• REFERENTS:
  ALESSANDRO BENEDETTI
  LIBERO LIGGIERI
  MICHELE FERRARI
  

• UNIT:
  GENOA
  

CNR-ICMATE Marine Experimental Station, 'Mareco', Bonassola (SP) - Italy

• REFERENTS:
  STEFANO BOLDRINI
  

• UNIT:
  PADUA
  

We can perform electrical characterizations of different nature, mainly of materials having ionic conductivity and of thermoelectric materials, as well as of devices based on these materials. For the materials having ionic conduction, such as those used for fuel cells or ceramic membranes for the separation of gas, we typically use Impedance Spectroscopy and IV curves to study electrolytes or cells/half-cells mounted in a test rig that allows to control the temperature (up to 1100 °C ). A proper power supply line equipped with mass -flow controllers and humidifiers allows controlling the atmosphere (oxidizing or reducing in the case of cell testing) used for the measurements. The measurements are performed typically with a Potentiostat/galvanostat.

The functional characterization of thermoelectric materials is performed by measuring the thermal conductivity (Laser Flash Thermal Diffusivity) and their electrical properties, electrical conductivity and the thermoelectric power, or Seebeck coefficient. The electrical properties are measured with a device specially designed and built in our laboratories that allows the simultaneous determination of both quantities. The measurement, typically carried out in an inert atmosphere, can be performed up to high temperature (800 °C). The electrical conductivity measurements are performed by means of an instrumental configuration with four wires using a generator coupled to a Keithley 6221 Nanovoltmeter 2182, which is used also to measure Seebeck coefficient. The apparatus and the measurement procedure is controlled via LabView through a CompactRIO platform.

Other test stations have been developed to measure contact resistance and to test thermoelectric modules. In the first a tungsten carbide microprobe (controlled with micrometric movement and stereoscopic microscope), measures the resistance in 4-wire configuration to vary the position of the probe, allowing for example the determination of the contact resistance between the thermoelectric material and an electrode. The test station for thermoelectric modules allows measuring the electrical properties (electrical power), and thermal (heat flux through the module) of devices subjected to a temperature gradient, allowing the determination of their thermoelectric conversion efficiency. The modules, with 60 mm side maximum dimension, are placed between a heater, which allows to reach 600 °C, and a water-cooled cold side. The mechanical pressure exerted on the module is controlled with suitable load cells. An array of thermocouples on the column is used to measure the heat flow. The whole apparatus is placed in a vacuum chamber that allows carrying out tests in vacuum or inert atmosphere. A window, transparent in infrared region, allows monitoring the measures through thermography.
We can also perform a series of other electrical measurements, such as 4 probe method, with Van der Pauw technique, measurements of dielectric constant, determination of the carriers by means of Hall measurements, etc.

• REFERENTS:
  GIOVANNA CANU
  MARIA TERESA BUSCAGLIA
  VINCENZO BUSCAGLIA
  

• UNIT:
  GENOA
  

Analysis of powder materials for what concerns the density, the specific surface area, the open porosity in the range from 1 to 1000 nm, the determination of decomposition, phase transition and reaction temperatures by TG-DTA in controlled atmosphere, the densification by dilatometry (TMA). Acquisition and analysis of powder X-ray diffraction data. Particle size analysis by dynamic light-scattering (DLS) and Zeta potential measurement. Impedance spectroscopy in 10μHz to 32MHz frequency range and RT-200 °C temperature range.

• REFERENTS:
  STEFANO BOLDRINI
  FILIPPO AGRESTI
  

• UNIT:
  PADUA
  

The laser flash method allows to measure the thermal diffusivity (a) of a material as solid or liquid. A laser pulse (Nd: Glass) heat the flat surface of the sample. The heat propagates along its thickness with a consequent increase of the temperature to the opposite surface. The higher the thermal diffusivity of the sample, the faster the energy reaches the backside. An infrared detector (InSb) records changes in the temperature as a function of time. On the performance of the temperature profile is obtained the value of thermal diffusivity. The specific heat (Cp) of a sample can be derived through comparatives calculation methods if the measurement is recorded simultaneously with a standard of known Cp. From the relation λ = a * Cp * ρ we can obtain thermal conductivity λ, if known the density ρ of the sample.
The system may contain solid samples of various sizes (discs of 1 or ½ inch in diameter or 10 mm in diameter or square by 10 mm side).
The temperature range is from room temperature up to 1100 ° C with the possibility to work also in an inert atmosphere or in vacuum.
For a more precise determination of the thermal diffusivity of liquids, a photoacoustic device has been designed and realized. This system allows measurements up to 75 ° C and turns out to be more sensitive compared to more traditional techniques. In fact, the measure of the thermal diffusivity is not related to the absolute measurement of the thickness of the liquid, but depends on its variation during the measurement. The detector is a photoacoustic chamber to which a high-sensitivity microphone is connected.