Carbon black results

Several people in the 18th and 19th centuries attempted to produce a pure form of zinc oxide for medical purposes. They were unaware that their samples contained cadmium, which at that time was an unknown element. In 1817 Friedrich Strohmeyer (1776—1835), a German chemist, analyzed a zinc compound (calamine) he believed contained zinc oxide (ZnO). However, what he really found was zinc carbonate (ZnCO ), which, though at first unknown to him, contained some cadmium. Strohmeyer then treated his sample with acids until all the zinc was dissolved and thus removed. He then heated the residue with carbon black, resulting in a small ingot of soft, bluish-white metal that proved to be a new element—cadmium. Strohmeyer is given credit for the discovery of cadmium. 

Values of the surface potential and surface charge density on the carbon black resulting from adsorption of naphthalenesulfonate were calculated from the experimental adsorption isotherm (see Figure 7) by means of the derived constant potential isotherms. Both calculated and experimental results are presented in Figures 2 to 8. 

As indicated earlier, the essential structural feature of a rubber vulcanizate is its flexible three-dimensional network. It is this arrangement which leads to the characteristic elastic behaviour. Comparative values for some properties of typical vulcanizates of common elastomers are given in Table 18.1. When natural rubber is stretched, crystallization of the highly regular chains occurs and the material shows a high tensile strength. The addition of fillers such as carbon black results in some increase in strength but the effect is not so marked as with elastomers for which stress-induced crystallization is not possible. 

However, a high vinyl rubber is also made. The styrene content may be varied widely. The chain-end may be modified to improve affinity to carbon black, resulting in a better dispersion of the filler. These variations in molecular architecture were developed for satisfying the requirements of automotive tyres for a low energy loss and a high skid resistance. The anionic polymerisation provides a flexibility in designing molecular architecture such a flexibility is unavailable for the current practice of other polymerisation systems. 

Similar results with graphitized carbon blacks have been obtained for the heat of adsorption of argon,krypton,and a number of hydrocarbons (Fig. 2.12). In all these cases the heat of adsorption falls to a level only slightly above the molar heat of condensation, in the vicinity of the point where n = n . 

Examples are provided by the work of Carman and Raal with CF2CI2 on silica powder, of Zwietering" with nitrogen on silica spherules and of Kiselev" with hexane on carbon black and more recently of Gregg and Langford with nitrogen on alumina spherules compacted at a series of pressures. In all cases, a well defined Type II isotherm obtained with the loose powder became an equally well defined Type IV isotherm with the compact moreover both branches of the hysteresis loop were situated (drove the isotherm for the uncompacted powder, but the pre-hysteresis region was scarcely affected (cf. Fig. 3.4). The results of all these and similar... 

Chlorinated Polyethylene. Chlorinating polyethylene under pressure results in a polymer having a chlorine content varying from 25 to 42%. The polymer requires the incorporation of carbon black and minerals for achieving good physical properties. The polymers handle like conventional polymers and can be mixed and processed on conventional mbber equipment. 

In tires, carbon black is important because of the high flex fatigue and tear strength requirements of this product. Poor dispersion can result in premature cracking in both treads and sidewalls. In off-the-road tires poor dispersion results in excessive chip/chunk causing a significant loss in treadwear in addition to tread lug cracking which can lead to loss of an entire lug (radial tread bar). 

The metal fillers act as a reinforcing material that results in added strength and stiffness (126). They color the plastic gray for nickel, 2inc, stainless steel, and aluminum, and brown for copper. Metal additives are more expensive than carbon black or surface-active agents, but they get extensive use in EMI shielding appHcations. 

The carbon blacks used in plastics are usually different from the carbon blacks used in mbber. The effect of carbon black is detrimental to the physical properties of plastics such as impact strength and melt flow. Electroconductive grades of carbon black have much higher surface areas than conventional carbon blacks. The higher surface areas result in a three-dimensional conductive pathway through the polymer at much lower additive levels of the carbon black. The additive concentrations of electroconductive carbon blacks is usually j to that of a regular carbon black (132). 

In addition to combined hydrogen and oxygen, carbon blacks may contain as much as 1.2% combined sulfur resulting from the sulfur content of the aromatic feedstock that contains thiophenes, mercaptans, and sulfides. The combined sulfur appears to be inert and does not contribute to sulfur cross-linking during the vulcanization of mbber compounds. 

Aromaticity is the most important property of a carbon black feedstock. It is generally measured by the Bureau of Mines Correlation Index (BMCI) and is an indication of the carbon-to-hydrogen ratio. The sulfur content is limited to reduce corrosion, loss of yield, and sulfur in the product. It may be limited in certain locations for environmental reasons. The boiling range must be low enough so that it will be completely volatilized under furnace time—temperature conditions. Alkane insolubles or asphaltenes must be kept below critical levels in order to maintain product quaUty. Excessive asphaltene content results in a loss of reinforcement and poor treadwear in tire appHcations. 

The shrinkage in demand has resulted in a restmcturing of the carbon black-industry. Several of the principal multinational oil companies have left the business including Ashland, Cities Service Co., Phillips, and Conoco. Some plants have changed ownership. In the United States this has increased the production capacities of Degussa, Sid Richardson, and Huber. Today s U.S. industry consists of six principal producers. Rated capacities of the six U.S. manufacturers is shown in Table 13. Cabot Corp. and Columbian Chemicals are the leading producers, followed by Degussa, Sid Richardson, J. M. Huber Corp., and Witco. A survey of the future markets and present stmcture of the carbon black industry has been presented (1). 

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