| 1. |
- Afzal, Muhammad, et al.
(author)
-
Fabrication of novel electrolyte-layer free fuel cell with semi-ionic conductor (Ba0.5Sr0.5Co0.8Fe0.2O3-delta- Sm0.2Ce0.8O1.9) and Schottky barrier
- 2016
-
In: Journal of Power Sources. - : Elsevier. - 0378-7753 .- 1873-2755. ; 328, s. 136-142
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Journal article (peer-reviewed)abstract
- Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) is synthesized via a chemical co-precipitation technique for a low temperature solid oxide fuel cell (LTSOFC) (300-600 degrees C) and electrolyte-layer free fuel cell (EFFC) in a comprehensive study. The EFFC with a homogeneous mixture of samarium doped ceria (SDC): BSCF (60%:40% by weight) which is rather similar to the cathode (SDC: BSCF in 50%:50% by weight) used for a three layer SOFC demonstrates peak power densities up to 655 mW/cm(2), while a three layer (anode/ electrolyte/cathode) SOFC has reached only 425 mW/cm(2) at 550 degrees C. Chemical phase, crystal structure and morphology of the as-prepared sample are characterized by X-ray diffraction and field emission scanning electron microscopy coupled with energy dispersive spectroscopy. The electrochemical performances of 3-layer SOFC and EFFC are studied by electrochemical impedance spectroscopy (EIS). As-prepared BSCF has exhibited a maximum conductivity above 300 S/cm at 550 degrees C. High performance of the EFFC device corresponds to a balanced combination between ionic and electronic (holes) conduction characteristic. The Schottky barrier prevents the EFFC from the electronic short circuiting problem which also enhances power output. The results provide a new way to produce highly effective cathode materials for LTSOFC and semiconductor designs for EFFC functions using a semiconducting-ionic material.
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| 2. |
- Battiston, S., et al.
(author)
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Influence of Al and Mg Addition on Thermoelectric Properties of Higher Manganese Silicides Obtained by Reactive Sintering
- 2017
-
In: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 17:3, s. 1668-1673
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Journal article (peer-reviewed)abstract
- Higher manganese silicides (HMS), represented by MnSix (x = 1.71-1.75), are promising p-type candidates for thermoelectric (TE) energy harvesting systems at intermediate temperature range. The materials are very attractive as they may replace lead based compounds due to their nontoxicity, low cost of starting materials, and high thermal and chemical stability. Dense pellets were obtained through fast reactive sintering by spark plasma sintering (SPS). The addition -or nanoinclusion, of Al and Mg permitted the figure of merit enhancement of the material obtained with this technique, reaching the highest value of 0.40 at 600 degrees C. Morphology, composition and crystal structure of the samples were characterized by electron microscopies, energy dispersive X-ray spectroscopy, and X-ray diffraction analyses, respectively.
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| 3. |
- Battiston, S., et al.
(author)
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Synthesis and Characterization of Al-Doped Mg2Si Thermoelectric Materials
- 2013
-
In: Journal of Electronic Materials. - New York : Springer. - 0361-5235 .- 1543-186X. ; 42:7, s. 1956-1959
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Journal article (peer-reviewed)abstract
- Magnesium silicide (Mg2Si)-based alloys are promising candidates for thermoelectric (TE) energy conversion for the middle to high range of temperature. These materials are very attractive for TE research because of the abundance of their constituent elements in the Earth's crust. Mg2Si could replace lead-based TE materials, due to its low cost, nontoxicity, and low density. In this work, the role of aluminum doping (Mg2Si:Al = 1:x for x = 0.005, 0.01, 0.02, and 0.04 molar ratio) in dense Mg2Si materials was investigated. The synthesis process was performed by planetary milling under inert atmosphere starting from commercial Mg2Si pieces and Al powder. After ball milling, the samples were sintered by means of spark plasma sintering to density > 95%. The morphology, composition, and crystal structure of the samples were characterized by field-emission scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction analyses. Moreover, Seebeck coefficient analyses, as well as electrical and thermal conductivity measurements were performed for all samples up to 600A degrees C. The resultant estimated ZT values are comparable to those reported in the literature for these materials. In particular, the maximum ZT achieved was 0.50 for the x = 0.01 Al-doped sample at 600A degrees C.
