ZrO2 SiO2 Research Articles

Effects of dopants with various valences on densification behavior and phase composition of a ZrO2–SiO2 nanocrystalline glass-ceramic

Effects of dopants with different valences on the densification behavior and phase composition of a ZrO2–SiO2 nanocrystalline glass-ceramic (NCGC) during pressureless sintering were investigated in this study. The raw powder of Ca2+, La3+, Ce4+ and Ta5+ ions doped ZrO2–SiO2 (referred to as Ca-ZS, La-ZS, Ce-ZS, Ta-ZS, respectively) and pure ZrO2–SiO2 (PZS) sample were synthesized by sol-gel method, followed by pressureless sintering. Compared with the PZS sample, doping of Ca2+ and La3+ ions significantly promoted the densification of the NCGCs. The “densification promotion” effect was attributed to the formation of oxygen vacancies and the decrease of SiO2 viscosity due to doping of aliovalent cations. The dopants with various valences showed significant effects on the phase compositions of the NCGCs during sintering. Doping of Ca2+ ion accelerated the reaction kinetics between ZrO2 nanocrystallites and amorphous SiO2 to yield ZrSiO4. The La3+ ion acted as destabilizer of t-ZrO2, which resulted in a rapid tetragonal (t) to monoclinic (m) ZrO2 phase transformation during sintering, while in the Ta5+ and Ce4+ ions doped sample, the phase transformation occurred gradually. All the doping ions increased the lattice parameters and the volume of t-ZrO2 unit cell, while the effects of the doping ions on the lattice parameters of m-ZrO2 unit cell were more complex.

Thermo-oxidative investigation on SiO2 and SiO2–ZrO2 composites prepared by sol–gel route

Thermo-oxidative investigation on SiO2 and SiO2–ZrO2 composites prepared by sol–gel route

Investigation of adsorption-photocatalytic synergistic mechanism of globular TiO2–ZrO2–SiO2 composites by a synergy factor

Synergy is essential to maximize the photocatalytic performance of the catalyst, which makes the preparation of photocatalytic materials with the synergistic effect of adsorption and catalysis become an attractive research direction. Therefore, we have prepared TiO 2 –ZrO 2 –SiO 2 nano-powders by simple Pechini sol-gel method, which can effectively improve the synergistic effect of adsorption and degradation of photocatalytic materials. The results demonstrate that TiO 2 –ZrO 2 –SiO 2 possesses excellent photocatalytic performance and adsorption ability. And it can be deduced that in the TiO 2 –ZrO 2 –SiO 2 system, SiO 2 is as for adsorbent, and TiO 2 and ZrO 2 act synergistically as a photocatalyst. The enhanced photocatalytic ability of TiO 2 –ZrO 2 –SiO 2 is attributed to the acceleration of mass transfer by adsorption process, narrowed bandgap (Eg = 2.9 eV) and effective charge separation rate resulting from the formation of Ti–O–Zr. This work also studied the synergy effect between adsorption and photocatalytic properties in TiO 2 –ZrO 2 –SiO 2 , and synergy factor β is used to evaluate the synergistic effect. Moreover β > 1 in first 30 min of visible light irradiation demonstrates that the remarkable synergistic effect exists in TiO 2 –ZrO 2 –SiO 2 compound system. • TiO 2 –ZrO 2 –SiO 2 photocatalyst with both adsorption and photocatalytic properties was successfully prepared. • β (synergy factor) which explains the adsorption-photocatalytic synergistic effect of TiO 2 –ZrO 2 –SiO 2 system is remarkable. • The adsorption-photocatalytic performance can be regenerated.

Composite Films of HDPE with SiO2 and ZrO2 Nanoparticles: The Structure and Interfacial Effects.

