共查询到20条相似文献,搜索用时 125 毫秒
1.
J. Khler A. Simon L. van Wüllen S. Cordier T. Roisnel M. Poulain M. Somer 《无机化学与普通化学杂志》2002,628(12):2683-2690
Powder samples of NbOF3 und TaOF3 were prepared by heating mixtures of NbO2F and NbF5 or TaO2F and TaF5, respectively, in the corresponding stoichiometric ratio in platinum crucibles under argon atmosphere (180—220 °C). Both oxide fluorides are coulourless with a slight greyish tinge. They are sensitive to moisture and decompose in air at room temperature within hours. Both, NbOF3 and TaOF3 crystallize as a variant of the SnF4 type structure, space group I4/mmm. The structures have been refined from X‐ray powder diffraction data using the Rietveld method (a = 3.9675(1) Å, c = 8.4033(1) Å, RB = 3.60 %, Rp = 4.58 % for NbOF3 and a = 3.9448(1) Å, c = 8.4860(1) Å, RB = 2.07 %, Rp = 2.44 % for TaOF3). Characteristic building units are sheets of corner sharing MX6 octahedra which are stacked via van der Waals interactions to a three dimensional framework. The occupancy of the two crystallographic sites for the anions by O and F is discussed on the basis of structure refinements, bond order summations, IR and NMR data and calculations of the Madelung parts of the lattice energy. 相似文献
2.
M. Boča V. Danielik Z. Ivanová E. Mikšíková B. Kubíková 《Journal of Thermal Analysis and Calorimetry》2007,90(1):159-165
The phase diagrams of the systems KF-K2TaF7 and KF-Ta2O5 were determined using the thermal analysis method. The phase diagrams were described by suitable thermodynamic model. In
the system KF-K2TaF7 eutectic points at x
KF=0.716 and t=725.4°C and at x
KF=0.214 and t=712.2°C has been calculated. It was suggested that K2TaF7 melts incongruently at around 743°C forming two immiscible liquids. The system KF-Ta2O5 have been measured up to 8 mol% of Ta2O5. The eutectic point was estimated to be at x
KF∼0.9 and t∼816°C. The formation of KTaO3 and K3TaO2F4 compounds has been observed in the solidified samples. 相似文献
3.
A. I. Nikolaev N. V. Kirichenko V. G. Maiorov 《Russian Journal of Inorganic Chemistry》2009,54(4):505-511
Parameters for the preparation of concentrated tantalum, niobium, and titanium fluoride solutions by dissolution of their oxides or hydroxides in hydrofluoric acid were studied. Anatase titania, niobium oxide, and tantalum oxide calcined to 900°C were found to have high dissolution rates. Solid phases separated upon the dissolution of niobium, tantalum, and titanium oxides in hydrofluoric acid were identified as NbO2F, TaO2F, Ta3O7F, and TiOF2. Niobium hydroxide dissolution in an autoclave at the atmospheric pressure gave various complex salts: NH4NbOF4 and (NH4)3Nb2OF11. 相似文献
4.
The Relative Undercooling on Silica Glass Surfaces and other Substrates during the Chemical Transport of Solids via the Vapor-phase . The relative undercooling on etched surfaces of silica glass at the chemical transport of ZnS in a stream of gaseous iodine at 652–854°C is found to be ΔT = 37–43°. Scrapers on silica glass lead to a substantial smaller undercooling. During the deposition of ZnS (made from “pure” components) in a temperature gradient one finds a remarkable fractionation. In closed (etched) silica glass ampoules the relative undercooling is determined for the systems ZnS/I2, ZnSe/I2, ZnS/HCl; ZnS/H2, CdS/I2, CdSe/I2, Al2S3/I2 and Nb2O5/NbCl5 using a special furnace, The region free of nuclei (or crystals) for instance at T2 ≈ 800°C depending on the system (and T2) is ΔT ≈ 13–45°. The variation of the substrates showed: for fire polished silica surfaces for ZnS/I2 is ΔT ≈ 56°; for the different quartz-faces and ZnS/I2 is ΔT ≈ 13–35°. Generally, on different substrates (broken pieces, fragments) one finds for ZnS/I2 ΔT ≈ 20–28°. Using another way for the systems MoO3/Cl2, MoO3/Cl2, Ar, MoO3/Cl2, O2 and MoO3/HgCl2 with T2 a strongly decreasing value of ΔT is found. 相似文献
5.
