Specific Surface Area Of Powders Research Articles

Characteristics of Nano-Sized Yttria Powder Synthesized by a Polyvinyl Alcohol Solution Route at Low Temperature

Nano-sized yttria (Y2O3) powders were successfully synthesized at a low temperature of 400 degrees C by a simple polymer solution route. PVA polymer, as an organic carrier, contributed to an atom-scale homogeneous precursor gel and it resulted in fully crystallized, nano-sized yttria powder with high specific surface area through the low temperature calcination. In this process, the content of PVA, calcination temperature and heating time affected the microstructure and crystallization behavior of the powders. The development of crystalline phase and the final particle size were strongly dependant on the oxidation reaction from the polymer burn-out step and the PVA content. In this paper, the PVA solution technique for the fabrication of nano-sized yttria powders is introduced. The effects of PVA content and holding time on the powder morphology and powder specific surface area are also studied. The characterization of the synthesized powders is examined by using XRD, DTA/TG, SEM, TEM and nitrogen gas adsorption. The yttria powder synthesized from the PVA content of 3:1 ratio and calcined at 400 degrees C had a crystallite size of about 20 nm or less with a high surface areas of 93.95-120.76 m2 g(-1).

Synthesis, Characterization and Photocatalytic Activity of Copper (II)-Doped Titanium Dioxide Powders

Different concentration of copper (II) doped TiO2 photocatalyst powders were synthesized through the sol-gel method and characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET)-specific surface area, transmission electron microscopy (TEM), and Ultraviolet–Visible (UV-Vis) spectroscopy. Cu2+-doping in the TiO2 promotes the particle growth, decreases the specific surface areas of powders, extends the absorption to visible light regions, and exhibits the vis-photocatalytic activity for methylene blue (MB) degradation. Appropriate content of Cu2+-doping is an effective means to improve the photocatalytic activity of TiO2 for MB degradation under visible light irradiation.

Effect of Zr/Ce molar ratio on the structure of powders and Zr1−x Ce x O2 coatings on quartz fiber reinforced polyimide matrix composites via sol–gel process

In this investigation, Zr1−xCexO2 coatings were fabricated on quartz fiber reinforced polyimide matrix composites via sol–gel process at 400 °C. The phase evolution, structural and morphological characteristic of specimens were investigated by differential scanning calorimetric, Fourier transform infrared spectroscopy, powder X-ray diffraction and scanning electron microscopy. The significant phase evolution of final powders with the decreasing Zr/Ce molar ratio could be observed as follows: tetragonal (t′) → cubic + tetragonal (t′) → tetragonal (t″). BET specific surface areas of powders exhibited a decreased tendency with the increasing calcination temperature as well as the decreasing Zr/Ce molar ratio. The average crystallite size and the mean particle size increased with the elevated calcination temperature, while the particle size also increased with the increase in Ce content. The progressive addition of Ce could promote the sintering process and the densification of coating. Morphologies of coatings changed with the variation of the Zr/Ce molar ratio. The results indicate that Zr0.75Ce0.25O2 coating with the Zr/Ce molar ratio of 3 is a stable uniform coating with excellent adhesion.

Effect of Iron (III)-Doping on the Photocatalytic Activity of Titanium Dioxide Catalysts for Methylene Blue Degradation

Iron-doped TiO2 photocatalyst powders were prepared by the sol–gel method and characterized by Brunauer–Emmett–Teller (BET)-specific surface area, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Ultraviolet–Visible (UV-Vis) spectroscopy. Fe3+ doping in the TiO2 decreases the crystal grain size, increases the specific surface areas of powders, extends the absorption to visible light regions (400~500 nm), and lowers the photocatalytic activity for methylene blue (MB) degradation under UV irradiation. The photocatalytic degradation of MB in water was investigated as a function of the Fe3+ content in TiO2. It was found that under the irradiation of visible light, a small amount of Fe3+ dopant in TiO22 powders could obviously enhance the photocatalytic activity. When the Fe3+ content was in the range of 0.03–0.1 mol%, the photocatalytic activity of the samples was higher than that of undoped TiO2. Appropriate content of Fe-doping is an effective means to improve the photocatalytic activity of TiO2 for MB degradation under visible light irradiation.

