Tetragonal ZrO2 Phase Research Articles

Visible Light Assisted Photocatalytic Degradation of Methylene Blue Dye and Mixture of Dyes Using ZrO2-TiO2 Nanocomposites

Background: Different photocatalysts such as TiO2, ZnO and WO3 have been used for the degradation of organic pollutants. However, these materials have some limitations, which have been affected the catalytic efficiency in the various transformations. The composites of these materials with other oxides can produce better results by tuning structural as well as optoelectrical properties. The composite of TiO2 with ZrO2 has attracted attention due to its use in different areas, as ZrO2 and TiO2 have similar physicochemical features. Methods: This research contains the preparation of ZrO2-TiO2 nanocomposites by hydrothermal method and analysis of photocatalytic activity for the degradation of methylene blue and a mixture of dyes under visible light irradiation. Results: Physicochemical characterization of ZrO2-TiO2 nanocomposites has been studied by using different techniques. Prepared catalysts has shown anatase phase of TiO2 and tetragonal phase of ZrO2. XRD, FESEM and HRTEM have supported the nanocrystalline nature of the composites. The photocatalytic activity of composites and bare TiO2 samples were demonstrated for the degradation of methylene blue dye. Enhanced activity has been shown by composite having Ti:Zr 3:1 molar proportion, i.e., Ti3Zr. Effect of concentration of methylene blue, pH of the solution and catalyst loading have been studied by using Ti3Zr. In addition, the degradation of a mixture of three dyes, namely methylene blue, rhodamine B and methyl orange, has been studied. Conclusion: In summary, prepared ZrO2-TiO2 composites found to be nanocrystalline and visible light active. These catalysts have shown activity for photocatalytic degradation of methylene blue and a mixture of dyes.

Mesoporous zirconia surfaces with anti-biofilm properties for dental implants

Cytocompatible bioactive surface treatments conferring antibacterial properties to osseointegrated dental implants are highly requested to prevent bacteria-related peri-implantitis. Here we focus on a newly designed family of mesoporous coatings based on zirconia (ZrO2) microstructure doped with gallium (Ga), exploiting its antibacterial and pro-osseo-integrative properties. The ZrO2 films were obtained via sol–gel synthesis route using Pluronic F127 as templating agent, while Ga doping was gained by introducing gallium nitrate hydrate. Chemical characterization by means of x-ray photoelectron spectroscopy and glow discharge optical emission spectroscopy confirmed the effective incorporation of Ga. Then, coatings morphological and structural analysis were carried out by transmission electron microscopy and selected area electron diffraction unveiling an effective stabilization of both the mesoporous structure and the tetragonal ZrO2 phase. Specimens’ cytocompatibility was confirmed towards gingival fibroblast and osteoblasts progenitors cultivated directly onto the coatings showing comparable metabolic activity and morphology in respect to controls cultivated on polystyrene. The presence of Ga significantly reduced the metabolic activity of the adhered oral pathogens Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans in comparison to untreated bulk zirconia (p < 0.05); on the opposite, Ga ions did not significantly reduce the metabolism of the oral commensal Streptococcus salivarius (p > 0.05) thus suggesting for a selective anti-pathogens activity. Finally, the coatings’ ability to preserve cells from bacterial infection was proved in a co-culture method where cells and bacteria were cultivated in the same environment: the presence of Ga determined a significant reduction of the bacteria viability while allowing at the same time for cells proliferation. In conclusion, the here developed coatings not only demonstrated to satisfy the requested antibacterial and cytocompatibility properties, but also being promising candidates for the improvement of implantable devices in the field of implant dentistry.

Preliminary In Vitro Wear Assessment of Ceramic Cemented Femoral Components Coupled with Polyethylene Menisci.