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| 4. |
- Bitaraf Haghighi, Ehsan, et al.
(author)
-
Cooling performance of nanofluids in a small diameter tube
- 2013
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In: Experimental Thermal and Fluid Science. - : Elsevier. - 0894-1777 .- 1879-2286. ; 49, s. 114-122
-
Journal article (peer-reviewed)abstract
- This article reports convective single-phase heat transfer performance in laminar flow for some selected nanofluids (NFs) in an open small diameter test section. A 0.50 mm inner diameter, 30 cm long stainless steel test section was used for screening single phase laminar convective heat transfer with water and five different water based NFs. Tested NFs were; Al2O3 (two types), TiO2 (two types) and CeO2 (one type), all 9 wt.% particle concentration. The effective thermal conductivity of the NFs were measured with Transient Plane Source (TPS) method and viscosity were measured with a rotating coaxial cylindrical viscometer. The obtained experimental results for thermal conductivity were in good agreement with the predicted values from Maxwell equation. The local Shah correlation, which is conventionally used for predicting convective heat transfer in laminar flow in Newtonian fluids with constant heat flux boundary condition, was shown to be valid for NFs. Moreover, the Darcy correlation was used to predict the friction factor for the NFs as well as for water. Enhancement in heat transfer for NFs was observed, when compared at equal Reynolds number, as a result of higher velocity or mass flow rate of the NFs at any given Reynolds number due to higher viscosity for NFs. However, when compared at equal pumping power no or only minor enhancement was observed.
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| 5. |
- Bitaraf Haghighi, Ehsan, 1980-, et al.
(author)
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Measurement of temperature–dependent viscosity of nanofluids and its effect on pumping power in cooling systems
- 2013
-
Conference paper (peer-reviewed)abstract
- Nanofluids are engineered colloids of nanoparticlesdispersed homogenously in a base fluid, which theirthermophysical properties are changed by adding solidnanoparticles. Among the characteristic parameters,viscosity is one of the most important, as it directly affectsthe pumping power in cooling systems. In this study, theviscosity of water based Al2O3, ZrO2, and TiO2 (with 9wt%for all) nanofluids was measured and its impact on pressuredrop in a simple tubular pipe was estimated for bothlaminar and turbulent flow by classical correlations. Theeffect of temperature on the viscosity of these nanofluidswas also studied in the temperature range of 5˚C - 30˚C. Toassess the applicability of the classical correlations, pressuredrops across an open 30cm long, 0.50mm diameterstainless steel test section was measured for water andnanofluids by a differential pressure transducer. Theaverage viscosity increments compared to water in thetemperature range of 5˚C - 30˚C are 105%, 98% and 31% forAl2O3, ZrO2, and TiO2 nanofluids respectively. Moreover, theresults show that the viscosity of nanofluids decreases withthe increase of temperature; however the relative viscosity,which is defined as the viscosity ratio between a nanofluidand its base fluid is constant in 5˚C - 30˚C temperaturerange.
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| 6. |
- Bitaraf Haghighi, Ehsan, et al.
(author)
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Shelf stability of nanofluids and its effect on thermal conductivity and viscosity
- 2013
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In: Measurement science and technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 24:10, s. 105301-
-
Journal article (peer-reviewed)abstract
- This study proposes a method and apparatus to estimate shelf stability of nanofluids. Nanofluids are fabricated by dispersion of solid nanoparticles in base fluids, and shelf stability is a key issue for many practical applications of these fluids. In this study, shelf stability is evaluated by measuring the weight of settled solid particles on a suspended tray in a colloid versus time and correlated with the performance change of some nanofluid systems. The effects of solid particle concentration and bath sonication time were investigated for selected nanofluids. The results show the applicability of this simple method and the apparatus to evaluate nanofluid shelf stability. Furthermore, it shows that Stokes' law is not valid for determining the settling time of the tested nanoparticles probably due to their complicated shape and presence of surface modifiers. The effect of shelf stability on thermal conductivity and viscosity was illustrated for some nanofluids. Experimental results show that water-based Al2O3 nanofluids have quite good shelf stability and can be good candidates for industrial applications.
