Adsorption-desorption Phenomena Research Articles

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Study of the adsorption of organic substances at a mercury electrode by the Kalousek commutator technique

Summary The polarographic method of discontinuously changing potential (4–128 Hz) known as the Kalousek commutator technique, was used for the study of adsorption-desorption phenomena of tri-n-butyl phosphate, thymol and sodium lauryl sulphate on the mercury from aqueous solutions. The dropping mercury electrode and the hanging mercury drop electrode were used. The desorption waves were measured at potentials more negative than the electrocapillary maximum. The corresponding adsorption isotherms were obtained from the concentration dependence of the wave heights. The method is proposed for the analytical determination of surface active substances in dilute solutions.

Determination of some methylcarbamate insecticides by a.c. polarography and cyclic voltammetry

The study of adsorption-desorption phenomena represents an important extension to the range of organic compounds that can be determined by electrochemical methods. The present work has utilized this approach for the determination of a range of methylcarbamate insecticides. The tensammetric behaviour of this class of compound at the mercury electrode has been investigated by a.c. polarography and the optimum experimental conditions for their analytical determination have been derived. Cyclic voltammetry has also been used to study the electrode process and by using the peak obtained on the cathodic sweep it was possible to extend the limit of detection to the ppm level.

Relation of Measured Outgassing Pressures to Surface Adsorption in Satellite Borne Pressure Gauges

Two different pressure gauges were mounted in the Explorer 32, a spin stabilized, aeronomy satellite, in such a way that they were alternately exposed to a beam of atmospheric gas and to a nearly total vacuum. During exposure to the nearly total vacuum, it was possible to measure the pressure in the gauge enclosure produced by gas desorbed from the gauge surfaces. This outgassing pressure was found to depend in a fixed way upon the ambient atmospheric density and the elapsed time since the satellite was last at perigee. The main features of the variation of outgassing pressure with time near perigee were reproduced using a Langmuir model of surface adsorption, with an adsorption probability near 10−4 and a desorption rate from a surface covered with one monolayer of gas near 1013 particles per sq cm per sec. The results of this study show that the adsorption-desorption phenomena have a component that occurs during times comparable to an orbit period (100 min).

Adsorption–Desorption of Residual Gases in High Vacuum

Measurements have been made on the adsorption and desorption of residual gases in an ultra-high-vacuum ion-pumped system using mass spectrometer analysis. The predominant residual gases in our system are hydrogen, carbon monoxide, and water vapor at a total pressure of about 5×10−10 Torr. Mass analysis indicates two hydrogen peaks, one carbon monoxide peak, and no water vapor peak on thermally heating a molybdenum ribbon from room temperature to 1000 °C. Desorption and readsorption are observed continuously by monitoring ion desorption induced by an extremely low density (∼10−7A/cm2) electron beam. Data obtained by this technique correlated very well with that obtained by thermal flashing and aids in understanding the reactions that are occurring. The use of electron-induced ion desorption coupled with mass analysis is seen to be a very useful tool in studying adsorption–desorption phenomena in high vacuum by allowing continuous observation as substrate conditions are changed.

The use of a thermistor for detecting eluent fronts in liquid-solid chromatography.

The adsorption-deso rp tion phenom enon which occ urs when a mul ticomponent liquid is forced t hrough a column of solid adso rbent is acco mpa nied by an evo lution of heat.. The res ulting temperature cha nge occurring within the colum n m ay be monitored and correlated with t he composit ional changes oceurri ng in the liquid phase. The co nstruc t ion a nd use of t he rmisto r sensing cells is descri .bed. These cells a re a n in tegra l part of the column, and t hey ar~ maill tal ned at a pl) rOpl:late temp eratures by eit her co nstan t temperature, liquidclrculatmg baths or by t ra nSlsto l'lzed temperature co ntrollers. Bo t h met hods of temperature con trol are described, and vario us app li cations of t he cells a re discussed.

Hydrophobic monolayers adsorbed from aqueous solutions

Experimental methods are described for the preparation and examination of hydrophobic monomolecular films adsorbed, and isolated from aqueous solutions of certain types of polar-nonpolar organic compounds. The use of contact angle measurements for the quantitative characterizations of the hydrophobic and oleophobic properties of such films permits the evaluation of the various factors governing their formation, structure, and repellency characteristics. The present paper reports the results of studies on several members of a homologous family of primary amines of the normal alkyl type adsorbed onto platinum surfaces. The critical limits to hydrophobic film formation and the degree of hydrophobicity are found to be functions of the amine concentration and the pH of the generating solution. A definite correlation is established for the relative effectiveness of these factors and the length of the hydrocarbon chain in the aliphatic portion of the amine molecule. The marked response of hydrophobic film formation to pH and concentration is interpreted as an adsorption-desorption phenomenon in which the equilibrium conditions are determined by the solubility and degree of ionization of the individual amines. The short chain amines (up through dodecyl) are found to be most adsorptive in the alkaline region, whereas film formation of the hexadecylamine is limited to the highly acid regions. The intermediate tetradecylamine evinces a transitional behavior, having two separate pH regions favorable to film formation. The identity of adsorbed monomolecular films isolated hydrophobically from aqueous solution and oleophobically from the molten amine or from solution in hexadecane is established. The use of water as solvent increases the number of molecular types available for study as reproducible, repellent films. The method is proposed as a possible approach to the examination of films important in the fields of selective adsorption, mineral flotation, corrosion inhibition, and “pickling” of metals.