Effect of addition of intermetallic componds on the catalytic activity of La2CuO4

Decomposition of nitrous oxide has been studied on pure La₂CuO₄, La₂CuO₄ with 5 wt.% CaNi₅ and La₂CuO₄ with 5 wt.% NiO in the temperature range 200–480°C at 200 Torr initial pressure of reactant gas. The addition of 5 wt.% CaNi₅ decreases the energy of activation drastically in comparison with La₂CuO₄. The results are explained on the basis of the dispersity of Ni/NiO on La₂CuO₄.

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La₂CuO₄ 5.% CaNi₅ 5 .% NiO , 200–480°C 200 . 5 . % CaNi₅ . Ni/NiO La₂CuO₄.

     

Oxygen adsorption on silver-gold alloy

Oxygen adsorption on Ag/Au alloys has been studied by field-emission microscopy (FEM). A decrease in the silver concentration of alloy is accompanied by a drastic fall in its ability to absorb oxygen. Using the interacting bonds method (IBM), the adsorption heat of atomic oxygen on the (100) plane of the silver-gold alloy has been calculated.

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. , . (100) .

     

Radical scavenging properties of a flavouring agent–Vanillin

Using pulse radiolysis technique, the one-electron oxidation of vanillin (V-OH) with azide radicals, at pH 6 and 9 resulted in the formation of vanillin phenoxyl radical with k = 6.7 × 10⁷ and 2.5 × 10⁹ dm³ mol^-1 s^-1, respectively. The transient absorption spectra of the vanillin phenoxyl radical (V-O) formed either at pH 6 or 9, showed a _max at 410 nm. At pH 5, the OH radicals seem to form an adduct with vanillin, _max at 430 nm and k(OH + V-OH) = 3.3 × 10⁹ dm³ mol^-1 s^-1, while at pH 9, the OH radical reaction resulted in the formation of vanillin phenoxyl radical with _max at 410 nm and k(OH + V-O-) = 6.6 × 10⁹ dm³ mol^-1 s^-1. The reactivity of NO₂radicals with vanillin is lower by orders of magnitude signifying an incomplete reaction. In general, the rate constants for the reaction of OH, N, NO radicals with vanillin were higher at pH 9 than at the lower pH. Its reactivity with other one-electron oxidants like CCl₃OO, CHCl₂OO and CH radicals and the ability to chemically repair tryptophanyl and guanosyl radicals with k = 1.5 - 4 × 10⁷ dm³ mol^-1 s^-1 indicate its antioxidative behaviour.     

Formation of oxalates and carbonates in the thermal decompositions of alkali metal formates

The influences of gaseous and solid reactants on the yields of oxalates and carbonates in the thermal decompositions of alkali metal formates have been studied. A mechanism of formation of these products is proposed, which explains the influences of basic and acidic species formed in the medium on the thermal decompositions of the alkali metal formates.

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Zusammenfassung Der einfluß von gasförmigen und festen Reaktanten auf die Ausbeute von oxalaten und Karbonaten bei der thermischen Zersetzung von Alkalimetallformiaten wurde untersucht. Es wurde ein Mechanismus für die Bildung dieser Produkte vorgeschlagen, der den Einfluß der während der thermischen Zersetzung von Alkalimetallformiaten entstehenden Basen und Säuren erklärt.

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, . , , .

     

Killing of Invasive Species of Ship’s Ballast Water in 20t/h System Using Hydroxyl Radicals

A pilot-scale experiment of 20t/h for the treatment of ships ballast water was done in this paper. With the method of strong ionization discharge of dielectric barrier, O₂ in air and H₂O at gas state are ionized and dissociated into large numbers of OH radicals, and then dissolved into a part of ballast water to form dissolved OH with the concentration of 24.3 mg/L. When the dissolved OH concentration is 0.63 mg/L, the kill efficiencies of bacteria, mono-algae, protozoan reached 100% within 2.67 s. The contents of chl-a, chl-b, chl-c and carotenoid were decreased to 35–64% within 8.0 s and not be tested after 5 min. At the same time, the ballast water quality was greatly improved. Therefore, the treatment of ships ballast water using OH radicals is a kind of advanced oxidation technology, which is considered as zero pollution, zero emission and zero residual in the process of the production, of OH radicals and the treatment of ballast water.Key Project of National Foundation Research from Science and Technology Ministry of China, (2002CCC00900). Key and General Projects of National Natural Science Foundation of China (NSFC: 60031001, 60371035).     

