Black carbon

Carbon black pigments are classified into six classes lamp black, furnace black, thermal black, acetylene black, channel black and gas black. They all differ in their typical properties such as particle size, jetness, undertone and surface chemistry. 

Carbon black is the oldest synthetic carbon modification and is in fact one of the oldest chemical products. Carbon black was even used in the cave paintings of the Old Stone Age as a black dye. Its manufacture in the form of lamp black was, according to very early documents, known to the Ancient Egyptian and Ancient Chinese cultures. 

Carbon black has been produced for several thousand years and is one of the oldest chemical products 

Structure of spherical primary carbon black panicles  

The worldwide production capacity for carbon black in 1995 was estimated to be 7.3 10 t/a. Table 5.7 6 gives a survey of the carbon black production capacities in 1995 for different regions and countries. The value for Eastern Europe are uncertain. 

Three companies, Cabot, Degussa and Columbian Chemicals, account for 40 to 50% of the worldwide carbon black production capacity. 

Carbon black is an extremely fine powder of great commercial importance, especially for the synthetic rubber industry. The addition of carbon black to tires lengthens its life extensively by increasing the abrasion and oil resistance of rubber. 

Carbon black consists of elemental carbon with variable amounts of volatile matter and ash. There are several types of carbon blacks, and their characteristics depend on the particle size, which is mainly a function of the production method. 

Carbon black is produced by the partial combustion or the thermal decomposition of natural gas or petroleum distillates and residues. Petroleum products rich in aromatics such as tars produced from catalytic and thermal cracking units are more suitable feedstocks due to their high carbon/hydrogen ratios. These feeds produce blacks with a 

Carbon black is a large volume industrial commodity but its food use is very small.40 

Carbon black is derived from vegetable material, usually peat, by complete combustion to residual carbon. The particle size is very small, usually less than 5 /rm, and consequently is very difficult to handle. It is usually sold to the food industry in the form of a viscous paste in a glucose syrup. Carbon black is very stable and technologically a very effective colorant. It is widely used in Europe and other countries in confectionery. 

In the US in the 1970s when the GRAS list was being reviewed, safety data were requested on carbon black in view of the possibility that it might contain heterocyclic amines. Apparently, the cost of obtaining the data was higher than the entire annual sales of food grade carbon black so the tests were never done. Carbon black is not permitted in the US. 

Carbon blacks (Cl Pigments Black 6 and 7) dominate the market for black pigments, providing an outstanding range of technical 

Carbon blacks are manufactured from hydrocarbon feedstocks by partial combustion or thermal decomposition in the gas phase at high temperatures. World production is today dominated by a continuous furnace black process, which involves the treatment of viscous residual oil hydrocarbons, containing a high proportion of aromatics, with a restricted amount of air at temperatures of 1400-1600 °C. 

Azo pigments, both numerically and in terms of tonnage produced, dominate the yellow, orange and red shade areas in the range of 

In dye chemistiy, the relationship between the molecular structure of a dye and its technical performance, including colour and fastness properties, is now well-established. As discussed at length in Chapter 2, computational methods have emerged as indispensible tools in the development of our fundamental understanding of the properties of coloured molecules and in the design of new products. Molecular modelling techniques, which include a range of methods based on quantum mechanics and molecular mechanics, allow the molecular and physical properties of a particular dye to be predicted by calculation with some confidence, and without the need to resort to synthesis. The same principles apply to the molecular structures of 

The morphology of a crystal is determined by the relative rates of growth of different crystal faces as the crystal forms. The surface attachment energy ( att) may be defined for a particular crystal face as the energy released as a growth slice attaches to the surface of a growing crystal, and is related to the lattice energy ( cryst) by the relationship  

Carbon black is probably the most common particle reinforcement through its extensive use in the rubber fabrication industry. 

