Determination of Carbon Black Content & Ash Content – Rubber Accessories

Carbon Black Content & Ash Content - Rubber Accessories

Carbon Black Content 

Pyrolysis Method


  • Electrical combustion furnace – maintained at 1000°± 25°C.
  • Muffle furnace – 550°± 25°C, 1000 ± 25°C
  • Silica or porcelain crucible
  • Combustion tube.
  • Porcelain  boat (combustion type)
  • Nitrogen gas cylinder.
  • Weighing balance.
  • Desiccator


  • Determination of fillers, in test specimen
  • Heat the furnace with the combustion boat to temperature 1000± 25°C.
  • Place the boat in furnace maintained at temperature 1000°C for 15 minutes.
  • Cool in Desiccator and weigh accurately to 0.001 g as M1.
  • In the boat, weigh about 1 g of homogenized sample and take the mass of sample with boat as M2.
  • Draw out the combustion tube a little bit from the hot zone and pass nitrogen for 1 minute to drive the air.
  • Put the boat with sample into the combustion tube slightly away from hot zone.
  • Connect the nitrogen gas flow and push the tube such that boat is in the hot zone of furnace.

  • At first dense, black-brown smoke will come out of combustion tube and finally turns into white smoke.
  • When white smoke becomes thinner, draw out the combustion tube from the furnace.
  • Continue the nitrogen flow for 2-3 minutes more.
  • Cut off the nitrogen supply into the tube.
  • Take out the boat carefully avoiding spilling and keep it in a Desiccator till it is cooled.
  • Weigh the boat with the ignited sample as M3.

Calculate total fillers, percent by mass accordingly as follows

 Total fillers, percent by mass = M3 – M1 x 100 / M2 – M1


  • M3= mass in g of the boat with the sample after ignition,
  • Ml = mass in g of empty boat, and
  • M2 = mass in g of the boat with sample.

 Determination of  Ash Content


  • Heat the crucible at 550°± 25°C in muffle furnace for half an hour.
  • Remove the crucible and cool in Desiccator.
  • Weigh quickly and note the dry weight of crucible as B.
  • Weigh 1.0 g of test specimen into this weighed crucible. Note mass of sample as C.
  • Place the crucible with sample in the furnace and close the door completely.
  • After 1 hour, open the furnace door 3 to 5 cm and continue heating for 30 minutes.
  • As soon as all carbonaceous materials are burned off, remove the crucible from the furnace.
  • Cool in a Desiccator and weigh the mass of ash and crucible as A.

Calculate ash, percent by mass as follows:-

  Ash, percent by mass = A – B   x 100 / C



A = mass in gram of ash and crucible.

B = mass in gram of crucible.

C = mass in gram of test specimen


Calculate the carbon black content as follows:

Carbon black,
percent by mass = Total fillers – Total ash.

REFERANCE: – IS 3400 (part 22):1984 Methods of test for vulcanized rubber – chemical analysis.

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