John J. Freeman

Studies of activated charcoal cloth. III. Mesopore development induced by phosphate impregnants

Abstract Nitrogen adsorption isotherms have been determined at 77 K on samples of activated charcoal cloth prepared from viscose rayon cloth after impregnation of the latter with aqueous solutions containing various phosphate compounds. The results obtained indicate that a much wider range of isotherm type and hysteresis loop may be achieved with phosphate impregnants than with the borates studied previously. Analyses of the isotherms employing the αs method indicate that although all the adsorbents were highly microporous (pore width

Evolution of micropore structure of activated charcoal cloth

Abstract A series of microporous charcoal cloths of burn-offs between 20 and 92% have been prepared and studied by means of nitrogen, isobutene, methanol, and water adsorption isotherm measurements. The results indicate that at a level of burn-off of about 50%, the polarity of the surface falls to a minimum while the micropore volume, when expressed in terms of the same initial weight of carbon, reaches a maximum. At higher levels of burn-off both pore widening and pore narrowing occur. In addition, significant shrinkage of the carbon structure occurs at all stages of burn-off. The results are discussed in terms of a simple model, and it is concluded that densification of the carbon structure during activation exerts a significant influence on the evolution of the micropore structure.

Studies of activated charcoal cloth. I. Modification of adsorptive properties by impregnation with boron-containing compounds

Adsorption isotherms of nitrogen have been determined at 77 K on samples of activated charcoal cloth prepared from viscose rayon cloth after impregnation of the latter with aqueous solutions of various boron-containing compounds. Application of the αs-method of isotherm analysis revealed that all the adsorbents were highly microporous but, in addition, some possessed an appreciable surface area located outside the micropore structure. This “external” area was especially large (200–300 m2 g−1) in the case of activated charcoal cloths derived from samples initially impregnated with aqueous solutions containing boric acid/Nacl or boric acid/borax.

Studies of activated charcoal cloth. V: Modification of pore structure by impregnation with certain transition metal salts and oxo-complexes

Abstract Samples of activated charcoal cloth have been prepared by pretreatment of viscose rayon with a number of transition metal oxo-complexes (Mo, V, and W) and chlorides (Fe and Co), followed by carbonization in nitrogen and activation in carbon dioxide at 850°C. Significant modification of both adsorptive properties and fiber morphology occurred, resulting in chars having a wide range of pore structure type according to the particular impregnant employed. The development of microporosity was limited in cases where overall char reactivity was enhanced. Sodium orthotungstate was found to induce the hollowing out of fiber ends during activation.

Studies of activated charcoal cloth. II. Influence of boron-containing impregnants on the rate of activation in carbon dioxide gas

The influence of aqueous solutions of boron-containing compounds as impregnants of viscose rayon cloths on the subsequent activation of the derived carbonised materials in CO2 gas at 850°C has been studied. The presence of Na+ (or other alkali metal ions) is essential for the enhancement of the rate of activation above that observed for the untreated cloth or for the cloth initially impregnated with aqueous boric acid solutions. However, in terms of the activation rate generated, borax is more effective as an additive to boric acid solutions than sodium chloride. The results are interpreted in terms of the catalytic abilities of various alkali metal ions in the systems studied and the complexity of the borate species generated at different pH values in the aqueous impregnant solutions employed.

Adsorption of nitrogen and water vapour by activated Kevlar® chars

Abstract Fibrous activated carbons were prepared from Kevlar® (i.e. poly (p-phenylene terephthalamide), in the form of a commercially available woven textile. The cloth was carbonised in nitrogen and activated in either steam or carbon dioxide to varying burn-offs at 1123 K. The resultant activated chars were characterised by nitrogen adsorption, water sorption, and elemental analysis. It was found that significant differences existed between the chars activated in steam and carbon dioxide. Kevlar® chars were found to have a greater affinity for water vapour than comparable rayon chars. The pore volume developed in Kevlar® chars tended towards a maximum value as the burn-off increased.

The preparation and adsorptive properties of ammonia-activated viscose rayon chars

Abstract Viscose rayon chars have been activated in ammonia under varying conditions in order to investigate whether the presence of N-containing groups in the char structure led to a limitation of pore development in the micropore range, as is the case for polyarylamide-derived chars. It was found that two types of nitrogen species are formed and that the resultant chars are all, except in one case, essentially microporous. The amount of nitrogen present is limited as the process of “deactivation” of active sites by reaction with ammonia occurs. This may account for the limitation of pore development. Introduction of nitrogen into the char does not produce significant pore narrowing. This tends to confirm the predominant role of precursor crystallinity in determining the nature of the pore structure formed during activation.

Rates of activation and scanning electron microscopy of polyarylamide-derived chars

Abstract Fibrous activated carbons were prepared from Kevlar® (poly (p-phenylene terephthalamide)) and Nomex® (poly (m-phenylene isophthalamide)) by carbonisation in nitrogen and subsequent activation in steam of carbon dioxide to varying burn-off s at 1123 K. The resultant chars were characterised by activation rate studies, scanning electron microscopy and, in the case of the Nomex chars, energy dispersive X-ray analysis. It was found for both the polyarylamide-derived chars that significant differences existed between the chars activated in steam and carbon dioxide. Steam reacts much faster than carbon dioxide with these chars at elevated temperatures. This may be due to its smaller molecular size, resulting in an increase in diffusion and accessibility in and out of the constricted char structure, its higher intrinsic reactivity, or to specific reactions with metallic residues. The catalytic activity of metallic residues, rather than the crystallinity differences between the two polymers, is the suggested reason why Kevlar chars are nearly three times more reactive than Nomex chars. The appearance of the external surfaces of all the chars can be related to the percentage burn-off and the activation gas used. The presence of metallic residues leads to pitting on activation, which increases with progressive burn-off. At high burn-offs, the action of metallic residues in steam and carbon dioxide results in homogeneous and localised surface pits, respectively.

Element-containing carbon fibres: recent USSR/Eastern European research in fibre technology

This review is a survey of carbon fibre research work undertaken in the Soviet Union and Eastern European countries as reported in the literature up to the end of 1987. Matrix-modified fibres, ordered/crystalline structures, adsorption from gaseous and solution phases, catalytic properties, and the development of ion-exchange fibres and protective heat-resistant coatings are discussed in the context of comparable Western research.

Socializing the Self: Autoethnographical Performance and the Social Signature

The further we move towards control over the reproduction of images, events and experiences, the more enhanced, perhaps even desperate, our attempts at capturing the real have become. As the site in which the represented other of character is made manifest through the viscerally authentic performer, live work has always shown a tension between self and the shadows it throws; and no form is at the same time as shadowy and substantial as autobiography. Because the search for the defining features of autobiographical performance has become something of a sub- industry in itself - a critical search to equate the paradoxical elements of facts and subjectivity, honesty and artifice - this chapter needs to come clean about what it will be attempting to add to the field, and also what it will not.