Mass spectrometric diagnosis of the surface nitriding mechanism in a d.c. glow discharge

Reactive constituents have been investigated in a molecular beam generated in the cathode surface glow area and surface boundary layer. Mixtures of nitrogen and hydrogen form NH_x(x=0–4) compounds, which are of relevance in heterogeneous, plasma vs. metal nitriding reactions. Ammonia decomposition leads to NH_x(x=2–4). Strong cataphoretic enrichment of hydrogen has been observed in the cathode glow area. Heterogeneous reactions of NH_x with iron lead to the formation of iron nitrides via intermediates such as FeNH_2–3. In a pulsed d.c. glow discharge, increased sputtering and decreased hydrogen enrichment have been observed.     

Pt immobilized spontaneously on porous MXene/MAX hybrid monolith for hydrogen evolution reaction

Designing efficient electrocatalysts with low Pt loadings for hydrogen evolution reaction(HER) is urgently required for renewable and sustainable energy conversion.Here,we report a strategy that Pt nanoparticulates are spontaneously immobilized on porous MXene/MAX monolith as HER catalysts by utilizing the redox reaction between Ti_3C_2T_x MXene and [PtCl_4]~2 in H_2 PtCl_6 aqueous solution.By taking advantage of homogeneously distributed Pt nanoparticulates on highly electrically conductive porous Ti_3C_2T_x/Ti_3AlC_2 monolith,the as-prepared electrocatalysts show high catalytic performance for hydrogen evolution.Specifically,the binder-free electrocatalysts have Pt loadings as low as 8.9 μg/cm~2,with low overpotential of 43 mV at a curre nt density of 10 mA/cm~2 and low Tafel slope that three times lower than porous Ti_3C_2T_x/Ti_3AlC_2 without Pt loading.This strategy offers a new approach to constructing ultra-low Pt-loading HER catalysts on the basis of in situ redox reaction between noble metal ions and MXenes.     

Preparation of Fe/B powders by mechanical alloying

Steels with a high boron content are valuable as a neutron shield in waste containers and as control absorbers in nuclear reactors. The purpose of this study was to obtain by mechanical alloying an iron powder with 50% boron (by weight) and then powder-metallurgy materials. The elementary powders were mixed in a high-energy mill for 36 h in an inert atmosphere. Samples were withdrawn at intervals, and the powder was characterized by differential thermal analysis, X-ray diffraction and electron microscopy. The Fe/B powders withdrawn at different intervals of milling were diluted with further additions of iron up to a final content of 10% boron. The mixtures were uniaxially compacted at 500 MPa; their green density was verified, and they were sintered in argon at 1150°C. Their physical properties (density and dimensional change) and bending strength were evaluated and microstructural studies and fracture tests were performed.     

Electrocatalytic properties of surface oxides on gold,platinum, and stainless steel electrodes in electrooxidation of malic acid

Electrocatalytic properties of oxides formed at gold, platinum, and stainless steel electrodes in the malic acid electrooxidation in 0.1 M Na₂SO₄ are studied. Gas chromatographic analysis of the electrolyte after holding the potential at 1.0 V for 8 h shows that on platinum and gold electrodes 2 mmol of acetaldehyde are produced and on stainless steel, 45 mmol. The acetaldehyde yield is the highest on stainless steel.From Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 304–309.Original English Text Copyright © 2005 by Avramov Ivi, Popi, Antonovi.This article was submitted by the authors in English.     

原子吸收光谱法测定拉伸断口铬镍钼钛钢样品中主成分

研究了毫克级铬镍钼风样品中主成分镍的火焰原子吸收光谱法（FAAS法）和铬、钼、钒、钛、铝的塞曼恒温平台石墨炉原子吸收光谱法（ZSTPF－AAS法）。采用了微波溶样技术作为防污染样品预处理技术，采用石墨管硅涂层改进技术提高了仪器的测试精度。其中铬、镍、钼、钒、钛、铝的相对标准偏差分别为2.7%,0.97%,8.6%,7.3%,1.7%,7.3%。其加标回收率分别为96.5%,97%,96.7%,93%,98%,91%。通过分析，发现在较低温度下铬镍钼钛钢断面上有轻微的钼偏析现象，可能是拉伸断裂的主要化学影响因素。     

Thermal analysis of low alloy Cr-Mo steel

The paper deals with results of thermal analysis of low-alloyed chromium-molybdenum steel. The methods of analysis were dilatometry, differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The Ac₁ and Ac₃ temperatures of the steel samples measured by dilatometry and DTA during the heating period were in good agreement. Generated by cooling a martensitic structure first became apparent at 503 K. Tempering of the as-quenched samples showed the presence of the second tempering stage in the region between 473 and 573 K. At that stage heat capacity decreased from 0.48 to 0.32 J g^-1 K^-1, as a result of conversion of transition carbide due to heat consumption. After normalization of the as-quenched samples the heat capacity values were restored to between 0.42 and 0.47 J g^-1 K^-1 in the temperature range from 373 to 673 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molecularly-imprinted polypyrrole-modified stainless steel frits for selective solid phase preconcentration of ochratoxin A

