ZrO2 SiO2 Research Articles

Influence of vanadium content on structure and activity of V2O5–ZrO2–SiO2 catalyst for propane dehydrogenation

In order to create alternative vanadium oxide-supported catalysts for the process of non-oxidative propane dehydrogenation to propylene, we studied the effect of the increased content of vanadium oxide in the V2O5–ZrO2–SiO2 composition on its structure and catalytic properties. Zirconium silicate hydrogel in the form of finished spherical granules with the SiO2 content of more than 50% was prepared by direct sol-gel synthesis from zirconium oxychloride and sodium metasilicate using the droplet coagulation technology. Catalysts were fabricated by impregnation of hydrogel with an aqueous solution of vanadyl sulfate salt, hydrothermal treatment and calcination in air. By using scanning electron microscopy, X-ray diffraction analysis and low-temperature nitrogen adsorption/desorption method, we showed that amorphous samples with a developed mesoporous structure (with the pore diameter of ~6 nm and the specific surface area of ~300 m2 g–1) were formed when the content of the supporting V2O5 on zirconium silicate was 10, 20, 25, and 30 wt.%. In the course of temperature increase in the propane dehydrogenation reaction, the catalyst samples crystallized in the reaction mixture propane–inert gas with the formation of tetragonal zirconia. When the content of V2O5 was 25% or 30%, additional phases of reduced vanadium oxides and traces of the zirconium vanadate phase were formed. After the reaction, the specific surface area of the catalysts decreased significantly and the average pore size of the samples with 25% and 30% V2O5 increased to ~30 nm. The propylene yield reproducibly observed on the samples with 25% and 30% V2O5 was lower than that on the samples with 10% V2O5; however, it remained quite high, which was probably due to the expanded diameter of the pores and the appearance of additional ZrV2O7 sites that are active with respect to the dehydrogenation of light alkane.

Microwave heating and synthesis method influence in SiO2–ZrO2 mixed oxides preparation and its use as heterogeneous catalyst for biodiesel obtainment

ZrO2–SiO2 mixed oxides were obtained by two different methods. The influence of microwave-assisted hydrothermal treatment and the differences of two different synthesis methods were investigated. The obtained materials were characterized by DSC, XRD, SEM and FTIR spectrometry. The N2 adsorption analysis data (BET and BJH) was used for the determination of textural properties of the mixed oxides. The two synthesis methods point out differences in the way Zr is incorporated in the silica matrix. The microwave heating was responsible to change the textural properties but not the crystallinity. Finally, the catalytic activity was tested in the transesterification of soybean oil and esterification of oleic acid, both with methanol. The reaction conversions were measured by H-NMR. None of the samples presented catalytic activity in the transesterification of soy oil with methanol. However, the oleic acid was esterified with methanol at subcritical conditions.

Color matching ability of resin composites incorporating supra-nano spherical filler producing structural color

