[Show abstract][Hide abstract] ABSTRACT: tNanocrystalline La0.8Sr0.2Al0.9Mn0.1O3(LSAM) was synthesized by a microwave-assisted citrate method,and characterized by electron microscopy and X-ray diffraction. Electrical behavior of LSAM was investi-gated by impedance spectroscopy and activation energy of conduction was obtained. Joining of sinteredbodies of LSAM and yttria-stabilized tetragonal zirconia polycrystals (YTZP), an extensively studied oxy-gen ion conducting electrolyte, was examined by isostatic hot pressing methods. Characteristics of thejoining region were evaluated with microprobe Raman spectroscopy, and products formed at the inter-face, primarily strontium zirconate, was confirmed by examination of high temperature chemical reactionbetween LSAM and YTZP powders. The electrical properties of the LSAM were exploited for developmentof a high temperature oxygen sensor in which LSAM functioned as the electrode and YTZP as electrolyte.
Sensors and Actuators B Chemical 07/2014; 203:670. · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The objective of this workshop was to focus on new directions in carbon nanomaterial research, with a particular focus on new frontiers in nanotube alignment and applications of nanofluids. The first Carbon Nano Material Workshop was held at the Radisson Hotel, Rapid City, South Dakota, from October 30 to November 1, 2011, and was organized by Dr. G. P. “Bud” Peterson, Georgia Institute of Technology, and Dr. Haiping Hong, South Dakota School of Mines and Technology. More than 70 people from various government agencies, national labs, universities, and industries attended the workshop. The workshop agenda follows. The workshop included keynote plenary sessions and invited and contributed sessions, as well as a dedicated poster session of selected presentations assembled from an open call for papers.
[Show abstract][Hide abstract] ABSTRACT: We report in this article the friction and wear results of polyalphaolefin (PAO 10) base oil with the addition of 3 wt% boron nitride (BN) and molybdenum disulfide (MoS2) nanoparticles with nominal size of 70 and 50 nm, respectively. The formulations were tested using cast iron cylinder liner segments reciprocating against aluminum alloy piston skirt segments at 20, 40, and 100 °C. The results showed that, at a load of 250 N and a reciprocating frequency of 2 Hz, BN did not lower friction whereas MoS2 nanoparticles were very effective at reducing both friction and wear, compared with the base oil. The viscosities of both formulations were similar to the base oil, which allowed for a direct comparison between them. Raman spectroscopy showed the formation of an aligned MoS2 layer on the cast iron liner surface, which most likely functions as a tribofilm. In the case of the cast iron liner tested with BN nanolubricant, no traces of BN were found. The effect of surfactants was also studied, and it was found that some surfactants were not only beneficial in dispersing the nanoparticles in oil, but also in producing some reduction in friction and wear, even when used as stand-alone additives in PAO 10.
[Show abstract][Hide abstract] ABSTRACT: Three essential aspects of the turbulent-flow, convective heat transfer of nanofluids relevant to their applications are comparatively reviewed in detail based on both theoretical analyses and experimental data. These aspects are: (a) selection – the comparison criteria of the thermophysical property-related heat transfer performance of nanofluids and their base fluids, (b) design – the predictions of the heat transfer coefficients of nanofluids based on homogeneous fluid models by using nanofluid effective thermophysical properties, and (c) effectiveness – the enhancements of the heat transfer coefficients of nanofluids over their base fluids. This review, including research from the inception of nanofluids to date, quantifies the accuracy of bases for future nanofluid evaluation.
International Journal of Heat and Mass Transfer 10/2012; 55(s 21–22):5380–5396. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Directionally solidified eutectics are in situ composites grown from the melt. Due to the differences in the thermoelastic properties of the different phases present in the material, these composites often exhibit residual stresses that can affect their mechanical properties. In this work we use neutron diffraction to investigate residual stresses in Al2O3–ZrO2 eutectic composites as a function of temperature, for samples processed at two different growth rates, 10 mm/h and 750 mm/h. Our results show that the stress-free temperature is in the range of 1200 ± 200 °C. We explain the experimental observations based on the thermoelastic properties of the phases in the material and confirm our measurements using a simple, self-consistent model.
Materials Science and Engineering: A. 01/2012; 541:61–66.
[Show abstract][Hide abstract] ABSTRACT: Aluminum‐doped lanthanum strontium manganese oxide (LSAM) has been investigated as an electrically conductive ceramic material. LSAM formulations with varying amounts of aluminum were synthesized using standard ceramic processing followed by pressure‐less sintering in air. Electrical conductivity of LSAM was measured as a function of aluminum content and temperature. Optimum LSAM formulations were joined to yttria‐stabilized tetragonal zirconia (YTZP) using a high‐temperature deformation process. Electron microscopy, X‐ray diffraction, and Raman spectroscopy were used to evaluate the joint interface. Joining was attributed to the formation of a reaction layer of strontium zirconate. Joining of LSAM to oxygen‐ion conducting YTZP has implications in using this approach as interconnect for variety of high‐temperature applications, including fuel cells and gas sensors.