A special form of the LeChatelier-Shreder equation describing the equilibrium between the crystalline phase and the melt in
system A-AB in which the substance AB partially dissociates upon melting was applied to systems KF-K3NbF8, K2NbF7-K3NbF8 and to KF-K3TaF8, K2TaF7-K3TaF8 subsystems of the binary systems KF-K2NbF7 and KF-K2TaF7 in which the additive compounds K3NbF8 and K3TaF8 are formed. Using the phase diagram of the system KF-K2NbF7 determined by McCawley and Barclay (1971) and the values of the fusion enthalpy of K3NbF8 taken from literature, the intervals of the dissociation degree values of K3NbF8 for both branches of the liquidus curve of K3NbF8 were calculated. The calculated values of the dissociation degree depend on the coordinates of the liquidus curve of K3NbF8 of the pertinent phase diagram, on its used branch and section, and on the value of the fusion enthalpy of K3NbF8. For the measured fusion enthalpy of K3NbF8 (57 kJ mol−1), a common interval of the dissociation degree values of K3NbF8 for both branches of the liquidus curve of K3NbF8 is 0.71–0.72. Similarly, intervals of the dissociation degree values of K3TaF8 for both branches of the liquidus curve of K3TaF8 were calculated using the phase diagram of the system KF-K2TaF7 determined by Boča et al. (2007) and the measured fusion enthalpy of K3TaF8 ((52 ± 2) kJ mol−1). The error of the determination of the fusion enthalpy of K3TaF8, the common interval of the dissociation degree values of K3TaF8 for both branches of the liquidus curve of K3TaF8 is 0.68–0.69. 相似文献
6.
《Journal of fluorine chemistry》1988,38(2):183-186
Unit cell dimensions of seven oxofluorometallates of transition metals were investigated by powder X-ray diffraction method. The compounds K3NbO2F4 and K3TaO2F4 were found to be isomorphous with cubic (FCC) structure and having lattice parameters 8.885 and 8.942 Å respectively. Similarly, the compounds K2NbOF5 (a = 8.367 Å, c = 13.038 Å) and K2TaOF5 (a = 8.463 Å, c = 13.139 Å) were also found to be isomorphous with a tetragonal structure. The compound K3Zr2O2F7 (a = 9.367 Å) was found to possess a cubic (FCC) structure. Both K2V2O5F2 (a = 6.739 Å, c = 10.635 Å) and K2VO3F (a = 5.984 Å, c = 10.914 Å) have a hexagonal structure. 相似文献
7.
Quartz (SiO2) glass was implanted with 5 × 1016 57Fe ions/cm2 at a substrate temperature of 500 °C, and annealed at temperatures between 700 and 950 °C. The implanted and annealed plates were characterized by conversion electron Mössbauer spectroscopy (CEMS), and measured by a Kerr effect magnetometer or a vibration sample magnetometer. Kerr effect measurement of as-implanted SiO2 glass showed ferromagnetism at room temperature. CEM spectrum of the as-implanted glass consisted of magnetic relaxation peaks of finely dispersed metallic Fe species, and paramagnetic doublets of Fe3+ and Fe2+ species. The sample heated at 700 °C contained large grains of metallic Fe and a lot of oxidation products of Fe2+ species. After oxidation at temperatures higher than 800 °C, the samples showed also ferromagnetism, which was attributed mainly to ferromagnetic ε-Fe2O3 precipitated in SiO2 matrix. Small amounts of α-Fe2O3 were produced at 950 °C. The results suggest that ion implantation and oxidation make a transparent ferromagnetic glass possible. 相似文献
8.
