Preparation and dispersion stability of aqueous metal oxide nanofluids for potential heat transfer applications: a review of experimental studies

Journal of Thermal Analysis and Calorimetry - Nanofluids have recently attracted attention of many researchers due to their growing potential applications in heat transfer devices. They possess...     

Spectrophotometric Determination of Trace Amounts of Vanadium Based on its Catalytic Effect on the Reaction of Diphenylamine and Hydrogen Peroxide

 In this work a kinetic spectrophotometric method for the determination of trace amounts of vanadium is presented. The method is based on the catalytic effect of the vanadium(V) on the reaction between diphenylamine (DPhA) and hydrogen peroxide in a concentrated solution of formic acid. The formation of the deep-blue oxidation product is followed by a filter spectrophotometer, equipped with an optical fiber assembly, on line with a PC provided with the suitable software. The measurements were taken at 583 nm, with an immersed type cell of 1 cm light path length. The optimization of the operating conditions regarding concentrations of the reagents, temperature and interferences are also investigated. The working curve is linear over the concentration range 0.40–4.0 μg/ml vanadium(V). The relative standard deviation for a standard solution of 0.6 μg/ml of vanadium is 0.5% (n = 5). The proposed method proved highly sensitive, selective and relatively rapid for the assay of vanadium, at low level of 0.40 μg/ml without any pre-concentration step. The method was applied to alloys and cosmetics samples. The results were compared to those received with a reference method. Good agreement was attained, with a mean error of 0.5%. Received February 25, 2000. Revision May 15, 2000.     

On the underestimated influence of synthetic conditions in solid ionic conductors

The development of high-performance inorganic solid electrolytes is central to achieving high-energy- density solid-state batteries. Whereas these solid-state materials are often prepared via classic solid-state syntheses, recent efforts in the community have shown that mechanochemical reactions, solution syntheses, microwave syntheses, and various post-synthetic heat treatment routines can drastically affect the structure and microstructure, and with it, the transport properties of the materials. On the one hand, these are important considerations for the upscaling of a materials processing route for industrial applications and industrial production. On the other hand, it shows that the influence of the different syntheses on the materials'' properties is neither well understood fundamentally nor broadly internalized well. Here we aim to review the recent efforts on understanding the influence of the synthetic procedure on the synthesis – (micro)structure – transport correlations in superionic conductors. Our aim is to provide the field of solid-state research a direction for future efforts to better understand current materials properties based on synthetic routes, rather than having an overly simplistic idea of any given composition having an intrinsic conductivity. We hope this review will shed light on the underestimated influence of synthesis on the transport properties of solid electrolytes toward the design of syntheses of future solid electrolytes and help guide industrial efforts of known materials.

Influence of synthesis and processing on the nature of ultimate product and the ionic transport properties of superionic conductors.     

Construction of a Triphenyltetrazolium Liquid Membrane Ion Selective Electrode and its Analytical Application to the Assay of Vitamin C

 The construction of a liquid triphenyltetrazolium cation (TT⁺) ion-selective electrode (ISE) based on [TT⁺]₃[P(W₃O₁₀)₄] salt dissolved in 2-nitrotoluene is described. The liquid membrane electrode exhibits a rapid and almost Nernstian response to triphenyltetrazolium cations in the concentration range from 2×10⁻⁴ to 1×10⁻² mol l⁻¹. The Nernstian slope is 56–58 mV decade⁻¹ which remains constant for at least two months. The response is virtually unaffected by pH changes in the range 3–12. Major interferents are periodate and malate. Deviation from linearity is also observed in the presence of bromide, iodide and thiocyanate, due to their precipitation with triphenyltetrazolium cations. Analytical applications such as direct potentiometry for the determination of TT⁺ in aqueous solutions and indirect potentiometry for the assay of ascorbic acid (vitamin C) in pharmaceutical preparations are described. Ascorbic acid in the range of 150–500 mg l⁻¹, under specified experimental conditions, can be determined with mean relative error of 1.9%. Received February 25, 2000. Revision April 4, 2000.     

