Search

Electrical measurement of copper connectors

Thermoelectric materials can convert heat into electricity when a temperature gradient is present. The investigation of conductive polymers such as polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) as active materials for thermoelectric generators in the room temperature range is gaining interest because of several key advantages offered by these materials. The relative ease of solution processing, their mechanical stability and flexibility together with low density and low thermal conductivity make conductive polymers suitable for integration in a thermoelectric generator. Polymers offer remarkably low thermal conductivity values but modest Seebeck coefficient and electrical conductivity. In this work, polymer/inorganic nanocomposites of PANI with carbon particles such as single wall carbon nanohorns (SWCNHs) were prepared via solution mixing of the precursors in order to increase the electrical conductivity by means of polymer matrix/nanohorn electronic junctions. The electrical conductivity and Seebeck coefficient were estimated on PANI/SWCNH films and pressed pellets and through-plane thermal conductivity was determined on films. The thermal stability of PANI/SWCNH composites was evaluated by means of TGA/DSC coupled with residual gas analysis. It was found that a proper concentration of SWCNHs in PANI-(+/-)-camphor-10-sulfonic acid (CSA) film was effective in increasing the electrical conductivity without decreasing the Seebeck coefficient.

Thermoelectric (TE) materials can convert heat into electricity when a temperature gradient is present. The investigation of conductive polymers such as polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT) as active materials for thermoelectric generators in the room temperature range is gaining interest because of several key advantages offered by these materials. The relative easiness of solution processing, their mechanical stability and flexibility together with low density and low thermal conductivity make conductive polymers suitable for integration in a thermoelectric generator. Polymers offer remarkably low thermal conductivity values but modest Seebeck coefficient and electrical conductivity. Polymer/inorganic composites of PANI were produced by adding high-conductive single wall carbon nanohorns (SWCNHs) or thermoelectric metal chalcogenides nanoparticles belonging to the tetrahedrite family Cu12Sb4S13 as fillers to improve the thermoelectric performance by means of polymer matrix/inorganic particle electronic junction. Electrical conductivity, Seebeck coefficient and thermal conductivity were estimated on PANI-based composite films and pressed pellets. The thermal stability was evaluated by means of thermogravimetric analysis/differential scanning calorimetry coupled with residual gas analysis .

Many conventional thermoelectric materials are anisotropic: the structural complexity, useful to improve the material efficiency, often leads to a strong dependence of the material properties on the different spatial direction considered. This aspect, lately subject of increasing interest, has been often neglected in the study of polycrystalline samples, because of their randomly oriented grain structure. Recently, looking for further improvements in thermoelectric efficiency, techniques for the sintering of polycrystalline samples able to preserve the natural anisotropy of the compounds have been studied and developed. The common target is to produce bulk samples easier to deal with as respect to single crystals, with improved thermal and mechanical properties, preserving the optimal electrical characteristics. In some cases, the latter depending on the crystallographic direction considered. The present work reports the results obtained for material fast sintering and texture inducing using open die pressing technique, focusing on the effects produced by the mechanical processing. The open die pressing results to be effective in the fast sintering of different classes of materials. The process is easily scalable and does not require special expensive facilities. It also induces a strong texturing effect in the polycrystalline bulks preserving the anisotropy of electrical properties. Both structural analyses and microscopy display strong orientation of the material after sintering. Here, recent results obtained on sintering SnSe and tetrahedrites powders are reported.

