Simultaneous determination of neodymium and erbium in rare earth mixture with 5,7-dibromo-8-hydroxyquinoline and TX-100 by third-derivative spectrophotometry

The absorption spectra of 4f electron transitions of the complexes of neodymium and erbium with 5,7-dibromo-8-hydroxyquinoline in the presence of octylphenol poly(ethyleneglycol)ether have been studied by normal and third-derivative spectrophotometry. The proposed method is free of interference of other rare earths. The calibration graphs were linear up to 18 g/ml of neodymium and 21 g/ml of erbium (in the final solution). The derivative molar absorptivities are 395 l.mol^–1.cm^–1 for neodymium and 3421.mol^–1.cm^–1 for erbium. The corresponding values of Sandell's sensitivity were 0.36 and 0.49 g.cm^–1, respectively. The relative standard deviations evaluated from ten independent determinations of 2.5 g/ml of neodymium and erbium are 1.5 and 3.8% for neodymium and 1.8 and 4.1% for erbium in absence and presence of 70 g of lanthanum, respectively. The detection limits (signal to noise ratio=2) are 0.23 g/ml for neodymium and 0.30 g/ml for erbium. The method has been used for the determination of neodymium and erbium in mixed rare earths with satisfactory results.     

Selective determination of neodymium and erbium in mixtures with other lanthanides by second-derivative spectrophotometry of complexes with benzoyl-indan-1,3-dione and cetylpyridinium chloride

The absorption spectra of 4f electron transitions of the neodymium and erbium complexes with benzoyl-indan-1,3-dione and cetylpyridinium chloride have been studied by conventional and derivative spectrophotometry. The second-derivative spectrum has been used to eliminate the interference of the other lanthanides, and to increase the sensitivity by a further factor of 4–6. Beer's Law is obeyed for 6–29 g/ml Nd and 7–33 g/ml Er. The relative standard deviations evaluated from 10 independent determinations of 5.0 g/ml Nd and Er were 1.1% (Nd) and 1.6% (Er). The detection limits obtained from the sensitivity of the calibration graphs and 3s _b, (standard deviation of the blank,n = 11) were 0.63 g/ml Nd and 0.61 g/ml Er. The quantification limits (10s _b) were 2.1 g/ml Nd and 2.0 g/ml Er. A method for the direct determination of neodymium and erbium in rare earth mixtures with good accuracy and selectivity is proposed.     

Mechanism of o-xylene conversion on magnesium modifications of Y zeolite

o-Xylene conversions has been investigated in the presence of MgNaY zeolites with different Si/Al ratios and degrees of exchange. Disproportionation proceeds to a higher degree than does isomerization. The distribution of reaction products is attributed to geometric factors. The results are in agreement with a monomolecular mechanism of isomerization.

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- MgNaY Si/Al . , , . . .

     

Solid state reactions between nickel(II) sulphide and oxides of manganese and iron

Thermogravimetry and differential thermal analysis have shown that, when nickel(II) sulphide and manganese or iron oxides are heated together, several reactions occur depending on the molar ratio of the reactants. Detailed examinations of these reactions have shown that there are a number of intermediate stages, including the formation of sulphates.

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Zusammenfassung Thermogravimetrie und Differentialthermoanalyse zeigen, daß bei gemeinsamer Erhitzen von Nickel(II)-Sulfid und Manganoder Eisenoxiden, in Abhängigkeit von dem Molarverhältnis der Reaktionspartner verschiedene Reaktionen stattfinden. Das eingehende Studium dieser Reaktionen zeigte das Auftreten einer Anzahl Zwischenstufen, darunter auch die Bildung von Sulfaten.

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Résumé On montre par thermogravimétrie et analyse thermique différentielle que plusieurs réactions peuvent se produire suivant les rapports molaires des constituants lorsque l'on chauffe du sulfure de nickel(II) avec des oxydes de manganèse ou de fer. L'étude détaillée de ces réactions a mis en évidence un certain nombre d'étapes intermédiaires, avec formation de sulfates.

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, (II) , . , , .