Applications of fuzzy sets in curve fitting

This paper presents several methods for functional approximation with variable-knot variable-degree splines, with variable-knot first order splines, which are relatively easy to find, as the intermediate input. By means of a fuzzy characteristic function determining how “sharp” the angle at each knot is (the higher the polynomial degree, the “sharper” its first order spline approximation bends), we can decide whether we can group certain adjacent segments together to be approximated by a single higher order polynomial segment. Some simulation experiments have also been done.     

Monitoring of time variation and effect of some meteorological parameters in polynuclear aromatic hydrocarbons in Ioannina, Greece with the aid of HPLC-fluorescence analysis

This paper describes the monitoring of 16 polynuclear aromatic hydrocarbons (PAH) in the suspended particulate matter in the area of Ioannina. A total of 244 samples were collected from five locations throughout the city. These samples were analyzed in order to acquire a complete picture of the PAH abundance and distribution above the city of Ioannina. The sampling sites covered the center of the city as well as the suburban territory. The monitoring lasted for one year starting in November 1996. Higher values of PAH were found at the sites surrounding the city center, while at the rest of the area the concentration of PAH was substantially lower. The effect of ambient temperature and humidity on PAH abundance and distribution was also evaluated. As a result it was revealed that higher concentrations of PAH are favored by low temperatures and high values of humidity. Regarding the seasonal variation of PAH it was found that their concentrations are elevated during the winter months where heating systems are operating. On a daily basis it appears that the highest abundances of PAH occur on Wednesdays while the lowest on Sundays. The mean yearly concentration values of benzo[a]pyrene varied between 0.32+/-0.02 and 2.63+/-0.08 ng m(-3) for the various sites. Compared with the reported values the PAH levels in the area of Ioannina can be characterized as medium to low.     

Semiclassical path integral theory of a double‐well potential in an electric field

A recently published methodology based on semiclassical path integral (SCPI) theory was implemented in the case of a model of a double‐well potential perturbed by a static electric field, with application to the inversion frequency of NH₃. This model was chosen as an idealized case for testing of the present approach, as well as for quantum mechanical models that might be applied in the future. The calculations were concerned with the variation of the frequency of inversion as a function of field strength, F, and of distance, x_f (from the symmetric point x_o = 0), where the field is “felt.” It is found that this variation occurs sharply in very small regions of values of these parameters, and the system switches from internal oscillation to diffusion to the continuum. The fact that the theory is in analytic form allows the extraction of results and conclusions not only at the full SCPI level, but also at the Jeffreys–Wentzel–Kramers–Brillouin (JWKB) level. Comparison shows that the discrepancy sets in as the field strength increases, in accordance with the well‐known limitations of the JWKB method regarding its dependence on the degree of variation of the potential as a function of position. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Oxidation investigation of nickel nanoparticles

This work reported an experimental investigation of complete oxidation of nickel nanoparticles using simultaneous thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Nickel nanoparticles and their elemental compositions were characterized by Brunauer-Emmett-Teller (BET) analysis, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The oxidation experiments were performed under isoconversion conditions for seven heating rates, varying from 2 to 20 K min(-1), with temperatures up to 1000 degrees C. The experiments revealed unique oxidation behaviour of nickel at the nanometre scale, such as early oxidation and melting phenomena, variable activation energies and different oxidation kinetics between low and high conversion ratios. Unlike its bulk counterpart where the activation energy is a constant, the activation energy of nickel nanoparticles depended on the conversion ratio, ranging between 1.4 and 1.8 eV. The oxidation kinetics of nickel nanoparticles changed from the classical diffusion controlled mechanism to a pseudo-homogeneous reaction as conversion ratios were over 50%. The oxidation mechanisms of nickel nanoparticles were further discussed and future studies to enhance understanding were identified.