Document BR47aKVrMGEpdOpL3V3ppQ2wm

V -/ Detection of Quartz in Talc by X-ray Diffraction Principle X-ray diffraction is a convenient method for determining the presence of crystalline impurities, such as quartz, in talc. It is necessary that at least the three strongest diffraction lines of quartz be present in the x-ray pattern to confirm the presence of quartz in the talc: 3.34^, 4 .2 6 4 , l822dA. It has been experimentally determined that compression of a talc sample containing quartz into a pellet results in an x-ray diffraction pattern having more intense quartz peaks than the pattern obtained from a packed-powder sample of the same talc. Using this pressed pellet technique, it is possible to detect the three strongest quartz peaks at a minimum level of 2% w/w. Apparatus 1. X-ray diffractometer with nickel-filtered CuK~< radiation and a suitable 1-1/4" circular sample holder for the pelletized sample. 2. Hydraulic press capable of maintaining'from 15,000-24,000 lb. (as calculated on a 3" ram). 3. 1-1/4" pellet press. Reagents 1. Boric acid Procedure 1. Sample preparation Approximately 2 gm of sample talc is transferred to the die-holder and evenly distributed on a polished, scratch free die; approximately 4 gm of boric acid is then dis. tributed on top of the talc layer. The two layers are then compressed into a pellet whose talc face is free of flaws*. .The amount of pressure necessary for a good talc face may vary from talc to talc and can only be experimentally determined. 2 . Ins trumentation The sample pellet is x-ray scanned through three critical quartz regions under instrumental condi tions which have previously been determined sensi tive to the 2% w/w quartz level. As an example, the following conditions have been employed on the Siemans Diffractometer (Model No. M386-X-A4) and Siemens Counter and Recorder (Type T ) : Radiation: Cu with K d filter at 40 KV and 24 ma * Divergence slic: 1/2 Receiving slit: 0.2 mm Goniometer speed: 1/2 20/minute Recorder speed: 600 mm/hour Attenuation = 1 x 10^ impulses/second Time constant, T [sj = 1 Rise time = 0.18 Attenuator = 20 3. X-ray Diffraction Scans The sample pellet is first scanned from 25.5-27.5 20 for the presence of a peak at 26.7(io.1)2Q. If no peak is detected, quartz is absent at the lower limit of detection. If a peak is observed in the above scan, the pellet is then scanned through the 19.5-21.5 29 region for a quartz reflection at 20.8(i0.1) 20. The absence of a peak confirms the absence of quartz at or above 2% w/w . If both peaks are observed, the sample is then scanned from 49.0-51.0 20 for the presence of a peak at 50.1(10.2) 20. The presence of all three peaks confirms that the talc contains quartz at a level equal to or greater than 2% w/w.