Precipitation Of Cobalt Research Articles

Energetic and kinetic evaluations in a quasi-binary Cu–1 at.% Co 2Si alloy

By means of differential scanning calorimetry (DSC), the precipitation process from a supersaturated solid solution of Cu–0.65 at.% Co–0.33 at.% Si (Cu–1 at.% Co 2Si) was investigated. On the basis of enthalpimetric calculations, it was found that the decomposition begins with cobalt precipitation. The clustering of atoms of cobalt initiates the precipitation of silicon, and particles of the stoichiometric Co 2Si composition are finally formed. Kinetic parameters were obtained by a convolution method based on the Mehl–Johnson–Avrami formalism. Their values are all in agreement with the experimental observed behavior displayed by the DSC traces.

Role of carbon dioxide and ion transport in the formation of sub-embryonic fluid by the blastoderm of the Japanese quail

1. The explanted blastoderm of the Japanese quail was used to explore the role of ions and carbon dioxide in determining the rate of sub-embryonic fluid (SEF) production between 54 and 72 h of incubation. 2. Amiloride, an inhibitor of Na+/H+ exchange, at concentrations of 10-3 to 10-6 M substantially decreased the rate of SEF production when added to the albumen culture medium. N-ethylmaleimide, an inhibitor of V type H+ ATPase, also decreased this rate but only to a small extent at the highest dose applied, 10-3 M. Both inhibitors had no effect on SEF production when added to the SEF. 3. The inhibitors of cellular bicarbonate and chloride exchange, 4-acetamido-4-'isothiocyano-2, 2-'disulphonic acid (SITS) and 4,4'diisothiocyanostilbene-2,2-'disulphonic acid (DIDS), had no effect upon SEF production. 4. Ouabain, an inhibitor of Na+/K+ ATPase, decreased SEF production substantially at all concentrations added to the SEF (10-3 to 10-6 M). Three sulphonamide inhibitors of carbonic anhydrase, acetazolamide, ethoxzolamide and benzolamide, decreased SEF production when added to the SEF at concentrations of 10-3 to 10-6 M. Benzolamide was by far the most potent. Neither ouabain nor the sulphonamides altered SEF production when added to the albumen culture medium. 5. Using a cobalt precipitation method, carbonic anhydrase activity was localised to the endodermal cells of the area vasculosa. The carbonic anhydrase activity was primarily associated with the lateral plasma membranes, which together with the potent inhibitory effect of benzolamide, suggests the carbonic anhydrase of these cells is the membrane-associated form, CA IV. 6. The changes in SEF composition produced by inhibitors were consistent with the production of SEF by local osmotic gradients. 7. It is concluded that a Na+/K+ ATPase is located on the basolateral membranes of the endodermal cells of the area vasculosa, and that a sodium ion/hydrogen ion exchanger is located on their apical surfaces. Protons for this exchanger would be provided by the hydration of CO2 catalysed by the membrane-associated carbonic anhydrase. Furthermore, it is proposed that the prime function of the endodermal cells of the area vasculosa is the production of SEF.

Selective removal of cobalt species using nanofiltration membranes.

Selective removal of cobalt species from simulated nuclear liquid waste was investigated with different nanofiltration (NF) membranes at various solution pH levels, initial cobalt concentrations, and background ion concentrations. This study provides insight into the understanding of the relationships between rejections of a target compound (cobalt) and chemical equilibria of various species in the feed solution during NF. Particularly, the ratio of electrostatic rejection to steric rejection for different membranes used was quantitatively evaluated to find outthe relative significance in NF. Substantial cobalt rejection by NF was achieved along with partial separation of monovalent ionic species, although it depended on the level of liquid pH and the presence of background species. Greater cobalt rejection at increased pH was attributed to the precipitation of CoCO3(s) associated with natural carbonates originating from atmospheric CO2 gas rather than that of Co(OH)2(s). A loose NF membrane (e.g., NTR7410) gave as high a rejection as other tighter ones due to the stronger influence of electrostatic rejection, particularly at low pH where no cobalt precipitation was occurring. The decrease of cobalt rejection with the addition of boric acid was found to occur due to the formation of complexes between cobalt and boric acid, which was verified by the analyses of solution turbidity and near-infrared spectroscopy.

