Electrical characterization

Topic

4-point measurement of the electrical resistance.

Electrically conductive ceramic materials may contribute to innovative solutions for electrical functions under high temperatures and/or chemical aggressive environment. For a successful application, detailed information about temperature dependence of the electrical resistance, charge carrier density or Seebeck coefficient are required. Due to the characteristics of the ceramic materials, the exact measurement of these parameters is associated with numerous problems. Specific modifications of the equipment and the characterization methods are needed. Besides the electrical characterization of metals and ceramics, thermoelectric modules and heating elements can be investigated using application-oriented test equipment.

 

Measurement of the electrical resistance depending on temperature

 

The temperature-dependent measurement of the electrical resistance under controlled atmosphere of a tube furnace offers the chance to gather additional information apart from electrical conduction. Oxidation, phase transformations and mechanical cracking can be identified with outstanding sensibility. Even a quantification of these processes may be possible if the indirect information of electrical resistance can be precisely linked to the material alteration. The concept of the measurement compensates undesired influences from contacts and thermal effects.

 

Technical opportunities

 

  • Precise analysis of the electrical resistance between 10-4 and 106 Ohm
  • Variable arrangement of measurement (4 point or 2 point method)
  • Characterization under argon, nitrogen, hydrogen and air atmosphere
  • Temperature range from -170 up to 1000 °C
Combined measurement of Seebeck coefficient, electrical resistance and Hall voltage.

Combined Hall, Seebeck and resistance measurement depending on temperature

 

The electrical charge carriers significantly determine the electrical and thermoelectric properties. The analysis of electrical conductivity and Hall coefficient allows to calculate the number and mobility of free charge carriers and to identify the type of carriers. The Seebeck coefficient is essential to evaluate the thermoelectric efficiency of a material. This coefficient is indirectly associated with the charge carrier density as well. The investigation of both physical properties on a single sample is helpful to eliminate undesired effects of different samples. Accurate calculations can only be performed in this way particularly for inhomogeneous materials.

 

Technical opportunities

 

  • Measurement of Seebeck voltage (< 20 µV/K)
  • Measurement of Hall voltage and calculation of charge carrier density and carrier type
  • Measurement of electrical resistance (10-4 up to 106 W)
  • Measurement under argon or nitrogen atmosphere up to 500 °C
Test stand for characterization of thermoelectric modules.

Characterization of thermoelectric modules

 

Thermoelectric modules are the core component of a thermoelectric generator. A temperature gradient between the hot and the cold side of the module initiates the generation of an electrical voltage. The test stand defines the temperature of the hot and the cold side. The data of the no-load voltage and of the load dependent I-U performance curve can be logged for variable temperatures over long periods or for thermal cycling conditions. This allows to simulate real applications and to characterize numerous module geometries in different situations.

 

Technical opportunities

 

  • Temperatures from room temperature up to 600 °C
  • Temperature difference up to 500 K
  • Measurement under nitrogen atmosphere
  • Long-term measurements with stable or cycling thermal conditions
Test stand for heating elements up to 1600 °C.

Test stand for heating elements

 

Electrical heating elements are frequently used in industrial processes. Besides metallic elements electrical conductive ceramics play an important role in this field. Ceramic materials are advantageous particularly at high temperatures in corrosive or chemical reactive atmospheres. Materials can be investigated with regard to their process behavior using variable voltage, temperatures and different heating and cooling rates. The gathering of the electrical parameters such as power input, element temperature and time-controlled alterations of those parameters is computer-assisted.

 

Technical opportunities

 

  • Voltage up to 400 V AC
  • Electric current up to 600 A AC
  • Measurement under air, nitrogen or argon atmosphere
  • Element temperature max. 1600 °C, programmable temperature-time processes