THE DIELECTRIC BEHAVIOR AT LOW TEMPERATURES OF SEVERAL GASES ADSORBED UPON POROUS VYCOR GLASS

1962 ◽  
Vol 40 (1) ◽  
pp. 92-103 ◽  
Author(s):  
I. D. Chapman ◽  
R. McIntosh
Keyword(s):  
Low Temperatures ◽  
Molecular Layer ◽  
Dielectric Behavior ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Threshold Temperature ◽  
Hydroxyl Groups ◽  
Vycor Glass ◽  
Oh Groups ◽  
Adsorbed Phase

The complex dielectric constants of several systems comprising a gas adsorbed on Vycor glass have been measured at temperatures between 0 °C and −180 °C and frequencies between 3 kc/sec and 4 Mc/sec. The real and imaginary parts of the dielectric constant of the adsorbed phase have been computed. Loss maxima occurring at low temperatures are observed for some of the matter in the monolayer and are assumed to be due to complexes formed between the gas first admitted and hydroxyl groups which are covalently attached to the surface of the glass. The complexes may be considered either as dipoles having two equilibrium positions, or as highly damped oscillators. Ethyl chloride adsorbed in the first molecular layer and not bonded to OH behaves as an oscillatory system for which no loss is observed in the frequency and temperature ranges studied. Ethyl chloride adsorbed in the multilayers behaves similarly but shows a slightly greater temperature coefficient of ε′. Both these types of adsorbed ethyl chloride interact with the complexes and reduce the threshold temperature at which loss is observed in the complex. Methyl chloride interacts with OH groups in a similar fashion, but n-butane does not.

NOTE ON THE DIELECTRIC CONSTANTS OF ETHYL CHLORIDE AND n-BUTANE ADSORBED ON NONPOROUS TiO2

1953 ◽  
Vol 31 (11) ◽  
pp. 998-1003 ◽  
Author(s):  
M. H. Waldman ◽  
J. A. Snelgrove ◽  
R. Mcintosh
Keyword(s):  
Temperature Dependence ◽  
Silica Gel ◽  
Porous Silica ◽  
Adsorbed Molecule ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Capacity Change ◽  
Adsorbed Phase ◽  
Porous Silica Gel ◽  
Linear Sections

The dielectric constants of ethyl chloride and n-butane adsorbed on nonporous TiO2 were measured. The plot of capacity change versus volume adsorbed was found to reveal two linear sections in the case of ethyl chloride with an abrupt change in the slope of the plot occurring at the Vm value calculated using the B.E.T. or Hüttig adsorption equations. With n-butane the plot was linear beyond Vm. For ethyl chloride on rutile a slight temperature dependence in the polarization was observed for the volume of gas adsorbed above Vm, while a negligible temperature dependence was noted for the portion below Vm. It is postulated that the observations with the polar gas on the nonporous rutile can be explained by a change from oscillatory to rotational motion of the adsorbed molecule after the monolayer is complete. It was noted that gases adsorbed on nonporous TiO2 behaved differently from gases adsorbed on porous silica gel. This appears to lead to the necessity of postulating changes of density for the adsorbed phase on silica gel.

AN INFRARED STUDY OF THE ADSORPTION OF AMMONIA ON POROUS VYCOR GLASS

1964 ◽  
Vol 42 (4) ◽  
pp. 802-809 ◽  
Author(s):  
N. W. Cant ◽  
L. H. Little
Keyword(s):  
Hydrogen Exchange ◽  
Lone Pair ◽  
Acid Sites ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Infrared Study ◽  
Vycor Glass ◽  
Oh Groups ◽  
Surface Hydroxyl ◽  
Adsorption Sites

The infrared spectrum of ammonia adsorbed on porous glass at 20 °C and 150 °C has been studied in the region 1450–4000 cm−1. No absorption band due to the asymmetric bending mode of ammonia was observed but in the NH stretching region, bands occurred at 3280 cm−1, 3320 cm−1, 3365 cm−1, and 3400 cm−1. The bands at 3320 cm−1 and 3400 cm−1 were easily removed by evacuation and are due to ammonia molecules hydrogen bonded through the nitrogen atom to surface hydroxyl groups. The bands at 3280 cm−1 and 3365 cm−1 were not removed by evacuation even at 150 °C and are due to ammonia molecules held to surface Lewis acid sites by the nitrogen lone-pair electrons. The site for this adsorption is not a surface hydroxyl group. These results are further evidence for the existence of the two adsorption sites proposed by Folman and Yates. Deuteration of the surface OH groups was easily accomplished with D2O vapor at 300 °C and the rate of hydrogen exchange between adsorbed ammonia molecules and surface OD groups was found to be rapid.

