Characterization of Li1−x Ni1+x O2 prepared by the thermal-assisted precipitation process

Li_1−x Ni_1+x O₂ was prepared by the thermal-assisted precipitation process of LiOH · H₂O and Ni(CH₃COO)₂ · 4H₂O at a pH of 6–13 followed by the high temperature calcination for a variety of prolonged times. Phases, morphologies and constituents were characterized using an x-ray diffractometer (XRD), a scanning electron microscope (SEM), an energy dispersive x-ray (EDX) analyzer an atomic absorption spectrophotometer (AAS) and titration. Maximum [I₍₀₀₃₎/I₍₁₀₄₎] and minimum [I_(006+102)/I₍₁₀₁₎] intensity ratios were used to determine the preparation conditions. In addition, possible formation reactions of the precursors and calcined products were proposed. The article was submitted by the authors in English.     

Superparamagnetic and ferromagnetic behavior of ZnFe2O4 nanoparticles synthesized by microwave-assisted hydrothermal method

Zinc ferrite (ZnFe₂O₄) nanoparticles were successfully synthesized from Zn(NO₃)₂ · 6H₂O and Fe(NO₃)₃ · 9H₂O by microwave hydrothermal method at 150°C for 1 h. Cubic ZnFe₂O₄ with particle size below 7 nm was formed in the solution at pH ≥ 6. The crystallinity and particle size of ZnFe₂O₄ nanoparticles were increased after calcination. The effects of pH of the precursor solution and calcination on the particle size and crystallinity of the particles were studied. At room temperature the products show superparamagnetic and ferromagnetic properties, determined by their size. The formation mechanism of ZnFe₂O₄ was also discussed according to the experimental results.

     

Hydrothermal synthesis of hexagonal WO3 nanowires with high aspect ratio and their electrochemical properties for lithium-ion batteries

One dimensional WO₃ nanowires with high aspect ratio of >200 were synthesized by hydrothermal method. The effects of reaction temperature and time on phase and morphologies were studied and discussed. In this research, a suitable hydrothermal condition is at 200°C for 48 h. XRD, SEM, and TEM results show that the product is hexagonal WO₃ phase with diameter of 25 nm and several ten micrometers long with growth in the c direction. The electrochemical properties were tested for rechargeable lithium batteries. The WO₃ NWs electrode exhibits a stability trend over the 30 cycle testing. Some long-term activation process is attributed to the WO₃ NWs electrode during charge/discharge reaction.

     

A tube-by-tube reduction method for simultaneous heat and mass transfer characteristics for plain fin-and-tube heat exchangers in dehumidifying conditions

This study proposed a new method, namely a tube-by-tube reduction method to analyze the performance of fin-and-tube heat exchangers having plain fin configuration under dehumidifying conditions. The mass transfer coefficients which seldom reported in the open literature, are also presented. For fully wet conditions, it is found that the reduced results for both sensible heat transfer performance and the mass transfer performance by the present method are insensitive to change of inlet humidity. Unlike those tested in fully dry condition, the sensible heat transfer performance under dehumidification is comparatively independent of fin pitch. The ratio of the heat transfer characteristic to mass transfer characteristic (h_c,o/h_d,o C_p,a) is in the range of 0.6~1.0, and the ratio is insensitive to change of fin spacing at low Reynolds number. However, a slight drop of the ratio of (h_c,o/h_d,o C_p,a) is seen with the decrease of fin spacing when the Reynolds number is sufficient high. This is associated with the more pronounced influence due to condensate removal by the vapor shear. Correlations are proposed to describe the heat and mass performance for the present plate fin configurations. These correlations can describe 89% of the Chilton Colburn j-factor of the heat transfer (j_h) within 15% and can correlate 81% of the Chilton Colburn j-factor of the mass transfer (j_m) within 20%.     

Effect of fin pattern on the air-side performance of herringbone wavy fin-and-tube heat exchangers

In the present study, new experimental data on the air-side performance of fin-and-tube heat exchangers having herringbone wavy fin configuration are presented. Different from most previous studies, the present experiments have been performed to determine the effects of fin patterns and edge corrugations on the air-side performance of the heat exchangers. The experimental apparatus consists essentially of a well-insulated open wind tunnel and herringbone wavy fin-and-tube heat exchangers made from aluminium wavy finned, copper tube. Two types of wavy fin patterns commonly in industrial use are investigated. Air and hot water are used as working fluids in air-side and tube-side, respectively. From the experimental results, it is found that the fin pattern has a significant effect on the heat transfer and flow characteristics. The corrugation at the fin edge enables the Colburn factor to decrease but it has almost no effect on the friction factor.     