Marcela Stoia Mircea Stefanescu Thomas Dippong Oana Stefanescu Paul Barvinschi 《Journal of Sol-Gel Science and Technology》2010,54(1):49-56
The paper presents a study on the preparation of Co2SiO4/SiO2 nanocomposites by a new modified sol–gel method. We have prepared gels starting from tetraethylorthosilicate (Si(OC2H5)4), cobalt nitrate Co(NO3)2·6H2O and some diols: ethylene glycol (C2H6O2), 1,2propanediol (C3H8O2) and 1,3propanediol (C3H8O2), for a final composition: 30% CoO/70% SiO2. During the heating of the gels at 140 °C, a redox reaction takes place between NO3
− ions and diol with formation of some carboxylate anions. These carboxylate anions react with the Co(II) ions to form coordination
compounds embedded in silica matrix, as evidenced by FT-IR spectrometry and thermal analysis. These Co(II) coordinative compounds
thermally decompose in the range 250–300 °C to the corresponding oxides: CoO and/or Co3O4 inside the matrices pores. When CoO results, it reacts with SiO2 at low temperature leading to Co2SiO4, which crystallizes at 700 °C. XRD patterns of the samples annealed at temperatures lower than 700 °C were characteristic
to amorphous phases. The samples annealed at temperatures ≥700 °C, contain Co2SiO4 (olivine) as unique crystalline phase inside the amorphous silica matrix, according to XRD patterns. As evidenced by TEM
images, Co2SiO4 nanoparticles are homogenously dispersed inside the silica matrix. 相似文献
9.
V. Ya. Kavun A. B. Slobodyuk N. A. Didenko R. L. Davidovich 《Journal of Structural Chemistry》2016,57(5):917-925
19F, 1H NMR and DSC methods are used to study the ion mobility and phase transitions in hexafluoro complex compounds of tantalum(V), niobium(V), and titanium(IV) with the tetramethylammonium cation. A transformation of the NMR spectra observed in a temperature range 77(130)-450 K is found to be associated with a change in the type of ion motions in the anion and cation sublattices of the studied compounds. In a temperature range 170-450 K the main types of ion motions are isotropic reorientations of TaF6, NbF6, TiF6 octahedra and tetramethylammonium ions. Two endothermic effects with the maxima at 232.5 K and 256.5 K for [N(CH3)4]TaF6 and 235 K and 250 K for [N(CH3)4]NbF6, which are observed in the DSC curve in the range 170-400 K correspond to phase transitions that have almost no effect on the NMR spectral parameters the a temperature range 230-260 K. For the [N(CH3)4]2TiF6 compound, an endothermic effect at 422 K is observed, corresponding to the phase transition from the rhombohedral to the cubic modification. 相似文献
10.
Eu5F[SiO4]3 and Yb5S[SiO4]3: Mixed‐Valent Lanthanoid Silicates with Apatite‐Type of Structure By the reaction of Eu, EuF3, Eu2O3 with SiO2 in evacuated gold ampoules, using NaF as flux, at a temperature of 1000 °C for ten hours, dark‐red, platelet‐shaped single crystals of Eu5F[SiO4]3 are obtained. Similarly dark‐red, but pillar‐shaped single crystals of Yb5S[SiO4]3 are obtained by the reaction of Yb, Yb2O3 and S with SiO2 in the presence CsBr as flux in evacuated silica ampoules at 850 °C and an annealing time of seven days. Both compounds crystallize hexagonally (P63/m, Z = 2; Eu5F[SiO4]3: a = 954.79(9), c = 704.16(6) pm; Yb5S[SiO4]3: a = 972.36(9), c = 648.49(6) pm) in the case of Eu5F[SiO4]3 analogous to the mineral fluorapatite and for Yb5S[SiO4]3 as a bromapatite—type variety. The crystal structure containing isolated [SiO4]4— tetrahedra distinguishes two rare‐earth cation positions with coordination numbers of nine (M1) and seven (M2), in which the position M1 of the europium fluoride silicate is almost exclusively occupied by Eu2+ cations, whereas in ytterbium sulfide silicate it contains di‐ and trivalent Yb cations in the ratio 1 : 1. In both cases, however, the M2 position is only populated with M3+. 相似文献
11.
