Diffusion Of Cobalt Research Articles

Joining of tungsten carbide to nickel by direct diffusion bonding and using a Cu–Zn alloy

The objective of this work was to study various aspects of liquid and solid state diffusion bonding of cylindrical samples of WC (with 6% Co) and commercially pure nickel (99.5%) produced by direct bonding and brazing using a 25 μm thick 70Cu 30Zn (wt%) alloy as joining element. Joining experiments were carried out on WC/Ni and WC/Cu Zn/Ni combinations at temperature of 980 °C using 1, 15, 25 and 35 min holding times in argon (Ar). The results show that it is possible to create a successful joint at temperature and times used. Joining occurred by the formation of a diffusion zone. The joining interface is feasible because it presents a homogeneous interface with no several interfacial cracking and porosity. In both combinations, it can be observed a diffusion of cobalt decreasing in the direction of the metal, as well as, the diffusion of nickel decreasing in the direction of the ceramic.

Formation of Hollow Spheres upon Oxidation of Supported Cobalt Nanoparticles

Oxidation of cobalt nanoparticles supported on montmorillonite was studied using transmission electron microscopy and temperature programmed reduction of the oxide particles. It has been shown that hollow shells of cobalt oxide were formed in this process, consisting of the mixture of CoO and Co3O4 oxides. A linear relationship between the thickness of shells and the initial particles size was established which suggests that both diffusion of cobalt ions through the oxide layer and diffusion of the oxygen into cobalt occur, but particles sintering is negligible compared with the reverse diffusion of cobalt. The lower critical diameter of cobalt particles was estimated, above which formation of hollow shells occurred. The hollow shells formation is suggested to be the reason for cobalt redispersion upon oxidation−reduction cycling of supported heterogeneous catalysts.

Structural phenomena in glassy carbon induced by cobalt ion implantation

Glassy carbon (GC) was implanted by 150 keV Co+ ions to the doses of 1×1016 (low dose) and 1×1017 ions/cm2 (high dose). The low dose implantation results in GC structure disordering with formation of amorphous carbon (a-C). Analysis of Rutherford backscattering (RBS) and Raman spectra has revealed 15 at.% of sp3-bonded C atoms in the a-C structure. The in-pane size of sp2 clusters was estimated to be 1.1 nm. On the contrary, the high dose ion implantation results in ordering of the a-C structure. Content of the sp3 atoms in a-C was reduced to about 5% and, respectively, the in-plane sp2 cluster size was increased up to 2.8 nm. Together with the a-C structure ordering the Raman spectra identifies formation of transpolyacetylene (TPA)-like chains after the high-dose Co+ implantation. In parallel, RBS suggests an enhanced diffusion of the implanted cobalt within the modified carbon layer. Correlation of the RBS and Raman results argues a driving role of cobalt diffusion in the TPA-like chains formation and a-C ordering. Great surface roughening observed after the high dose Co+ implantation suggests also the pronounced cobalt clustering causing large flux of “free volume” to the surface.

Effect of Boron Concentration on Adhesion and Cutting Performance of Diamond-Coated Cemented Carbide Tools

Diamond thin films doped with various boron concentrations were grown on WC-Co cemented carbide tools by hot-filament-assisted chemical vapor deposition (HFCVD). The trimethyl borate dissolved in acetone solution was used as the boron resource (B/C=0%, 0.1%, 0.3%, 0.5%). The surface morphology of diamond films with different boron contents was investigated by Scanning electron microscopy, the adhesive strength was calculated by means of indentation test under a load of 1500N. A real cutting performance was carried out on Al metal matrix composites material (20vol%SiC, 15μm), and the insert flank wear was examined by measuring the scars that appeared on the cutting edge with tool microscope. The research results shown the surface morphology and structure of the diamond films changed owing to boron doping. As the doping levels increased, the average grain size of the films decreased from 10 to 2μm. A significant improvement in adhesion and cutting performance were observed as the boron contents increased from 0% to 0.5%. The adhesion and cutting performance were best when the boron concentration was 0.3%. Adequate boron can effectively suppress the cobalt diffusion to the substrate surface and avoid the catalytic effect of cobalt at the high temperature. It is of great significance for improvement of the adhesive strength and cutting performance of diamond-coated tools using above method.

Study of ion beam mixing in Pt/Co bilayer by ion beam analysis

Ion beam mixing of the Pt/Co bilayers (400Å/700Å) were carried out using 600keV Pt+ ions with fluences ranging from 1×1015ions/cm2 to 1.2×1016ions/cm2 at room temperature. The sputtering of top Pt layer and the diffusion of platinum and cobalt caused by the ion beam at the interface were revealed by RBS. The interface broadening variance for each fluence was extracted from the RBS spectra after subtracting the contribution to broadening variance due to surface roughness as measured by AFM. The linear dependence of interface broadening variance with fluence shows that ion beam mixing is diffusion controlled in Pt/Co bilayers.