Low-Pressure Chromatographic Separation of p-Hydroxybenzoates Using Sequential Injection with Lab-on-Valve System and Miniature Monolithic Column

The use of a small guard column (5-mm length) as a miniature analytical column in low-pressure liquid chromatography based on a sequential injection with lab-on-valve system was demonstrated. A strong initial mobile phase was used to rapidly deliver the sample zone to the column prior to simultaneous separation of analytes with weaker mobile phase. Separation of methyl-, ethyl-, propyl-, and butyl-4-hydroxybenzoates (MP, EP, PP, and BP) was achieved within about 120 s with sufficient peak resolution (all higher than 1.3) using 2,500 µL of mobile phase (composed of 1,087 µL of MeOH) per run. Detection limits were found to be 6.5, 8.0, 0.5, and 0.6 μmol L^?1 for MP, EP, PP, and BP, respectively. The system was tested with common commercially available skin lotions and wet wipe products. The analysis results were in good agreement with those obtained from the high-performance liquid chromatography with a 10-cm-length packed column.     

Optimization of the finned double-pipe heat exchanger using nanofluids as working fluids

Journal of Thermal Analysis and Calorimetry - The heat exchanger pipe diameter has a significant effect on the flow characteristics as well as on the initial investment, operation and overall cost....     

Numerical evaluation on thermal–hydraulic characteristics of dilute heat-dissipating nanofluids flow in microchannels

The present work deals with numerical investigations on heat transfer characteristics and friction factor of aqueous CuO nanofluids flow in a set of four microchannels connected in parallel under laminar regime. For each single phase, volume of fluid, mixture and Eulerian models, a particular computer code is developed to carefully simulate this problem. The three-dimensional steady-state governing equations are solved through finite volume method. The primary aim of this study is to comparatively distinguish the most appropriate and accurate model for numerical studies of nanofluids in microchannels. The results are compared with one another and the data obtained from an experimental work. Regarding the results, an acceptable consistency is observed for all models with the experimental data. The current study truly demonstrates that applying single-phase model to simulate and evaluate the laminar flow of CuO–water nanofluid inside microchannels with uniform wall temperature is more modest, precise and reliable compared with two-phase models.

     

Degradation of rhodamine B photocatalyzed by Eu-doped CdS nanowires illuminated by visible radiation

CdS nanowires doped with different contents of Eu dopant were synthesized by solvothermal method. XRD, SEM, TEM and Raman analyses certified that the as-synthesized samples were hexagonal CdS uniform nanowires. The pure CdS nanowires were 1–3 ?μm long and 80 ?nm diameter with the 1st and 2nd order longitudinal phonon modes at 298 and 594 ?cm^?1. The 3% Eu-doped CdS wires were 800 ?nm–2.5 ?μm long and 75 ?nm diameter with the 1st and 2nd order longitudinal phonon modes at 296 and 593 ?cm^?1. CdS nanowires grew along the [001] direction due to the surface energy effect. The photocatalytic properties of CdS and Eu-doped CdS nanowires were investigated for the degradation of rhodamine B (RhB) illuminated by visible radiation. In this research, Eu dopant played the role in promoting the photocatalytic kinetics because Eu³⁺ ions act as an electron acceptor to promote charge separation and photocatalytic activity. Both ^●OH and ^●O₂^? were the main active radicals used to transform RhB molecules into CO₂, H₂O and other intermediates.     

Combined magnetic and single-crystal X-ray structural study of the linear chain antiferromagnet [(CH3)4N][MnCl3] under varying pressure

The magnetic susceptibility and single-crystal X-ray structure of the one-dimensional Heisenberg antiferromagnetic chain tetramethylammonium manganese trichloride (TMMC) have been studied under pressure as a facile route to develop structure-property relationships. The X-ray structure of TMMC was determined at 0, 2.1, 3.8, 6.8, 12.2, and 17.0 kbar using diamond-anvil cell techniques and synchrotron radiation. The space group is confirmed to be P6(3)/m up to 17 kbar, and structural refinement shows that the Mn-Mn separations between and along the chains change by about 3.4 and 2.5%, respectively, over 17 kbar. A structural transition from hexagonal to monoclinic symmetry possibly occurs at 17 kbar, associated with a loss of crystal quality. Variable-temperature magnetic susceptibility data were taken at 0, 0.3, 1.5, 2.9, 4.0, 5.2, and 6.5 kbar and show that the intrachain coupling constant changes from -6.85 to -7.81 K over this range. The interchain coupling constant of -0.54 K can also be extracted from the Fisher model modified for interacting chains. The pressure-temperature diagram shows the slope of the intrachain antiferromagnetic coupling with pressure, DeltaT(IAF)/DeltaP, changes from 0.5 to 1.6 K/kbar at 2 kbar where the structure changes from P2(1)/a to P2(1)/m. Comparison of the magnetic and structural data are consistent with the power-law relationship developed by Bloch where J proportional, variant r-n, r = Mn...Mn separation and n approximately 10.