CoO Content Research Articles

Thermodynamics of oxygen solutions in iron-nickel, iron-cobalt and iron-manganese melts

The oxygen solubility in Fe-Ni, Fe-Co, and Fe-Ni melts has been calculated. The calculation of oxide phase composition over Fe-Ni, Fe-Co and Fe-Mn melts was carried out at 1873 K. The FeO oxide is mainly contained in the oxide phase of the Fe-Ni system; the NiO content rapidly increases only when the Ni mole fraction is close to unit. In case of the Fe-Co system, the FeO also is contained mainly in the oxide phase and the CoO content rapidly increases as the Co mole fraction increases above 0.8. The MnO oxide is contained mainly in oxide phase of the Fe-Mn system; in this case, when the Mn mole fraction is more than 0.02, the MnO mole fraction in oxide phase is more than 0.9.

Genesis of peculiarly zoned Co, Zn and Mn-rich chromian spinel in serpentinite of Bou-Azzer ophiolite, Anti-Atlas, Morocco

The peculiar Co, Zn and Mn-rich chromian spinels are hosted by magnetite veins, serpentinites and chromitites of the mantle section of the Proterozoic Bou-Azzer ophiolite, Morocco. The spinel is complexly zoned either optically or chemically, and exhibits anomalously high MnO, ZnO and CoO contents (up to 22, 7.5 and 2 wt%, respectively). It has four distinct optical zones particularly in the magnetite veins and less typically in serpentinites. The highest level of these elements, probably divalent, is recorded within the ferritchromite zone and/or within the core zone if the ferritchromite zone is absent. These elements as well as Fe exhibit enrichment along grain boundaries and fractures of the altered spinels. Fe, Mn, Zn and Co were most probably supplied from olivine upon severe serpentinization during and after obduction of the ophiolite. The enrichment of the Bou-Azzer chromian spinel in Mn, Zn and Co was governed mainly by the fluid/mineral (spinel) ratio and partition coefficient between spinel and the relevant fluid among many factors. The Co-, Zn- and Mn-rich chromian spinels can be used as an exploration guide for Co-Ni-Zn-Cu sulfide mineralization associated with serpentinized peridotites.

Influence of CoO on stability of nonlinear electrical properties and dielectric characteristics in Pr 6O 11-based ZnO varistor ceramics

The nonlinear electrical properties, dielectric characteristics, and stability of the varistor ceramics of Zn–Pr–Co–Cr–Dy oxide system were investigated at various CoO contents. The sintered density of varistor ceramics increased from 5.25 to 5.55 g cm −3 with increasing CoO contents. The varistor voltage decreased from 235.3 to 86.0 V mm −1 with increasing CoO contents. As the CoO content increased, the nonlinear exponent increased up to 1.0 mol.% CoO, whereas further incorporation decreased the nonlinear exponent. Varistor ceramics containing 1.0 mol.% CoO exhibited the highest nonlinearity, in which the nonlinear exponent was 66.6 and the leakage current was 1.2 μA. Furthermore, varistor ceramics containing 1.0 mol.% CoO exhibited the highest stability, where the variation rate of varistor voltage, nonlinear exponent, and leakage current were −1.9%, −10.9%, and +275%, respectively, under DC accelerated aging stress of 0.95 V 1 mA /150 °C/24 h.

Effect of CoO on nonlinear electrical properties of praseodymia-based ZnO varistors

The microstructure, nonlinear properties, and dielectric characteristics of the varistors, which are composed of ZnO–Pr 6O 11–CoO–Cr 2O 3–Dy 2O 3-based ceramics, were investigated at various CoO contents. The increase of CoO content improved the densification of ceramics as increasing density in the range of 5.25–5.55 g/cm 3. The CoO served as a prompter of grain growth as increasing average grain size from 9.9 to 27.2 μm. The varistor voltage decreased from 235.3 to 86.0 V/mm with increasing CoO content. The highest nonlinearity was obtained from the varistors with 1.0 mol% CoO, with 66.6 in nonlinear exponent and 1.2 μA in leakage current. The further CoO addition decreased the nonlinearity.