     

A new catalyst for hydrodesulfurization of heavy residue

Catalytic hydrodesulfurization plays an important role in the conversion of sulfur laden residual oils. Cobalt molybdate catalysts are more commonly used for this process. In the present study, a precipitation technique at constant pH value was used to prepare alumina support. This material has very narrow pore size distribution centered around the pore diameter of about 8 nm. It also has a large surface area and pore volume and, therefore, can be used as a support for CoMo RDS catalysts. The results of temperature-programmed desorption of ammonia indicated that this catalyst has higher surface acidity than the conventional catalysts. The high surface acidity could enhance the cracking ability of the catalyst. The RDS reaction results showed that the samples prepared by precipitation are more active and more stable than the conventional catalysts, at least in the first 72 h. The results can be attributed to its unique pore structure and high surface acidity.

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. . pH. 8 . CoMo . , , . , , , , , - 72 . .

     

Spectrophotometric determination of lead in environmental objects with the new highly effective reagent HOCAC

Summary A simple method has been developed for determination of traces of lead with the new organic reagent HOCAC (hexaoxacycloazochrom). The method was used for lead determinations in waters, soils and food after extraction or sorption of the lead followed by direct reagent addition to the acid re-extract or eluate. It is possible to determine Pb down to 2 g in 1 l water after extraction or down to 10 g in 1 l water and down to 500 g in 1 kg potatoes or soil after sorption.     

On acrylonitrile polymerization in the presence of zinc salts

Acrylonitrile polymerization photoinitiated at 365 nm by pyrene and/or azobisisobutyronitrile in the presence of zinc salts in N,N-dimethylformamide solution has been studied by the rotating sector method. It was found that the ratio of the rate constants for propagation and termination (k_p/k_t) increases on addition of zinc salts (chloride, nitrate, acetate). This increase was more pronounced for the azobisisobutyronitrile photoinitiated polymerization of acrylonitrile then for its pyrene photoinitiated polymerization. The results confirm the previously expressed view concerning the dual role of zinc chloride in initiation as well as in propagation steps of acrylonitrile polymerization photoinitiated by aromatic hydrocarbons.

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, 365 / N,N- . , (k_p/k_t) ( , , ). , . , , , .

     

The effect of preparation conditions on the activity and stability of copreciptitated Ni/Al2O3 catalysts for the methanation of carbon monoxide

The activities and stabilities of coprecipitated Ni/Al₂O₃ methanation catalysts depend markedly on their preparation and pretreatment. The results are discussed in relation to the structure of the precipitate and to changes which occur during calcination and reduction.

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Ni/Al₂O₃ . , .

     

The thermal decomposition of alkaline earth metal salicylates

The thermal decompositions of the salicylates of magnesium, calcium, strontium and barium were investigated using thermogravimetry and differential thermal analysis, together with the analysis of intermediate products formed during the decomposition processes. One intermediate product was isolated and identified during the decomposition of the magnesium salt, and two for each of the remaining metal salts.

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Zusammenfassung Die thermische Zersetzung der Salicylate von Magnesium, Calcium, Strontium und Barium sowie die Analyse der während des Vorganges gebildeten Zwischenprodukte wurden durch die thermogravimetrische und Differential-Thermal-Analyse untersucht. Im Verlaufe der Zersetzung des Magnesiumsalzes wurde ein Zwischenprodukt isoliert und identifiziert, bei den übrigen Metallsalzen je zwei.

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Résumé On a étudié par thermogravimétrie et analyse thermique différentielle la décomposition thermique des salicylates de magnésium, calcium, strontium et baryum et l'on a analysé les produits intermédiaires qui se forment pendant la décomposition. C'est ainsi que l'on a isolé et identifié un produit intermédiaire au cours de la décomposition du sel de magnésium et deux pour chacun des autres sels.

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, , , , , . , - .

     

Why do ternary compounds exist? — Thermoanalytical investigations on binary systems of metal chlorides

Ternary chlorides are stable if they can be formed from each pair of the other compounds in a system with a gain in energy. Especially, the energy of formation from the two adjacent compounds, the energy of synproportionation must be negative. At 0 K this condition is fulfilled, if (lattice) enthalpy is won. At higher temperature also theT·S-term of the Gibbs-Helmholtz-equation can be of significance: a loss in H must be compensated by a gain inT·S, if a (high-temperature) compound shall exist.This conception was proved experimentally on systems ACl/MCl₂ and ACl/LnCl₃(Ln=Lanthanides). By DTA and X-ray powder patterns the phase diagrams of the pseudobinary systems were elucidated, to yield the stoichiometry and structures of the existing compounds. By solution calorimetry the formation enthalpies at room temperature from the binary parent-compounds were determined. Measurements with a galvanic cell for solid electrolytes at temperatures higher than 300 °C yield the free enthalpies and entropies of synproportionation.The main result of these measurements is, that compounds with isolated coordination polyhedra (K₂CoCl₄=tetrahedra; Rb₃LaCl₆=octahedra) can have a sufficiently high gain in entropy to be stable at temperatures > 0 K.

