ASTM D2416 Test Method for Coking Value of Tar and Pitch (Modified Conradson)
9. Procedure
9.1 Ignite a clean porcelain or silica crucible in a muffle furnace at 900°C or over a gas flame for 1 h. Cool in a desiccator and weigh to the nearest 1 mg.
9.2 Transfer a 3-g representative portion of the dry tar or pitch to the tared crucible and weigh to the nearest 5 mg. Place this crucible in the center of the Skidmore crucible. Level the sand in the metal crucible and place the Skidmore crucible in the exact center. Apply covers to both the Skidmore and metal crucibles, the one on the latter fitting loosely to allow free exit to the vapors as formed.
9.3 Place the triangle on the insulator, center the metal crucible in the insulator with its bottom resting on top of the triangle, and cover the whole with the sheet-iron hood and chimney in order to distribute the heat uniformly during the coking process. The assembly, including the insulator ring will be at approximately room temperature.
9.4 Cover the opening of the furnace with the furnace lid and set the controller to maintain a temperature of 900 more or less 10°C (see 5.8). With the furnace at this temperature, remove the lid, immediately center the assembly (see 9.3) over the furnace opening and start timing the test period. The positioning of the assembly must be done quickly to avoid excessive loss of heat. Apply heat to the sample for exactly 30 min without changing the setting of the controller. The temperature should recover to 900°C in 15 min. At the end of 30 min, remove the assembly from the heat source and allow to cool for about 15 min. Remove the porcelain crucible with heated tongs, place in a desiccator, cool, and weigh.
10. Calculation
10.1 Calculate the coking value of the sample as follows:
Coking value, wt. % = 100A/B
where:
A = weight of residue, and
B = weight of sample.
