Upper bounds to atomic electron densities in position and momentum spaces

Modified functions r ^–(r) and p ^–(p) of the spherically averaged electron densities (r) in position space and (p) in momentum space are found to be convex (i.e., the second derivatives are nonnegative everywhere) for all the 103 ground-state atoms from hydrogen (atomic number Z=1) to lawrencium (Z=103), if the parameters are chosen to be 0.6 and 1.4. The convex property of r ^–(r) and p ^–(p) is used to derive upper bounds to the density functions (r) and (p) in terms of their radial moments r ^s and p ^s or frequency moments ^t and ^t . In most cases, the present bounds are shown to be more general and more accurate than those reported in the literature.     

Spin probe studies on high temperature (T >T g) microdynamics of polyamide 66 fibers

Summary Short-range segmental motions of the amorphous phase of polyamide 66 were studied by means of spin probe radicals. In a dry sample the relaxation in the temperature range 366–426 with an activation energy 27.6 kJ/mol was found. In a sample containing traces of water two processes, and relaxations, with activation energies 47.0 kJ/mol and 22.0 kJ/mol, respectively, were found. relaxation was dominant in the higher temperature range (410–460 K) while relaxation was active at lower temperatures (365–410 K).

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Zusammenfassung Die inneren, lokalen Drehbewegungen in den amorphen Bereichen des Polyamid 66 wurden mit Hilfe der Paramagnersondenmethode untersucht. Wasserfreies Polyamid 66 zeigt den-Relaxations-prozeß (die Aktivierungsenergie 27.6 kJ/Mol) im Temperaturbereich von 366 K bis 426 K, wasserhaltiges Polyamid 66 zeigt zwei Prozesse,- und-Relaxationen, deren Aktivierungsenergien 47.0 kJ/Mol und 22.0 kJ/Mol sind. Die-Relaxation dominiert in dem höheren Temperaturbereich (von 410 K bis 460 K) und die-Relaxation in dem niederen Temperaturbereich (von 365 K bis 410 K).

     

Free radical properties of the magnesium oxide surface, I

Free radical properties of MgO catalysts obtained by thermal decomposition of Mg(OH)₂ in nitrogen, hydrogen and oxygen have been investigated. All the oxides show one-electron donor properties (reduction of adsorbed tetracyanoethylene and trinitrobenzene). Only the MgO calcined in oxygen shows one-electron acceptor properties (oxidation of adsorbed perylene). Acetaldehyde transformations were studied on the above catalysts. The MgO calcined in oxygen appeared to be the most active. Presumably, its activity is due to one-electron acceptor centers on the surface.

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- MgO, Mg(OH)₂ , . ( ). MgO, , ( ). . MgO. . , .

     

Poisoning of Raney nickel catalyst for slurry phase hydrogenation of P-nitrotoluene

The poisoning effect of thiophene, dichloroethane and heavy metal compounds on the catalytic activity of Renay nickel has been investigated and the catalytic activity correlated with the poison concentration. The poisoning occurs in the following order: Hg(II)-chloride>Zn-acetate> Hg(II)-acetate>dichloroethane>thiophene> >Pb-acetate.

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, , . : Hg(II)->Zn->Hg(II)-> >>Pb-.

     

Applications of thermoelectrometry to metal-ion modified polyimide films

As part of a research program to decrease the electrical resistivity of polyimide films with ionic additives a variable temperature three probe electrical resistivity measurement system has been designed and constructed. Sample temperature, electrification time, atmosphere, and measurement mode are computer controlled. As a data interpretation aid, temperature cycled analysis can be routinely performed. Surface resistivities in the range 10³–10¹⁵ ohm and volume resistivities in the range 10⁵–10¹⁸ ohm-cm are theoretically measurable under well controlled experimental conditions from room temperature to 250°. The electrical resistivity measurement system is useful for the evaluation of polymer films or films in general. Application of the system for analysis of cobalt, lithium and tin ion-modified polyimide films and some experimental considerations are presented. Correlation of the electrical measurements with differential scanning calorimetry, thermomechanical analysis, and thermogravimetric analysis is demonstrated.

