Brick carbon

Corrosion. Ammonium bifluoride dissolves in aqueous solutions to yield the acidic bifluoride ion the pH of a 5% solution is 3.5. In most cases, NH4HF2 solutions react readily with surface oxide coatings on metals thus NH4HF2 is used in pickling solutions (see Metal surface treatments). Many plastics, such as polyethylene, polypropylene, unplasticized PVC, and carbon brick, are resistant to attack by ammonium bifluoride. 

Sodium fluoride is normally manufactured by the reaction of hydrofluoric acid and soda ash (sodium carbonate), or caustic soda (sodium hydroxide). Control of pH is essential and proper agitation necessary to obtain the desired crystal size. The crystals are centrifuged, dried, sized, and packaged. Reactors are usually constmcted of carbon brick and lead-lined steel, with process lines of stainless, plastic or plastic-lined steel diaphragm, plug cock, or butterfly valves are preferred. 

In North America, a special, high conductivity, low permeability, "hot-pressed" carbon brick is utilized almost exclusively for hearth walls. Because of their relatively small size and special, heat setting resin cement, and because the brick is installed tightly against the cooled jacket or stave, differential thermal expansion can be accommodated without refractory cracking and effective cooling can be maintained. Additionally, the wall thickness is generally smaller than 1 m, which promotes the easy formation of a protective skull of frozen materials on its hot face. Thus hearth wall problems and breakouts because of carbon wall refractory failure are virtually nonexistent. 

Carbon brick and block ate used to line the cupola well (73) or cmcible. When properly installed and cooled carbon linings last for many months or even years of intermittent operation. Their resistance to molten iron and both acid and basic slags provides not only insurance against breakouts but also operational flexibility to produce different iron grades without the necessity of changing refractories. Carbon is also widely used for the tap hole blocks, breast blocks, slagging troughs, and dams. 

Ceramic or carbon-brick linings are frequently used as facing linings over plastic or membrane linings when surface temperatures exceed those which can be handled by the unprotected materials or when the membrane must be protec ted from mechanical damage. This type of construction permits processing of materials that are too corrosive to be handled in low-cost metal constructions. 

Kohlenstoff-hydrat, n. carbohydrate, -kalium, n. potassium carbide, -kem, m. carbon nucleus. -kette,/. carbon chain, -legiening,/, carbon alloy, -metall, n. carbide, kohlenstoffrelch, a. rich in carbon. Kohlenstoff-silicium, n. carbon silicide. -ske-lett, n. carbon skeleton, -stahl, m. carbon steel, -stein, m. carbon brick, -sticlKtoff-titan, n. titanium carbonitride. -sulfid, n. 

The electrolysis of alumina is carried out in electrolyte cells made of mild steel which are lined inside with an insulating refractory and carbon (either carbon bricks or carbon and coal tar pitch). The cell bottom is connected to the cathode terminal and serves as the cathode. Carbon electrodes introduced from the top serve as anodes. A more detailed description is given below. 

Hot melt silicones, 22 35 Hot molding, 12 733 Hot-pressed carbon brick, 12 764 Hot pressing, ceramics processing,... 

Nonmetallic conductors and corrosion products. Carbon brick in vessels is strongly cathodic to the common structural alloys. Impervious graphite, especially in heat-exchangers, is cathodic to structural steel. Carbon-filled polymers can act as active cathodes. Some oxides or sulfates are conductors, such as mill scale (magnetite Fe304), iron sulfides on steel, lead sulfate on lead can act as effective cathodes with an important area to that of the anodes. Very frequently, the pores of the conductive film are the preferable anodic sites that leads to localized corrosion (pitting).5... 

In phosphoric acid production plants, both red shale and fireclay brick have excellent resistance to all concentrations of phosphoric acid at temperatures up to 250°F, provided the acid contains no HF. If HF is present in the phosphoric acid, carbon brick construction must be used. As a rough rule-of-thumb, HF levels above 50 ppm in phosphoric acid require tank linings of carbon brick bonded and jointed with a carbon (or barytes) filled furan mortar over a suitable membrane to match the steel or concrete substrate structure. 

