Walter Eysel

The caloric calibration of scanning calorimeters

Abstract The present recommendation of the GEFTA working group “Calibration of Scanning Calorimeters” allows a precise heat and heat flow rate calibration of scanning calorimeters, largely independent of instrumental, sample-related and experimental parameters. Electric energy, electric power, heats of transition and heat capacities of suitable calibration substances are used for calibration. The measuring method, measuring and evaluation procedure, calibration materials, significant influencing factors, sources of error and detailed examples are presented for these calibration methods. Besides specific problems of heat measurement (interpolation of the baseline for the peak area determination) and heat capacity measurement (interpolation between initial and final isotherms, determination of the true heating rate of the sample, thermal lag of the sample), general aspects (thermodynamic fundamentals, difference between heat and heat flow rate calibration factor, weighing procedure) are also discussed.

The temperature calibration of scanning calorimeters: Part 2. Calibration substances

The recommendation for temperature calibration consists of two parts. Part 1 (see section 2.3) presented a correct method for the calibration of scanning calorimeters (DSC) and of instruments for differential thermal analysis (DTA), irrespective of the instrument type. The present paper recommends calibration substances for the range 120-1350 K. Sections 2 and 3 indicate the documents to be taken into account and define the most important terms used. Section 4 consists of general requirements to be met by the calibration substances, a list of the substances and explanations with respect to their use. Basically, such materials have been selected as calibration substances which define fixed points of the International Temperature Scale of 1990 (ITS-go). Added to these are fixed point materials from the previously valid International Practical Temperature Scale of 1968 (IPTS-68, see References in Table 1). Moreover, two substances are recommended for temperature ranges for which no suitable fixed point material exists, and the respective uncertainty of measurement is stated.

Temperature, heat and heat flow rate calibration of scanning calorimeters in the cooling mode

Abstract The current publication continues the series of recommendations of the ‘Calibration’ Working Group of the German Society for Thermal Analysis (GEFTA) for temperature, heat and heat flow rate calibration of scanning calorimeters. It deals with calibration in the cooling mode. The procedures to be applied are essentially identical to those applied in the heating mode. Due to the general occurrence of supercooling for first-order phase transitions during cooling, liquid crystals and substances with higher-order phase transitions are recommended for temperature calibration. Substances with weak supercooling or substances for which the temperature dependence of the transformation enthalpy is known are recommended for heat calibration. The thermodynamic fundamentals relevant to the temperature dependence of phase transition enthalpies and phase transition temperatures are discussed. Detailed examples make it easy to follow the recommendations.

Na2CrO4 (I) solid solutions: crystal chemistry, defects and ionic conductivity

Abstract In the system Na2CrO4-CaCrO4 a field of solid solutions Na2-x+Cax2+□x CrO4 was found extending up to 40% CaCrO4, i.e. 20% cation vacancies (□). These defects are the reason for a remarkable ionic conductivity with a maximum of σ = 10−1 (Ω.cm)−1 at 7.5% □ and at 500°C. In the chromate and the corresponding selenate system four new phases were found: Na6Ca (CrO4)4 , Na4Ca(CrO4)3, Na4Ca(SeO4)3 and high-CaSeO4.