Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

Darstellung,Thermisches Verhalten und Gitterparameter von Erbiumfluorooxalattetrahydrat ErFC2O4 · 4H2O

Zusammenfassung Erbiumfluorhydrat ErF₃ · 1.1 H₂O bildet in Oxalsäurelösungen Erbiumfluorooxalattetrahydrat ErFC₂O₄ · 4 H₂O. Das ErFC₂O₄ · 4 H₂O ist grobkristallin, unlöslich in verdünnten Säuren und Laugen und löslich in konzentrierter Schwefelsäure. Beim thermogravimetrischen Abbau bildet es die Verbindungen ErFC₂O₄ · 2 H₂O, ErFC₂O₄ · · H₂O, ErFC₂O₄, ErOF und ErO_1.5. Die Kristallstruktur des ErFC₂O₄ · 4 H₂O ist orthorhombisch mit den Gitterkonstantena=11.217±0.007 Å,b-13.046±0.008 Å,c=9.191±0.005 Å undZ=6.

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Erbium fluoride hydrate ErF₃ · 1.1 H₂O forms in solutions of oxalic acid erbium fluorooxalate tetrahydrate ErFC₂O₄ · 4 H₂O. The ErFC₂O₄ · 4 H₂O is coarse-crystalline, insoluble in diluted acids and bases and soluble in concentrated sulphuric acid. During thermal decomposition ErFC₂O₄ · 2 H₂O, ErFC₂O₄ · H₂O, ErFC₂O₄, ErOF and ErO_1.5 are formed. The crystal structure of ErFC₂O₄ · 4H₂O is orthorhombic, with lattice constantsa=11.217±0.007 Å,b=13.046±0.008, Å c=9.191±±0.005Å andZ=6.

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Résumé Le fluorure d'erbium hydraté (ErF₃ · 1.1 H₂O) forme dans l'acide oxalique fluorooxalate d'erbium tétrahydraté (ErFC₂O₄ · 4 H₂O), un précipité consistant à gros cristaux insoluble dans les acides et bases dilués, mais soluble dans l'acide sulfurique concentré. Au cours de sa décomposition thermique on obtient ErFC₂O₄ · 2 H₂O; ErFC₂O₄ · H₂O; ErFC₂O₄, ErOF et ErO_1.5. ErFC₂O₄ · 4 H₂O a une structure cristalline ortorhombique avec les paramètres suivants:a=11.217±0.007 Å,b=13.046±0.008 Å,c-9.191 ±0.005 Å,Z=6.

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ErF₃ · 1.1 H₂O, ErFC₂O₄ · 4H₂O. ErFC₂O₄ · 4H₂O, - , , . : ErFC₂O₄ · 2H₂O. ErFC₂O₄ · H₂O, ErFC₂O₄, ErOF ErO_1·5. ErFC₂O₄ · 4 H₂O a=11,217±0,007 Å,b=13,046±0,008 Å,c=9,191± 0,005 Å Z=6.

     

Surface Energy Changes of Heat Treated TEOS Derived Silica Xerogels

The surface energy of monolithic silica xerogels was examined by measuring the interaction of organic probes with xerogels heated at temperatures close to the gel-to-glass transition temperature. Values of the dispersive component of the surface energy, , between 60 and 80 mJ m^-2 have been observed using n-alkanes for silica xerogels heated at 700, 800 and 900°C. At 1000°C, decreases to 8.37 mJ · m^-2. Also the differential heat of adsorption, variation of standard free energy and entropy of adsorption decrease when the silica xerogel is heated at 1000°C, showing a lower interaction potential of the organic probes with the silica surface. For the silica xerogels heated between 700 and 900°C, the acid character varies in accordance with the variation of the chemical nature of the silica. Upon heating at 1000°C, both acid and base characters are very close in accordance with a neutral surface. Within the experimental conditions used in this work, the surface of the obtained monolithic silica xerogels behaves as a glass surface when the treating temperature is 1000°C.     

Heterogenized rhodium complexes as hydrogen transfer catalysts

Cationic rhodium(I) norbornadiene complexes with polystyrene-immobilized imidazole, tetramethylbiimidazole or phosphine ligands in the presence of potassium hydroxide catalyze hydrogen transfer from isopropanol to acetophenone and 1-hexene. [Rh(NBD) (poly-PPh₂)₂] ClO₄ complexes are particularly efficient for the reduction of acetophenone, but slow decomposition to rhodium metal is observed.