Energetic and kinetic evaluations conducted in a quasi-binary Cu-1 at% Co2Si alloy through DSC

By means of differential scanning calorimetry (DSC) the precipitation process from a supersaturated solid solution of Cu−0.65 at% Co−0.33 at% Si (Cu−1 at% Co2Si) was investigated. On the basis of enthalpimetric calculations it was found that the decomposition begins with cobalt precipitation. Clustering of atoms of cobalt initiates the precipitation of silicon, and particles of the stoichiometric Co2Si composition are finally formed. Kinetic parameters were obtained by a convolution method based on the Mehl–Johnson–Avramiformalism. Their values are all in agreement with the experimentally observed behavior displayed by DSC traces. Decay kinetics of cobalt and silicon matrix during simulated isothermal calculations using DSC data reveals good agreement with similar computed results reported in literature. Precipitate dissolution obeys quite well to a three-dimensional diffusion kinetic law previously developed.

Optimal conditions of ion-exchange synthesis of cobalt(II) hydroxide with AV-17-8 anion exchanger in the OH form

Ion-exchange synthesis of cobalt(II) hydroxide by treatment of aqueous solutions of cobalt salts with OH form of AV-17-8 anion exchanger was studied. The influence of time, anion of cobalt salt, number of precipitation stages, and anion exchanger swelling on the degree of cobalt(II) precipitation was examined.

In situ resistivity study of copper–cobalt films: precipitation, dissolution and phase transformation

In situ sheet resistance measurements were used to study copper films alloyed with various concentrations of cobalt during annealing at temperatures up to 1000°C. The films were initially characterized by a high resistivity, several times that of pure copper, because of the presence of cobalt dissolved in copper. A large decrease in resistance, that occurs when the temperature reaches 100–150°C, is likely to be the consequence of the precipitation of cobalt associated with grain growth in the copper film. In this process, the free energy change that accompanies precipitation is added to the usual driving force that causes grain growth, namely, the overall decrease in interface energy. An activation energy of approximately 1 eV was found by varying the ramp rates during in situ resistance analysis, indicating the dominance of grain boundary diffusion. Further increases in temperature led to other changes in resistance that can be attributed to precipitate dissolution, and the reaction of cobalt with a tantalum adhesion layer. The activation energy of approximately 2 eV determined for this latter reaction is characteristic of the lattice diffusion of cobalt in copper. A rather extensive discussion considers (a) the modalities of the resistance changes that may be observed during heating and cooling solid solution alloys; and (b) the use that can be made of these changes to determine such process characteristics as activation energies.

Behaviour of Co(II) in solutions obtained by dissolution of cobalto–cobaltic oxide in NH 3–SO 2–H 2O medium

In an earlier study [Hydrometallurgy 58 (2000) 193], detailed kinetic work on dissolution of Co 3O 4 in an ammoniacal system using SO 2 as the reductant was carried out. It was observed that under certain experimental conditions, Co(II) becomes unstable and precipitates as Co(NH 3) 4S 2O 6·2H 2O. With a view to study the precipitation behavior of Co in the Co 3O 4–NH 3–SO 2 system, the present systematic work was done. A 2 3 factorial design was used to study the effects of three leaching parameters, i.e., NH 3, SO 2 and temperature on the dissolution and the precipitation of Co(II). The conditions for maximum Co precipitation were then chosen to study the effect of various parameters such as time and temperature of storage and initial cobalt concentration on extent of precipitation. It was observed that an increase in storage time and initial cobalt concentration increased the precipitation of Co(II). With a decrease in storage temperature, an increase in Co(II) precipitation was observed. In order to minimize the Co precipitation, the effect of addition of ammonium sulphate was studied. The increase in ammonium sulphate concentration from nil to 280 g L −1 resulted in a decrease of cobalt precipitation from 58% to 5%.

