Showing papers on "Langmuir published in 1971"

The use of molecular beams in the study of catalytic surfaces

Abstract: One Langmuir is a dosage for one second at 10−e Torr or an equivalently longer period at lower pressures. It is approximately equal to a coverage of one monolayer if the sticking coefficient were unity.

Phase equilibria, vapor pressure, and kinetic studies in the uranium-- nitrogen system.

Abstract: Uranium mononitride was studied in an automatic recording balance-furnace system capable of high vacuum or precisely controlled gas pressure. The decomposition pressure of U2N3, which was measured at 1483° and 1607°K, agreed with values in the literature. Uranium sesquinitride compositions were substoichiometric at the U-rich boundary, with compositions of UN1.48±0.01 at 1483°K and 130 torr N2 and UN1.45±0.01 at 1607°K and 700 torr N2. UN has very narrow composition limits (UN0.995 to UN0.997) from 1100° to 2450°K at N2 pressures below 700 torr. In vacuum at 1538°K, the composition is UN0.9954±0.0001. Vaporization rates for single-phase UN were studied by the Knudsen and Langmuir methods using temperatures from 1900° to 2860°K and N2 pressures from 10-4 to 130 torr. The enthalpy of vaporization (ΔH°298) for the reaction UN(s) =U(g)+1/2N2(g) was 199±1 kcal/mol at 10-3 to 1.0 torr N2. The Langmuir data indicated an evaporation coefficient of 0.3 for U from 10-4 to 1.0 torr N2. A UN pellet (99.0% of theoretical density) was tested for spalling and cracking by repeated cycling between the UN and U2N3 phase regions at 130 torr N2. At 1131°K, the nitriding rate to form U2N3 was 5.2×10-3 mg/min-cm2 in 130 torr N2. After extensive nitriding and denitriding (19 cycles for times to 69 h), the bulk volume expansion of the pellet was 8.5%. The surface was not friable or powdery and the overall structural integrity was sound.

Adsorption of dimer, trimer, stearic, oleic, linoleic, nonanoic and azelaic acids on ferric oxide

Abstract: The adsorption isotherms of solutions of dimer, trimer, stearic, oleic, linoleic, nonanoic and azelaic acids in organic solvents, (mostly hexane) have been determined on an alpha ferric oxide with a surface area (B.E.T. N2 adsorption) of 99 m2 (99 × 1020 A2) per gram. They all showed limiting adsorption as grams adsorbed per gram of iron oxide beyond a concentration of about 1 g/100 cc, analagous to the Langmuir type monolayer isotherm. Areas per molecule were calculated and compared with areas of close-packed models in positions parallel to and perpendicular to the surface. The calculated areas corresponded more closely to the flat or parallel positions. Heats of adsorption were determined and were in the range of 27–71 kcal/eq, suggesting chemisorption of the COOH group at the surface. The value of dimer acid suggests that both COOH groups are chemisorbed. Models show that the parallel position permits both COOH groups to touch the surface. The perpendicular position generally does not permit both COOH groups to touch the surface. Dimer acid showed a value (71 kcal/eq) higher than the monobasic acids (44–55 kcal/eq), possibly due to interaction of the ring structure (partly aromatic) with the surface. Azelaic acid from an 80–20t-butanol-hexane solvent showed a lower value of 27 kcal/eq, possibly due to adsorption of a hydrogenbonded alcohol-acid moiety as such.

The silica gel‐water vapor sorption therm

Abstract: The sorption isotherms for moist air and silica gel were determined at a total pressure of one atmosphere and 82, 100, 125, 150, 175 and 200°F. A small hysteresis effect was noted. The silica gel-moist air system can best be described by either of two equations. The first is the distribution function description of the Polanyi characteristic curve. If the data are described by this equation the adsorption process can be explained in terms of Polanyi's potential theory. Alternately, the data may be described by a double Langmuir expression.

Mechanism of Adsorption of Phenols by Carbon Black from Aqueous Solution

Abstract: The adsorption of phenols by carbon black from aqueous solution was investigated. to discuss the mechanism of interaction on the adsorbent surface, referring to the partition coefficient in n-octanol/water system, Px.The shape of adsorption isotherm was discussed with respect to the position of substituents and also the degree of dissociation.There was found a linear relationship between Langmuir constant a and log Px. This result was explained thermodynamically on the assumption of a surface layer on the carbon black, concluding that the surface layer is considered to play the similar role to n-octanol layer in the partition experiment.Free energy of adsorption calculated from Langmuir constant b seemed to be an apparent one and to be influenced predominantly by the free energy of binding.Regarding the relationship between the adsorbed amount at an identical equilibrium concentration, Mc, and the equilibrium concentration at an identical adsorbed amount, Cm, the following equation was derived:log Mc=(1/λ)log (1/Cm)+κwhere λ and κ are constant.Plotting log Mc against log Px the derivatives were classified into groups I and II, suggesting the increase in adsorption of group I may be predominantly due to the tendency of the hydrophobic bonding, while that of group II may be influenced by the free energy of binding in addition to the tendency of the hydrophobic bonding.