There are several different ways of manufacturing of carbon black. The oldest method is burning vegetable oil in a small lamp, then collecting the carbon black accumulated on the tile cover. This was developed by the ancient Chinese and is called the lampblack process. Subsequently, natural gas was used as a source for what is called the channel black process [26, 53, 54]. This method burns natural gas at about 1,300 C and collects carbon black deposited on steel channels. When exposed to air at high temperature, channel process carbon blacks appear to become porous. 

In the acetylene black process, acetylene is burned with air depleted of oxygen. This gives pure carbon blacks, but of large particle size. 

The oil furnace process involves a liquid hydrocarbon, usually a heavy petroleum oil, which is injected, sprayed, and mixed with preheated air and natural gas in a reactor. Part of the hydrocarbon is burned to maintain the reaction temperature ranges of 1,450 to 1,800 °C and the remainder is converted to carbon black. This process has a lower residence time and yields a narrower distribution of carbon black aggregate sizes, higher surface activity, and open aggregates (branched or grapelike (bulky)). 

carbon black is produced commercially by the above oil furnace procedure, the incomplete combustion of refinery heavy bottom oils. These carbon blacks are referred to as furnace blacks , as opposed to earlier carbon blacks that, as described above, were produced from natural gas and are called channel blacks . 

The term carbon black is often narrowed to designate the materials produced by two basic methods known as channel and thermal processesJ i Other carbon blacks are lampblack and acetylene black (see below). 

Channel Process. I n the channel process, thousands of small flames of natural gas impinge on a cool metallic surface which can be a channel, a roller, or a rotating disk. The carbon black forms on the cool surface and Is then exposed to high temperature in air to oxidize the surface of each particle. These particles are in the form of small spheroids. The channel carbon black has the smallest particle size (-10 nm), the highest surface area, and the highest volatile content of all carbon blacks. 

Thermal Process. In the thermal process, the carbon black is formed by the thermal decomposition of natural gas in the absence of air in a preheated firebrick-lined chamber. The process produces a coarser grade than the channel process with particle size up to 500 nm and lower surface area. 

Composition and Properties. Table 10.2 lists the composition and typical properties of carbon black. 

Appiications. A primary use of carbon black is as a filler in rubber to improve the strength, stiffness, hardness, and wear- and heat-resistance. Carbon-black fillers are found in practically every rubber product. 

Coal is a fossilized vegetable product containing mostly C, H, O, and N. The carbon content increases with the age of the coal. 

Degradation of hydrocarbons between 1000 and 2000 C yields an isotropic form of coal. This pyrolytic coal is suitable for use in artificial organs, as, for example, in artificial heart valves. It is compatible with muscle fiber and blood proteins and consequently causes little blood coagulation. 

Carbon black is formed from the burning of gaseous or liquid hydrocarbons under conditions of restricted air access. According to electron micrographs taken with a phase contrast microscope, carbon black has a graphitelike microstructure with lattice distances of 0.35 nm. The layers lie parallel to the particle surface. Since discrete crystalline regions cannot be observed, the structure of carbon black is better described in terms of a paracrystalline state rather than a random distribution of graphite crystals. 

Carbon black possesses a microporosity. The pores have diameters that are integral multiples of 0.35 nm, that is, they result from lattice vacancies. They are not through pores in the usual sense. The large internal surface area makes carbon black an attractive adsorbent. In addition, it is also used as a reinforcing filler. The reinforcing effect presumably results from the reaction of surface lone-electron pairs on the carbon black with the material to be reinforced, for example, with poly(dienes). 

Bitumin is a naturally occurring, almost black material that is also obtained in mineral-oil refining. It consists of high-molecular-weight hydrocarbons dispersed in oil-like material. 

Although synthetic and of relatively high cost, carbon blacks are produced in vast quantities for use in polymers. This is mainly due to their widespread use as a reinforcing agent for elastomers, especially in tyre applications. Worldwide production was estimated to be 6.2 Mt in 1999, of which about 90% was used in rubber applications [30]. 

