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The surface and catalytic properties of oxide ternary materials consisting of niobium-phosphorus-silicon, Nb-P-Si, with Nb/P = 1 and general formula xNb2O5·xP2O5·(100–2x)·SiO2, with x = 2.5, 5, 7.5, and 10, and Si content ranging from 95 to 80 mol% are presented. Amorphous gel-derived samples were obtained, characterized by a very high degree of silicon cross-linking with presence of Si O Nb bridges, allowing phosphorus to be stably anchored to the matrix through Nb O P bonds. The morphology (surface area and porosity), the intrinsic acidity (density and average strength of the surface acid sites, by PEA-TPD in a TGA-DSC coupled instrument), and the nature of the acid sites were determined. The LAS/BAS ratio has been evaluated by FTIR of adsorbed pyridine in absence/presence of water to discover the differences between the intrinsic and effective nature of the acid sites. The amount of acid sites decreased with the Nb-content in the samples as well as the surface average acid strength. Both LAS and BAS are maintained in the presence of water, even if BAS are predominant in any case. The catalytic performances of the Nb-P-Si samples in the reaction of inulin hydrolysis were investigated in aqueous solution under mild conditions (below 100 °C).

A method is developed for rapid preparation of titania substrates using a sol–gel preparation route in combination with an amphiphilic block copolymer (BCP) template, acting as structure directing agent. The method consists in performing the spin coating of an initial solutions of BCP and titania species in a controlled atmosphere using a flux of solvent vapors (Rapid-Flux-Solvent-Atmosphere, RFSA method). The method is demonstrated in the case of thin films of polystyrene-b-poly(oxyethylene) BCP (PS-PEO) with cylindrical morphology of PEO domains in the PS matrix, characterized by the selective inclusion of titanium species inside the PEO cylinders. Upon removal of the organic matrix by heat treatment at 600 °C, titania substrates of different morphology are obtained depending on the concentration of titania precursor and processing conditions. The method allows preventing the negative effect of hydrolysis and condensation reactions of Ti species and titania substrates with morphology reminiscent of that one achieved in the hybrid nanostructured thin films are obtained. The RFSA method is simple, direct, and it is of particular interest for systems that require a short processing time to eliminate the solvent and to obtain regular nanostructured thin-films over large area. Merit figures such as the degree of hexagonal order and the degree of coverage of the surface with titania motifs are identified to characterize the hybrid composites and titania substrates.

Manganese oxide catalysts supported on monolithic yttria stabilized zirconia honeycombs were studied for H 2 O 2 decomposition in view of space propulsion applications. The materials were prepared by impregnation (IM), precipitation (PR) and sol–gel (SG) methods and characterized by N 2 adsorption, SEM and H 2 temperature programmed reduction (TPR). The catalytic activity for H 2 O 2 decomposition was studied under vapour phase conditions. The tests were carried out in a flow apparatus at T = 200 °C, gas hourly space velocity (GHSV) = 2.00 and 2.67 s −1 , H 2 O 2 concentrations of 11.3 mol%. The redox properties of the catalysts were markedly influenced by the preparation method. In the SG catalyst, a large fraction of Mn was not reducible in the TPR tests differently from the PR and IM materials. Despite this effect, the SG catalyst showed an activity comparable or higher than that of PR and IM, due to a more effective dispersion of Mn species. A too strong effect of space velocity on H 2 O 2 conversion was attributed to an autocatalytic effect. A radical mechanism was hypothesized: it was assumed that a reaction between O 2 and Mn species produced radicals that promoted the overall reaction.

