Tips & Tricks
Crucibles and their selection
Crucibles and their lids are made of materials resistant to high temperatures, usually porcelain or an inert metal.
Ceramics such as alumina, zirconia, and especially magnesia will tolerate the highest temperatures. One of the first metals used in crucible production was platinum; more recently, metals such as nickel and zirconium have also been used. The type of crucible used for thermoanalytical measurements can have a strong influence on the measurement results obtained. Additionally, the crucible can also influence the characteristics of the instrument’s measuring cell.
The measurements shown here on indium in Al, Pt, stainless steel and Al2O3 crucibles clearly demonstrate that both the Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity and the mass of the crucible have an effect on the DSC and DTA peak shape.
The calibration procedures take these effects into consideration and eliminate the influence of the crucible material on the measurement results.
Important Factors for Selection of Suitable DSC, TGA and STA Crucibles for Your Sample
The DSC crucible should have a flat bottom and be made of a material with a high Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity. This guarantees optimum heat transfer and low temperature gradients between the sample, crucible and sensor.
The crucible should be made of an inert material in order to prevent reactions with the sample in the programmed temperature range. Exceptions are crucibles for which a catalytic effect on the sample is desired (e.g., copper crucible for Oxidative-Induction Time (OIT) and Oxidative-Onset Temperature (OOT)Oxidative Induction Time (isothermal OIT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition. Oxidative-Induction Temperature (dynamic OIT) or Oxidative-Onset Temperature (OOT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition.OIT tests, etc.).
The crucible should not exhibit anyphase transitions or other effects in the programmed temperature range; the Melting Temperatures and EnthalpiesThe enthalpy of fusion of a substance, also known as latent heat, is a measure of the energy input, typically heat, which is necessary to convert a substance from solid to liquid state. The melting point of a substance is the temperature at which it changes state from solid (crystalline) to liquid (isotropic melt).melting point or fusion temperature must exceed the maximum application temperature to a sufficient degree.
The dimension, shape and specific heat of the crucible should be optimized to achieve and/or maintain the highest caloric sensitivity and lowest time constant for the measuring system. Optimized parameters will result in sharp, well-defined and clearly separated peaks.
Crucibles should be reusable, especially special ones for specific applications.