Showing papers on "Langmuir published in 1975"

The Application of a Simple Chemical Model of Natural Waters to Metal Fixation in Particulate Matter

Abstract: A simple chemical model was used to investigate the mechanisms controlling the distribution of metals between soluble and particulate fractions in natural waters. The model particulates used were potassium bentonite, hydrous MnO2, and solid humic acid. The soluble species in natural waters were modelled by soluble humic acid, tannic acid, and bicarbonate. The sorption curves for Cu(II), Cd(II), and Zn(II) onto humic acid and MnO2 obeyed Langmuir adsorption isotherms whereas the sorption of the above ions onto bentonite followed a Freundlich isotherm. Chemical analysis of the total model using atomic absorption spectroscopy and differential pulse anodic stripping voltammetry indicated that copper distribution depends on the pH of the suspension: above pH 6.0, 50 % of the copper is sorbed onto the particulates whereas the copper in solution is in a complexed form; between pH 6 and 3.8 the soluble copper is distributed between organic complexes and "free" copper ion; between pH 4.2 to 2.5 copper is being des...

Surface contamination of active electrodes in plasmas: Distortion of conventional Langmuir probe measurements

Abstract: Laboratory experiments were conducted to determine the effectiveness of a newly developed pulse technique in eliminating surface contamination effects and associated hysteresis in Langmuir probe current‐voltage characteristics. We found that (i) the pulse technique was superior to the conventional continuous sweep approach to Langmuir probe diagnostics; (ii) substantial potentials can develop across contaminating surface layers and that these potentials can vary in the conventional Langmuir procedure resulting in determinations of electron energies higher than actually present in the ambient plasma; and (iii) attempts to achieve ’’clean‐probe’’ operation by heating can be of limited value.

Current Flow in Ion-Acoustic and Langmuir Turbulence Plasma Interaction

Abstract: The process of Langmuir and ion-acoustic turbulence interaction due to turbulent bremsstrahlung collisions is considered. It is shown that the ion-sound turbulence excites the Langmuir turbulence even for isotropic particle distributions but for anisotropic ion-sound turbulent waves. The presence of both ion-sound and Langmuir turbulence may lead to the excitation of currents which cause strong magnetic fields.

Adsorption and desorption of Cd on humic acid fraction of soils

Abstract: The adsorption of ionic Cd has been investigated on three humic acids isolated from podzol, rendzina and brown Mediterranean soils of Tuscany. The adsorption isotherms have been determined at 5 and 25°C. Cadmium adsorption was described by the Langmuir adsorption equation. Langmuir parameters were related to the functional groups content of humic acids and decreased in the following order: rendzina>brown Mediterranean soil>podzol. Adsorption was independent on temperature and increased with pH. Desorption experiments with 0.1 N NH4OAc and 0.25 M Cu (OAc)2 proved that Cd is adsorbed on humic acid about 50% in an exchangeable form and 50% in coordination complexes.

Hopping conduction in Langmuir films

Abstract: The dc conductance of Langmuir films of the Cd salts of fatty acids CH3‐ (CH2)n‐2‐COOH, with various n, has been measured at liquid‐nitrogen temperature. The conductivity decreases exponentially with increasing chain length of the fatty acid molecules. This agrees well with the theoretical prediction for hopping conduction in a multilayer system associated with interface states.

Influence of polysaccharide structure on dextran adsorption by montmorillonite

Abstract: Two dextrans of similar molecular weight (⩾2 × 10 6 ) but containing different structural linkages (B-215F: 95% α-1→ 6 and 5% α-1→ 3 and Polytran: 75% β-1→ 3 and 25% β-1→ 6) were adsorbed on Na-montmorillonite. Adsorption isotherms showed strong, H-2-type (high-affinity. Langmuir mono-layer adsorption) clay-dextran interactions for both polymers. Maximum adsorption of the Polytran dextran (60 mg 100mg clay) was 33 per cent greater than that of the B-512F dextran (44.5 mg 100mg clay) for comparative equilibrium systems. Stable clay-Polytran complexes containing up to 47% dextran were prepared. Excess Na 2 SO 4 (0.1 m ) did not affect the quantity of dextran adsorption by montmorillonite at the 15% dextran concentration. Acid hydrolysis and modified Pregl method-C analyses did not quantitatively recover adsorbed dextran from complexes containing more than 13 mg of dextran adsorbed per 100 mg of clay. Loss on ignition determinations were in good agreement with the difference measurements of dextran adsorption, suggesting that part of the C was expelled as something other than CO 2 in the ignition determinations. The maximum adsorption segment for Polytran was much smaller than the individual molecule. In contrast, the maximum adsorption segment for the B-512F dextran appeared to be the same magnitude as the individual polymer molecule. Adsorption segment length was regarded as a manifestation of the relative proportions of primary and secondary alcohol groups of the molecules.

