HIGH-TEMPERATURE (323-1323 K) FURNACE DESIGN FOR A TRANSMISSION POWDER DIFFRACTOMETER

The design of a vertical-tube furnace for use with a transmission-mode X-ray powder diffractometer is discussed in detail. The X-ray beam pa sses through a 3 mm slit cut perpendicular to the furnace-tube axis. T wo Pt-Pt/10%Rh thermocouples are located within the pyrophyllite furna ce-tube wall at the top and bottom of the 3 mm slit. The potential dif ference between these thermocouples is used to adjust the power suppli ed to the upper and lower halves of the furnace. By selecting the desi red potential difference at each measuring temperature, gradients from 0 to 1 K across the 3 mm slit can be easily achieved over the entire temperature range of the furnace (i.e. 323 to 1323 K). The furnace is housed in a cooling jacket that can be adjusted vertically to optimize the diffraction geometry. Samples are loaded in capillaries of 0.3 mm outer diameter, mounted on a rotating goniometer head, and centred ho rizontally and vertically. This sample geometry yields very low sample -position errors. The design also allows 180-degrees coverage in 2thet a and variable sample environments (i.e. flowing gas, air and vacuum).