Ascorbic Acid-Assisted Eco-friendly Synthesis of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanoparticles as an Anode Material for High-Performance Lithium-Ion Batteries

We have synthesized NiCo₂O₄ nanoparticles (NCO NPs) using an ascorbic acid-assisted co-precipitation method for the first time. When NCO NPs are used as an anode material for lithium-ion batteries, the cell exhibits superior lithium storage properties, such as high capacity (700 mA h g^?1 after 300 cycles at 200 mA g^?1), excellent rate capabilities (applied current density range 100–1200 mA g^?1), and impressive cycling stability (at 1200 mA g^?1 up to 650 cycles). The enhanced electrochemical properties of NCO NPs are due to the nanometer dimensions which not only offers a smooth charge-transport pathway and short diffusion paths of the lithium ions but also adequate spaces for volume expansion during Li storage. Hence, this eco-friendly synthesis approach will provide a new strategy for the synthesis of various nanostructured metal oxide compounds, for energy conversion and storage systems applications.     

Facile Synthesis of Anatase TiO<Subscript>2</Subscript> Nanospheres as Anode Materials for Sodium-Ion Batteries

Anatase TiO₂ nanospheres (ATNSs) were successfully prepared through a facile solvothermal method followed by a thermal treatment. The sample was characterized by scanning electrons microscopy, transmission electron microscopy, x-ray diffraction, Raman spectrum and nitrogen adsorption techniques. When tested as an anode material for sodium-ion batteries, the electrode of ATNSs delivered a large discharge capacity of 208 mAh g^?1 after 100 cycles at a current density of 50 mA g^?1, indicating excellent cycling performance. This could be attributed to the uniform structure of the nanospheres with large surface area and porous nature, providing more active sites, buffering volume change, and facilitating the sodium ion intercalation as well as rapid diffusion during the charge/discharge process. Cyclic voltammetry demonstrated that the sodium storage mechanism is mainly controlled by pseudocapacitive behavior, resulting in a large capacity and outstanding cycling stability.     

Optical properties and the electronic structure of Co<Subscript>2</Subscript>TiGe and Co<Subscript>2</Subscript>TiSn Heusler alloys

The frequency dependences of the real part ε₁(ω) and imaginary part ε₂(ω) of the complex dielectric constant of the Heusler alloys Co₂TiGe and Co₂TiSn have been studied in the spectral range of 0.1–5 eV. It has been established that the interband electron transitions play a dominant role in the formation of the optical properties of these alloys. An anomalous behavior of the optical properties in the IR range of spectrum, namely, the absence of the Drude component of the optical conductivity σ(ω), has been revealed. The results of the studies have been discussed based on the calculations of the electronic structure of the alloys.     

Effects of nano-TiO<Subscript>2</Subscript> dispersion on thermoelectric properties of Co<Subscript>4</Subscript>Sb<Subscript>11.7</Subscript>Te<Subscript>0.3</Subscript> composites

Nano-TiO2/Co4Sb11.7Te0.3 composites were prepared by mechanical alloying (MA) and cold isostatic pressing (CIP) process.The phase composition,microstructure,and thermoelectric properties were characterized.The diffraction spectra of all samples well corresponds to CoSb3 skutterudite diffraction plane.TiO2 agglomerates into irregular clusters.They locate at the grain boundaries or some are distributed on the surface of Co4Sb11.7Te0.3 particles.For composites with high TiO2 content (0.6% and 1.0% TiO2),the phonon scattering by TiO2 particle,pores,and small size grains can result in a remarkable reduction in thermal conductivity.The maximum value of ZT is 0.79 for sample with 0.6 wt.% TiO2 at 700 K,which is 11% higher than that of non-dispersed sample.     

Thermoelectric properties of In<Subscript>z</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> skutterudites

In this study, indium-filled CoSb₃ skutterudite is synthesized via encapsulated induction melting and subsequent annealing at 823 K for six days, and the crystal structure, lattice constant, filler position, phase homogeneity and stability were investigated. All of the In-filled CoSb₃ samples were n-type conducting samples. The temperature dependence of the electrical resistivity showed In_zCo₄Sb₁₂ is a highly degenerate semiconducting material. The thermal conductivity was reduced considerably by In filling. The highest thermoelectric figure of merit value was achieved when the In filling fraction is 0.25. It was found that the ZT of the In-filled CoSb₃ (In_zCo₄Sb₁₂) was higher than that of the In-substituted CoSb₃ (Co_3.75In_0.25Sb₁₂ and Co₄Sb_11.75In_0.25). This is mainly due to the lower thermal conductivity and higher Seebeck coefficient.     