ObjectiveThe aim of this study was to evaluate the optical properties of supra-nano spherical fillers with different diameters and the color matching ability of resin composites (RC) incorporating these fillers. MethodsTwo types of SiO2–ZrO2 nano fillers with different diameters (150nm and 260nm) were used. The size distribution of each filler was measured and filler morphology was observed. The colors and spectral reflection spectra were measured by a spectral reflectometer. Experimental RCs incorporating ϕ150-nm/ϕ260-nm filler (D150RC/D260RC) were prepared. For the base dentin part, disc specimens (Estelite Astelia: A1B, A2B, A3B, A3.5B, or A4B) were prepared with a cylindrical cavity. Estelite Astelia with NE shade was layered on top as the enamel layer. Disk specimens with different cavity depths were prepared using A3B shade. Experimental RC was used to fill the cavity, and spectral reflection spectrums were obtained and analyzed. Filtek Supreme Ultra (FSU) with A3B shade was used (n=10) as a control. ResultsBoth ϕ150-nm and ϕ260-nm nano fillers showed uniform spherical shape and exhibited no aggregation. The maximum peaks of the spectral reflection spectra of the ϕ150-nm and ϕ260-nm nano fillers were 380nm and 580nm, producing structural colors close to blue and yellow, respectively. The spectral reflection spectrum of FSU had a broad peak at 540nm, and D150RC had a significant peak at 420nm. The D260RC specimen had a broad peak at 680nm. The peaks of D150RC and D260RC significantly decreased in accordance with the shift in base RC shade from A1B to A4B. There was no significant difference in the peak of the reflection spectral spectra among different cavity depths of D260RC. These results suggest that the experimental RC could reflect base RC colors via the matrix resin, and the amount of transmitted light from the base RC was not much different with cavity depth. SignificanceD260RC producing structural color demonstrated a broad spectrum and reduction in brightness and chromatic value by adapting to surrounding restorative materials, suggesting its ability to enhance the chameleon (blending) effects to improve color matching. D260RC showed better color matching ability than resin composite containing uniformly sized ϕ150-nm SiO2–ZrO2 supra-nano spherical filler.

Thermodynamic modeling of ZrO2–Y2O3–SiO2 and ZrO2-Gd2O3–SiO2 systems

Thermodynamic modeling in ZrO2–Y2O3–SiO2 and ZrO2-Gd2O3–SiO2 is part of a broader effort to develop thermodynamic databases that can help offer insight on reactions between thermal barrier coatings (TBCs) based on ZrO2–Y2O3/Gd2O3 and molten silicate deposits in gas turbine engines. The main purpose of the present work is devoted to providing a set of self-consistent thermodynamic parameters for ZrO2–Y2O3–SiO2 and ZrO2-Gd2O3–SiO2 systems by means of the CALPHAD (CALculation of PHAse Diagram) method. Firstly, the ZrO2–SiO2 and Gd2O3–SiO2 sub-systems are assessed. By combining with thermodynamic parameters of ZrO2–Y2O3, Y2O3–SiO2 and ZrO2-Gd2O3 in the literatures, phase equilibria in these two ternary systems are extrapolated and calculated. However, comparing the experimental data and the calculations reveals major inconsistencies, which contains three-phase equlibrium and a quaternary reaction. The bad predictions are mainly due to overestimating or underestimating phase stabilities of compounds in the binary sub-systems. Accordingly, Y2O3–SiO2 and ZrO2-Gd2O3 systems have been re-assessed based on new experiments. Finally, the experimental data for ternary systems are well reproduced by the improved thermodynamic descriptions. Our work exhibits that the accurate thermodynamic parameters of the sub-systems are significant to provide a reliable basis for thermodynamic extrapolations and calculations in higher-order systems.

Slurry-Phase Hydrocracking of a Decalin–Phenanthrene Mixture by MoS2/SiO2–ZrO2 Bifunctional Catalysts

Slurry-phase hydrocracking is one of the most advanced technologies for the conversion of inferior heavy oil to light fuel oil. In this work, MoS₂ was combined with SiO₂–ZrO₂ mixed oxides to offer a new class of bifunctional catalysts for slurry-phase hydrocracking. In the bifunctional catalysts, SiO₂–ZrO₂ mixed oxides with abundant mesopores and acid sites act as cracking catalysts. They were presynthesized by a sol–gel-hydrothermal method and systematically characterized by X-ray diffraction (XRD), N₂ adsorption, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), NH₃-temperature programed desorption (NH₃-TPD), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The effect of Si/Zr molar ratios on the chemical structure, especially the acid properties of SiO₂–ZrO₂ mixed oxides were examined. Subsequently, a mixture of decalin–phenanthrene was selected as the model system to investigate the performance of bifunctional catalysts. It was found that the conversions of decalin and phenanthrene were significantly improved for MoS₂/SiO₂–ZrO₂ bifunctional catalysts. Further analysis indicated that the Bronsted acid sites of SiO₂–ZrO₂ mixed oxides played an important role in the improvement of decalin and phenanthrene conversions.