Success of total knee replacement (TKR) depends on the prosthetic design and materials. The use of metal components is well established with the disadvantage of allergic reactions. Ceramics have been recently proposed because of high wear resistance, excellent biocompatibility, wettability, and suitable mechanical properties. This study was aimed at investigating in vitro wear resistance of Zirconia Toughened Alumina (ZTA)/Ultra-high-molecular-weight polyethylene (UHMWPE) of TKR femoral components. An in vitro protocol was designed with the application of relevant load profile, 6-degrees-of-freedom knee simulator, and 8 × 105 cycles on the ZTA/UHMWPE configuration under bovine calf serum. Before and after wear test, the femoral components were investigated by using the Scanning Electron Microscope (SEM) and the X-Ray Diffraction (XRD) analyses, and stylus surface roughness measurements. The proposed pre-clinical test yielded repeatable results. In particular, gravimetric results showed that, after 8 × 105 cycles, the mean weight loss of the polyethylene mobile components is 5.3 ± 1.1 mg. The surface roughness measurements (Ramax) performed after the wear test showed no significant variation on the UHMWPE menisci. A slight increase of roughness has been found on the ZTA (0.02 µm before wear test, 0.28 µm after the test). SEM observations did not show significant modification of the surface morphology. Tetragonal to monoclinic phase ratio was measured by XRD before and after wear test to evaluate stability of tetragonal ZrO2 phase. Minimal conversion of tetragonal to monoclinic phase was found from 5.4 to 8%. Although this study is a preliminary evaluation limited to in vitro tests, it provides novel pre-clinical indications about the potential of ceramic TKR femoral components.

Influence of different plasma spraying methods on the physical properties of YSZ coatings

Yttria-stabilized zirconia (YSZ) coatings were deposited at various arc currents of atmospheric plasma spraying. Two different technological configurations were used to form YSZ coatings; in first case, the plasma torch moved along the coated surface, while in another case, the coatings were formed on rotating substrate surface placed in front of the plasma torch. The thermal tests of the YSZ coatings were performed at temperature of 800 °C for 10 min. The surface morphology, elemental composition, phase structure and microhardness of YSZ coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Vickers indentation, respectively. It was obtained that the increase of the arc current from 180 A to 240 A enhanced the oxidation of the surface of the YSZ coatings. The XRD results indicated that the as-sprayed coatings consisted of the tetragonal ZrO2 phase. The YSZ/substrate ratio increased steadily from 0.05 to 4.4 (before the thermal effect) with the increase of the current from 160 A to 240 A, when coatings were sprayed on the rotating substrates. However, neither the substrate position nor the thermal effect influences the phase structure of the YSZ coatings. The YSZ coatings sprayed on the rotating substrates were less porous, had lower amount of micro or macro cracks, demonstrated higher adhesion and better resistance to the thermal impact compared to the YSZ coatings deposited on the immobile substrates.

The crystal and electronic structures, dynamical stabilities and thermal properties, elastic constants and mechanical stabilities, Born effective charges and dielectric constants of a novel tetragonal ZrO2 phase: First-principles calculations

Among six ZrO2 phases, the tetragonal ZrO2 with space group P42/nmc (D4h15, No. 137) (termed as t-ZrO2-I) has the largest average dielectric constant, but its highest elastic anisotropy easily makes a stress concentration and micro-crack and thus the lower mechanical strengths. In this paper, using first-principles calculations, we explore the crystal and electronic structures, dynamical stabilities and thermal properties, elastic constants and mechanical stabilities, Born effective charges and dielectric constants of a novel tetragonal ZrO2 with space group P42/mnm (D4h14, No. 136) (termed as t-ZrO2-II). The larger average dielectric constant, the higher yield, plastic and fracture strengths, the smaller elastic anisotropy and thus the smaller stress concentration and less micro-crack, the mechanical and dynamical stabilities show the novel t-ZrO2-II is a better dielectric and structural material than t-ZrO2-I reported previously.

Microstructural and mechanical characteristic of ceramic composite coating developed by electrophoretic deposition

Ceramic-composite coating consisted of Yttria Stabilized Zirconia (YSZ), Fe2O3 and aluminum powder has been successfully formed on Inconel 625 substrate by electrophoretic deposition (EPD). The coating density depends not only on the stability of the EPD suspension but also on the applied voltage. In the present study, a single stage voltage treatment at 60V and a two-stage voltage treatment at 30V followed by 60V of the EPD were used. A fresh green body of ceramic coating was dried at room temperature for 24 hours prior to heat-treated at temperature of 1200 °C for 4 hours with heating rate of 2°C/min using horizontal heated furnace under argon gas inert. The effect of single- and two-stage treatments on the microstructural and mechanical hardness of the coating were investigated by Field Emission-Scanning Electron Microscopy and Vickers hardness test, respectively. The elemental composition of the coating was analysed by Energy Dispersive Spectroscopy and the crystalline phases were identified by x-ray diffractometer. The results showed that a less porous structure, and therefore, higher hardness was observed on the coating formed by a two-stage voltage than that of resulting from a single-stage voltage. The crystalline phase formed on the coatings was dominated by a tetragonal phase of ZrO2.

