Mechanical alloying of dispersion-hardened Ni3Al-B from elemental powder mixtures

Mechanical alloying and hot extrusion were studied as a means to dispersion harden an intermetallic compound based on Ni ₃ Al- B from elemental powder mixture. The oxide used for the dispersoids was partially stabilized zirconia. During mechanical alloying the microstructure evolved according to the characteristic stages found in other mechanical alloying systems. Completion of the alloying reaction required 16 h, beyond which loss of the crystalline property set in. Experimental observation of the grain refinement during mechanical alloying agreed with a prediction based on an existing model. Compared to V- cone mixing, the mechanical alloying produced a homogeneous distribution of fine dispersoids. The refined grain structure and dispersoids resulted in a high tensile yield strength over a wide range of temperatures.     

Oxide removal and desorption of oxygen from partly oxidized thin films of copper at low pressures

Partly oxidized copper films were annealed in a controlled vacuum of 10^–7 Pa at a temperature of 450° C. The changes discussed below were observed in situ with a specially designed high-resolution transmission electron microscope. The thin, (100)-oriented, single-crystal films of copper had been oxidized immediately prior to the annealing studies at the same temperature and at an oxygen partial pressure of 7×10 ^–1 Pa, until the desired fraction of the copper film was converted to oxide. It was observed that the oxide disappeared during annealing as long as some copper was left unoxidized. The disappearance of the oxide is explained as being due to dissociation of the oxide at the oxide-metal interface followed by diffusion of oxygen into the metal and desorption of oxygen from the surface of the unoxidized copper. The rate of disappearance of the oxide was found to be proportional to the surface area of unoxidized copper, i.e., the desorption was found to be the rate — limiting step. In the case of heavily oxidized films (>50%), holes were observed to develop in the oxide near the oxide-metal interface after an annealing period of 2–3 hr. Upon resumption of the oxidation, these holes first disappeared, and the normal oxidation behavior was then resumed. The formation of holes may be explained by vacancy clustering. When completely oxidized films were annealed, recrystallization of the oxide was observed.This work was performed at the Ames Research Center and funded by NASA Grants Nos. NCA2-OP390-403 and NSG-2025.     

Production of tungsten boride from CaWO4 by self-propagating high-temperature synthesis followed by HCl leaching

In this study, the conditions of producing tungsten boride powder from calcium tungstate (CaWO₄) by self-propagating high-temperature synthesis (SHS) followed by HCl leaching techniques were investigated. In the first stage of the experimental study, the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of CaWO₄, Mg and B₂O₃. It was found that increasing B₂O₃ content in the initial mixture resulted in an increase of W₂B₅/WB ratio along with Mg₃B₂O₆ in the SHS product. In the second step, Mg and Ca containing byproducts (i.e. MgO, Mg₃B₂O₆ and Ca₃B₂O₆) found in the SHS product were leached out by using aqueous HCl solution to obtain a clean tungsten boride product. The effects of particle size, temperature, time, acid concentration and solid/liquid ratio were selected as leaching parameters. The acid leaching experiments of the SHS product synthesized at 1:8:2.5 initial molar ratio of CaWO₄:Mg:B₂O₃ showed that optimum leaching conditions could be achieved by using 2.85 M HCl at 1/10 S/L ratio and the temperature of 80 °C for 60 min.     

Preparation of Mn−Zn ferrite from spent zinc-carbon batteries by alkali leaching,acid leaching and Co-precipitation

The treatment of spent zinc-carbon batteries for the recovery of valuable metals followed by conversion to Mn−Zn ferrite has been conducted employing two-stage alkali and acid leaching and co-precipitation method. In the first stage, leaching process was carried out with 4 M NaOH, which resulted in a recovery of 63.4 %Zn and 0.1% Mn. Electrowinning of alkali leaching solution containing 12.75 g/L Zn at a current density of 0.2 A/cm² produced Zn metal of 15 nm to 30 nm size and 99.9% purity. The second stage leaching of residue with 3 M H₂SO₄ and 6 vol.% H₂O₂ at a solid/liquid ratio of 1∶10 indicated the leaching efficiency of 98.0% Zn, 97.9% Mn and 55.2% Fe. The obtained leaching solution was finally adjusted to suitable mole ratios of Mn∶Zn∶Fe (1∶1∶4) by the addition of Zn and Fe sulfate salts followed by pH control to produce Mn−Zn ferrite powder. The characterization of the ferrite powder showed uniform nano-crystalline particles of about 20 nm size with spinel structure.     