Dielectric behavior of low boiling chlorides in the liquid, solid, and adsorbed states

1968 ◽  
Vol 46 (18) ◽  
pp. 2945-2957 ◽  
Author(s):  
T. McMullen ◽  
E. D. Crozier ◽  
R. McIntosh
Keyword(s):  
Sodium Chloride ◽  
Hydrogen Chloride ◽  
Surface Coverage ◽  
Dielectric Behavior ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Adsorbed Hydrogen ◽  
Adsorption Studies ◽  
Very High ◽  
Monolayer Coverage

The complex dielectric constants of hydrogen, methyl, and ethyl chlorides have been measured, for the purpose of comparison with the present and future adsorption studies. The hydrogen chloride results agree with those of Cole and Swensen (22). Studies of hydrogen and ethyl chlorides adsorbed on finely divided sodium chloride show two particularly interesting phenomena. Adsorbed hydrogen chloride shows an unusually high polarizability at monolayer surface coverage, which then decreases again with increasing adsorption. Adsorbed ethyl chloride also shows a very high polarizability at a particular surface coverage, but this maximum occurs at about one-fourth of monolayer coverage, and is accompanied by loss, in contrast to the former case.

DIELECTRIC RELAXATION IN LIQUIDS: II. ISOMERIC PENTANEDIOLS

1961 ◽  
Vol 39 (11) ◽  
pp. 2139-2154 ◽  
Author(s):  
D. W. Davidson
Keyword(s):  
Hydrogen Bonding ◽  
High Frequency ◽  
Low Temperatures ◽  
Dipole Moments ◽  
Frequency Dispersion ◽  
Liquid Structure ◽  
Dielectric Constants ◽  
Oh Groups ◽  
High Frequencies ◽  
Static Dielectric Constants

For five pentanediols the infrared spectra, the dipole moments, and the static dielectric constants show an increasing degree of internal hydrogen bonding with increasing proximity of the OH groups. The dielectric dispersion loci at low temperatures are skewed arcs over most of the dispersion range. Values of the parameter β decrease from ca. 1 to 0.55 in the series 1,5-, 1,4-, 1,2-, 2,4-, and 2,3-pentanediol, which is also the order of increasing relaxation time τ0 at low temperatures. Increased τ0 is associated with increased irregularity of intermolecular hydrogen bonding, an effect which supports the view that relaxation proceeds by a co-operative mechanism which is facilitated by regularity in the liquid structure. At temperatures of "structural relaxation", values of log τ0 are linear in (T–T∞)−1; the proportionality constants, but not the T∞'s, are the same for all five diols.The experimental behavior at relatively high frequencies departs from both the skewed-arc and Glarum equations, although less from the latter. These departures are compared with the high frequency dispersion regions in n-propanol.

THE DIELECTRIC BEHAVIOR OF VAPORS ADSORBED ON SILICA GEL

1953 ◽  
Vol 31 (1) ◽  
pp. 72-83 ◽  
Author(s):  
J. A. Snelgrove ◽  
H. Greenspan ◽  
R. Mcintosh
Keyword(s):  
Temperature Coefficient ◽  
Silica Gel ◽  
Liquid State ◽  
Saturation Pressure ◽  
Adsorbed Water ◽  
Dielectric Behavior ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Oscillatory Motion ◽  
Molar Polarization

Experiments to determine the dielectric constants of adsorbed butane, ethyl chloride, and water on an activated silica at frequencies up to 3.7 Mc. per sec. are reported. No Debye-type dispersion was observed for the polar adsorbates down to −30 °C, the lowest temperature employed. Mixtures of ethyl chloride and water, and of butane and water, were also studied. The assumption that adsorption of ethyl chloride and water occurs with both adsorbates sharing two types of sites sufficed to explain the findings for this system. No explanation was apparent to account for the behavior of the butane–water system.Formulae due to Kurbatov and to Snelgrove and McIntosh have been used to interpret the results obtained with polar adsorbates. On the assumption that the adsorbates have densities equivalent to those for the liquid state at the same temperature, it is concluded that adsorbed water undergoes oscillatory motion. The first quantities of ethyl chloride adsorbed behave as though the molecules may rotate freely within an angle of 98°. The ethyl chloride adsorbed nearer the saturation pressure shows oscillatory motion, as a negligible temperature coefficient of the molar polarization is observed.