In addition to their economic importance, carbon blacks exhibit extreme forms of some of the most difficult characterisation issues in the particulate fillers area, especially regarding size and shape determinations, and surface chemistry. However, largely because of their commercial value, more has been done to make advances in these fields than with most other fillers and this pioneering work has much to teach us in a general sense. 

Carbon blacks are, in effect, soots prodnced by incomplete combustion of volatile organic materials, principally oil and gas. As snch they have been made and used as pigments for well over a thousand years. Their prodnction as fillers for polymers has only been carried out since the early part of this centnry. Dnring this time, there have been four main processes resulting in prodncts of different characteristics furnace, channel, thermal and lamp blacks. 

In the channel black process, diffusion flames burning natural-gas impinge on reciprocating metal channels where carbon is deposited. Rotating drums may also be used. The carbon is scraped off, collected, micro-pulverised and then usually pelletised. These blacks have a much higher combined oxygen content than furnace blacks. This process is little nsed now largely dne to unfavourable economics and environmental problems. 

The thermal process produces low-structure blacks of fairly large particle size. These have certain niche applications and, hence, while not as economically attractive as the furnace ronte, some thermal black continues to be made. The process is carried out batch-wise by decomposing methane (from natural gas) into carbon and hydrogen in the absence of air, in a furnace at about 1300 °C. The furnace is preheated by burning an air-fuel mixture, the fuel often being the hydrogen from the process itself. 

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Explosives based on liquid oxygen and a fuel, generally carbon black. 

Residue (slurry) or clarified oil (CLO) used as refinery fuel or as a base in the manufacture of carbon black. 

These effects can be illustrated more quantitatively. The drop in the magnitude of the potential of mica with increasing salt is illustrated in Fig. V-7 here yp is reduced in the immobile layer by ion adsorption and specific ion effects are evident. In Fig. V-8, the pH is potential determining and alters the electrophoretic mobility. Carbon blacks are industrially important materials having various acid-base surface impurities depending on their source and heat treatment. 

Fig. V-8. Electrophoretic mobility of carbon black dispersions in 10 KNO3 as a function of pH. (From Ref. 93.)...

There are complexities. The wetting of carbon blacks is very dependent on the degree of surface oxidation Healey et al. [19] found that q mm in water varied with the fraction of hydrophilic sites as determined by water adsorption isotherms. In the case of oxides such as Ti02 and Si02, can vary considerably with pretreatment and with the specific surface area [17, 20, 21]. Morimoto and co-workers report a considerable variation in q mm of ZnO with the degree of heat treatment (see Ref. 22). 

The above methods for obtaining D, as well as other ones, are reviewed in Refs. 3-12, and Refs. 7-9 give tables of D values for various adsorbents. For example, D is close to 3 for the highly porous silica gels and close to 2 for nonporous fumed silica and for graphitized carbon black coconut charcoal and alumina were found to have D values of 2.67 and 2.79, respectively [7]. 

Many solids have foreign atoms or molecular groupings on their surfaces that are so tightly held that they do not really enter into adsorption-desorption equilibrium and so can be regarded as part of the surface structure. The partial surface oxidation of carbon blacks has been mentioned as having an important influence on their adsorptive behavior (Section X-3A) depending on conditions, the oxidized surface may be acidic or basic (see Ref. 61), and the surface pattern of the carbon rings may be affected [62]. As one other example, the chemical nature of the acidic sites of silica-alumina catalysts has been a subject of much discussion. The main question has been whether the sites represented Brpnsted (proton donor) or Lewis (electron-acceptor) acids. Hall... 

Fig. XVn-21. (a) Differential heat of adsorption of N2 on Graphon, except for Oand , which were determined calorimetrically. (From Ref. 89.) (b) Differential heat of adsorption of N2 on carbon black (Spheron 6) at 78.5 K (From Ref. 124).

