Carbon black comminution

POWDER. Any solid, dry material of extremely small particle size ranging down to colloidal dimensions, prepared either by comminuting larger units (mechanical grinding), combustion (carbon black, lampblack), or precipitation via a chemical reaction (calcium carbonate, etc ). Powders that are so fine that the particles cannot be detected by rubbing between... 

Particle Shape. Shape Factors. The method of formation plays a major role in shaping the resultant particles. Particles generated by comminution, attrition, or disintegration resemble the parent material. However, if the method of formation is condensation from vapor or precipitation from solution, the smallest unitary particle may be spherical or cubical. Often condensation is followed immediately by solidification and the formation of chainlike aggregates (e.g., iron oxide fumes, carbon black). In liquid suspensions, similar particle aggregation or flocculation is important in determining suspension behavior. 

Methods currently used to determine this require the filler to be comminuted by means of ultrasound - but this causes severe degradation of the agglomerates in carbon blacks, and also distorts the distribution of silicas. An alternative method has been developed using transmission electronic microscopy, in which the filler morphology retained is similar to that obtained in the incorporation process. 

The methods proved to be very useful for the evaluation of the surface properties of various solids with mixed surface characteristics and changes in the surface character following oxidation, heat reduction, and comminution treatments. For example the effect of heat treatments on the amount of polar sites in a high surface area carbon black is shown in Figure 15, and the effect of graphite comminution in air and in liquid hydrocarbons is given in Table 2. 

What Kaneko et al. (1992a) are doing is to make use of the exponential rise in surface area which occurs with diminution of particle size (comminution) as is found with the carbon blacks. Here, the large surface areas are not associated with internal porosity but with external surfaces of small spheres of carbon black with diameters of nanometers. 

In addition to the two mechanisms of comminution and stretching, elastomer and carbon black have to be compacted.Compaction, or massing, is the displacement of entrapped air in the machine by applied compressive force. This requires deformation of elastomer domains to match the shape of the carbon black, followed by relaxation of the elastomer in the deformed state. In another case study, Nakajima and Harrell estimated that about 6% of the energy used in incorporation was required for compaction. 

Figure 3.4 Schematic illustration of mechanisms incorporating carbon black into elastomer, a) lamination, b) comminution.

The increase of the compound modulus on ageing may result from an increase of bound rubber and regeneration of entanglement at the interface of the comminuted rubber particles, as discussed in section 4.4 and [24], Also, a spatial rearrangement of carbon black caused by the memory of the matrix rubber may occur. As the memory recovers very slowly, the compound tends to go back to the previous state, where the dispersion was poorer and the modulus was higher. These three effects may be erased by remilling. 

Rubber compounds tend to give a smooth extrudate without melt fracture. Also, the magnitude of the extrudate swell is smaller than that of the gum ruhher [5]. Compounds consist of supermolecular flow units, which form during compounding. No fracture occurs at the entrance of the capillary because it is a fluid material. Consequently, the memory of deformation at the entrance is smaller than that of gmn rubber, which is an elastic material. This explains the low extrudate swell. The supermolecular flow units are carbon black with adsorbed rubber and comminuted particles of the matrix rubber. There is some resemblance between the rheology of rubber compoimds and that of PVC both are in a particulate state during flow [5]. 

The Babylonians and Assyrians cemented stone slabs as well as bricks with bitumen (which is sometimes also referred to as asphalt), a mixture of a black or brown natural organic material with a pitchy luster and comminuted mineral. Bitumen is a thermoplastic solid material when heated above 50°C, it softens and becomes a thick, viscous liquid that reverts to a solid on cooling. It is composed of a natural mixture of hydrocarbons (organic substances composed of carbon, hydrogen, and oxygen) that occurs in natural... 

---