A molecularly-imprinted polymer (MIP) was prepared by electropolymerization of pyrrole (Py) onto a stainless steel frit, using ochratoxin A (OTA) as the template, in order to make a micro solid phase preconcentration (SPP) device. The OTA template was removed with 1% triethylamine (TEA) in methanol. Compared to non-imprinted polypyrrole (PPy), the molecularly-imprinted polypyrrole (MIPPy) enhanced the selective binding of OTA. The percentage recovery improved from 0 to 40% when the OTA sample solution was acidified with 1 M HCl (1% by volume). At a flow rate of 0.2 mL/min, maximum OTA binding was reached in 6 min after a total loading of 3.2 ng OTA. Final elution of the OTA was analyzed by high performance liquid chromatography (HPLC) with fluorescence detection, using 20:80 v/v acetonitrile–ammonia buffer (NH₄Cl/NH₃, 20 mM, pH 9.2) as the mobile phase. The MIPPy-SPP-HPLC results clearly demonstrated that the MIPPy-SPP device afforded selective preconcentration of OTA from red wine samples, at OTA concentration levels as low as 0.05 ppb, prior to HPLC analysis.     

Sol-gel ZrO2 coatings for chemical protection of stainless steel

ZrO₂ coatings deposited on 316 L stainless steel sheets were synthesized by sol-gel method using Zr(OC₃H₇)₄ as precursor and isopropanol, glacial acetic acid, and water as solvents for application with ultrasounds. Different solutions for dip-coating were prepared with compositions varying between 0.025 and 0.9 mol/dm³ of ZrO₂. X-ray diffraction shows that the films densified at 800°C are crystalline with a tetragonal structure. The thickness of the coatings varied from 0.35–0.75 m. The influence of the ZrO₂ coatings on the corrosion behavior of stainless steel substrates in aqueous NaCl was studied through potentiodynamic polarization curves at 1 mV/s. The values of the electrochemical parameters allow for an explanation of the role of the films in the increased resistance of steel against corrosion in moderately aggressive environments.     

Assessment of corrosion resistance of surface-coated galvanized steel by analysis of the AC impedance spectra measured on the salt-spray-tested specimen

In the present work, corrosion resistance of surface-coated galvanized steel was quantitatively determined by an analysis of the alternating current (AC) impedance spectra measured on the salt-spray-tested specimen. To evaluate the corrosion resistance of the surface-coated galvanized steel, AC impedance spectroscopy was performed on the salt-spray-tested specimen previously exposed to salt-sprayed corrosive environment. From the analysis of the impedance spectra, the area fraction transient of white rust θ ₂(t) was theoretically derived from the equivalent circuit equation by using two fitting parameters. The values of the two fitting parameters were determined by fitting the empirical transient equations to the area fraction of the resin coating layer and to the total resistance obtained from the impedance spectra measured, respectively. From the analyses of θ ₂(t) for four kinds of surface-coated galvanized steels with various resin coating layers, it is indicated that as the values of the two fitting parameters decrease in the order of CP, GI, OD and OM (commercial trade names) specimens, the corrosion resistance increases in that order as well. Furthermore, from the quantitative comparison of the two fitting parameters with the polarization resistance of the upper resin coating layer R _p determined from the potentiodynamic polarization curve, it is suggested that the two fitting parameters decrease in value as well with increasing R _p.     

Protective properties of redox polymer film deposited on stainless steel

We propose a novel composite organic-inorganic coating in the form of a redox polymer film for protection of stainless steel against general corrosion in strong acid medium (2 M H₂SO₄). We utilize an anion exchange polymer, protonated poly(4-vinylpyridine), into which hexacyanoferrate anions have been introduced. Owing to the presence of Fe(CN)₆^3–/4– at the interface formed by the film and the steel, a sparingly soluble metal hexacyanoferrate (mostly Prussian blue, PB) is formed as an overcoating on the steels surface, presumably on the passive (metal oxide) layer. The redox polymer film on the steel seems to act as a composite three-dimensional bilayer-type coating in which hexacyanoferrate(III,II) anions (that are capable of effective charge storage) exist in the outer portions of the film, whereas the inner PB layer improves the systems overall adherence and stability. By analogy to a conducting polymer (e.g. polyaniline, polypyrrole), introduction of the redox polymer composite film leads to stabilization of the steel substrates potential within the passive range.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)