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Zusammenfassung Ternäre Chloride sind stabil, wenn sie sich aus allen Paaren der restlichen in einem System existierenden Verbindungen unter Energiegewinn darstellen lassen. Insbesondere muß die Bildungsenergie aus den beiden Nachbarverbindungen, die Synproportionierungsenergie, netativ sein. Bei 0 K ist diese Bedingung erfüllt, wenn dabei (Gitter-) Enthalpie gewonnen wird. Bei höheren Temperaturen kann auch derT·S-Term der Gibbs-Helmholtz-Gleichung ausschlaggebend werden: ein Verlust an H muß durch einen genügend großen Gewinn anT·S kompensiert werden, damit eine (Hochtemperatur-) Verbindung existieren kann.Dieses Konzept wurde experimentell an Systemen ACl/MCl₂ und ACl/LnCl₃ (Ln=Lanthanoid) bewiesen. Durch DTA und Röntgenpulveraufnahmen wurden die Phasendiagramme der pseudobinären Systeme erstellt, um Zusammensetzung und Strukturen der existierenden Verbindungen zu ermitteln. Mittels Lösungskalorimetrie wurden die Bildungsenthalpien bei Raumtemperaturen aus den binären Ausgangsverbindungen gemessen. Messungen mit einer galvanischen Zelle für Festelektrolyte bei Temperaturen >300 °C lieferten die freien Enthalpien und Entropien für die Synproportionierungsreak-tionen. Als wichtigstes Resultat ergab sich, daß Verbindungen mit isolierten Koordinationspolyedern (K₂CoCl₄=Tetraeder; Rb₃LaCl₆=Oktaeder) einen so großen Entropiegewinn aufweisen, daß sie bei hohen Temperaturen stabil sein können.

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, . . , () . - T·S , H T·S . l/l₂ ACl/LnCl₃, Ln — . . . 300° . , (₂l₄ — , RbLaCl₆ — ) , .

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Support by the Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industry is gratefully acknowledged.     

On differential geometric formalization of chemical reaction kinetics statical aspects

In this article the basic mathematical structure of chemical reaction kinetics is investigated. For this purpose the methods of modern differential geometry are used. Using this approach the various aspects of species, reactions and stoichiometry can be separately treated.

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. . , , .

     

The influence of second-nearest neighbor interactions on the thermodynamic properties of B2 phases with substitutional defects

In order to explain some discrepancies between the theoretical predictions and the experimental data for the thermodynamic properties of substitutional B 2 phases,Chang's theoretical model is extended by including the influence of second-nearest neighbor interactions. For this purpose a new parameter is introduced which is defined as the ratio of the interchange energies between second-nearest and first-nearest neighbors. Theoretical equations are derived for the compositional dependence of the activity and the partial molar enthalpy. Using literature data, the following phases are re-evaluated in terms of the disorder parameter and the newly introduced parameter : -AuZn, -AuCd, -AgMg, and -NiZn. Very good agreement is found between the theoretical curves and the experimental data for the four systems. The values of obtained range from 0.0 for -NiZn to 0.5 for -AuZn. The inclusion of second-nearest neighbor interactions has little influence on the values of . It is shown that the behavior of the activity curve in -AuZn can be explained in a physically more meaningful way by including interactions between all second-nearest neighbors rather than interactions between gold substitutional defects only, as was done byLibowitz.With 5 Figures     

Thermal degradation of single 7-cholesteryl acetate hydroperoxide

Summary The thermal degradation products of the 7- and 7-cholesteryl 3-acetate hydroperoxides obtained by thermal oxidation of cholesteryl 3-acetate are reported and discussed. The hydroperoxides were degraded in both the vapour and condensed phases. The main components identified were 7-ketocholesteryl 3-acetate, 7- and 7-hydroxycholesteryl 3-acetates and the products generated from the loss of the hydroperoxide group and/or of acetic acid. Remarkable is the finding of the epoxy-hydroxy derivatives of cholesteryl acetate among the degradation products.     