Expression, purification and molecular modeling of iron-containing superoxide dismutase from Acidithiobacillus ferrooxidans

The superoxide dismutase(SOD) from Acidithiobacillus ferrooxidans may play an important role in its tolerance to the extremely toxic and oxidative environment of bioleaching. This gene was cloned and then successfully expressed in Escherichia coli. The expressed protein was finally purified by one-step affinity chromatography to homogeneity and observed to be dimer according to SDS-PAGE and MALDI-TOF-MS. The metal content determination and optical spectra results of the recombinant protein confirmed that the protein was an iron-containing superoxide dismutase. Molecular modeling for the protein revealed that the iron atom was ligated by His26, His75, Asp158 and His162.     

Facile regeneration vitreous microfibrous entrapped supported ZnO sorbent with high contacting efficiency for bulk H2S removal from reformate streams in fuel cell applications

In this study, a microfibrous carrier consisting of 3 vol.% of 8 μm (diameter) glass fibers is used to entrap 45 vol.% of 150 to 250 μm (diameter) SiO₂ support particulates. ZnO is then nanodispersed onto the support by impregnation at the loading of 17 wt.%. At equivalent bed volumes, ZnO/SiO₂-entrapped materials provide twofold longer breakthrough times for H₂S (with a 67% reduction in sorbent loading) compared with packed beds of 1 to 2 mm commercial extrudates. Five-log reductions in H₂S concentration with up to 75% ZnO utilization at breakthrough are achieved. H₂S concentrations from 60 to 2000 parts per million in volume (ppmv) can be reduced to as little as 0.6 ppmv at 400°C in 30% H₂O at a face velocity of 1.7 cm/s for layers as thin as 1.0 mm. At 500 to 600°C, ZnO/SiO₂-entrapped materials provide much higher regenerability in air than do 1 to 2 mm commercial extrudates. The use of glass fibers permits greater than 50 regeneration cycles. This paper was presented at the ASM Materials Solutions Conference & Show held October 18–21, 2004 in Columbus, OH.     

氨基功能化CoFe2O4-SiO2 磁性复合材料的制备及其在去除水中重金属离子的吸附性能

钴-铁氧体纳米粒子(CoFe₂O₄ NPs)通过改良的共沉淀法制备,CoFe₂O₄-SiO₂磁性复合材料通过st?ber法合成,为了吸附重金属离子CoFe₂O₄-SiO₂进行了氨基功能化。这种吸附剂的晶体结构、形貌、颗粒尺寸、化学组成和分子结构采用X射线衍射图谱(XRD)、扫描电子显微镜(SEM)以及傅里叶变换红外光谱(FTIR)进行表征。此复合材料具有优良的磁性能,由于其高的饱和磁化强度,磁铁可以将其在30秒内快速分离。同时,CoFe₂O₄ NPs的磁性能可以通过烧结温度进行调节,随烧结温度提高,磁性能增强。溶液的pH及反应时间对重金属离子吸附的影响进行了研究,此外此吸附剂对Cu (II)、Cd (II)、Mn (II) 和Zn (II)具有较高的吸附容量和去除率,这一结果使此复合材料可以潜在应用于废水中重金属离子的吸附上。     

Selective single pulse femtosecond laser removal of alumina (Al2O3) from a bilayered Al2O3/TiAlN/steel coating

We studied surface modification of a double layer protective coating on steel induced by single fs laser pulse irradiation in ambient air. The outer alumina (Al₂O₃) layer, which protects against aggressive environments, was 1.7 μm thick and the titanium aluminum nitride (TiAlN) layer in contact with the steel surface had a thickness of 1.9 μm. The pulses (λ = 775 nm, τ = 200 fs) were generated by a Ti:sapphire laser source. The pulse energy was varied from 0.32 μJ to 50 μJ, corresponding to an incident laser fluence of 0.11 J cm^− 2 to 16.47 J cm^− 2. The surface damage threshold was found to be 0.20 J cm^− 2 and the alumina layer removal was initiated at 0.56 J cm^− 2. This selective ablation of alumina was possible in a wide range of fluences, up to the maximum applied, without ablating the TiAlN layer beneath.