Исследование роли фосфиновых комплексов никеля различных степеней окисления в каталитической димеризации олефинов

Ni(II), Ni(I) Ni(O) . , , , Ni(O) Ni(I) - Ni(I) Ni(II) Ni(O).

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The interaction of organoaluminium compounds with phosphine complexes of Ni(II), Ni(I) and Ni(0) has been studied under the conditions of catalytic propylene dimerization. The active complexes are formed from Ni(II) compounds, the regeneration of the latter is ensured by repeated reduction, oxidation of Ni(0) to Ni(I), and by disproportionation of Ni(I) into Ni(II) and Ni(0).

     

On the change of thermal parameters in a glass during a Na/Tl ion-exchange-characterized by DTA measurements

The Na/Tl exchange is investigated in two silicate glasses (Na₂O·2SiO₂ and crown-flint KF₃) by estimation of concentration or refractive index profiles, resp. (c _Tl(x) orn(x)). The forms of the profiles are discussed in connection with changes of the glass transition temperature T_g owing to an increase of Tl₂O contents, determined by DTA on homogeneous glass samples. During the Na/Tl exchange the local and temporal enlargement of the Tl₂O content causes a drastic decrease ofT _g(x, t) values and of the viscosity (x, t), which yields a remarkable acceleration of the Na/Tl interdiffusion.

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Zusammenfassung Der Na/Tl-Austausch wird in zwei Silicatgläsern (Na₂O.2SiO₂ und Kron-Flintglass KF3) anhand der Bestimmung von Konzentrations- oder Brechzahlprofilen (c _Tl(x) odern(x)) untersucht. Die Profilformen werden im Zusammenhang mit Änderungen der Glastransformations-TemperaturT _g bei steigendem Tl₂O-Gehalt diskutiert, die mittels DTA an homogenen Glasproben bestimmt wurden. Während des Na/Tl-Austausches verursacht die lokale und zeitliche Erhöhung des Tl₂O-Gehaltes ein drastisches Absinken derT _g(x, t)-Werte bzw. der Viskosität (x, t), das zu einer bemerkenswerten Beschleunigung der Na/Tl-Interdiffusion führt.

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(Na₂O.2SiO₂ «») Na/Tl ₁(x) 321in(x). , , . Na/Tl _g(, t) i (x,t), Na/Tl .

     

Redox reactions of basic fuchsin in homogeneous aqueous media

The pulse-radiolysis technique has been employed to understand the reaction mechanism and to characterize the transient species involved in the redox processes taking place in the radiation chemistry of basic fuchsin (BF⁺). One-electron reduction and oxidation reactions of BF⁺ have been carried out in homogeneous aqueous solutions employing various reducing (e _aq ^– , (CH₃)₂COH, CO ₂ ^– ) and oxidizing (N ₃, Br, Cl ₂ ^– Br ₂ ^– ) radicals. The absorption spectra of the transients formed in the above reactions have been attributed to semi-reduced and semi-oxidized species of BF⁺, respectively. The kinetic and spectroscopic properties of these transients have been evaluated. The reaction with H and OH radicals have also been performed and compared with those of specific one-electron reducing and oxidizing radicals. These reactions have been inferred predominantly by addition to BF⁺. Protolytic equilibria involving semi-reduced species of basic fuchsin have been studied over the pH range from 2 to 10 and the pK _a has been determined to be 3.9.     

