ASTM D4715 Test Method for Coking Value of Tar and Pitch (Alcan)
7. Bulk Sampling
7.1 Samples from shipments shall be taken in accordance with Practice D4296, and shall be free of foreign substances. Thoroughly mix the sample immediately before removing a representative portion for the determination or for dehydration.
8. Dehydration of Sample
8.1 Hard Pitch - If the solid bulk sample contains free water, air-dry a representative portion.
8.2 Soft Pitch - If the presence of water is indicated by surface foam on heating, maintain a representative portion of the bulk sample at a temperature between 125 and 150°C in an open container until the surface is free from foam. Take care not to overheat, and remove heat source immediately when foam subsides.
8.3 Tar - Dehydrate a representative portion of the bulk sample at atmospheric pressure using a simple side-arm distillation apparatus similar to the one in Test Method D850 and stop the distillation when the temperature reaches 170°C. Separate any oil from the water that has distilled over (if crystals are present, warm sufficiently to ensure their solution), and thoroughly mix the oil with the residual tar in the still after the latter has cooled to a moderate temperature.
9. Preparation of Working Specimen
9.1 Hard Pitch - If the pitch can be crushed at room temperature, prepare a 20 more or less 1 g working specimen by suitable crushing, mixing, and quartering of a representative portion of the dry specimen. The crushing can be performed with a small jaw crusher and a mortar and pestle. No particle in the representative specimen should be larger than 5 mm in any dimension. Crush this specimen so that it will pass a 300 µm (U.S. Standard No. 50) mesh sieve. If the ambient temperature is high, the operation can be facilitated by chilling the sample beforehand.
9.2 Soft Pitch and Tar - For soft pitch and tar samples, melt the sample and take a sufficient amount of the molten mass for the test. The melting temperature must not exceed 150°C and the melting period not longer than 10 min. It is also possible to transfer the required portion of a soft pitch directly to the porcelain crucible, without preliminary treatment.
9.3 Preservation of Samples - Store samples as large lumps or as solidified melts in closed containers. Discard working samples 24 h after crushing and sieving as changes in composition sometimes occur in pulverized pitch.