Diffusion of 60Co, 137Cs and 152Eu in Opalinus Clay

AbstractThis study addresses the diffusion of representative sorbing elements, cobalt, cesium and europium in the Opalinus Clay (OPA). The methodology used here to determine diffusion coefficients is the ‘instantaneous planar source’ method. In this setup, a paper filter impregnated with tracer is introduced between two clay samples, avoiding contact between the tracer and the experimental vessels. The apparent diffusion coefficients (Da) perpendicular to the bedding plane, obtained with this experimental method and fitting the experimental results with an analytical solution, were Da(Co) = (2.4-3.5)·10-14 m2/s, Da(Cs) = (5.9-8.0)·10-14 m2/s, and Da(Eu) = (1.0-2.1)·10-15 m2/s. With cobalt and cesium, classical in-diffusion experiments were also performed for comparison, and similar Da values were obtained but with a large dispersion. To analyze the possible effects of the paper filter impregnated with the tracer on the determinations of Da with the analytical solution, one experiment was also analyzed using a detailed stochastic model of the setup. The good agreement between the two modeling approaches confirms the validity of this experimental setup and the analytical model fitting procedure.

Cobalt diffusion during doping of ZnSe single crystals

Cobalt diffusion into single crystals of the compound semiconductor ZnSe has been studied under the conditions of the SZnSe-SCoSe-LZn-V phase equilibrium at temperatures from 700 to 970°C, and the diffusion coefficients of cobalt in (100)-and (111)-oriented single-crystal samples of zinc selenide have been determined as functions of temperature. The diffusion rate of cobalt along the [111] direction is shown to exceed that along [100].

Radiotracer study of cobalt diffusion and solubility in electronic-grade germanium wafers

The diffusion rate of Co in Ge is found to be as fast as 2 × 10 - 6 cm 2 s - 1 at 900 °C, whereas the Co solubility comes close to 1 × 10 16 cm - 3 at the same temperature. Based on these properties and its acceptor activity, Co may cause serious contamination problems during the fabrication of Ge-based electronic devices. In contrast to an early radiotracer study [L.Y. Wei, J. Phys. Chem. Solids 18 (1961) 162], we observe common diffusion profiles of complementary error function type, which are indicative of a constant diffusivity depending only on temperature. A preliminary analysis of the data points to the dissociative diffusion mechanism involving interstitial–substitutional exchange via vacancies. However, in contrast to Cu, which migrates via the vacancy-controlled mode of the dissociative mechanism, the diffusion of Co may be rate-limited by the transport properties of its interstitial modification ( Co i ) .

A comparative study of CrN, ZrN, NbN and TaN layers as cobalt diffusion barriers for CVD diamond deposition on WC–Co tools

Chromium, zirconium, niobium and tantalum nitrides layers have been sputtered onto WC–12 wt.% Co substrates as diffusion barriers and buffer layers for improving performances of diamond surface coating. X-ray diffraction shows under specific reactive sputtering conditions, only MN (M = Cr, Zr, Nb, Ta) type phase exits. Their electric resistivity has been measured on samples deposited onto silica under the same conditions and related to those published. Surface and transverse scanning electron microscopy shows a dense columnar morphology. Thermo chemical computing proves the stability of those nitrides against Co, hydrogen and methane up to 1150 K (877 °C). A computed diagram of nitrogen partial pressure is given for their carburization with methane showing the highest stability for ZrN and TaN. Diamond deposition for 5 h up to 1153 K (880 °C) highlights a different behaviour for each of those materials. Auger Electron Spectroscopy (AES) profiles show a massive diffusion of cobalt through the decomposed CrN layer, a transformation of TaN and NbN into carbide without diffusion of cobalt while ZrN is outstandingly well preserved.

Deposition of Diamond Films on Smooth Surfaces of Cemented Carbide Inserts with Cobalt Boride Interlayers

Improving adhesion and surface roughness of diamond films on WC–Co substrate is the key factor of the widespread application of diamond coated tools. A new pretreatment method has been performed for smooth Co-cemented carbide inserts in order to lower the surface roughness of diamond films under the premise of good adhesion between diamond films and substrates. The effect of the new pretreatment on the adhesion of the diamond films is investigated. Research results show that the boronization pretreatment can effectively suppress cobalt diffusion to the surface and avoid catalytic effect of Co at high temperature. This new pretreatment can avoid the surface roughening of inserts and ensure the deposition of smooth diamond films. Investigation shows that the optimum boronization compounding is a powder mixture of 70%B4C+15.5%KBF4+1.5% La2O3+13%Na2CO3. Adhesion between substrates and diamond films is evaluated by Rockwell A indentation tests and the cutting performance of the diamond-coated tools is investigated by the cutting tests. Diamond films on smooth cemented carbide inserts with cobalt boride interlayer have high adhesive strength and low surface roughness. Diamond-coated tools with boronization pretreatment have a 5-fold increase in tool life compared with untreated ones.