Role of CeO2/ZrO2 mole ratio and nickel loading for steam reforming of n-butanol using Ni–CeO2–ZrO2–SiO2 composite catalysts: A reaction mechanism

This study presents steam reforming of n-butanol to synthesis gas using high surface area mesoporous Ni–CeO2–ZrO2–SiO2 composite catalysts. The reaction proceeds through a combination of dehydrogenation, dehydration, and cracking reactions with propanal, butanal, and C2–C4 hydrocarbons as intermediate compounds. The ceria forms a solid solution with zirconia, promotes dispersion of nickel, and enhances oxygen storage/release capacity. The carbon conversion to synthesis gas (CCSG) and hydrogen yield are thus enhanced with increasing CeO2/ZrO2 mole ratio up to 1:2 and decreased slightly for higher mole ratios. The CCSG and hydrogen yield are also boosted by increasing the amount of nickel in the catalyst up to 20 wt%. 1:2 CeO2/ZrO2 mole ratio and 20 wt% nickel content are thus deliberated as optimum. The optimum catalyst exhibits stable catalytic performance for about 30 h time-on-stream. The study further presents the effect of temperature and steam/carbon mole ratio on n-butanol steam reforming.

Dependence of the refractive index of transparent ZrO2–SiO2 aerogels on the density and zirconium content

In this work ZrO2–SiO2 aerogels with ZrO2 content of 3, 6 and 10 mol. % in the form of transparent blocks were synthesized using the sol-gel method. The possibility of introducing ZrO2 into a SiO2 aerogel without considerable decline of the optical characteristics of the material was shown for the first time. Aerogel samples were studied by several techniques including UV–Vis, ATR-FTIR spectroscopy and nitrogen adsorption, the refractive index was determined using beam tests (“Extracted beams” of the VEPP-4M complex). It was shown that the addition of ZrO2 to SiO2 aerogel increases the refractive index without increasing of the aerogel density. For the first time, the possibility of obtaining highly transparent ZrO2–SiO2 aerogel blocks with acceptable optical characteristics for radiator in Cherenkov detectors has been demonstrated. This result makes it possible to achieve high refractive indices in the production of aerogel blocks for Cherenkov detectors to increase their performance.

Selective ALD of SiN using SiI4 and NH3: The effect of temperature, plasma treatment, and oxide underlayer

The initial growth of silicon nitride (SiN) thin films was studied during thermal atomic layer deposition (ALD) using silicon tetraiodide (SiI4) and ammonia (NH3) onto various oxide underlayers (native SiO2, sapphire, ALD Al2O3, and ALD ZrO2) at two deposition temperatures (200 and 350 °C). We found that the SiI4/NH3 process shows earlier nucleation on high-k oxide underlayers (sapphire, ALD Al2O3, and ALD ZrO2) compared with SiO2 at 200 °C. Interestingly, an NH3-plasma treatment reverses the selectivity between high-k oxides and SiO2: SiN growth has no nucleation delay on NH3-plasma-treated SiO2 but is severely delayed on NH3-plasma-treated high-k oxides at both temperatures (an incubation period of at least 300 cycles at 200 °C and 50 cycles at 350 °C).

High thermal stability of SiO2–ZrO2 aerogels using solvent-thermal aging

The ZrO2–SiO2 aerogels (ZSA) with varied particle size were synthesized by solvent-thermal aging (STA) method. The effects of STA temperature (60, 110, 170 and 210 ​°C) on microstructure and thermal stability of the ZSA were investigated by SEM, TEM, FT-IR and XRD. The ZSA-210 presents the minimum shrinkage (9.3%), and it has the largest retention values of specific surface area (59.2%) and pore volume (90.8%) after 1000 ​°C heat treatment for 1 ​h. Compared with the aerogels prepared by traditional aging, the ZSA prepared by STA can maintain a low thermal conductivity (0.0285–0.0328 ​W ​m−1 ​K−1) while improving the compression strength (~1.28 ​MPa, 10% strain). STA can restrain viscous flow between ZSA particles by particles growth and skeleton coarsening; and STA can restrain the growth of t-ZrO2 by forming more Si–O–Zr bonds in the system. The work will be meaningful for the design of super thermal insulation materials with high thermal stability and low thermal conductivity.