Carbon Brick Carbon brick, though costing much more than acid brick, is required in some CRM applications because of its high resistance to HF and con-... 

Sulfur Mortars Hot melt-and-pour sulfur mortars are ancient, doubtless one of the oldest of all chemical resistant materials still used today. They are very resistant to non-oxidizing acids and weak alkalies below 200°F over a pH range of 0-12. Three types of sulfur mortars are typically employed (1) One containing an all-silica filler with minimum plasticizer, used to bond acid brick (2) A mortar with an all-carbon filler and minimum plasticizer, used primarily to lay carbon brick for nitric-hydrofluoric acid pickling tanks (to clean stainless steels) and the underlying floors and (3) A much more flexible all-silica filled product with double the amount of plasticizer of the other two mortars, used to join vitrified clay (terra cotta) pipe conveying waste acids and other effluent chemicals, and to assemble "pole line hardware" for the power industry. 

Caution. Lead is an electrically conductive material. The designer should be careful not to place carbon brick and/or carbon-filled mortar in contact with or very close to lead linings where the service includes an electrolyte in solution, as lead and carbon will form a galvanic couple, with the carbon as anode and the lead cathodic. This will result in the wasting of the lead. If carbon brick or carbon-filled mortars are to be employed in the same design, an electrical insulating barrier should be placed between them and the lead. Such barriers may be Teflon or other fluorocarbon sheet, a thick layer of a carbon-free, chemically inert mortar, or a thick layer of ceramic or organic fiber. 

Carbon bricks are used in chemical-resistant construction in exposures which cannot readily be handled by other kinds of brick. Inasmuch as their cost is nearly 10 times that of shale or fireclay, and they provide not nearly as much insulation nor resistance to mechanical abuse, their selection is dictated by only the most compelling reasons. These reasons may be divided into four categories ... 

Carbon brick is currently manufactured in the western hemisphere by only one company and the greatest volume of its product goes into steel mills and into other metallurgical uses. (At the time of this writing one other manufacturer has started production of an acceptable carbon brick.) Because it is employed primarily in refractory service, it has always been manufactured in refractory sizes-in the 9" X 4.5" X 2.5" or 9" x 4.5" x 3" modules. All standard shapes-spiits, soaps, arches, keys and wedges-are available. The tolerances in manufacture and supply are ... 

The reader will note that domestic carbon brick, with a high coefficient of thermal conductivity, gives little insulation to a membrane (if there is one) behind it and, therefore, where such insulation is required, a considerable thickness of these brick must be employed. Note also that the coefficient of thermal expansion of domestic brick is less than half of that of shale and about half of that of fireclay. Thus, mating these two types of brick together in a single construction is difficult for the designer, and in the areas of considerable thermal change, close to impossible. 

The carbon will, of course, burn if exposed to heat and a source of oxygen. The manufacturers are all pretty well agreed that carbon brick can be used in normal atmospheres only to a limit of about 660°F (340°C), though in a reducing atmosphere (absence of oxygen) it can be used at temperatures as high as 5000°F (2760°C). 

Table 16-5 Comparative Results of Abrasion Test for Fireclay and Carbon Brick (ASTM C704)...

From the above, it would appear that the carbon brick is not greatly different in abrasion resistance from the fireclay brick. Where construction requires masonry internals, such as support plates and packed scrubbers, yet the exposures include hydrofluoric acid or strong alkalis, beams, stringers and plates... 

The masonry units used in the pulp and paper industry include fireclay, shale, and carbon brick, structural glazed tile and Portland cement/aggregate brick. Structural glazed tile and Portland cement/aggregate brick are relatively unique to this industry and have not been widely used outside of it. 

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