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1.
Transparent and porous boehmite, -Al2O3 (500°C) and -Al2O3 (900° and 1000°C) thin sheets (50–100 m) have been prepared from boehmite sols. -Al2O3 shows about 48% porosity and 292 m2/g surface area. On transformation from -Al2O3 (500°C) to -Al2O3 (900°C), the porosity still remains high, i.e. 45%; however, the surface area becomes 138 m2/g. The porosity and surface area of -Al2O3 become about 41% and 97 m2/g respectively on further heating to 1000°C. A gradual increase of average pore radius during this thermal treatment suggests that coarsening of the pore occurred during the densification process. Both -Al2O3 and -Al2O3 show high degree of transmission from UV to NIR wavelength region. Cerium exists in +4 oxidation state in the boehmite as well as in the - and -Al2O3. The ultraviolet absorption edge of the alumina was tailored by varying the concentration of cerium. 相似文献
2.
Zusammenfassung Auf Grund thermischer und röntgenographischer Unter-suchungen wurde das vollständige Phasendiagramm Ni–Te aufgestellt. Die Anlage für die thermische Analyse wurde teilweise automatisiert, so daß ausgewählte Temperaturintervalle mit einstellbaren Heiz- udn Kühlgeschwindigkeiten periodisch durchlaufen werden konnten. Zwischen Ni und der kub. f. z. Hochtemperaturphase 1 (Ni3±x
Te2) liegt ein Eutektikum bei 34 At% Te und 1004,5°C. 1 schmilzt kongruent bei 38 At% Te und 1021,5°C und hat eine maximale Phasenbreite von 37 At% Te (1004,5°C) bis 43,5 At% Te (880°C). Nickelreiches 1 wandelt sich zwischen 796 und 789°C in eine Ordnungsphase 1 um, die bei 37,7 At% Te und 731°C eutektoidisch in Ni und 2 zerfällt. 1 und 1 wandeln sich unterhalb bei 790°C in die tetragonale 2-Phase um, deren maximaler Homogenitätsbereich von 38,8 At% Te (731°C) bis 41 At% Te (775°C) reicht. Bei 42,5 At% Te und 775°C zerfällt 1 eutektoidisch in 2 und 2. Die 2-Phase (NiTe0,85) bildet sich peritektisch bei 880°C und zerfällt bei 690°C nach 2 1 + . Orthorhombisches 1 disproportioniert sich peritektoidisch bei 742,5°C in 2 und 2. 2 bildet bei 873°C und 49,5 At% Te ein Eutektikum mit der -Phase vom NiAs-Typ. hat einen kongruenten Schmelzpunkt von 900,5°C bei 56 At% Te und eine maximale Phasenbreite von 52 At% Te (690°C) bis 66,6 At% Te (448,5°C). Mit Te bildet die -Phase ein entartetes Eutektikum bei 448,5°C. Die Phasen 2, 1 und wurden röntgenographisch verifiziert und die Abhängigkeit der Gitterparameter der -Phase von der Konzentration vermessen.
Mit 2 Abbildungen 相似文献
Transition metal-chalcogene systems, III: The system Ni–Te
Based on thermal and X-ray measurements the complete Ni–Te phase diagram was constructed. The equipment for thermal analysis was partially automated so that selected temperature intervals could be periodically scanned by programmed heating and cooling rates. Between Ni and thefcc high temperature phase 1 (Ni3±x Te2) a eutectic exists at 34 at% Te and 1004.5°C. 1 melts congruently at 38 at% Te and 1004.5°C, and has a maximum phase width from 37 at% Te (1004.5°C) to 43.5 at% Te (880°C). Nickel-rich 1 transforms between 796 and 789°C into an ordered phase 1 which decomposes eutectoidally into Ni and 2 at 37.7 at% Te and 731°C. 1 and 1 transform at temperatures below 790°C into the tetragonal 2-phase which has a maximum range of homogeneity from 38.8 at% Te (731°C) to 41 at% Te (775°C). At 42.5 at% Te and 775°C 1 decomposes eutectoidally into 2 and 2. The 2-phase (NiTe0.85) is formed by the peritectic reactionL + 1 2 at 880°C and decomposes at 690°C according to 2 1 + . Orthorhombic 1 disproportionates peritectoidally at 742.5°C into 2 and 2. 2 forms at 873°C and 49.5 at% Te a eutectic with the -phase of the NiAs-type. has a congruent melting point of 900.5°C at 56 at% Te and a maximum phase width from 52 at% Te (690°C) to 66.6 at% Te (448.5°C). Te and the -phase form a degenerate eutectic at 448.5°C. The phases 2, 1, and were verified by X-ray diffraction and the lattice parameters of the -phase were determined as a function of concentration.