Effect of SiO2–ZrO2 introduction on visible-light degradation of RhB over anatase TiO2

A TiO2-based ternary oxide was synthesized as a visible-light photocatalyst (TiO2/ZrTiO4/SiO2, SZT) by introducing SiO2–ZrO2 into TiO2 through sol–gel method. The related material compositions and microstructures were characterized, and the optical and photochemical performances were evaluated and compared with pure anatase TiO2. By introducing SiO2–ZrO2, the grain size of TiO2 was reduced from 29.9 nm in the pure anatase phase to 11.5 nm in SZT, accompanied by the formation of ZrTiO4. Moreover, the synthesized SZT demonstrated greatly lowered photoluminescence intensity and electrochemical impedance, and significantly increased photocurrent. The new photocatalyst also exhibited superior adsorption and photocatalytic ability for RhB, and higher catalytic stability. The improved photodegradation performance was attributed to the enhanced charge transfer and charge carrier separation as a result of the refined grains, the formation of TiO2/ZrTiO4 heterojunction, and a higher amount of built-in oxygen vacancies.

Hafnium silicate formation during the reaction of β‐cristobalite SiO2 and monoclinic HfO2 particles

AbstractHafnium silicate (HfSiO4; hafnon) is under consideration as an environmental barrier coating material for high‐temperature applications. However, its rate of formation from mixtures of monoclinic HfO2 and crystalline (β‐cristobalite) SiO2 powders is unknown. Here it has been synthesized and its formation rate measured during their solid‐state reaction at temperatures from 1250°C to 1400°C. Rietveld refinement of X‐ray diffraction patterns indicates that at 1250°C the hafnon phase fraction increases linearly with time, while at the highest reaction temperature, the hafnon phase fraction exhibited a parabolic dependence upon time. Between these two limiting temperatures, a region of linear behavior preceded a transition to parabolic kinetics, with the transition occurring at an earlier time as the reaction temperature increased. Arrhenius relations fitted the kinetics of hafnium silicate formation in both the linear and parabolic regimes. Scanning electron microscopy indicated that the reaction proceeded by diffusion of SiO2 into HfO2, similar to the mechanism by which zirconium silicate has been formed from vitreous SiO2 and tetragonal ZrO2. The initial linear rate of reaction is consistent with the growth of the contact area between the SiO2 and HfO2 particles combined with rapid permeation of the Si4+ and O2− through the initial, incompletely formed hafnon. After a thin hafnon layer had formed between the reactants, the rate of hafnium silicate growth slowed and further growth was governed by the rate of diffusion of Si4+ and O2− through the reaction product consistent with the observed parabolic dependence of the phase fraction upon time.

A novel combination of precursor pyrolysis assisted sintering and rapid sintering for construction of multi-composition coatings to improve ablation resistance of SiOC ceramic modified carbon fiber needled felt preform composites