Microscopic cross section for ion-molecule reactions with polar molecules

Using Kapitsa's method of separating rapidly varying processes from slower translational motions, a microscopic capture cross section for gas phase ion-molecule reactions is derived (centrifugal barrier approximation), leading to rate coefficients lying between the values of Langevin's theory and those of the locked dipole approximation (LD).

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, , - ( ), , , , LD-.

     

Properties of double chlorides in the systems ACl/NdCl3 (ANa-Cs)

The pseudobinary systems ACl/NdCl₃ (A=Na-Cs) were reinvestigated by means of DTA. The following double chlorides were found primarily detected compounds are underlined):Na ₃Nd₅Cl₁₈; K₃NdCl₆, K₂NdCl₅,KNd ₂Cl₇;Rb ₃NdCl₆, Rb₂NdCl₅,RbNd ₂Cl₇; Cs₃NdCl₆,Cs ₂NdCl₅,CsNd ₂Cl₇.With a galvanic cell for solid electrolytes the thermodynamic functions of formation from ACl and NdCl₃ together with the free enthalpies of synproportionation from the compounds adjacent in the phase diagrams were measured. They revealed, that only the compounds A₂NdCl₅ are stable at ambient temperature. All other compounds are existing by a gain of entropy only at higher temperatures.The crystal structures of the compounds were determined by X-ray analysis on powders: the compounds are isotypic with the analogous double chlorides of La and Ce (A₃NdCl₆: high-temperature-modification = elpasolite-type; at room-temperature = metastable K₃MoCl₆-type; A₂NdCl₅=K₂PrCl₅-type; ANd₂Cl₇=-KEr₂F₇-type; Na₃Nd₅Cl₁₈=Na₃La₅Cl₁₈-type). Magnetic susceptibilities in the range from 80 to 300 K were measured with a Gouy-balance.

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Zusammenfassung Die pseudobinären Systeme ACl/NdCl₃ (A=Na-Cs) wurden mittels DTA neu untersucht. Folgende Doppelchloride wurden gefunden (erstmalig beschriebene Verbindungen sind unterstrichen):Na ₃Nd₅Cl₁₈; K₃NdCl₆, K₂NdCl₅,KNd ₂Cl₇;Rb ₃NdCl₆, Rb₂NdCl₅,RbNd ₂Cl₇; Cs₃NdCl₆,Cs ₂NdCl₅,CsNd ₂Cl₇.Mit einer galvanischen Zelle für feste Elektrolyte wurden die thermodynamischen Funktionen für die Bildung aus ACl und NdCl₃ sowie die freien Enthalpien für die Synproportionierung aus den im Zustandsdiagramm benachbarten Verbindungen gemessen. Es zeigte sich, daß nur die Verbindungen A₂NdCl₅ bei Normaltemperaturen stabil sind. Alle anderen Verbindungen existieren aufgrund von Entropiegewinnen nur bei höheren Temperaturen. Anhand von Röntgen-Pulveraufnahmen wurden die Kristallstrukturen ermittelt. Die Verbindungen sind isotyp zu den entsprechenden Doppelchloriden des Lanthans und Cers (A₃NdCl₆: Hochtemperaturmodifikationen = Elpasolith-Typ; bei Normaltemperatur metastabil im K₃MoCl₆-Typ; A₂NdCl₅=K₂PrCl₅-Typ; ANd₂Cl₇=-KEr₂F₇-Typ; Na₃Nd₅Cl₁₈=Na₃La₅Cl₁₈-Typ). Mit einer Gouy-Waage wurden die magnetischen Suszeptibilitäten im Temperaturbereich 80–300 K gemessen.

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ACl/NdCl₃, =NaCs. , : Na₃Nd₅Cl₁₈, K₃NdCl₆, K₂NdCl₅, KNd₂Cl₇, Rb₃NdCl₆, Rb₂NdCl₅, RbNd₂Cl₇, Cs₃NdCl₆, Cs₂NdCl₅, CsNd₂Cl₇. , . , A₂NdCl₅. . . , . A₃NdCl₆ , — K₃l₆. A₂NdCl₅ — K₂rl₅, ANd₂Cl₇ — -KEr₂F₇, Na₃Nd₅Cl₁₈- Na₃La₅Cl₁₈. 80–300 .

