Graphite reaction with carbides

Reaction with carbon (graphite) at above 400°C produces a series of carbides, such as KC4, KCs, and KC24. With carbon monoxide, an unstable explosive carbonyl forms ... 

The carbide BejC is made by hot pressing BeO with C at 1400-1650°C. Flowing Hj or vacuum accelarates the reaction. Molten Be in contact with graphite forms the carbide at the interface, but further reaction is slow. The presence of Hj accelerates this reaction by transporting carbon to all surfaces are not in direct contact with graphite. A more efficient method involves heating Be and C powders together at 1100-1150°C. The red-brown color of the carbide is altered by impurities and stoichiometry. 

The alkali metal-graphite compounds are extremely reactive. They ignite in air and may react explosively with water. In the controlled reaction with water or alcohol only alkali hydroxide and hydrogen result there is no acetylene or any other hydrocarbon. Fredenhagen concluded from this that the compounds could not be carbides. Mercury dissolves the alkali metal out of the lattice. When treated with liquid ammonia, CgMe gives up only a third of the alkali metal and takes in its place two molecules of ammonia (see Section IIIA4). 

Carbothermic reactions are sohd-sohd reactions with carbon that apparently take place through intermediate CO and CO2. The reduction of iron oxides has the mechanism Fe Oy-H CO =>xFe-t C02, C02 + C=>2C0. The reduction of hematite by graphite at 907 to 1007°C in the presence of hthium oxide catalyst was correlated by the equation 1 — (1 — x) = kt. The reaction of sohd ihnenite ore and carbon has the mechanism FeH03-l- CO=>Fe -I-Ti02 + C02, CO2 + C = 2CO. A similar case is the preparation of metal carbides from metal and carbon, C -I- 2H2 CH4, Me -I- CH4 MeC -I- 2H2. 

In the early zircon chlorination plants such as used by W. J. Kroll [K3] at Albany, Oregon, zircon was first converted to zirconium carbide by reaction with graphite in a graphite-lined arc furnace at 1800 C ... 

The alkali metals form only ionic carbides, mostly simple ionic salts of acetylene, M2C2, which liberate acetylene on reaction with moisture. There has been much recent interest in permetalated and hypermetalated hydrocarbon species, or methanides . Most studied in this respect has been lithium, presumably because of its volatility and amenability to calculation. Mass spectrometric and calculational evidence has been presented for CLie, CLis, and C2Li4, but real samples of CLi4, C3Li4, and C5Li4 are preparable. All are pyrophoric powders. The heavier metals form another class of carbide , the graphite intercalation compounds, but as the electron has not been totally freed from the metal, these were considered in the previous section. 

Iron catalysts present special problems for the determination of the adsorbed species. The iron may be carburized during the reaction and this leads to a change in the bulk composition of iron catalyst with time on stream. Bianchi et al. determined that iron was partly converted into a mixture of e -Fe2 2C and x Fe2 5C during the reaction using Mossbauer spectroscopy. The adsorbed carbon surface species were determined to be present in three forms small amounts of reactive CH species which produced the bulk of the hydrocarbon products during reaction, a carbidic species with some associated hydrogen, and inactive graphitic carbon species. 

Vapour-phase Species. The chemical properties of carbon vapour have been reviewed by Skell et al The report describes the preparation of and compositions of the vapour and discusses the chemistry of the constituent species, particularly C, Cg, C3, and C4. Several papers describing detailed aspects of the chemistry of these vapour-phase species have also been published. Chemical reactions of C, Cg, and C3, formed by laser-induced vaporization of either graphite or tantalum carbide, with oxygen, hydrogen, or methane have been studied by means of time-resolved mass spectrometry and gas-phase titrations in an attempt to determine the relative abundances of these three species in the vapour phase (Table 1). The techniques developed and... 

B4C reacts with CO2 to yield B2O3 and CO or free carbon [96]. Boron carbide neither interacts with sulfur and phosphorus vapors, nor with nitrogen up to 1200°C. BN can be formed upon reaction with nitrogen at higher temperatures, or when ammonia is added. With chlorine it reacts above 1000°C to form BCI3 and graphite. Bromine and iodine do not react with B4C [98],... 

A rather different approach has been developed for reaction sintered silicon carbide (RSSC), first developed in the former Soviet Union. In this process a powder preform of mixed graphite and silicon carbide is immersed in a liquid bath of molten silicon. The silicon wets and infiltrates the preform, reacting with the finely-divided graphitic component (carbon black). In the best case, all graphite is reacted and the residual sihcon content is no more than a few percent. The product of the reaction, silicon carbide, firmly bonds the silicon carbide preform powder... 

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