Tuning the Electric Field Response of MOFs by Rotatable Dipolar Linkers

2019 ◽  
Author(s):  
Johannes P. Dürholt ◽  
Babak Farhadi Jahromi ◽  
Rochus Schmid
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Structural Changes ◽  
Dielectric Behavior ◽  
Two Dimensions ◽  
Dielectric Constants ◽  
Electric Response ◽  
Dipole Strength ◽  
Metal Organic ◽  
Dynamics Simulations

Recently the possibility of using electric fields as a further stimulus to trigger structural changes in metal-organic frameworks (MOFs) has been investigated. In general, rotatable groups or other types of mechanical motion can be driven by electric fields. In this study we demonstrate how the electric response of MOFs can be tuned by adding rotatable dipolar linkers, generating a material that exhibits paralectric behavior in two dimensions and dielectric behavior in one dimension. The suitability of four different methods to compute the relative permittivity κ by means of molecular dynamics simulations was validated. The dependency of the permittivity on temperature T and dipole strength μ was determined. It was found that the herein investigated systems exhibit a high degree of tunability and substantially larger dielectric constants as expected for MOFs in general. The temperature dependency of κ obeys the Curie-Weiss law. In addition, the influence of dipolar linkers on the electric field induced breathing behavior was investigated. With increasing dipole moment, lower field strength are required to trigger the contraction. These investigations set the stage for an application of such systems as dielectric sensors, order-disorder ferroelectrics or any scenario where movable dipolar fragments respond to external electric fields.

scholarly journals Development of Highly Efficient, Glassy Carbon Foam Supported, Palladium Catalysts for Hydrogenation of Nitrobenzene

Nanomaterials ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 1172
Author(s):  
Ádám Prekob ◽  
Mahitha Udayakumar ◽  
Gábor Karacs ◽  
Ferenc Kristály ◽  
Gábor Muránszky ◽  
...  
Keyword(s):  
Zeta Potential ◽  
Glassy Carbon ◽  
Palladium Nanoparticles ◽  
Palladium Catalysts ◽  
Sucrose Solution ◽  
Supported Catalyst ◽  
Carbon Foam ◽  
Hydroxyl Groups ◽  
Polyurethane Elastomers ◽  
Oh Groups

Glassy carbon foam (GCF) catalyst supports were synthesized from waste polyurethane elastomers by impregnating them in sucrose solution followed by pyrolysis and activation (AC) using N2 and CO2 gas. The palladium nanoparticles were formed from Pd(NO3)2. The formed palladium nanoparticles are highly dispersive because the mean diameters are 8.0 ± 4.3 (Pd/GCF), 7.6 ± 4.2 (Pd/GCF-AC1) and 4.4 ± 1.6 nm (Pd/GCF-AC2). Oxidative post-treatment by CO2 of the supports resulted in the formation of hydroxyl groups on the GCF surfaces, leading to a decrease in zeta potential. The decreased zeta potential increased the wettability of the GCF supports. This, and the interactions between –OH groups and Pd ions, decreased the particle size of palladium. The catalysts were tested in the hydrogenation of nitrobenzene. The non-treated, glassy-carbon-supported catalyst (Pd/GCF) resulted in a 99.2% aniline yield at 293 K and 50 bar hydrogen pressure, but the reaction was slightly slower than other catalysts. The catalysts on the post-treated (activated) supports showed higher catalytic activity and the rate of hydrogenation was higher. The maximum attained aniline selectivities were 99.0% (Pd/GCF-AC1) at 293 K and 98.0% (Pd/GCF-AC2) at 323 K.

