GRAINLESS MEDIA FOR IMAGE REGISTRATION 



Fig. 21. Iron-rich spot in a firebrick derived 

 from impurity in original clay. The iron oxide has 

 melted during firing and reacted with the firebrick 

 giving a silicate inclusion. This is not as detri- 

 mental as iron oxide itself since in the latter case 

 the deposition of carbon from furnace gases may 

 be catalysed. Microradiograph. Cobalt radiation. 

 X25 



deposition which occurs when firebricks are 

 used for blast furnace linings. Microscopical 

 work on these materials is difficult due to 

 the fine grain size and the optical properties 

 of the altered products. 



REFERENCES 



1. GoLY, p., Compt. Rend., 156, 686 (1913). 



2. KiRCHBERG, H. AND MoLLER, H., Mitt. Kaiser 



Wilhelm Inst, fur Eisenforschung, 23 (part 

 17), 309-314 (1941). 



3. Cohen, E. and Schloegl, I., To be published 



in proceedings of the second international 

 conference on X-ray microscopy and micro- 

 radiography held in Stockholm (1959). 



4. Jackson, C. K., pp. 623-627 of "X-ray Mi- 



croscopy and Microradiography," (1957), 

 Academic Press, New York. (Edited by 

 V. E. Cosslett, A. Engstrom and H. H. 

 Pattee, Jr.). 



5. Niskanen, E., Norelco Reporter, VI, No. 3, 



p. 70 (1959). 



6. Cohen, E., Metallurgia, 41, 227-233 (1950). 



7. McBriar, E. Maud, Johnson, W., Andrews, 



K. W., AND Da VIES, W., /. Iron Steel Inst., 

 177, 316 (1954). 



8. Johnson W. and Andrews, K. W., Iron and 



S^eeZ, 31, 437-444 (1958). 



9. Cohen, E., J. Iron and Steel Inst., 175, 160-166 



(1953). 



10. CocKBAiN, A. G. AND JoHNSON, W., Traus. 



Brit. Ceram. Sac, 57, No. 8, 511-526 (1958). 



11. Trillat, J. J., Compt. Rend., 214, 164-166 



(1942). 



12. PosPisiL, R., Hutnike Listy, 1 (9), 193-197 



(1947). 



W. Johnson 



GRAINLESS MEDIA FOR IMAGE 

 REGISTRATION (See also p. 564) 



It was inevitable that attempts should be 

 made in microradiography and historadiog- 

 raphy to avoid the limitations imposed in 

 enlargments of contact images by graininess 

 of photographic emulsions. The solution of 

 this problem has taken two courses, with 

 very successful results. From among various 

 x-ray-sensitive substances which will show 

 no structure even in electron microscope 

 ranges of enlargement, Ladd, Hess and Ladd 

 (1) found that faces of ammonium dichro- 

 mate crystals, and some polymers such as 

 pol3^inyl films were most useful. In both 

 cases the solubility of the medium changes 

 in proportion to the amount of exposure to 

 the x-ray beam, with the result that the 

 microradiographic image can be etched into 

 a relief by suitable solvents. Anhydrous al- 

 cohols are used for developing the image on 

 the dichromate crystals, and a 30 % solution 

 of acetone in water the image on the plastic 

 sheets, in which cross-hnking between 

 polymer molecules has resulted from absorp- 

 tion. A cast, thin enough to permit the pas- 

 sage of an electron beam is then made of the 

 relief surface with silicon monoxide, carbon 

 or other materials generally used for making 

 rephcas for electron microscopy. This replica 

 is shadow-cast with metal vapors directed 

 at an angle to the surface and then examined 

 in the electron microscope up to 200,000 

 diameters magnification. 



581 



