ZrO2 Nanocomposite Powder Research Articles

In situ self-assembly preparation and characterization of CaO–ZrO2 nanopowders under vacuum

CaO–ZrO2 nanocomposite powders were prepared by in situ self-assembly method under vacuum. The effects of calcium oxide content on the physical phase composition and microscopic morphology of the as-prepared nanopowders were investigated. The results showed that the content of the tetragonal phase in the powders gradually increased with increasing calcium oxide content. When the calcium oxide content reached 10 wt%, the prepared CaO–ZrO2 nanopowders were a pure tetragonal phase with good dispersion and average particle size about 57 nm. In comparison to the situation in air, the amorphous carbon particles formed by the pyrolysis of organic matter under vacuum were evenly distributed on the surface of the nanocomposite particles or between them. In this way, direct contact of the nanoparticles was avoided, thus inhibiting their rapid growth at high temperatures and facilitating the formation of fine grains with high surface energy. The preliminary results indicated that the smaller average particle size and narrower particle size distribution of the nanocomposite powders prepared in vacuum were significantly beneficial for improving the bending strength of the nanoceramic products compared to that in air. It is expected to provide valuable information for further optimization of the controllable preparation of high-quality nanoceramic powders.

Formation mechanism and phase transformations in mechanochemically prepared Al2O3-40wt% ZrO2 nanocomposite powder

ABSTRACTZirconia dispersed alumina nanocomposite powder has been synthesized by mechanochemical technique using inorganic reagents. The reactions were designed in a way to achieve 40wt% zirconia. Differential thermal analysis (DSC)/Thermogravimetric (TG), Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction study (XRD) along with Rietveld analysis was applied at different stages to obtain information on phase transformations and mechanisms in the temperature range of 400–1300 °C. The analysis revealed that Al2O3 and ZrO2 do not form by direct displasive reactions. In this system the CaO present in the milled powder mixture absorbs the HCl formed by the hydrolysis of the AlCl3 and ZrCl4 powders present in the milled powder mixture and helps in the completion of the reactions. The milled ZrCl4 and AlCl3 powders initially convert into amorphous Zr(OH)4 and crystalline bayerite (Al(OH)3) phases at 350 °C respectively and later decompose to their respective oxides at different stages upon the subsequent heat treatment. Upon heating, the intermediate hydroxide phases lose water and convert to nanostructured powders. The following phase transformations sequences are suggested for the aluminum and zirconium powders:The formed hydroxide phases and the phase transformation sequences for the alumina and zirconia powders obtained by this method is different from individually prepared alumina and zirconia powders reported by others. This finding is due to the effect of milling the powders together.

Thermal evolution of Fe - ZrO2 nanocomposite: Insights from calorimetric and microscopy investigations

This article presents the results of an experimental study on the evolution of phases during annealing of ball milled Fe – ZrO2 nanocomposite powder using Differential Scanning Calorimetry, X-ray Diffraction and Electron Microscopy techniques. The formation of FeO phase from Fe and Fe3O4 is identified through Differential Scanning Calorimetry and confirmed using Synchrotron Diffraction and Transmission Electron Microscopy. Qualitative X-ray phase analysis showed the stoichiometry of the FeO phase as Fe0.87O. This phase is expected to be beneficial as it offers strengthening in the Fe matrix and is thermally stable. The activation energy of formation of the Fe0.87O phase was estimated to be ~195kJmol−1. This phase is also found to be partially stabilizing the cubic phase of ZrO2, at high temperatures. A cubic⇆tetragonal transformation of ZrO2 was identified at 1140K. A rather broad peak was observed for Fe α→γ transformation in the Calorimetry thermograms as the Fe grains were nanocrystalline which became sharper as the crystallites grew in size.

Extremely fine structured cathode for solid oxide fuel cells using Sr-doped LaMnO3 and Y2O3-stabilized ZrO2 nano-composite powder synthesized by spray pyrolysis

A solid oxide fuel cell (SOFC) for high power density operation was developed with a microstructure-controlled cathode using a nano-composite powder of Sr-doped LaMnO3 (LSM) and Y2O3-stabilized ZrO2 (YSZ) synthesized by spray pyrolysis. The individual LSM-YSZ nano-composite particles, formed by crystalline and amorphous nano-size LSM and YSZ particles, showed spherical morphology with uniform particle size. The use of this powder for cathode material led to an extremely fine microstructure, in which all the LSM and YSZ grains (approximately 100–200 nm) were highly dispersed and formed their own network structures. This microstructure was due to the two phase electrode structure control using the powder, namely, nano-order level in each particle and micro-order level between particles. An anode-supported SOFC with the LSM-YSZ cathode using humidified H2 as fuel and ambient air as oxidant exhibited high power densities, such as 1.29 W cm−2 under a voltage of 0.75 V and a maximum power density of 2.65 W cm−2 at 800 °C. Also, the SOFC could be stably operated for 250 h with no degradation, even at a high temperature of 800 °C.

Effect of the addition of different sintering aids on the densification behavior of zirconia-toughened alumina nanocomposite powder

AbstractIn the present study, Al2O3-5 wt.% ZrO2 nanocomposite powder was fabricated via the sol–gel method, and then the sintering behavior was investigated using various sintering aids (MgO, TiO2 and MgO/TiO2) at different temperatures. In this regard, the size and structure of fabricated powder, and hardness, fracture toughness and density of sintered samples were studied. The results of X-ray diffraction indicated the presence of α-alumina and tetragonal zirconia. Scanning electron micrographs revealed agglomerated nanometer-sized spherical particles ranging in size from 60 to 150 nm. Energy-dispersive X-ray mapping micrographs also demonstrated the homogeneous dispersion of zirconia in alumina. Moreover, density results indicated that using 0.5 wt.% MgO/0.5 wt.% TiO2 produced the best results, as the relative density reached 95 % at 1 500 °C. Finally, it was observed that the presence of MgO and TiO2 induces higher hardness and lower fracture toughness.

