Determination of surface area of carbon black

Iodine adsorption number is a standard titrimetric test for the determination of the surface area of the carbon black: Metrohm have developed a method to completely automate this difficult procedure

Carbon blacks are powdered forms of highly dispersed elemental carbon manufactured by controlled vapour-phase pyrolysis of hydrocarbons.

There are a number of different types of carbon black, produced by different industrial processes, including acetylene black, channel black, furnace black, lamp black and thermal black.

Average particle diameters in several commercially-produced carbon blacks range from 0.01 to 0.4 micrometres (um), while average aggregate diameters range from 0.1 to 0.8um.

Most types of carbon black contain over 97 to 99% elemental carbon.

Carbon blacks may also contain chemically bound hydrogen, oxygen, nitrogen and sulfur.

The oxygen content is of greatest importance for their application.

Oxygen is bound to the surface in the form of mainly acidic or basic functional groups.

Because of their source materials, the methods of their production and their large surface areas and surface characteristics, commercial carbon blacks typically contain varying quantities of adsorbed by-products from the production processes, particularly aromatic compounds.

Typical classes of chemicals adsorbed onto the carbon black surface are carcinogenic polycyclic aromatic hydrocarbons (PAHs), nitro derivatives of PAHs and sulfur-containing PAHs.

The presence of these compounds can significantly increase the hazards of carbon black exposure.

It is used mainly as a reinforcing agent in rubber products such as tyres, tubes, conveyer belts, cables and other mechanical rubber goods; used as a black pigment in printing, lithographic, letterpress, carbon paper and typewriter ribbon inks, paints, coatings, lacquers, plastics, fibres, ceramics, enamels, paper, record discs and photocopier toner; leather finishes; manufacture of dry-cell batteries, electrodes and carbon brushes; electrical conductors; conductive and antistatic rubber and plastic products; electromagnetic interference shielding; videodiscs and tapes; UV stabilisation of polyolefins; and high temperature insulating material.

Carbon black is also known as acetylene black, channel black, furnace black, lamp black, lampblack, thermal black, and noir de carbone.

Iodine adsorption number is a standard titrimetric test for the determination of the surface area of the carbon black.

A know amount of standardised iodine is added to a weighed amount of carbon black and it is reacted for a given time with stirring.

The solution is then filtered (to remove the black) and the excess iodine is back titrated with standardized sodium thiosulphate.

A high iodine adsorption number corresponds to a high surface area of the black.

A high surface area black is associated with improved bonding to, for example, rubber molecules and high tint in formulated products.

Historically, this analysis has been carried out manually with all sorts of problems - for example; reaction times, and stirring rates of the iodine to the black, and a coloured (black!) solution making it extremely difficult to define the colour endpoint.

Analysts see the endpoints at different points because the method is so subjective.

Metrohm have developed a method to completely automate this difficult procedure.

The fully automated system consists of a 2 Tower Version 778 Robotic Sample Processor in combination with a 794 Basic Titrino.

A combined Pt ring Metrosensor is used as the indicator electrode.

The sample rack accommodates 24 x 75 ml beakers.

Sample preparation and reaction takes place on tower 1.

50 ml of iodine is added directly to 1g of carbon black via a 800 Dosino, and is agitated and then allowed to settle.

Pipetting and filter rinsing takes place on tower 2.

10 ml of the reacted iodine/carbon black sample is pipetted via another 800 Dosino through a special filter apparatus, and into the external titrating vessel, where the Redox titration with sodium thiosulphate takes place.

The filter apparatus is then back flushed with more iodine again using the 800 Dosino.

The internal membrane pump adds diluent water prior to the titration.

The same pump rinses the external titration vessel and the electrodes with a sophisticated spin rinse spray nozzle.

The use of a 772 pump unit, attached directly to the 778 Robotic Sample Processor, guarantees an effective aspiration of the sample after titration.

The whole system is controlled by Tiamo Titration software.

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