Derivatives of the Fluorite Type: [Fe(NH3)6][TaF6]2 and [Ni(NH3)6][TaF6]2 Light blue single crystals of [Fe(NH3)6][TaF6]2 and [Ni(NH3)6][TaF6]2 are obtained from 36 : 1 : 6 molar mixtures of (NH4)F, iron/nickel and tantalum powders, respectively, in sealed Monel metal ampoules at 400 °C. They both crystallize isotypic with [Co(NH3)6][PF6]2 (cubic, Fm-3m, Z = 4, a = 1259.0(2)/1260.4(2) pm) in a structure that can be derived from the basic fluorite-type of structure according to [Ca][F]2≡[Fe(NH3)6][TaF6]2, for example. 相似文献
12.
New Oxychlorides of the Rare-Earth Metals with Vanadium and Rhenium i) New compounds Ln12.33V6O23(OH)Cl20 (Ln = La, Ce) were prepared by heating mixtures of LnCl3, LnOCl and V2O5 (4 : 8 : 3) in evacuated, sealed silica ampoules (850 °C, 4 d). Single crystals could be obtained by chemical vapor transport (T2 → T1, T2 = 900 °C, T1 = 800 °C, 14 d, p(Cl2, 298 K) ≈ 70 mbar). The single-crystal study of the lanthanum compound [a = 17.8818(25) Å, c = 4.0567(7) Å, Z = 1, 1035 independent I0, 70 parameters, R1 = 3.52%] showed that vanadium has CN = 4 (tetrahedrally) and lanthanum has CN = 9 (threefold capped trigonal prismatic). A strong relationship to the structures of the Pr3NbO4Cl6- and the La2TaO4Cl3-type could be discussed. ii) Further we obtained dark red powder of La3ReO6Cl3 by heating (740 °C, 5 d) a mixture of ReO3 and LaOCl (1 : 3) in sealed silica ampoules under argon atmosphere (p{Ar, 298 K} = 1 atm). This new rhenium-compound crystallizes in the hexagonal space group P63/m (No. 176) [a = 9.4164(6) Å, c = 5.4248(4) Å] and is isostructural to La3WO6Cl3. 相似文献
13.
Oana ?tef?nescu Corneliu Davidescu Mircea ?tef?nescu Marcela Stoia 《Journal of Thermal Analysis and Calorimetry》2009,97(1):203-208
In this paper we present a study regarding the obtaining of iron oxides embedded in silica matrix, using a modified sol-gel
method. This method consists in the formation, inside the silica matrix, of some Fe(III)-carboxylate compounds, resulted in
the redox reaction between Fe(NO3)3 and diol.
We have synthesized four gels, starting from tetra-ethyl orthosilicate, Fe(NO3)3·9H2O and different diols: ethylene glycol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol, for a final composition 50% Fe2O3/50% SiO2. The obtained gels have been thermally treated at 130°C, when the redox reaction Fe(NO3)3-diol took place with formation of the precursors in the xerogels pores. The thermal decomposition of all four precursors
took place up to 300°C. 相似文献
14.