The microstructure of a magnetically hard Zr<Subscript>2</Subscript>Co<Subscript>11</Subscript> alloy

Electron-microscopic and electron-graphic analysis has demonstrated that the Zr₂Co₁₁ compound has a complex structure. All grains consist of thin plates of a high-temperature rhombohedral phase, which are parallel to the (0001) crystallographic plane; the crystal lattices in the neighboring regions have a twin orientation relative to each other. The transformation of the rhombohedral phase into a low-temperature orthorhombic phase is accompanied by an additional splitting of these plates into regions in which the [001]_orth axes are parallel to the [0001]_rhomb axes, and the [010]_orth axes are rotated through an angle of about 120°. These twin regions, alternating in the samples, favor the minimization of elastic stresses. In electron-diffraction patterns, there are also observed satellites, which testify the existence of structural incommensurate modulation in the [010] direction of the orthorhombic lattice with a period of modulation equal to 18–19 Å.     

Gas sensing properties of nano-crystalline SnO<Subscript>2</Subscript>-CuO compounds

We fabricated a micro gas sensor for hydrogen sulfide (H₂S) gas using MEMS technology and the sol-gel process, and synthesized SnO₂-CuO as a sensing material by the sol-gel method. Synthesized particles of SnO₂-CuO were characterized with an average particle size of about 40 nm as measured by FE-SEM imagery and XRD peaks. The sensing material was coated on the micro platform and annealed at 400 °C. The maximum gas sensitivity (R_s= R_g/R_a) was 0.005 at 300 °C for 1.0 ppm — H₂S. The gas sensitivity showed linear behavior with increasing H₂S concentration.     

Pressureless Sintering of TiB<Subscript>2</Subscript>-B<Subscript>4</Subscript>C Ceramic Matrix Composite

The effect of TiB₂ addition on sinterability and mechanical properties of B₄C material was investigated. It was found that addition of TiB₂ aids the sintering process and permits pressureless sintering at temperatures between 2050 and 2150 °C. This also alleviates grain growth during sintering. The relative density reaches 98.5% of the theoretical density by increasing the percentage of TiB₂ in the composition. The mechanical properties such as hardness, fracture toughness, and bending strength were improved remarkably by addition of TiB₂.     

Fabrication and Properties of Plasma-Sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> Composite Coatings

Al₂O₃ /xZrO₂ (where x = 0, 3, 13, and 20 wt.%) composite coatings were deposited onto mild steel substrates by atmospheric plasma spraying of mixed α-Al₂O₃ and nano-sized monoclinic-ZrO₂ powders. Microstructural investigation showed that the coatings comprised well-separated Al₂O₃ and ZrO₂ lamellae, pores, and partially molten particles. The coating comprised mainly of metastable γ-Al₂O₃ and tetragonal-ZrO₂ with trace of original α-Al₂O₃ and monoclinic-ZrO₂ phases. The effect of ZrO₂ addition on the properties of coatings were investigated in terms of microhardness, fracture toughness, and wear behavior. It was found that ZrO₂ improved the fracture toughness, reduced friction coefficient, and wear rate of the coatings.     

Surface modification of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> with Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> for lithium ion batteries

Cr 2 O 3-coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode materials were synthesized by a novel method. The structure and electrochemical properties of prepared cathode materials were measured using X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The measured results indicate that surface coating with 1.0 wt% Cr 2 O 3 does not affect the LiNi 1/3 Co 1/3 Mn 1/3 O 2 crystal structure (α-NaFeO 2 ) of the cathode material compared to the pristine material, the surfaces of LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples are covered with Cr 2 O 3 well, and the LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with Cr 2 O 3 has better electrochemical performance under a high cutoff voltage of 4.5 V. Moreover, at room temperature, the initial discharging capacity of LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with 1.0 wt.% Cr 2 O 3 at 0.5C reaches 169 mAh·g 1 and the capacity retention is 83.1% after 30 cycles, while that of the bare LiNi 1/3 Co 1/3 Mn 1/3 O 2 is only 160.8 mAh·g 1 and 72.5%. Finally, the coated samples are found to display the improved electrochemical performance, which is mainly attributed to the suppression of the charge-transfer resistance at the interface between the cathode and the electrolyte.     