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| 7. |
- Burks, Terrance, 1969-, et al.
(author)
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Removal of Chromium(VI) Using Surface Modified Superparamagnetic Iron Oxide Nanoparticles
- 2013
-
In: Separation science and technology (Print). - : Informa UK Limited. - 0149-6395 .- 1520-5754. ; 48:8, s. 1243-1251
-
Journal article (peer-reviewed)abstract
- This study describes the removal of Chromium(VI) from aqueous solutions using surface tailored superparamagnetic iron oxide nanoparticles (SPION) coated with bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex-301). The synthesized Cyanex-301 coated SPION has been characterized by Transmission Electron Microscopy (TEM), Fourier-Transfer Infrared Spectroscopy (FT-IR), X-ray Photonic Spectroscopy (XPS), and Thermogravimetric Analysis (TGA). The adsorption mechanism was proposed to be via complexation between the thiol group on Cyanex-301 and Cr(VI) ions based on the XPS and FTIR analysis. It has been found that the equilibrium can be attained in less than 2hr. The adsorption behavior of Cr(VI) on the Cyanex-301 coated SPION can be well described by the Langmuir model and the maximum adsorption capacity for Cr(VI) was estimated to be 30.8mg/g. The selectivity of the Cyanex-301 coated SPION adsorbent towards Cr(VI) ions was found to be high and the maximum loading capacity obtained is up to an order of magnitude higher than that of other adsorbents reported in the literature. The desorption studies showed that more than 70% of Cr(VI) can be recovered using HNO3 as eluting solution. Our findings suggest a high potential of the designed adsorbent material for the treatment of industrial wastewater containing Cr(VI).
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| 8. |
- Doddapaneni, Venkatesh, et al.
(author)
-
Engineered PMMA-ZnO nanocomposites for improving the electric arc interruption capability in electrical switching applications : Unprecedented experimental insights
- 2017
-
In: Composites Science And Technology. - : Elsevier. - 0266-3538 .- 1879-1050. ; 141, s. 113-119
-
Journal article (peer-reviewed)abstract
- Polymer inorganic nanocomposites (PINCs) have been engineered for controlling the electrical arc and to improve the arc interruption capability of the electrical switching applications, like circuit breakers. Several PINCs are fabricated by formation of ZnO quantum dots (QDs) in a poly (methyl methacrylate) (PMMA) matrix via in-situ polymerization method to avoid agglomeration of QDs, leading to a good spatial distribution of QDs in the polymer matrix. These PINCs have been characterized in detail for the morphology of QDs, interaction between QDs and polymer matrix, and ultraviolet (UV) radiation absorption. ZnO QDs have been assessed to have particle diameter of 3.5 nm, and their presence in the PMMA is revealed by the unique luminescence characteristics of the QDs under UV light. The presence of ZnO QDs broadened the range of UV radiation absorption of PMMA and the absorption edge is gradually shifted from 270 nm to 338 nm with step-wise loading of ZnO QDs. The PINCs are tested to determine their reproducibility and impact on the electrical arcs of current 1.6 kA generated using a specially designed test-setup. Interaction of PINCs with the electrical arcs generates ablation of chemical species towards core of the electrical arc, resulting in increase of voltage leading to cool-down the arc temperature. This experimental study demonstrates for the first time that these PINCs are reproducible, reliable and provides superior arc interruption capability.
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| 9. |
- Doddapaneni, Venkatesh, et al.
