ASTM D2764 Standard Test Method for Dimethylformamide-Insoluble (DMF-I) Content of Tar and Pitch
7. Hazards
7.1 Fumes of the solvents should be removed by means of proper hoods from all working areas. The working area should be kept free of sparks and flames. DMF fumes should not be inhaled, and prolonged contact of DMF with the skin should be avoided.
7.2 Observe proper laboratory procedures for handling and diluting hydrochloric acid.
8. Bulk Sampling
8.1 Samples from shipments shall be taken in accordance with Practice D4296 and shall be free of foreign substances. The sample shall be thoroughly mixed immediately before removing a representative portion for the determination or for dehydration.
9. Dehydration of Sample
9.1 Hard Pitch - If the solid bulk sample contains free water, air-dry a representative portion in a forced draft oven at 50 °C.
9.2 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 257 °F and 302 °F (125 °C and 150 °C) in an open container until the surface is free offoam. Take care not to overheat, and remove heat source immediately when foam subsides.
9.3 Tar - Dehydrate a representative portion of the bulk sample in accordance with Test Method D370, but stop the distillation when the temperature reaches 338 °F (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.
10. Preparation of Working Sample
10.1 Hard Pitch - If the pitch can be crushed at room temperature, prepare a 20 g working sample by suitable crushing, mixing, and quartering of a representative portion of the dry sample. The crushing can be done with a small jaw crusher and a mullite mortar and pestle. No particle in the representative sample shall be larger than 5 mm in any dimension. Crush this sample so that all of it will pass the 250 µm (No. 60) sieve but have a minimum of fine particles. Store the sieved working sample in a tightly closed container and use within 24 h (see 10.4).
10.2 Soft Pitch - If the pitch is too soft to grind and too sticky to mix, heat a representative portion ofthe dry sample to the lowest temperature that will permit passage through the 600 µm (No. 30) sieve, taking care to avoid excessive loss of volatile matter. Do not exceed 10 min for this melting period. Pass the heated sample through the 600 µm sieve to remove foreign matter.
10.3 Tar - Heat a representative portion of the dry tar to the lowest temperature that will permit passage through the 600 µm (No. 30) sieve, then filter through this sieve to remove foreign matter.
10.4 Preservation of Working Samples - Store samples as large lumps or as solidified melts in closed containers. Discard working samples 24 h after crushing and sieving since changes in composition sometimes occur in pulverized pitch.
11. Crucible Preparation
11.1 If the crucible, after thorough cleaning (11.2), has been used for less than six determinations, clean it as follows. Remove the mat, wash the crucible with distilled water, dry, and ignite in a muffle furnace for 1 h at about 1472 °F (800 °C). Cool the crucible slowly by placing it in a drying oven for 1 h after removal from the furnace to prevent cracking and place it in a desiccator while still warm.
11.2 After the crucible has been used for six determinations, remove any residual ash from pores in the filtering area by boiling in 1 + 1 hydrochloric acid. Add equal volume of concentrated hydrochloric acid to distilled water. Then boil the crucible in distilled water, thoroughly back wash with distilled water, dry, and ignite as in 11.1.