Herein, we investigated the influence of two types of nanoparticle fillers, i.e., amorphous SiO2 and crystalline ZrO2, on the structural properties of their nanocomposites with high-density polyethylene (HDPE). The composite films were prepared by melt-blending with a filler content that varied from 1% to 20% v/v. The composites were characterized by small- and wide-angle x-ray scattering (SAXS and WAXS), small-angle neutron scattering (SANS), Raman spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). For both fillers, the nanoaggregates were evenly distributed in the polymer matrix and their initial state in the powders determined their surface roughness and fractal character. In the case of the nano-ZrO2 filler, the lamellar thickness and crystallinity degree remain unchanged over a broad range of filler concentrations. SANS and SEM investigation showed poor interfacial adhesion and the presence of voids in the interfacial region. Temperature-programmed SANS investigations showed that at elevated temperatures, these voids become filled due to the flipping motions of polymer chains. The effect was accompanied by a partial aggregation of the filler. For nano-SiO2 filler, the lamellar thickness and the degree of crystallinity increased with increasing the filler loading. SAXS measurements show that the ordering of the lamellae is disrupted even at a filler content of only a few percent. SEM images confirmed good interfacial adhesion and integrity of the SiO2/HDPE composite. This markedly different impact of both fillers on the composite structure is discussed in terms of nanoparticle surface properties and their affinity to the HDPE matrix.

Enhancement of the H2-permselectivity of a silica-zirconia composite membrane enabled by ligand-ceramic to carbon-ceramic transformation

This work reports the preparation of a carbonized SiO2–ZrO2 composite membrane with enhanced H2 permselectivity via a sol-gel process. The sol-gel synthesis of the precursor SiO2–ZrO2-acetylacetonate composite was optimized by studying the effect that the water/alkoxide molar ratio exerted on the final properties of carbon-SiO2-ZrO2. Characterization by thermogravimetry, XRD, and N2 adsorption revealed that utilizing a water/alkoxide molar ratio of 60 was optimal for the retention of carbon and for promoting the qualities of amorphousness and microporosity. Furthermore, using a Si/Zr ratio of 9/1 in a carbon-SiO2-ZrO2 membrane resulted in a high level of H2 permselectivity. This membrane showed H2 permeance of 16 x 10−7 mol m−2 s−1 Pa−1 and H2/N2 and H2/CH4 ideal selectivities of 75 and 148, respectively. More importantly, the H2 permselectivity of the carbon-SiO2-ZrO2 membrane exceeded that of a similarly pore-distributed unmodified SiO2–ZrO2 membrane with an H2 permeance of 3 x 10−7 mol m−2 s−1 Pa−1. This enhanced H2 permselectivity was attributed to the increase in pore volume contributed by ultra-micropore-bearing carbon nanoparticles.

Cascade conversion of glucose to 5-hydroxymethylfurfural over Brønsted–Lewis bi-acidic SiO2–ZrO2 catalysts

Cascade conversion of glucose to 5-hydroxymethylfurfural over Brønsted–Lewis bi-acidic SiO2–ZrO2 catalysts

Superacid ZrO2–SiO2–SnO2 Mixed Oxide: Synthesis and Study

Superacid ternary ZrO2 SiO2 SnO2 oxide has been synthesized by the sol-gel method with a different atomic ratio Zr:Si:Sn. The highest strength of acid sites has been observed in the ranges of 20 ≤ Zr4+ ≤ 29, 60 ≤ Si4+ ≤ 67, 11 ≤ Sn4+ ≤ 20 at.%. According to the XPS spectra and 119Sn, 29Si MAS NMR spectra of ZrO2 SiO2 SnO2 a partial shift of electron density from zirconium to silicon ions was observed resulting in the formation of superacid Lewis sites. It was shown that superacid Zr29Si60Sn11 mixed oxide efficiently catalyzes acylation of toluene with acetic anhydride at 423 K in a flow reactor with 45% conversion of anhydride at 100% selectivity towards p-methylacetophenone.

Three-Dimensional Insights into Interfacial Segregation at the Atomic Scale in a Nanocrystalline Glass-Ceramic.

The distribution of dopant atoms plays a key role in the effectiveness of doping, thereby requiring delicate characterizations. In this study, we found that energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) techniques in scanning transmission electron microscopy (STEM) were not adequate to reveal the distribution of yttrium and the chemical composition of the ZrO2/SiO2 heterophase interface in an yttrium-doped ZrO2-SiO2 nanocrystalline glass-ceramic. Atom probe tomography (APT) is rarely utilized to characterize ceramics due to some inherent difficulties. However, we successfully revealed the three-dimensional distribution of ZrO2 nanocrystallites and SiO2 matrix at the atomic scale with APT under optimized and well-controlled conditions. We also found that the ZrO2 nanocrystallites had a special core-shell structure, with a thin Zr/Si interfacial layer as a shell and a ZrO2 solid solution as a core. Yttrium dopants showed interfacial segregation at both ZrO2 grain boundaries and the ZrO2/SiO2 heterophase interfaces.