Influence of sintering parameters on the microstructure and mechanical properties of nanosized 3Y-TZP ceramics

The fracture toughness of 3Y-TZP ceramics obtained from a nanocrystalline powder with an optimized microstructure and highly transformable tetragonal grains was investigated. Samples of ZrO2-3 mol% Y2O3 were sintered at temperatures between 1250 and 1400 °C, with isothermal holding times of up to 16 h. Samples sintered at 1250 °C exhibited relative densities ranging between 92% and 98%, which increased with increasing isothermal duration, while samples sintered at 1300, 1350, or 1400 °C achieved densification higher than 98% for all isothermal treatments. Crystallographic analysis indicated the presence of a highly transformable ZrO2-tetragonal phase (c/a√2=1.0148-1.0154) for all conditions studied. The average grain size ranged from 0.18±0.04 mm (1250 °C-0 h) to 0.64±0.08 mm (1400 °C-16 h), indicating activation energy of 141.3 kJ/mol for grain growth and a growth exponent of 2.8. Both Vickers hardness (1025 to 1300 HV) and fracture toughness (4.0 to 7.8 MPa.m1/2) increased with increasing sintering temperature and time due to increased densification, reduced porosity, and maintenance of potentially high fracture toughness by the t→m phase transformation.

Formation of nano‐ZrO2 by laser surface treatment of ZrB2‐SiC–based composite

AbstractThis study aims at reducing the oxidation by forming a prior‐protective‐oxide scale by laser‐surface‐treatment of two ZrB2‐SiC based composites namely ZrB2‐20v/oSiC‐2v/oB4C‐0.24v/oCf (ZSC) and ZrB2‐20v/oSiC‐2v/oB4C (ZS). ANSYS 15.0 was used to determine laser processing regime. Rigorous theoretical calculations provided temperature distribution, laser parameters and resulting laser power densities required to produce tetragonal ZrO2. Both the theoretical prediction as well as experimentation show that the laser‐surface‐treatment with the laser power densities of 31.85 and 56.61 W/mm2 for 20 and 30 s render formation of nano‐tetragonal‐ZrO2 (100–130 nm) at room temperature (RT). Morphology and size of the nano‐tetragonal‐ZrO2 grains depends on the laser exposure time. Nano‐grain size helps in stabilizing tetragonal ZrO2 phase at RT without the need of Y2O3 addition. Nano‐tetragonal‐ZrO2 may facilitate better ability for pegging, prevent scale‐spallation and act as thermal barrier coating (TBC).

XRD study of ceria stabilized zirconia (CSZ) microsphere synthesized by external gelation

Ceria stabilized zirconia microsphere has been synthesized by external gelation. XRD investigations were carried out at each thermal treatment to study the process of zirconia oxide formation. The diffraction patterns at thermal treatment 60°C, 120°C and 200°C still appeared to be broadening because there were still amorphous hydrocarbon compounds. The peak of diffraction started to look at 400°C although it was always broadening, this was because the oxide has begun to form but has not crystallized. Perfect crystallization appears on heat treatment at 1200°C as the tetragonal ZrO2 phase.

Hydrothermally prepared Ag-CeZrO2 nanocomposite for efficient diesel soot oxidation

Air pollution caused by diesel soot emission, is a serious environmental issue. In order to prevent the soot being released into the atmosphere, the catalyzed combustion of the soot trapped in diesel particulate filter (DPF) is performed, normally at high temperature. Among different noble metal dopants, Ag is effective in decreasing the active temperature, which can catalyze graphitic oxidation by penetrating into bulk graphite. The optimum 5 wt% Ag loading in Ag-ZrO2NPs were reported earlier. In our previous study, we demonstrated the catalytic properties of Ag-ZrO2 nanoparticles (NPs) with optimum 0.9 wt% Ag loading, which showed its cost effectiveness when compared with the high cost of Ag noble metal. The catalytic oxidation peak position declined gradually 455 °C to 399 °C with corresponding sintered temperature from 400 °C to 800 °C respectively.In this study, further decrease in soot oxidation temperature (387 °C) was achieved by incorporating ceria into the Ag-ZrO2 system (Ag-CeZrO2). A facile hydrothermal synthesis method was utilized for preparation of Ag-CeZrO2 nanocomposites. After the incorporation of ceria to Ag-ZrO2 system, the tetragonal phase of ZrO2 was observed instead of multi phases (tetragonal and monoclinic) ZrO2. In the present study, the soot combustion behavior of Ag-ZrO2 and Ag-CeZrO2 catalysts is described in details..

