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Photopiroelectric calorimetry

Researchers: Dorin Nicolae Dădârlat, Carmen Tripon

Keywords: photopyroelectric technique, thermal parameters, specific heat, thermal conductivity, diffusivity, effusivity, phase transitions

Description

Photopyroelectric calorimetry is a highly accurate technique which provides a complete thermal characterization (determination of all thermal parameters) of any chemically non-aggressive material in condensed phase (solid or liquid).

The technique can also be used in the study of physical and chemical processes associated with the variation of thermal parameters, as a function of composition, temperature or time.

 Applications

Areas of application: thermal characterization of materials

  • characterization of thermal parameters for materials of practical interest: conductors, insulators, semiconductors, magnets, ferroelectrics, thermoelectrics
  • study of type I phase transitions: melting, solidification
  • study of type II phase transitions: magnetic and ferroelectric transitions, with calculation of critical exponents, establishing the optical absorption bands of visible and IR absorbing layers.

Systems: which can be themally characterized: liquids or liquid mixtures, nanofluids, semi-liquid materials, solids with various properties (thermal and electrical insulators or conductors, magnetic materials, ferroelectric materials, thermoelectrics, high critical temperature superconductors, semiconductors, etc.), foodstuffs (juices, oils, butter, cheese, margarine), composite materials (oxidic glasses, porous building materials).

Industries: 

  • Food industry: study of the quality, aging and counterfeiting of some food products (oils, margarines, juices, cheese).
  • Building materials industry: characterization of thermal parameters (specific heat, conductivity, diffusivity and thermal effusivity)
  • Dentistry: establish the thermal biocompatibility of dental materials of various types

 Infrastructure

In INCDTIM there are 3 photopyroelectric calorimetry lines composed of:

  • Radiation sources: YAG lasers (600 mW), HeNe (30 mW); electromechanical and optoacoustic light modulators; lock-in nanovoltmeters (Stanford SR830) for signal processing
  • Optomechanics: lenses, mirrors, visible and IR transparent windows, micrometer tables with 3- and 6-axis control respectively, picomotors (30 nm step)
  • Radiation sensors: LiTaO3, PZT, PVDF, HgCdTe, InSb
  • Detection cells with temperature monitoring, consisting of Peltier elements, programmable voltage source, electronic thermometer, thermostatic bath
  • IT facilities: computer, programs for data acquisition and processing

The main performances of the existing equipment are:

  • pyroelectric sensor detectivity greater than 100 cm∙Hz1/2/W
  • minimum detectable temperature variation: 1 μK
  • minimum controllable temperature rate: 100 mK
  • temperature range: -20°C÷100°C
  • signal to noise ratio >100

Duration of an investigation varies from several minutes up to several hours (in case of temperature dependencies).

Advantages

 High accuracy: 98% for thermal diffusivity measurement and 95% for thermal effusivity.

 Very small sample quantity required: 0.2÷0.3 ml for liquids and a few mg for solids.

 Measurements do not require prior chemical processing of the sample

 It is the only calorimetry technique that allows, under certain conditions, the determination of all static and dynamic thermal parameters in a single measurement.

Estimated costs

The cost of a themal characterization is 250 lei/sample and consists of:

 time of use of the equipment

 workmanship, which includes personnel and indirect costs associated with sample preparation, analysis and interpretation of results, editing of the analysis/research report.