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Zusammenfassung Als Teil eines Forschungsprogramms zur Herabsetzung des elektrischen Widerstandes von Polyimidfilmen mit ionischen Additiven wurde ein 3-Proben-Meßsystem zur Ermittlung des elektrischen Widerstandes in Abhängigkeit von der Temperatur entworfen und konstruiert. Probentemperatur, Elektrisierungszeit, Atmosphäre und Meßmethoden waren computergesteuert. Als Dateninterpretationshilfe kann eine hinsichtlich der Temperatur zyklische Analyse routinemäßig ausgeführt werden. Die Oberflächenwiderstände sind im Bereich von 10³–10¹⁵ Ohm und die Volumenwiderstände im Bereich von 10⁵–10¹⁸ Ohm-cm unter gut kontrollierten experimentellen Bedingungen von Raumtemperatur bis 250° theoretisch meßbar. Das elektrische Widerstandmeßsystem ist nützlich für die Bewertung von Polymerfilmen oder Filmen im allgemeinen. Die Anwendung des Systems zur Analyse von mit Co-, Li- und Sn-Ionen modifizierten Polyimidfilmen und einige experimentelle Hinweise werden angegeben. Es wird gezeigt, daß die mit dem beschriebenen System erhaltenen Resultate mit durch DSC, thermomechanische Analyse und TG erhaltenen Werten korrelieren.

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, , . , , . . 10³–10¹⁵ , 10⁵–10¹⁸ 250°. , . , , , . , .

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The financial support of the National Aeronautics and Space Administration is gratefully appreciated. The assistance of John Swartzentruber in performing many of the measurements is recognized.     

Ammonia decomposition on Ir and Pt wires

The rates of ammonia decomposition on polycrystalline Ir and Pd wires were measured at temperatures between 900 and 2000 K and at pressures between 50 and 770 Torr. Rates on Ir were fitted with a Langmuir-Hinshelwood unimolecular reaction rate expression. Rates on Pd could not be fitted with a rate expression, although activation energies were obtained.

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Ir Pd 900–2000 50–770 . Ir --. Pd . .

     

Non quasi-stationary state pyrolysis. Induction period of neopentane pyrolysis

The principle of an apparatus using an isothermal continuous flow stirred tank reactor to study homogeneous gas phase reactions at space times of the order of 1 sec is given. With this apparatus, the induction period of neopentane pyrolysis (as an example) has been clearly shown.

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, , 1 . , , .

     

The use of TA — GLC — MS as a quantitative specific EGA technique for the investigation of complex thermal decomposition reactions: The thermal decomposition of calcium propanoate

A versatile and flexible system is described for evolved gas analysis using a GLC, MS (mass scan and SIM modes) and GLC-MS. Gases evolved from materials in two differential thermal analysis units, a thermobalance or a micro-furnace linked directly to the MS or GLC can be analysed. Details are given of computer controlled data acquisition and processing. The techniques are applied to the thermal decomposition of calcium propanoate. Mechanisms are suggested to account for the observed decomposition products and the solid state process. Evidence is presented to support the view that the latter occurs via nucleation followed by two-dimensional growth with an activation energy of 315 kJ mol^–1 and a pre-exponential factor of 4.8×10²¹s^–1.

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Zusammenfassung Ein vielseitiges und flexibles System zur Analyse von gebildeten Gasen wird beschrieben, das GLC, MS (in Massen-scanning und SIM Betriebsweise) und GLC-MS umfaßt. Damit können die in zwei differentialthermoanalytischen Einheiten, einer Thermowaage oder einem direkt mit dem MS- oder GLC-Gerät gekoppelten Mikroofen aus den zu untersuchenden Substanzen entwickelten Gase analysiert werden. Einzelheiten der komputerkontrollierten Datengewinnung und Steuerung werden angegeben. Die Techniken werden zur Untersuchung der thermischen Zersetzung von Calciumpropionat herangezogen. Mechanismen werden vorgeschlagen, die die beobachteten Zersetzungsprodukte und die Festkörperreaktion erklären. Beweise werden dafür erbracht, daß bei letzterer eine Keimbildung und darauffolgendes zweidimensionales Wachstum vor sich geht, wobei die Aktivierungsenergie 315 kJ·mol^–1 und der präexponentielle Faktor 4.8·10²¹·s^–1 beträgt.

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- (), - (MC) MC. - , , . . . . , , 315 .^–1 4,8·10^{21 –1}.

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The authors gratefully acknowledge the provision of an equipment grant and Research Studentships to G.S. and S.B.W. by the SERC.     

Infrared study of photooxidation of nitrogen oxides and ammonia adsorbed on alumina

Changes in the IR spectra of nitrogen oxides and ammonia adsorbed on Al₂O₃ caused by UV irradiation indicate that in the presence of gaseous or liquid (–196°C) O₂ photooxidation takes place, resulting mostly in the formation of surface NO ₃ ^– ions.