Molecular dynamics simulation of phase transition by thermal spikes in monoclinic ZrO&lt;sub&gt;2&lt;/sub&gt;

Owing to its excellent corrosion, radiation and high temperature resistance, ZrO&lt;sub&gt;2&lt;/sub&gt; has been considered as a strong candidate material for inert fuel for the incineration of actinides. In this paper, a combination of thermal spike model and molecular dynamics is used to simulate the phase transition process of ZrO&lt;sub&gt;2&lt;/sub&gt; in the nuclear radiation environment. Based on the thermal spike model, two coupled diffusion equations are established with considering the multiple physical process of energy deposition and transmission after the implantation of swift heavy ions into target material. The space-time evolution characteristics of ZrO&lt;sub&gt;2&lt;/sub&gt; lattice temperature are obtained by solving the coupled diffusion equations numerically. Then the phase transformation of ZrO&lt;sub&gt;2&lt;/sub&gt; form monoclinic phase to tetragonal phase under the thermal spike is investigated on an atomic scale by means of molecular dynamics. It is found that a cylindrical track with a radius of 7 nm is generated in the center of ZrO&lt;sub&gt;2&lt;/sub&gt; after the implantation of swift heavy ion with an electronic energy loss of 30 keV·nm&lt;sup&gt;–1&lt;/sup&gt;. The lattice melts immediately in the center of track, accompanied with the coordination number of Zr decreasing from 7 to 4–6. Then at about 2 ps, the melting zone gradually turns cool and recrystallized. And in the center of the melting zone, voids begin to form and are surrounded by a highly disordered amorphous region. Meanwhile, tetragonal phase of ZrO&lt;sub&gt;2&lt;/sub&gt;, whose coordination number of Zr is 8, is formed at the periphery of the amorphous region, which is also confirmed by the XRD calculation results. As energy transfers from track center to the surround, the tetragonal region gradually develops into the whole system, accompanied with the increase of voids size. The simulation results indicate that the irradiation of ZrO&lt;sub&gt;2&lt;/sub&gt; with swift heavy ions can lead to a transformation from the monoclinic to the tetragonal phase when the deposited electronic energy loss exceeds an effective threshold ~21 keV·nm&lt;sup&gt;–1&lt;/sup&gt;, greater than the experimental value (12 keV·nm&lt;sup&gt;–1&lt;/sup&gt;), which was mainly due to the large difference between the simulated and measured incident ion fluences and the accuracy of the force field used in the molecular dynamics.

Thermal stability of atmospheric pressure plasma jet-deposited ZrO2 top coats and sputtered RuAl/RuAlZr/Ru bond coats on Inconel 617

In this study, the feasibility of using ZrO2 coatings, fabricated through the atmospheric pressure plasma jet technique, as top coats in thermal barrier systems was explored. Inconel 617 was used as the substrate material, and sputtered laminated RuAl/RuAlZr/Ru was used as the bond coat. >20-μm-thick ZrO2 coatings were deposited through several iterations of deposition at 500 °C and annealing at 600 °C; here, ZrO2 existed in the tetragonal phase. The tetragonal ZrO2 was stable after annealing at up to 700 °C but transformed into a mixture of tetragonal and monoclinic ZrO2 phases when annealed at >800 °C. The thermal stability of the ZrO2/RuAl/RuAlZr/Ru/Inconel 617 assembly was evaluated at 800–900 °C in air. The variations in volumetric fractions of the tetragonal and monoclinic ZrO2 phases were recorded; 44% of the tetragonal phase remained after 100 h of annealing at 800 °C, whereas 80% of the tetragonal phase had transformed into the monoclinic phase after 4 h of annealing at 900 °C. Observation of BC after annealing at 800 °C indicated that a dense thermally grown oxide scale, comprising O and Al, formed between the ZrO2 and RuAl layers, which impeded the inward diffusion of O. The inhibition of O diffusion declined with the crystallization of the thermally grown oxide scale into the δ-Al2O3 phase when the annealing time was extended.