Emulsification, drying and film formation of alkyd emulsions

A method was developed and optimised for the emulsification of a conventional short oil alkyd resin which was solid at room temperature. The method was based on the emulsion inversion point (EIP) method whereby hot water (90°C) was added to molten alkyd resin (90°C) containing the emulsifier. Under slow mixing and addition of water, a point was reached where the emulsion instantaneously phase inverted from a water in oil emulsion (W/O) to an oil in water emulsion (O/W). Using optimum conditions, emulsions with droplet of diameters less than 0.8 μm were obtained. The drying and film formation of long oil alkyd emulsions were investigated with emphasis on loss of dry upon storage. The main reason for loss of dry was adsorption of the cobalt (drier) on pigment surfaces as a precipitated hydroxide. Titanium dioxides with alumina surface treatment and organic pigments were most detrimental to drying. Acrylate- and phosphate-based dispersants also deactivated cobalt presumably due to complexation and precipitation of cobalt. Emulsions prepared with an emulsifiable cobalt drier containing 2,2′-bipyridyl (complexing agent for cobalt) showed the best resistance to loss of dry. Films formed from the emulsions showed that surfactant migrated to the film surface which when washed with water leaves holes or pits in film. The pits were arranged in a hexagonal pattern, characteristic of Bénard cells which form due to interfacial tension gradients generated in the film during evaporation of water.

Formation and Release of Cobalt(II) Sorption and Precipitation Products in Aging Kaolinite–Water Slurries

The uptake and release behavior of cobalt(II) was studied over thousands of hours in CO2-free aqueous suspensions of kaolinite under three pairs of total cobalt concentration (CoT) and near-neutral pH (7.5–7.8) conditions. Dissolved cobalt, aluminum, and silicon concentrations were monitored by ICPMS, and cobalt-containing products were identified by EXAFS spectroscopy. In each uptake experiment, cobalt sorbed to kaolinite as a mixture of surface-adsorbed monomers or polymers and hydrotalcite-like precipitates of the approximate composition CoxAl(OH)2x+2(An−)1/n, where 2≤x≤4 and An− is nitrate or silicate anion. Precipitate stoichiometry varied with experimental conditions, with the highest Co:Al ratio in the high CoT/high pH experiment. Cobalt surface adsorption occurred within seconds, whereas precipitation was slower and continued for the duration of the experiments. Consequently, the proportion of precipitate in the sorbed mixture increased with time in all experiments. The most rapid precipitation occurred in the high CoT/high pH experiment, where solutions were most supersaturated with respect to cobalt hydrotalcite. Precipitates incorporated some previously adsorbed cobalt, as well as cobalt from solution. Cobalt release from the solid phase was effected by lowering solution pH to 7.0. Release experiments initiated after shorter sorption times returned a larger fraction of cobalt to solution than those initiated after longer sorption times, for a fixed duration of release. In other words, sorption product stability increased with sorption time. Specifically, under the conditions of the release experiments, the hydrotalcite-like precipitates are more stable than smaller adsorbates, and precipitates that formed over longer time periods are more stable than those that formed rapidly. The latter result suggests that precipitates ripened or modified their structure or composition to become more stable over the course of the several-thousand-hour sorption experiments. Precipitates that formed over hundreds of hours or longer did not dissolve over thousands of hours at the lower pH.