Kinetics and spectral properties of electron and •OH adducts of dimethylpyridines: a pulse radiolysis study

The reactions of e_aq ^-, OH, O^- and SO^- ₄ with 2,4-, 2,6- and 3,5-dimethylpyridines have been investigated in aqueous solution by pulse radiolysis with optical detection. Both e_aq ^- and OH radicals have high reactivity toward these compounds with k = (4-8) × 10⁹ dm³ mol^-1 s^-1. The rates of O^- and SO₄ ^- reactions ((1-3) × 10⁹ dm³ mol^-1 s^-1) were lower compared to the rate observed with the OH radical. The transient absorption spectra obtained in the reaction of e_aq ^- with three isomers exhibited a weak broad band around 340-410 nm. The absorption maxima of the intermediates formed in the OH and SO₄ ^- reactions were centred around 320-330 nm ( = 2450-3500 dm³ mol^-1 cm^-1) with an additional broad peak in the range 460-520 nm which are attributed to the corresponding OH adducts. The spectra in the O^- reaction have absorption maxima between 300 and 320 nm and it reacts both by addition and H-abstraction from the CH₃ group. A reaction mechanism consistent with the observed results is proposed.     

Thermal studies on titanyl,zirconyl and hafnyl dithiocarbamato complexes

The dithiocarbamato complexes of titanyl(IV), zirconyl(IV) and hafnyl(IV), abbreviated as MO(S₂CNRR)₂·nH₂O(M=Ti, Zr or Hf,R=H,R=C₅H₉;R=H,R=C₇H₁₁,n=1 for Ti andn=2 for Zr and Hf), were prepared in aqueous medium and characterized by elemental analyses, magnetic susceptibility measurements and IR spectral studies. The thermal behaviour of these compounds under non-isothermal conditions was investigated by thermogravimetric, derivative thermogravimetric and differential scanning calorimctric techniques in nitrogen and oxygen atmospheres. The intermediates obtained at the end of various thermal decomposition steps were identified on the basis of analyses and IR spectral studies. Kinetic parameters, such as apparent activation energy and order of reaction, were determined by the graphical method of Coats and Redfern. The heats of reaction for the different decomposition steps were calculated from the DSC curves.

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Zusammenfassung Die Thiocarbamato-Komplexe von Titanyl(IV), Zirkonyl(IV) und Hafnyl(IV) der allgemeinen Formel MO(S₂CNRR)₂·n H₂O (M=Ti, Zr oder Hf;R=H, R=C₅H₉;R=H, R=C₇H₁₁;n=1 für Ti undn=2 für Zr und Hf) wurden in wässrigem Medium hergestellt und durch Elementaranalyse, Messung der magnetischen Suszeptibilität und IR-Spektraluntersuchungen charakterisiert. Das thermische Verhalten dieser Verbindungen unter nicht-isothermen Bedingungen wurde durch TG, DTG und DSC in Stickstoff- und Sauerstoffatmosphäre untersucht. Die nach verschiedenen thermischen Zersetzungsschritten erhaltenen Zwischenprodukte wurden durch chemische Analyse und IR-Spektroskopie identifiziert. Kinetische Parameter, wie die scheinbare Aktivierungsenergie und die Reaktionsordnung, wurden nach der graphischen Methode von Coats und Redfern bestimmt. Für die einzelnen Zersetzungsschritte wurden die Reaktionswärmen aus den DSC-Kurven berechnet.

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, . MO(S₂CNRR)₂·nH₂O (M=I, Zr, Hf,R=H,R ¹=C₅H₉, C₇H₁₁,n=1 I =2 ) , . , . , , . - . .

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The authors are grateful to Dr. Shyam Kumar for helpful discussions.     

Iron Catalysis of SO2 Oxidation in the Atmosphere

The mechanisms of SO₂ oxidation catalyzed by iron ions in the droplet phase of the convective cloud in the lower atmosphere were examined. The relations of the catalytic SO₂ decrease to the concentration of the iron ions and to the intensity of fluxes to the droplet of the OH _(g) and HO _2(g) radicals were characterized. The determining role of the replacement of the low-reactive HO _2(g)(O^– _2(aq)) radical by the reactive SO^– _5(aq) radical in the sulfite medium during daytime was revealed. This process occurred due to the coupling of the decay of the radicals and their regeneration in the liquid-phase reactions O^– _2(aq) + FeOH²⁺ _(aq) Fe²⁺ _(aq) + OH^– _(aq) + O_2(aq), HSO^– _5(aq) + Fe²⁺ _(aq) FeOH²⁺ _(aq) + SO^– _4(aq)HSO ₃ ^- _(aq),O_{2 (aq)} SO^– _5(aq).     