Ya. V. Zonov T. V. Mezhenkova V. M. Karpov V. E. Platonov 《Russian Journal of Organic Chemistry》2008,44(11):1652-1656
The reaction of perfluoro-1-methylindan with SiO2-SbF5 depending on the amount of SiO2 led to the formation after hydrolysis of the reaction mixture of perfluoro-3-methylindan-1-one, perfluoro-4-methylisochromen-1-one, 6-(1-carboxy-2,2,2-trifluoro-ethyl)-2,3,4,5-tetrafluoro-benzoic and 6-(carboxymethyl)-2,3,4,5-tetrafluorobenzoic acids. Heating in the SbF5 medium perfluoro-1-methylindan in a glass ampoule at 130°C, or perfluoro-3-methylindan-1-one at 70°C provided a solution of a perfluoro-4-methylisochromenium salt that on treating with anhydrous HF was converted into perfluoro-4-methyl-1H-isochromen, and on hydrolysis, into perfluoro-4-methylisochromen-1-one. 相似文献
15.
Klaus Müller‐Buschbaum 《无机化学与普通化学杂志》2002,628(8):1761-1764
Er2(CO3)2(C2O4)(H2O)2 — Synthesis, Crystal Structure and the Thermal Decomposition of a Carbonate‐Oxalate‐Hydrate of Erbium The hydrothermal reaction of an equimolar ratio of Er2O3 with the aminoacid L‐cysteine in evacuated glass ampoules in H2O at 130 °C gave transparent, pink crystals of the formula Er2(CO3)2(C2O4)(H2O)2. It crystallises in the monoclinic space group Cm (Z = 2, a = 777.3(2) pm, b = 1492.0(3) pm, c = 473.09(8) pm, b = 90.12(9)°). The thermal decomposition of Er2(CO3)2(C2O4)(H2O)2 was investigated. 相似文献
16.
E. G. Ilyin M. V. Simonov V. Kovalev I. V. Leontieva I. M. Aladzheva T. A. Mastryukova 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Reactions of PF5 and TaF5 with [Ph2P(O)]2 C=CH2 (I) and [Ph2P(O)]2 C=PPh3 (II) in MeCN and CH2Cl2 were studied by means of 19F, 31P, 1H and 13C NMR spectroscopy. It has become evident, that one or two phosphoryl groups in (I) and (II), as well as in cis- and trans-Ph2P(O)CH=CHP(O)Ph2, are involved in complex formation. The formation of tetra-fluoro cations PFL and PF4L along with pentafluorocom-plexes PF5L and TaF5L was found. Ligands are coordinated with central ions of complexes as chelates. The trans-atoms F1 of TaF 5L are nonequivalent because of nonsymmetric position to the Ph3P-group. The F1-atoms in PF4L are supposed to be symmetric to the Ph3P-group. The formation of tri-fluorocomplexes TaOF3L was also observed. Since the position of 19F NMR resonance lines of TaOF3L is near to that of pentafluorocomplexes, it can be supposed that either the change of Ta coordination number takes place, either oxygen atom comes into complex with inner sphere in the reaction with ligand or during hydrolysis. 相似文献
17.
G. Carturan R. Ceccato R. Campostrini V. M. Sglavo 《Journal of Sol-Gel Science and Technology》1995,5(1):57-64
The thermal behaviour of samples with nominal composition 80/20=SiO2/SnO2, class B, 76.8/19.2/4.0=SiO2/SnO2/Sb2O5, class C1, and 76.8/19.2/2.0/2.0=SiO2/SnO2/Sb2O5/Sb2O3, class C2, is studied in the interval 25–1050°C by various instrumental methods. Results on these classes of samples, obtained from
alkoxide precursors, are compared themselves and with samples of class A obtained from Si(OEt)4 and SnCl4. The segregation and crystallization of SnO2 occurs at 400°C in the presence of microdomains of SnO2·nH2O in the SiO2 gel matrix (class A), whereas it is observed at 700°C for samples B and C composed of Sn and Sb cations homogeneously dispersed
in SiO2. This fact implies different mechanisms of SnO2 nucleation and growth. The crystallization of SiO2 is observed at 1200°C for samples A, at 1050°C for B and at 800°C for C. For this latter, the presence of Sb-oxide/ SiO2 reactive glass is invoked to the low-temperature crystallization of SiO2.
