X-RAY MICROSCOPY 



Fig. 11. Microradiograph on gold ore tailings 

 showing three types of particles — those unat- 

 tached to any gangue, those attached to quartz 

 gangue which could be further separated and a 

 very fine dissemination in pyrite which is beyond 

 the possibilities of physical separation. X75 



Fig. 12. Sintered iron ore. Heterogeneous 

 structure of granular oxides (Fe304), holes and 

 slag pools containing dendrites. Microradiograph 

 Ni radiation. X18 



whereas the predominant oxide is usually 

 Fe304 in a properly sintered ore. In order to 

 carry out x-ray diffraction on a thin section, 

 the use of any supporting material is very 

 undesirable due to absorption, and speci- 

 mens are usually impregnated with balsam 



or cold-setting plastic to give mechanical 

 strength. If, however, radiographs only are 

 required, it is quite permissible to prepare 

 the section on a microscope cover slide and 

 take the radiographs with the specimen still 

 mounted on it. 



Figs. 14 and 15 show further radiographs 

 on sintered iron ore where the conditions of 

 operation have been altered to find the op- 

 timum conditions for sintering. This particu- 

 lar sinter contained a 20% addition of flue 

 dust which provided sufficient extra heat to 

 give a general coarsening of the texture and 

 large scale solution of iron as evidenced by 

 the secondary dendrites and skeletal crystals 

 of magnetite. The marginal break-up and 

 recrystallization of large ore lumps also 

 show the characteristic "shaded" cracks 

 which are always found to precede the final 

 break-up and recrystallization. 



The examination of used steel plant re- 

 fractories by microscopic methods presents 

 difficulties due to the opaque nature of the 

 parts where iron oxide has been heavily ab- 

 sorbed. Reflected light techniqvies are pos- 

 sible, particularly with diamond polished 

 specimens, but even here the friable nature 

 of the material makes the interpretation of 



Fig. 13. Structure of dendrites of FeO in slag 

 pool of Fig. 12. Microradiograph Ni radiation. 

 X180 



578 