Effect of field cooling on magnetic properties of ultrafine CoO/Co particles

In CoO-Ag granular films with small CoO contents, we have observed ultrafine Co particles inside or on the surface of the CoO particles. After field cooling under the external magnetic field of 50 kOe, a sustained magnetization (or vertical) shift and exchange field shift were observed. The magnetization shift and the exchange field shift increased as the cooling field is increased and temperature decreased, in correlation to each other.

Influence of cobalt oxide addition on electrical properties of ZnO-Pr6O11-based varistor ceramics

Influence of cobalt oxide addition on electrical properties of ZnO-Pr6O11-based varistor ceramics

Nickel or cobalt doped zinc oxide varistors

AbstractZinc oxide containing either Ni or Co dopants in various proportions has been investigated. Only zincite phase was found by XRD analysis. Incorporation of Ni or Co into the ZnO structure resulted in a marked shift in the XRD peaks. Remarkable microstructural uniformity was obtained by the addition of 1 mol-% of either Ni or Co oxides. Densification was achieved through atomic diffusion along grain boundaries. All samples showed non-linear I–V dependence. Ni concentration had a non-monotonic effect on breakdown voltage and the non-linear coefficient decreased with increasing Ni content. In contrast, breakdown voltage and non-linear coefficient increased with increasing CoO content.

The effect of CoO addition on electrical properties and DC accelerated aging behaviors of Zn–Pr–Co–Cr–Dy oxides-based varistors

The microstructure, electrical properties, and DC accelerated aging characteristics of varistors, which are composed of ZnO–Pr 6O 11–CoO–Cr 2O 3–Dy 2O 3 ceramics, were investigated at various CoO contents. The varistor ceramics was more densified as increasing density in the range of 5.25–5.55 g cm −3 with increasing CoO contents. The varistor with CoO of 1.0 mol% exhibited the highest nonlinearity, with 66.6 in nonlinear exponent and 1.2 μA in leakage current, and also the highest stability in the light of nonlinear properties and dielectric characteristics. Furthermore, the varistor with CoO of 1.0 mol% exhibited superior DC accelerated aging characteristics to other varistors in nonlinear properties and dielectric characteristics. Finally, it is assumed that the CoO is moderate contents in the range of 1.0–2.0 for this composition.

All Alkoxide Sol–Gel Route to CoO-TiO2Nano-Powders

CoO-TiO2 anatase materials have become highly interesting after the discovery of ferromagnetism above room-temperature, which makes them promising candidates for spintronic devices. There is however still uncertainty, and even contradictory ideas on the origin of the ferromagnetism and detailed microstructures ofthese materials. Here the synthesis and studies of CoO-doped TiO2 nano-phase powders with 0-12 mol% CoO using Co-methoxy-ethoxide and Ti(OPri)4 as precursors is presented. The amorphous precipitates or gels obtained by: (1) air hydrolysis and (2) quench hydrolysis with excess of water were amorphous and completely homogeneous in their Co:Ti ratio. Infrared (IR) spectroscopic and thermo-gravimetric (TG) studies showed that the air-hydrolysed samples Containrd a small amount of methoxy-ethoxide groups, besides coordinated water, while the quench-hydrolysed samples contained large amounts of coordinated water and lacked organic groups. According to the X-ray diffraction (XRD) patterns, the air-hydrolysed samples heated to 600°C contained both anatase and rutile. The rutile formationis ascribed to influence from the residual organic groups. The quench-hydrolysed precipitates yielded phase pure anatase at 480 and 600°C for the 0-6.7 mol% CoO range. At CoO contents of 8-12 mol%, the XRD i studies showed that anatase was obtained at 600°C, but in the 12% case, CoTiO3 was also detected. In addition, the 8-12 mol% samples showed two peaks in the Raman spectrum that might be due to CoO dissolved in anatase at high concentration. The studies were performed with TGA, IR and Raman-spectroscopy, XRD, scanning and transmission electron-microscopes (SEM and TEM, respectively) equipped with energy-dispersive X-ray spectrometers (EDS).