The main aspects of the sol–gel synthesis of ZnO thin films were critically examined with particular reference to the optimization of the process parameters that influence specific properties of the films, such as the transparency, the crystallization behavior and the electrical resistivity. Starting from zinc acetate dihydrate, anhydrous ethanol and triethanolamine, a valuable sol–gel route was set. This route allowed the preparation of transparent ZnO thin films by dip-coating. Triethanolamine, thanks to its high chelating efficiency towards Zn2+, permitted to prepare stable zinc acetate dihydrate solutions wholly at room temperature. The structural, optical and morphological characteristics of the films were examined by glancing incidence X-ray diffraction, UV–vis spectroscopy and atomic force microscopy. Single layer films, with a thickness of about 120 nm, characterized by a high adhesion force (about 140 Kg cm−2), were obtained. The crystallization behavior of dip-coated amorphous films was explored in the 500–600 °C range; polycrystalline films, formed by randomly oriented ZnO nanocrystals (about 20 nm), with an average transmittance higher than 90% in the visible region, were obtained. Finally, a strong influence of annealing environment on electrical resistivity was observed.

Cu/ZrO 2 catalysts prepared by the sol–gel method were characterized by XRD, N 2 adsorption, DTA/TG, TPR and N 2 O dispersion measurements and tested as catalysts for the oxidative steam reforming of methanol (OSRM). Two synthesis procedures, based on the Cu precursors Cu(CH 3 COO) 2 ·H 2 O ( A -ZrCu samples) and Cu(NO 3 ) 2 ·2.5H 2 O ( N -ZrCu samples) respectively, were compared to investigate the consequence of synthesis parameters on the physical and chemical properties of the prepared materials. The adopted procedures resulted in remarkable differences in thermal behaviour: the crystallization of tetragonal ZrO 2 was shifted to higher temperature in N -ZrCu samples in comparison with pure ZrO 2 , while this effect was not observed in A -ZrCu. XRD data indicated that Cu 2+ ions were incorporated into the ZrO 2 lattice in N -ZrCu samples. Though both synthesis lead to very high surface areas, the textural properties of the reduced samples suggested the existence of different interactions between Cu ions and the ZrO 2 matrix in A -ZrCu and in N -ZrCu. The Cu/ZrO 2 systems showed noticeable catalytic activity for the oxidative steam reforming of methanol, even without the pre-reduction treatment, but the catalytic response is drastically affected by the preparation procedure and the pre-treatments. N -ZrCu samples gave higher methanol conversion and yield to H 2 . Moreover, the distribution of secondary products was completely different: N -ZrCu produced a lot of CO, while A -ZrCu gave large amounts of CH 2 O and (CH 3 ) 2 O.

Second harmonic generation properties have been studied in 23 K2O · 27Nb2O5 · 50 SiO2 glass subjected to thermal poling. The poling-induced optical nonlinearity, with χ(2) = 3.8 pm/V, has been related to structural modifications within a surface layer of a few microns on the anode side, as evidenced by means of confocal micro-Raman mapping along the sample thickness. The data indicate that the structural changes result from a charge transport process that causes network modifications in an alkali depleted layer whose thickness is comparable with that of the non-linear region. The Raman data also indicate that in the alkali depleted layer the network polymerization degree increases as a consequence of ion migration. The origin of the nonlinearity and the mechanisms activated by poling are discussed. The mechanism of non-bridging-oxygen to bridging-oxygen bond switching is proposed to explain ion migration and the subsequent structural changes in the glass. © 2009 Elsevier B.V. All rights reserved.

Transparent glasses having molar composition (23-x)K{sub 2}O.xNa{sub 2}O.27Nb{sub 2}O{sub 5}.50SiO{sub 2} (x=0, 5, 10, 15 and 23) have been synthesized by the melt-quenching technique and their devitrification behaviour has been investigated by DTA and XRD. Depending on the composition, the glasses showed a glass transition temperature in the range 660-680 deg. C and devitrified in several steps. XRD measurements showed that the replacement of K{sub 2}O by Na{sub 2}O strongly affects the crystallization behaviour. Particularly, in the glasses with only potassium or low sodium content the first devitrification step is related to the crystallization of an unidentified phase, while in the glass containing only sodium, NaNbO{sub 3} crystallizes. For an intermediate sodium content (x=10 and 15) a potassium sodium niobate crystalline phase, belonging to the tungsten-bronze family, is formed by bulk nucleation. This system looks promising to produce active nanostructured glasses as the tungsten-bronze type crystals have ferroelectric, electro-optical and non-linear optical properties. Preliminary measurements evidenced SHG activity in the crystallized glasses containing this phase. - Graphical abstract: Synthesis of glasses (23-x)K{sub 2}O.xNa{sub 2}O.27Nb{sub 2}O{sub 5}.50SiO{sub 2} (x=0, 5, 10, 15 and 23) from which SHG active phases crystallize by bulk nucleation for non-linear optical nanostructured glasses.