Effects of calcining temperature on SnO<Subscript>2</Subscript> sensors for CO and NO<Subscript>x</Subscript> gases

Nitrogen oxides (NO_x) and carbon monoxide (CO) are among the most dangerous chemical species to human health present in the atmosphere. Acute CO toxicity leading to unconsciousness, respiratory failure or death can occur after 1 hr of exposure when ambient CO levels reach 1000 ppm, whilst increase of NO_x emissions can contribute to acid deposition, pollution of groundwater, eutrophication of surface waters, and tropospheric ozone and ecosystem damage. In this work, pure SnO₂ sensors for CO and NO_x were prepared by spin coating solutions derived from a washed Gel-precipitate followed by a calcining step. SnO₂ sensors of nanometer grain size prepared by this process showed good sensitivity to CO and NO_x gases. The increase of calcining temperature not only affected grain size and surface morphology, but also caused a decrease in sensitivity of the SnO₂ sensors.     

The Microstructure and Thermoelectric Properties of Yb-Filled Skutterudite Yb<Subscript>0.1</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> Under Cyclic Thermal Loading

This paper is devoted to investigating the microstructure and thermoelectric properties of Yb-filled skutterudite Yb_0.1Co₄Sb₁₂ under a cyclic thermal loading from room temperature to 773 K. The results indicate after 1000 cycles, the surface morphology changes dramatically, and clear grain boundaries appear on the surface of the sample. The grain sizes of the sample change little after 1000 cycles, and the main phase is still skutterudite; however, a trace amount of YbSb also exists. In addition, the electrical conductivity and thermal conductivity decrease distinctly after 1000 cycles, but the absolute value of the Seebeck coefficient increases a little. Consequently, the ZT value decreases slightly from 0.75 at 800 K before cycling to 0.69 after 1000 cycles. It indicates that the effect of the cyclic thermal loading on the ZT of the Yb_0.1Co₄Sb₁₂ material is not distinct.     

Structural,electrical, and optical properties of reactively sputtered SnO<Subscript>2</Subscript> thin films

SnO₂ thin films prepared by reactive rf magnetron sputtering have been investigated to examine the effect of deposition parameters on its crystallinity and electrical and optical properties. Of particular interest was whether the nonequilibrium nature of sputtering could create large departures from the bulk defect properties, especially in amorphous films. Two deposition parameters were examined: substrate temperature (T_sub) and oxygen content. The films were characterized by X-ray diffraction (XRD), optical transmission, four point probe electrical conductivity, and Hall effect measurements. The crystallinity was found to be enhanced by the incease in each of the three processing variables. Below a substrate temperature of 300 °C a large processing window for depositing amorphous SnO₂ was found.     

Casting-Based Production of Al-TiC-AlB<Subscript>2</Subscript> Composite Material Through the Use of KBF<Subscript>4</Subscript> Salt

High volume fraction TiC-AlB₂ reinforced Al composite material has been produced by a casting process based on the use of KBF₄ salt. The reaction between the salt compound led to the release of AlB₂ precipitates in commercial purity Al melt whereas the improved wettability between the TiC particles and the formed slag caused their spontaneous entry. The resulting double reinforced composite showed no sign of severe TiC dissolution-reaction.     

Electrochemical corrosion behaviors of amorphous Co<Subscript>69</Subscript>Fe<Subscript>4.5</Subscript>Ni<Subscript>1.5</Subscript>Si<Subscript>10</Subscript>B<Subscript>15</Subscript> alloy

The corrosion behavior of an amorphous Co₆₉Fe_4.5Ni_1.5Si₁₀B₁₅ alloy ribbon was examined as a function of solution temperature (15 °C to 55 °C) and pH (3 to 11). The results of potentiodynamic polarization tests in H2SO4 solution, NaCl solution, and HCl + NaOH solution at various levels of pH showed that the corrosion resistance for the alloy ribbon significantly deteriorated with increasing temperature and decreasing pH for given conditions. The Co₆₉Fe_4.5Ni_1.5Si₁₀B₁₅ alloy was actively dissolved in solutions at pH 3 to 9 but passivated in a solution at pH 11. By comparison of the corrosion behaviors of Co₆₉Fe_4.5(Nb,Cr,Ni)_1.5Si₁₀B₁₅ alloys in the solution at pH 11, Ni was considered to contribute less in improving the corrosion resistance of the alloy than did Cr and Nb.     