Fig. XVII-21. Continued) (c) Isosteric heats of adsorption of n-hexane on ice powder Vm = 0.073 cm STP. (From Ref. 125). (d) Isosteric heats of adsorption of Ar on graphitized carbon black having the indicated number of preadsorbed layers of ethylene. (From Ref. 126.)...

It is noted in Sections XVII-10 and 11 that phase transformations may occur, especially in the case of simple gases on uniform surfaces. Such transformations show up in q plots, as illustrated in Fig. XVU-22 for Kr adsorbed on a graphitized carbon black. The two plots are obtained from data just below and just above the limit of stability of a solid phase that is in registry with the graphite lattice [131]. 

Fig. XVII-22. Isosteric heats of adsorption for Kr on graphitized carbon black. Solid line calculated from isotherms at 110.14, 114.14, and 117.14 K dashed line calculated from isotherms at 122.02, 125.05, and 129.00 K. Point A reflects the transition from a fluid to an in-registry solid phase points B and C relate to the transition from the in-registry to and out-of-registry solid phase. The normal monolayer point is about 124 mol/g. [Reprinted with permission from T. P. Vo and T. Fort, Jr., J. Phys. Chem., 91, 6638 (1987) (Ref. 131). Copyright 1987, American Chemical Society.]...

The analysis is thus relatively exact for heterogeneous surfaces and is especially valuable for analyzing changes in an adsorbent following one or another treatment. An example is shown in Fig. XVII-24 [160]. This type of application has also been made to carbon blacks and silica-alumina catalysts [106a]. House and Jaycock [161] compared the Ross-Olivier [55] and Adamson-Ling... 

Such isothemis are shown in figure B 1,26.4 for the physical adsorption of krypton and argon on graphitized carbon black at 77 K [13] and are examples of type VI isothemis (figure B 1.26.3 ). Equation (B1.26.7)) further... 

Figure Bl.26.4. The adsorption of argon and krypton on graphitized carbon black at 77 K (Eggers D F Jr, Gregory N W, Halsey G D Jr and Rabinovitch B S 1964 Physical Chemistry (New York Wiley) eh 18).

Carbon black Pastes Cosmetics Polymer solutions Drilling muds Protein solutions Fog Soils... 

Commercially produced elastic materials have a number of additives. Fillers, such as carbon black, increase tensile strength and elasticity by forming weak cross links between chains. This also makes a material stilfer and increases toughness. Plasticizers may be added to soften the material. Determining the effect of additives is generally done experimentally, although mesoscale methods have the potential to simulate this. 

Antistatic agents require ambient moisture to function. Consequently their effectiveness is dependent on the relative humidity. They provide a broad range of protection at 50% relative humidity. Much below 20% relative humidity, only materials which provide a conductive path through the bulk of the plastic to ground (such as carbon black) will reduce electrostatic charging. 

Fig. 2.11 Curves of the differential enthalpy of adsorption of nitrogen against surface coverage 0 (= for samples of Sterling carbon black heated at the following temperatures (a) 1500°C (fc) 1700°C (c) 2200 C (d) 2700°C. The curve for 2000°C was similar to (c). but with a lower peak. The calorimetric temperature was 77-5, 77-7, 77-4, 77-4 K in (a), (fc), (c) and (d) respectively.

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 . 

Fig. 2.13 Adsorption of nitrogen on a carbon black before graphitiz-ation. - The difTerential heat of adsorption Ji, plotted against n/n , was determined calorimetrically at 78 K (O, , A) and was also calculated from the isotherms at 78 6 and 90-1 K (+ ). (Courtesy Joyner and Emmett.)...

Fig. 2.15 Isosteric heat of adsorption of nitrogen on molecular (low-evergy) solids and on carbons (high-energy solids), plotted as a function of i/n . (A) Diamond (B) gruphitized carbon black. P.33 (D) Benzene (E) Teflon. The curve for amorphous carbon was very close to Curve (A). (Redrawn from a Figure of Adamson . )...

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