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  • 1955-1959  (12)
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  • 1
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 1. The adsorption energy of nonpolar molecules is calculated by a method which takes into consideration three terms in the potential of the dispersive forces by means of constants calculated on the basis of the polarizabilities and magnetic susceptibilities, Other factors taken into consideration in the development of the method are inductive potential (through the mean polarizability of the adsorbate and the mean electrostatic field of the adsorbent) and the repulsion potential (through an exponential constant calculated from the individual constants of adsorbent and adsorbate and with summation of all of the interactions of the given energy center of the molecule of adsorbate over all of the centers of the lattice of the adsorbent). The exponential repulsion constant was determined from the minimum condition of the summed energy of all of the interactions at the equilibrium distance from the adsorbent surface. 2. The calculated values of the energy of adsorption of noble gases, nitrogen and thirteen hydrocarbons of various structures (normal and isomeric alkanes, an alkene, cyclanes and aromatics) on graphite are close to the measured heats of adsorption on graphitized carbon blacks. 3. The calculated values of the energy of adsorption of n-alkanes, benzene and toluene on magnesia are likewise close to the measured heats of adsorption. 4. In the case of adsorption on graphite the contributions of the first, second and third terms of the energy of the dispersive forces and the absolute value of the repulsion energy constitute 90–95, 5–10, 0.5–1 and 35–40%, respectively, of the total energy of the dispersive forces for the investigated adsorbates. In the case of adsorption of MgO the contributions of the first, second, and third terms of the energy of the dispersive forces, the energy of the inductive forces and the absolute magnitude of the repulsion energy constitute about 81–83, 12–14, 3, 2 and 42–48%, respectively, of the total energy of the attractive forces (dispersive and inductive).
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  • 2
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 1. Determination of the absolute isotherms of adsorption and of the differential heat of adsorption of vapors of n-pentane, n-heptane and n-octane on graphitized carbon black were carried out in a calorimeter with constant heat exchange. These isotherms were compared with those previously determined for n-hexane. 2. The thermodynamic characteristics of the adsorption of the vapors and of wetting were determined for these hydrocarbons. Standard values of the heat, the total and free energy and the entropy of adsorption are linear functions of the number of carbon atomsn in the molecule of these hydrocarbons. The heat of. wetting is independent ofn. 3. An approximate equation is given for calculation of the constant of the adsorption isotherm of the above n-alkanes on graphite for differentn and for various temperatures. The equation is consistent with the experimental isotherms. 4. The theoretically calculated dependence of the energy of adsorption of n-alkanes on graphite — Φ = = 0.9 + 1.85 n kcal/mole adequately represents the heats of adsorption of these hydrocarbons on the homogeneous surface of graphitized carbon black.
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  • 3
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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  • 4
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 1. Roasting carbon blacks at 1700 in a stream of hydrogen considerably reduces surface roughness and makes the surface more homogeneous. Roasting charcoal under these conditions destroys part of its pores and considerably reduces the pore volume. On charcoal the adsorption isotherm of nitrogen vapor rises more steeply than on carbon black. 2. Isotherms for the adsorption of krypton and methane vapors on graphitized bodies of homogeneous surface below the critical temperature of the adsorption layer have a stepwise form. Above the critical temperature there are no breaks in the isotherms, but they retain the wavelike character.
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  • 5
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 1) We used the adsorption method to investigate the changes in the pore structure of large-pore magnesium hydroxide during thermal treatment in vacuo. 2) During the transition from magnesium hydroxide to oxide at 350° the specific surface increases due to the formation of fine cracks in the primary flakes constituting the large-pore shell of magnesium hydroxide. When the sample is heated at 500° the specific surface somewhat decreases due to a fusion of these fine cracks. The structure of large capillaries does not change at 350 and 500°. 3) When heated at 1000° (in vacuo) magnesium oxide undergoes noticeable sintering, but the dimensions of large pores still do not decrease appreciably. At 1400° the large pores also undergo extensive constriction.
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  • 6
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 1. Using the electron-microscope method of carbon replicas, a study was made of the porous structure of a starting uniformly large-pored magnesium hydroxide sample, calcined at 200°, and of the magnesium oxide specimens obtained from it by calcination at 1000 and 1400°. 2. The skeleton of magnesium hydroxide has a corpuscular structure and is composed of plate-like crystallite. The plate-like character of the skeleton particles of the original magnesium hydroxide was still retained at calcination temperatures up to 1000°. Calcination at 1400° led to a pronounced sintering of the skeleton. 3. Based on electron-microscopic data, an estimate was made of the specific surface area and dimensions of the pores of both original specimen and after calcination at 1000°. The obtained results are found to be in harmony with those obtained earlier by the adsorption method.
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  • 7
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The details of an earlier theoretical calculation of the energy of adsorption of simple and complex non-polar molecules on graphite were presented. The power sums of type $$\Sigma r_{i\bar j} ^n $$ were calculated for different distances of the adsorbate molecule from the external base plane of graphite, at n=6, 8, 10 and 12, as were also the exponential sums of type $$\Sigma e - ^{r_{ij} /} \rho $$ , at δ=0.28 A. Using approximate quantum mechanics equations, we calculated the constants of three terms of the energy of dispersive attraction, and also the constants of repulsion from the equilibrium condition. The additive scheme was used to calculate the potential curves and equilibrium adsorption energies of complex molecules.
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  • 8
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 1. Adsorption isotherms have been determined and compared for the vapors of water, methanol, and benzene on a number of carbon blacks which had been subjected to different thermal treatments. With increasing treatment temperature, there were decreases in both the amount of surface oxygen, capable of exchange reaction with aqueous NaOH, and in surface roughness of the blacks. The surface of the blacks became much more uniform after treatment in a hydrogen stream at 1700°. 2. Adsorption of water vapor fell rapidly with increasing graphitization, mainly as the result of removal of surface oxides. With blacks graphitized in a hydrogen stream at 1700°, water vapor adsorption was very small, even in the region of high pressure ratios. 3. Adsorption of methanol vapor on graphitized blacks dropped markedly in the region of low pressure ratios, as the result of destruction of surface oxides. In this case, decrease in surface roughness played a secondary role. 4. Adsorption of benzene vapor on graphitized blacks decreased, with decreasing surface roughness and surface coverage with chemical compounds, in the region of low surface coverage. 5. The surface properties of blacks of different origin were very similar after graphitization in a hydrogen stream at 1700δ.
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  • 9
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Adsorption energies of isolated atoms and simple nonpolar molecules on graphite were calculated on the basis solely of electric, magnetic, and geometric properties. The results of the theoretical calculation are in good agreement with experimental calorimetric data.
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  • 10
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 1. In its radiolysis ethylene is converted mainly into butane, acetylene, and liquid hydrocarbons. 2. Apart from butane and acetylene, the gaseous products include small amounts of CH4, C2H6, C4H8, and H2 and also traces of propene. The liquid products boiling up to 130° consist of C6 and C8 aliphatic hydrocarbons. The higher fractions contain considerable amounts of aromatic and unsaturated hydrocarbons. 3. The formation of butane, hexanes, octanes, and other higher alkanes proceeds by the condensation of aliphatic diradicals having even numbers of carbon atoms with one another and subsequent hydrogenation. 4. The yield in the reaction is 16 molecules per 100 ev. 5. Reduction of the initial pressure raises the extent of the decomposition of ethylene without affecting the course of the reaction. Dilution of the ethylene with nitrogen considerably increases the degree of conversion with a sharp lowering of the yield of gaseous hydrocarbons. Dilution with hydrogen has almost no effect on the radiolysis of ethylene.
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