Adhesion promotion of Cu on C by Cr intermediate layers investigated by the SIMS method

Copper-carbon composites are candidate materials for heat sinks for high speed/high-performance electronic components. They combine high thermal conductivity with low density and a tailorable coefficient of thermal expansion (CTE). Because of the low wettability of carbon by copper, a thin layer of chromium can be deposited to promote both the adhesion and the thermal contact of copper with the carbon fibers. Therefore, in a first step layers of Cr and Cu were deposited by magnetron sputtering on plane vitreous carbon substrates (Sigradur G), which serve as a model for carbon fibers. From pull-off-adhesion measurements an interlayer thickness of Cr in the range of 2-10 nm was found to provide the optimal adhesion for 1 micro m thick copper overlayers. To model the later serial fabrication of the composite that involves a hot pressing step following the deposition, the C/Cr/Cu samples were heat treated at 800 degrees C under vacuum for 1 h. Adhesion on the heat-treated samples was superior in comparison to the untreated ones. To obtain information about the adhesion mechanism secondary ion mass spectrometry (SIMS) investigations were done on the depth distribution of the main elements copper, chromium, and carbon. Two samples, one as deposited and one subjected to heat treatment after deposition, were compared in this investigation. We found that heat treatment mainly modifies the distribution of Cr in the C/Cr/Cu system.     

The determination of oxygen in brass and zinc by a vacuum carbon-reduction techniques

A vacuum carbon-reduction technique for the determination of oxygen in brass and zinc has been studied. As a preliminary, zinc is removed from the samples, sealed in predegassed graphite capsules, in a silica furnace maintained at ca. 850°C under vacuum in a vacuum fusion instrument. The residual contents of the capsules are then analysed in sequence at 1450°C in the main furnace of the apparatus, to which they are transferred without breaking the vacuum. The procedure developed affords a detection limit of 0.5–1 ppm of oxygen for samples weighing ca. 1.5 g.     

Electrochemical studies on the corrosion of brass in seawater under anaerobic conditions

This paper reports an electrochemical study on the corrosion of brass in deoxygenated nonbuffered and buffered natural and artificial seawater solutions under anaerobic conditions. Cyclic voltammograms of brass and copper in natural seawater (NSW) and artificial seawater (ASW) were obtained in the passive and transpassive potential regions. The corrosion resistance of brass in natural and artificial seawater was evaluated, and open-circuit potentials were recorded over exposure period of 1 week. Brass samples from 3-month exposures in deoxygenated nonbuffered ASW and NSW, under open-circuit potential, have been imaged by scanning electron microscopy, and the elemental composition of the corrosion products was obtained by energy dispersive spectrometry analysis. It has been concluded that, under anaerobic conditions, the aggressivity of NSW is higher, with brass being less resistant to corrosion than copper, and that buffer contributes to reduce the aggressivity of both media.     

Homogeneous nucleation and growth in supersaturated zinc vapor investigated by molecular dynamics simulation

Homogeneous nucleation and growth of zinc from supersaturated vapor are investigated by nonequilibrium molecular dynamics simulations in the temperature range from 400 to 800 K and for a supersaturation ranging from log S=2 to 11. Argon is added to the vapor phase as carrier gas to remove the latent heat from the forming zinc clusters. A new parametrization of the embedded atom method for zinc is employed for the interaction potential model. The simulation data are analyzed with respect to the nucleation rates and the critical cluster sizes by two different methods, namely, the threshold method of Yasuoka and Matsumoto [J. Chem. Phys. 109, 8451 (1998)] and the mean first passage time method for nucleation by Wedekind et al. [J. Chem. Phys. 126, 134103 (2007)]. The nucleation rates obtained by these methods differ approximately by one order of magnitude. Classical nucleation theory fails to describe the simulation data as well as the experimental data. The size of the critical cluster obtained by the mean first passage time method is significantly larger than that obtained from the nucleation theorem.     

