Thermophysical Property Measurements

Reliable thermophysical property data are an absolute prerequisite to developing computational simulations of modern metal casting processes. The Materials Processing Center has invested in commercial thermophysical property measurement instruments to evaluate many such data of commercial foundry alloys. In addition, the Center has developed a number of techniques that provide accurate data for which commercial instruments are not available. Thermophysical property measurement technology remains an area of active research within the Center. Research collaborations over the years with leading commercial measurement laboratories (Thermophysical Properties Research Laboratory, Inc, W. Lafayette, IN and Anter Laboratories, Pittsburgh, PA) and NIST (Gaithersburg, MD) help ensure the integrity of the measurement techniques and the thermophysical property databases.

Thermal diffusivity/conductivity

Measurements of the thermal diffusivity of solid and molten metals are performed using the flash diffusivity technique. In this technique, a fast pulse of energy is applied to one side of a thin sample and the temperature on the opposite (back) side monitored. The rate of increase in temperature on the back side can be correlated with the thermal diffusivity of the material. The thermal conductivity can then be evaluated if the density and the specific heat of the material are also known. Auburn University uses an Anter Flashline 5000 Thermal Diffusivity Instrument.

 

 

 

 

 

 

Specific and latent heats

The specific and latent heats of solid and molten materials are characterized by differential scanning calorimetry where the temperature increase/decrease of unknown samples are compared against standard materials subjected to similar power inputs. Auburn University uses a Rheometrics Scientific STA 1500 DSC/DTA/TGA instrument.

 

 

 

 

 

 

Thermal Expansion and Density

The thermal expansion of solid samples is measured by a contact dilatometer and directly compared against a standard reference material subjected to the same thermal conditions. The density is evaluated at room temperature by the Archimedian technique and then calculated over the range of temperatures for which the thermal expansion has been measured. Auburn University uses an Anter Unitherm 1161 High Temperature dilatometer. The thermal expansion upon melting and subsequent heating of liquid alloys is characterized by custom non-contact laser-based dilatometer scanning the surface of the molten pool.

 

 

 

 

 

 

Viscosity

The viscosity of molten alloys is measured by the oscillating vessel technique at Auburn University using a custom device. In this technique, torsional oscillations are induced in a torsional spring system containing a crucible with a known quantity of molten metal. The rate of decay of the oscillations is directly related to the viscosity of the molten metal.

 

 

 

 

 

 

 

Electrical Resistivity

The electrical resistivity of metals (molten or solid) is measured by the magnetic induction technique. In this approach, a crucible of metal is rotated in a DC magnetic field. The sample rotation induces eddy currents in the sample that create a retarding torque against the applied rotation. The magnitude of the torque is correlated with the electrical resistivity of the metal.

 

 

 

 

 

 

 

 

 

Surface Tension

The surface tension of molten metals is measured by the oscillating droplet technique. Small (~3 mm dia) samples of metal are levitated and melted in a precise electromagnetic coil and the natural oscillations of the molten droplet determined by a photodetector. The surface tension can be evaluated from the droplet's natural frequency of oscillation.

 

 

 

 

 

 

Emissivity - A comparative technique is currently under development at Auburn University which has potential for measurements on solids and liquid metals.