(author)
-
New experimental insights for controlling the electrical arcs in electrical switching applications : a comparative study on PMMA nanocomposites of Au and ZnO
- 2017
-
In: Composites Science And Technology. - : Elsevier. - 0266-3538 .- 1879-1050.
-
Journal article (other academic/artistic)abstract
- Polymer inorganic nanocomposites (PINCs) are developed, not only due to scientific interest but also improving theelectric arc interruption process in the electrical switching applications like circuit breakers. The novelty of this work isin integrating the current developments in PINCs into electrical switching application in order to extend the limits of thepower switching devices. Several PINCs are fabricated by using pre-synthesized Au nanoparticles (NPs) of size 2.75 ±0.4 nm and poly (methyl methacrylate) (PMMA) matrix via in-situ polymerization method. Six homogeneous PINCsamples with ultra-low wt% of Au NPs varying from 0.0003 to 0.005 wt% have been fabricated. We find that thepresence of Au NPs improved the convective heat transfer and visible optical radiation absorption of PMMA. Thefabricated PINCs are tested for their arc interruption performance and the results are compared with ZnO PINCs in ourearlier work. The results of the experiments insights demonstrate the impact of PINCs on the electrical arcs and theirpotential advantages of having PINCs for the electric arc interruption process in high power switching devices.
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| 10. |
- Doddapaneni, Venkatesh, et al.
(author)
-
On the electrical arc interruption by using PMMA/iron oxide nanocomposites
- 2016
-
In: Materials Research Express. - : Institute of Physics (IOP). - 2053-1591. ; 3:10
-
Journal article (peer-reviewed)abstract
- An experimental study is undertaken on the fabrication of poly (methyl methacrylate) (PMMA)/iron oxide nanocomposites to determine their potential use for electrical arc interruption in the electrical switching applications such as circuit breakers. Monodisperse iron oxide nanoparticles of average size ¡«11 nmare synthesized via thermal decomposition method and then homogeneously dispersed in the PMMAmatrix by in situ polymerization.PMMA/iron oxide nanocomposites with different nanoparticle loading have been fabricated to study the effect of loading content on the thermal energy absorption. Detailed physicochemical characterizations on synthesized material are performed using X-ray powder diffraction, scanning electron microscopy, TEM, thermogravimetric analysis and differential scanning calorimetry at different processing stages. Atest-setup was designed to evaluate the quality of the nanocomposites for electric arc interruption capability. The results showed that PMMA/iron oxide nanocomposites have a clear impact on the electric arc interruption and therefore should be considered as promising candidates for electrical switching applications.
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| 11. |
- Famengo, A., et al.
(author)
-
Phase Content Influence on Thermoelectric Properties of Manganese Silicide-Based Materials for Middle-High Temperatures
- 2013
-
In: Journal of Electronic Materials. - New York : Springer. - 0361-5235 .- 1543-186X. ; 42:7, s. 2020-2024
-
Journal article (peer-reviewed)abstract
- The higher manganese silicides (HMS), represented by MnSi (x) (x = 1.71 to 1.75), are promising p-type leg candidates for thermoelectric energy harvesting systems in the middle-high temperature range. They are very attractive as they could replace lead-based compounds due to their nontoxicity, low-cost starting materials, and high thermal and chemical stability. Dense pellets were obtained through direct reaction between Mn and Si powders during the spark plasma sintering process. The tetragonal HMS and cubic MnSi phase amounts and the functional properties of the material such as the Seebeck coefficient and electrical and thermal conductivity were evaluated as a function of the SPS processing conditions. The morphology, composition, and crystal structure of the samples were characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction analyses, respectively. Differential scanning calorimetry and thermogravimetric analysis were performed to evaluate the thermal stability of the final sintered material. A ZT value of 0.34 was obtained at 600A degrees C for the sample sintered at 900A degrees C and 90 MPa with 5 min holding time.
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| 12. |
- Fiameni, S., et al.