The use of a continuous-flow helium cryostat in low-temperature calorimetry

For experimental investigation of the temperature-dependences of specific heat and thermal conductivity in the range 4–300 K a continuous-flow helium cryostat has been developed. Its adaptation for low-temperature calorimetry and its use for measurement of the temperature-dependences of the specific heats of bulk samples of metals and insulators are described in this note. The phase transition from the normal to the superconductive state has been measured on NbTi and its critical temperature determined. Two methods of determination of the temperature-dependences of the specific heats of metals and insulators have been developed. The inaccuracy of specific heat determination did not exceed 2 % with metal materials and 5 % with insulating materials.

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Zusammenfassung Ein Heliumkryostat mit kontinuierlichem Strom wurde für Versuchszwecke zur Untersuchung der Temperaturabhängigkeit der spezifischen Wärme und der Wärmeleitfähigkeit im Bereich von 4 bis 300 K entwickelt. Sein Einsatz als Tieftemperaturkalorimeter sowie seine Anwendung zur Messung der Temperaturabhängigkeit der spezifischen Wärme einer Anzahl von Metall- und Isoliermaterialproben werden beschrieben. Der Phasenübergang vom normalen in den Supraleitungszustand wurde an NbTi gemessen und seine kritische Temperatur bestimmt. Zwei Methoden wurden zur Bestimmung der Temperaturabhängigkeit der spezifischen Wärme von Metallen und Isolatoren entwickelt. Die Ungenauigkeit der Bestimmungen der spezifischen Wärme war unterhalb von 2 % bei metallischen und unterhalb von 5 % bei isolierenden Materialien.

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Résumé Un cryostat à circulation continue d'hélium, destiné à la détermination expérimentale de la chaleur spécifique et de la conductivité thermique en fonction de la température entre 4 et 300 K, a été mis au point. Son utilisation comme calorimètre à basses températures est décrite ainsi que son application à la mesure de la chaleur spécifique en fonction de la température d'échantillons massifs de métaux et isolants. La transition de phase de l'état normal à l'état supraconducteur a été étudiée sur un échantillon de NbTi et la température critique a été déterminée. Deux méthodes ont été mises au point pour déterminer la variation de la chaleur spécifique en fonction de la température des métaux et isolants. L'imprécision de la détermination de la chaleur spécifique est inférieure à 2 % pour les métaux et 5 % pour les isolants.

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4–300 . ë . NbTi . . 2%, 5%.

     

Precipitation of aluminium hydroxide in the presence of surfactant and its effect on the surface acidity

Surface acidity of aluminas prepared by precipitation from sodium aluminate solutions and nitric acid with and without surfactant were determined by IR spectroscopy. It was found that the amounts of aprotic acidic sites increase with increasing pH of precipitation and with increasing concentration of surfactant used in the course of precipitation and washing of the precipitate.

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, -. , -, .

     

Thermal and mechanical studies on the cure time optimisation of polysulphide resin

The effect of two commercially available metal oxide curing agents, PbO₂ and MnO₂, on the cure time, kinetic parameters and ultimate tensile strength of the polysulphide polymer was investigated. The kinetic parameters for the thermal decomposition of the two systems were evaluated from their TG data. Both the energy of activation and pre-exponential factor showed a systematic increase with increase in cure and levelled off after the reaction. The cure time was also followed by determining the mechanical properties of the samples at regular intervals. The ultimate tensile strength values and the kinetic parameters follow similar trend with respect to the cure time. The kinetic parameters and the ultimate tensile strength for the PbO₂ cured polysulphide system were on the higher side.