Cobalt precipitation by reduction with sodium borohydride

The reduction of cobalt(II) with borohydride is very complicated, as evidenced by the fact that various authors have obtained different reaction stoichiometries and have proposed a number of mechanisms. To clarify the cobalt reduction process, the reaction stoichiometry and reduction efficiency were studied using a controlled rate of addition of sodium borohydride in the temperature range 5–35°C and at pH values from 2 to 7.8. The efficiency of cobalt reduction increased with increasing concentration of NaOH in the reducing solution, the best reduction efficiency without the precipitation of cobalt hydroxide being 1 mole of sodium borohydride to reduce 1 mole of cobalt(II). The reduction efficiency increased with increasing pH, from nil at pH 2 to 96% at pH 6, and decreased with increasing temperature. X-ray diffraction patterns and TEM patterns of the recovered precipitates showed them to be amorphous. After a 2 h heat treatment at 500°C, the X-ray diffraction pattern of the precipitate showed well defined peaks due to Co 2B, with the main peak attributable to cobalt. The single crystal TEM pattern obtained was consistent with that of Co 2B. The particle size was about 20–100 nm. The atom ratio of Co to B increased with increasing temperature. Zinc ions have a dramatic inhibitory effect on cobalt reduction. Several tens of micromoles per litre of zinc ions completely inhibit cobalt reduction with borohydride. The main cause of inhibition is that zinc ions compete with those of cobalt for borohydride ions and zinc borohydride forms and hydrolyzes rapidly.

亜鉛浸出液の浄液に関する研究 亜ヒ酸，銅イオン，亜鉛末によるコバルト浄液法の反応機構

Cobalt precipitation by zinc dust with co-addition of arsenious oxide and copper ion in a practical operation was simulated by the experiments using a galvanic cell with a diaphragm and this mechanism for removal of cobalt was explained as follows; a galvanic cell was formed between zinc dust and copper particles, which were precipitated first by zinc dust, and cobalt is deposited on copper particles by this galvanic cell and arsenious oxide in a solution accelerated the rate of precipitation of cobalt by co-deposition of As-Co. The anode side reaction of this galvanic cell is Zn=Zn2++2e-and a main cathode reaction is 2H++2e-=H2 (g). Cobalt is difficult to be precipitated on copper without arsenious oxide. The galvanic current between zinc and copper becomes higher by addition of arsenious oxide. The over potential of the cathode reaction sifts the cathode potential to belower potential than the deposition potential of Co-As, and this Co-Aseasily deposits on copper cathode with hydrogen.

Organic Additive-Mediated Synthesis of Novel Cobalt(II) Hydroxides

Electrochemical precipitation of cobalt(II) hydroxide from nitrate solutions containing organic molecules, such as glucose, fructose, lactose, glycerol, and citric acid, yields a new modification of cobalt(II) hydroxide (a = 3.09 ± 0.03 Å, c = 23.34 ± 0.36 Å) that is isostructural with α-nickel hydroxide; precipitation in the absence of organic additives gives the stable, brucite-like, βCo(OH)2.

Cobalt(II) removal from water by chemical reduction with sodium borohydride

The stoichiometry and kinetics of Co 2+ reduction with NaBH 4 in aqueous solution have been studied. A substantial excess of borohydride is needed to achieve complete Co 2+ removal from water, mainly due to borohydride consumption in the BH 4 −/H 2O reaction unless the pH is sufficiently alkaline. In this case, cobalt precipitation occurs mainly as Co(OH) 2. Absence of dissolved oxygen in the reactor is required to avoid rapid reoxidation of reduced cobalt. The elemental analysis of the reduced species is consistent with Co 2B. The ease of sludge reoxidation and the final boron concentration in the effluent resulting from the needed excess of borohydride are serious disadvantages of this technique for Co 2+ removal. A kinetic model has been proposed to describe the behaviour of the system. The model reproduces reasonably well the experimental results, although some discrepancies were observed in the early stages of the process. These can be mainly attributed to mass-transfer limitations.

Carbonic anhydrase in the membrane of the endoplasmic reticulum of male rat liver.

