A. Montenero

Micro-Raman investigation of iron oxide films and powders produced by sol–gel syntheses

Films and powders of iron oxide (Fe2O3) prepared by two different sol–gel syntheses, starting from Fe(NO3)3·9H2O or FeCl3·6H2O, were investigated by Raman microscopy. Different phases with different morphology were produced according to the preparation. The spectra obtained in the micro-Raman configuration were compared with the ambiguous data in the literature given by conventional Raman techniques. The principal difficulty in the correct interpretation of the Raman spectrum of the iron oxides is the co-existence of different phases. Contradictory results are also explained by laser–induced thermal effects which easily change the wavenumbers and lineshapes of the phonons. A Stokes–Anti-Stokes procedure was utilized to control the local temperature during the measurement and also for calibration of the wavenumbers. The micro-Raman spectra of hematite, magnetite and other iron oxides are presented and compared with literature data. Copyright

IR spectra and structure of V2O5GeO2Bi2O3 glasses

This paper reports a study of the structure V2O5GeO2Bi2O3 glasses by IR spectroscopy to obtain information about the competitive role of each of V2O5, GeO2 and Bi2O3 in the formation of the glass network. The amorphous samples were obtained by the twin-roller technique. Bi2O3 leads to transformation of the layered and chain vanadate structure and depolymerization of three-dimensional germanate lattice. The bismuthate complexes can be viewed as deformed BiO6 groups. It is established that with a decrease in the V2O5 content VO4 groups are formed. GeO4 structural unit with different degrees of polymerization arer present in the network in the entire concentration range.

Ceramic thin films by sol-gel processing as novel materials for integrated humidity sensors

Thin films based on 10 at% alkali-doped TiO 2 and on iron oxide with very large humidity sensitivity were prepared using a sol-gel technique. Prototype humidity sensors were prepared by depositing metal alkoxide solutions onto Al 2 O 3 substrates with comb-type Au electrodes, by dip-coating and heating in air. Heating to 300°C produces continuous films, free of porosity, which appear as layers covering the substrates, with no detectable grains. The humidity sensing electrical properties of the films were evaluated using electrochemical impedance spectroscopy (EIS) measurements. Resistance changes, although the films are dense, even larger than those reported for porous ceramics are recorded, as high as 9 and 8 orders of magnitude in the relative humidity range tested (4-87%), for the iron oxide and 10 at% K-doped titania films heated to 300°C, respectively. These outstanding results are interpreted in terms of conduction mechanisms different from the mechanism usually accepted for porous ceramics. EIS results confirmed that, for 10 at% alkali-doped TiO 2 films, charge carriers are alkali ions and not surface protons.

Raman scattering characterization of gel-derived titania glass

The preparation by the sol-gel method of bulk vitreous TiO2 is reported and its transformation both by controlled thermal treatment and by laser-induced heating in the anatase and rutile crystalline forms is studied by Raman spectroscopy. The results are compared with those existing for amorphous TiO2 thin films. The dependence of the Raman frequencies and linewidths on the incident laser power is presented and the Raman spectrum of the brookite (a third naturally occurring form of TiO2) is also reported as a comparison.

Sol-gel derived hydroxyapatite coatings on titanium substrate

Biomaterials, in particular those used for orthopaedic prostheses, consist of a metallic substrate, exhibiting excellent mechanical properties, coated with a ceramic layer, which guarantees resistance to the corrosion and an elevated bioactivity. In this paper the preparation of sol-gel films of hydroxyapatite, HA (Ca10(PO4)6(OH)2), on titanium substrate is described. The samples were obtained through the dip-coating method, starting from a colloidal suspension of hydroxyapatite. In order to increase the adhesion between the HA film and the metallic substrate, the same substrate has been preliminarily coated either with titanium oxide, TiO2 (in the anatase or rutile phase), or calcium titanate, CaTiO3 (perovskite). Also these latter films have been deposited from a sol-gel solution. The characterization of the films through XRD, SEM, and AFM gave good results for the crystallinity of the deposited HA; for what concerns the sample morphology, the films turned out to be homogeneous and crack-free.