Competitive Adsorption of Phenol and Sodium Dinonyl naphthalenesulfonate on Nickel Oxide Powder

Abstract: : The adsorption of phenol at the nickel oxide-cyclohexane interface and the displacement of adsorbed phenol by sodium dinonyl naphthalenesulfonate were studied. The presence of physisorbed water on nickel oxide increased phenol adsorption. From adsorption isotherm plateaus, it was found that the cross-sectional area for phenol was 33.4 sq A on 'dry' nickel oxide and 24.3 sq A on 'wet' nickel oxide, corresponding approximately to tilted and vertical configurations in the adsorbed state. Competitive adsorption studies of phenol and sodium dinonyl naphthalenesulfonate on 'dry' nickel oxide have indicated that competitive adsorption at high surface coverages deviated from Langmuir behavior. An approximate competitive adsorption equation, based on the Flory- Huggins isotherm, was developed to correct for the effect of adsorbate size on competitive adsorption. Competitive adsorption data fit this modified equation.

A study on adsorption of poly(methyl methacrylate) on aluminium silicate

Abstract: Effect of temperature, solvent power, and molecular weight on the adsorption of poly methyl methacrylate (PMMA) on aluminium silicate has been studied. Kinetics of adsorption have been also investigated at 30° and 45 °C. The values of rate constants at these temperatures are 1.4 · 10−2 and 1.0 · 10−2 min−1 respectively. The adsorption data have been analysed according to the Langmuir and the Simha-Frisch-Eirich (SFE) isotherms. The results could be adequately explained in terms of the Langmuir isotherm. Der Einflus von Temperatur, Losungsmittel und Molekulargewicht auf die Adsorption von Polymethylmethacrylat an Aluminiumsilikat und die Kinetik der Adsorption wurden untersucht. Die Geschwindigkeitskonstanten betragen 1,4 · 10−2 bei 30 °C und 1,0 · 10−2 min−1 bei 45 °C. Die Adsorptionsdaten wurden nach Langmuir und Simha-Frisch-Eirich ausgewertet. Zur Deutung der Ergebnisse erwies sich die Langmuir-Isotherme als geeignet.

The exchange of 45Ca and 32P with hydroxyapatite as interpreted by adsorption from solution

Abstract: A theory has been developed based on Langmuir kinetics for the adsorption of a component from solution by a reversible and an irreversible process, simultaneously. The theory has been applied to the removal of traces of 45 Ca and of 32 P from saturated solutions of their nonradioactive counterparts as calcium and phosphate ions by isotopic exchange at the surface of hydroxyapatite. In testing the theory, a computer-programmed nonlinear least-square fit was used to evaluate the physically significant characteristic parameters. This has been accomplished for a number of similar experiments, each of which had a different pH, slurry density, and tagged ion concentration. The results of this study confirm that the approach is feasible and that the assumed model is reasonable. Not only does the theory fit the data, but the magnitude of the derived quantities is internally consistent. No change in calcium to phosphate ratio of the respective surface sites was evident from one experiment to another.

Adsorption Studies with a Bakeable Quartz Automatic Recording Ultramicrobalance

Abstract: A torsional quartz balance designed and fabricated by the Rodder Instrument Company, has been successfully integrated into a bakeable ultrahigh-vacuum system. Working sensibilities of 0.01 µg are obtained routinely and dynamic response is rapid enough to permit adsorption studies on clean metal surfaces with a sticking coefficient near unity. Adsorption of carbon monoxide on platinum foils has been measured and found to agree with irreversible Langmuir kinetics with a sticking coefficient of 0.38. This agrees with measurements made by flash filament desorption. Adsorption of ethylene is more complicated, but the results are consistent with more detailed mechanistic studies performed in this laboratory on 〈111〉 single-crystal platinum.

Homogeneity of Catalytically Active Surface of Decationated Zeolite in Isomerization of o-Xylene

Abstract: The catalytic activity of decationated zeolite for isomerization of o-xylene was investigated at 340∼460°C using a pulse method, and the homogeneity of the active surface was qualitatively confirmed from the activation energy obtained and the result of partial piosoning with ammonia.The reaction rate sharply increased with the increase of the ion exchange level of the zeolite, of which the heat of adsorption and apparent activation energy were substantially independent. Increasing the pretreatment temperature of the zeolite above 400°C, showed no appreciable change of the activation energy, whereas the reaction rate decreased considerably. The catalytic activity of decationated zeolite was reversibly poisoned by the introduction of ammonia to the reaction system. Postulating the Langmuir assumption for the effective adsorption of ammonia on the active surface, the reaction rate was proportionally reduced to the coverage by ammonia and the adsorption constant of ammonia was almost independent of the ion exchange level and of the pretreatment temperature.

Kinetics of adsorption of a mixture of two substances, when the limiting step is external mass exchange

Abstract: 1. A study was made of the adsorption kinetics of a mixture of two substances, when the limiting step is external mass exchange. 2. On the example of the Langmuir isotherms it was shown that the concentration of the substance that is adsorbed more weakly passes through a maximum. This is in agreement with the experimental data. A solution of the equations of the kinetics for such isotherms was given. 3. Methods for approximately estimating the maximum concentration for isotherms of an arbitrary type were discussed.