Densification and sintering dynamics of 10NiO-NiFe2O4 composites doped with CaO

The effects of CaO content in the range from 0 to 4.0%, and sintering temperature on the phase composition, relative density and electrical conductivity of 10NiO-NiFe2O4 composites doped with CaO were studied. The results show that there is no change of structure for NiO or NiFe2O4; there is apparent oxygen absorbing and releasing behavior during the heating process in air for 10NiO-NiFe2O4 composites. Introduction of CaO can accelerate the densification of 10NiO-NiFe2O4 composites. The maximum value of relative density is 98.75% for composite doped with 2.0% CaO and sintered at 1 200 ℃, which is beyond about 20% for the undoped composites. The sintering activated energy of sample containing 2% CaO decreases by 15.87 kJ/mol, compared with that of the undoped sample.     

Effect of electrolysis superheat degree on anticorrosion performance of 5 Cu/（10NiO-NiFe2O4） cermet inert anode

5Cu/(10NiO-NiFe2O4) cermet inert anodes were prepared by cold-pressing and sintering process, and the effect of superheat degree of melting K3AlF6-Na3AlF6-AlF3 on their anticorrosion performance was studied under electrolysis conditions. The results show that, the fluctuation of cell becomes small with increasing of superheat degree, which is helpful to inhibit the formation of cathodic encrustation; the concentration of impurities from inert anode in bath goes up to certain degree, but it is far smaller than those in traditional high-temperature bath. Increasing the superheat degree of melting K3AlF6-Na3AlF6-AlF3 has unconspicuous effect on the contents of impurities in cathodic aluminum. The total mass fractions of Fe, Ni and Cu in aluminum are 15.38% and 15.09% respectively under superheat degree of 95 and 195 ℃. From micro-topography of anode used view, increasing the superheat degree can aggravate corrosion of metal Cu in inert anode, and has negative influence on electrical conductivity of electrode to some extent.     

Thermoelectric Properties of Ca_3Co_4O_9 Ceramics

Ca3Co4O9 ceramics were prepared using the sol-gel process with ordinary pressing sintering and their thermoelectric properties were measured from room temperature to 673 K. The experimental results show that single phase Ca3Co4O9 can be fabricated at 750-900 ℃ in different citrate acid molar proportions for 0.2-1.0. For all the oxides, both the Seebeck coefficients S and the electrical conductivitiesκincrease with the increasing temperature. The Seebeck coefficients S are all positive. The thermal conductivities κ increase with the increasing temperature also and the lattice thermal conductivityκl plays an important role to the thermal conductivity κ. The citrate acid molar proportions have a large influence on the particle sizes, which influences the thermoelectric properties of the ceramics. The figure of merit increases with the increasing temperature and reaches 4.5×10-5 K-1 at 573 K for the sample in the citrate acid molar proportion of 0.46.     

Enhanced Thermoelectric and Mechanical Properties of n-type Bi_2Te_(2.7)Se_(0.3) Bulk Alloys by Electroless Plating with Cu

Bi_2Te_(2.7)Se_(0.3)/Cu core/shell powders were prepared by electroless plating and hydrogen reduction, and then sintered into bulk by spark plasma sintering in order to improve the thermoelectric and mechanical properties of n-type Bi-Te thermoelectric material. After electroless plating, with the increasing of Cu content, Seebeck coefficient keeps increasing and power factor enhances significantly. The highest power factor increases by three times and reaches 23.8 W·cm-1·K-2 at room temperature in Bi_2Te_(2.7)Se_(0.3) with 0.22 wt%Cu sample, which means electrical transport properties of Bi_2Te_(2.7)Se_(0.3)/Cu samples have been improved.Meanwhile, the ZT values of Bi_2Te_(2.7)Se_(0.3)/Cu samples can be enhanced at different temperature zone by adjusting the Cu content. Bi_2Te_(2.7)Se_(0.3) with 0.05 wt% Cu sample has the best thermoelectric properties in high temperature zone, and the ZT peak value increases from 0.35 to 0.85 at 623 K. When the Cu content increases to 0.15 wt%,the ZT peak value moves to the low temperature(373 K) and increases from 0.24 to 0.71. At the same time, the mechanical properties increases with the increasing of Cu content.     

