Digitally controlled high-precision thermostat for X-ray investigations on lyotropic and thermotropic liquid crystals

The construction of a special hot air generation system for X-ray diffraction investigations of lyotropic and thermotropic mesophases at different temperatures is described. The sample is positioned at the center of the X-ray diffractometer contained in a long cylindrical capillary, and resides at a small goniometer head used to adjust the precise position and inclination of the sample. It was decided to use air as the medium and initially the medium was intended to flow axially. A stream of air is blown from a small and high rectangular opening sideways toward the sample. The gas streaming out of the vessel has to pass through a vortex cell. The air leaving the vortex cell forms a core of whirling gas with constant temperature. A temperature sensor is mounted longitudinally above the sample and is positioned inside the same airflow core. The sensor provides the input signal for a microprocessor-based controller which regulates the power of the heating or cooling system in the inlet tube providing constant temperature in the gas core.