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(I) , , , 1-. [Rh(NBD) (-PPh₂)₂]ClO₄ , .

     

Fine Patterning of Transparent, Conductive SnO2 Thin Films by UV-Irradiation

Finely patterned transparent, conductive SnO₂ thin films have been prepared. UV-light from a high-pressure mercury lamp was irradiated through a mask on the precursor films prepared from SnCl₂ with acetyl acetone in the ambient atmosphere, and this irradiation led to the change of solubility of the films in alkaline solution. Patterns with a width of about 3 to 50 m and thickness of about 0.1 m were formed with a pitch of about 2 to 20 m. The resistivity of the films heat-treated at 500°C after UV irradiation was about 1 × 10^–2 cm, which was almost the same resisitivity for the films heat-treated at 500°C without UV irradiation.     

Thermal decomposition of cyano complexes of the type M(NH3)3Ni(CN)4 (M=Cu,Zn, Cd)

Three complex compounds with the compositions Cu(NH₃)₃Ni(CN)₄ (CuA), Zn(NH₃)₃Ni(CN)₄ (ZnA), and Cd(NH₃)₃Ni(CN)₄ (CdA) were prepared and identified. Their structures were examined by the methods of infrared spectroscopy and X-ray powder diffraction and compared with one another. The thermal stabilities and stoichiometries of thermal decomposition were investigated with a derivatograph. It follows from the results that the thermal stability increases in the sequence CuA < ZnA < CdA.

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Zusammenfassung Drei Komplexverbindungen der Zusammensetzung Cu(NH₃)₃Ni(CN)₄ (CuA), Zn(NH₃)₃Ni(CN)₄ (ZnA) und Cd(NH₃)₃Ni(CN)₄ (CdA) wurden dargestellt und identifiziert. Die Strukturen der Verbindungen wurde infrarotspektroskopisch und röntgendiffraktometrisch untersucht und miteinander verglichen. Die thermische Stabilität und die Stöchiometrie der thermischen Zersetzung wurden mittels eines Derivatographen untersucht. Die thermische Stabilität nimmt in der Reihenfolge CuA < ZnA < CdA zu.

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Cu(NH₃)₃Ni(CN)₄ (CuA), Zn(NH₃)₃Ni(CN)₄ (ZnA) Cd(NH₃)₃Ni(CN)₄ (CdA). , . . , CuA     

Thermal analysis of a drug-polymeric excipient solid system

Differential scanning calorimetry has been applied to the study of the solid system cross-linked polyvinylpyrrolidone/trimethoprim.Different results have been systematically obtained on co-ground and not co-ground mixtures, suggesting some type of interaction to take place between components as a consequence of co-grinding.A simple phenomenological model of the interaction is proposed, which quite satisfactorily agrees with thermal data.

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Zusammenfassung Das feste System von vernetztem Polyvinyl-pyrolidin/Trimethoprim wurde mittels DSC untersucht. Unterschiedliche Ergebnisse wurden systematisch für zusammen und nicht zusammen verriebene Mischungen gefunden, was auf eine Wechselwirkung zwischen Komponenten beim Verreiben hindeutet. Ein einfaches phänomenologisches Modell dieser Wechselwirkung wird vorgeschlagen, das mit thermischen Daten befriedigend übereinstimmt.

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— . . , . , .

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This work has been partially supported by Ministero Pubblica Istruzione (Fondi 60%).     

Thermal analysis of the interaction of phosphorite with condensed phosphates of calcium

The thermal reactions between Maardu (Estonia) phosphorite and acidic phosphates were investigated. TG, DTG and DTA of mixtures with H₃PO₄, Ca(H₂PO₄)₂ · H₂O, Ca₂P₂O₇ and [Ca(PO₃)₂]_n in different molar ratios showed a maximum mass loss when the CaO P₂O₅ value was 2. The main temperature ranges of the mass losses were determined. The probable reactions relating to the mass losses are given on the basis of the thermal curves and IR spectra.

