Graphite reactivity

Answer The reactor gains reactivity from the metal cooling which takes place almost instantaneously, and it loses reactivity as the graphite cools end xenon builds up in the absence of b urnout. The graphite reactivity loss and the xenon growth quickly overcomes the momentary reactivity Increase from the cooling metal and drives the reactor subcritical until 2U-36 hours after a shutdown. 

Amorphous carbon, having a far greater effective surface area than either diamond or graphite, is the most reactive form of carbon. It reacts with both hot concentrated sulphuric and hot concentrated nitric acids in the absence of additional oxidising agents but is not attacked by hydrochloric acid. 

Black phosphorus is formed when white phosphorus is heated under very high pressure (12 000 atmospheres). Black phosphorus has a well-established corrugated sheet structure with each phos phorus atom bonded to three neighbours. The bonding lorces between layers are weak and give rise to flaky crystals which conduct electricity, properties similar to those ol graphite, it is less reactive than either white or red phosphorus. 

Mote stable catalysts ate obtained by using fluorinated graphite or fluorinated alumina as backbones, and Lewis acid halides, such as SbF, TaF, and NbF, which have a relatively low vapor pressure. These Lewis acids ate attached to the fluorinated soHd supports through fluorine bridging. They show high reactivity in Friedel-Crafts type reactions including the isomerization of straight-chain alkanes such as / -hexane. 

Fused Salt Electrolysis. Only light RE metals (La to Nd) can be produced by molten salt electrolysis because these have a relatively low melting point compared to those of medium and heavy RE metals. Deposition of an alloy with another metal, Zn for example, is an alternative. The feed is a mixture of anhydrous RE chlorides and fluorides. The materials from which the electrolysis cell is constmcted are of great importance because of the high reactivity of the rare-earth metals. Molybdenum, tungsten, tantalum, or alternatively iron with ceramic or graphite linings are used as cmcible materials. Carbon is frequently used as an anode material. 

Red mercuric oxide, identical chemically to the yellow form, is somewhat less reactive and more expensive to produce. An important use is ia the Ruben-MaHory dry cell, where it is mixed with graphite to act as a depolarizer (see Batteries). The overall cell reaction is as follows ... 

Alkali-metal graphites are extremely reactive in air and may explode with water. In general, reactivity decreases with ease of ionization of M in the sequence Li > Na > K > Rb > Cs. Under controlled conditions H2O or ROH produce only H2, MOH and graphite, unlike the alkali-metal carbides M2C2 (p. 297) which produce hydrocarbons such as acetylene. In an important new reaction CgK has been found to react smoothly with transition metal salts in tetrahydrofuran at room temperature to give the corresponding transition metal lamellar compounds ... 

Some pigments promote corrosion owing to their content of soluble salts, their reactivity, or their electrochemical action, and thus should be avoided. Rust of the spotted type can be the consequence of their presence in a paint, especially the hrst coat, e.g. of graphite (noble to steel), some red oxides of iron, gypsum, ochre or lamp black. 

The physicochemical properties of carbonaceous materials can be altered in a predictable manner by different types of treatments. For example, heat treatment of soft carbons, depending on the temperature, leads to an increase in the crystallite parameters, La and Lc and a decrease in the d(0 0 2) spacing. Besides these physical changes in the carbon material, other properties such as the electrical conductivity and chemical reactivity are changed. A review of the electronic properties of graphite and other types of carbonaceous materials is presented by Spain [3],... 

Jorne et al. [36] investigated the reactivity of graphites in acidic solutions that are typically used for Zn/Cl2 cells. The degradation of porous graphite is attributed to oxidation to C02. The rate of C02 evolution gradually decreased with oxidation time until a steady state was reached. The decline in the C02 evolution rate is attributed to the formation of surface oxides on the active sites. 

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