Effect of the silicon powder content on the properties of Al_2O_3-SiC-Me composites

By means of transient plastic phase process, the Al2O3-SiC-Me composites were produced throungh adding metal aluminium and silicon-powder to Al2O3-SiC materials. Under the condition of the same content of silicon and aluminium mixed-powder, the effect of silicon powder addition on properties of Al2O3-SiC-Me composites was studied by means of XRD and EPMA analyses in the temperature range of 300℃―1600℃. The results indicated that the content of metal phase in the sample at 1600℃ increases with increasing silicon powder content. At the same time, when the temperature is lower than 1100℃, the strength of samples gradually increases with increasing temperature. However when the temperature is higher than 1100℃, the strength of samples gradually decreases with increasing temperature, and this change is very small. The results also indicated that at the same sintering temperature, the sample with 6% silicon powder has the maximum strength.     

Effects of Electroless Plating with Cu Content on Thermoelectric and Mechanical Properties of p-type Bi_(0.5)Sb_(1.5)Te_3 Bulk Alloys

Bi_(0.5)Sb_(1.5)Te_3/Cu core/shell powders were prepared by electroless plating and hydrogen reduction, and then sintered into bulk by spark plasma sintering. After electroless plating, with increasing the Cu content, the electrical conductivity keeps enhancing significantly. The highest electrical conductivity reaches 3341 S/cm at room temperature in Bi_(0.5)Sb_(1.5)Te_3 with 0.67 wt% Cu bulk sample. Moreover, the lowest lattice thermal conductivity reaches 0.32 W/m·K at 572.2 K in Bi_(0.5)Sb_(1.5)Te_3 with 0.67 wt% Cu bulk sample, which is caused by the scattering of the rich-copper particles with different dimensions and massive grain boundaries. According to the results, the ZT values of all Bi_(0.5)Sb_(1.5)Te_3/Cu bulk samples have improved in a high temperature range. In Bi_(0.5)Sb_(1.5)Te_3 with 0.15 wt% Cu bulk sample, the highest ZT value at 573.4 K is 0.81. When the Cu content increases to 0.67 wt%, the highest ZT value reaches 0.85 at 622.2 K. Meanwhile, the microhardness increases with increasing the Cu content.     

Thermotics Study of the Semimetallic Nylon1010 Composite

Thermal expansion characteristics of semimetal nylon composites （nylon 1010 incorporated with metal oxides） were analyzed with thermal expansion instrument. The changes of composite weight after being heated and the heat absorption and release of the composites were analyzed by carrying out TG-DSC experiments. Experimental results show that the average thermal expansion coefficient of the composites rises as the average diameter of the metal oxides decrease from room temperature to 160 ℃. Thermal dynamics and physical properties of the nylon composites change with the addition of the oxides; the crystallization temperature rises from 180 ℃ of pure nylon to 190 ℃ （maximum） and the melting point of the oxide composites also increases continuously with the addition of the oxides. The water content of the oxide/nylon composite is related to the kind and content of the oxide. The water content reaches its maximum when the content of oxide is 10%, and the 10% Al2O3/nylon composite has a water absorption ratio up to 1%.     

Thermoelectric Properties and Electronic Structure of Ca3Co2O6

The nanosized Ca3Co2O6 powder was synthesized via sol-gel process.The phase composition was characterized by means of X-ray diffraction.Polycfrystalline swnples of Ca3Co2O6 were prepared by a sintering procedure of nanosized power.The seebeck cofficient and electrical conductivity of the samples were measured from 450K up to 750 K.The results show that the Seebeck coefficient increases with the increasing temperature.The electronic structures were calculated using the self-cwtsistent full-potential linearized augmentedc plane-wave (LAPW) method within the density functional theory.The relationship between thermoelectric property and electronic structures was discussed.     