(author)
-
Effect of Synthesis and Sintering Conditions on the Thermoelectric Properties of n-Doped Mg2Si
- 2014
-
In: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 43:6, s. 2301-2306
-
Journal article (peer-reviewed)abstract
- Magnesium silicide (Mg2Si)-based alloys are promising candidates for thermoelectric (TE) energy conversion in the middle-high temperature range. The detrimental effect of the presence of MgO on the TE properties of Mg2Si based materials is widely known. For this reason, the conditions used for synthesis and sintering were optimized to limit oxygen contamination. The effect of Bi doping on the TE performance of dense Mg2Si materials was also investigated. Synthesis was performed by ball milling in an inert atmosphere starting from commercial Mg2Si powder and Bi powder. The samples were consolidated, by spark plasma sintering, to a density > 95%. The morphology, and the composition and crystal structure of samples were characterized by field-emission scanning electronic microscopy and x-ray diffraction, respectively. Moreover, determination of Seebeck coefficients and measurement of electrical and thermal conductivity were performed for all the samples. Mg2Si with 0.1 mol% Bi doping had a ZT value of 0.81, indicative of the potential of this method for fabrication of n-type bulk material with good TE performance.
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| 13. |
- Fiameni, S., et al.
(author)
-
Introduction of Metal Oxides into Mg2Si Thermoelectric Materials by Spark Plasma Sintering
- 2013
-
In: Journal of Electronic Materials. - New York : Springer. - 0361-5235 .- 1543-186X. ; 42:7, s. 2062-2066
-
Journal article (peer-reviewed)abstract
- Oxide incorporation into thermoelectric Mg2Si-based materials was performed starting from commercial Mg2Si and commercial metal oxides by applying ball milling and spark plasma sintering (SPS) processing. The SPS conditions, such as sintering temperature, pressure, and holding time, were optimized with the aim of obtaining both full densification and oxide incorporation. Thermoelectric characterizations, such as Seebeck coefficient and electrical and thermal conductivity, were carried out and related to the pellet compositions. The morphology, composition, and crystallographic structure of the samples were characterized by field-emission scanning electron microscopy, energy-dispersive spectrometry, and x-ray diffraction analyses, respectively.
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| 14. |
- Haghighi, Ehsan Bitaraf, et al.
(author)
-
Accurate basis of comparison for convective heat transfer in nanofluids
- 2014
-
In: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933 .- 1879-0178. ; 52, s. 1-7
-
Journal article (peer-reviewed)abstract
- Thermal conductivity and viscosity of alumina (Al2O3), zirconia (ZrO2), and titania (TiO2) nanofluids (NFs) were measured at 20°C. All the NF systems were water based and contained 9wt.% solid particles. Additionally, the heat transfer coefficients for these NFs were measured in a straight tube of 1.5m length and 3.7mm inner diameter. Based on the results, it can be stated that classical correlations, such as Shah and Gnielinski, for laminar and turbulent flow respectively, can be employed to predict convective heat transfer coefficients in NFs, if the accurate thermophysical properties are used in the calculations. Convective heat transfer coefficients for NFs were also compared with those of the base fluids using two different bases for the comparison, with contradictory results: while compared at equal Reynolds number, the heat transfer coefficients increased by 8-51%, whereas compared at equal pumping power the heat transfer coefficients decreased by 17-63%. As NFs have higher viscosity than the base fluids, equal Reynolds number requires higher volumetric flow, hence higher pumping power for the NFs. It is therefore strongly suggested that heat transfer results should be compared at equal pumping power and not at equal Reynolds number.
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| 15. |
- Iqbal, Asad M., et al.
