P.J. Reucroft

Gas-induced swelling in coal

Abstract Dilatometric studies were carried out on three coal samples in various gaseous environments. The carbon contents of the three samples were 65.8%, 78.3% and 83.8% d.a.f., respectively. The sample with the lowest carbon content has shown the maximum length increase (0.5%) on exposure to a CO 2 atmosphere. This corresponds to a volume increase of 1.31%. Volume increases of the order of 9% are necessary to account for the surface areas usually found by CO 2 adsorption on coal (200–250 m 2 g −1 ). However, the dilatomeric studies have generally not reached equilibrium even after 280 h of exposure to CO 2 . The 1.31% volume increase value is thus probably a lower limit, a higher value should be obtained at equilibrium.

Vapor adsorption on coal- and wood-based chemically activated carbons: (I) Surface oxidation states and adsorption of H2O

Abstract X-ray photoelectron spectroscopy (XPS) was employed to evaluate the surface element distribution/concentration and surface chemical structure of coal- and wood-based chemically activated carbons and to investigate the effect of these features on the adsorption of water vapor at low relative pressure and room temperature. It was found that high surface area carbon samples generally show low concentrations of surface oxygen and low surface area carbon samples generally show high concentrations of surface oxygen. The concentrations of carbon surface oxygen groups such as C–O and CO generally decrease with increasing heat treatment temperature. Increased water vapor adsorption on the lower surface area activated carbons can be correlated with higher concentrations of surface oxygen functional groups.

Deposition and structural characterization of ZrO2 and yttria-stabilized ZrO2 films by chemical vapor deposition

Zirconium oxide films were deposited by metal-organic chemical vapour deposition using zirconium acetylacetonate as the source material. Use of water vapor together with oxygen as secondary reagents ensured the deposition of carbon-free, pure zirconium oxide films. A study was carried out to investigate the phase structure of films grown under different deposition conditions. Metastable tetragonal zirconium oxide was a dominant phase when the deposition temperature was low or the film contained large amounts of carbon impurity. Simultaneous decomposition of zirconium acetylacetonate and yttrium dipivaloylmethane with water vapor and oxygen was used to obtain highly texturized yttria stabilized zirconium oxide films at relatively low deposition temperatures. The dominant phase was changed from tetragonal to cubic as the amount of yttrium within the films increased. A zirconium oxide film grown at 620 °C, containing about 6 at.% yttrium, was highly texturized, and consisted of a cubic phase with a = 0.5122nm

Surface area and swellability of coal

Sorption data have been obtained for a range of vapours on a Kentucky No.12 coal. The data at high relative vapour pressures (P/P0 > 0.3) are interpreted in terms of coal swelling. The sorption data at low relative vapour pressures (P/P0 < 0.3) are used to obtain information on surface area. The results indicate that surface areas obtained in this way are influenced by vapour-induced swelling effects.

Diffusion barrier and electrical characteristics of a self-aligned MgO layer obtained from a Cu(Mg) alloy film

Diffusion barrier characteristics and electrical properties of self-aligned MgO layers obtained from a Cu(Mg) alloy film have been investigated. Self-aligned surface and interfacial MgO layers were formed upon annealing a Cu(Mg) film in an oxygen ambient and prevented interdiffusion of Cu in SiO2 up to 700 °C. The thermal stability of a pure Cu/TiN/Si multilayer system has been significantly enhanced up to 800 °C by the MgO layers by forming a MgO/Cu/MgO/TiN/Si multilayer system. A combined structure of Si3N4(500 A)/MgO(100 A) increased the breakdown voltage up to 20 V from 15 V and reduced the leakage current density down to 3×10−9 A/cm2 from 1×10−8 A/cm2 compared to a pure copper system. Consequently, the deposition of Cu(Mg) alloy followed by annealing in an oxygen ambient gives rise to the formation of a self-aligned MgO layer with excellent diffusion barrier and electrical characteristics and the film can be applied as a gate electrode in thin-film transistor/liquid-crystal displays, resulting in a r...