In this work, thermoelectric module (TEM) prototypes based on magnesium silicide and higher manganese silicide were developed (Fig. 1). Different designs of modules and different brazing materials were tested, with a focus on device feasibility and reliability. Contact resistivity measurement of the silicide/metal brazed electrode and finite element analysis of thermal induced stress were also performed, to guide the design of TE modules. The electrical power and the efficiency were evaluated with a specially developed testing system. [1] Furthermore, infrared thermography was used as a diagnostic tool to investigate internal thermal and electrical interfaces. The testing apparatus (Fig. 1) is based on the heat flow meter method at the cold side of the module and it is conceived to test TE modules (single or in cascade) with a footprint up to 60x60 mm2. The system works from room temperature up to about 900 K, under vacuum or inert atmosphere. Electrical characterizations were performed both in a steady state condition, and with fast pulsed current-voltage (I-V) measurements, thus without disturbing the measurement, providing high reliability on the efficiency determination. Measurements of commercial modules and of silicide-based module prototypes are presented.

Silicide-based thermoelectric modules (TEMs) for power generation operate at mid-high temperature range. In the operating conditions, thermal stresses in materials with different coefficient of thermal expansion may reduce the mechanical strength of the modules. In this work, a finite element (FE) evaluation of the mechanical strength of a 16 legs thermoelectric module prototype operating with 300 K temperature difference is presented.

The efficient separation of pure H2 from a gas mixture is a critical stage for large scale production of this energy carrier. H2-selective membranes represent an appealing option to recover hydrogen from low-quality gas e.g. from biomass. Protonic-ceramic have received considerable attention due to their potential application as mixed ionic-electronic conductor (MIEC) separation membranes for H2 production. In MIEC membranes, the separation and transport of H2 occurs electrochemically in the form of protons and electrons. In a non-galvanic mode, the membrane must have both high electronic and high proton conductivities [1]. Still, a stable single phase material with those properties is rather challenging. Indeed, an enhancement of proton conductivity through doping is generally related to a decrease on the electronic conductivity and on the stability of this kind of ceramics. Another strategy is to obtain the desired functional properties through composite membranes formed by two compatible ceramic phases. In this work, BaCe0.85-xZrxY0.15O3-? perovskites and doped CeO2 fluorites have been combined in different volume ratios to fabricate "ceramic-ceramic" composite membranes for H2 separation. It has been demonstrated that barium cerate-zirconate solid solutions BaCe0.85-xZrxY0.15O3-? (x: 0.20, 0.30) stabilize the perovskite structure without sacrificing protonic conductivity [2]. On the other hand, doped ceria oxides shows remarkable n-type electronic conductivity under H2 separation conditions. Furthermore, they enhance the stability against CO2 and H2O of the cerate material in the composite membranes. The optimal preparation and sintering conditions of the dense membranes have been determined through XRD and SEM techniques. OCV and a.c. impedance spectroscopy (EIS) have been carried out to study the electrochemical behaviour of the composites. In addition, the stability against CO2 and syn-gas (mandatory under operational H2 separation conditions) was evaluated by different methods. Finally, the H2-permeation of these dense membranes was measured, reaching hydrogen fluxes among the highest achieved for bulk mixed protonic-electronic membranes reported so far. References [1] T. Norby, R. Hausgrud, Nonporous Inorganic Membranes, 2006, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. [2] S. Barison Et al., J. Mater. Chem., 2010, 18, 5120- 5128.

Valutazione e confronto di tre soluzioni per il recupero di calore dai fumi di una microturbina mediante generatore termoelettrico (TEG).