The morphology of zinc dimethacrylate reinforced elastomers investigated by SEM and TEM

The morphologies of various ZDMA-reinforced elastomers, including styrene butadiene rubber (SBR), ethylene-propylene-diene monomer (EPDM), nitrile-butadiene rubber (NBR), ethylene-propylene monomer (EPM), poly(α-octylene-co-ethylene) elastomer (POE) and hydrogenated nitrile-butadiene rubber (HNBR), were studied by using SEM and TEM. The observation on the compounds showed that during the compounding process, the dimension of ZDMA particles reduced, and could even form dispersion structures with nanometer size (<100 nm). It is shear stress of compounds during mixing rather than polarity of matrix rubber that plays the most important role to determine dispersion state of ZDMA in compounds. High shear stress facilitates dispersion of ZDMA. Only in elastomers having the lower shear stress such as POE and EPM, original dimension features of ZDMA particles make considerable effects on dispersion level of ZDMA in compounds. The observation on cured composites displayed that there are two kinds of micro-dispersed structures: micron dispersion—residual ZDMA particles and nano-dispersion—the aggregate of poly-ZDMA. The higher saturation and polarity of rubbers and the better dispersion level of ZDMA in compounds benefit in situ polymerization of ZDMA, resulting in the lower amount of residual ZDMA particles (micron dispersion). In the elastomer with higher saturation such as POE, EPM, EPDM and HNBR, the dimensions of nano-dispersions are slightly larger. For the ZDMA/POE, formula effect on morphology of the composite was also discussed. It was found that the loading of ZDMA and peroxide impact remarkably on the amount and dimension of nano-particles in the composite.     

Pitting corrosion of zinc in alkaline medium by thiocyanate ions

This paper describes the use of potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques in order to study the pitting corrosion susceptibility of a Zn electrode in KOH solutions containing KSCN as a pitting corrosion agent. Measurements were conducted under different experimental conditions. The results demonstrated that in the absence of KSCN, the anodic voltammetric response displays two anodic peaks prior to reaching the oxygen evolution potential. The first anodic peak A₁ is related to the electroformation of Zn(OH)₂. Peak A₁ is followed by a wide passive region which extends up to the appearance of the second anodic peak A₂. The latter is assigned to the formation of ZnO₂. Addition of SCN⁻ ions to the KOH solutions stimulates the anodic dissolution through peak A₁ and breaks down the passive layer prior to peak A₂. The breakdown potential decreases with an increase in SCN⁻ concentration and temperature, but increases with an increase in KOH concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases slightly with increasing applied positive potential, SCN⁻ concentration, and temperature.     

Platinum electrochemical corrosion and protection in concentrated alkali metal chloride solutions investigated by potentiodynamic nanogravimetry

Platinum nanogravimetry potentiodynamic profiles in cyclic scans have shown significant dependence on alkali metal chloride concentration and effect of cations. Pt EQCM electrode mass drift in consecutive cyclic scans in 0.5 M LiCl, NaCl and CsCl was negative, similarly to the mass drift in aqueous solutions of H₂SO₄ with HCl additive, and this was due to electrochemical corrosion of platinum. The mass loss was prevented and inverted in 3 M solutions in the negative part of the scan, and the effect was attributed to shells of ion pairs firmly attached to the electrode surface via nonequilibrated Pt surface sites generated in the anodic scan. The increase in mass correlated with the increase in the Butterworth–van Dyke model resistance of quartz crystal resonator.     

Influence of cation on the cellulose dissolution investigated by MD simulation and experiments

Cellulose is the most abundant natural polymer on the earth, and effective solvents are essential for its wide application. Among various solvents such as alkali/urea or ionic liquids, cations all play a very important role on the cellulose dissolution. In this work, the influence of cation on the cellulose dissolution in alkali/urea via a cooling process was investigated with a combination of MD simulation and experiments, including differential scanning calorimetry (DSC) and NMR diffusometry (PFG-SE NMR). The results of DSC proved that the dissolution of cellulose in both solvents was a process within a temperature range, starting at above 0 °C and completing at low temperature (?5 °C for LiOH/urea and ?20 °C for NaOH/urea), indicating the necessity of low temperature for the cellulose dissolution. Molecular dynamic (MD) simulation suggested that the electrostatic force between OH^? and cellulose dominated the inter-molecular interactions. In our findings, Li⁺ could penetrate closer to cellulose, and displayed stronger electrostatic interaction with the biomacromolecule than Na⁺, thus possessed a greater “stabilizing” effect on the OH^?/cellulose interaction. PFG-SE NMR demonstrated a more significant binding fraction of Li⁺ than Na⁺ to cellulose, which was consistent with MD. These results indicated that the direct interactions existed between the cations and cellulose, and Li⁺ exhibited stronger interaction with cellulose, leading to stronger dissolving power.     