Synthesis of nanocrystalline yttria powder prepared by a polymer solution route

Nanometer-scaled yttria (Y2O3) powders were synthesized by a polymer solution route using polyvinyl alcohol (PVA) as an organic carrier. The PVA polymer contributed to a soft and porous powder microstructure, and homogeneous precursor gels containing PVA polymer were effective in making nanometer-sized yttria powders. In this process, the content of PVA and the calcination temperature strongly affected the microstructure and crystallization behavior of the yttria powders. The homogeneous precursors were crystallized to a stable yttria phase at 600 °C for 1 h. In this paper, a simple solution technique for the fabrication of nanometer-sized yttria powders is introduced. The effects of PVA on the powder morphology and on powder specific surface area were studied. The characterization of the synthesized powders was examined by using XRD, DTA/TG, SEM, TEM, a particle size analyzer and nitrogen gas adsorption. The yttria powder synthesized from PVA with a content ratio of 4:1 revealed a crystallite size of about 15 nm with a high surface area of 34.71 m2/g.

Structural and morphological study of mechanochemically synthesized tin diselenide

Mechanochemical synthesis of tin diselenide, SnSe2, was performed by high-energy milling of tin and selenium powder in a planetary ball mill. The mechanosynthesized product was characterized by X-ray diffraction, 119Sn MAS NMR and 119Sn Mossbauer spectroscopy, which confirmed the presence of the hexagonal SnSe2 phase after 100 min of milling. The size and morphology of tin diselenide particles were studied by specific surface area measurements, and transmission electron microscopy. The specific surface area of powders was found to increase with increasing time of mechanochemical synthesis. Electron diffraction revealed reflections that correspond to hexagonal SnSe2 modification. TEM observations show that the mechanochemical preparation route results in the formation of nanosized thick barrel-shaped SnSe2 platelets. SnSe2 nanoparticles show good absorption in the visible region of the UV-Vis optical spectrum and they evidence direct and indirect types of transitions in the lattice.

Forming a carbide coating on the surface of aluminum nanoparticles and producing nanopowders from Al-Al4C3 using the method of electric explosion of wire

The controlled feeding of butane to inert working gas in the process of producing aluminum nanopowders using the method of electrical explosion of wire (EEW) allows carbide coatings to be formed on the surface of aluminum particles, reducing the agglomeration of the particles and producing Al-Al4C3 nanopowders of various compositions and dispersivity. The dependences that the specific surface area of powder, the content of crystalline aluminum carbide, and the phase composition of powders have on the quantity of the butane fed at different values of energy input into the wire are presented. The morphology of the particles is examined. The powders were analyzed using BET, X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry-mass spectrometry (TG/DSC/MS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Synthesis of Nickel Oxide - Zirconia Composites by Coprecipitation Route Followed by Hydrothermal Treatment

Nickel oxide-yttria stabilized zirconia (NiO-YSZ) for use as solid oxide fuel cell anode were synthesized by coprecipitation to obtain amorphous zirconia and crystallized β-nickel gels of the corresponding metal hydroxides. Hydrothermal treatment at 200°C and 220 psi from 2 up to 16 hours, under stirring, was performed to produce nanocrystalline powder. The as-synthesized powders were uniaxially pressed and sintered in air. Powders were characterized by X-ray diffraction, laser scattering, scanning and transmission electron microscopy (SEM/TEM), gas adsorption technique (BET) and TG-DTA thermal analysis. Ceramic samples were characterized by dilatometric analysis and density measurements by Archimedes method. The characteristics of hydrothermally synthesized powders and compacts were compared to those produced without temperature and pressure application. Crystalline powders were obtained after hydrothermal process, excluding the calcination step from this route. The specific surface area of powders decreases with increasing time of hydrothermal treatment while the agglomerate mean size is not affected by this parameter.

