[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. DOI:10.1016/j.snb.2014.07.027 · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A combined imaging and microdiffraction technique using high-energy synchrotron X-rays is described and used to reveal microstructure, damage and strain evolution around notches in SiC/SiC composites. This technique allows for monitoring the material for cracks while loading and mapping the strain distribution in fibers and matrix with a resolution of tens of microns. We show that at current resolutions this technique is capable of measuring the strain distribution near crack tips in ceramic matrix composites and observe load transfer effects.
Scripta Materialia 10/2013; 69(7-7):497-500. DOI:10.1016/j.scriptamat.2013.05.032 · 3.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Oxygen tracer diffusion (D⁎) and chemical diffusion (D˜) were measured in dense Sr0.5Sm0.5CoO3 − δ (SSC) ceramics by Isotope Exchange Depth Profiling/Secondary Ion Mass Spectrometry (IEDP/SIMS) and electrical conductivity relaxation (ECR) over the temperature ranges of ~ 100–200 °C and 400–600 °C, respectively. In addition, the surface exchange coefficients were determined over the same temperature ranges. The transport properties and exchange kinetics of SSC are comparable to or better than those of other solid oxide fuel cell cathode candidates in the literature. The ionic conductivity of SSC was calculated using the Nernst-Einstein equation, and is comparable to that of leading solid oxide electrolytes at intermediate temperatures.
Solid State Ionics 02/2013; 232:138–143. DOI:10.1016/j.ssi.2012.11.024 · 2.56 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. DOI:10.1016/j.ijheatmasstransfer.2012.06.034 · 2.38 Impact Factor
[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 07/2012; 9(4). DOI:10.1111/j.1744-7402.2012.02773.x · 1.32 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 04/2012; 541:61–66. DOI:10.1016/j.msea.2012.02.001 · 2.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ceramic thin film coatings, such as MoN/Cu, are attractive for engine applications due to their low friction, high hardness and high wear resistance. However, there is a need to establish a reliable connection between the deposition parameters of the thin film and its tribological performance. In this study, two coating compositions, MoN and MoN with Cu were deposited on H-13 tool steel substrates in order to correlate compositional variables that result from processing to their respective tribological properties. The efficacy of the coating in protecting surfaces is highly dependent on its adhesion to the substrate and its tribological properties. Residual stresses resulting from the coating deposition were evaluated using an X-ray microprobe. Scratch testing was performed to measure the coating adhesion energy, and the wear rate was determined using a ball-on-flat contact configuration on a high frequency reciprocating test rig. It was observed that coatings with lower copper content performed better in the wear test and exhibited higher coating adhesion energy. A primary wear damage mechanism was coating removal by delamination and spallation, which is related to the adhesion energy. Since coating processing variables determine the structure and properties, and hence affect the tribological properties of these MoN based coatings, these parameters can be used to optimize coating composition for enhanced tribological performance.
Wear 03/2012; s 278–279:62–70. DOI:10.1016/j.wear.2012.01.007 · 1.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Compressive creep under constant load (stresses of 0.5-10 MPa) of a geopolymer was investigated between 975 and 1025°C. The geopolymer was derived from Class F fly ash, kaolin, granulated blast furnace slag, sodium and potassium silicate and carbonate. Silicate-based aggregates constituted 48% of the total mass. The temperature range of testing was small because of limited plasticity below 975°C and decomposition above 1050°C. The maximum accumulated strain was 15%. A regime of true steady-state creep probably did not exist. Damage occurred at aggregate/geopolymer interfaces, induced in part by the stress concentrations there. Microstructural evolution was also observed, with calcium segregating from the geopolymer matrix toward the aggregates interfaces. The tests revealed that the geopolymer supported modest compressive stresses and exhibited significant strain or pseudo-plasticity.
[Show abstract][Hide abstract] ABSTRACT: Nanofluids have the potential to increase thermal conductivities and heat transfer coefficients compared to their base fluids.
However, the addition of nanoparticles to a fluid also increases the viscosity and therefore increases the power required
to pump the fluid through the system. When the benefit of the increased heat transfer is larger than the penalty of the increased
pumping power, the nanofluid has the potential for commercial viability. The pumping power for nanofluids has been considered
previously for flow in straight tubes. In this study, the pumping power was measured for nanofluids flowing in a complete
system including straight tubing, elbows, and expansions. The objective was to determine the significance of two-phase flow
effects on system performance. Two types of nanofluids were used in this study: a water-based nanofluid containing 2.0–8.0vol%
of 40-nm alumina nanoparticles, and a 50/50 ethylene glycol/water mixture-based nanofluid containing 2.2vol% of 29-nm SiC
nanoparticles. All experiments were performed in the turbulent flow region in the entire test system simulating features typically
found in heat exchanger systems. Experimental results were compared to the pumping power calculated from a mathematical model
of the system to evaluate the system effects. The pumping power results were also combined with the heat transfer enhancement
to evaluate the viability of the two nanofluids.
KeywordsNanofluids–Fluid flow–Pumping power–Nanoparticle–Colloids
Journal of Nanoparticle Research 03/2011; 13(3):931-937. DOI:10.1007/s11051-010-0197-7 · 2.18 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 02/2011; 6(1):182. DOI:10.1186/1556-276X-6-182 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Forced convective boiling heat transfer of water and ethylene glycol/water mixtures with volume concentration ratios of 40/60, 50/50, and 60/40 in a 2.98-mm inner-diameter circular tube has been investigated for both horizontal and vertical upward flows. Boiling heat transfer rates of the test fluids were determined experimentally over a range of mass flux, vapor mass quality, and inlet subcooling through a boiling data reduction procedure that allowed analytical calculation of the fluid boiling temperatures along the experimental test section by applying ideal mixture and equilibrium assumptions along with Raoult's law. Based on the experimental findings that the heat flux in the nucleation-dominant-boiling region was dependent strongly on the wall superheat but almost independent of the mass flux and the inlet subcooling, prediction equations were developed for boiling heat transfer coefficients of water and ethylene glycol/water mixtures in small channels. The equations predict the experimental data well, and most of the predicted values are within ±30 % of the experimental data.
Journal of ASTM International 02/2011; 8(2):103378. DOI:10.1520/JAI103378
[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.
[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.
[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. DOI:10.1166/jnn.2010.2413 · 1.56 Impact Factor