A double-layer coating composed of MoSi2–SiO2–SiC/ZrB2–MoSi2–SiC was designed and successfully constructed by a novel combination of precursor pyrolysis assisted sintering and rapid sintering to improve the ablation resistance of SiOC ceramic modified carbon fiber needled felt preform composites (CSs). The ZrB2–MoSi2–SiC inner layer coating was in relatively uniform distribution in the zone of 0–3 mm from the surface of CSs through the slurry/precursor infiltration in vacuum and SiOC precursor pyrolysis assisted sintering, which played a predominant role in improving oxidation and ablation resistance and maintaining the morphology of CSs. The MoSi2–SiO2–SiC outer layer coating was prepared by the spray and rapid sintering to further protect CSs from high-temperature oxidation. The ablation resistance of CSs coated with double-layer coating was evaluated by an oxygen-acetylene ablation test under the temperature of 1600–1800 °C with different ablation time of 1000 and 1500 s. The results revealed that the mass recession rates increased with the rise of ablation temperature and extension of ablation time, ranging from 0.47 g/(m2·s) to 0.98 g/(m2·s) at 1600–1800 °C for 1000 s and from 0.72 g/(m2·s) to 0.86 g/(m2·s) for 1000–1500 s at 1700 °C, while the linear recession rates showed negative values at 1700 °C due to the formation of oxides, such as SiO2 and ZrO2. The ablation mechanism of the double-layer coating was analyzed and found that a SiO2–ZrO2–Mo4.8Si3C0.6 oxidation protection barrier would be formed during the ablation process to prevent the oxygen diffusion into the interior CSs, and this study provided a novel and effective way to fabricate high-temperature oxidation protective and ablation resistant coating.

Third-order nonlinear optical features of zirconia-added lead silicate glass ceramics embedded with Pb2Fe2O5 perovskite crystal phases and role of Fe ions

This study is aimed to identify the role of Fe2O3 in enhancing the efficiency of THG beam of Nd:YAG laser in lead zirconium silicate glass ceramics. The PbO–ZrO2–SiO2:Fe2O3 glass ceramics were synthesized by heat-treating the glasses for a prolonged time. XRD and SEM studies were performed to identify different crystalline phases in the samples. The SEM pictures have shown the presence of multiple crystallites of size in the range 0.1–0.6 µm, while characterization by XRD technique indicated the glass ceramic samples consist of perovskite Pb2FeIII2O5, FeII2SiO4, crystal phases. These studies have also demonstrated that there is an enhancement in the concentration of Fe3+ (Oh) crystalline phases with increasing quantity of Fe2O3 in the samples. Spectroscopic investigations (viz., IR and optical absorption) have further reinforced the above result and additionally indicated an increased degree of internal chaos in the material. The intensity of third harmonic generation (THG) beam of Nd:YAG laser (λ = 1064 nm) measured in the reflected regime after the pre-photopolarization of the samples indicated the largest intensity for the samples containing the highest concentration of Fe2O3. Thorough analysis of these results indicated that the tilted glass samples heat-treated with 0.5 mol% of Fe2O3 have significant chaotic internal structure and paved the way for obtaining intense THG signal with minimal phonon losses. Hence, such glass ceramics are predicted to be useful materials in the design of different optoelectronic devices.

Synthesis and Physicochemical and Catalytic Properties of Composites in the SiO2–ZrO2 System

Using coprecipitation, a sol–sol method, and molecular layering, we have synthesized SiO2–ZrO2 composites with SiO2 : ZrO2 ratios from 1 : 1 to 9 : 1 and a large specific surface area, which increases with growth silicon-containing component concentration. Using adsorption of Hammett indicators, we have assessed the concentration of acid–base centers in the pK range 1.3–9.6, which has been shown to vary from 68 to 160 μmol/g. Elemental analysis and IR spectroscopy data have demonstrated the presence of not only water but also nitrate ions and carbon dioxide on the surface of the samples. It has been shown that the use of nanoparticulate SiO2–ZrO2 oxides as heterogeneous catalysts—promoters for (2S,4R)-4-hydroxyprolyl-(S)-1-phenylethylamine trifluoroacetate, a chiral inducer in the asymmetric Biginelli reaction, makes it possible to raise ee (enantiomeric excess) from 39 to 68% and the reaction yield from 29 to 55%.

