EPR study of vanadium-containing amorphous silica formed by sol–gel method

Богомолова, Л.Д.; Jachkin, V.A.; Красильникова, Н.А.

doi:10.1016/s0022-3093(98)00745-5

Cited by 14 publications

(21 citation statements)

References 56 publications

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“…In [15] EPR was used to study quartz glass obtained by the sol-gel technology. The sol was based on tetraethylorthosilicate, whose hydrolysis and condensation were conducted in a mixture of ethanol and water.…”

Section: Investigation Of the Sol-gel Technology For Obtaining Glassesmentioning

confidence: 99%

Use of Electron Paramagnetic Resonance for Investigating Glasses and Raw Materials (Review)

Богомолова

Zhachkin

Pavlushkina³

2015

Glass Ceram

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It is shown that electron paramagnetic resonance can be used to study the fine structure of glasses and glass enamel materials as well as to find and identify defects in glass. The spectra of paramagnetic ions (Cu 2+ , V 4+ , Ti 3+ , Mo 5+ Mn 2+ , Fe 3+ ) are discussed. Specific examples of the detection of these ions in sitals, in which they are introduced as surface-active additives or are present as impurities entering the crystallized glass via the raw materials, are examined. It is determined that the most informative ions for studying the structure and phase separation of glass are Cu 2+ and V 4+ . Electron Paramagnetic ResonanceElectron paramagnetic resonance (EPR), discovered experimentally by E. K. Zavoiskii in 1944, is now widely used as a method of investigating different substances and processes in physics, chemistry, biology, geology, medicine, and other areas of science and technology. It should be noted that the EPR phenomenon has also been studied intensively from the theoretical and experimental standpoints. However, as a method of investigating substances or the processes occurring in them its importance is not diminishing but rather increasing because the range of new materials and their applications is expanding.EPR is a spectral method, based on resonance absorption of microwave electromagnetic radiation by paramagnetic particles, whose magnetic moments are tuned in resonance by applying a magnetic field.All substances contain electrons possessing orbital and spin magnetic moments, and one would think that EPR can be observed for all of them. However, the atoms and molecules comprising matter are constructed in such a manner that their filled electronic shells have a zero magnetic moment. EPR is observed only for 1) magnetic centers specially created by high-energy radiation (g-, x-rays, fast neutrons, ions of heavy particles, and others), 2) free radicals, and 3) atoms with initially unfilled inner electronic shells (transition elements (TE) with partially filled 3d-, 4d-, or 5d-shells, rare-earth elements with an unfilled 4f-shell and actinides with an unfilled 5f-shell). Such substances contain centers possessing constant magnetic moments, randomly oriented relative to one another in the absence of an external magnetic field. In accordance with Boltzmann's law most magnetic moments are oriented along the field.The energy of particles with a magnetic moment m directed parallel to an external magnetic field (lower energy level) is less than the energy of particles with m oriented opposite to the field (upper energy level). When a high-frequency electromagnetic field is applied absorption of electromagnetic energy equal to the energy difference DE between the upper and lower energy levels (in the case of a two-level system) occurs and is accompanied by re-orientation of the magnetic moment of the particle (resonance transition from the lower to the upper level). The resonance condition has the formwhere g is a spectroscopic splitting factor dependent on the nature of the magnetic moment and i...

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Section: Investigation Of the Sol-gel Technology For Obtaining Glassesmentioning

confidence: 99%

Use of Electron Paramagnetic Resonance for Investigating Glasses and Raw Materials (Review)

Богомолова

Zhachkin

Pavlushkina³

2015

Glass Ceram

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“…Even when air-dried, the gels still contained some liquid fraction, albeit that its effective viscosity was higher than that of a free aqueous solution. When the samples were frozen at 77 K, the molecular motion of the hydrated cation complexes became immobilised on the EPR spectroscopic timescale [55][56][57][58][59][60][61][62][63][64][65].…”

Section: B [ 10 -4 T ]mentioning

confidence: 99%

“…At low VO(II) concentrations (ca 1 mmol or less), the X-band EPR spectra recorded from borate, phosphate and silicate glasses [3,4,7] and also those from the sol-gel process products [57][58][59][60][61][62][63][64][65] are rich in hyperfine structure from the 51 V isotope (I = 7/2, natural abundance 99.76 %). VO(II) cations are especially useful as spin-probes, since they consistently give relative sharp EPR spectra from solutions recorded both at RT and when frozen to 77 K [71].…”

Section: Interpretation and Simulation Of Vo(ii) Epr Spectramentioning

confidence: 99%

“…It is well documented that Cu(II) and Mn(II) ions are very sensitive as spin-probes to monitor the structural changes that occur in silica xerogels during the process of calcination, or in general, the properties of the sol-gel process products, and numerous EPR experiments, have been devised for this purpose [5,. However, there have been far fewer systematic EPR studies made of Cu(II) and Mn(II) cations with which to explore the earlier stages of the silica sol-gel process [55][56][57][58][59], while VO(II) ions have been employed relatively rarely to investigate the silica sol-gel process at all [57][58][59][60][61][62][63][64][65].…”

Section: Introductionmentioning

confidence: 99%

“…The results demonstrated that EPR spectra of Cu(II), Mn(II) and VO(II) cations did not reflect the sol-to-gel transition in non-o-phen-doped systems, while the EPR spectra of vanadyl-o-phen complexes measured at different stages of the sol-gel process were very sensitive to their changing environment. Bogomolova et al [60] measured EPR spectra of sol-gel-derived silica glasses, doped with vanadium, at various stages of the TEOS-based sol-gel process (sol, fresh gel, aged gel, heat treated gel, glass). It was found that the vanadium is present in these systems as a hydrated complex, [VO(H 2 O) 6 ] 2?…”

Section: Introductionmentioning

confidence: 99%

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Tetraethyl orthosilicate (TEOS)-based sol–gel process monitored by EPR spectroscopy with VO(II) cations as a spin-probe

Mazúr

Husáriková

Rhodes

et al. 2015

J Sol-Gel Sci Technol

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The various stages of the TEOS-based sol-gel process were studied by EPR spectroscopy using a VO(II) spin-probe. A detailed analysis of the multicomponent VO(II) EPR spectra recorded at 77 K showed that three main types of individual signals appeared superimposed at the various stages of the sol-gel process, which corresponds to different environments of the paramagnetic VO(II) cations. The spin Hamiltonian parameters of each individual subspectrum remain unchanged throughout the various stages of the sol-gel process. However, the relative contribution of individual signals changed significantly as the sol-gel process proceeded. The results show that the VO(II) cations are not directly incorporated into the siloxane network, but are trapped relatively freely as [VO(H 2 O) 5 ] 2? complexes in a solution-like environment during the evolution of the sol-gel process. It was amply demonstrated that the sol-to-gel transformation from the viscous, colloid suspension to the viscoelastic gel can be successfully monitored by EPR spectroscopy with VO(II) as a spin-probe.Dedicated to the 70th anniversary of the discovery of Electron Paramagnetic Resonance

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