Mit 2 Abbildungen 相似文献
3.
V. N. Doroshenko V. N. Kaurkovskaya E. P. Yakubenko D. I. Pobokin I. R. Entinzon V. M. Ogenko 《High Energy Chemistry》2002,36(3):157-162
The solid-phase decomposition of the iron formate crystal hydrate Fe(HCOO)2 · 2H2O under exposure to 60Co -rays or 3.5-MeV electrons was studied. It was found that the irradiation of this salt to absorbed doses of 0.1–2 MGy resulted in the radiolysis of water of crystallization and the HCOO– anion and in the reduction or oxidation of the Fe2+ cation. The composition of the solid-phase (-Fe, -Fe, FeO, -Fe -Fe2O3, Fe3O4, and FeCO3) and gaseous (H2O, CO, CO2, HCOOH, and CH4) radiolysis products of the substance was determined. 相似文献
4.
H. Mehner S. Nagy H. -J. Schierhorn A. Vértes 《Journal of Radioanalytical and Nuclear Chemistry》1985,94(3):201-205
Radioactive as well as inactive cobalt precipitated from an aqueous solution onto the surface of -Fe2O3 was investigated by the Mössbauer spectroscopy of57Fe. The experiment performed with the57Co-doped sample showed that some of the cobalt atoms diffused into the -Fe2O3 lattice owing to 1 h of heat treatment carried out at 300 °C. 相似文献
5.
The complete oxidation of a volatile organic compound (toluene) over supported metal oxide catalysts
The complete oxidation of a volatile organic compound (toluene) was carried out over oxides of various metals (Cu, Mn, Fe, V, Mo, Co, Ni and Zn) supported with -Al2O3 catalyst. It was found that Cu/-Al2O3 was the best catalyst among them. With increasing calcination temperature, the specific surface areas and the surface oxygen of the catalyst decreased and, as a result, the catalytic activity decreased. Copper loadings on -Al2O3 had an influence on catalytic activity, and it was observed that 5 wt% Cu/-Al2O3 catalyst was the most active. Using TiO2 (rutile) and SiO2 as support instead of -Al2O3, the sequence of copper crystallinity degree with respect to supports was SiO2 > TiO2 (rutile) > -Al2O3, which was the opposite of the catalytic activity sequence. 相似文献
6.
Zusammenfassung Aluminiumhydroxidgele wurden aus Al-Nitratlösungen bei konstantem pH-Wert mittels NH4OH gefällt, Ca, Sr und Ba-Ionen in Form ihrer Nitrate vor der Fällung zugesetzt und die Menge der in -Al2O3 eingebauten Fremdionen bestimmt. Diese ist bei konstantem pH-Wert von Menge und Art des vorgelegten Ions abhängig und wird von der Alterungszeit in Lösung nicht beeinflußt.Die thermische Stabilität des -Al2O3 wird durch den Einbau von Erdalkaliionen erhöht, wobei die für eine maximale Stabilisierung benötigte Fremdionenmenge mit steigendem Ionenradius abnimmt.Röntgenographische Untersuchungen zeigten, daß das Intensitätsverhältnis von Interferenzen bei reinen und erdalkalihältigen -Al2O3-Präparaten konstant bleibt, die Gesamtintensität der Reflexe bei erdalkalihältigen Präparaten jedoch geringer und die Linienbreite größer ist als bei reinem -Al2O3.
