Low Gradient Furnace

Low Gradient Furnace (LGF)
This is the first European furnace insert for MSL. It is developed to conduct experiments in the field of Bridgman crystal growth. The LGF consists of two heated cavities separated by an insulating, “adiabatic” zone. It can establish restricted, but well-controlled gradients between two stable temperature plateaux. Crystal growth is performed by translating the furnace over a stationary sample. Thermomechanical stresses in the grown crystal are minimised by keeping the solidified part of the sample in the heated cavity throughout processing. This insert can also be used for thermo-diffusion experiments, maintaining the furnace stationary, and using only the temperature gradient capability. Isothermal experiments can also be carried out utilising suitable sample/cartridge configurations.

LGF performance characteristics
The LGF consists of seven separately controlled heating zones. The heater elements are based on pyrolytic boron-nitride/pyrolitic graphite heater technology, with carbon composite diffusers to provide thermal uniformity. The LGF provides high-stability thermal control by sapphire optical fibre thermometers (OFT) and a high performance control algorithm. The achievable temperature gradients depend on cartridge design and on the sample’s thermal conductivity. An electromagnet provides for controlled stirring of the melt by a rotating magnetic field.

LGF technical data:

Geometry:

Furnace bore diameter 30 mm

Hot cavity length 200 mm

Adiabatic zone length 50 mm

Cold cavity length 120 mm

Cartridge diameter £ 28 mm

Processing stroke 150 mm

Thermal performance:

Max temperature hot cavity 1873 K

Max temperature cold cavity 1750 K

Thermal stability ± 0.02 K
(above 1073 K)

Temperature gradients £ 50 K/cm
(for thermal conductivity < 30 W/mK)

Circumferential thermal unifomity £ 0.5 K

Magnetic field generation:

Field strength 0–5 mT
(perpendicular to sample axis)

Frequencies 0 and 5–400 Hz

Festkörperphysik