Amorphous nanoheterogeneities of the size less than 100 A have been formed in glasses of the Li2O–Nb2O5–SiO2 (LNS) and Li2O–ZnO–Nb2O5–SiO2 (LZNS) systems at the initial stage of phase separation and examined by transmission electron microscopy, small-angle X-ray and neutron scattering. Both LNS and LZNS nanoheterogeneous glasses exhibit second harmonic generation (SHG) even when they are characterized by fully amorphous X-ray diffraction (XRD) patterns. Chemical differentiation and ordering of glass structure during heat treatments at appropriate temperatures higher Tg lead to drastic increase of SHG efficiency of LNS glasses contrary to LZNS ones in the frame of amorphous state of samples. Following heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO3 and non-polar LiZnNbO4 in the LNS and LZNS glasses, respectively. Taking into account similar polarizability of atoms in LNS and LZNS glasses, the origin of the principal difference in the second-order optical non-linearity of amorphous LNS and LZNS samples is proposed to connect predominantly with the internal structure of formed nanoheterogeneities and with their polarity. Most probably, amorphous nanoheterogeneities in glasses may be characterized with crystal-like structure of polar (LiNbO3) phase initiating remarkable SHG efficiency or non-polar (LiZnNbO4) phase, which do not initiate SHG activity. It gives an opportunity to vary SHG efficiency of glasses in a wide rage without remarkable change of their transparency by chemical differentiation process at the initial stage of phase separation when growth of nanoheterogeneities is ‘frozen’. At higher temperatures, LiNbO3 crystals identified by XRD precipitate in LNS glasses initiating even more increase of SHG efficiency but visually observable transparency is impaired.

Cobalt–silicon mixed oxide materials (Co/Si=0.111, 0.250 and 0.428) were synthesised starting from Co(NO3)2·6H2O and Si(OC2H5)4 using a modified sol–gel method. Structural, textural and surface chemical properties were investigated by thermogravimetric/differential thermal analyses (TG/DTA), XRD, UV–vis, FT-IR spectroscopy and N2 adsorption at −196 °C. The nature of cobalt species and their interactions with the siloxane matrix were strongly depending on both the cobalt loading and the heat treatment. All dried gels were amorphous and contained Co2+ ions forming both tetrahedral and octahedral complexes with the siloxane matrix. After treatment at 400 °C, the sample with lowest Co content appeared amorphous and contained only Co2+ tetrahedral complexes, while at higher cobalt loading Co3O4 was present as the only crystalline phase, besides Co2+ ions strongly interacting with siloxane matrix. At 850 °C, in all samples crystalline Co2SiO4 was formed and was the only crystallising phase for the nanocomposite with the lowest cobalt content. All materials retained high surface areas also after treatments at 600 °C and exhibited surface Lewis acidity, due to cationic sites. The presence of cobalt affected the textural properties of the siloxane matrix decreasing microporosity and increasing mesoporosity.

