Clifford Lawrence Spiro

The inhibition of graphite oxidation by phosphorus additives

Abstract Impregnation of graphite with organic phosphate and phosphite esters has been found to result in increased resistance to air oxidation at elevated temperatures. Thermal decomposition of the phosphorus compounds at 200–600°C leaves a hydrophilic residue strongly adsorbed on the graphite surface at active sites where oxidation normally occurs.

The effects of boron additives on the oxidation behavior of carbons

Abstract Impregnation of graphite with aqueous solutions of boric oxide or with organo-borates has been found to result in marked reduction in the rate of oxidation of the graphite in dry or moist air between 600 and 1000°C. At these temperatures, the additives probably form a glassy oxide residue which blocks active sites on the graphite surface.

Catalysis of coal char gasification by alkali metal salts

Abstract A study has been made of the gasification behaviour, in carbon dioxide and steam, of a number of coal chars doped with small amounts of alkali metal carbonates. For a given additive, the magnitude of the catalytic effect increased with the rank of the parent coal. A progressive loss in catalytic activity on thermal cycling during steam gasification was associated with reaction of the alkali salts with mineral matter in the chars. The kinetic data were consistent with catalytic mechanisms involving oxidation/reduction cycles on the char substrates.

Production and characterization of smooth, hydrogen‐terminated diamond C(100)

We report the production of smooth and well‐ordered C(100) surfaces by exposure to a pure hydrogen plasma. A two domain 2×1 surface reconstruction is observed by low energy electron diffraction with half‐order spots visible using incident electrons with energies as low as 13 eV. High‐resolution electron energy loss spectroscopy reveals a large enhancement in specular reflectivity of low energy electrons following plasma treatment. The hydrogenated surface is stable in air and free of adsorbed hydrocarbons upon insertion into ultrahigh vacuum.

Eutectic salt catalysts for graphite and coal char gasification

Low melting binary and ternary eutectics of the alkali metal halides, carbonates and sulphates have been found to be more effective low temperature catalysts for the CO2 and steam gasification of graphite and coal chars than the pure salt components. The reduced melting points of the eutectic phase facilitate contact between the catalyst and the carbonaceous substrate.

Catalytic CO2-gasification of graphite versus coal char

Abstract The effects of alkali carbonate catalysts on the C0 2 -gasification of Illinois No. 6 hvB bituminous coal char, demineralized Illinois No. 6 coal char, Pittsburgh No. 8 hvA coal char, Navajo subbituminous coal char, Reading anthracite coal char, North Dakota A lignite char and spectroscopic grade highest purity graphite are reported. Alkali carbonate salts are effective Boudouard catalysts for all these substrates, but salient differences between coal char and graphite reactivity are observed. To account for these differences, a redox mechanism based on alkali hydride intermediates is proposed.

Space-filling models for coal. 2. Extension to coals of various ranks

Abstract Space-filling models of scale 10 8 :1 have been constructed for low-, intermediate-, and high-rank coal molecules. The molecules have been designed to conform to experimentally determined parameters, such as chemical composition, aromaticity and ring index. The molecules do not actually occur in nature, but are merely statistically-averaged structures. The low-rank coal species appears fluffy, porous and random, with essentially all interior atoms exposed as surface. The intermediate-rank coal model structure is more flat and oriented, with closed ended pores and only occasional non-coplanar protrusions due to aliphatic, alicyclic, and hydroaromatic moeities. The high-rank coal model is highly ordered with locally graphitic domains. Physicochemical properties and ultimate utilization of the various coals are discussed with respect to the model structures.

Significant parameters in the catalysed CO2 gasification of coal chars

Abstract Alkali and alkaline earth carbonates have been used to catalyse the C02 gasification of coal chars prepared by pyrolysis of Illinois No.6 coal. This study found that alkaline earth carbonates are fair gasification catalysts, though throughputs are insensitive to loadings in the range of 5–20 wt%. The order of efficacy is Ba > Sr > Ca. Alkali carbonates are excellent catalysts, with throughputs showing a dependence on loadings and atomic number. In particular, at high loadings (20 wt%) the order is Cs > K > Na > Li. As kinetic parameters for the alkali carbonate catalysed Boudouard reaction with coal chars differ significantly from those for graphites, an alternative redox cycle mechanism has been proposed involving an alkali hydride intermediate.

Space-filling models for coal: a molecular description of coal plasticity

Abstract Space-filling models for four proposed coal molecules have been constructed. Of the four, only one could be built without alteration; the others contained spatially or sterically inaccessible moeities. A primary conclusion of this study is that the three-dimensional aspects of proposed structures should be considered along with other parameters. Based on the molecular models, a mechanism for thermal decomposition and plasticity is proposed. The essential features of the mechanism include thermolysis of aliphatic, alicyclic, and hydroaromatic groups which protrude from aryl planes. These smaller fragments act as spacers and lubricants, enabling the resultant parallel aryl planes to flow in two dimensions, unhindered and protected from cross-linking. It is this mobility which is suggested to cause thermoplastic behaviour in bituminous coals.

The effects of chlorine pretreatment on the reactivity of graphite in air

Abstract Pretreatment of graphite with gaseous chlorine at elevated temperatures has been found to result in increased resistance to oxidation in air in the temperature range 600–900°C. The inhibiting effect was most pronounced following chlorination at 800–900°C. Organo-halogen compounds which thermally decompose to give adsorbed halogen on the graphite surface also acted as oxidation inhibitors, when impregnated into graphite or when introduced as vapor into the air stream. Chlorine pretreatment at 800°C resulted in the formation of circular pits on the graphite basal plane surface during subsequent oxidation at 900°C, in contrast to the hexagonal etch pits formed on pure untreated graphite crystals.