High Performance Hybrid Graphene Nano Filters as a Total dissolved solid remover

Graphene, a single-layer carbon sheet with its distinctive two-dimensional (2D) single-atomic-thick sp2 hybridized hexagonal packed lattice structure which is nearly friction less with high chemical inertness, and pliability which can be manufactured sustainably in great amounts with less expense, has shown many unique properties, Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (GO), offers a wide range of possibilities to produce nano-filters containing graphene membrane which is capable to remove ninety percent of the heavy contaminants from different sources of water and to reduce the level of total dissolved solids, salinity, and neutralizes the pH level further inorganic membrane used in synergism with graphene oxide shows improved efficiency and reduction in cost of production of separation membranes. In this review, we demonstrated real world application of graphene, Fabricated with Several Metal Oxides in synergism to illustrate enhanced photocatalysis properties, Flexural strength and anti-fouling characteristics of the material in comparisons to conventional membrane, photocatalytic metal oxides nanoparticles such as Titania TiO2, Zirconia ZrO2, Alumina Al2O3, and Silica SiO2 functions in the presence of Multiple Spectrums of Light by absorbing photons and releasing Oxygen Radical which degrades harmful water pollutants into less harmful substances.

Protection of 304 stainless steel by nano-modified silicone coating in cyclically alternate corrosion environment

A nano-modified silicone-based composite coating was developed to protect 304 stainless steel under a cyclically alternate corrosion condition. Each cycle contained alternate exposure in a neutral salt spray test chamber at 35 °C and in a muffle furnace at 400 °C. The results showed that the corrosion of 304SS was serious. The nano-modified silicone coating, which is composed of a continuous amorphous SiO2 matrix, dispersive Al, Al2O3, TiO2 and ZrO2 particles and discrete voids after the cyclically alternate corrosion, are inert at 400 OC in the environment containing NaCl deposit and oxygen and significantly improved the corrosion resistance of the 304SS.

Ablation behavior and mechanisms of 3D Cf/ZrB2-SiC composite applied in long-term temperature up to 2400 °C

To evaluate the long-term ablation behavior and mechanism of carbon fiber reinforced ultra-high temperature ceramics, 3D Cf/ZrB2-SiC composite with homogeneous architecture was prepared via vibration-assisted slurry impregnation combined with precursor infiltration and pyrolysis. The intact structure of sample was remained owing to the triple oxide layers after ablation at Tmax = 2440 °C for 500 s, a dense ZrO2 layer owing to particle accumulation and sintering, followed by a dense SiO2+ZrO2 layer due to inhibition in diffusion of glassy SiO2 and next porous ZrO2 layer, leading to superior ablation resistance with linear and mass ablation rates of 1.8 × 10−4 mm/s and 1.08 × 10-5 g/mm2·s, respectively.

High-temperature diffraction experiments and phase diagram of ZrO2 and ZrSiO4

Abstract High-temperature X-ray diffraction (XRD) experiments up to T = 2710 °C have been performed on ZrSiO4 and ZrO2 powders, using the container-less levitation technique. A two-dimensional imaging plate (IP) detector was used for short-time observation. The diffraction data in a wide area was projected in one dimension. The unit cell parameters, thermal expansions, and c/a ratios for ZrSiO4 (space group I41/amd and Z = 4), tetragonal ZrO2 (space group P42/nmc and Z = 2) and cubic ZrO2 (space group F m 3 ‾ m $Fm3‾{}m$ and Z = 4) were measured to understand the high-temperature behaviors. The transition temperature between tetragonal and cubic ZrO2 was specified to be between 2430 and 2540 °C. The pre-transitional behavior was observed around 2200 °C. As no clear change in unit cell volume is evident, the phase boundary between the tetragonal and the cubic phase has been shown to be a positive slope. The ZrO2 and ZrO2–SiO2 phase diagrams are proposed based on the chemical composition and the crystal structure.