P-type semiconducting Cu2O–CoO thin films prepared by magnetron sputtering

The preparation by magnetron sputtering of p-type semiconducting thin films consisting of a multicomponent oxide composed of Cu oxide and Co oxide is described. The electrical, optical, and crystallographical properties of films deposited by rf magnetron sputtering using (Cu2O)1−x–(CoO)x powder targets were strongly dependent on not only the deposition condition but also the calcination condition as well as the CoO content of the targets. These properties drastically changed in films prepared with a CoO content around 90 mol %. All prepared films, i.e., CoO content in the range from 0 to 100 mol %, were found to be p type, or positive hole conductors, as evidenced from the Seebeck effect: Resistivities in the range from 103 to 10−3 Ω cm. A hole concentration on the order of 1016 cm−3 and a mobility on the order of 10−1 cm2/V s were obtained in an amorphous multicomponent oxide film prepared with a CoO content of 50 mol %. Fabricated thin-film pin heterojunction diodes consisting of a p-type high-resistance multicomponent oxide combined with undoped ZnO and n-type Al-doped ZnO exhibited a rectifying current–voltage characteristic.

Influence of praseodymium oxide/cobalt oxide ratio on microstructure and electrical properties of zinc oxide varistor ceramics

The microstructure and electrical properties of varistor ceramics, which are composed of (99.5– x– y)ZnO+ xPr 6O 11+ yCoO+0.5Dy 2O 3 system, were investigated with Pr 6O 11/CoO mole ratio ( x/ y=0.5/0.5, 0.5/1.0, 1.0/0.5, 1.0/1.0) and sintering temperature. The density of varistor ceramics with Pr 6O 11=1.0 was almost constant with sintering temperature, whereas it was increased noticeably in Pr 6O 11=0.5. Increasing Pr 6O 11 content enhanced the densification for any CoO content and the density was greatly affected not by CoO content but by Pr 6O 11 content. The varistor ceramics with Pr 6O 11/CoO=0.5/1.0 exhibited a higher nonlinearity than any other composition ratios. In particular, the varistor ceramics sintered at 1350 °C. exhibited the best electrical properties, with nonlinear exponent of 37.8, leakage current of 7.6 μA, and dissipation factor of 0.059. It was found that Pr 6O 11/CoO ratio greatly affects various characteristics of varistor ceramics.

ZPCD계 바리스터 세라믹스의 전기적 특성에 Pr6O11/CoO 비의 영향

The microstructure and electrical characteristics of ZPCD (ZnO-<TEX>$Pr_{6}O_{11}$</TEX>-CoO-<TEX>$Dy_2O_3$</TEX>) -based varistor ceramics were investigated with various <TEX>$Pr_{6}O_{11}$</TEX>/CoO ratios and sintering temperatures. The density of varistor ceramics with <TEX>$Pr_{6}O_{11}$</TEX>=1.0 was almost constant with sintering temperature, whereas it was increased noticeably in <TEX>$Pr_{6}O_{11}$</TEX>=0.5. Increasing <TEX>$Pr_{6}O_{11}$</TEX> content enhanced the densification for any CoO content and the density was greatly affected not by CoO content but by <TEX>$Pr_{6}O_{11}$</TEX> content. The varistor ceramics with <TEX>$Pr_{6}O_{11}$</TEX>/CoO=0.5/l.0 exhibited a higher nonlinearity than any other composition ratios. In particular, the varistor ceramics sintered at <TEX>$1350^{\circ}C$</TEX> exhibited the best electrical properties, with nonlinear exponent of 37.8, leakage current of 7.6 <TEX>${\mu}$</TEX>A, and tan <TEX>$\delta$</TEX> of 0.059.

