Diffusion Of Cobalt Research Articles

Studies on diffusion of cobalt in austenitic chromium-nickel steels 0Kh16N15M3B and 1Kh18N10T

Studies on diffusion of cobalt in austenitic chromium-nickel steels 0Kh16N15M3B and 1Kh18N10T

Diffusion and electrotransport of iron, cobalt and nickel in thorium metal

The diffusion and electrotransport parameters for iron, cobalt and nickel were measured in α (f.c.c.) and β (b.c.c.) thorium over the temperature range 965 – 1625 °C. All three solutes have negative Z ∗ values corresponding to migration toward the anode and a marked temperature dependence of Z ∗ in both phases. From a least-squares treatment of the diffusivity data, values of D 0 and Q in the equation D = D 0 exp(− Q R ) were obtained for each solute as follows: iron, D 0 = 5 × 10 −3 cm 2s −1 and Q = 19.3 kcal mol −1 in α-thorium and d 0 = 4 × 10 −3 and Q = 17.1 in β-thorium; cobalt, D 0 = 5 × 10 −4 cm 2 s −1 and Q = 13.2 kcal mol −1 in α-thorium and D 0 = 4 × 10 −3 and Q = 15.6 in α-thorium; nickel, D 0 = 4 × 10 −3 cm 2 s −1 and Q = 18.6 kcal mol −1 in α-thorium and D 0 = 4 × 10 −4 and Q = 9.1 in (β-thorium. The D 0 and Q values are more characteristic of interstitial solute behavior than of substitutional solutes, as are the electromigration velocities for the temperature range investigated. These results indicate that iron, cobalt and nickel are fast diffusing solutes in thorium metal.

Sound production in the cockroach,Gromphadorhina portentosa: The sound-producing apparatus

1. The giant Madagascar cockroach,Gromphadorhina portentosa, hisses by expelling air from a pair of specialized abdominal spiracles. The anatomy and innervation of serially homologous respiratory and sound-producing spiracles were compared in order to determine the evolutionary steps by which a new behavior has developed. 2. The trachea leading to the sound-producing (fourth) spiracle shows a constriction proximally; distally it is greatly elongated with a conical bore (Fig. 2). These features, which are lacking in other spiracles, are sufficient to account for the character of the sound (Fig. 10). 3. The motoneurons innervating both types of spiracles were located by axonal diffusion of cobalt, and their morphology was determined in wholemounted ganglia. The number, ganglionic locations, and in some cases branching patterns of motoneurons serving the sound-producing and respiratory spiracles were essentially identical (Figs. 4, 5, 6). 4. Physiological activity was recorded along spiracle nerves and within spiracle muscle fibers; four units were identified for each spiracle, agreeing with the number of cells located anatomically. These included, for each abdominal spiracle, an opener exciter motoneuron, two closer exciter motoneurons, and one closer inhibitor motoneuron (Figs. 7, 8). 5. During normal respiration the output of these 4 units had similar phase relationships in all abdominal spiracles which were examined; lower firing rates in the motoneurons innervating the hissing spiracles rendered these nonfunctional during normal respiration (Fig. 9). 6. The findings are consistent with conservation of motor innervation and of central pattern generators during evolution.

Diffusion of niobium, iron, cobalt, nickel and copper in niobium

Abstract Self-diffusion in niobium and impurity diffusion of iron, cobalt, nickel and copper in single crystals and polycrystals of niobium have been studied by radio active tracer and electron microprobe methods. These two techniques, the advantages and disadvantages of which are discussed, give results in excellent agreement with each other and allow the establishment of a sequence for the diffusion coefficients D where: These results show that iron, cobalt and nickel diffuse abnormally fast in niobium whereas the latter displays no curvature (on an Arrhenius plot) in self-diffusion. Analysis of all available data for impurity diffusion in niobium shows that the solidus rule proposed by Roux and Vignes (1970) is completely quantitative as regards both activation energies and diffusion coefficients.

Defect structure in CoO

The total concentration of point defects and deviation from stoichiometry in Co1-yO have been determined experimentally as functions of temperature and equilibrium oxygen pressure in the temperature range 1000–1250°C and oxygen pressure range 10−3-1 atm. This total concentration of defects has also been calculated from known values of the coefficients of chemical diffusion and tracer self-diffusion of cobalt. The results of the two methods agree well. It has been found in the investigated range of temperature and oxygen pressure that the defect structure of cobaltous oxide is composed not only of defects due to deviation from stoichiometry, singly ionized cation vacancies, and an equivalent amount of electron holes, but also of intrinsic defects, probably of the Frenkel type.