Structure–selectivity relationship of a zirconia-based heterogeneous acid catalyst in the production of green mono- and dioleate product

A novel catalytic technique is vital to produce mono- and dioleate (GMO and GDO) from bioglycerol: a renewable resource and by-product of biodiesel. The advantage of this invention is the direct production of GMO and GDO through catalytic approach compared to the conventional method that requires transesterification and distillation processes. In this paper, glycerol esterification with oleic acid using a catalyst was experimented. The process was carried out over a hydrophobic mesoporous zirconia–silica heterogeneous acid catalyst (ZrO2–SiO2–Me&Et–PhSO3H) with three types of sulphated zirconia catalysts (SO42−/ZrO2) to produce high-selectivity GMO and GDO products. The catalytic performance of the hydrophobic ZrO2–SiO2–Me&Et–PhSO3H catalyst was benchmarked with that of SO42−/ZrO2 which was developed from three zirconium precursors. Results showed that the pore volume and hydrophobicity of the designed catalyst greatly could influence the product selectivity, thus enabling smaller substrates GMO and GDO to be dominated in the synthesis. This finding was supported by characterisation data obtained through N2 adsorption–desorption, X-ray diffraction and scanning electron microscopy. In addition, a good correlation was found between pore volume (pore size) and product selectivity. High pore volume catalyst favoured GDO production under identical reaction conditions. Pore volume and size can be used to control product sensitivity. The hydrophobicity of the catalyst was found to improve the initial reaction rate effectively.

High-temperature oxidation behaviors of ZrSi2 and its coating on the surface of Zircaloy-4 tube by laser 3D printing

The high-temperature oxidation behavior of ZrSi2 used as a coating material for nuclear fuel cladding was investigated for developing accident-tolerant fuel cladding of light water reactors. Bulk ZrSi2 samples were prepared by spark plasma sintering. In situ X-ray diffraction was conducted in air at 900, 1000, and 1100 °C for 20 h. The microstructures of the samples before and after oxidation were examined by scanning electron microscopy and transmission electron microscopy. The results showed that the oxide layer of zirconium silicide exhibited a layer-by-layer structure of crystalline ZrO2 and amorphous SiO2, and the high-temperature oxidation resistance was superior to that of Zircaloy-4 owing to the SiO2 layer formed. ZrSi2 was coated on the Zircaloy-4 tube surface using laser 3D printing, and the coated tube was oxidized for 2000 s at 1200 °C under a vapor/argon mixture atmosphere. The outer surface of the coated tube was hardly oxidized (10–30 μm), while the inner surface of the uncoated tube was significantly oxidized to approximately 300 μm.

Glass–Ceramics in Dentistry: A Review

In this review, we first briefly introduce the general knowledge of glass–ceramics, including the discovery and development, the application, the microstructure, and the manufacturing of glass–ceramics. Second, the review presents a detailed description of glass–ceramics in dentistry. In this part, the history, property requirements, and manufacturing techniques of dental glass–ceramics are reviewed. The review provided a brief description of the most prevalent clinically used examples of dental glass–ceramics, namely, mica, leucite, and lithium disilicate glass–ceramics. In addition, we also introduce the newly developed ZrO2–SiO2 nanocrystalline glass–ceramics that show great potential as a new generation of dental glass–ceramics. Traditional strengthening mechanisms of glass–ceramics, including interlocking, ZrO2–reinforced, and thermal residual stress effects, are discussed. Finally, a perspective and outlook for future directions in developing new dental glass–ceramics is provided to offer inspiration to the dental materials community.