Hydrogen separation from syngas at high temperatures (>=600°C) is one of the most important H2-producing technologies and it has attracted wide interest in the last decades. Mixed ionic-electronic conductor (MIEC) ceramic materials have received considerable attention due to their potential application as separation membranes in these processes [1]. In MIEC membranes, the separation and transport of H2 occurs electrochemically in the form of protons and electrons. In a non-galvanic mode, the membrane must have both electronic and proton conductivities [2]. Y-doped BaCe1-xZrxO3-? (BCZY) perovskite oxides are promising candidates for the development of such membranes because they combine the high proton conductivity of barium cerates with the chemical stability of barium zirconates in CO2-containing atmospheres, such as syn gas conditions [3]. However, the electronic conductivity exhibited by these materials may be not sufficient to work as H2 separation membranes. The performances of BCZY in this field can be improved by adding a second electronic conductor phase [2]. In the present work, symmetric dense cer-cer membranes for hydrogen separation based on BaCe0.65Zr0.20Y0.15O3-? (BCZ20Y15) and Ce0.85M0.15O2-? (M = Y and Gd, hereafter YDC15 and GDC15) were prepared. After checking the chemical compatibility between precursors, the optimal sintering conditions were individuated, obtaining dense and crack free samples with homogeneous grain distribution. The influence of different composites on electrical properties and H2 permeability performances was thoroughly studied. In particular, BCZ20Y15-YDC15 and BCZ20Y15-GDC15 membranes exhibited an improved hydrogen flow when the sweep side of the membrane was hydrated. In these conditions, the hydrogen flux of BCZ20Y15-GDC15 in the 50:50 volume ratio reached values of 0.27 mL·min-1·cm-2 at 755°C, currently one of the highest H2 flows obtained for bulk mixed protonic-electronic membranes. The stability of these materials under CO2-containing atmosphere was evaluated by thermogravimetry analyses. These composite systems showed a very good chemical stability under CO2-rich atmosphere, supporting their use for hydrogen separation membranes in practical applications. The influence of the different phenomena associated to the permeability mechanism, namely protonic transport, electronic conduction and water splitting, are still to be clarified and should be the beginning for a valuable discussion. [1] T. Norby and R. Haugsrud Dense ceramic mebranes for hydrogen separation in: A. F. Sammels and M.V. Mundschau Nonporous inorganic membranes for chemical processing Wiley-VCH Verlag GmbH & Co. KGaA (2006) 1-48. [2] J.W. Phair, S.P.S. Badwal Ionics 12 (2006) 103-115. [3] S. Barison, M. Battagliarin, T. Cavallin, L. Doubova, M. Fabrizio, C. Mortalò, S. Boldrini, L. Malavasi, R. Gerbasi Journal of Materials Chemistry 18 (2008) 5120-5128.

In this research, the effect of Sb-doping amount on Mg2Si, obtained by melting of the elements in Al2O3 crucibles was investigated. An Al-uptake originated from alumina crucibles with consequent material doping, as the reaction Mg+Al2O3->2Al+3MgO is thermodynamically favoured. The charge carrier concentration can be adjusted adding appropriate Sb amounts, leading to a reproducible synthesis of Sb:Mg2Si materials using cheap and industrial available Al2O3 crucibles. The so-obtained polycrystalline Sb-doped Mg2Si were crushed and consolidated via spark plasma sintering, obtaining dense pellets (>98%) with different amounts of Sb (0.1, 0.3, 0.5, 0.7, 1.0, 1.5 at %). The pellets were further annealed in order to prevent cracks during heating/cooling cycles. The structure and the composition of these materials are studied with powder X-ray diffraction, field-emission scanning electron microscopy coupled with electron dispersive spectroscopy. The functional properties (Seebeck coefficient, electrical resistivity and mobility and thermal conductivity) were evaluated in the RT-600°C range. The thermoelectric performance is then related to the composition of the different Sb-doped Mg2Si samples.

Mg2Si and related alloys have been considered appealing candidates as thermoelectric materials in the middle-high temperature range since their low toxicity, their low densities and the abundance of the constituent elements. In this work Mg2Si based (n-type) and higher manganese silicide (p-type) samples were tested under large temperature difference in a specifically designed test station. I-V curves and ZT direct measurement [1] were obtained in order to estimate their power density and efficiency. Results were compared with ZT values obtained by the independent measurements of ?, ? and ?. The role of the contact pressure on the thermal contact resistance was also evaluated. Furthermore, thermoelectric and thermal expansion compatibility between n- and p-type legs were investigated by means of finite element analysis and dilatometry: a unicouple device prototype based on these n- and p-type materials was produced and tested under realistic operating conditions.