XPS study of apatite-based coatings prepared by sol-gel technique

Abstract Biocompatible layers of hydroxyapatite and fluorhydroxyapatite were grown on Ti substrates by means of dip-coating into sol–gel. In order to improve the adhesion of apatite-based coatings, the substrates were a priori covered with calcium titanate. Therefore, the hydroxyapatite, fluorhydroxyapatite and CaTiO 3 coatings were produced and analysed. The chemical composition of the coatings (CaTiO 3 , CaTiO 3 +hydroxyapatite, and CaTiO 3 +fluorhydroxyapatite) was studied by using X-ray photoelectron spectroscopy (XPS). The data of quantitative XPS analysis displayed the different features (cleanness, homogeneity, etc.) of CaTiO 3 , hydroxyapatite, and fluorhydroxyapatite films after the growth and after the treatment in vitro.

Sol—gel processed TiO2-based thin films as innovative humidity sensors

Abstract Active elements for humidity sensors based on alkali-doped and undoped TiO2 films have been prepared by the sol-—gel technique. TiO2-based films are deposited onto Al2O3 substrates with comb-type Au electrodes by dip-coating, from the appropriate solutions, to obtain four different compositions of 1, 3, 6, and 10 at.% Li and K, with respect to the alkali metal/Ti system. The humidity-sensing electrical properties of the films are evaluated using d.c. and a.c. measurements. The electrical characterization of TiO2 films doped with 10 at.% K shows that this material has some unique properties. Resistence versus relative humidity(rh) values show variations as high as seven orders of magnitude in the humidity range tested. Very high humidity sensitivity is also observed at the lowest rh values (4−10% rh), at 40°C, when the resistence is measured at frequencies lower than 1 Hz. The results also show great stability over time. The possibility of modifying the rh sensitivity of TiO2, films doped with 10 at.% K by varying the frequency at which the resistance is measured is a characteristic that allows this material to be described as smart.

Hydroxy- and fluorapatite films on Ti alloy substrates: Sol-gel preparation and characterization

In this paper we describe the preparation of hydroxyfluorapatite (HFA) and fluorapatite (FA) films deposited on titanium alloys by means of the dip-coating method starting from a sol-gel prepared colloidal solution. These materials are compared with hydroxyapatite (HA) films prepared via sol gel and commercial films prepared by means of plasma spray. The film characterization from the point of view of the composition and crystallinity, performed by means of XRD, FTIR and Raman Spectroscopies, has shown a good purity degree, and compositional homogeneity for the sol-gel materials, though traces of carboxy-hydroxy apatite were found. Also, the samples exhibit a good crystallinity. SEM pictures, taken on HA coating deposited via sol-gel, revealed a homogeneous surface structure and optimum features to set up a good prosthesis-tissue interface.

Optical and magnetic properties of first-row transition metal ions in lead-silicate glass

Abstract First-row transition metal ions in lead-silicate glasses of composition: 37.9% mol PbO, 61.8% mol SiO2 have been studied with regard to the oxidation state and the coordination by means of optical and magnetic measurements. Optical spectra have been recorded at 300 and 77 K. All the observed bands are assigned as being due to d-d transitions in Td and/or Oh fields. Magnetic moments are of the order of the spin-only values. By ESR measurements we reveal and quantify titanium, vanadium and manganese oxidation states not detectable by the other techniques. It turns out that the various metal ions have the following oxidation states: Ti3+ and Ti4+, V4+ and V5+, Cr3+ and Cr6+, Mn2+ and Mn3+, Fe3+, Co2+, Ni2+, Cu2+. The coordination is 4-fold for Ti4+ and V5+ and 6-fold for Mn3+ and Cu2+. Moreover it has been found that Fe3+, Co2+ and Ni2+ are both 4-fold and 6-fold coordinated and that Cr3+ and Cr6+ oxidation states coexist in the same sample.

A study on the differentiation between amorphous piroxicam:β-cyclodextrin complex and a mixture of the two amorphous components

Amorphous piroxicam was prepared by the melt spinning method to prove that freeze-dried amorphous piroxicam:β-cyclodextrin is a true inclusion compound and not a dispersed mixture of the two amorphous components. Differential scanning calorimetry (DSC) and near-infrared Fourier transform Raman spectroscopy (NIR FT-Raman) established the success of the encapsulation. Thermal analysis can also be used to evaluate the inclusion complex purity with regard to crystalline and/or amorphous free piroxicam content.