Thermoelectric transport properties of BiCuSeO with embedded La0.8Sr0.2CoO3 nanoinclusions

The efficiency-upgrading role that La0.8Sr_(0.2)CoO_3(LSCO) plays in the thermoelectric properties of Bi Cu Se O(BCSO) has been studied. LSCO was introduced into BCSO, increasing the electrical conductivity from 3.3 to 52.3 S cm-1 at 303 K, from 35.8 to 97.3 S cm~(-1) at 873 K; respectively. The Seebeck coefficient of all composites still holds around or more than 200 μV/K. Based on the enhanced electrical conductivity and high Seebeck coefficient, the power factor is enhanced by approximately 35%, with the best sample reaching a maximum value of 476.7 μ Wm~(-1) K~(-2) at 873 K. The lattice thermal conductivity of the nanocomposites is reduced as LSCO content increases from 15 vol% to 30 vol% due to the phonon scattering by nanoparticles and grain boundaries, resulting in a significant reduction in total thermal conductivity. In short, the enhanced thermoelectric figure of merit of 0.67 at 873 K for the sample containing 20 vol% LSCO as compared to 0.53 for the pure sample; announces the promising effect of LSCO on improving thermoelectric properties of Bi Cu Se O.     

Microstructures and Mechanical,Electrical,High-temperature Properties of Cu/Ti_2AlC FGM Fabricated by Hot-pressing

The microstructure and the electrical, thermal, friction, and mechanical properties of Cu/Ti_2AlC fabricated by hot-pressing at 900 ℃ for 1 h were investigated in the present work. Microstructural observations have shown that the plate-like Ti_2AlC grains distribute irregularly in the network of Cu grains, and well-structured, crack-free bonds between the layers. With the increase in the content of Ti_2AlC from layer A to layer D, the electrical resistivity increases from 1.381×10~(-7)Ω·m to 1.918 ×10~(-7)Ω·m, the hardness increases from about 980.27 MPa to about 2196.01 MPa, and the friction coefficient from above 0.20 reduces to about 0.15. Oxidation rate increases with the increases of temperature. Exfoliation was obviously observed on the surface of oxidation layer A. The surface of layer D was still intact and the spalling and other defects were not found. The mass decreases in the acid solution, and increases in the alkaline solution. The largest corrosion rate is found in 6.5% HNO_3 or 4% Na OH solution.     

Preparation and properties of 4.25Cu-0.75Ni／NiFe2O4 cermet

4.25Cu-0.75Ni/NiFe₂O₄ cermets were prepared by doping NiFe₂O₄ ceramic matrix with the mixed powders of Cu and Ni or Cu-Ni alloy powder as the electrical conducting metallic elements. The effects of technological parameters, such as the adding modes of metallic elements, the ball milling time, the sintering time and the sintering temperature, on the relative density and resistivity of the cermets were studied. The results show that the resistivity of 4.25Cu-0.75Ni/NiFe₂O₄ cermets decreases with increasing temperature, and has a turning point at 590 °C, which is similar to that of NiFe₂O₄ ceramic. The sintering temperature and adding modes of metallic elements have a great influence on the properties of 4.25Cu-0.75Ni/NiFe₂O₄ cermets. When the sintering temperature increases from 1200 °C to 1300 °C, the relative density increases from 89.86% to 95.33%, and the resistivity at 960 °C decreases from 0.11 Ω · cm to 0.03 Ω · cm, respectively. When the metallic elements are added with the mixed powders of Cu and Ni, the cermets of finely and uniformly dispersed metallic phase, high density and electric conductivity are obtained. The relative density and resistivity at 960 °C are 90.23% and 0.04 Ω · cm respectively for the cermet samples sintered at 1200 °C for 2 h, which are both better than those of the cermets prepared under the same technique conditions but with the metallic elements added as 85Cu-15Ni alloy powders. Foundation item: Project (G1999064903) supported by the National Key Fundamental Research and Development Program of China; project(2001AA335013) supported by the National High Technology Research and Development Program of China; project (50204014) supported by the National Natural Science Foundation of China     

