of potassium atoms, are determined. The following values are obtained: E _f1 = 5.4 ± 0.05 eV, E _1f = 5.75 ± 0.05 eV, and δ_dif(K) ≈ 0.25. The difference in the energies of the diffusion of potassium into rhenium is lower than the energy of the diffusion of potassium into iridium. It is shown that the diffusion length in the process of the diffusion of potassium adatoms into rhenium is greater than in the case of diffusion into iridium. The noticeable diffusion of potassium atoms are observed when the voltage U ≥ +200 V is applied to the specimen and intensifies approximately following the linear law as U increases to 4000 V. The formation of a graphite monolayer on the rhenium surface due to the enormous prolongation of the lifetime of K adatoms under the graphite island compared to the lifetime of adatoms on the exposed rhenium surface increases greatly the effectiveness of potassium diffusion, which grows by ～10⁸ times, then approaches unity. This phenomenon can be used as a method for the active alloying of subsurface layers of solids by atoms.     

Synthesis and sintering behavior of a nanocrystalline α-alumina powder

Nanocrystalline α-alumina powders with a primary mean particle diameter of 10 nm were synthesized from aluminum nitrate and ammonia solution using a precipitation method. The presence of ammonium nitrate (a by-product of the precipitation reaction) in the Al(OH)₃ dry gel can reduce the formation temperatures of γ-, δ-, θ-, and α-Al₂O₃ during heating. The combined effect of 5 wt% α-alumina seed crystals, 100 nm in diameter, and 44% ammonium nitrate can reduce the θ-Al₂O₃→α-Al₂O₃ transformation temperature from 1200 to 900°C. The α-Al₂O₃ powder milled in anhydrous alcohol has an agglomeration strength of 76 MPa (soft agglomerated), while the one milled in deionized water has an agglomeration strength of 234 MPa (hard agglomerated). For both the soft and the hard agglomerated powders initial stage sintering is controlled by grain boundary diffusion, with activation energies of 365 and 492 kJ/mol, respectively. The alumina ceramic produced by sintering the soft agglomerated powder at 1400°C for 2 h has a mean grain size of 0.93 μm, a mean flexural strength of 700 MPa, and a fracture toughness of 4.75 MPa m^1/2.     

Preparation of ZrO2 spherical nanometer powders by emulsion processing route

ZrO2 precursor powders containing 3% Y2O3 were prepared via a single emulsion processing route and a double emulsion processing route. In both routes xylol was used as the oil phase, span-80 as the surfactant, and an aqueous solution containing zirconium or ammonia as the water phase. The calcination of the precursor powders was performed at 600 ℃ for 2 h, leading to tetragonal phase ZrO2 nanometer powders. The ZrO2 powders and the precursor powders were analyzed and characterized by means of TGA-DTA, XRD, TEM, BET and laser particle size analyser. The results indicate that xylol-span-80-water phase system contain more water phase, which to a certain extent overcomes the disadvantages of low output by emulsion route in preparing powders. The best volume ratio Vxylol ： Vspan-80 ： Vwater= 95 ： 5 ： 25 leads to the attaining of powders. The special tetragonal phase powders with less agglomeration were prepared via either the single emulsion processing route or the double emulsion processing route according with the ratio. But compared to the single emulsion processing route, the powders prepared via the double emulsion processing route display smaller particles with more even size distribution, the average size of around 15 nm.