Investigation of corrosion of a rotating iron electrode in HNO3 by in-situ Raman spectroscopy

Iron products resulting during reduction/oxidation processes in 0.15 M HNO₃ and 0.02 M HNO₃ with and without excess of supporting electrolyte are detected by Raman spectroscopy. The presence of ferrous species close to Fe depend on local pH changes and hydrodynamic conditions. Pre-corroded electrodes may be covered by Fe₃O₄ during cathodic treatment. The resulting oxides and hydroxides are not easily removable on stationary electrodes either at passivation potentials or during a slow reduction at −0.9 V vs. SCE. Simultaneous reduction of NO⁻₃ to HNO₂ also influences the corrosion process.     

Indoor corrosion of Pb: Effect of formaldehyde concentration and relative humidity investigated by Raman microscopy

In this work the effect of relative humidity (RH) and formaldehyde (H₂CO) concentration on Pb corrosion was investigated; a possible synergism between the aldehyde and CO₂ effects was also considered. Triphasic aqueous salt solutions were used to produce 54% and 75% RH that, together with the 100% RH condition, were combined with 0, 0.62, 55 and 2.0 10² mg m⁻³ formaldehyde concentrations to compose the wanted environments.The results pointed to the conclusion that even at low RH (54%) formates are produced at the metal surface as a consequence of formaldehyde adsorption, indicating that the aldehyde has an active role in Pb corrosion; formates were also observed at relatively low H₂CO concentration (0.62 mg m⁻³). No synergism between formaldehyde and carbon dioxide were observed as demonstrated by the Raman images from a corroded Pb coupon, showing that formate and carbonate contributions to the corrosion products were not spatially related.When compared to other volatile organic compounds (VOCs), formaldehyde harmful effect towards metals is frequently underestimated and the results here reported clearly indicate that, even at low RH, its concentration in indoor environments, where it tends to be produced and accumulated, has to be carefully controlled.     

Investigation of high current density on zinc electrodeposition and anodic corrosion in zinc electrowinning

Journal of Solid State Electrochemistry - In this work, the effects of high current density (500 A/m2, 600 A/m2, 700 A/m2, 800 A/m2) on zinc electrodeposition as well as the anodic corrosion...     

Surface treatment of zinc by Schiff’s bases and its corrosion study

The zinc metal surface is chemically modified by newly synthesized Schiff’s bases and its corrosion protection is investigated. The influence of concentration of Schiff’s bases on modification of zinc surface and immersion time in treatment bath are investigated and optimized for maximum corrosion protection efficiency. The electrochemical studies of treated zinc specimens are performed in aqueous acid solution using galvanostatic polarization technique. The treated zinc samples show good corrosion resistance. The recorded electrochemical data of chemically treated samples indicate a basic modification of the zinc surface. The protection efficiency of organic layer formed on zinc surface is tested by varying the acid concentration and temperature of the corrosive medium. The corrosion protection efficiency increases with the concentration of Schiff’s bases and immersion time. This is due to a strong interaction between zinc and the organic molecules, which results in the formation of a protective layer. This layer prevents the contact of aggressive medium with the zinc surface. The surface modification is confirmed by the scanning electron microscopy images. The interaction between metal atoms and Schiff’s bases is also established by IR studies. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 7, pp. 886–892. The text was submitted by the authors in English.     

Microstructure and corrosion resistance of electrodeposited zinc alloy coatings

A heat treatment effect on the microstructure and corrosion properties of electrodeposited Zn, Zn-Co, Zn-Fe and Zn-Ni alloy coatings was studied. Surface morphology examinations were carried with AFM, while XRD was used to determine metal lattice parameters, texture and phase composition. Low-temperature annealing (at 225 °C) caused the formation of intermetallic Fe/Zn compounds, a transformation of amorphous oxide inclusions to the crystalline form and a decrease in the Zn lattice parameter for Zn-Co and Zn-Fe alloys. The mentioned structural modifications were not accompanied, however, by corrosion behavior changes of these coatings. On the Zn-Ni alloy, the annealing caused a significant reduction in the diffraction peak width and simultaneous considerable augmentation of the corrosion current. This effect is related to the formation of a less disordered lattice for this alloy.Contribution to the 3rd Baltic Conference on Electrochemistry, GDASK-SOBIESZEWO, 23–26 APRIL 2003.Dedicated to the memory of Harry B. Mark, Jr. (February 28, 1934–March 3rd, 2003)     

Modeling the early stages of self-assembly in nanophase materials

The early stages of self-assembly of the elementary building blocks of nanophase materials are studied. The relative roles of entropic and energetic factors in determining the relative abundance of the final products present is analyzed using both a kinetic mean field model and a mesoscopic approach in which self-assembly is viewed as an encounter-controlled process on a discrete lattice. The relevance of the results in zeolite synthesis in connection with the ordered liquid phases recently discovered in these materials is discussed.     

