Carbonaceous shell

Pyrite occurs in sediments in the form of single crystals, crystal clusters, spheres, framboids or as replacement for organic structures. Miroprobe analysis of pyritic aggregates often show the presence of appreciable carbon, and some coarser carbonaceous matter is visible microscopically. Microcrystals of pyrites are frequently found in organic particles when examined in the TEM. Sometimes a thin bright rim occurs around each crystal, which indicates that it is enclosed within a carbonaceous shell (Oberlin et al., 1980)19). 

Figure 19.1 (a) The carbonaceous shell of coccolithophorids. (Reproduced with permission from Ref. [231]. Copyright 2011, Society for Applied Microbiology and Blackwell... 

The process for the thermal activation of other carbonaceous materials is modified according to the precursor. For example, the production of activated carbon from coconut shell does not require the stages involving briquetting, oxidation, and devolatilization. To obtain a high activity product, however, it is important that the coconut shell is charred slowly prior to activation of the char. In some processes, the precursor or product is acid-washed to obtain a final product with a low ash content (23,25). 

Fig. 7. First-order Raman spectra of (a) graphite, (b) inner core material containing nested nanotubes, (e) outer shell of carbonaceous cathode deposit (after ref. [24]).

Soot deposited on the chamber wall contained mostly carbonaceous particles, where no MWNTs were contained. The deposits on the cathode consist of two portions the inside is black fragile core and the outside hard shell. The inside include MWNTs scad poljd ral graphitic nanoparticles. The outer-shell part ojnsisted of the crystd of graphite. 

There are two main varieties of carbon (i) crystalline (e.g., graphite and diamond), and (ii) amorphous. The amorphous variety consists of carbon blacks and charcoals. Carbon blacks are nonporous fine particles of carbon produced by the combustion of gaseous or liquid carbonaceous material (e.g., natural gas, acetylene, oils, resins, tar, etc.) in a limited supply of air. Charcoals are produced by the carbonization of solid carbonaceous material such as coal, wood, nut shells, sugar, synthetic resins, etc. at about 600 °C in the absence of air. The products thus formed have a low porosity, but when activated by air, chlorine, or steam, a highly porous material is produced this porous product is called activated charcoal. Chemically speaking carbon blacks and charcoals are similar, the difference being only in physical aspects. Carbon blacks find use in the rubber industry and in ink manufacture. An important use of charcoals is as adsorbents. 

In some of the earliest recorded examples of adsorption, activated carbon was used as the adsorbent. Naturally occurring carbonaceous materials such as coal, wood, coconut shells or bones are decomposed in an inert atmosphere at a temperature of about 800 K. Because the product will not be porous, it needs additional treatment or activation to generate a system of fine pores. The carbon may be produced in the activated state by treating the raw material with chemicals, such as zinc chloride or phosphoric acid, before carbonising. Alternatively, the carbon from the carbonising stage may be selectively... 

Activated carbon is produced by destructive distillation of carbonaceous substances, such as wood, bones, and nut shells. The carbon obtained from distillation is then heated to 800-900°C with steam or carbon dioxide. 

Jan Baptist van Helmontj 1577-1644. Belgian physician and chemist who made a detailed study of carbon dioxide (gas sylvestre) and understood its preparation by the burning of charcoal or other carbonaceous organic material, by fermentation of beer and wine, and by action of vinegar on shells and limestone. See also ref. (86). 

To achieve a significant adsorptive capacity an adsorbent must have a high specific area, which implies a highly porous structure with very small micropores. Such microporous solids can be produced in several different ways. Adsorbents such as silica gel and activated alumina are made by precipitation of colloidal particles, followed by dehydration. Carbon adsorbents are prepared by controlled burn-out of carbonaceous materials such as coal, lignite, and coconut shells. The crystalline adsorbents (zeolite and zeolite analogues are different in that the dimensions of the micropores are determined by the crystal structure and there is therefore virtually no distribution of micropore size. Although structurally very different from the crystalline adsorbents, carbon molecular sieves also have a very narrow distribution of pore size. The adsorptive properties depend on the pore size and the pore size distribution as well as on the nature of the solid surface. 

The thermal decomposition of 7, 8 and 9 into fullerenic substructures is a milestone in fullerene formation and represents the first example of a macroscopic preparation of closed-shell carbon particles from acetylenic precursors. However, molecular allotropes of carbon, such as Cgo or higher fullerenes were not found among the decomposition products. It is interesting to note in this context that 10 [24], a structural isomer of 7 with a saddle-shaped solid state conformation, also shows thermal transformations, but in this case they occur at temperatures ca. 50 °C lower than those of 7 and are accompanied by a release of 50 kj mol-1 more energy. Although an insoluble carbonaceous material is formed during this process, further details of its nature are currently not known. 

The raw materials for activated carbon are carbonaceous matters, such as wood, peat, coals, petroleum coke, bones, coconut shells, and fruit nuts. Anthracite and bituminous coals have been the major sources. Starting with the initial pores present in the raw material, more pores, with desired size distributions, are created by the so-called activation process. After initial treatment and pelletizing, one activation process involves carbonization at... 

Activated carbons [171-182] are amorphous materials showing highly developed adsorbent properties. These materials can be produced from approximately all carbon-rich materials, including wood, fruit stones, peat, lignite, anthracite, shells, and other raw materials. The properties of the produced adsorbent materials will depend not merely on the preparation technique but as well on the carbonaceous raw material used for their production. Actually, lignocellulosic materials account for 47% of the total raw materials used for active carbon production [178],... 

Already the first infrared observations of late-type giant stars have revealed that many of them are indeed surrounded by thick dust shells (Woolf Ney 1969). These were rapidly found to consist of carbonaceous dust (some kind of soot) if the stellar spectrum indicates the star to be carbon-rich, and to be silicate dust (olivine, pyroxene) if the star is oxygen-rich (Gilman 1969). Since this dust is mixed into the interstellar medium due to mass loss by stellar winds, it was then assumed that silicate and carbon particles are abundant dust components in the interstellar medium. 

Although the first demonstration that amino acid racemization took place in fossils used mollusc shells (23), the application of this reaction in dating these materials has been extensively investigated only recently (19,20). Work on Mercenaria (19), Chione (20), and other species (24) has tested the application of racemization dating to fossil mollusc shells from geological contexts and Indian shell middens. These and other studies have shown that there are problems with amino acid racemization dating of carbonaceous fossils which are not encountered with bone. Reversible first-order racemization kinetics which are observed in bone... 

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