Development of an acetylacetonate-modified silica-zirconia composite membrane applicable to gas separation

In this work, an acetylacetonate-modified equimolar SiO2–ZrO2 composite-derived membrane with molecular sieving properties was successfully fabricated. The sol-gel method was successfully employed to chemically modify zirconium tetrabutoxide prior to co-hydrolysis and -condensation with tetraethoxysilane, the resulting sol then used to fabricate a gas separation layer. An acetylacetonate-modified SiO2–ZrO2-derived membrane prepared at 300 °C showed H2 permeance of 9.9 × 10 −7 mol m−2 s−1 Pa−1 with a H2/SF6 permeance ratio of 7,600, which was a significant improvement over pure SiO2–ZrO2-derived membranes (H2 permeance: 1.4 × 10 −6 mol m−2 s−1 Pa−1, H2/SF6 permeance ratio: 11). Heat-treatment of an acac−-modified SiO2–ZrO2-derived membrane prepared at temperatures that ranged from 250 °C (H2 permeance: 4.5 × 10−8 mol m−2 s−1 Pa−1, H2/CH4: 100, CO2/CH4: 60, H2/SF6: >18,000 at 50 °C) to 550 °C resulted in an improved H2 permeance of 3.4 × 10−6 mol m−2 s−1 Pa−1 with reduced permeance ratios (H2/CH4: 3, H2/SF6: 9) at 50 °C. A membrane prepared by heat-treating a 250 °C-fired membrane at 300 °C showed the best trade-off with H2 permeance-H2/SF6 permeance ratios above the trade-off line compared with membranes prepared at other temperatures.

Comparison of corrosion resistance of high chromia brick, high zirconia brick, fused AZS brick and Si3N4 bonded SiC brick against coal slag

Corrosion resistance of four typical refractories against coal-water slurry coal slag, was investigated in laboratory. These typical refractories are high chromia brick (Cr2O3–Al2O3–ZrO2), fused AZS brick (Al2O3–ZrO2–SiO2), high zirconia brick (ZrO2) and Si3N4 bonded SiC brick, respectively. The cup test and micro-structural analysis method were used to evaluate the corrosion resistance and reaction mechanism at high temperature. Meanwhile, potential reactions between refractories and slag are predicted using thermodynamic calculation. The result shows that infiltrated depth increases in following order: Si3N4 bonded SiC brick < fused AZS brick < high zirconia brick < high chromia brick. The ZrO2 dissolution and higher porosity for the high chromia brick synergistically result in the worst corrosion resistance. Whereas, for the high zirconia brick, the continuous slag infiltration accelerate dissolution of ZrO2 grains, which decreases corrosion resistance. Due to the extremely low porosity, slag infiltration can be effectively hindered, and fused AZS brick has better slag corrosion resistance. For the Si3N4 bonded SiC brick, poor wettability, protective SiO2 film and increased slag viscosity synergistically contribute excellent corrosion resistance.

Hybrid SiO2–ZrO2 coatings for restoring and repairing glasses damaged by sandblasting

The purpose of this work was to study the repairing of defect produced by sandstorms on the surface of car windshields and solar panels, by deposition of thin transparent sol-gel layers. Different silica-zirconia films (100-x SiO2 - x ZrO2, x = (10, 15, 20, 25 and 30 mol %) were prepared by the sol–gel process using TEOS and MTES as silica precursors and incorporating two different colloidal suspensions with silica or zirconia nanoparticles. The silica-zirconia sols were deposited by dip coating on soda-lime glass samples previously eroded by sandblasting. Film thickness and homogeneity were evaluated by ellipsometry and AFM, and the optical and mechanical properties were studied by UV–vis spectroscopy, the hardness by microhardness, and the roughness by tactile profilometer. The sol-gel coatings present a good quality and are able to restore the optical and mechanical properties of sandblasted samples thus increasing the service life. The incorporation of zirconia particles to SiO2 coatings increases the refractive index, from 1.42 to 1.57. Moreover, optical transmission of coated samples increases from 91.4 to 93% for 90SiO2–10ZrO2 coatings, and increases from 80% for eroded samples (Mp = 200 g) coated with SiO2–ZrO2 films up to 91% while micro-hardness is greatly improved from 10.17 GPa for the raw material to 17.62 GPa for 70SiO2–30ZrO2 coated sample.