Factors Affecting Passivation of Cu(Mg) Alloy Films

Variables affecting the passivation capability of Cu(Mg) alloy films, which were sputter deposited from a Cu (4.5 atom %) target, have been investigated. As-deposited Cu(Mg)/SiO 2 /Si multilayer samples were annealed for 30 min in various oxygen ambients at pressures ranging from 10 mTorr to 30 Torr and at various temperatures in the 200-800°C range. The results show that the passivation capability of a Cu(Mg) alloy film is a function of annealing temperature, O 2 pressure, and Mg content in the film. Increasing the annealing temperature favors formation of a dense MgO layer on the surface. Decreasing the O 2 pressure enhances the preferential oxidation of Mg over Cu. Furthermore, increasing the Mg content in the Cu(Mg) film promotes formation of a dense MgO layer. Vacuum preannealing before taking the as-deposited samples to O 2 annealings was found to be very effective in segregating Mg to the surface, facilitating the passivation capability of the Cu(Mg) alloy film even when the Mg content is low. In the current study, self-aligned MgO layers with low resistivity and an effective passivation capability over the Cu surface have been obtained by manipulating these factors when Cu(Mg) thin films are annealed.

Adsorption of phosgene and chloroform by activated and impregnated carbons

Equilibrium adsorption and desorption isotherm data at room temperature have been obtained for phosgene and chloroform vapors on BPL grade activated carbon, ASC whetlerite and four ASB impregnated carbons. Isotherm data were plotted in the form of the Dubinin-Polanyi equation. Experimental affinity coefficients (βex) for phosgene with chloroform as a reference, were calculated for all the carbons except ASC whetlerite from the slopes (k) of the Dubinin-Polanyi plot, and were compared with the theoretical affinity coefficients (βth) in order to assess the adsorption capabilities of different adsorbents. In the case of phosgene on ASC whetlerite carbon, significant chemisorption takes place along with physical adsorption and the resulting isotherm shows non-linear behavior. Attempts were made to separate the chemisorption contribution from the total adsorption and thus assess βex for the physical adsorption contribution.

Fabrication of aluminum oxide thin films by a low‐pressure metalorganic chemical vapor deposition technique

Amorphous Al2O3 thin films were grown on Si(100) and glass substrates by low‐pressure metalorganic chemical vapor deposition using aluminum acetylacetonate and water vapor as source materials. Water vapor played an important role in the oxidation process and produced carbon‐free, pure Al2O3 films. The deposition temperature could be lowered to 230 °C. The films were characterized by means of x‐ray diffraction, x‐ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, and ellipsometry.

Structural characterization of cobalt catalysts on a silica support

Abstract In situ X-ray diffraction was employed to characterize the structure of several cobalt catalysts on a silica support. The catalysts were reduced in flowing hydrogen at 350 °C for about 16 h and X-ray diffraction patterns were collected. After reduction metallic cobalt was found to be present in the hcp and fcc forms in the ratio of 7:3 and 17% of the hexagonal close-packed planes were found to be faulted. If surface atoms adjacent to stacking faults are sources of active sites, the density of active sites was estimated to be 4.0 × 10 19 per gram of cobalt.

Adsorption of cyanogen chloride and hydrogen cyanide by activated and impregnated carbons

Abstract Equilibrium adsorption and desorption isotherm data at room temperature are reported for cyanogen chloride and hydrogen cyanide vapors on BPL grade activated carbon, ASC whetlerite and several ASB impregnated carbons. Isotherm data have been analyzed in terms of the Dubinin-Polanyi equation. The experimental affinity coefficients ( β ex ) for the vapors, with respect to chloroform, were determined from the slope of the Dubinin-Polanyi plot. The relative adsorptive capabilities of the adsorbents were assessed by comparing the theoretical affinity coefficient ( β th ) with β ex · β th was estimated assuming that physical adsorption is the dominant adsorption process. Cyanogen chloride shows about 20% higher adsorption than predicted on BPL activated carbon and about 30% higher than predicted on the ASB impregnated carbons. Hydrogen cyanide shows about 30% higher adsorption than predicted on BPL activated carbon and about 45% higher adsorption than predicted on the ASB impregnated carbons. In the case of ASC whetlerite, the adsorption of both vapors was much greater than predicted and the isotherms displayed a levelling-off trend in the low pressure region indicating strong retention through chemisorptive interactions. No unique β ex could be determined from the original isotherms. An attempt was made to separate the chemisorption contribution from the total adsorption, and thus assess β ex for the physical adsorption contribution.