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Zusammenfassung Es wurde der Einfluß von zwei im Handel erhältlichen Metalloxidhärtemitteln. PbO₂ und MnO₂, auf die Aushärtungszeit, die kinetischen Parameter und die Zugfestigkeit von Polysulfidpolymeren untersucht. Die kinetischen Parameter für die thermische Zersetzung der zwei Systeme wurden aus deren TG-Daten ermittelt. Sowohl die Aktivierungsenergie als auch der präexponentielle Faktor wachsen mit fortschreitender Aushärtung ständig an und erreichen nach Verlauf der Reaktion einen konstanten Wert. In gleichmäßigen Zeitabschnitten wurde die Aushärtungszeit auch durch Bestimmen der mechanischen Eigenschaften der Proben verfolgt. In Bezug auf die Aushärtungszeit zeigen die Zugfestigkeit und die kinetischen Parameter einen ähnlichen Verlauf. Die kinetischen Parameter und die Zugfestigkeit von mit PbO₂ gehärteten Polysulfidsystemen zeigen bessere Werte.

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, , , . , . . , . , . , , .

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We thank Dr. R. Ramaswamy for supplying the resin and Dr. K. V. C. Rao and Director, VSSC for the kind permission to publish this work.     

Thermoanalytical investigation of mixtures containing oxalic acid,sodium hydrogen oxalate and sodium oxalate

The ternary system containing H₂C₂O₄ · 2H₂O, NaHC₂O₄ · and Na₂C₂O₄ was investigated. It was ascertained that the termal curves of the mixtures were not the algebraic sums of their component curves. All thermal decomposition stages were interpreted and the means of performing qualitative and quantitative analyses in the system were given.

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Zusammenfassung Das H₂C₂O₄ · 2 H₂O, NaHC₂O₄ · H₂O und Na₂C₂O₄ enthaltende ternäre System wurde untersucht. Es wurde festgestellt, daß die thermischen Kurven der Gemische nicht den algebraischen Summen ihrer Komponentenkurven entsprachen. Sämtliche Stufen der thermischen Zersetzung wurden zugeordnet und die Möglichkeiten der Durchführung qualitativer und quantitativer Analysen im System angegeben.

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Résumé On a étudié le système ternaire contenant H₂C₂O₄ · 2H₂O, NaHC₂O₄ · H₂O et Na₂C₂O₄. On a établi que les courbes thermiques des mélanges ne correspondaient pas à la somme algébrique de leurs courbes composantes. On a interprété toutes les étapes de la décomposition thermique et donné les moyens d'effectuer des analyses qualitatives et quantitatives du système.

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, ₂₂₄. 2₂, NaHC₂O₄. ₂ Na₂C₂O₄. , . .

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The authors thank Mr E. Chromiak for the preparation of sodium hydrogen oxalate monohydrate, and Mrs Z. Wietrzyska-Lalak for her help in X-ray analysis.     

Review of some metallurgical problems suitable for quantitative calorimetric treatment

A review is given of various metallurgical problems treated in the author's laboratory, for which quantitative calorimetry gave very valuable information. Measurements of thermodynamic data for phase diagram calculations, vacancies in ordered alloys, annealing of steels, and the recovery and crystallization of amorphous alloys are successively examined.

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Zusammenfassung Es wird eine Übersicht über verschiedene, in unserem Laboratorium bearbeitete metallurgische Probleme gegeben, für die durch quantitative Kalorimetrie sehr genaue Informationen erhalten werden. Es wird auf Messungen thermodynamischer Daten für Phasendiagrammberechnungen, auf Fehlstellen in geordneten Legierungen, auf das Tempern von Stahl sowie auf Aufarbeitung und Kristallisation von amorphen Legierungen eingegangen.

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, . , , .

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Dedicated to Professor Dr Kurt Komarek on his 60th birthday.     

A new procedure for determination of the acid and base strength distribution of colored catalysts

A new procedure for determining the strength distribution of acid and base centers of colored catalysts by the indicator method has been proposed. The procedure basing on the use of a platinum gauze container for the colored catalyst enables us to eliminate the difficulties in the identification of the color of the indicator.

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. , , , .

     

Ba(OH)2 as catalyst in organic reactions, part XIV. Michael addition catalyzed by barium complex salts in the homogeneous phase

Michael addition to chalcone is catalyzed by barium complex salts in the homogeneous phase under various conditions. The nature of these intermediates is analyzed. These complex salts are described for the first time. The Michael adduct of malonodinitrile to chalcone is described for the first time.

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, , . . . . .