Mit 4 Abbildungen 相似文献
Aluminium hydroxide gels have been prepared from aluminum nitrate solutions by precipitation with NH4OH at constant pH. Ca-, Sr- and Ba-ions where added as nitrates prior to the precipitations, and the amount determined, which was incorporated in the -Al2O3. At constant pH-value incorporation is dependent on the amount and the kind of ion present, and independent of aging in solution.The thermal stability of -Al2O3 is enhanced by the presence of ions of alkaline earths. The amount of foreign ions necessary for maximum stabilisation decreases thereby with increasing ionic radius.Investigation of X-ray diffractions showed that the ratio of intensities of the interference remains constant with pure -Al2O3 and preparations containing alkaline earths, while the total intensity of the reflexes with alkaline earths decreases, and the width of the lines increases, compared with pure -Al2O3.
Mit 4 Abbildungen 相似文献
7.
M.S. Worthington B.D. Glass L.J. Penkler 《Journal of inclusion phenomena and macrocyclic chemistry》1996,25(1-3):153-156
The solubilizing potential and complexing tendencies of six cyclodextrins (CyD) with nifedipine in aqueous solution were evaluated using phase solubility methods. Solubility curves of nifedipine with -CyD, 2-hydroxypropyl--CyD (2HP--CyD) and 2-hydroxypropyl--cyclodextrin (2HP--CyD) were classified as type AL, while for heptakis (2,6-dimethyl)--CyD (DIMEB), randomly methylated--CyD (RAMEB) and -CyD, Ap type phase behaviour was observed. Stability constants, calculated from phase solubility diagrams, decreased in the order: DIMEB > RAMEB > -CyD > 21HP--CyD > -CyD > 2HP--CyD. 相似文献
8.
R. J. Gehrke 《Journal of Radioanalytical and Nuclear Chemistry》2000,246(2):449-450
Review of a recent paper reporting the -ray energies and intensities associated with the decay of 241Am has resulted in the conclusion that some of the rays were misidentified. The misidentified -rays are not associated with the decay of 241Am, but rather are prompt -rays from alpha-induced reactions. 相似文献
9.
The predictive accuracy for estimating infinite dilution activity coefficients by a modification of the UNIFAC method wherein the group interaction parameters were based on only data (referred to as -based UNIFAC) has been studied. Estimates and measured values were compared for six prototypical solutes in a series of homologous n-alkanes, l-alcohols and alkanenitrile solvents. Despite the fact that the interaction parameters were derived using only data, this approach still gave serious errors due to several inherent problems in the original UNIFAC model. Its performance is sometimes even poorer than that of the original UNIFAC method. For example for nitromethane in alcohols and p-dioxane in nitriles values predicted by the -based UNIFAC are essentially zero. The large errors for these systems are most likely due to inaccurate interaction parameters in the -based UNIFAC method. 相似文献
10.
K. -H. Frömming V. Wedelich W. Mehnert 《Journal of inclusion phenomena and macrocyclic chemistry》1987,5(5):625-629
- and -Cyclodextrin (CD) and heptakis-2,6-di-O-methyl--cyclodextrin (DIMEB) form soluble inclusion compounds with mefenorex (MEF); with -CD a partial inclusion occurs. No solid inclusion compound could be obtained with the four CDs. -, -CD and DIMEB, but not -CD, enhance the nitrosation rate of MEF if the nitrosation assay procedure (NAP test) is applied. During this reaction with - and -CD, solid inclusion compounds of the CDs and nitrosomefenorex (NMEF) precipitate.Part of the Ph.D. thesis of V. Wedelich, Freie Universität Berlin, 1985. 相似文献
11.
Jerome A. Imonigie Donal H. Macartney 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(2):195-203
The effects of -, -, dm-(heptakis(2,6-di-O-methyl)--) and -cyclodextrins (CD) on the kinetics of the electron-transfer reaction of the ferrocenemonocarboxylate anion (FCA–) with bis(pyridine-2,6-dicarboxylato)cobaltate(III) have been investigated in aqueous solution (0.20 M Na2HPO4, pH 9.2) at 25.0°C. Substantial decreases in the rate constants for the electron-transfer reactions were observed upon cyclodextrin inclusion of the reductant, due to an increase in the FCA0/– reduction potential and to the insulation of the reductant from oxidant. The inclusion stability constants for {FCA·CD}– were evaluated from the1H NMR and kinetic data, and the order of the stability constants was found to be -CDdm-CD-CD>-CD. 相似文献
12.
