K.C. Nagpal

Modification of PAN precursor—Its influence on the reaction kinetics

Abstract Polyacrylonitrile (PAN) fibers of special grade variety for making carbon fibers, have been modified by stretching in the presence of a plastisizer to 70% maximum strain. By doing so, the diameter of the original fibers is reduced from 12.5 μ. to 10 μ, and the angle of orientation of the molecular chains along the fiber axis is reduced to almost half of its original value as determined by the X-ray flat-plate technique. The tensile strength and the Youngs modulus values of the modified samples show an improvement of about 70% and 100%, respectively. A systematic study on the reaction kinetics up to 265°C by following DSC, TGA, and TMA has revealed various interesting deviations in the characteristics of modified PAN precursors over those of the original sample. The implications of these are discussed.

Crystallinity of PAN precursors

Etude de la cristallinite de fibres de polyacrylonitrile utilisees comme precurseurs de fibres de carbone

The optical properties of CuGa0.5In0.5Se2 thin films

CuGa0.5In0.5Se2 thin films with thickness in the range 50 to 280 nm were deposited by thermal evaporation of prereacted material on glass substrates. The films were found to be polycrystalline with single phase having chalcopyrite structure as that of bulk material. The optical constants of these films were determined by transmittance and reflectance measurements at normal incidence for light in the wavelength range 400 to 1200 nm. Three characteristic energy gaps of 1.30, 1.55 and 2.46 eV were obtained from an analysis of the optical absorption spectrum. The optical constants of the films appear to be independent of the substrate temperature.

Application of John's isotherm to predict the adsorption of a binary gas mixture from the adsorption of individual component gases

Abstract It is shown that one can predict the adsorption of a binary gas mixture from the adsorption of individual component gases by means of Johns isotherm. It is found that the slope and intercept of Johns adsorption isotherm for binary mixture is equal to mean of the slopes and intercepts of individual adsorption isotherms. The relation given by Lewis et al . may be used to prove the validity of the above method.

The complete identity of the isotherm equations of dubinin and john for determination of the volume and degree of microporosity of carbon

Abstract Complete identity of adsorption isotherms of Dubinin and John is proved by showing that the slope D of Dubinin equation is equal to slope D0 of Dubinin type equation derived from Johns isotherm and also showing that the terms involved in D and D0 are fundamentally the same. It is shown that the degree of microporosity is proportional to n the slope of Johns isotherm. B the measure of microporosity in Dubinin equation is inversely proportional to n. The advantages of Johns isotherm are also given.

Characterization of structural parameters of porous materials by a new adsorption isotherm

A new adsorption isotherm equation, log logP=C+n logv, has been developed which characterizes many properties of the structure of porous materials, such as monolayer capacity of isotherms of Types I, II and IV, limiting micropore volume at extremely low pressure, degree and dispersion of micropores, mesopore surface area, mean pore size, etc. The equation has been successfully extended to binary and ternary mixtures, data for which have been obtained from the individual isotherms. It is also shown that a linear plot of the new isotherm implies that the distribution of adsorption volume with adsorption potential is Gaussian. Various other well know isotherm equations have been deduced from this new equation. The equation is direct and involves fewer mathematical calculations for solving the structural parameters of porous materials.

Determination of mesopore surface area in presence of micropores

A modified t-method known as tJ method, capable of finding mesopore surface area in absence or presence of micropores in which adsorption may be pressure dependent or pressure independent is described by the application of Johns adsorption isotherm equation.

A new criterion to determine the separation factor for the adsorption isotherm of a gas mixture

We show that the separation factor can be found by applying Johns adsorption isotherm of gas mixture

Determination of surface area/monolayer capacity or limiting micropore volume of carbons from binary and ternary mixtures

It is shown that one can predict the adsorption of binary and ternary mixtures in any percentage ratio from the adsorption of individual component gases by means of Johns isotherm equation. The surface area of mesoporous materials or the limiting micropore volume of microporous materials from binary and ternary mixture adsorption isotherms is given. The relation given by Lewis et al. may be used to prove the validity of the above method and determine the contribution of each component of the mixture.