APPLICATION OF THE EBSD TECHNIQUE FOR INVESTIGATIONS INTO MICROSTRUCTURE OF Pt-Rh ALLOY THIN WIRES USED FOR GAUZES IN CATALYTIC AMMONIA OXIDATION PROCESS

摘要

The work covered investigations into microstructure of wires made of Pt-Rh alloys and Pt-Rh alloys modified with microaddition of boron and addition of yttrium as well as determination of correlation between crystallographic orientation and susceptibility to selective catalytic pickling of grain surfaces. It is very difficult to investigate both texture and grains orientation on surface of wires of diameter about 0.060 mm when using traditional X-ray methods, but it can be possible by Electron Backscatter Diffraction (EBSD) techniquee. Topography of the surface and analysis of crystallographic orientation of individual grains on the surface of wires made of PtRh8 alloy have shown that during their operation in industrial installation a selective pickling of surface takes place which leads to exposing of crystallographic planes {111}. The results of investigations indicate that because of the rate of catalytic pickling of the wire surface the more advantageous is a structure of large grains with small grain surface energy, and consequently with small disorientation and of parallel, or almost parallel crystallographic planes {111} to the surface of the wire. It was established that formation of such a microstructure becomes facilitated by introduction of microadditives such as boron or yttrium into the alloy.