Moo-Jin Kim Soo-Hyun Chang Jung-Sik Choi Wha-Seung Ahn 《Reaction Kinetics and Catalysis Letters》2004,82(1):27-32
Partial oxidation of n-heptane to syngas at 400–450°C was investigated over Rh and Rh-Ni based catalysts. The Rh/-Al2O3 catalyst exhibited much better catalytic activity than the Rh-Ni/-Al2O3 catalyst. A combination of the Rh-based catalyst with the WGS reaction catalyst (Fe3O4—Cr2O3) increases the hydrogen selectivity but has no distinct effect on shifting the balance of the partial oxidation of n-heptane.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
13.
E. Chibowski M. Bolívar A. V. Delgado F. González-Caballero 《Colloid and polymer science》1993,271(7):688-695
Changes in nitrofurantoin surface free energy components, Lifshitz-van der Waals,
s
LW
, electron donor,
s
–
, and electron acceptor,
s
+
, due to adsorption of the aminoacids: lysine, alanine and glutamic acid, were determined by means of the thin-layer wicking technique. It was found that the aminoacids slightly increase the
s
–
component already at 10–4 M concentration. They reduce the
s
+
component practically to zero, and a very sharp increase of
s
–
was observed when the nitrofurantoin surface was precovered from the solutions at concentrations larger tan 10–4 M. It is concluded that the adsorption of the aminoacids takes place via hydrogen bonding and electrostatic interactions between nitrofurantoin surface and aminoacid molecules. The increase in the
s
–
parameter is probably caused by the presence of carboxyl groups in the aminoacid molecules. 相似文献
14.
Influence of radiation dose in the range of 0.5–2.0 MGy of60Co -rays on the isothermal decomposition of sodium bromate at 633.0 K shows that irradiation increases the initial gas evolution {ie37-1}, shortens the induction period (I), enhances the rate of reaction in the accelerating and decay stages. The data fit well the Prout-Tompkins relationship, indicating that nucleation occurs in a chain branching manner during the process. The fraction decomposed, , increases with increasing radiation dose. 相似文献
15.
Tsykoza L. T. Ismagilov Z. R. Ushakov V. A. Kuznetsov V. V. Ovsyannikova I. A. 《Kinetics and Catalysis》2003,44(6):806-812
The phase composition of supported Mn–Al–O catalysts and their activity in the reaction of methane oxidation were studied depending on the composition of aluminum oxide supports (-Al2O3 with different -Al2O3 contents modified with individual Mg, La, and Ce oxides or Mg + La and Mg + Ce oxide mixtures) and calcination temperatures (500, 900, and 1300°C). It was found that the Mn–Al–O catalysts based on -alumina containing -Al2O3 and modified with Mg, La, or Ce additives are more active and thermally stable (up to 1300°C) than the samples based on pure -Al2O3. A conclusion was drawn that a higher degree of disorder of the structure of -Al2O3, compared to that of -Al2O3, is favorable for a deeper interaction of manganese and modifying additives with the support at the early stages of the synthesis and for the formation of Mn–Al compounds with complex composition (solid solutions and/or hexaaluminates) at 1300°C. These compounds are responsible for the stability and high activity of the catalysts in methane oxidation. 相似文献
16.
A. N. Al-Noaimi G. A. El-Shobaky A. S. Ahmad H. G. El-Shobaky 《Journal of Radioanalytical and Nuclear Chemistry》1994,185(2):231-242
The effects of -irradiation (20–160 Mrad) and lithium oxide doping (0.75–6 mol%) on the surface and catalytic properties of unloaded Co3O4 solid have been investigated. The surface characteristics of various solids were determined from nitrogen adsorption isothems taken at –196 °C and their catalytic activities were measured by following the kinetics of CO-oxidation by O2 at 100–150 °C using a static method. The results showed that -rays brough about a decrease of 21% inS
BET of Co3O4 due to widening of its pores and led also to a considerable increase in its catalytic activity. A maximum increase of 91% was observed upon exposure to a dose of 80 Mrad. Lithium oxide-doping at at 500 °C resulted in an increase of 150% inS
BET of treated solid without changing its mean pore radius. This treatment was also accompanied by an increase of about 50% in its catalytic activity measured at 150 °C. Gamma-irradiation and Li2O-doping of unloaded Co3O4 did not change the magnitude of apparent activation energy of catalysis of CO-oxidation by O2 but increased the concentration of catalytically active sites contributing in the catalytic process. In other words, -rays and lithium oxide doping did not alter the mechanism of catalytic oxidation of CO by O2 over unloaded cobaltic oxide solid. 相似文献
17.