International Journal of Applied Ceramic Technology 01/2012; 9(4). · 1.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Partial substitution of Al for Si and B for C has enabled us to synthesize, using spark plasma techniques, doped nanoensembles of SiC that have Seebeck coefficients of 330 microV/K at 900 K. In attempting to attain an understanding of the Seebeck coefficient, we have extended earlier density functional calculations on stacked graphene sheets to 3C SiC nanoclusters with substitutions of Al in Si sites and B in C sites. The calculations show that both types of doping lead to hole states resulting in pronounced decreases in the HOMO-LUMO gap. As a consequence, some of the Al hole states are located near the Fermi level analogous to the situation encountered in stacked graphene sheets. Each of the large number of discrete electronic states introduced into SiC due to doping are associated with a particular Al and B configuration. The implications of these studies are discussed.
Nanoscience and Nanotechnology Letters 01/2011; 3(1):114-118. · 1.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An overview of systematic studies that address the complexity of nanofluid systems and advance the understanding of nanoscale contributions to viscosity, thermal conductivity, and cooling efficiency of nanofluids is presented. A nanoparticle suspension is considered as a three-phase system including the solid phase (nanoparticles), the liquid phase (fluid media), and the interfacial phase, which contributes significantly to the system properties because of its extremely high surface-to-volume ratio in nanofluids. The systems engineering approach was applied to nanofluid design resulting in a detailed assessment of various parameters in the multivariable nanofluid systems. The relative importance of nanofluid parameters for heat transfer evaluated in this article allows engineering nanofluids with desired set of properties.
Nanoscale Research Letters 01/2011; 6(1):182. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Experimental data are presented for the thermal conductivity, viscosity, and turbulent flow heat transfer coefficient of nanofluids with SiC particles suspended in ethylene glycol (EG)/water (H2O) mixture with a 50/50 volume ratio. The results are compared to the analogous suspensions in water for four sizes of SiC particles (16-90 nm). It is demonstrated that the heat transfer efficiency is a function of both the average particle size and the system temperature. The results show that adding SiC nanoparticles to an EG/H2O mixture can significantly improve the cooling efficiency while water-based nanofluids are typically less efficient than the base fluids. This is one of the few times that substantial nanofluid heat transfer enhancement has been reported in the literature based on a realistic comparison basis of constant velocity or pumping power. The trends important for engineering efficient heat transfer nanofluids are summarized.
Journal of Applied Physics 01/2011; 109. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The physical mechanisms and mathematical models of the effective thermal conductivities of nanofluids have long been of interest to the nanofluid research community because the effective thermal conductivities of nanofluids cannot generally be fully explained and predicted by classical effective medium theories. This review article summarizes considerable progress made on this topic. Specifically, the physical mechanisms and mathematical models of the effective thermal conductivities of nanofluids are reviewed, the potential contributions of those physical mechanisms are evaluated, and the comparisons of the theoretical predictions and experimental data are presented along with opportunities for future research.
Journal of Nanoscience and Nanotechnology 08/2010; 10(8):4824-49. · 1.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of average particle sizes on basic macroscopic properties and heat transfer performance of alpha-SiC/water nanofluids was investigated. The average particle sizes, calculated from the specific surface area of nanoparticles, were varied from 16 to 90 nm. Nanofluids with larger particles of the same material and volume concentration provide higher thermal conductivity and lower viscosity increases than those with smaller particles because of the smaller solid/liquid interfacial area of larger particles. It was also demonstrated that the viscosity of water-based nanofluids can be significantly decreased by pH of the suspension independently from the thermal conductivity. Heat transfer coefficients were measured and compared to the performance of base fluids as well as to nanofluids reported in the literature. Criteria for evaluation of the heat transfer performance of nanofluids are discussed and optimum directions in nanofluid development are suggested.
[Show abstract][Hide abstract] ABSTRACT: Boron-doped nanographite ensembles (NGEs) are interesting thermoelectric nanomaterials for high temperature applications. Rapid induction annealing and quenching has been applied to boron-doped NGEs using a relatively low-cost, highly reliable, laboratory built furnace to show that substantial improvements in thermoelectric power factors can be achieved using this methodology. Details of the design and performance of this compact induction furnace as well as results of the thermoelectric measurements will be reported here.
Review of Scientific Instruments 04/2010; 81(4):043909-043909-6. · 1.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heat transfer enhancement criteria for nanofluids over their base fluids are presented based on three separate considerations: Reynolds number, flow velocity, and pumping power. Analyses presented show that, among the three comparisons, the constant pumping power comparison is the most unambiguous; the constant flow velocity comparison can be quite reasonable under certain conditions but the constant Reynolds number comparison (the most commonly used in the engineering literature for nanofluids) distorts the physical situation, and therefore, should not be used.