Erosion performance of coatings produced by shrouded plasma spray process on a Co-based superalloy

Erosion studies were carried out using an air-jet erosion test rig at a velocity of 40 m s − 1 and impingement angles of 30° and 90° on uncoated Co-based Superalloy (3Fe–10Ni–20Cr–1.5Mn–0.3Si–0.08C–15W–Balance Co) as well as plasma spray NiCrAlY-, Ni–20Cr- and Ni 3Al-coated superalloy specimens at room temperature. Coatings were characterised before the erosion test. The eroded surfaces have been examined by SEM/EDAX and optical Profilometer. From the EPMA analysis of the as-sprayed plasma coatings the tendency for diffusion of cobalt, tungsten and iron from the substrate into the coatings has been indicated. Ni 3Al coating gave the least erosion rate at a 90° impact angle, whereas the NiCrAlY coating gave the lowest erosion rate at 30°. The Ni–20Cr coating gave the highest erosion rate with both the impact angles. The bare cobalt-based superalloy showed better erosion resistance as compared to the plasma-sprayed coatings. The overall ductile behaviour has been revealed by the scanning electron microscope for both the bare and coated alloys.

Surface softening and hardening of WC-Co using pulsed laser irradiation

The surface of cobalt-containing tungsten-carbide was treated using a pulsed Nd: YAG laser beam under atmospheric conditions in order to control its surface hardness by means of surface diffusion or concentration of cobalt. Elemental analyses of the treated surfaces revealed a laser fluence of 0.25 J/cm 2 to be the most suitable condition for the concentration of cobalt and the removal of surface contaminants, such as hydrocarbons and oxygen gas, without damaging the surface. At this laser fluence, the concentration of cobalt was reduced close to the center of irradiation but increased in the area surrounding the irradiation center. This concentration of cobalt resulted in a softening of the WC-Co surface by over 10% compared to the non-treated surface, as measured by a Knoop hardness tester under a load of 9.8 × 10 − 2 N.

Dynamic Formation of Coordination Polymers versus Tetragonal Prisms and Unexpected Magnetic Superexchange Coupling Mediated by Encapsulated Anions in the Cobalt(II) 1,3-Bis(pyrid-4-ylthio)propan-2-one Series

The reactions of cobalt(II) halides and flexible ligand L [L=1,3-bis(pyrid-4-ylthio)propan-2-one] under different conditions generated a series of complexes with various structural motifs ranging from tetragonal-prismatic cages to 1-3D coordination polymers. The layer diffusion of cobalt(II) chloride and L in methanol/acetone at 25 degrees C gave rise to a 3D polymer, [Co(L)2Cl2].Me2CO. At 30 degrees C, the slow diffusion of diethyl ether into the blue dimethylformamide (DMF) solution of complex 1 afforded a 1D polymer, Co(L)Cl2(DMF)2. However, at 10 degrees C, the diffusion of diethyl ether into the DMF solution of complex 1 produced a tetragonal-prismatic cage, [Co2(L)4Cl2]Cl2.Et2O.DMF.2MeOH.4H2O. The reaction of cobalt(II) bromide and L in DMF at 10 degrees C yielded a dimer, [Co2(L)4Br2]Br2.6DMF.2H2O, with a cage structure similar to. The preparation of the series of compounds indicates the subtle relationship between structures and tunable reaction conditions. It is also found that the structural motifs vary according to the ligand conformations and that the formation of tetragonal-prismatic cages and may be templated by anionic guests. Magnetic studies on complexes in a temperature range 4-300 K disclose that L is unfavorable for a long-range magnetic interaction; however, intramolecular spin-coupling constants of -19.6 and -21.5 cm-1 for and indicate rather strong magnetic superexchanges arising from the overlap of the dz2 orbitals of the cobalt(II) and pz orbitals of the encapsulated halide anions. Electron paramagnetic resonance (EPR) spectra of complexes 3 and 4 in solution and solid give information that both complexes are high-spin cobalt(II) compounds with a rhombic distortion of the axial zero-field splitting. Interestingly, the intramolecular magnetic-exchange coupling in 3 and 4 mediated by the encapsulated anion Cl- or Br- is also reflected by the EPR spectra.