Phosphate adsorption by synthetic amorphous aluminosilicates

Abstract: Summary Phosphate adsorption isotherms were determined for four synthetic amorphous aluminosilicate gels with A1: A1 + Si molar ratios of 0.29 to 0.88. The concomitant silicate release and acid consumed to maintain the pH of the suspensions constant were also measured. The adsorption isotherms were analysed applying a two-term Langmuir equation–assuming two types of sites. The experimental points fitted the predicted adsorption curves only up to a certain amount of phosphate adsorbed. The deviation at high phosphate adsorption values suggested the presence of more than two types of adsorption site. A comparison of phosphate adsorbed with the silicate released and acid consumed to maintain the pH constant indicated that, for a 3 h reaction time at concentrations below about 10 μmol cm−3, phosphate exchanges mainly with aquo and hydroxo ligands and with adsorbed silicate. At higher concentrations phosphate is adsorbed (i) on sites arising from the disruption of hydroxy aluminium polymers in the gels and (ii) by the displacement of structural silicate.

Charge relationships of phosphate sorption

Abstract: IT is generally accepted that the mobility of phosphate in soil systems is largely governed by sorption-desorption reactions1,2, but the mechanisms involved in these reactions have remained largely obscure. Studies3–5 have shown that sorption of phosphate by soils can be described by at least two Langmuir equations over a solution phosphate concentration range of up to approximately 8 × 102 µmol 1−1.Interpretation of these data has been complicated by the lack of an equilibrium condition, implicit in the Langmuir equation, and by the limited number of data points on the sorption isotherms. An alternative approach described here provides a reliable basis for the development of the sorption mechanisms.

Kinetics of Electrogenerative Hydrogenation over Platinum Black Electrocatalyst

Abstract: The kinetics of the electrocatalytic hydrogenation of ethylene at positive potentials has been studied over polytetrafluoroethylene-bonded, porous platinum black electrodes in perchloric acid electrolyte. Pore diffusion was generally not a significant factor except at low concentrations of reactants. Steady-state kinetic parameters and deuterium exchange results suggest that surface reaction of hydrogen with ethyl radicals is rate limiting. A mechanistic model is proposed and examined in terms of Temkin adsorption of hydrogen atoms in the low potential region (less than 0.18 V). Strong Langmuir adsorption of ethylene appears to take place for all mechanisms considered. The energy production of the electrogenerative reactor is favored by high electrolyte concentration, high alkene partial pressure, elevated temperatures, and increased catalytic loading.

Surface Tension of Aqueous Solutions of Disodium Monoalkyl Phosphates and Their Mixtures

Abstract: Disodium mono-dodecyl, mono-tetradecyl, and mono-hexadecyl phosphates were synthesized and the surface tension of aqueous solutions of each disodium monoalkyl phosphate (SAP) and of their mixtures were measured. On the basis of the surface tension values thus obtained, the influence of the hydrocarbon chain length of SAP and the effect of the mixing of SAP on the adsorption and the micelle formation were discussed. A modified Szyszkowski equation was derived from the Gibbs adsorption equation and the modified Langmuir adsorption equation by using the activity instead of the concentration. The modified Szyszkowski equation gave calculated values which were in good agreement with the experimental values of the surface tension. It was also found that the energy of adsorption per methylene group, ω, is 682 cal/mol. In mixed solutions, the modified Szyszkowski equation was used to obtain results in good agreement with the measured values of the surface tension, assuming an ideal mixing of SAP in the adsorption...

Phosphate sorption isotherms for some Sierra Leone soils

Abstract: Phosphate sorption isotherms were obtained for three acid highly weathered soils of Sierra Leone, by equilibrating air dry samples for 24 h with 0.01 M KH2PO4 solution at 25 °C. The Langmuir and Temkin equations were used to evaluate the sorption capacities for phosphate. Phosphate sorption maxima of 2439, 2137 and 1429 mg/kg soil and x/log c of 774, 718 and 610 were calculated; where x=phosphate sorbed (mg/kg soil) and c=equilibrium phosphate concentration (μmol dm−3). Qualitative relationships between these sorption parameters and other soil variables are shown.

