ASTM D5187 Standard Test Method for Determination of Crystallite Size (Lc) of Calcined Petroleum Coke by X-Ray Diffraction
8. Sample Preparation
8.1 For recommended practices for obtaining, handling and preparing coke samples, refer to Test Methods D2013 and D2234 and Practices D346 and D4057. The equipment and procedures for crushing and dividing are also described in these test methods.
8.2 Reduce and divide the gross sample to obtain a laboratory analysis sample.
8.3 Divide, by riffling, a minimum of 100 g from the laboratory analysis sample.
8.4 Crush 100 g of the test sample such that 98 % will pass through a 75 µm (No. 200) sieve.
8.5 Techniques - Any of the following techniques can be used for packing the sample into the X-ray diffractometer specimen holder:
8.5.1 Back Fill Technique - Put the window on a glass slide (Slide 1) and transfer sufficient quantities of sample into the window. Work the sample towards the corners of the holder by use of a glass slide or spatula. Press down using a flat glass slide and scrape off any excess material. Place a glass slide (Slide 2) on top of the sample and secure with tape. Remove Slide 1 to expose a flat, smooth surface before inserting into the diffractometer for analysis.
8.5.2 Front Fill Technique - Place a confining ring over the round sample holder and fill the holder cavity and ring with sample. The ring will initially overfill the sample holder. Work the sample into the entire cavity and ring. Scrape the excess off with a glass plate or spatula. Press down using a flat glass slide. Remove any excess material on the front face of the holder. Repress the sample with the glass slide while turning clockwise and anti-clockwise. Continue until the sample is level with the holder face. Place the sample in diffractometer holder.
8.5.3 Side Loading Technique - Pack the sample following the procedure used by the National Institute of Standards and Technology and the Joint Committee on Powder Diffraction Standards to prepare standard powder diffraction patterns. Clamp a glass slide over the top face to form a temporary cavity wall. With the holder in a vertical position, drift the powdered sample into the end opening. If necessary, use a cardboard pusher cut to fit the cavity to lightly compress the sample so it will remain in the cavity. Return the holder to a horizontal position and carefully remove the glass slide. Place the sample in diffractometer holder.
8.5.4 Briquetting Technique - Weigh out 4.0 g of the sample onto a watch glass and pipette exactly 3 mL of the binding agent onto the sample and mix thoroughly with a spatula. Place the sample under an infrared heat lamp and allow the acetone to evaporate. Typically, about 1 or 2 min will be required to eliminate the acetone odor from sample. Break up the caked sample with a spatula and transfer to an aluminum cap whose diameter is compatible with the sample holder of the diffractometer. Place the cap in a briquetting press and press at 7000 psi (48 MPa). Transfer the pelletized sample to the sample holder and insert into the diffractometer for analysis.
9. Calibration
9.1 Calibration consists of ensuring that the diffractometer is in correct mechanical and optical alignment and intensities have been maximized through the procedures described in the instrument manufacturer's documentation. This is best accomplished by a service engineer or in-house technician who has been well instructed in the correct alignment procedures suggested by the manufacturer.
9.2 Proper angles and intensities are monitored by a reference material such as NIST silicon and corrective actions taken if necessary.
