Papers by Keyword: Nanosized Powder

Abstract: The process of obtaining a uniform dispersion of nanosized powders by applying two step process of mixing and adjusting viscosity was studied. The mixed paste was used as the electrode of direct ethanol fuel cells (DEFC). And power density of the fuel cells was measured. A high power density was realized by addition of acetone and propanol solvents to nanosized silica powder. However acetaldehyde concentration during the operation of these fuel cells did not decrease. An excess methanol was added to membrane electrode assembly composition of DEFC. The power density and current of DEFC were improved by adding methanol solvent. However, methanol addition over 55 % did not improve dispersion of nanosized powders. Transmission electron microscopy observation suggests that over 55% of methanol addition does not give good dispersion of nanosized powders.

Abstract: The formation mechanisms of paramagnetic centers originating from Zr³⁺ and Cr³⁺ ions and the influence of the nanoparticle composition on thermal generation processes of these paramagnetic centers in ZrO₂ structure were studied by electron paramagnetic resonance. A set of nanosized zirconium oxide powders (nominally pure ZrO₂, ZrO₂ doped with correspondingly Y₂O₃ and Sc₂O₃, Cr₂O₃ and Y₂O₃, as well as Cr₂O₃) was investigated: The influence of annealing on the EPR lines of Zr³⁺ and Cr⁵⁺ ions was found to be different. Annealing curves of EPR signals caused by Cr⁵+ ions have a maximum in temperature range 500–600 °C. Mechanisms of Zr³⁺ and Cr⁵⁺ ions formation were discussed.

Abstract: CeO₂ nano-sized crystalline powders were prepared by sol-gel combustion method from ammonium cerium nitrate and citric acid, and the dependences of the particle size of synthesized powder on the precursor gel were investigated. The precursor gels and the synthesized powders were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray scattering (XRD). The colloid particle with nanometer size was firstly observed by FE-SEM, and its size variation had the same tendency as that of CeO₂ powders with the varying of the ratio of metal ions to citric acid. Furthermore, the probable reasons for the effect of gel structure on properties of nano-sized ceria powders prepared by sol-gel combustion were explained.

Abstract: For resistive oxygen sensor elements of Ce1-xZrxO2 (x = 0.0, 0.05, 0.1, 0.2), grain diameter was varied in the range of 86 – 300 nm by changing sintering temperature or changing Zr content. The grain diameter decreased with increasing Zr content. The response time was approximately proportional to the square of the grain diameter. In the relationship between the amplitude of sensor output, An and the frequency, f of sine wave of variation in oxygen partial pressure, the gradient in the high-frequency region of a plot of log An vs. log f in was approximately –0.5. From these results, it was concluded that the sensor response was determined by the oxygen vacancy diffusion rate. The grain diameter of Ce0.8Zr0.2O2 element was 86 nm and the response time at 1073 K was 9 ms, which result opens the door to the technological development of independent control of engine cylinders.

Abstract: ZnO varistors with higher voltage gradients are expected in the power system, and the key to this property is to diminish the grain size. In this paper, nano-sized ZnO particles are used as the raw material in order to obtain small grains. Pellets are fabricated by two sintering methods: the conventional pressureless sintering and the spark plasma sintering (SPS). For the samples fabricated by the conventional sintering, the average grain size varies from 1 μm to more than 10 μm when the sintering temperature changes from 900 oC to 1200 oC. The voltage gradient can reach as high as 2020 V/mm. The grain size of the SPS samples is less than 1 μm, and the voltage gradients can reach 963 V/mm.

Abstract: WC nanosized powders are synthesized by the plasma arc discharge process and annealing under an inert (Ar) atmosphere. The high temperature used during discharging at local region causes the work-piece and electrode to melt and evaporate. The melted tungsten on the arc discharge electrode and carbon arising from decomposition CH4 gas forms WC1-x nanosized powders. The WC1-x phase is encapsulated in a amorphous carbon shell. The WC1-x nanosized particles are annealed at 1200~1400°C under an Ar atmosphere. The WC1-x nanosized powder is transformed to the W2C phase, and then it becomes WC above at 1400°C.

Abstract: By means of magnetic pulsed compaction and sintering of weakly aggregated alumina based nanopowders the jet forming nozzle samples for hydroabrasive cutting were fabricated. The ceramics were obtained from pure alumina, as well as from alumina, doped by TiO2, MgO and AlMg. The ceramic properties of the channel surface and the nozzle volume were investigated. It was shown that the samples sintered from AlMg doped Al2O3 powder had the best desired mechanical properties and structural characteristics: relative density ~0.97, channel microhardness – 18-20 GPa, channel surface roughness ~0.7 /m, average crystallite size ~1 /m.

Abstract: Nano-sized zinc containing β-tricalcium phosphate (ZnTCP) powders were synthesized by a co-precipitation method. The co-precipitation took place in an ice-water bathed beaker, after further washing, freezing, lyophilizing and calcining at 800°C, the precipitates transformed to ZnTCP powders. The XRD pattern of the ZnTCP powders demonstrated a pure β-TCP phase. TEM observation revealed the particle size is about 100-120nm, which is favorable for TCP particles to form composites, such as polymer based composite, and as well to attain a desired microstructure. It was found zinc incorporation could eventually result in the decrease of particle size, thus be beneficial for its further application.

Abstract: The phosphoryl oligosaccharides of calcium (POC), extracted from potato starch, are composed of phosphorus oligosaccharides and calcium ions. Ultrafine calcium phosphate particles, whose main phase was hydroxyapatite (Ca10(PO4)6(OH)2: HAp), could be prepared through the hydrothermal treatment of POC solution at a temperature between 110 and 130°C; X-ray diffraction indicated the crystallinity of HAp in the resulting powder to be poor and similar to that of living bone. The present HAp powder was regarded to be calcium deficient carbonate apatite with the OH- group being partly substituted by a carbonate (CO3 2-) group. The solubility of the resulting powder in dilute hydrochloric acid was higher compared to that of commercially available HAp, suggesting excellent bioabsorbability for the present powder.