Photocatalytic activity of titanium dioxide coatings: Influence of the firing temperature of the chemical gel

Heterogeneous photocatalysis can be exploited for the decomposition of micro-organisms which have developed on the surfaces of building materials. In this work, the efficiency of titanium dioxide coatings on fired clay products is examined. The sol–gel method is used to synthesize a fine TiO 2 powder with a specific surface area of 180 m 2 g −1. Thermal treatment of the chemical gel at 340 °C leads to crystallisation in the anatase phase and with further temperature increase, crystallite growth. For thermal treatments in the range 580–800 °C, there is a progressive transition from anatase to rutile. However, despite a decrease in specific surface area of the powder attributed to aggregation/agglomeration, the coherent domain size deduced from X-ray diffraction measurements remains almost constant at 23 nm. Once the transition is completed, increase of thermal treatment temperature above 800 °C leads to further crystallite growth in the rutile phase. The thermally treated titania powders were then sprayed onto fired clay substrates and the photocatalytic activity was assessed by the aptitude of the coating to degrade methylene blue when exposed to ultraviolet light. These tests revealed that the crystallite size is the important controlling factor for photocatalytic activity rather than the powder specific surface area or the anatase/rutile polymorph ratio.

Mixture of fuels approach for solution combustion synthesis of nanoscale MgAl 2O 4 powders

Nanoscale MgAl 2O 4 powders were synthesized via a microwave-assisted solution combustion process using various mixtures of urea, glycine and starch as fuel. The effects of starch addition on characteristics (e.g. specific surface area and crystallite size) of the as-resulted powders were also investigated. The experimental results revealed that the specific surface area of the powders was significantly increased as the starch content rose from 0 to 35.6 wt.%, followed by a slight decrease when it was further raised to 54.7 wt.%. The scanning electron microscope micrographs disclosed that starch addition also affected the morphology of porous nanoparticles’ agglomerates and was remarkably beneficial to dissipate the as-produced nanoparticles. Higher degree of dissipation and larger specific surface area of the powders resulted from starch addition were mainly attributed to a larger amount of gases evolved during combustion and/or lower combustion temperature.

Phase controlled structure formation of the nanocrystalline zirconia using thermal plasma technique

Nanocrystalline ZrO2 powder was synthesized by dc transferred arc thermal plasma reactor by homogeneous gas phase condensation mechanism. ZrO2 is an oxide ceramic with a high melting point, good chemical resistance and high mechanical strength. When doped with certain oxides, ZrO2 shows high ionic conductivity. ZrO2 is also recognized as a superior thermal barrier material. Thermal plasma synthesis of oxide nano materials shows pressure dependent crystalline phase and crystallite size. The X-ray diffraction analysis clearly shows that as the ambient oxygen gas pressure increases from 100 Torr to 1000 Torr the abundance of tetragonal phase goes on increasing. The morphology of the as synthesized ZrO2 powder was found to be spherical and independent on the ambient gas pressure as seen from the Scanning Electron Microscopy studies. The specific surface area of powder was calculated using the nitrogen gas adsorption Brunauer, Emmett, Teller surface area analysis technique and found no much variation.

Formation of zirconia films by the aerosol gas deposition method

Recently, zirconia films have attracted considerable attention because of their potential applications in solid oxide fuel cells and as thermal barrier coatings and oxygen sensors. Herein, we report that high-density zirconia films can be formed at room temperature by using the aerosol gas deposition (AGD) technique and discuss the conditions required for film formation. The experimental results indicate that the particle size and specific surface area of the zirconia powder used determine the success of film fabrication by AGD. Films are successfully formed when the mean particle size and specific surface area of the powder are in the range 2.1–3.5 µm and 4.4–6.5 m2/g, respectively.

Medium Temperature Solid Oxide Fuel Cells Based on the Micro-Meso-Macro-Porous Cathodes and Anodes

A series of electrochemical impedance experiments have been carried out in order to investigate the effect of cell chemical composition on the determination of electrochemical characteristics of strontium-doped rare earth cobaltite cathodes. The impedance responses at different electrode potentials of the half-cell and symmetric single-cell setups are compared and analyzed by the equivalent circuit modeling method. The deconvolution of impedance spectra for single cells has been achieved by differential derivative of impedance real part versus ac frequency plot analysis method. The performance of electrolyte-supported Ni/Ce0.9Gd0.1O2-δ|Ce0.9Gd0.1O2-δ|Ln0.6Sr0.4CoO3-δ symmetric single-cells has been optimized for anode diffusion layer porosity, anode functional layer starting powder specific surface area (SBET,powder), and cobaltite-based cathode material composition in a single designed experiment according to the so-called response surface methodology. The combination of electrochemical impedance spectroscopy, equivalent circuit fitting, and mathematical statistics methods proved to be a powerful tool for interpreting solid oxide fuel cell data.