Transparent conducting impurity-co-doped ZnO:Al thin films prepared by magnetron sputtering

This report describes the effects of impurity-co-doping on transparent conducting Al-doped ZnO (AZO) films prepared by DC magnetron sputtering using a target composed of dopant powder added to a mixture of ZnO and Al 2O 3 powder. The chemical stability of transparent conducting AZO films could be improved by co-doping Cr or Co without significantly altering the original electrical and optical properties. A reduction in etching rate, as well as a low resistivity of 3.0×10 −4 Ω cm, was obtained in transparent conducting AZO:Cr films prepared using Zn powder added into the oxide target with an Al 2O 3 content of 2 wt.% and a Cr 2O 3 content of 1 wt.%. In addition, a reduction in etching rate, as well as low resistivity, was obtained in transparent conducting AZO:Co films prepared with an Al 2O 3 content of 2 wt.% and a CoO content of 0.5–2 wt.% or a CoCl 2 content of 1.5–3 wt.%.

Photoacoustic Spectra of ZnO-CoO Alloy Semiconductors

Photoacoustic spectra (PA) of Zn1-xCoxO alloy semiconductors sintered as powdered samples were measured to estimate the optical absorption. Photoacoustic spectroscopy (PAS) is insensitive to the light scattering effects on the samples. CoO molecular percentages in the alloy were changed from 0 to 20 mol%. The samples were sintered at 600 or 950°C for 24 h in a quartz glass tube. From the PA spectra in the short wavelength region, we plotted (ρh ν)2 vs h ν and estimated the band-gap energy (Eg) of the alloy semiconductors, where ρ is the PA signal intensity and h ν is the excitation light photon energy. Eg of ZnO-CoO alloy decreases as the CoO content increase and reaches to 2.19 eV in the 20 mol% CoO sample. Although the band-gap variation in the lower-CoO-content samples (CoO content below 10 mol%) is large, it becomes small in the high CoO concentration samples. This result concurred with the result of dissolving CoO in ZnO as obtained by X-ray diffraction measurement.

Distribution Equilibria of Fe, Co and Ni between MgO-saturated FeOx-MgO-SiO2 Slag and Ni Alloy.

As a fundamental study related to the recycle of Ni-Fe-Co alloy, the distribution equilibrium of Fe, Co and Ni between MgO saturated FeO x -MgO-SiO 2 slag and nickel alloy was investigated at 1 773, 1 823 and 1 873 K with controlled oxygen partial pressure between 10 -4 to 10 2 Pa. The distribution ratios of Fe, Co and Ni at 1 773 K vary from 0.61 to 26, 0.040 to 4.2 and 0.0030 to 0.34 respectively with increasing oxygen partial pressure. The distribution ratios of Fe, Co and Ni between MgO saturated FeO x -MgO-SiO 2 slag and nickel alloy suggest that most of nickel and cobalt can remain in the alloy phase with lower oxygen partial pressure, and iron can be eliminated adequately from nickel alloys with higher oxygen partial pressure. However, the solubility of nickel and cobalt oxide in the slag also increases with increasing the oxygen partial pressure. Lower oxygen partial pressure and higher temperature are favorable for decreasing the loss of nickel and cobalt into slag. An oxygen partial pressure at which the separation coefficients show minimum was observed. The MgO solubility in the FeO x -MgO-SiO 2 slag decreases when the NiO content exceeds about 25 % at higher oxygen partial pressure. The activity coefficients of NiO and CoO in slags were calculated and found that their values increased with increasing of the NiO and CoO contents in slag respectively.

Densification and Mechanical Property of NiO-CoO and NiO-CoO-MgO System Ceramics.

The densification behavior and the mechanical properties of NiO-CoO and NiO-CoO MgO systems were investigated. Al2O3 of 2mass% was added in those systems as a sintering aid. Samples were prepared by hot isostatic press (HIP) treatment performed after a conventional ressureless sintering. The density of the NiO-CoO system did not depend on CoO content. On the other hand, the densification of NiO-CoO system was slightly prevented by the addition of MgO. Those samples have microstructure dispersed with (Ni, Co) Al2O4 or (Ni, Co, Mg) Al2O4 spinels in a NiO-CoO or NiO-CoO-MgO solid solution matrixes and the addition of CoO or MgO had no effect on the microstructure. In the NiO-CoO system, the bending strength increased, and the Vickers hardness increased with increasing the CoO content. Swelling around the Vickers mark, which is often observed in materials with plastic deformation ability, was observed. In the bending strength and the Vickers hardness of the NiO-CoO-MgO system increased with increasing the MgO content. These results suggested that the addition of CoO improved a brittle property of the NiO ceramic and the addition of MgO increased both the strength and the hardness of the NiO-CoO solid solution ceramic.

