Yttria Nanopowders Research Articles

Study on Pyrolysis Behavior of Yttrium Oxalate and Kinetic of Yttria Grain Grown

The precursor of yttria was prepared by yttrium nitrate and ammonium oxalate in water solution. Pyrolysis behavior of the precursor and the characterization of yttria phase transformation were studied through thermoanalysis. The grain growth kinetic behavior of yttria nanopowders was investigated by the X-ray powder diffraction (XRD) result of the powders obtained through roasting the precursor. Pattern of the yttria powders and agglomeration of its grain were measured by means of SEM and laser particle size analysis methods. The results suggested that cubic crystal phase yttria could be obtained by sample calcination for 1 h under 823 K. When the precursor was calcined under conditions of temperature ranging from 823 K to 1173 K, yttria grain ranging 7 nm ~ 16 nm could be obtained ,with grain growth exponent of n< 0.2 . In addition , an significant increase in grain-growth-rate constant was observed as the temperature went up. The higher temperature, the faster growth. Grain growth activation energy was different in low-temperature and high-temperature fields. The activation energy was 77.42 kJ•mol-1 when the temperature was lower than 965 K, and became 524.36 kJ•mol-1 when the temperature was higher than 965 K. Yttria powders is highly dispersed whose agglomerates sized about 400 nm after being dispered in deionezed water.

Synthesis of Highly Sinterable Neodymium Ion doped Yttrium Oxide Nanopowders by Microwave Assisted Nitrate-Alanine Gel Combustion

Microwave assisted gel combustion synthesis of neodymium doped yttria (Nd:Y2O3) nanopowders using L-alanine complexing agent is being reported. Gelation of metal nitrates with L-alanine followed by combustion in microwave and subsequent calcinations at 1000°C for 3 h under oxygen supply gave phase pure nanopowders characterized by FTIR and XRD. Highly sinterable Nd:Y2O3 nanopowders with size range 20–80 nm, close to spherical and uniform morphology were obtained as observed by TEM compared to particles in size range 40–160 nm, with polyhedral morphology, obtained by sol-gel route. Compaction of calcined powders by cold isostatic press at 400 MPa followed by sintering at 1700°C for 7 h gave ceramic with 26% transmission which increased to 32% after 10 h without any sintering aid for microwave gel combustion compact, compared to 6.7% transmission for sol-gel route compacts. XRD of sintered samples showed retention of phase purity in all the cases. SEM of sintered samples showed good grain fusion for close to spherical particles of microwave assisted gel combustion route than polyhedral particles of sol-gel route. Since spherical particles undergo faster densification and sintering, microwave assisted route gave highly sinterable nanopowders compared to sol-gel route.

Carbonate-precipitation synthesis of Yb 3+:Y 2O 3 nanopowders and its characteristics

Ytterbium-doped yttria (Yb 3+:Y 2O 3) nanopowders for transparent ceramics were synthesized by using a carbonate-precipitation method. The characteristics of precursor and powders calcined at different temperatures were investigated. The pure yttria phase can form through calcining at 700 °C. The Yb 3+:Y 2O 3 nanopowders calcined at 1100 °C were well dispersed with a spherical morphology, and had a narrow particle size distribution with a mean particle size of about 70 nm. By using 1100 °C-calcined powders, nearly full dense Yb 3+:Y 2O 3 ceramics were fabricated at 1750 °C for 8 h without any additives under vacuum conditions. The fluorescence spectrum of the sintered ceramics illustrates that there are two emission peaks locating at 1028 and 1071 nm respectively, all corresponding to the 2 F 5/2 → 2 F 7/2 transitions of Yb 3+ ion. Homogeneous Yb 3+:Y 2O 3 nanopowders synthesized by carbonate-precipitation method are suitable for the fabrication of IR-transparent ceramics.

Synthesis and spectral properties of Yb 3+/Ho 3+ co-doped yttria 2 μm transparent ceramics

Yb/Ho co-doped yttria transparent ceramics, Yb/Ho:Y 2O 3, were prepared by vacuum sintering with additional 0.5 wt.% tetraethyl orthosilicate (TEOS) as sintering aid from the Yb/Ho co-doped yttria nanopowders synthesized by co-precipitation method. The optical quality of transparent ceramics was improved significantly, as increasing the sintering temperature from 1800 °C to 1850 °C as well as the holding time from 20 h to 25 h, respectively. The absorption spectrum was measured to find out the advisable emission source wavelength. The 2 μm emission bands were observed under laser diode excitation at 980 nm in the co-doped sample with 5 mol% of Yb 3+ and 1 mol% of Ho 3+, and broad emission bandwidth were obtained.