V. G. Dedgaonkar D. B. Sarwade 《Journal of Radioanalytical and Nuclear Chemistry》1995,199(3):191-196
Gamma radiation induced decomposition of ammonium perchlorate (AP), pelletized in a KCl/KBr matrix has been followed IR spectrophotometrically. AP absorption peaks decreased in intensity as the -dose increased progressively. Irradiation of powdered AP produces ClO
3
–
; its yield increases, attains a maximum and decreases beyond a dose of 0.5 MGy. The result is similar but much slower in the case of -irradiated pellets of pure AP. 相似文献
18.
Shen Shuifa Liu Jingyi Gu Jiahui Yu Xiaohan Li Yan Yin Duanzhi Shi Suanghui 《Journal of Radioanalytical and Nuclear Chemistry》2000,246(2):423-428
The -ray spectra of 188Re decay have been studied by using a compton-suppressed spectrometer and a three parameters --T list coincidence system. Six -rays at 557, 810, 1463, 1867, 1936 and 2022 keV and three levels at 1443, 1936 and 2022 keV are confirmed again. Eight new -rays at 309.60±0.04, 826.90±0.02, 979.29±0.08, 1086.13±0.03, 1103.7±0.4, 1828.2±0.1, 1842.5±0.2, 1982.5±0.2 keV have been identified, three new levels at 309.60, 1828.2 and 1982.5 keV are assigned. The –-decay branching ratio is deduced. 相似文献
19.
Fumio Nishioka Isao Nakanishi Takaji Fujiwara Ken-ichi Tomita 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(3-4):701-714
The crystal structure of the -cyclodextrin (-CyD) molecular complex with aspirin (acetylsalicylic acid), salicylic acid, and water, (C42H70O35)2 (C9H8O4)2 (C7H6O3) 23.3H2O, was determined by X-ray structure analysis. The crystal data is space group Pl, a=19.777(5), b=15.247(3), c=15.475(4) Å, =102.63(2)°, =116.96(2)°, =104.12(2)°, V=3729(2) Å3, Dm=1.409(2) g/cm3, DX=1.419 g/cm3, and Z=1. The two -CyDs form a dimer unit with hydrogen bond networks among the secondary hydroxyl groups of both -CyDs. This -CyD dimer includes three guest molecules of two different types in its hydrophobic cavity. Two of them are aspirin, which are separately included in each cavity of the -CyD unit, with their hydrophobic benzene rings protruding into the hydrophobic cavities of the host -CyDs. The remaining guest molecule is the hydrolyzed product of an aspirin, that is salicylic acid, which is sandwiched in the space constructed by the -CyD dimer formation, and is statistically disordered at three sites. 相似文献
20.
Cindrić Marina Matković-Čalogović Dubravka Vrdoljak Višnja Kamenar Boris 《Structural chemistry》1998,9(5):353-358
Oxidation of molybdenum(II) thiopivalate and thiobenzoate in the presence of -picoline or pyridine results in the formation of dinuclear molybdenum(V) complexes of the general formulae [Mo2O2(-O)2(-SO4)L4] with L = -picoline or pyridine and [Mo2O2(-O)(-S)(-SO4)L4] with L = -picoline. As determined by X-ray structure analysis, two complexes with -picoline differ in their bridging cores: In one complex, two Mo atoms are doubly bridged through two oxygen atoms; in the other, one Mo atom is doubly bridged through oxygen and sulfur atoms. However, they both crystallize together. The product is solvated with -picoline and water molecules. Molybdenum atoms exhibit distorted octahedral coordinations. The same complexes were prepared also through direct reactions of [Mo2O3(O2CCH3)4] with thiopivalic and thiobenzoic acid in the presence of -picoline or pyridine. The appearance of the oxo-oxygens and sulfido-sulfur as well as sulfato ligand is explained by the molybdenum-catalyzed oxidation of thiocarboxylates. 相似文献