The structure and crystallization behavior of glasses with 25La2O3 · 25B2O3 · 50GeO2 composition, melted in platinum (P glass) and corundum (A glass) crucibles, were studied by DTA, X-ray diffraction and FTIR spectroscopy. The Al2O3 dissolved from corundum crucible in the A glass was estimated to be in the range 5–7 wt%. This alumina content had almost no influence on glass transition temperature but strongly affected the structure and crystallization behavior of the A glass. In fact, the P glass showed good texture-forming ability: high quality textured glass-ceramic plates based on stillwellite-like LaBGeO5 crystals were easily obtained. On the contrary, the presence of alumina stabilized the A glass from which binary phases crystallize first, and only afterwards they are transformed in stillwellite by secondary crystallization: so in this glass texturing is hindered. Crystallization and texturing behavior of P and A glasses were well related to FTIR data. P glass contained both threefold and fourfold coordinated boron while in the A glass the presence of aluminum forced boron to assume almost exclusively threefold co-ordination. Hence the easier crystallization of stillwellite phase and the good textures obtained from the P glass contrary to the A glass, can be well understood since all boron atoms have tetrahedral co-ordination in stillwellite LaBGeO5 crystal.

Glasses from which the ferroelectrics phase KTiOPO 4 can crystallise have been prepared and studied. Namely, two glasses having the 92(K 2 O·2TiO 2 ·P 2 O 5 )·8SiO 2 (KTP-8Si) and the 88(K 2 O·2TiO 2 ·P 2 O 5 )·12SiO 2 (KTP-12Si) molar compositions have been synthesised by the melt quenching technique. They were examined by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The KTP-8Si glass devitrifies in a single step forming KTiOPO 4 phase, whereas the KTP-12Si glass firstly crystallises in an unknown phase and then, at higher temperatures, KTiOPO 4 crystallites grow. Proper heat treatments performed on the KTP-8Si glass at temperatures just below the glass transition range produce transparent samples the glassy matrix of which contains crystalline nanostructure of the KTP phase.

Lead germanate glasses of the xPbO(1 - x)GeO2 compositions with x ranging from 0.200 to 0.625 have been synthesised and their crystallisation behaviour and vibrational properties studied by differential thermal analysis (DTA) and Raman spectroscopy. Raman spectra of the Pb5Ge3O11 ceramics also have been measured and compared to lead germanate glass spectra and literature data on beta -PbO, Ge atoms in low lead glasses are supposed to be surrounded by four to six oxygen atoms, while the high-lead glass (x = 0.625) corresponding to stoichiometry of the Pb5Ge3O11 ferroelectrics contains predominantly fourfold coordinated germanium. Structural resemblence of high-lead germanate glasses to the Pb5Ge3O11 crystal is proposed rather than to beta -PbO. The 'boson' peak range in the spectra of lead germanate glasses is discussed taking into account the similarities of the spectra of glassy and crystalline Pb5Ge3O11. (C) 2001 Elsevier Science B.V. All rights reserved.

The crystallization of the K2O . Nb2O5. 2SiO2 (KNS-50) glass has been studied by DTA, XRD, SEM and FTIR. The as-quenched glass crystallizes in two steps during a DTA run. In the first step only potassium niobates crystallize while at the higher temperature step KNbSi207 ferroelectric crystallizes. Heat treatments of the bulk glass at temperatures not far from T-g produce a nanocrystalline structure penetrating the whole volume of the glass and clearly observed by high resolution SEM as isometric nuclei. The observed nanostructure is the result of two processes occurring during the heat treatment amorphous phase separation followed by the crystallization of the high alkali and niobium content glassy phase. The heat-treated glass, in which the nanostructure is grown, shows an additional DTA peak at about 900 degrees C related to the crystallization of an unknown crystalline phase, nor obtained in the as-quenched glass. The existence of the nanostructure clarifies the origin of SHG discovered recently in potassium niobium silicate glasses. (C) 2000 Elsevier Science B.V. All rights reserved.