Heating Rates for a Beat Frequency Laser Heated Plasma

Abstract: The heating of magnetized plasmas through the utilization of a beat frequency harmonic which is excited at a frequency near to that of a Langmuir mode in the plasma is examined. Heating rates are o...

Adsorption from solution, permeation through cellulose membrane, partition coefficient and surface tension of several antidepressants and phenothiazines.

Abstract: The physico-chemical properties of several antidepressants were studied in comparison with those of tranquilizing phenothiazines, intending to obtain some information useful to understanding of biopharmaceutical and pharmacological mechanisms of antidepressants. The adsorption isotherms of drug by carbon black (CB) were all observed in Langmuir type. The results suggested that the aromatic rings of drug molecules participate in the adsorption and that there is no special difference in behavior at the surface of CB between antidepressants and phenothiazines. Radii of drug molecule were evaluated by various methods, i. e., r1 from the molecular volume, r2 from the assembled Stuart type molecular model, r3 from the area occupied by one molecule at the surface of CB in the adsorption, and r4 from the apparent diffusion constant in the cellulose membrane permeation, giving a good correlation between r1 and r4. Then the permeation through cellulose membrane was considered to belong to the simple diffusion through small pores. Contrary to such a previous investigation as in the case of barbiturates, there was no clear relationship among the parameters to indicate the hydrophobicity, i.e., the adsorbability onto hydrophobic adsorbent CB, partition coefficient between n-octanol or chloroform and buffer solution, and the surface tension. It was found that both lytic effect of histamine-contraction and inhibitory effect of adrenaline-contraction have relation to the adsorbability onto CB from aqueous solution.

Nonlinear Penetration of a Langmuir Wave into a Plasma Density Gradient

Abstract: The nonlinear Schr?dinger equation, descriptive of an intense Langmuir wave near critical density, is solved for the steady state of reflection from a linear unperturbed density profile.

Auslegung von Adsorptionsanlagen zur Gasreinigung

Abstract: Die Auslegung von Adsorptionskolonnen beinhaltet die Berechnung des Konzentrationsverlaufs am Austritt aus den Adsorbern (Durchbruch). Die analytischen Losungen fur den Grenzfall der linearen Sorptionsisothermen werden auf den Fall einer Langmuir-Isotherme naherungsweise erweitert. Der in die Rechnung eingehende effektive Diffusionskoeffizient wird, wie bei Versuchen zur Sorptionskinetik am Einzelkorn nachgewiesen, auf die Normaldiffusion, einen Diffusionswiderstand sowie auf Steigung und Krummung der Sorptionsisothermen zuruck-gefuhrt. Versuche mit Aktivtonerde als Adsorbens und CCl4 als Adsorbat in N2 als Tragergas bestatigen die vorstehenden Ansatze. The design of an adsorption column involves the calculation of the concentration profile at the outlet of the column (break-through profile). This problem is solved by extending the analytic solution for linear sorption isotherms to isotherms of Langmuir type. The value of the effective diffusion coefficient which is necessary in the calculations, has been derived from the normal diffusion coefficient and the diffusion resistance as well as the slope and the curvature of the isotherms. Experiments performed with argilaceous earth and CCl4 using N2 as a carrier gas show the applicability of the calculations for practical purposes.

Comportamento do fósforo em solos tropicais. I. Isotermas de adsorção

Abstract: Tropical soils containing large amounts of iron and aluminum sesquioxides can fix high amounts of phosphorus. The process is usually studied by way of adsorption isotherms. This paper shows that at intermediate concentration equilibrium solutions, the phosphorus adsorption can be represented either by the Langmuir or Freundlich equations. High correlations were obtained between the maximum adsorption and the concentration of the free iron oxides extracted by citrate-ditionite. However there were no significant correlations with the aluminium sesquioxide extracted with 0.5N sodium hydroxide. The initial phosphorus fractions added to the soils were bound with high energy to the iron constituents up to the maximum adsorption value, after which binding energy tended to decrease. In contrast, the combination of phosphorus with the aluminium constituents increased constantly as the concentration of added phosphorus was increased.