M. Alam

Diamond formation in air by the Fedoseev-Derjaguin laser process

Abstract Diamond and other high-pressure phases of carbon were synthesized in air by exposing fine particles of carbon black to carbon dioxide and Nd-YAG laser radiation. The high-pressure phases were separated from the carbon black by selective oxidation and were characterized by electron and x-ray diffraction. Formation of cubic diamond, chaoite and graphite was confirmed.

High‐pressure phases of SiO2 made in air by Fedoseev–Derjaguin laser process

Exposure of a falling stream of 1 μm average size α‐quartz particles to a continuous wave or pulsed CO2 laser beam in air resulted in the formation of a complete series of high‐pressure phases of silica: coesite, stishovite, and apparently even denser forms with α‐PbO2 and Fe2N structures. Since the laser exposure technique works with the carbon black to diamond transition, the technique is confirmed as a simple and generally applicable means to achieve the same effects as exposure to several hundred kilobars pressure.

Reaction between CO2 and coke doped with NaCN

Abstract The role of NaCN as a catalytic precursor in the reaction between coke and carbon dioxide is examined. The experimental work included determination of reaction rate, examination of the chemical stability of NaCN and characterization of coke at various stages of reaction. The extent of sodiumcarbon contact was physically modelled by examining the distribution of potassium in the interior of a KCN doped coke sample after partial reaction. Physical evidence is presented to demonstrate that at 1123 K, the vapor cycle mechanism is the predominant mode of catalysis with catalyst concentration and specific surface area being the two most important directly measureable rate determining factors. Analysis of the rate data on the basis of a structural model demonstrated that when NaCN was used, the enhancement of the rate was inadequate for the diffusion of CO2 through the porous coke to be important.

Structural effects in the reaction between carbon dioxide and coke doped with various potassium bearing catalytic precursors

The rate of reaction between carbon dioxide and coke with and without the additions of KCN, KOCN, and K2CO3 was studied using thermogravimetry. Since both potassium and carbon are lost during the reaction, the concentration of potassium in the coke samples was determined as a function of the extent of the reaction by atomic absorption spectrometry. The changes in the specific surface area due to the reaction were studied by the nitrogen adsorption technique. The changes in the pore structure of coke were investigated by mercury porosimetry and scanning electron microscopy. The distribution of potassium in the coke structure was examined as a function of the reaction time by the energy dispersion X-ray technique. Furthermore, since sulfur is known to influence the rate of the C-CO2 reaction, the sulfur content of the coke samples with or without the addition of catalytic precursors was monitored as a function of the extent of reaction. The influences of the structural parameters and the concentration of potassium on the rate of the coke-CO2 reaction were determined. The rate data were analyzed on the basis of a structural model to examine the contributions of the chemical reaction and the pore diffusion on the overall rate of the coke-CO2 reaction.

A comparative study of the roles of KCN and NaCN as catalytic precursors in the Boudouard reaction

The rate of reaction between carbon dioxide and coke with or without added KCN and NaCN was studied using thermogravimetry. The chemical stability of KCN or NaCN during catalysis, the changes in the concentration of potassium or sodium in coke and the pore structure of coke were studied as a function of time. The influences of these variables on the rate of coke-CO2 reaction were determined. Since the catalysis depends on the catalyst-carbon contact, the distribution of potassium in the coke structure was examined. A porous solid reaction model was used to examine the contributions of chemical reaction and pore diffusion in the overall rate of coke-CO2 reaction.

Desulphurization of coal-derived char using mixtures of steam and methane

Abstract Results of a laboratory scale experimental study on the desulphurization of coal char by steam-methane mixtures are presented. The char was prepared from a high sulphur, medium volatile, bituminous coal. The variables studied were temperature and reacting gas composition. The concentration of sulphur, specific surface area, pore size distribution and char reactivity were determined before and after the desulphurization reaction. A significant amount of sulphur was removed when coal char was reacted with 3–20 mol% steam in steam-methane mixtures in the temperature range 703–823 K. Carbon gasification was effectively eliminated by this technique. Although small increases in both the specific surface area and pore volume occurred, the reactivity of the char was practically unaffected by the desulphurization reaction.