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Zusammenfassung Die thermische Reaktion zwischen Phosphorit aus Maardu (Estnien) und sauren Phosphaten wurde untersucht. TG, DTG und DTA von Gemischen mit H₃PO₄, Ca(H₂PO₄)₂ · H₂O, Ca₂P₂O₇ und [Ca(PO₃)₂]_n in verschiedenen molaren VerhÄltnissen zeigten den grö\ten Massenverlust bei dem VerhÄltnis von CaO P₂O₅=2. Die wichtigsten Temperaturbereiche der Massenverluste wurden bestimmt. Die den Massenverlusten zugeordneten wahrscheinlichen Reaktionen werden aus den erhaltenen thermischen Kurven und IR Spektren ermittelt.

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Résumé Etude de l'effet thermique lié à la réaction entre la phosphorite de Maardu (Estonie) et les hydrogénophosphates. Etude par TG, TGD et ATD de mélanges de H₃PO₄ avec Ca(H₂PO₄)₂ · 2 H₂O, Ca₂P₂O₇ et [Ca(PO₃)₂]_n réalisés avec différents rapports molaires; mise en évidence d'une perte de masse maximale pour le rapport CaO P₂O₅ égal à deux. Détermination des principaux domaines de température où s'effectuent les pertes de masse. On donne les réactions probables correspondant aux pertes de masse en s'appuyant sur les courbes d'analyse thermique et spectres infrarouges.

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() . TG, DTG DTA H₃PO₄, Cc(H₂PO₄)₂. H₂O, Ca₂P₂O₇ [Ca(PO₃)₂] _n , CaOP₂O₅ 2. . , .

     

Contribution of electron-deficient platinum to benzene hydrogenation and its activation by water

The activity of metallic (Pt^o) and electron-deficient (Pt) platinum in Pt/Al₂O₃ catalysts has been studied in the low temperature hydrogenation of benzene. Reaction kinetics has been clarified. It is shown that water preadsorption does not affect the character of kinetic curves, but enhances the reaction rate due to an increase in the specific activity of Pt.

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(Pt^o) (Pt) Pt/Al₂O₃- . . , , Pt.

     

Ein neuer Typ quaternärer Oxometallate: K3Na2[InO4]

With K₃Na₂[InO₄] the first example of new kind of oxides of the type A₃A₂[MO₄] with R(A)>R(A) was prepared in form of colourless single crystals by oxidation of the intermetallic compound KNaIn₂. Intimate mixtures of the educts (K₂O₂: K_0.5Na_0.5In=1.2:1) were heated in sealed Ag-tubes (380 °C, 2 d, then 480 °C, 5 d). K₃Na₂[InO₄] crystallizes monoclinic (P2₁/n) witha=1012.6 pm,b=969.9 pm,c=725.4 pm, =91.02°;Z=4. The crystal structure was elucidated by four-circle diffractometer (PW 1100, Ag-K, 6047I _o(hkl),R=7.3%,R _w=4.4%). The new typ forms a very complicated 3-dimensional network ³ {Na₂InO₄} stuffed by 3 K⁺. The Madelung part of lattice energy, MAPLE, is calculated and discussed.

Professor Edwin Hengge zum 60. Geburtstag am 21. Juli 1990 gewidmet     

The Iron Behaviour in Aluminosilicate Gel-Derived Materials

Electron spin resonance (ESR) measurements have been carried out on a 10Fe₂O₃ · 10Al₂O₃ · 80SiO₂ gel heat-treated at different temperatures in air and under reducing conditions. ESR spectra were obtained at 300, 50 and 5 K. The effective g value (g = h/H), linewidth (H_pp) and ESR amplitude (A) depend on heat-treatment temperature of the gel-derived samples. ESR spectra exhibit different magnetic characteristics as a function of heat-treatment temperature and atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM) and a.c. susceptibility (_a.c.) analyses were used to better understand the ESR results. The results show that in the samples heat-treated in air, up to 700°C, Fe³⁺ ions are incorporated in the glass network in tetrahedral and/or octahedral co-ordinations. In the samples heat-treated between 250 and 700°C was not detected, by ESR, the presence of iron oxide aggregates. However, the formation of hematite particles was observed by XRD and SEM. The presence of iron oxide aggregates was detected (by ESR) in the samples heat-treated at temperatures higher than 700°C. These aggregates are formed, at 1200 and 1300°C, by hematite and magnetite particles as proved by XRD. The ESR spectra and a.c. susceptibility, of the samples heat-treated at 250°C (under reducing conditions), show a behaviour characteristic of small magnetite particles presence. The sample heat-treated at 500°C (under reducing conditios) contains magnetite particles (XRD). In the ESR spectra of the sample heat-treated at 1000°C, under reducing conditions, was not detected any resonance signal.     