(author)
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Relaxation dynamics and polydispersivity associated with defects and ferroelectric correlations in Ba-doped EuTiO3
- 2017
-
In: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:46
-
Journal article (peer-reviewed)abstract
- We present the frequency- and temperature-dependent dielectric response of Eu1-xBaxTiO3 (0 <= x <= 0.5) in detail. Excluding grain boundary effects, four relaxation mechanisms were observed. Relaxation dynamics were observed to arise due to hopping conduction associated with defects, namely oxygen vacancies as well as Eu3+ and Ti3+ ions. Dielectric relaxation analysis led to the identification of Ti ions in two different environments with different relaxation rates in the overall EuTiO3 perovskite structure. The emergence of another relaxation mechanism associated with ferroelectric order as a consequence of the formation of polar regions was also observed for higher Ba concentrations. The addition of Ba led to the identification of relaxation dynamics associated with hopping conduction between Eu ions, Ti ions (in the regions with and without oxygen vacancies) and with the formation of ferroelectric polar regions. Furthermore, the polydispersivity and relaxation times were extracted within the framework of the modified Debye model. Relaxation times have been observed to increase with a decrease in temperature while larger values of polydispersivity reveal a wide distribution of relaxation times due to the presence of lattice parameter and energy barrier distributions.
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| 16. |
- Jacquot, A., et al.
(author)
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Anisotropy and inhomogeneity measurement of the transport properties of spark plasma sintered thermoelectric materials
- 2013
-
In: Thermoelectric Materials Research and Device Development for Power Conversion and Refrigeration. - : Materials Research Society. - 9781605114675 ; , s. 89-95
-
Conference paper (peer-reviewed)abstract
- We report on the development and capabilities of two new measurement systems developed at Fraunhofer-IPM. The first measurement system is based on an extension of the Van der Pauw method and is suitable for cube-shaped samples. A mapping of the electrical conductivity tensor of a Skutterudite-SPS samples produced at the Instituto de Microelectrónica de Madrid is presented. The second measurement system is a ZTmeter also developed at the Fraunhofer-IPM. It enables the simultaneous measurement of the electrical conductivity, Seebeck coefficient and thermal conductivity up to 900 K of cubes at least 5x5x5 mm 3 in size. The capacity of this measurement system for measuring the anisotropy of the transport properties of a (Bi,Sb)2Te3 SPS sample produced by KTH is demonstrated by simply rotating the samples.
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| 17. |
- Jaffari, G. Hassnain, et al.
(author)
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Extrinsic contributions to the dielectric response in sintered BaTiO3 nanostructures in paraelectric and ferroelectric regimes
- 2017
-
In: Physica. B, Condensed matter. - : ELSEVIER SCIENCE BV. - 0921-4526 .- 1873-2135. ; 525, s. 70-77
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Journal article (peer-reviewed)abstract
- Post sintering studies of BaTiO3 (BTO) nanoparticles are presented in detail. Bulk nanostructures were prepared via three different compaction processes, namely, uniaxial cold pressing (UCP), Cold Isostatic Pressing (CIP) and Spark Plasma Sintering (SPS). Effect of compaction technique on microstructures have been investigated and correlated with electrical response for each sample. In addition to the transport properties, temperature and frequency dependent dielectric response of variously sintered samples and bulk counterpart was recorded. Several aspects have been identified that are essential to be taken into account in order to completely understand physical processes. Drastically distinct features were observed in paraelectric (PE) regime well above ferroelectric (FE)-PE transition temperature. These features include intra grain conduction with a reduction in the magnitude of PE to FE peak dielectric constant magnitude. Role of strain, grain boundary conduction associated with observation of Maxwell Wagner relaxation and hopping conduction in dielectric and ferroelectric response have been observed and discussed. Densification with presence of oxygen vacancies, significantly enhances conductivity associated with the hopping of the carriers, in turn deteriorated ferroelectric response.
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| 18. |
- Jarahnejad, Mariam, et al.