Fabrication and characterization of bioactive zirconia-based nanocrystalline glass-ceramics for dental abutment

Zirconia-based ceramics are becoming a popular biomaterial in dental implantology due to their natural silver-white color, excellent mechanical properties, and good biocompatibility. However, zirconia-based ceramics are biologically inert, which limits their ability to integrate with the surrounding human tissues. To solve this problem, the bioactive elements of calcium (Ca) and phosphorus (P) were doped in high-strength ZrO2–SiO2 nanocrystalline glass-ceramics (NCGCs) to overcome the biological inertness of ZrO2-based ceramics. XRD results showed that tetragonal zirconia (t-ZrO2) and monoclinic zirconia (m-ZrO2) were the only two crystalline phases after spark plasma sintering. Ca and P dopants acted as destabilizer of t-ZrO2, enhancing its transformability to m-ZrO2 during sintering. The amount of t-ZrO2 exerted significant effects on the average flexural strength of the NCGCs. The NCGC with 45 mol% ZrO2 were composed of 64.5 vol% t-ZrO2 and 35.5 vol% m-ZrO2 after sintering at 1230 °C. And, the average flexural strength and Vickers hardness of the NCGC was 615 MPa and 1049 HV, respectively. In comparison, the NCGC with 65 mol% ZrO2 were composed of 12.6 vol% t-ZrO2 and 87.4 vol% m-ZrO2 after sintering at 1150 °C. The average flexural strength and Vickers hardness of the NCGC was 293 MPa and 839 HV, respectively. Interestingly, the NCGCs exhibited a plastic deformation behavior during flexural strength test, which was different from traditional brittle ceramics. The ion release results demonstrated that Ca2+ and Si4+ ions kept on releasing from the surface of the material. The formation of hydroxyapatite in the in-vitro apatite formation test indicated that the NCGCs had good biological activity. The doped ZrO2-based NCGCs combined moderate strength and good bioactivity. Hence, the NCGCs show promising potential to be used in sub-gingival regions, such as dental abutments.

Ablation behavior of SiC whisker and ZrB2 particle-filled ZrO2 sol-gel composite coating under high-intensity continuous laser irradiation

In this study, laser ablation-resistant composite coating consisting of zirconium diboride (ZrB2) particulate and silicon carbide (SiC) whisker with zirconia (ZrO2)-sol binder was prepared to meet requirements of anti-laser ablation ability. Laser ablation behavior of as-prepared coating was investigated under varying laser powers. Results revealed that the highest back-surface temperature of coated aluminum substrate was only 150 °C when irradiated at a power density of 6.3 kW/cm2 for 10 s, which is below the maximum allowable temperature of the aluminum alloy substrate (200 °C). After ablation for 10 s, the mass ablation rate of the composite coating was 4.45 mg/s. Apparently, the composite coating exhibited outstanding ablation resistance against high-intensity continuous laser irradiation. At initial stage of ablation, combination of self-healing effect of liquid ZrO2–SiO2 layer and volatilization of B2O3 provide effective joint protecting mechanism. With increasing ablation time, ZrO2 ceramic barrier layer, product of the pyrolysis of ZrO2 gel and ZrB2 filler, becomes progressively more important in maintaining excellent laser ablation resistance behavior, which is normally effective at around ablation pit.

Using a 3D Computer Model of the T–x–y Diagram of the ZrO2–SiO2–Al2O3 System to Resolve Contradictions in the Initial Experimental Data

Using a 3D Computer Model of the T–x–y Diagram of the ZrO2–SiO2–Al2O3 System to Resolve Contradictions in the Initial Experimental Data

Core-shell structured SiO2@ZrO2@SiO2 filler for radiopacity and ultra-low shrinkage dental composite resins

To overcome the interfacial problem between X-ray radiopaque ZrO2 fillers and polymer resin in dental composites, monodispersed SiO2@ZrO2@SiO2 (SZS) microspheres with narrow size distribution were prepared by a controlled sol-gel method. In the presence of SiO2 coating layer over SiO2@ZrO2 (SZ) microspheres, they were easily silanized same as SiO2 microspheres. Ethoxylated bisphenol A dimethacrylate (EBPADMA) with a higher molecular weight and a lower viscosity was used as base resin monomer mixed with a low amount of diluent triethylene glycol dimethacrylate (TEGDMA). Additionally, the addition of a small amount of pore agent acetone dicarboxylic acid (ADCA) produced some voids, thereby effectively reducing the polymerization shrinkage of the resin. The prepared dental composites combining 52 wt% monodispersed silica microsphere, 20 wt% SZS microspheres, exhibited significantly enhanced capacity in radiopacity (higher than tooth enamel) and very low shrinkage (<0.1%). It also has better mechanical properties than resin composites filled with SiO2 microspheres, and its strength can meet practical applications. The properties of the radiopaque dental composite were to be further tuned by varying the amount of SZS microspheres contents, and the radiopaque resin has an advantage over the commercial one in that it is clinically nondestructive.