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This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.     

Performance of Pt?Sn/Al2O3?Cl catalysts in isopropanol decomposition

Highly dispersed TiO₂-supported copper with strong interactions with the support has been prepared. After reduction at 770 K, H₂ chemisorption is suppressed. Two types of copper sites exist, one easily and reversibly oxidized by O₂ at room temperature, and another interacting with the support.

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, TiO₂, . 770 H₂ . , O₂ , - .

     

Oxygen solubility in the superconducting compound YBa2Cu3O x (6⩽x⩽7), studied by TG and barometric measurements

Thermogravimetry in controlled oxygen atmospheres and barometric measurements between 300 and 1200 K were performed on the YBa₂Cu₃O _x superconducting phase. The complete reversibility of the exchange of a certain part of the oxygen, as found even at 250 °C, and the observed relationship between oxygen partial pressure, oxygen content and temperature, can be explained by the dissolution of oxygen in YBa₂Cu₃O _x . It is concluded that samples with highx values (), as necessary for good superconducting properties, can be obtained at high temperatures only at high oxygen pressures, but they were obtained by annealing at normal pressure between 250 and 350 °C.

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Zusammenfassung Die supraleitende Phase YBa₂Cu₃O _x wurde mit Hilfe von Thermogrametrie und barometrischen Messungen im Bereich 300 bis 1200 K untersucht. Die sogar bei 250 °C beobachtete Reversibilität des Austausches von einem Teil des Sauerstoffs sowie die gefundenen Beziehungen zwischen Sauerstoffaktivität (Partialdruck), Sauerstoffgehalt und Temperatur können durch eine Lösung von Sauerstoff in YBa₂Cu₃O _x erklärt werden. Aus den Ergebnissen kann gefolgert werden, daß Proben mit hohemx (7), die gute Supraleitungseigenschaften zeigen, bei hohen Temperaturen nr unter hohem Sauerstoffdruck hergestellt werden können. Sie werden jedoch auch durch Tempern bei Normaldruck bei 250 bis 350 °C erhalten.

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YBa₂Cu₃O_x 300–1200 . , 250°, , , YBa₂Cu₃O_x. , ( 7), , . , 250 350°.

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The authors thank Mrs. W. Höppner, Mrs. B. Thaut and Mr. F. Hansch for careful experimental assistance.     

Enhancement of catalytic activity by effect of graphite on Ru?Pt/C catalysts

Surface composition and catalytic activity of Ru–Pt/C catalysts were determined. A surface enrichment in Pt was found over the entire composition range. Catalytic activity showed a maximum value (140) on 66% Ru bimetallic catalyst. These results are correlated with the nature of the impregnating salts and with the conductive properties of graphite.

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Ru–Pt/C. Pt . (140) 66% Ru . .

     

Steroid compounds from the Pacific starfishesLuidia quinaria andDistolasterias elegans

One new and four previously known steroid compounds were identified from the Pacific starfishesLuidia quinaria andDistolasterias elegans. The structure of the new steroid was established from spectral data and chemical correlations with other steroids such as 5-cholestane-3,5,6,15,16,26-hexaol 3-sulfate (1). The previously known compounds were identified as 5-cholestane-3,5,6,15,26-pentaol 15-sulfate (2) fromLuidia quinaria and sodium (24S)-O-(-d-giucopyranosyll-5-cholestane-3,6,8,15,24-pentaol 6-sulfate (3), sodium (24S)-5-cholestane-3,6,8,15,24-pentaol 24-sulfate (4), and sodium tornasterol A sulfate (5).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 473–476, February, 1996.     

Nuclear interferences of uranium and thorium in a reactor neutron activation analysis determination of cerium using the radionuclides141Ce and143Ce

The interference contributions of uranium and thorium to the determination of cerium based on radionuclides¹⁴¹Ce and¹⁴³Ce produced by irradiation in a reactor core was determined. The values of the interference contributions for¹⁴¹Ce were 0.28±0.01 g Ce/g U and /2.01±0.05/x10^–3 g Ce/g Th, and for¹⁴³Ce 1.33±0.03 g Ce/g U and /9.0±0.2/x10^–3 g Ce/g Th.