(author)
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Experimental investigation on viscosity of water-based Al2O3 and TiO2 nanofluids
- 2015
-
In: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 54:5, s. 411-422
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Journal article (peer-reviewed)abstract
- This article investigates the influence of temperature, concentration, and size of nanoparticles, and addition of surfactants on dynamic viscosity of water-based nanofluids containing alumina (Al2O3) and titania (TiO2) nanoparticles. Two viscometers, a capillary and a falling ball, were used for the measurements in the temperature range of 20-50 A degrees C and the particle concentration of 3-14.3 wt.%. The results indicate that the viscosity of nanofluids is reduced by increasing the temperature, similar to their base fluids. Moreover, surfactants, which are used to improve the shelf stability of nanofluids, most likely increase their viscosity. The correlations derived from the linear fluid theory such as Einstein and Batchelor, especially for solid concentration above 1.5 wt.% are not accurate to predict viscosity of nanofluids, while the modified Krieger-Dougherty equation estimates viscosity of nanofluids with acceptable accuracy in a specific range of solid particle size to aggregate size.
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| 19. |
- Kanas, Nikola, et al.
(author)
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Influence of processing on stability, microstructure and thermoelectric properties of Ca3Co4 - (x)O9+delta
- 2018
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In: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 38:4, s. 1592-1599
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Journal article (peer-reviewed)abstract
- Due to high figure of merit, Ca3Co4 - O-x(9) (+ delta) (CCO) has potential as p-type material for high-temperature thermoelectrics. Here, the influence of processing including solid state sintering, spark plasma sintering and post-calcination on stability, microstructure and thermoelectric properties is reported. By a new post-calcination approach, single-phase materials were obtained from precursors to final dense ceramics in one step. The highest zT of 0.11 was recorded at 800 degrees C for CCO with 98 and 72% relative densities. In situ high-temperature X-ray diffraction in air and oxygen revealed a higher stability of CCO in oxygen (similar to 970 degrees C) than in air (similar to 930 degrees C), with formation of Ca3Co2O6 which also showed high stability in oxygen, even at 1125 degrees C. Since achievement of phase pure high density CCO by post-calcination method in air is challenging, the phase stability of CCO in oxygen is important for understanding and further improvement of the method.
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| 20. |
- Khan, Abdullah, et al.
(author)
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Fabrication, spark plasma consolidation, and thermoelectric evaluation of nanostructured CoSb3
- 2014
-
In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 612, s. 293-300
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Journal article (peer-reviewed)abstract
- Nanostructured powders of thermoelectric (TE) CoSb3 compounds were synthesized using a chemical alloying method. This method involved co-precipitation of oxalate precursors in aqueous solution with controlled pH, followed by thermochemical treatments including calcination and reduction to produce stoichiometric nanostructured CoSb3. Moreover, CoSb3 nanoparticles were consolidated by spark plasma sintering (SPS) with a very brief processing time. Very high compaction densities (>95%) were achieved and the grain growth was almost negligible during consolidation. An iterative procedure was developed to maintain pre-consolidation particle size and to compensate Sb evaporation during reduction. Significant changes in particle size and morphology were observed, and the post-reduction cooling was found to be an important stage in the process. The spark plasma sintering (SPS) parameters were optimized to minimize the grain growth while achieving sufficient densification. Grain sizes in the range of 500 nm to 1 mu m, with compaction density of 95-98% were obtained. Preliminary measurements of thermal diffusivity and conductivity showed the dependence on grain size as well as on porosity. TE transport properties were measured in the temperature range of 300-650 K. Sample showed p-type behavior with a positive Seebeck coefficient, which increases with increasing temperature. Electrical conductivity measurements indicate metallic behavior and it decreases with increasing temperature. Thermal conductivity also decreases with increasing temperature and major contribution is due to the lattice component. A TE figure of merit of 0.15 was achieved for high purity CoSb3 nanostructured TE material at 650 K and these results are comparable with the values reported for the best unfilled/undoped CoSb3 in the literature.
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| 21. |
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| 22. |
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| 23. |
- Nikkam, Nader, 1978-, et al.