Crystallization and dielectric properties of SrO–BaO–Nb2O5–GeO2 tungsten–bronze glass–ceramics

2001 ◽  
Vol 16 (7) ◽  
pp. 2057-2063 ◽  
Author(s):  
Jiin-Jyh Shyu ◽  
Hsin-Wei Peng
Keyword(s):  
Heat Treatment ◽  
Dielectric Properties ◽  
Tungsten Bronze ◽  
Glass Ceramics ◽  
Dielectric Behavior ◽  
Dendritic Morphology ◽  
Dielectric Constants ◽  
Two Stage ◽  
Tetragonal Tungsten Bronze ◽  
Stage Heat Treatment

The crystallization and dielectric properties of SrO–BaO–Nb2O5–GeO2 glass–ceramics were investigated. One- and two-stage heat-treatment methods were used to convert the parent glass to glass–ceramics. Strontium barium niobate (SBN) with a tetragonal tungsten-bronze structure formed as the major crystalline phase. When the crystallizing temperature/time was increased, the secondary crystalline BaGe2O5 phase coexisted with SBN. BaGe2O5 formed as a surface layer grown from the surface into the interior of the sample. The dendritic morphology of SBN crystals was examined. The glass–ceramics crystallized by two-stage heat treatment have higher dielectric constants than those crystallized by one-stage heat treatment. The highest dielectric constant that was obtained in the present glass–ceramics was 320. The glass–ceramics showed relaxor-type dielectric behavior.

scholarly journals A note on some further determinations of the dielectric constants of organic bodies and electrolytes at very low temperatures

1898 ◽  
Vol 62 (379-387) ◽  
pp. 250-266 ◽  
Keyword(s):  
Dielectric Constant ◽  
Low Temperatures ◽  
Tuning Fork ◽  
Dielectric Constants ◽  
The Past ◽  
Method Of Measurement ◽  
The Given ◽  
Past Summer

In several previous communications we have described the investigations made by us on the dielectric constants of various frozen organic bodies and electrolytes at very low temperatures. In these researches we employed a method for the measurement of the dielectric constant which consisted in charging and discharging a condenser, having the given body as dielectric, through a galvanometer 120 times in a second by means of a tuning-fork interrupter. During the past summer we have repeated some of these determinations and used a different method of measurement and a rather higher frequency. In the experiments here described we have adopted Nernst’s method for the measurement of dielectric constants, using for this purpose the apparatus as arranged by Dr. Nernst which belongs to the Davy-Faraday Laboratory.

Adsorption of Benzene from Aqueous Solution Using Base Modified Expanded Perlite

2012 ◽  
Vol 622-623 ◽  
pp. 1779-1783
Author(s):  
Richard Appiah-Ntiamoah ◽  
Xuan Thang Mai ◽  
Francis W.Y. Momade ◽  
Hern Kim
Keyword(s):  
Zeta Potential ◽  
Adsorption Capacity ◽  
Linear Regression Analysis ◽  
Basic Medium ◽  
Maximum Adsorption Capacity ◽  
Hydroxyl Groups ◽  
Expanded Perlite ◽  
Oh Groups ◽  
Base Solution ◽  
Ph Range

In this study, the adsorption capacity of expanded perlite (EP) for benzene at low concentrations in water was investigated after EP was treated with sodium hydroxide (NaOH). IR spectra used to characterize the modified EP showed that there was no bonding between NaOH and the hydroxyl groups on the surface of EP. However, the NaOH provided a basic medium for negatively charged surface oxide ions (-SO-) to form on EP. This fact was corroborated by pH readings of the modification solution. This reduced in pH from 10 to 9 at the end of the reaction which indicated that the hydroxyl OH- groups on the EP underwent deprotonation and hence releases H+ into the solution, and also positive sites on EP adsorbed OH- ions from the base solution. Mahir et al. in their paper Zeta potential of unexpanded and expanded perlite samples in various electrolyte media confirmed that EP has no isoelectric point and exhibits negative zeta potential in the pH range of 2-11. The surface oxides (-SO-) were believed to have given EP it adsorptive potential. Adsorption isotherm values correlated reasonably well with the Langmuir isotherm model and it parameters (qo and K) were obtained using linear regression analysis. A maximum adsorption capacity (qo) value of 19.42 mg/g was achieved.

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