Synthesis and characterization of Fe-15 wt.% ZrO2 nanocomposite powders by mechanical milling

Fe-15wt.% ZrO2 nanocomposite powder was synthesized via mechanical milling with an aim to study the morphology of the powder particles and refinement of the oxide and Fe crystallites during milling. Detailed microstructural and microchemical investigations were carried out in order to optimize the milling condition and to highlight the advantages for the choice of ZrO2. A homogeneous mixture was confirmed by X-ray mapping and ZrO2 dispersoids were observed to retain crystallinity even after 100h of milling. It was also observed that both Fe and ZrO2 crystallites refine to very fine nanocrystalline (nc) sizes after such milling. The result has 2-fold significance: (a) Yttria, which is a standard dispersoid in oxide dispersion strengthened (ODS) steels, usually amorphised under similar conditions, which is detrimental to its structural stability and (b) nanocrystallites of Fe have useful magnetic properties. Modified Williamson–Hall technique (mod. W–H) was employed to measure the size and dislocation density of the matrix ferrite phase. Nanoindentation technique was used to evaluate the nanohardness of the milled powder as a function of milling duration.

Influence of TiO<sub>2</sub> and ZrO<sub>2 </sub>Nano Particles Addition in Al<sub>2</sub>O<sub>3</sub> Base Coating Using Plasma Spraying

The additive (3wt%) nano-particles of anatase-TiO2 and monoclinic-ZrO2 were prepared using ball-milling method to form Al2O3/3wt%TiO2 and Al2O3/3wt%ZrO2 nanocomposite powders. The incorporation of nano-particles can significantly enhance the microstructure and mechanic properties of Al2O3-base coating. The phase of microstructure coating was present mostly of γ-Al2O3 and α-Al2O3 phases, while anatase-TiO2 was transformed to rutile-TiO2 and monoclinic-ZrO2 was changed to tetragonal-ZrO2 due to such high temperature of plasma plume. SEM microstructures of the coatings mainly displayed a lamellar structure of Al2O3 with interlarmellar pores and well dispersed splats of TiO2 and ZrO2 phases. The Al2O3/3wt%ZrO2 presented the lowest value of friction coefficient and sliding wear rate. It was found that the plasma-sprayed composite coating possessed better wear resistance than that of monolithic Al2O3 coating. The addition of nano-particles was found to improve friction coefficient and sliding wear resistance.

Characterization of the Near-Eutectic Al2O3–40 wt% ZrO2 Composite Coating Fabricated by Atmospheric Plasma Spray. Part I: Preparation and Characterization of Nano Al2O3–ZrO2 Powder Using Sol–Gel Method

Al(NO3)3·9H2O, ZrOCl2·8H2O, and NH4OH solution were used as starting materials to synthesize Al2O3-40 wt% ZrO2 nano composite powder for plasma spraying by sol–gel method. The results showed that δ-Al2O3 and θ-Al2O3 transformed to α-Al2O3 gradually with the heating temperature rising from 900°C to 1200°C, and only α-Al2O3 existed when the temperature reached 1200°C, while m-ZrO2 and t-ZrO2 coexisted in the system. Meanwhile, the content of m-ZrO2 went up dramatically with the rise of heating temperature and holding time. When the xerogel was heated below 1100°C with the holding time lower than 8 h, the grain size of obtained powder was less than 100 nm. In addition, the grain size of composite powder was more than 100 nm and the growth rate of α-Al2O3 was much larger than that of t-ZrO2 when the heating temperature was raised to 1200°C.

Synthesis and characterization of Al2O3–ZrO2 nanocomposite powder by sucrose process

Nanocrystalline alumina–zirconia powders were prepared by a modified chemical route using sucrose, polyvinyl alcohol (PVA) and metal nitrates followed by a post calcination process. The process involved dehydration of Al3+–Zr4+ ions-sucrose–PVA solution to a highly viscous liquid which on decomposition process produced a black precursor material. The obtained precursor were then calcined at various temperatures: 1,050, 1,100, 1,150, 1,200 and 1,250 °C for different soaking times (1, 2, 4 h) in air. The formation of a nanocomposite composed of α-alumina (~20 nm) and tetragonal (t) zirconia (~19 nm) crystallites were confirmed for the sample calcined at 1,200 °C for 2 h, based on our XRD and TEM results. However, for the samples calcined below 1,150 °C the composite formed were composed of metastable alumina (γ, δ, θ) as well as t-zirconia phases. Interestingly, the zirconia phase retained its tetragonal structure for all the samples calcined above 1,050 °C. This is possibly related to the “size effect” and reduction of surface enthalpy of the zirconia crystallites surrounded by Al3+ cations.

Magnetic properties and grain growth stability of nanocomposite Fe–ZrO2 granular solids prepared by mechanical milling

Correlations between the grain size [or the diffracting particle size (DPS)] and the magnetic properties of mechanically milled Fe–ZrO2 nanocomposite powders are reported. Nanocomposite powders with iron volume fractions below, near, and above the percolation value were annealed at temperatures between 573 and 1083 K and investigated. The composite as-milled powders exhibited enhanced coercivities (≳300 Oe) compared to similar mechanically milled iron powders. The iron diffracting particle size (grain size) as a function of annealing temperature showed two regimes. The first regime, corresponding to temperatures at and below 773 K, consisted of enhanced coercivities and remanence ratios with a relatively stable iron diffracting particle size of ∼25 nm. In the second temperature regime, above 773 K, the DPS increased, but remained well below the value for pure iron. Concomitant with this increase, large reductions in the coercivities were observed in the second regime.