Concentrations Of Al2O3 Nanoparticles Research Articles

Suppression of activation energy and superconductivity by the addition of Al2O3 nanoparticles in CuTl-1223 matrix

Low anisotropic (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (CuTl-1223) high Tc superconducting matrix was synthesized by solid-state reaction and Al2O3 nanoparticles were prepared separately by co-precipitation method. Al2O3 nanoparticles were added with different concentrations during the final sintering cycle of CuTl-1223 superconducting matrix to get the required (Al2O3)y/CuTl-1223, y = 0.0, 0.5, 0.7, 1.0, and 1.5 wt. %, composites. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray, and dc-resistivity (ρ) measurements. The activation energy and superconductivity were suppressed with increasing concentration of Al2O3 nanoparticles in (CuTl-1223) matrix. The XRD analysis showed that the addition of Al2O3 nanoparticles did not affect the crystal structure of the parent CuTl-1223 superconducting phase. The suppression of activation energy and superconducting properties is most probably due to weak flux pinning in the samples. The possible reason of weak flux pinning is reduction of weak links and enhanced inter-grain coupling due to the presence of Al2O3 nanoparticles at the grain boundaries. The presence of Al2O3 nanoparticles at the grain boundaries possibly reduced the number of flux pinning centers, which were present in the form of weak links in the pure CuTl-1223 superconducting matrix. The increase in the values of inter-grain coupling (α) deduced from the fluctuation induced conductivity analysis with the increased concentration of Al2O3 nanoparticles is a theoretical evidence of improved inter-grain coupling.

Electroless Deposition of Ni-Cu-P Coatings Containing Nano-Al2O3Particles and Study of Its Corrosion Protective Behaviour in 0.5 M H2SO4

Ni-Cu-P/nano-Al2O3composite coatings are prepared on mild steel from an alkaline electroless plating bath containing different concentrations of Al2O3nanoparticles. The protective effect of codeposited nanoparticles on the corrosion behaviour of the coatings is studied in 0.5 M H2SO4solution. The electrochemical methods, that is, electrochemical noise (ECN), electrochemical impedance spectroscopy (EIS), and polarization measurements, are used to characterize the corrosion properties of the coatings. The results show that the inclusion of nanosized particles leads to significant improvement of corrosion resistance of the coatings. The highest corrosion resistance is obtained at 20 ppm of nanoparticles concentration in the plating bath. The ECN measurements results are in good agreement with results obtained from two other electrochemical methods after trend removal. The SEM images prove that nano-Al2O3particles were embedded in the Ni-Cu-P matrix and are dispersed uniformly on the coating surface.

CO2 absorption enhancement by Al2O3 nanoparticles in NaCl aqueous solution

In this study, Al2O3 nanoparticles and NaCl aqueous solution are combined into Al2O3/NaCl aqueous solution nanofluids to enhance the CO2 absorption of the base fluid (NaCl aqueous solution). The absorption experiments are carried out in the bubble type absorber system. The particle concentration ranges from 0.005 to 0.1 vol%. It is found that the optimum concentration of Al2O3 nanoparticles is 0.01 vol% in the NaCl aqueous solution-based nanofluids and then CO2 solubility is enhanced to 11.0%, 12.5% and 8.7% for Al2O3/NaCl aqueous solution at 30 °C, 20 °C and 10 °C, respectively. It is concluded that the effect of nanoparticles on the mass transfer enhancement is more significant in the region of unsaturated state than that of the saturated state.

Friction and Wear Characteristics of Water-Based ZnO and Al2O3 Nanofluids

In recent years, nanofluids have been an active area of research due to their enhanced thermal conductivity over base fluids. However, the tribological properties of nanofluids have not been thoroughly studied. In this research, friction and wear characteristics of water-based nanofluids was carried out. Commercially available water-based nanofluids with 50% ZnO and 50% Al2O3 nanoparticle concentration were used as the lubricant. The 50% concentration nanofluids were diluted using deionized water and an ultrasonic bath into different volume concentrations. The effects of nanoparticle type, particle concentration, and surface roughness of the specimen on the friction and wear characteristics were investigated. The friction and wear tests were performed using a UMT-2 Micro-Tribometer with a ball-on-disk configuration. The surface roughness and wear volume were measured using a WYKO 3D optical surface profiler, and chemical characterization analysis was done using a PHI 5000 VersaProbe X-ray photoelectron spectroscope (XPS). It was found that nanoparticles have a great effect on the friction and wear characteristics of lubricants.

Effect of Nano-Al<sub>2</sub>O<sub>3</sub> Particles on the NiP/nano-Al<sub>2</sub>O<sub>3</sub> Coatings’ Properties

Composite coatings were prepared using electroless nickel bath containing different concentrations of Al2O3nano-particles. The analyses of coating compositions, carried out by EDS, showed that there is marginal difference between phosphorus contents of NiP and NiP/nano-Al2O3deposits. The structure of the coatings was examined by scanning electron microscopy (SEM), and X-ray diffraction (XRD). It has been found that the co-deposition of nano-Al2O3particles with Ni disturbs the NiP coating’s regular surface structure and increases its surface roughness. DC and AC electrochemical tests were carried out on such coatings in a 3.5wt.% solution of NaCl in order to evaluate their corrosion resistance. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests both showed that, the corrosion resistance of NiP-Al2O3coatings firstly increases and then decreases when Al2O3concentration in electroless bath is increasing, but the corrosion resistance of NiP-Al2O3composite coating is better than that of amorphous NiP coating.

