Design, performance, and experiment capabilities of the AGHF: ESA's advanced gradient furnace for spacelab

Abstract

AGHF is a Bridgman Furnace Facility for directional solidification experiments in microgravity environment with very well controlled heater temperatures up to 1400°C. A laboratory model and an engineering model exist, the flight model will be built at the end of 1991. The furnace uses heater elements made of W-Re wire wound on a solid TZM heat diffuser, diffuser temperature control by Pt/PtRh thermocouples to ±0.2 K, and a water cooled cooling zone regulated by a thermostatic valve to ±0.3 K. AGHF experiments use front loaded cartridges, which can use conductive coupling to the cooling zone by a liquid metal ring or radiative cooling. The laboratory model furnace, mounted in a dedicated vacuum chamber with peripherals controlled by a commercial computer, was intensively tested up to 1400°C, as specified for the AGHF by ESA, and at 1500°C in a life test under a technology development programme of ESA. Notable laboratory model results are gradients of 95 K/cm in solid Ni of 18 mm dia, with conductive cooling zone coupling by liquid metal, and 70 K/cm with radiative cooling in ZrO 2. EM test are not yet complete, but first tests indicate similar or better results, especially of gradient constancy vs pulling stroke over 140 mm. The first heater model sustained 400 h at 1000°C, 800 h at 1300°C, and 400 h at 1500°C.