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- - , Al₂O₃, , (–196°C) NO ₃ ^– .

     

Influence of the nonmetallic component in binary chromium compounds on their catalytic activity in carbon monoxide oxidation

Oxidation kinetics of carbon monoxide on chromium carbide, nitride and boride has been studied. The activity of chromium compounds was compared with the electronic state of the chromium atom according to XPS data. A reaction mechanism is proposed and an assumption is made on the predominant effect of the nonmetallic component on the character of change in the catalytic activity of chromium compounds.

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, . . .

     

Synthesis and thermal study of some adducts of morpholine with nickel(II) nitrite,sulphate and perchlorate

The preparations of the nickel-morpholine (Morph) complexes Ni(NO₂)₂·3Morph and Ni(ClO₄)₂·4Morph·2H₂O are described. The thermal treatment of this perchlorate and of NiSO₄·2Morph led to the isolation of Ni(ClO₄)₂·2Morph·2H₂O and NiSO₄·Morph. The magnetic moments, diffuse reflectance spectra and infrared spectra of these compounds are all compatible with a pseudo-octahedral environment around the nickel atom.

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Zusammenfassung Die Darstellung der Nickel-Morpholin(Morph)-Komplexe Ni(NO₂)₂·3Morph und Ni(ClO₄)₂·4Morph·2H₂O wird beschrieben. Die thermische Behandlung dieses Perchlorates und von NiSO₄·2Morph ergibt Ni(ClO₄)₂·2Morph·2H₂O und NiSO₄Morph. Magnetisches Moment sowie diffuse Reflektionsspektren und Infrarotspektren dieser Verbindungen sind kompatibel mit einer pseudooktaedrischen Koordination des Nickelatoms.

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, () : Ni(NO₂)₂·, NiSO₄·2 Ni(ClO₄)₂·4·2H₂O. NiSO₄· Ni(ClO₄)₂·2·2H₂O. , , .

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The authors are indebted to Consejeria de Cultura y Educación de la Comunidad Autónoma de Murcia for financial support.     

Frequencies, anharmonicities, and dissociation energies of OH groups in H-mordenite

Harmonic frequencies, anharmonicities and dissociation energies of surface hydroxy groups in H-mordenite have been determined. The application of the Lippincott-Schroeder potential function for similar problems is proposed.

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, -. - .

     

Hydrogenation of ethylene on gadolinium X, Y and L-type zeolites

It is shown that Gd-zeolites have a catalytic activity towards ethylene hydrogenation at 1 atm. This activity decreases with an increase in the SiO₂/Al₂O₃ ratio from 2.2 to 6.1 and 4.1, i.e. upon going from an X type zeolite to Y and L. For these types of zeolite the activity grows with an increase in Gd³⁺ content from 50 to 80%. Oxygen addition to the reaction mixture stabilizes the catalytic activity of zeolites.

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, qv 1 . , SiO₂/Al₂O₃ 2,2 6,1 4,1, .. X Y L. , 50 80%. .

     

Kinetics of catalyst regeneration by coke combustion. I. Increased reaction rate due to the presence of chromium

A kinetic study has been carried out of the regeneration of a commercial Cr₂O₃/Al₂O₃ catalyst by coke combustion. The results obtained show that the reaction rate is several orders of magnitude higher than that obtained on catalysts without transition metals.

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Cr₂O₃/Al₂O₃ . , , .

     

Reactivity of alkylperoxyl radicals in reactions with aromatic nitrons

Interaction of tetradecylperoxyl radicals with two aromatic nitrons has been studied.

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.

     

Kinetics of the oxidation of some polycyclic aromatic hydrocarbons by lead tetraacetate in aqueous acetic acid and perchloric acid medium

The state of metal cations in CuCr₂O₄/-Al₂O₃ catalysts under its operation in catalytic heat generators has been examined. IR spectra of adsorbed CO indicate copper ion reduction in the catalyst to Cu⁺, whose surface concentration was determined. Diffuse reflectance spectra have revealed that the initial catalyst contains Cr(VI), disappearing after reaction.

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CuCr₂O₄/-Al₂O₃ (). - CO , Cu⁺. Cu⁺. , Cr(VI), .