Effect of BaO addition on relative density and electric conductivity of xNi/10NiO-NiFe2O4 cermets

xNi/10NiO-NiFe₂O₄ (x=5, 10, 17) cermets and those doped with 1% BaO (mass fraction) were prepared by cold isostatic pressing at 200 MPa and sintering in nitrogen atmosphere at 1 473 K. The effects of BaO addition on relative density, microstructure and electric conductivity of cermets were investigated. The results show that relative densities of xNi/10NiO-NiFe₂O₄ cermets (x=5, 10, 17) doped with 1% BaO at 1 473 K in nitrogen atmosphere are increased by 0.49%, 1.45% and 2.99% compared with those of the undoped BaO cermets, respectively. Moreover, the electric conductivities (21.98, 28.37 and 50.10 S/cm) of xNi/10NiO-NiFe₂O₄ cermets (x=5, 10, 17) doped with 1% BaO at 1 233 K are improved compared with those (18.70, 22.79 and 39.58 S/cm) of xNi/10NiO-NiFe₂O₄ cermets (x=5, 10, 17), respectively. This indicates that perhaps the addition of BaO or formation of BaFe₂O₄ and Ba₂Fe₂O₅ has an active effect on electric conductivities of xNi/10NiO-NiFe₂O₄ (x=5, 10, 17) cermets.     

Effect of metallic content on mechanical property of Ni/（10NiO-NiFe2O4 ） cermets

1 INTRODUCTIONThe use of inert or non-consumable anodes forreplacement of consumable carbon anodes in Hall-H啨roult electrolysis cells for the production of alu-minum has been a technical and commercial goalfor many decades .In the present process ,consumable carbon an-odes are used,andthe anode product is CO2. Withaninert anode ,the cell reaction will be :Al2O3=2Al +23O2(1)The basic requirements for aninert anode are :1) to exhibit a lowcorrosion rate in the high tem-perature melts an…     

Effect of CaO doping on corrosion resistance of Cu/（NiFe2O4-10NiO） cermet inert anode for aluminum electrolysis

The CaO-doped Cu/（NiFe2O4-10NiO） cermet inert anodes were prepared by the cold isostatie pressing-sintering process, and their corrosion resistance to Na3AlF6-K3AlF6-Al203 melt was studied. The results show that the relative density of 5Cu/（NiFe2O4-10NiO） cermet sintered at 1 200 ℃ increases from 82.83% to 97.63% when 2% CaO （mass fraction） is added. During the electrolysis, the relative density of cermet inert anode descends owing to the chemical dissolution of additive CaO at ceramic grain boundary, which accelerates the penetration of electrolyte. Thus, the corrosion resistance to melts of Cu/（NiFe2O4-10NiO） cermet inert anode is reduced. To improve the corrosion resistance of the cermet inert anode, the content of CaO doped should be decreased and the technology of cleaning the ceramic grain boundary should be applied.     

Effect of metallic phase species on the corrosion resistance of 17M/（10NiO-NiFe2O4） cermet inert anode of aluminum electrolysis

1 INTRODUCTIONThere are many disadvantages in the presentaluminumelectrolysis with carbon anode ,such assevere energy consumption,carbon wasting,envi-ronmental pollution and so on.Inert electrode sys-tem can overcome these disadvantages[1 3]. Re-cently ,the researches of the inert anode materialshave mainly been concentrated on alloys[4]and cer-met materials[5 ,6]. NiFe2O4based cermets , whichpossess not only high electrical conductivity ofmetal but also good corrosion resistance of cera…     