Enhanced AC magnetic properties of Fe-based soft magnetic composites coated with an electrically insulated SiO2–ZrO2 layer

Enhanced AC magnetic properties of Fe-based soft magnetic composites coated with an electrically insulated SiO2–ZrO2 layer

Effect of the crystalline layer on the electrical behaviour of 17.7Li2O·5.2ZrO2·68.1SiO2·9.0Al2O3 glass ceramic monoliths

Li2O–ZrO2–SiO2–Al2O3 (LZSA) glass ceramic systems are usually obtained from powder technology to obtain materials with a low thermal expansion coefficient (CTE). However, in these cases, there is a high residual porosity. An alternative to reduce the porosity involves the production of monoliths. Nevertheless, there is still a lack of crystallisation kinetics and the final properties of glass ceramic monoliths are affected such as electrical properties. This study aims to evaluate the electrical behaviour as function of the crystalline layer thickness formed on the monolith surface of a 17.7Li2O·5.2ZrO2·68.1SiO2·9.0Al2O3 (molar basis) glass ceramic LZSA composition. Monoliths thermally treated at 750, 800, and 850 °C were chosen to evaluate based on the range of the crystalline layer growth. Electrochemical impedance spectroscopy was used for the electrical characterisation of LZSA glass and the glass ceramics. The resistivity increased with increasing thermal treatment temperature due to the formation of lithium-based crystalline phases. The electrical conductivity at 25 °C of the glass ceramic thermally treated at 850 °C decreased to 1.4 × 10−13 S cm−1 from 8.7 × 10−11 S cm−1 for LZSA glass. Based on the electrical behaviour, monoliths thermally treated at 850 °C can be considered potential for dielectric industrial applications.

Sol–Gel Waveguide-Based Sensor for Structural Health Monitoring on Large Surfaces in Aerospace Domain

The potential of sol–gel-based optical sensors is investigated for applications in the aerospace domain. To this aim, a low-cost and non-intrusive sol–gel sensor based on waveguides, arranged as a 2D matrix structure, is fabricated by UV photolithography for delamination and damage detection. Two different organic–inorganic sol–gels were selected to fabricate the photonic device: TiO2–SiO2 and ZrO2–SiO2, acting as the waveguide core and the cladding, respectively. A systematic study was performed to determine the manufacturing parameters controlling their properties. The results show that large surfaces can be functionalized via sol–gel methods using the direct laser-writing approach. The structures are characterized in terms of refractive index, and the guiding properties were investigated through simulations and experiments, indicating an excellent behavior regarding the light guidance in a straight waveguide or in the 2D matrix structure grid. Additionally, preliminary tests show that the presence of impact can be easily detected after damage through the induced optical losses on large surfaces. This proof of concept sensor is a promising tool for structural health monitoring. To achieve the ultimate goal, the integration of this photonic sensor will be later performed on aircraft wings.

Microstructure and Ablation Behavior of W/ZrC/SiC Coating on C/C Composites Prepared by Reactive Melt Infiltration and Atmospheric Plasma Spraying

A W/ZrC/SiC multilayer coating is prepared on carbon/carbon (C/C) composites by reactive melt infiltration (RMI) and atmospheric plasma spray (APS). The morphology and microstructure of the coating are characterized by scanning electron microscopy coupled with energy dispersive spectrometry (SEM‐EDS), X‐ray diffraction (XRD), and focused ion beam (FIB) and transmission electron microscopy (TEM). Microstructure analysis reveals that the gradient coatings exhibit smooth surface morphology, well‐defined interfaces, uniform thickness, and a highly dense architecture. After 60 s of ablation, the linear ablation rates (LARs) and mass ablation rates (MARs) of the coated composites stand at 2.58 × 10−3 mm s−1 and 5.25 × 10−3 g s−1, respectively. In general, the reason for the great ablation resistance of W/ZrC/SiC‐coated C/C composites is the comprehensive effect of the multilayer coating. The outer W coating is used as the first barrier layer to resist most thermal shocks. Then, the molten eutectics SiO2–ZrO2 formed in the ZrC/SiC layer at service temperature can fill the pores and act as a second diffusion barrier for oxygen and heat.