Investigation of the early stages in soraphen A biosynthesis

The unusual benzoate starter unit in soraphen A derives from phenylalanine via cinnamate in a beta-oxidative (plant-like) pathway; 3-phenyl-3-hydroxypropanoate incorporates directly into soraphen by loading onto module 2 of the PKS and indirectly from the beta-oxidative pathway to generate benzoyl CoA.     

Study of the inhibition of the corrosion of copper and zinc in HNO3 solution by electrochemical technique and quantum chemical calculations

The corrosion inhibition of copper and zinc in 0.1 M HNO₃ by 1,2,3,4-tetrazole (TTZ) and some of its derivatives has been analysed in a comparative study. Two experimental techniques have been used such as weight-loss and electrochemical polarization measurements. The results obtained reveal that the addition of these compounds reduces preferentially the corrosion of Cu rather than that of Zn. The adsorption of tetrazolic compounds on a copper surface was more favourable than their adsorption on a zinc surface. Moreover the inhibition efficiency calculated for copper was found to attain 95% in the presence of 1-phenyl-5-mercapto-1,2,3,4-tetrazole (PMT) while it remains constant at 1% for all compounds tested using zinc as electrode. Relationship between molecular structure and their inhibition efficiency was elucidated by quantum chemical calculations using the density functional theory (DFT).     

Heterogeneous directional mobility in the early stages of polymer crystallization

Recently, we demonstrated via large-scale molecular dynamics simulations a "coexistence period" in polymer melt ordering before crystallization, where nucleation and growth mechanisms coexist with a phase-separation mechanism [Gee et al., Nat. Mater. 5, 39 (2006)]. Here, we present an extension of this work, where we analyze the directional displacements as a measure of the mobility of monomers as they order during crystallization over more than 100 ns of simulation time. It is found that the polymer melt, after quenching, rapidly separates into many ordered hexagonal domains separated by amorphous regions, where surprisingly, the magnitude of the monomer's displacement in the ordered state, parallel to the domain axial direction, is similar to its magnitude in the melt. The monomer displacements in the domain's lateral direction are found to decrease during the time of the simulation. The ordered hexagonal domains do not align into uniform lamellar structures during the timescales of our simulations.     

Spectrophotometric determination of bismuth in copper and cartridge brass by the iodide method

An improved spectrophotometric method is proposed for the determination with iodide of trace amounts of bismuth in copper and cartridge brass. The sample is dissolved in nitric acid and the bismuth is separated from the copper by an ammoniacal precipitation in the presence of iron(III) hydroxide as a gathering agent. The hydroxide precipitate is dissolved in hydrochloric acid, sulfuric acid is added, the solution is evaporated to a few ml, hydrobromic acid is added to volatilize the antimony and tin, and the solution is evaporated to fumes of sulfuric acid. The bismuth iodide color is then developed with a composite potassium iodide—sodium hypophosphite reagent. Factors affecting the bismuth iodide color are investigated.     

Copper corrosion in soil: influence of chloride contents, aeration and humidity

The corrosion of copper in a typical Portuguese soil was studied. The original soil was characterised, and modifications were produced by adding chloride, and HClO₄ solutions, or by increasing its relative humidity. The aggressiveness degree of the various soil samples was determined. Copper coupons exposed for 3 months in the original and in the modified soil samples were analysed. The average corrosion rates determined from gravimetric data were in good correlation with the soil aggressiveness. The morphology of the corroded copper surfaces, with and without corrosion products, was analysed by visual observation, optical microscopy and scanning electron microscopy. Energy dispersive spectroscopy was used for the semi-quantitative analysis of the corrosion products and X-ray diffraction spectroscopy to identify the crystalline products. Cuprite has been identified on the copper samples corresponding to the interfaces Cu|S6 and Cu|S8, plus paratacamite on the copper coupon exposed to the soil with higher concentration of chloride (S6). Polarisation curves of copper samples in neutral solutions made by adding different amounts of chloride ions to the soil washing water, under deaereated conditions, were recorded and analysed. The passivity breakdown potential has shown, as expected, a displacement to the cathodic direction as the Cl⁻ ion concentration increases.