Experimental investigation and thermochemical assessment on the SnO<Subscript>2</Subscript>-CuO system

Differential thermal analysis/theromgravimetry (DTA/TG) measurements performed in air have established that above 1273 K the SnO₂-CuO initially stochiometric system transforms into a system of the SnO₂-CuO_x type, with the value of x depending on temperature T and p _{O 2} oxygen partial pressure values. The dissociation process of CuO to Cu₂O, as well as the formation of a liquid phase with an uptake of oxygen, has been experimentally verified. Above the minimum value of the oxygen partial pressure for which the only components of the system are SnO₂ and CuO (i. e., over p_{O 2} = 24 atm), the phase diagram was calculated by modeling the behavior of the liquid phase with a sub-regular approximation. A homogeneous liquid phase with no tendency toward immiscibility was found to be energetically favorable over the entire compositional range of the SnO₂-CuO system for T ≥ 1470 K. As a result of the calculations, the phase diagram is given for p_{O 2} = 24 atm; the diagram is a simple eutectic type with the eutectic composition placed in the CuO-rich domain (i.e., copper oxide molar fraction x = 0.873 and melting at 1470 K). The phase diagram calculated for the SnO₂-CuO system is compared with the data reported for other CuO-based systems.     

Microstructure Characterization of the FeAl<Subscript>2</Subscript>O<Subscript>4</Subscript>-Based Nanostructured Composite Coating Synthesized by Plasma Spraying Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al Powders

The microstructure of the coating prepared by reactive plasma spraying Fe₂O₃/Al composite powders was characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicated that the coating exhibited nanostructured microstructure which consisted of FeAl₂O₄, Fe or Fe solid solution, Al₂O₃ and a little FeAl. In the composite coating, spherical Fe particles (tens of nanometers to hundreds of nanometers) were distributed uniformly within the equiaxed and columnar nanograins FeAl₂O₄ matrix. There were two kinds of Al₂O₃ phases present in the composite coating. One kind was nano-sized Al₂O₃ particles uniformly dispersed within the matrix, forming eutectic structure of (FeAl₂O₄ + γ-Al₂O₃); the other was 1-1.5 μm Al₂O₃ particles embedded individually within the matrix. The composite coating had higher toughness than the conventional microstructured Al₂O₃ coating.     

SnO<Subscript>2</Subscript>-core/SiO<Subscript>x</Subscript>-shell coaxial whiskers with a needle-like morphology

Needle-shaped structures of tin oxide (SnO₂) were coated with a shell layer of SiO_x via a sputtering method. The diameters of the SiO_x-coated structures gradually became thinner, leading to the formation of sharp tips. The whiskers consisted of a crystalline SnO₂ core surrounded by an amorphous SiO_x shell. The photoluminescence (PL) spectrum with a Gaussian fitting exhibited yellow-green and orange light emission bands, and the overall shape and intensity of the PL spectrum were not changed by the SiO_xcoating. The results of this study suggest that sputtering can be employed to achieve the layered growth of shell layers on a variety of nanostructures.     

Synthesis of nano-sized Co<Subscript>3</Subscript>O<Subscript>4</Subscript> powder by spray conversion method for anode material of lithium battery

A nano-sized Co₃O₄ powder was prepared using a spray conversion method that could be applied for mass production. The spray-conversion process consisted of spray drying of a metallic liquid solution, a calcination treatment, and a ball milling process. The calcined Co₃O₄ powder consisted of agglomerated spherical clusters with nano-sized particles. After milling for 24 h, agglomerated powders were fragmented into fine powders sized below 60 nm. The lithium/cobalt oxide cell was charge-discharged at a constant current density of 0.2 mAcm⁻² and showed a first discharge capacity of 1100 mAhg⁻¹. The discharge capacity of the Li/Co₃O₄ cell drastically decreased with cycle number. By increasing the carbon content of the anode, the cycle life was improved. For a Co₃O₄ electrode containing 40 wt.% carbon, the discharge capacity was over 400 mAhg⁻¹ after 50 cycles. The spray conversion method might be a useful method to prepare nano-sized Co₃O₄ powder for the anode material of lithium batteries.