[Show abstract][Hide abstract] ABSTRACT: The thermal conductivity and viscosity of various shapes of alumina nanoparticles in a fluid consisting of equal volumes of ethylene glycol and water were investigated. Experimental data were analyzed and accompanied by theoretical modeling. Enhancements in the effective thermal conductivities due to particle shape effects expected from Hamilton–Crosser equation are strongly diminished by interfacial effects proportional to the total surface area of nanoparticles. On the other hand, the presence of nanoparticles and small volume fractions of agglomerates with high aspect ratios strongly increases viscosity of suspensions due to structural constrains. Nanoparticle surface charge also plays an important role in viscosity. It is demonstrated that by adjusting p H of nanofluid, it is possible to reduce viscosity of alumina nanofluid without significantly affecting thermal conductivity. Efficiency of nanofluids (ratio of thermal conductivity and viscosity increase) for real-life cooling applications is evaluated in both the laminar and turbulent flow regimes using the experimental values of thermal conductivity and viscosity.
Journal of Applied Physics 08/2009; · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Thermoelectric power factors of nanocarbon ensembles have been determined as a function of temperature from 400 to 1200 K. The ensembles, composed of mixtures of nanographite or disperse ultrananocrystalline diamond with B <sub>4</sub> C , are formed into mechanically rigid compacts by reaction at 1200 K with methane gas and subsequently annealed in an argon atmosphere at temperatures up to 2500 K. The ensembles were characterized using scanning electron microscopy, Raman, x-ray diffraction, and high resolution transmission electron microscopy techniques and found to undergo profound nanostructural changes as a function of temperature while largely preserving their nanometer sizes. The power factors increase strongly both as a function of annealing temperature and of the temperature at which the measurements are carried out reaching 1 μ W / K <sup>2</sup> cm at 1200 K without showing evidence of a plateau. Density functional “molecular analog” calculations on systems based on stacked graphene sheets show that boron substitutional doping results in a lowering of the Fermi level and the creation of a large number of hole states within thermal energies of the Fermi level [P. C. Redfern, D. M. Greun, and L. A. Curtiss, Chem. Phys. Lett. 471, 264 (2009)]. We propose that enhancement of electronic configurational entropy due to the large number of boron configurations in the graphite lattice contributes to the observed thermoelectric properties of the ensembles.
Journal of Applied Physics 05/2009; · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Thermal conductivity and mechanical effects of silicon carbide nanoparticles uniformly dispersed in water were investigated. Mean size of SiC particles was 170 nm with a polydispersity of ∼30% as determined from small-angle x-ray scattering and dynamic light scattering techniques. Room temperature viscosity of the nanofluids ranged from 2 to 3 cP for nominal nanoparticle loadings 4–7 vol % . On a normalized basis with water, viscosity of the nanofluids did not significantly change with the test temperature up to 85 ° C . Optical microscopy of diluted nanofluid showed no agglomeration of the nanoparticles. Thermal conductivity of the fluid was measured as a function of the nominal nanoparticle loading ranging from 1 to 7 vol % . Enhancement in thermal conductivity was approximately 28% over that of water at 7 vol % particle loadings under ambient conditions. Enhancements in thermal conductivities for the nanofluids with varying nanoparticle loadings were maintained at test temperatures up to 70 ° C . Results of thermal conductivity have been rationalized based on the existing theories of heat transfer in fluids. Implications of using this nanofluid for engineering cooling applications are discussed.
Journal of Applied Physics 04/2009; · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ceramic bars of zirconia toughened–alumina composites were fabricated by pressureless sintering in air at 1450°C for 4h. Composite samples were fabricated with two different compositions: zirconia with 60vol.% alumina (ZT60A) and zirconia with 40vol.% alumina (ZT40A). Average four-point-bend strengths for the ZT40A and ZT60A were 480±45MPa and 410±120MPa, respectively. Three-layered sandwich structures were fabricated by joining two bars of sintered ZT60A with a sintered ZT40A bar. High-temperature plastic joining was accomplished at 1350°C at a strain rate of 5×10−6s−1 and a compressive stress ranging from 30–40MPa. Bend tests conducted on the layered structure exhibited average strengths of 707±81MPa. Strength enhancements for the multilayered structure were higher than those predicted by stress analysis. Stress enhancements were compared with the residual stresses measured in the layered sample using X-ray micro-diffraction at the Advance Photon Source (APS). Scanning electron microscopy (SEM) was also conducted to identify the location of failure causing flaws.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing - MATER SCI ENG A-STRUCT MATER. 01/2009; 517(1):78-84.