Carbon black special grades

A convenient method for assessing the extent of surface oxidation is the measurement of volatile content. This standard method measures the weight loss of the evolved gases on heating up to 950°C in an inert atmosphere. The composition of these gases consists of three principal components hydrogen, carbon monoxide, and carbon dioxide. The volatile content of normal furnace blacks is under 1.5%, and the volatile content of oxidized special grades is 2.0 to 9.5%. 

Table 11 Hsts the types and appHcations of special pigment-grade carbon blacks. Included in this Hst are thermal black and lampblack. Over 40 special black grades have been developed based on the furnace process having a broad range of surface areas, from 20 m /g to over 1500 m /g. The lower surface area products are used in printing inks and tinting. The high area, more expensive products find use in high color enamels and lacquers.

Table 11. Types and Applications of Special Pigment Grades of Carbon Blacks...

For very many years it has been common practice to improve the electrical conductivity of plastics and rubbers by the incorporation of certain additives like special grades of carbon black. Such materials were important, for example, in hospital operating theatres where it was essential that static charges did not build up, leading to explosions involving anaesthetics. 

Electrical Conductivity. The electrical conductivity of carbon blacks is inferior to that of graphite, and is dependent on the type of production process, as well as on the specific surface area and structure. Since the limiting factor in electrical conductivity is generally the transition resistance between neighboring particles, compression or concentration of pure or dispersed carbon black, respectively, plays an important role. Special grades of carbon black are used to donate to polymers antistatic or electrically conductive properties. Carbon blacks with a high conductivity and high adsorption capacity for electrolyte solutions are used in dry-cell batteries. 

The furnace black process is currently the most important production process. It accounts for more than 95 % of the total worldwide production. The advantages of the furnace black process are its great flexibility in manufacturing various grades of carbon black and its better economy compared to elder processes. The following comparison makes this apparent for similar grades of carbon black, the production rate of one flame is ca. 0.002 kg/h for channel black, ca. 0.2 kg/h for gas black, and ca. 2000 kg/h for a modern furnace black reactor. However, in spite of the more advantageous furnace black process, the production processes listed in Table 27 (except for the channel black process) are still in use for the production of special carbon blacks which cannot be obtained via the furnace black process. 

Battery grade carbon blacks produced by a specially designed partial combustion process include the ENSACO/SUPER P carbon black and the by-products of the Shell gasification process, known as Ketjen Black.74 78... 

Concentration of antistats in plastics is mostly 0.1 to 2 %. Special grades of electroconducting (EC) carbon black are used in PO at levels higher than 10 % (Accorsi and Yu, 1998). Other conducting fillers incorporating antistatic effects, such as metals or organic semiconductors (e.g. polypyrrole) are not commonly used in plastics for contact with food. 

In the final analysis 60 distinctly different carbon blacks were selected to give a good separation of variables. Included with these were several standard commercial grades, several blacks obtained from other suppliers, and many special, noncommercial grades. 

In fuel cell catalysis, finely divided platinum particles are used on suitable support materials such as special grades of carbon blacks. Techniques for investigating the interactions between the platinum particles and protons under hydrogen pressures typical of catalyst operation are needed for optimization of catalyst morphology and performance as well as development of economic catalysts. 

The addition of finely divided solids to rubber matrices is commonly practiced to increase the performance and service life of these materials. Indeed, without an active filler, a synthetic elastomer like Styrene Butadiene Rubber (SBR )would not be of much use. For instance, a tire made of pure vulcanized SBR would not last more than a few hundred miles. The introduction of coarse filler particles, such as milled quartz or clays, improves the situation so that the tire lasts thousands of miles. However, using active fillers like special grades of carbon black or silica has produced modem tires that operate satisfactorily for tens of thousands of miles. 

Carbon black is much more widely used in the rubber industry, which accounts for 93% of its sales, than in plasties. Special grades have nevertheless found a number of niche applications in the plastics industry, as a way to increase the electrical conductivity of plastics and promote electrostatic dissipation, as a black pigment, and as a way of improving weathering ability. 

The composition of these gases consists of three principal components hydrogen, carhon monoxide, and carbon dioxide. The volatile content of normal furnace blacks is imder 1.5%, and the volatile content of oxidized special grades is 2-22%. 

The surface area can be calculated from particle size measured with transmission electron microscope (TEM) (ASTM D3849). Generally, for rubber grade, the surface areas determined by TEM are in reasonable agreement with surface areas determined by nitrogen adsorption measurements. However, for those carbon blacks that have highly developed micropores such as special pigment blacks and blacks used for electrical conductivity, the surface areas calculated from their particle diameters are smaller than those calculated from gas absorption, as the internal surface area in the micropore is excluded. 

Besides reinforcement for rubber, the principal functions that carbon black imparts to a compoimd material are color, ultraviolet damage resistance, electrical conductivity, nondegradation of polymer physical properties, and ease of dispersion. The carbon blacks used for these purposes are classified as special-grade blacks. Smaller volume applications exploit other principal attributes, such as chemical inertness, thermal stability, and an open porous structure. The secondary attributes include chemical and physical purity, low affinity for water adsorption, and ease of transportation and handling. 

Dispersion. The ability to disperse the special grades is an important consideration in almost all applications. The customer s milling costs can be comparable to the purchase price of the carbon black. In other cases, the inability to achieve an excellent dispersion impairs the ability to realize the full performance of the blacks or it creates other undesirable characteristics. For example, a black plastic part will not appear as dark nor have a smooth surface if the black cannot be fully dispersed. 

The furnace process involves spray injection of a low end fraction of crude oil into a heated chamber. The temperature, shape of the iujectors of the oil, rate of injection, shape of the reactor, and other factors are controlled to produce carbon black fillers of different particle sizes and structures. The particle size and structure control and the reinforcing character of carbon black are the bases of their classification system (Table 8). There are approximately 30 common grades of carbon black used iu the rubber iudustiy. There are also numerous specialty grades produced for use in plastics, conductive applications, and proprietary grades produced for use in tires and other special-purpose products (14). 

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