(author)
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Effect of nanoparticle morphology on thermal conductivity and rheology of Zinc Oxide nanofluids
- 2012
-
Conference paper (peer-reviewed)abstract
- Nanofluids are stable dispersions of engineered nanometer-sized particles which have shown potential to enhance heat transfer properties. Nanoparticle morphology might influence the heat transport properties of the nanofluid. In this work our aim is to investigate the influence of nanoparticle morphology in the heat transfer and rheological properties of ZnO nanofluids. ZnO nanoparticles and nanorods were synthesized and dispersed in ethylene glycol, as the base fluid, to obtain nanofluids with different percentages of nanoparticle loading. Ultrasonic agitation was used for obtaining a stable suspension and the use of surfactants was avoided. The concentrations of ZnO nanofluids were varied between 1 wt% and 3 wt%. The physicochemical properties of nanofluids were characterized by using various techniques including particle size analyzer, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FT-IR). The thermal conductivity of prepared nanofluids were measured by Transient Hot Wire (THW) method and our finding on the physicochemical, transport and rheological properties of the ZnO nanofluids, containing nanoparticles with different morphology, are presented in detail.
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| 24. |
- Nikkam, Nader, et al.
(author)
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Experimental investigation on the effect of SiO2 secondary phase on thermo-physical properties of SiC nanofluids
- 2017
-
In: International Communications in Heat and Mass Transfer. - : Elsevier. - 0735-1933 .- 1879-0178. ; 87, s. 164-168
-
Journal article (peer-reviewed)abstract
- Nanofluids (NFs), wherein solid nanoparticles (NPs) are dispersed in traditional heat exchange fluids, are recognized for improving the performance of traditional fluids by enhancing their thermal conductivity (TC). The presence of impurities or undesired phases in commercial NPs may influence the thermo-physical properties of NFs including TC and viscosity, which makes it difficult to understand the real effect of NPs on heat transport characteristics of NFs. Moreover, the presence of these impurities in commercial NPs is unavoidable and their removal from commercial NPs with no negative impact on composition of NPs is challenging. To study the impact of impurities on thermo-physical properties of NFs a systematic experimental work was performed using commercial alpha-SiC and SiO2 NPs as the secondary phase as it commonly co-exists in commercial SiC batches. For this purpose, a series of NFs containing 9 wt% of alpha-SiC/SiO2 NP mixture with different content of SiO2 NPs from 5 to 50% were fabricated and investigated. The results show that as the undesired impurity phase (SiO2) increases, TC of NFs decreases slightly while viscosity increases dramatically. This may be a sound path to tuning the viscosity of the NFs while the achieved high TC is mildly influenced by the secondary phase.
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| 25. |
- Nikkam, Nader, et al.
(author)
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Experimental investigation on thermo-physical properties of copper/diethylene glycol nanofluids fabricated via microwave-assisted route
- 2014
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 65:1-2, s. 158-165
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Journal article (peer-reviewed)abstract
- This study investigates the fabrication, thermal conductivity and rheological characteristics evaluation of nanofluids consisting of copper nanoparticles in diethylene glycol base liquid. The fabricated Cu nanofluids displayed enhanced thermal conductivity over the base liquid. Copper nanoparticles were directly formed in diethylene glycol using microwave-assisted heating, which provides uniform heating of reagents and solvent, accelerating the nucleation of metal clusters, resulting in monodispersed nanostructures. Copper nanoparticles displayed an average primary particle size of 75 ± 25 nm from SEM micrographs, yet aggregated to form large spherical particles of about 300 nm. The physicochemical properties including thermal conductivity and viscosity of nanofluids were measured for the nanofluids with nanoparticle concentration between 0.4 wt% and 1.6 in the temperature range of 20-50 C. Proper theoretical correlations/models were applied to compare the experimental results with the estimated values for thermal conductivity and viscosity of nanofluids. For all cases, thermal conductivity enhancement was higher than the increase in viscosity showing the potential of nanofluids to be utilized as coolant in heat transfer applications. A thermal conductivity enhancement of ∼7.2% was obtained for nanofluids with 1.6 wt% nanoparticles while maximum increase in viscosity of ∼5.2% was observed for the same nanofluid.
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