The structure and the devitrification behavior of barium aluminoborate glasses, examined by Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction are reported. The glass compositions are expressed by the general formula: (50 - x/2)BaO .(50 - x/2)B2O3. xAl(2)O(3) with x = 2, 4 and 8. All the as-quenched glasses were phase separated. Aluminum acting as glass former gives a more polymerized structure increasing the glass stability with respect to the devitrification process. Surface crystallization was found to be dominant for all glasses, forming beta BaB2O4 nanocrystals as the main crystalline phase. (C) 1999 Elsevier Science B.V. All rights reserved.

The effect of replacing GeO2 by TiO2 on the glass-transition temperature and devitrification behaviour in lithium tetragermanate glass has been studied by differential thermal analysis, and Fourier-transform infrared spectra. The glass compositions are expressed by the general formula Li2OxTiO2(4-x)GeO2 with 0.00 less than or equal to x less than or equal to 1.00. The anion network of all glasses was found to contain GeO4 and GeO6 groups in the same molar ratio. The grass-transition and crystallisation temperature values are both increased by the progressive replacement of GeO2 by TiO2. Glasses with x < 0.5 devitrify into lithium tetragermanate crystals. Glasses with x greater than or equal to 0.5 devitrify in two steps into two non-identifiable phases. The influence on the crystallisation mechanisms of the specific surface of the samples was also pointed out. (C) 1997 Elsevier Science B.V.

The effect of replacing PbO by Li 2 O on the glass structure, on the glass transition temperature and on devitrification behaviour in a series of glasses in the lead tetragermanate-lithium tetragermanate composition range has been studied by differential thermal analysis, X-ray diffraction and Fourier-transform infrared spectra. The anion network of all glasses contains GeO 4 and GeO 6 groups in the same molar ratio. The glass transition temperature is increased by the progressive replacement of Pb 2+ by Li + ions. All glasses, except the lead tetragermanate glass, exhibit internal crystal nucleation without any addition of nucleating agent. The crystallizing phases have been identified and related to devitrification mechanisms.

The surface and bulk crystallisation of lead tetragermanate glass has been studied by differential thermal analysis. The influence of the specific surface area of the sample and the nucleation heat-treatment on the crystallisation is pointed out. Infrared spectroscopy measurements suggest that the addition of PbO to germanium oxide leads to a change in the coordination number of germanium atoms from 4 to 6. The phases which crystallise during the DTA runs were identified by X-ray diffraction as hexagonal and monoclinic PbGeO 4 O 9 . The activation energy of crystal growth was also evaluated from DTA curves. A value of about 300kJ mol −1 was calculated from surface and bulk crystallisation.

The effects of the addition of MgO and TiO2 to fly ash on the nucleation and crystal growth mechanisms of the derived glass are investigated with the aid of differential thermal analysis, dilatometry, X-ray diffraction and scanning electron microscopy (SEM). Phase separation occurs on heating the investigated glass. The glass-ceramic materials obtained contain anorthite (CaOAl2O32SiO2) and cordierite (2MgO2Al2O35SiO2) as the main crystalline phases. The morphology of the glass-ceramic material was investigated by SEM and it was consistent with the double-framework structure of the phase-separated glass and it was constituted by a low viscosity phase almost completely crystallised and high viscosity phase scarcely or not crystallised, depending on the heat-treatment.

The devitrification behaviour and the electrical conductivity of five glasses near the lithium metasilicate composition have been studied using differential thermal analysis. X-ray diffraction and impedance analysis. All the studied glasses devitrify in two steps. The influences of replacing SiO2 by Al2O3and of the LiO2 content on the activation energy of crystal growth and of electrical conductivity have been pointed out.

The conditions leading to failure, under cathodic polarization, of high strength wires used to prestress concrete tubes, have been studied. A mechanism of nucleation and growth of microcracks in areas charged with hydrogen has been evidenced. Nucleation of cracks is rapid with a high current density and a lower pH, conditions that can be approached when excessive cathodic protection is applied to wires and the pH of the concrete decreases below the natural basic values by elution of OH−1 ions or by action of acidic solutions.