Diffusion of60Co in niobium single crystals

Abstract Diffusion of 60Co in niobium single crystals was measured by precision grinding over a wide temperature range 1074°-1900°C. The results are expressed by Diffusion rates for cobalt are about two orders of magnitude faster than self-diffusion of niobium. This suggests that some solutes probably diffuse in niobium by other than a simple vacancy mechanism. Thus fast diffusion of cobalt in niobium is similar to that found in the anomalous b.c.c. metals, Zr, Ti and γ-U

Axonal pathways in the brain-retrocerebral neuroendocrine complex of Manduca sexta (L.) (Lepidoptera: Sphingidae)

Axonal pathways of the various neurosecretory cell groups in the brain of larvae and pupae of Manduca sexta were studied, using a cobalt diffusion and precipitation technique. Five groups of cells were found to send axons to each retrocerebral complex. Axons from the fused nervi corporis cardiaci I and II arise from 2 ipsilateral dorsomedial groups, a controlateral anteromedial group, and a controlateral dorsolateral group. Axons from the NCC III arise from a group of ipsilateral tritocerebral neurosecretory cells. All of the cell groups sending axons through the NCC I+II innervate the corpus allatum. By contrast, only a few of the axons making up the NCC I+II appear to terminate in the corpora cardiaca (CC). The tritocerebral cells send axons to the CC only. Extensive migration of neurosecretory cells takes place during metamorphosis. The dorsomedial cells of the larva migrate laterad to become the lateral neurosecretory cells of the pupa and adult. The anteromedial cells of the larva migrate dorsad to become the medial neurosecretory cells of the pupa and adult.

Diffusion of Cobalt out of Cobalt‐Hardened Gold Measured with Auger Electron Spectroscopy

The diffusion of cobalt out of a gold layer is considered. The theory is discussed to relate measured quantities to diffusion coefficients. Measurements were taken and appropriate calculations made to obtain values for the coefficients at 100° and 150°C. Arrhenius plot extrapolations are then made to obtain approximate values at ambient temperatures.

A paraelectric defect in sodalite : R.C. Alig, RCA Laboratories, Princeton, New Jersey 08540, U.S.A. and A.T. Fiory, Bell Telephone Laboratories, Murray Hill, New Jersey 07971, U.S.A.

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.

Characteristics of Polarographic Catalytic Waves Observed with Bovine-Serum Albumin: Kinetic or Diffusion Control

Conditions are described under which the catalytic Brdicka currents observed in ammoniacal buffer solutions containing cobalt(III) hexammine chloride or cobalt(II) and very little bovine-serum albumin (0.1-0.2 muM) are purely kinetically controlled. Under these conditions the kinetic current at pH 9.3-10.3 exhibits a sharp maximum followed by a decrease of the current to a well-defined minimum. The maximum and minimum are eliminated in the presence of 5 mM or more concentrated calcium chloride when a short plateau occurs at the potential of the maximum followed by a well-defined second wave. Both currents are kinetically controlled. When the albumin concentration is 2 muM or greater, the kinetic currents approach diffusion control, the rate of diffusion of cobalt(III) or (II) being close to rate determining. Under these conditions the currents become proportional to the cobalt(III) or (II) concentration in the concentration range between 25 and 200 muM.

Diffusion of iron, chromium and cobalt in GaAs.: S S Khludkov et al, Neorg Mater, 8 (6), June 1972, 1044–1048 ( in Russian)

Diffusion of iron, chromium and cobalt in GaAs.: S S Khludkov et al, Neorg Mater, 8 (6), June 1972, 1044–1048 ( in Russian)

The contribution of different types of point defects to diffusion in CoO and NiO during oxidation of the metals

Starting from a general model for the defect structure of nickel and cobalt oxides, the concentrations and diffusion coefficients of the major defects in these oxides are determined as functions of temperature and oxygen pressure. At the higher oxygen pressures, the majority of cation defects are mononegative metal ion vacancies while at lower oxygen pressures appreciable concentrations of dinegative metal ion vacancies are present. It is shown that it is highly probable that the onion defects are dipositive oxygen vacancies. However, these are minority defects over the whole stability range of the oxides. It is not possible with the methods discussed here to determine their individual concentrations and diffusion coefficients. On the basis of this defect structure, a model for the oxidation of Co and Ni is proposed; the deductions from this model are compared with experimental results and good agreement is observed. It is shown that more than one type of defect contributes to the total transport through the oxide. For cobalt, these are mono- and dinegative metal ion vacancies; for nickel, dipositive oxygen vacancies also make a significant contribution.