An experimental investigation of thermo-physical properties and heat transfer performance of Al2O3-Aviation Turbine Fuel nanofluids

Aviation Turbine Fuel (ATF)-Al2O3 nanofluids are investigated for better heat transfer performance in a potential application of regeneratively cooled semi-cryogenic rocket engine thrust chambers. The volume concentration of Al2O3 nanoparticles is varied between 0 and 1%. To ensure a realistic evaluation, all properties of the nanofluids are experimentally measured rather than resorting to available formulae or empirical correlations. Among the thermo-physical properties, thermal conductivity and specific heat are measured separately using experimental set-ups fabricated in-house whereas the viscosity is determined using a commercial viscometer. The heat transfer coefficient is determined using a horizontal double tube counter-flow heat exchanger under turbulent flow conditions. At 1% particle volume concentration, the enhancement in the thermal conductivity is 40%, whereas the viscosity increases by 38%. The measured specific heats of the nanofluids do not exhibit appreciable difference within the range of the particle volume concentrations investigated. The heat transfer coefficient increases by 30% at 1% particle volume concentration and correspondingly leads to an enhancement of 10% in the Nusselt number. For the same value of pressure drop, the heat transfer performances of nanofluids are compared with those of ATF. The experimental results show that the maximum enhancement in the heat transfer coefficient observed for the same pressure drop is 28% and even the least enhancement obtained is 2%.

Thermal Physics and Critical Heat Flux Characteristics of Al2O3–H2O Nanofluids

This study investigates the influence of the thermal physics of nanofluids on the critical heat flux (CHF) of nanofluids. Thermal physics tests of nanoparticle concentrations ranged from 0 to 1 g/L. Pool boiling experiments were performed using electrically heated NiCr metal wire under atmospheric pressure. The results show that there was no obvious change for viscosity and a maximum enhancement of about 5 to 7% for thermal conductivity and surface tension with the addition of nanoparticles into pure water. Consistently with other nanofluid studies, this study found that a significant enhancement in CHF could be achieved at modest nanoparticle concentrations (<0.1 g/L by Al2O3 nanoparticle concentration). Compared to the CHF of pure water, an enhancement of 113% over that of nanofluids was found. Scanning electron microscope photos showed there was a nanoparticle layer formed on the heating surface for nanofluid boiling. The bubble growth was photographed by a camera. The coating layer makes the nucleation of vapor bubbles easily formed. Thus, the addition of nanoparticles has active effects on the CHF.

Thermal conductivity and viscosity of Al2O3 nanofluid based on car engine coolant

Various suspensions containing Al2O3 nanoparticles (<50 nm) in a car engine coolant have been prepared using oleic acid as the surfactant and are tested to be stable for more than 80 days. Thermal conductivity and viscosity of the nanofluids have been investigated both as a function of concentration of Al2O3 nanoparticles as well as temperature between 10 and 80 °C. The prepared nanofluid, containing only 0.035 volume fraction of Al2O3 nanoparticles, displays a fairly higher thermal conductivity than the base fluid and a maximum enhancement (knf/kbf) of ∼10.41% is observed at room temperature. The thermal conductivity enhancement of the Al2O3 nanofluid based on engine coolant is proportional to the volume fraction of Al2O3. The volume fraction and temperature dependence of the thermal conductivity of the studied nanofluids present excellent correspondence with the model proposed by Prasher et al (2005 Phys. Rev. Lett. 94 025901), which takes into account the role of translational Brownian motion, interparticle potential and convection in fluid arising from Brownian movement of nanoparticles for thermal energy transfer in nanofluids. Viscosity data demonstrate transition from Newtonian characteristics for the base fluid to non-Newtonian behaviour with increasing content of Al2O3 in the base fluid (coolant). The data also show that the viscosity increases with an increase in concentration and decreases with an increase in temperature. An empirical correlation of the type log(μnf) = A exp(−BT) explains the observed temperature dependence of the measured viscosity of Al2O3 nanofluid based on car engine coolant. We further confirm that Al2O3 nanoparticle concentration dependence of the viscosity of nanofluids is very well predicted on the basis of a recently reported theoretical model (Masoumi et al 2009 J. Phys. D: Appl. Phys. 42 055501), which considers Brownian motion of nanoparticles in the nanofluid.

Effects of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Nanoparticle on the Microstructure and Magnetic Properties of Co/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Coatings Prepared by Composite Plating

Nanocomposite Co/Al2O3 coatings were fabricated by composite electrodeposition. The nanosized Al2O3 particles were suspended in aqueous cobalt sulfamate solution and subsequently co-deposited on a Cu substrate. The samples were characterized by Scanning electron microscopy and Atomic force microscopy for determination of surface morphology. X-ray diffraction technique concomitant with Transmission electron microscopy were utilized to identify the phases and emanation of microstructure while magnetic properties of the Co/Al2O3 nanocomposite coatings were investigated by vibrating sample magnetometer. The results indicated that, the Al2O3 nanoparticles suspended in the plating solution acquired a positively charge due to the presence of Co ions. These positively charged Al2O3 particles drift towards the cathode by electrophoresis and are reduced by Co ions to form the Co/Al2O3 composite film. The Co grains in the films show hcp structure with (11 2 0) preferred orientation. The grain size and surface roughness of the Co/Al2O3 compositesis found to decrease with increasing Al2O3 volume fraction while the magnetization of the composite films decreases with increasing concentration of Al2O3 nanoparticles. However the coercivity of the coatings was found to increase with increasing Al2O3 content. It could be delineated from the TEM micrographs that the Al2O3 nanoparticles dispersed in the Co matrix inhibited the grain growth of Co matrix resulting in pinning of the magnetic domains due to which the coercivity of the composite layers was found to increase.