Synthesis and Characterization of the β-BaB2O4 Phase Obtained by the Polymeric Precursor Method

A modified polymeric precursor method based on the Pechini process was used to synthesize -BaB₂O₄ (-BBO) crystalline phase. D-sorbitol (C₆H₁₄O₆) was used as a polymerizing agent to avoid the loss of boron during the samples' calcination and crystallization. The -BBO stoichiometric crystalline phase was only obtained when sorbitol was added to the solution. The results of Raman spectroscopy show that the amorphous phase is only completely eliminated when the samples are heat-treated at 750°C for 20 h. Thin films of -BBO phase displaying a preferred orientation were obtained when crystallized at 750°C for 2 h and deposited on sapphire substrate.     

Some physico-chemical and catalytic properties of nickel(II) oxide promoted with gadolinium(III) oxide

Chemical and phase compositions of NiO–Gd₂O₃ catalysts have been studied. It has been found that the Gd₂O₃ dopant retards the sintering of NiO and increases its deviation from stoichiometry. Catalytic activity for CO oxidation does not change monotonically with an increase in Gd₂O₃ content in the catalysts.

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NiO–Gd₂O₃ . , Gd₂O₃ NiO - . Gd₂O₃ .

     

Effect of Thermal Activation of Supported Catalysts Pt/MeOx,Where MOx = Al2O3, CeO2, La2O3, and ZrO2, for Complete Oxidation

A sharp increase in the atomic catalytic activity (ACA) of supported platinum catalysts in the model reaction of n-pentane complete oxidation is found on going from the preliminary calcination temperature of 500–600°C to a temperature of 700°C. ACA increases by an order of magnitude for the Pt/-Al₂O₃ system, 3 times for Pt/ZrO₂, and 1.5 times for Pt/CeO₂. The per-gram activities of all catalysts decrease because of a decrease in the dispersion of supported platinum with an increase in the temperature of preliminary calcination.     

Quantum-chemical study of allylstannanes

It has been shown by the MNDO method that in allyl compounds of tin, the atomic orbitals of the heteroatom interact with the -orbital through the bridge group, but interact with the ^*-orbital mainly through space. The position and intensity of the long-wave electronic transitions for methylvinylstannane should not depend on the conformation, with the ,- and , pseudo--conjugation effects being approximately identical, whereas for allylstannane, the ,-conjugation is considerably stronger. In molecules containing several allyl fragments bonded to heavy atoms, ,-conjugation is far weaker than ,-conjugation in polyenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2071–2076, September, 1991.     

Thermal and Temporal Aging of Two Step Acid-Base Catalyzed Silica Gels in Water/Ethanol Solutions

Dissolution and reprecipitation of silica during aging in water improve the wet gels mechanical stiffness and strength, and hence shrinkage during supercritical drying is reduced. We have investigated how the strength and stiffness of a 2-step TEOS acid-base catalyzed wet gel can be improved by aging in a solution of water/ethanol (20–40 vol%) at various temperatures (20–70°C) and time (2 h and 24 h) and how this influences the aerogels properties. The linear shrinkage during supercritical drying was reduced from 29% to 2% by introducing the aging step in the 20 vol% water/ethanol solution for 24 h at 60°C.We have also in previous works introduced the idea of preparing ambient pressure dried silica aerogels by increasing the wet gels stiffness by aging in a TEOS solution until shrinkage during drying is almost eliminated. The gels aged in the water/ethanol solutions were further aged in a TEOS/ethanol solution and the effect of the increasing water content in the pore liquid was studied. A xerogel density of 0.20 g/cm³ is reported for gels with a shear modulus (G) of 30 MPa.     

Cationic Pd(II)-complex formation in the Pd(acac)2-Et2NH-BF3?OET2 system and its activity in butadiene-amine telomerization

Pd(acac)₂ reacts with Et₂NH and BF₃OEt₂ to produce [(acac) Pd(Et₂NH)₂]BF₄. This complex is highly active in butadiene-secondary amine telomerization reactions.

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Pd(acac)₂ Et₂NH BF₃OEt₂, [(acac) Pd(Et₂NH)₂]BF₄. .