We have prepared subcellular fractions of male rat liver homogenate by the method of Lewis and Tata [Lewis, J. A. & Tata, J. R. (1973) J. Cell Sci. 23, 447-459], further purifying the membranes of the microsomal fraction by exposure to 0.01% Triton X-100 and centrifugation. We determined the purity of the fractions with marker enzymes and measured carbonic anhydrase (CA; EC 4.2.1.1) activity in intact and solubilized particulates with 18O exchange between CO2/HCO3- and water. We measured the concentration of CA by titration with a sulfonamide inhibitor, ethoxzolamide, obtaining an average value of 3.8 mumol/mg of microsomal membrane protein. The equilibrium constant for binding ethoxzolamide was 0.49 x 10(-9) M. The Km for CO2 was 1.7 mM and the turnover number was 560,000 sec-1, characterizing this as a membrane-bound, high-activity isozyme of type IV. By electron microscopy of tissue sections after staining with a cobalt precipitation technique, CA was seen in small cytoplasmic vesicles in hepatocytes and in microsomal particles and membranes. There was a sulfonamide-resistant (isozyme type III) and a sulfonamide-sensitive (isozyme type II) CA in the cytosol but none in the rapidly sedimenting endoplasmic reticulum. We conclude that there is no CA normally within the matrix of the cell endoplasmic reticulum but that the CA type III found in the microsome may have been captured from the cytosol during resealing. Thus the adult male rat hepatocyte contains CA type IV in the membrane of the endoplasmic reticulum and CA type II and CA type III in the cytoplasm.

Visualization of O-2A progenitor cells in developing and adult rat optic nerve by quisqualate-stimulated cobalt uptake

Some macroglial cells of the O-2A lineage express glutamate receptor channels of the quisqualate/kainate type and take up extracellular cobalt when activated by glutamate agonists. These cells can be identified both in vitro and in situ following precipitation and intensification of the intracellular cobalt. We have used this technique to characterize these cells in the developing and adult rat optic nerve. In purified cultures of optic nerve cells, O-2A progenitor cells and type 2 astrocytes took up cobalt in the presence of quisqualate, while oligodendrocytes, type 1 astrocytes, and microglial cells did not. When whole optic nerves of various postnatal ages were exposed to quisqualate and cobalt, a subpopulation of glial cells took up cobalt. Cobalt uptake in vitro and in situ was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione. The number, morphology, and spatial distribution of cobalt-filled cells in situ varied with age. In perinatal nerves, 9% of glial cells took up cobalt. These cells had a simple unipolar or bipolar morphology and were two to three times more concentrated at the chiasm end than at the eye end of the nerve. During subsequent development, this gradient disappeared and the cobalt-filled cells became progressively more complex in morphology and increased in number and density, reaching a peak toward the end of the second postnatal week. The number subsequently declined to about 16,000 (7%) in the adult nerve. The processes of some cobalt-filled cells appeared to contact nodes of Ranvier. All cobalt-filled cells in 2 1/2-week-old optic nerves had a similar ultrastructural appearance and did not resemble either mature oligodendrocytes or astrocytes. Our results suggest that the cells stimulated by quisqualate to take up cobalt in the optic nerve are the in vivo counterpart of O-2A progenitor cells. We found no evidence that any of these cells are type 2 astrocytes.

Histochemical localization of carbonic anhydrase in the testis and epididymis of the rabbit.

The distribution of carbonic anhydrase (CA) was studied in the testis and epididymis of mature, male rabbits using a cobalt precipitation method. CA was found only in the endothelium of the capillaries in the testis. The epididymal duct was divided into initial, middle and terminal segments. Strong cytoplasmic CA was present in the apical cells in the initial and middle segments. Vacuoles with CA staining in the membranes were found in the principal cells in the middle segment. Intensely stained basal cells were present in the terminal segment. In the last part of the terminal segment and the first of the ductus deferens the basolateral cell membranes were also stained. The function of the enzyme is discussed especially in relation to acidification of the epididymal fluid and facilitation of CO2 diffusion.

REVERSIBLE EXTRACTION OF IONIC SPECIES USING ELECTROCHEMICALLY ASSISTED ION EXCHANGE Part 1: Cobalt(II) using alpha-Zirconium Hydrogen Phosphate.

