OPTICAL MINERALOGY 



tioned by microtomy may sometimes be and Wolff (9) describe the use of thin sec- 

 ground suitably by substitution of a gradu- tions in the study of the degeneration of 

 ated series of garnet and emery papers for alumina-silica firebrick during use in the 

 the usual lubricated, powdered abrasives, thermal cracking of natural gas to hydrogen 

 The use of a low curing temperature and a and carbon. Free and combined silica in the 

 somewhat viscous cementing agent will bricks were being reduced to volatile silicon 

 minimize solution of the specimen. For in- monoxide, leaving corundum as a granular 

 stance, a liquid epoxy resin, such as Shell residue. Changes in the pattern of the attack 

 "Epon" 815 with a room-temperature curing from level to level in the checkerwork as re- 

 agent such as diethylenetriamine , may be vealed by thin sections indicated carbon, 

 used for the embedding and cementing at rather than hydrogen or carbon monoxide, 

 room temperature of materials such as urea to be the principal reducing agent, 

 and Bisphenol A which would readily dis- Other typical industrial applications of 

 solve in and react with the resin at higher thin section microscopy, taken from actual 

 temperatures. Some compromise with desired experience, are described briefly below, 

 refractive index and penetration of the spec- Catalyst Degradation Studies. A clay- 

 imen may be involved. bonded, diatomaceous catalyst carrier was 



The petrographer's use of the standard subjected to a corrosive environment in 

 thickness of .02-.03 mm for his thin sections which blackening of the pellets, due to ear- 

 not only insures adeciuate transparency for bonization of organic reactants, and eventual 

 most nonopaque rock specimens but is also disintegration of the pellets took place. Ex- 

 indispensable to his direct identification of amination of the used pellets in thin section 

 mineral species in the section (1). In many revealed distinguishable crystalline species, 

 industrial studies, particularly those in resulting from attack of the clay binder, 

 which the species are identified or charac- which w^ere not present in the virgin catalyst, 

 terized through microscopy of separate, pow- The species were either identified or charac- 

 dered portions of the specimen or those in terized by microscopic examination of the 

 which only the structure of the sample is of powdered, used catalyst and further details 

 interest, the thickness of the section is not concerning the degradation were developed 

 critical and may be dictated only by the through systematic study of thin sections of 

 transparency of the material and the diame- pellets taken from selected locations in the 

 ter of the smallest feature which is of inter- catalyst bed. Clusters of carbon were defi- 

 est. In some cases the section may be 0.25 nitely associated with an iron-containing 

 mm or more in thickness. On the other hand, crystalline species and the disintegration of 

 for semi-opaque materials such as cements the pellets was tentatively tied to the ob- 

 (4) and filled plastics (5, 6) the section must served disparity between the large diame- 

 be as thin as .01-.015 mm; in such cases the ters of the clusters of new crystals and the 

 microscopist may elect to use, w^here applica- smaller diameters of the skeletal pores, 

 ble, the metallographer's polished sections Deposition of Silica Gel on Catalyst 

 or, for soft materials, the petrographer's Carrier. Attempts to deposit a uniform coat- 

 "peels" (7). ing of silica gel on the component particles 



The ceramics and refractories industries of a catalyst carrier consisting of bonded 



have probably drawn more heavily than quartz fragments yielded a product which 



other industiies upon petrographic thin sec- did not have the desired surface properties, 



tions in their microscopic studies. Tj^pical Examination of thin sections of these grains 



applications are illustrated by Insley and revealed that the deposited silica gel was 



Frechette (4) and by Norton (8). Wright merely plugging the large external pores of 



474 