     

Catalytic activity of the Al2O3?Cr2O3?Fe2O3 system II. Influence of nitrogen bases on hydrocarbon aromatization

The physico-chemical properties of the Al₂O₃–Cr₂O₃–Fe₂O₃ catalyst system have been correlated with n-hexane dehydrocyclization. Using a poisoning technique, the ionic and radical steps of the reaction have been determined.

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- Al₂O₃–Cr₂O₃–Fe₂O₃ -. , .

     

Thermal and structural relationships within the Cd-picoline-chloride family including the α, β and γ-types

Thermal and structural properties of complexes of CdCl₂ with picolines were studies. The structures of tetra-- and tetra--picoline as well as di-- and di--picoline complexes were found to be identical and their thermal decomposition paths were analogous. New polynuclear complexes which could not be obtained from solution have been prepared through thermal decomposition. Their symmetry and cell dimensions were determined.

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Zusammenfassung Es wurden die thermischen und strukturellen Eigenschaften von CdCl₂-Komplexen mit Pikolinen untersucht Die Strukturen der tetra-- und tetra--, sowohl der di-- und di--Pikolinkomplexe wurden als gleich befunden, der Verlauf ihrer thermischen Zersetzung war ähnlich. Auf dem Wege der thermischen Zersetzung konnten neue polynukleare Polymerkomplexe hergestellt werden, was in Lösung nicht gelang. Es wurden deren Symmetrie und Zellabmaße ermittelt.

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. , ---, - , . , . .

     

Thermal and X-ray analysis studies of UO3 gel microspheres

The thermal decomposition behaviour of UO₃ gel microspheres has been studied. Thermal analysis involved DTA, TG, DTG and X-ray examination. The effects of washing the UO₃ gel microspheres with hot water and with ammonia solution were investigated, as were the effects of soaking the microspheres in ammonia solution before or after washing on the crystallite size. The results indicate that the thermal decomposition of UO₃ gel microspheres includes five steps: the first two for dehydration, the third for ammonia removal, the fourth for ammonia oxidation and the last step for UO₃ recrystallization.

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Zusammenfassung Die thermische Zersetzung von UO₃-Gelmikrokugeln wurde mittels DTA, TG, DTG und Röntgendiffraktometrie untersucht. Die Auswirkungen des Waschens der UO₃-Gelmikrokugeln mit heißem Wasser und mit Ammoniaklösungen sowie der Einfluß des Wässerns der Mikrokugeln vor und nach dem Waschen mit Ammoniaklösungen auf die Kristallitgröße wurden untersucht. Die thermische Zersetzung der UO₃-Gelmikrokugeln verläuft in 5 Schritten: in den ersten beiden erfolgt die Dehydratisierung, im dritten die Abgabe und im vierten die Oxydation von Ammoniak und schließlich im letzten Schritt die Rekristallisation von UO₃.

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, , ₃. , . , ₃ , , — , — , ₃.

     

Microcalorimetric and FT-IR spectroscopic study of benzene adsorption on α-Fe2O3 and γ-Al2O3

The adsorption of benzene at room temperature on-Fe₂O₃ and on-Al₂O₃ powders was investigated by heat-flow microcalorimetry and FT-IR spectroscopy.On iron oxide a chemisorption-combustion step is followed by a highly exothermic adsorption step, reversible at r.t.Few combustion centres exist on alumina if reducing pretreatment is not carried out. Two reversible adsorption steps are subsequently observed and were interpreted as due to interaction with two different types of surface hydroxy groups.

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Zusammenfassung Die Adsorption von Benzol an-Fe₂O₃- und-Al₂O₃-Pulvern bei Raumtemperatur wurde mittels Wärmefluß-Kalorimetrie und FT-IR-Spektroskopie untersucht. Beim Eisenoxid folgt auf dem Chemisorptions-Verbrennungs-Schritt ein bei Raumtemperatur reversibler, stark exothermer Adsorptionsschritt. Aluminiumoxid besitzt einige Oxydationszentren, sofern keine reduzierende Vorbehandlung erfolgt. Zwei aufeinanderfolgende reversible Adsorptionsschritte treten auf und werden der Wechselwirkung mit zwei verschiedenen Typen von Oberflächenhydroxylgruppen zugeschrieben.

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-Fe₂O₃ -l₂₃. - , . , , . , .

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This work was supported by the CNR Progetto Finalizzato Chimica Fine e Secondaria. Prof. Vincenzo Lorenzelli is gratefully thanked for the kind loan of instrumental facilities and helpful discussions.