CARBON BLACKS

Baby kuriakose
Rubber Technologist.

Among the reinforcing fillers used in rubber industry, a lion's share is constituted by different types of carbon blacks. They are essentially elemental carbon prepared by converting liquid or gaseous hydrocarbons into elemental carbon by partial combustion or thermal decomposition. Depending on the process adopted for the preparation, carbon blacks and lampblacks. The furnance blacks, channel blacks and lamp blacks. The furnace blacks are produced by incomplete combustion of natural gas or heavy aromatic residue oils from the petroleum industries, in refractory lined steel furnaces and separating the carbon formed by means of cyclones and filter bags. Finally, they are pelletised and packed, In the thermal process, natural gas or oil is thermally decomposed at about 1300°C in the absence of free air, in cylindrical furnances filled with an open checker work of silice bricks. The channel blacks are produced by feeding the natural gas or oil into thousands of small burner tips where the small flames inpinge either on to a large rotating drum or on to reciprocating channel irons. The black deposited is scraped out and collected. Lamp black is made by burning oil and allowing the black formed to settle out by gravity in a series of chambers.

The properties imparted by carbon blacks to the rubber Vulcanizates depend on several factors like particle size, structure, physico-chemical nature of the particle surface, chemical nature of the particle surface and particle porosity of the particle surface and particle porosity of the carbon blacks. Carbon blacks, are actually fused clusters of individual carbon particles. The particle size of the blacks range from 10 to 25 nm for the channel blacks, 20 to 80 nm for the furnace blacks and 180 to 470 nm for the thermal ones. The aggregation of carbon particles into long chains is referred to as 'structure' of the blacks. Compared with the other processes, the furnace process gives high structure blacks. The structure of the blacks can be controlled by modifying the furnace design and by the appropriate selection of the raw material. The physico-chemical nature of the particle surface is indicated by the degree of orientation of the particles in layer planes. Those which are less reinforcing were found to have highly oriented layers where as the reinforcing ones are irregular in shape and have less crystallite orientation. The carbon particles contain very small amounts of hydrogen, oxygen and sulphur on the surface, as phenolic, ketonic and carboxylic groups. The presence of these groups affect the rate of cure of the mixed compound.

The physical properties of some of the commercially available carbon blacks are given in the table below.

 

Name	Abbreviations	ASTMD1765 Number	Particle size Dia	ASTM lodine Number	Stricture (Cm³-DEP/ 100 g)
Supper Abrasion Furnance	SAF	N-110	22	140	115
Intermediate super Abrasion Furnace	ISAF	N-220	28	120	115
Easy processing channel	EPC	S-300	32	-	95
High Abrasion Furnace	HAF	N-330	32	80	105
Fine Extrusion Furnace	FF	N-440	42	50	60
Fast Extrusion Furnace	FEF	N-550	47	42	120
General Purpose Furnace	GPF	N-660	70	35	90
Semi-Reinforcing Furnace	SRF	N-770	83	26	70
Fine Thermal	FT	N-880	190	-	33
Nedium Thermal	MT	N-990	300	-	33
Lamp black	-	-	100	18	120