Abstract In electrochemically assisted ion exchange (EIX), a water splitting reaction is used to promote the ion-exchange properties of materials which are incorporated into electrodes. Thus cobalt(II) may be extracted using alpha-zirconium hydrogen phosphate (ZrP) in a matrix of an unreactive polymer in which a platinised titanium electrode is embedded. Although ZrP is an inefficient ion-exchanger under normal (non-assisted ) conditions, EIX promotes the cation exchange behaviour by generation of hydroxyl ions (0H-) at the cathode. There was no observable precipitation of cobalt(II) hydroxide and no plating-out of the cobalt. The process of exchange proceeds entirely by an ion exchange mechanism. There is some base hydrolysis of the ZrP in the vicinity of the cathode, particularly in the first few cycles. Elution may be achieved by reversal of the applied electrical potential in conjunction with a solution pH of less than 2.3. For comparable electrodes, the rate of exchange, using EIX, is significantly g...

TEM and HREM Investigation of The Precipitation of Cobalt and Nickel In Polycrystalline Silicon

ABSTRACTThe precipitation behavior of cobalt and nickel at grain boundaries in multicrystalline silicon is investigated. The metals are diffused into the specimens from a surface source between 800 -1000 °C and the precipitation after cooling is studied by conventional and high resolution TEM. Cobalt and nickel disilicide precipitates nucleate both in the bulk and at grain boundaries. They form few large (micrometer size) plate-like or three-dimensional precipitates depending on the cooling rate. Cobalt disilicide with a slightly larger lattice mismatch has a higher tendency to nucleate at large angle grain boundaries. Both suicides nucleate preferentially at coherent twin boundaries forming a few atomic layers thick platelet parallel to the {111} twin plane. HREM and image simulations are performed to analyze the Si / MS12 / twin interface structure (M = Co, Ni).

Histochemical Localization of Carbonic Anhydrase in the Female Genitalia of Pigs during the Oestrous Cycle

The ovaries and internal genital tracts of cycling gilts were studied for localization of carbonic anhydrase activity using a post-embedding cobalt precipitation technique. Carbonic anhydrase activity was present in selective capillary endothelia and epithelial cells of the genitalia. The ovarian parenchyma, irrespective of the stage of the oestrous cycle considered, was unstained. The secretory cells of the deep furrows in the uterotubal junction and those in the isthmic region of the oviduct of the oestrous female showed a clear membrane-bound localization. The surface epithelium in the tubal ampulla showed a conspicuous cytoplasmic carbonic anhydrase activity during oestrus and the early luteal phase. Neither the intensity nor the localization of the histo-enzymatic reaction in the females varied with their hormonal status (i.e. stage of the oestrous cycle). The localization of the enzyme in particular regions of the female pig genitalia that normally act as sperm reservoirs (uterotubal junction--tubal isthmus) or where fertilization--early embryo development occur (i.e. ampulla) might be related to the control of the acid-base status of luminal fluid.

Histochemical Localization of Carbonic Anhydrase in the Testis and Epididymis of the Boar

The testis and epididymis of sexually mature, fertile boars were studied for localization of carbonic anhydrase (CA) using a cobalt precipitation technique. In the testis, cytoplasmic CA was found in the Sertoli cells and in the capillaries surrounding the seminiferous tubules. The epididymal duct was divided into initial, middle and terminal segments, and regional differences in CA activity were observed. The cell membranes of the basal cells were stained in the initial and middle segments. Strong cytoplasmic CA staining was present only in the apical cells in the initial and middle segments. The basolateral cell membranes were stained in the principal cells of the terminal segment and the ductus deferens. As a rule the capillaries surrounding the epididymal duct were unstained. The enzyme, specifically localized in regions of the male genitalia acting as sperm reservoirs, might be related to the quiescence of the stored spermatozoa by influencing the acid-base status of the epididymal fluid.