New MoO3-CeO2-ZrO2 and WO3-CeO2-ZrO2 nanostructured mesoporous aerogel catalysts for the NH3-SCR of NO from diesel engine exhaust

New MoO3 or WO3 modified CeO2-ZrO2 aerogel catalysts were elaborated using the sol gel method combined to supercritical drying for the NO-SCR by NH3 in excess of O2. XRD, N2-Physisorption, NH3-TPD, H2-TPR and DRUV-Vis spectroscopy were used to analyse the samples. The results reveal that all the aerogel powders (ZrO2, CeO2-ZrO2, MoO3-ZrO2, WO3-ZrO2, MoO3-CeO2-ZrO2 and WO3-CeO2-ZrO2), calcined at 500°C, are nanostructured and mesoporous materials, developing essentially the diffraction peaks of the ZrO2 tetragonal phase, which was stabilized by the presence of cerium. Ce, Mo and W species were found highly dispersed on the zirconia surface, their nature and the diverse interactions developed between them affect the crystallites size of ZrO2, acidity, reducibility, surface oxygen mobility of catalysts and influence extremely their SCR activity. Higher NO-SCR performances are obtained, between 200 and 500°C, over the new ternary MoO3-CeO2-ZrO2 and WO3-CeO2-ZrO2 catalysts compared to corresponding binary systems (CeO2-ZrO2, MoO3-ZrO2 and WO3-ZrO2). This discloses a synergism in the NO-SCR related to the existence of strong interactions Ce↔Mo and Ce↔W. Interestingly, above 90 % NO conversions into essentially N2 (≥ 97 %) are achieved between 350 and 500°C over the most efficient MoO3-CeO2-ZrO2 ternary catalyst.

Atomistic Mechanisms of Thermal Transformation in a Zr-Metal Organic Framework, MIL-140C.

To understand the mechanisms responsible for thermal decomposition of a Zr-MOF (MIL-140C), we perform atomistic-scale molecular dynamics (MD) simulations and discuss the simulation data in comparison with the TEM images obtained for the decomposed Zr-MOF. First, we introduce the ReaxFF parameters suitable for the Zr/C/H/O chemistry and then apply them to investigate the thermal stability and morphological changes in the MIL-140C during heating. Based on the performed simulations we propose an atomic mechanism for the collapse of the MIL-140C and the molecular pathways for carbon monoxide formation, the main product of the MIL-140C thermal degradation. We also determine that the oxidation state of the ZrOx clusters, evolved due to the thermal degradation, approximates the tetragonal phase of ZrO2. Both simulations and experiments show a distribution of very small ZrOx clusters embedded in the disrupted organic sheet that could contribute to the unusual high catalytic activity of the decomposed MIL-140C.

Structural elucidation and optical properties of LiZrO2–LiBaZrO3 nanocomposite doped with Mn2+ ions

Nanocomposites of LiZrO2 – LiBaZrO3: xMn2+ (x = 0–0.06 molar ratios) were prepared by the co-precipitation method. The prepared samples were characterized by X-ray diffraction (XRD), UV-visible spectrometry, photoluminescence (PL), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) techniques. Analysis of XRD data shows two phases: the cubic phase of BaZrO3 perovskite and the tetragonal phase of ZrO2. Mn2+ ions were predominantly distributed in the tetrahedral sites and a few ions are situated at the octahedral sites of the composites. UV-visible spectroscopy of these samples presents two optical band energies, decreasing exponentially with increasing concentration of the Mn2+ ion. PL spectra of Mn2+-doped samples display three broad emission bands: a band centered at wavelength,λ =416 nm (blue), another with peak maximum atλ =527 nm (green) and the third (with relatively the lowest intensity) at about 600 nm (orange-red). The blue (λ =416 nm) band was dominant at low Mn2+ concentrations (x≤0.03) but the green band (λ =527 nm) became dominant at higher Mn2+ concentrations (x&gt;0.03). The CIE coordinates revealed colour changes from blue to green at a concentration of 0.05 mole ratio and white light at 0.06 mole ratio. The phosphor presented in this work is a promising material for use in display devices such as flat panel displays, colour plasma displays, signage lights and backlights.

Cooperativity Between Zirconium Dioxide Nanoparticles and Extreme Pressure Additives in Forming Protective Tribofilms: Toward Enabling Low Viscosity Lubricants

Realizing the efficiency benefits of low viscosity lubricants requires novel strategies to avoid failures resulting from increased boundary contact. Zirconium dioxide (ZrO2) nanoparticles (NPs) form protective tribofilms through tribosintering at lubricated contacts in pure hydrocarbon base oils, suggesting they hold promise for reducing boundary contact-induced failures. However, their tribological behavior alongside co-additives found in fully formulated oils has not been examined in depth. Here, the macroscopic tribological performance of dispersed ZrO2 NPs (1 wt% loading; 5 nm diameter nearly spherical ZrO2 tetragonal phase NPs with organic capping ligands for oil solubility) with and without the presence of co-additives found in fully formulated commercial gear oils was studied using a mini-traction machine (MTM). The results show that ZrO2 NPs reproducibly develop surface-bound ~ 100 nm thick tribofilms on both contacting surfaces under a wide range of rolling-sliding contact conditions, from 0 to 100% slide-to-roll ratio. Steady-state traction coefficient values of ZrO2 tribofilms formed alongside co-additives (0.10–0.11) do not substantially differ from ZrO2 tribofilms formed in neat polyalphaolefin base oils (0.10–0.13). However, there is improvement in the tribological performance of the contact, with at least a twofold reduction of wear of the steel. This behavior is proposed to be a result of cooperating mechanisms, where the extreme pressure additives adsorbed on the steel surfaces protect them against early adhesive wear, during the time that a protective ZrO2 tribofilm incorporating the co-additives forms on the steel surfaces, preventing further wear.