Influence of oxygen and nitrogen addition during growth of CVD diamond on pure cobalt substrates

It was shown that in MPCVD reactors the use of common H and CH 4 flows, can lead to the formation of free-standing diamond films directly on pure cobalt substrates. The characteristic low adhesion of these films can be explained by the formation of a graphitic layer between the substrate and the film. Scanning electron microscopy analysis shows special areas at the film grain boundaries that were subsequently identified as cobalt inclusions by EDS. In this work we have studied the influence of oxygen and nitrogen addition on the film's growth morphology. Once again SEM and EDS were used to access respectively the films growth morphology and cobalt content. Our results clearly indicate that the addition of oxygen during the initial stages of diamond nucleation prevents diffusion of cobalt into the film. Further, we believed that this effect is likely due to the formation of a cobalt-oxide layer between the film and the substrate. Also, the addition of nitrogen and oxygen the later during nucleation or during growth leads to an increase in the film's growth rate. A preferential (111) surface morphology with clear octahedron facets and films with dominant (100) crystallographic planes are detected. A model is presented for the growth of CVD diamond on cobalt substrates with the addition of oxygen and nitrogen.

Influence of magnetization change on solute diffusion in iron

The activation energy for solute diffusion in the ferromagnetic state of iron can be represented by Q p(1 + αs 2), where Q p is the activation energy in the paramagnetic state, s is the ratio of the spontaneous magnetization at T K to that at 0 K. The constant α for self-diffusion and diffusion of cobalt, chromium, molybdenum, niobium and titanium in α-iron has been determined experimentally. Compiling these values of α, we find that the constant α can be expressed as a linear function of ΔM, which is the change of magnetization of iron on dilution with solute elements, if ΔM is taken for the first and second shells of the solute atom.

Cobalt Diffusion in Different Microstructured WC-Co Substrates during Diamond Chemical Vapor Deposition

Cobalt Diffusion in Different Microstructured WC-Co Substrates during Diamond Chemical Vapor Deposition

Cobalt diffusion in different microstructured WC-Co substrates during diamond chemical vapor deposition

Our investigation on diamond deposition using cemented tungsten carbide (WC-Co) has shown that diamond particles deposit at different rates onto micrograin and coarse-grain WC-Co substrates. Diamond deposition was carried out using a parallel-plate plasma-enhanced chemical vapor deposition system, which utilized the bias-enhanced growth (BEG) process. BEG was performed at four different times: 15, 20, 25, and 30 min. The resultant diamond-based deposits were characterized for morphology, microstructure, and crystallinity using scanning electron microscopy. It was found that diamond nucleation initiated at the grain boundaries of the substrates. The present article discusses the possible reasons that can potentially explain our key findings. In particular, the CO diffusion from the bulk material through the grain boundaries and onto the substrate surface using a theoretical approach.

Cobalt-Chromium Powder Alloys and Retention Coatings Made from Them for Orthopaedic Stomatology

An alloy of Co-Ni-Mo-Cr is prepared by diffusion impregnation with chromium from point sources of cobalt-nickel-molybdenum alloy powder synthesized by combined reduction. Optimum regimes are determined for preparing alloy powder by combined reduction of cobalt, nickel, and molybdenum oxides (reduction temperature 1325 K, isothermal soaking time 3 h) and diffusion impregnation with chromium (temperature 1373 K, isothermal soaking time 4 h). The adhesive strength of a facing coating with material of a dental prosthesis manufactured using the alloy developed is studied. It is shown that with application of retention layers the adhesive strength increases by a factor of three to five compared with using cast spheres (beads).

Interdiffusion Studies in Co-Fe-Ni Alloys

Interdiffusion in Co-Fe-Ni alloys was studied in 1373-1588 K temperature range. The Danielewski-Holly model was used for the description of the interdiffusion process in ternary Co- Fe-Ni diffusion couples both for the finite and infinite geometry. Using the inverse method the average intrinsic diffusivities of components in the Co-Fe-Ni system were calculated and compared with the results of the other authors. The activation energies of cobalt, iron and nickel intrinsic diffusion have been found in 1373-1588 K temperature range.

Effect of tungsten 0–8 wt.% on the oxidation of Co–Cr alloys

The nature and the morphology of the formed oxide layers at the alloys’ surface have great importance on the quality of the ceramic/metal bond. This study shows the effect of the tungsten addition on the formation and the growth of the oxide layers on the Co–Cr alloys in preoxidation temperature range 950–1050 °C, thus including the temperature range of the ceramisation process that these alloys will undergo later. Their characterization, by microprobe analysis, scanning electron microscopy (SEM), spectrography with luminescent discharge (SLD) and low angle X-ray diffraction, reveals the formation of two distinct layers: the first one, from the external surface, is formed only of pure CoO, while the second one is a mixture of Cr 2O 3 particles and cobalt–tungsten oxide dispersed in a CoCr 2O 4 matrix. The tungsten addition up to 8 wt.% modifies considerably the thickness of the formed layers as a consequence of its accumulating in the second layer, thus blocking the cobalt diffusion towards the alloy surface.