Low temperature diffusion of cobalt and cadmium in silver

The diffusion of 109Cd and 60Co in monocrystalline silver was investigated over a temperature range from about 375 to 650°C using a chemical film sectioning technique. Penetration depths studied were limited to a region that has previously exhibited unusually steep penetration profiles for high temperature diffusion of 60Co in Ag. This anomalous behavior or “near-surface effect” is characterized by abnormally low diffusivities for penetration depths up to several microns from the surface. For both of the isotope tracers, a near-surface effect was observed at the higher temperatures of the range. However, the diffusivities measured at the lower temperatures were in agreement with extrapolations of hightemperature lattice diffusion data in the literature. An apparent transition in diffusion mechanism was noted from plots of the logarithm of the diffusivity vs. the reciprocal of the absolute temperature. The transitional behavior is described in terms of oxidation kinetics. A possible mechanism for the near surface effect, that has an activation energy and pre-exponential factor corresponding to that observed in the transition is discussed in detail.

Comments on “diffusion of cobalt in plutonium” by M.J. Dapth, M.P. Dariel and A. Rosen in Scripta Met., 5, 191–194 (1971)

Comments on “diffusion of cobalt in plutonium” by M.J. Dapth, M.P. Dariel and A. Rosen in Scripta Met., 5, 191–194 (1971)

Correlation effects and effects of cobalt additions on cobalt and nickel diffusion in NiO

The correlation factor for cobalt diffusion in NiO has been determined by the simultaneous diffusion of 55Co and 60Co in NiO over the temperature range 1179–1649°C. The results indicate that ƒ Co increases from 0·57 at 1179°C to 0·78 at 1649°C. The temperature dependence of the cobalt diffusivity in NiO in air is expressed by D Co = (9·12±0·58) × 10 −3 exp (−54,160±460/RT) cm 2/sec. Small additions of cobalt solute to NiO result in an equal enhancement of the cobalt and nickel diffusivities. The primary cause of the enhancement is the increased concentration of free vacancies with the cobalt additions. The nearest-neighbor interactions between solutes and vacancies are found to be negligible.

On the Deviations from Parabolic Oxidation of Co‐25 w/o Cr at High Temperature

Large deviations from parabolic behavior have been observed during the oxidation of Co‐25 w/o (weight per cent) Cr alloys. The rate‐controlling process of the oxidation at high oxygen pressures is solid‐state diffusion of cobalt through channels in the inner layer; thus a model decribing the deviation from parabolic behavior in terms of time dependency of the mean cross section of these channels is suggested.

Diffusion of Chromium, Manganese, Cobalt, and Nickel in Molten Iron Saturated with Carbon

Diffusion of Chromium, Manganese, Cobalt, and Nickel in Molten Iron Saturated with Carbon

Diffusion of Cobalt in Beta-Uranium

The solute diffusion of cobalt in beta-uranium was measured using the thin-layer sectioning technique. The results can be expressed by D= 1.54×10−2 exp(−27 450/RT) cm2/sec. The diffusivities of cobalt are higher by about three orders of magnitude than the self-diffusion coefficients in beta-uranium. The possibility of cobalt diffusing by means of the combined substitutional-interstitial mechanism has been examined.

A study of the wear processes on cemented carbide cutting tool by a radioactive tracer technique

A method based on the use of neutron activated cutting tool, for studying the wear processes on cemented carbide cutting tool during machining has been developed. Cutting was performed on a steel billet with a carbon content of 0·6 per cent, at machining speeds of 120, 200, 250 and 340 m/min. The radioactive cobalt ( 60Co) and tantalum ( 182Ta) transferred to the chips were registered on a multi-channel gamma spectrometer. The distribution of the radioactive cobalt, tantalum and tungsten on the chips was studied by means of autoradiographic technique. Results indicate that a distinct cobalt diffusion is observed at lower speeds during the running-in period of the cutting tool. Further, the results suggest that the dominating process in TiC-, TaC-containing hard metals, in addition to cobalt diffusion and possible decomposition of the free tungsten carbide phase, also involves a decomposition of the complex carbide phase, i.e. carbide particles. This probably occurs in the iron deposit transferred to the surface of the tool area in contact with the work piece during machining. This product is then transferred to the chips.

Diffusion of Cobalt, Silver, and Gold in Praseodymium

The thin-layer lathe-sectioning technique has been used to measure the solute diffusivities of cobalt, silver, and gold in dhcp and bcc praseodymium. The diffusivities in the bcc phase can be described DAg=3.2×10−2 exp(−21 500/RT) and DAu=3.3×10−2 exp(−20 100/RT) cm2/sec. In polycrystalline samples the average of the diffusivities along the two axes of dhcp praseodymium can be expressed by DCo=4.7×10−2 exp(−16 400/RT), DAg=1.4×10−1 exp(−25 400/RT), and DAu=4.3×10−2 exp(−19 700/RT) cm2/sec. These diffusivities are substantially higher than the self-diffusion coefficients of praseodymium. The change in the crystalline structure of the matrix affects only slightly the solute diffusivities, contrary to its effect on the self-diffusion coefficients. The remarkable similarity of these results with those concerning the solute diffusion of noble metals in Group III-B and IV-B metals, suggests that the same diffusion mechanism by interstitials operates in both cases.