G. Carturan, R. Ceccato, R. Campostrini, G. Principi, and U. Russo, submitted to J. Sol-Gel Sci. Tech. 相似文献
18.
Eduard V. Ganin Vladimir O. Gelmboldt Larisa V. Koroeva Marina S. Fonari Yurii A. Simonov Janusz Lipkowski Sergei A. Kotlyar Gerbert L. Kamalov 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(3-4):345-354
The reaction of Nb2O5 and Ta2O5 with an aqueous solution of hydrofluoric acid, HF in the presence of biphenyl-20-crown-6 (BP20C6, L1) or [1.5]dibenzo-18-crown-6 ([1.5]DB18C6, L2) results in the complexes [L1·(H3O)][NbF6] (1), [L1 (H3O)][TaF6] (2), [2L2·(H7O3)][NbF6] (3) and [2L2·(H7O3)][TaF6] (4). Complexes 1–4 were identified by the elemental and X-ray structural analysis and IR spectroscopy. Complexes 1 and 2 are isostructural, with the H3O+ oxonium ion embedded in one crown molecule via OH···O hydrogen bonds. Complexes 3 and 4 represent the supramolecular isomers distinctive by the crown conformations and crystal packing, with the (H7O3)+ cation enclosed in the cage of two crown molecules. Being poor H-bond acceptors, NbF6− and TaF6− anions do not compete with the crown oxygen atoms for the oxonium hydrogen atoms, but are involved in the numerous C–H···F
short contacts responsible for the extended supramolecular architectures in all cases. A change of crown ethers’ conformation
in complexes 1–4 and a correlation between the degree of proton hydration and an accessibility of the crown ether oxygen atoms is observed.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
19.
Tetraphenyl Imidodiphosphate as Ligand in Fluoro Complexes. 3. Fluoro Complexes of Niobium, Tantalum, and Antimony Tetraphenyl imidodiphosphate forms with NbF5, TaF5, and SbF5 the addition complexes MF5 · LH and (MF5)2(μ-LH). The imidodiphosphate acts in the latter as bidentately bridging ligand. Furtheron, it reacts with NbF5 and TaF5 by replacing fluoride forming tetrafloro and trifluoro complexes: [MF4(μ-L)]2 and MF3(η2-L)(OPh) or μ-O[MF3(η2-L)]2, resp., (M ? Nb, Ta). SbF5 does not form substitution complexes. The constitution and conformation of the complexes have been concluded from n.m.r. spectroscopic data. 相似文献
20.
Absorption of ammonia on tantalum hydroxide synthesized by a hydrofluoric acid method 总被引:1,自引:0,他引:1
Ammonia is strongly absorbed on tantalum hydroxide prepared by ammonia neutralization of TaF7
2− or TaF6
− complexes. FTIR analysis of tantalum hydroxide shows a characteristic peak around 1,400 cm−1, attributed to NH4
+. TG and FTIR analyses show that the NH4
+ decomposes at about 500 °C. The correct chemical formula of tantalum hydroxide prepared by ammonia neutralization of TaF7
2− or TaF6
− is thus TaO
x
(OH)5-x
(NH4)
x
. This conclusion is also confirmed by TG and FTIR analysis of tantalum hydroxide treated with various concentrations of inorganic
acid at room temperature. The NH4
+ in tantalum hydroxide can be exchanged completely in aqueous HNO3 solution, and the weight loss of the resulting sample is ended at about 415 °C by TG analysis. The NH4
+ can also be exchanged completely with aqueous H2SO4 solution; however, SO4
2− is weakly absorbed on the tantalum hydroxide. Finally, the NH4
+ can be exchanged partially with aqueous H3PO4 solution; however, PO4
3− is strongly absorbed on the tantalum hydroxide. 相似文献