The Effects of Composition and Sintering Conditions on Zirconia Toughened Alumina (ZTA) Nanocomposites

Zirconia Toughened Alumina (ZTA) Nanocomposites were prepared using Nano sized Zirconia (ZrO2) powders doped with 3% mol of yttria (Y2O3) nanopowders. Diffusion of α-alumina (Al2O3) nanoparticles as well as yttria into the Zirconia lattice network drives monoclinic – tetragonal martensitic transformation. Zirconia toughened alumina (ZTA) composites containing different amount of partially stabilized Zirconia (PSZ) 5, 10, 15 and 20% mol, were prepared via wet mixing and axial pressing. After sintering at different temperatures,1450, 1550 and 1650 °C, phase change in the samples were monitored. X-ray diffraction patterns showed that at constant composition, tetragonal zirconia was increased by temperature increasing due to intensification of diffuse coefficient of alumina and yttria in the system. At constant temperature, remained monoclinic zirconia was increased with Zirconia content increasing.

Gelcasting of alumina–zirconia–yttria nanocomposites with Na-alginate system

The alumina–zirconia–yttria (AZY) nanopowders ranging from 30–110 nm were synthesized via the sol–gel method. θ-Alumina and t-zirconia phases were identified in the nanopowders calcined at 900 °C for 1 h. Sodium alginate was used for gelcasting process of green bodies. The viscosity of castable slurries with highest nanopowder loading, 15 vol.%, is about 800 mPa.s. The dried gels were pressureless sintered at 1400, 1450 and 1500 °C for 3 h. Grain boundary diffusion seems to be the controlling sintering mechanism with increasing zirconia content from 5 up to 10 wt.%, whereas in the range of 10–15 wt.% zirconia content increase, lattice diffusion is the controlling.

Preparation of ceria and yttria nanopowders via thermal decomposition of oxalates, carbonates, and hydroxides

Ceria and yttria nanopowders have been prepared through thermal decomposition of various precursors. The nature of precursors has been shown to have a significant effect on the microstructure of the powders. The stability of the powders to particle (crystallite) growth has been studied as a function of heat-treatment temperature and duration.

Fabrication of yttrium aluminum garnet transparent ceramics from yttria nanopowders synthesized by carbonate precipitation

Nanocrystalline yttria powders have been successfully synthesized by using yttrium nitrate as starting salt and ammonium hydrogen carbonate as precipitant. It was found that a small amount of ammonia sulfate in the yttrium nitrate solution can effectively reduce the agglomeration and the resultant powders display good dispersion. Pure cubic phase yttria powders were prepared by calcining the precipitate at 1100 °C for 4 h. The size of the as-prepared yttria powders was about 60 nm in diameter and showed excellent sintering activity. The as-prepared yttria nanopowders and commercial ultrafine alumina powders were used to fabricate YAG ceramics by solid-state reaction method and transparent YAG ceramics have been obtained by vacuum sintering at 1760 °C for 6 h.

Effect of grain size on the sinterability of yttria nanopowders synthesized by carbonate-precipitation process

Yttria nanopowders have been synthesized by carbonate precipitation process. The thermal decomposition behavior of the carbonate precipitate, crystal phase, microstructure and sinterability of the powders were examined. The precipitate precursor was decomposed completely at 700 °C and then crystallized well into cubic yttria phase. Our results suggested that the most favorable calcination temperature was 1100 °C for obtaining good dispersion, high-reactive yttria nanopowders. The nanopowders were almost spherical and had weak agglomeration and narrow particle size distribution with a mean grain size of about 80 nm. Using these yttria nanopowders, nearly full dense yttria ceramic with ∼99.2% of theoretical density was obtained at 1600 °C for 2 h without any additives.

Synthesis of Yttria Nanopowders Doped with Rare Earth via a Coconut Water-Based Sol-Gel Process

Synthesis of Yttria Nanopowders Doped with Rare Earth via a Coconut Water-Based Sol-Gel Process

Precipitation synthesis and sintering of yttria nanopowders

Yttria nanopowders were synthesized using a chemical precipitation method. pH value at the end of the precipitation process has a significant effect on the size and morphology of the precursor and the yttria powders. Under the same calcination condition, the yttria powders made from the precursor obtained at a pH of 8 are smaller in mean particle size and narrower in size distribution than those made from the precursor obtained at a pH of 10. It was found that the optimum calcination temperature is 1000 °C, and the yttria powder obtained is fine (30 nm) and well dispersed. Using the yttria powder, transparent yttria ceramics was produced by vacuum sintering at 1700 °C for 4 h without any additives.