Partial molar volumes of NiO and CoO liquids: implications for the pressure dependence of metal-silicate partitioning

Volumetric measurements have been conducted on 7 Ni- and Co-containing sodium disilicate liquids within a compositional range varying from 0 to 9 mol% of NiO and from 0 to 23 mol% of CoO and over a large temperature interval (i.e., above their respective glass transition temperature and up to at least 1473 K). Their molar volumes and thermal expansivities have been determined by combining high-temperature measurements using the Pt-based double-bob Archimedean method and low-temperature measurements using the method described by Webb et al. [S.L. Webb, R. Knoche, D.B. Dingwell, Determination of silicate liquid thermal expansivity using dilatometry and calorimetry, Eur. J. Mineral. 4 (1992) 95-104] based on an assumed equivalence of the relaxation of volume and enthalpy at the glass transition. The molar volume of the present liquids decreases with increasing NiO and CoO contents and the Co-containing liquids exhibit a greater molar volume than the Ni-containing liquids at equivalent molar concentrations. The present results were analysed using a regression equation from which the partial molar volume of NiO and CoO liquids was obtained by the least squares method. This procedure yields partial molar volumes valid over the entire temperature range of 11.506 ± 0.687 and 14.884 ± 0.149 cm 3/mol and temperature derivatives of 2.684 ± 1.6 × 10 −3 and 1.441 ± 0.4 × 10 −3 cm 3/mol K, respectively for NiO and CoO at 800 K. The behavior of M-Fe metal-silicate exchange partition coefficient (M = Ni, Co), based on present molar volume determinations, has been estimated as a function of pressure over a wide temperature range. The metal-silicate exchange partition coefficients of both Ni and Co decrease with increasing pressure within the entire temperature range considered in this study (i.e., 800–3000 K).

New green pigments; ZnO–CoO

A zinc oxide pigment with an admixture of cobalt oxide has been prepared as a new green pigment for colouring plastics and paints. The effect of the CoO content in the starting mixture on the colour hue of the pigment has been evaluated and calcination conditions of the pigment synthesis have been established. The optimum conditions for the synthesis of pigments and the properties of the products (colour hue and structure) have been estimated.

DIELECTRIC BEHAVIOUR AND AC CONDUCTIVITY OF SODIUM BORATE GLASS CONTAINING CoO

Sodium borate glasses of composition (Na 2B 4O 7) 100− x (CoO) x , with x=0, 3, 5 and 7 mol%, were prepared by melting oxide mixtures in a platinum crucible at 1050°C in an electric furnace in air for 2 h, and then quenching in air. The IR spectra, AC conductivity and dielectric behaviour of the quenched glasses are the subject of the present work. Properties such as dielectric constant, loss factor tangent and electrical conductivity as a function of frequency and temperature are reported. The AC conductivity is proportional to ω s and increased as cobalt content was decreased. The value of the exponent ( s) decreased with decreasing CoO content. From the IR spectra, it was found that increasing CoO does not seem to introduce any new absorption band. Also, the activation energies for AC conductivity and the activation energies associated with the relaxation process for different glass samples are calculated.

傾斜機能材料 高周波用異方性傾斜Ｎｉ‐Ｚｎフェライト

Ni-Zn ferrites with graded magnetic anisotropy for high frequency of megahertz order were prepared by the addition of CoO. When the CoO content increased, resonance frequency was expanded. However, initial permeability was decreased and anisotropy field was increased. Therefore we tried to prepare Ni-Zn ferrite with high initial permeability and high resonance frequency by the addition of graded CoO content. Troidal core samples were made to layer Ni-Zn ferrite with different CoO content. As the result, the sample which had large CoO content with inner layer, steep gradation and little Ni-Zn ferrite with outer layer showed excellent high frequency characteristics. The Ni-Zn ferrite added CoO with graded CoO content 0, 5, 0 wt.% had initial permeability of 80 for 20-60 MHz.