Electrical conductivity of （Na3AlF6-40%K3AlF6）-AlF3-Al2O3 melts

The effects of contents of AlF3 and Al2O3, and temperature on electrical conductivity of （Na3AlF6-40%K3AlF6）- AlF3-Al2O3 were studied by continuously varying cell censtant （CVCC） technique. The results show that the conductivities of melts increase with the increase of temperature, but by different extents. Every increasing 10 ℃ results in an increase of 1.85 × 10^-2, 1.86× 10^-2, 1.89 × 10^-2 and 2.20 × 10^-2 S/cm in conductivity for the （Na3AlF6-40%K3AlF6）-AlF3 melts containing 0%, 20%, 24%, and 30% AlF3, respectively. An increase of every 10 ℃ in temperature results an increase about 1.89× 10^-2, 1.94 × 10^-2, 1.95 × 10^-2, 1.99× 10^-2 and 2.10× 10^-2 S/cm for （Na3AlF6-40%K3AlF6）-AlF3-Al2O3 melts containing 0%, 1%, 2%, 3% and 4% Al2O3, respectively. The activation energy of conductance was calculated based on Arrhenius equation. Every increasing 1% of AlF3 results in a decrease of 0.019 and 0.020 S/cm in conductivity for （Na3AlF6-40%K3AlF6）-AlF3 melts at 900 and 1 000 ℃, respectively. Every increase of 1% Al2O3 results in a decrease of 0.07 S/cm in conductivity for （Na3AlF6-40%K3AlF6）-AlF3-Al2O3 melts. The activation energy of conductance increases with the increase in content of AlF3 and Al2O3.     

Thermoelectric properties of Ca3Co4O9 ceramics

Ca₃Co₄O₉ ceramics were prepared using the sol-gel process with ordinary pressing sintering and their thermoelectric properties were measured from room temperature to 673 K. The experimental results show that single phase Ca₃Co₄O₉ can be fabricated at 750–900 °C in different citrate acid molar proportions for 0.2–1.0. For all the oxides, both the Seebeck coefficients S and the electrical conductivities κ increase with the increasing temperature. The Seebeck coefficients S are all positive. The thermal conductivities k increase with the increasing temperature also and the lattice thermal conductivity κ _l plays an important role to the thermal conductivity κ. The citrate acid molar proportions have a large influence on the particle sizes, which influences the thermoelectric properties of the ceramics. The figure of merit increases with the increasing temperature and reaches 4.5×10⁻⁵ K⁻¹ at 573 K for the sample in the citrate acid molar proportion of 0.46.     

Effects of Electroless Plating with Cu Content on Thermoelectric and Mechanical Properties of p-type Bi<Subscript>0.5</Subscript>Sb<Subscript>1.5</Subscript>Te<Subscript>3</Subscript> Bulk Alloys

Bi_0.5Sb_1.5Te₃/Cu core/shell powders were prepared by electroless plating and hydrogen reduction, and then sintered into bulk by spark plasma sintering. After electroless plating, with increasing the Cu content, the electrical conductivity keeps enhancing significantly. The highest electrical conductivity reaches 3341S/cm at room temperature in Bi_0.5Sb_1.5Te₃ with 0.67wt% Cu bulk sample. Moreover, the lowest lattice thermal conductivity reaches 0.32 W/m·K at 572.2 K in Bi_0.5Sb_1.5Te₃ with 0.67wt% Cu bulk sample, which is caused by the scattering of the rich-copper particles with different dimensions and massive grain boundaries. According to the results, the ZT values of all Bi_0.5Sb_1.5Te₃/Cu bulk samples have improved in a high temperature range. In Bi_0.5Sb_1.5Te₃ with 0.15wt% Cu bulk sample, the highest ZT value at 573.4 K is 0.81. When the Cu content increases to 0.67wt%, the highest ZT value reaches 0.85 at 622.2 K. Meanwhile, the microhardness increases with increasing the Cu content.