Correlation of luminescence and Judd-Ofelt intensity parameters in red ZrO2: Eu3+, Al3+ phosphor: The influences of Al3+ ions

This paper reports findings of synthesis of dual Eu3+/Al3+ doped ZrO2 phosphors (Zr0.99-xO2:0.01Eu3+, xAl3+) to achieve strong red emission, mainly by variation of Al3+(0 ≤ x ≤ 7). Zr0.99-xO2:0.01Eu3+, xAl3+ phosphors were synthesized via a co-precipitation route followed by annealing to 1000 °C in air. We utilized X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence spectra (PL), and Judd-Ofelt (J-O) theory to characterize the obtained Zr0.99-xO2:0.01Eu3+, xAl3+ phosphors for optoelectronic applications. It was found that the Zr0.99-xO2:0.01Eu3+, xAl3+ phosphors were in a tetragonal ZrO2 phase with the size of micro/nanoparticles of approximately 500 nm. The 3.0 mol% Al3+-doped phosphors showed dominant red 5D0→7F2 transitions. With calculations of Judd-Ofelt intensity parameters Ωλ (λ = 2 and 4), it was clear that the red electric dipole transition was pronounced for Zr0.99-xO2:0.01Eu3+, xAl3+ phosphors. The study offers a synthesis method for tetragonal Zr0.99-xO2:0.01Eu3+, xAl3+ red phosphors with strong photoluminescence which was also used for temperature sensing. A maximum relative sensitivity was 2.84% K−1 at 305 K, it also makes these potential candidates for optical temperature sensors.

The Effect of Pressing Load on 8 mol% Yttria Stabilized Zirconia Grade 204NS-G

The aim of this study is to understand the compaction characteristics of as received granulated 8 mol% yttria-stabilized zirconia (8YSZ). The samples were compacted at different loads and sintered at 1550 °C with the heating rate of 5°C/min for 5 hours. The densification, morphology analysis and crystal structure of the sintered were compared. The densification of granulated 8YSZ achieved 67% as increasing pressing load (0.1 tonne to 0.4 tonne). Rietveld quantitative phase analysis demonstrates that the tetragonal-ZrO2 phase reduces in granulated 8YSZ. The amount of cubic-ZrO2 phase dramatically dropped for both granulated as the pressing load increased. From the morphology analysis, granulated sample found to be porous observed on the surface as compaction load applied. Compaction load has no significant effect on the densification of granule sintered 8YSZ in the current study. The maximum densification was only reached 67% by using granulated 8YSZ powder with 0.4 tonne pressing load.

Features of the phase composition, acidity, and isomerization activity of Pt/WO3/ZrO2 catalysts

Textural characteristics, phase composition, and acidic properties of Pt/WO3/ZrO2 catalysts for C7-alkanes isomerization were studied. It was shown that the most active and selective catalysts are samples with WO3 content of 15–25 wt.% with a fraction of the active tetragonal phase of ZrO2 of 73–94 wt.%. It was found that an increase in the number of Bronsted acid sites contributes to an increase in the activity of tungstated zirconia catalysts in the isomerization of n-heptane.

Effect of the iron amount on the physicochemical properties of Fe–ZrO2 aerogel catalysts for the total oxidation of Toluene in the presence of water vapor

In this work, a series of xFe–ZrO2 aerogel catalysts, with different amounts of iron were prepared and tested in the total oxidation of toluene. The xFe–ZrO2 aerogel catalysts obtained demonstrate the diffraction peaks of ZrO2 tetragonal phase and a high surface area and porosity. The iron content influences the physicochemical and catalytic properties of the samples. Among the iron-based catalysts, the one with 5% Fe shows the best activity between 300 and 550 °C with 96% C6H5–CH3 conversion to CO2 at 550 °C.