Shrinkage of metal ceramic briquettes during sintering

layers. The experimental data of Dedrick and Gerds [4] and Shaler [5] do not support Frenkel’s assumption that the mechanism whereby metal particles are sintered can be regarded as a viscous flow of the crystalline body. Kuczynski [6] and Dedrick and Gerds [4] concluded that sintering resulted from bulk diffusion. However, the conclusions made by Kuczynski and Dedrick and Gerds cannot apply to the actual conditions under which metal powder briquettes are sintered since the experimental conditions did not cover sintering times and surface states common for metal ceramic production practices. Pines [7] regards shrinkage as the diffusion of «holes» outside, through the briquette. This idea has not been verified experimentally. Dawihl [8] attributed shrinkage to the contraction of particles resulting from the recrystallization inside individual grains in which their shape becomes more regular. We have established [9] that the specific surface area of metal powders changes intensively when heated, and the self-diffusion of atoms over particles is governed by the general equation of diffusion in metals. We assume that the surface rearrangement of powder particles is critical for the shrinkage and sintering of metal powder briquettes. Based on these assumptions, we performed experiments to study how the reduction in the specific surface area of powders when annealed influenced the shrinkage of the briquettes and made an attempt to find a relation between the shrinkage process and surface diffusion of atoms. 1. PRELIMINARY EXPERIMENTS AND SHRINKAGE HYPOTHESIS To study how the specific surface area of the starting powder influences the shrinkage of metal ceramic samples after sintering, we pressed 5 × 10 × 40 mm plane samples from iron powders of the same fractional composition but different specific surface areas. The specific surface area was controlled by varying the annealing temperature of the powder mixture or individual powder fractions. The specific surface area of the powder was determined with Deryagin’s gas permeability method [10]. The samples were measured before and after sintering. The reduction in the cross-sectional area of the samples was used to measure the shrinkage.

Preparation, sintering and electrical properties of nano-grained multidoped ceria

Multiply doped ceria nanopowders were synthesized by applying MGNP (modified glycine/nitrate procedure). The overall concentration of dopants was kept constant (x=0.2) whereby Gd ion as the main dopant was gradually substituted by Sm and by Sm+Y. The compositions of solid solutions were calculated by applying defect model introducing anion vacancy radius. Characterization of powders involved BET, TEM, XRD and chemical analyses. Densification was performed at 1500°C, in an oxygen atmosphere for 1h. The results showed that with increasing number of dopants, specific surface area of powders increased, followed by decrease of crystallite and grain sizes. Densification degree was also found to rise with increasing number of dopants. According to impedance measurements it was found that ionic conductivity was the highest 1.14×10−3Scm−1 at 450°C in sample doped with Gd, Sm and Y simultaneously.

Effect of biological media on the physical, chemical, and magnetic properties of carbonyl iron and nickel powders

The paper examines changes in carbonyl iron and nickel powders subjected to model biological media: water media and media containing human blood plasma. It is established that carbonyl iron powder interacts with biomedia containing blood plasma six times as fast as with water media. No oxidation or corrosion is observed in the process. The magnetic properties of the powder after the interaction with plasma-containing media do not practically deteriorate. Iron powder is intensively absorbed by blood plasma, Fe3+ ions forming complex compounds with proteins. On the contrary, carbonyl nickel is not absorbed by blood plasma for five days, and the powder specific surface area and particle morphology remain practically unchanged after the interaction. Blood plasma seems to dissolve and transform metals according to the human body’s demands. In the case of carbonyl iron, this process proceeds faster than corrosion does. In the case of carbonyl nickel, the opposite is observed.

Comparative Research on the Synthesis of Aluminum Titanate Powders by Nonhydrolytic and Hydrolytic Sol-Gel Method

Aluminum titanate powder was synthesized by nonhydrolytic and hydrolytic sol-gel method,respectively.The sol-gel process,the phase transformation and the sintering properties of powders were studied by TG-DTA,XRD,FT-IR and SEM analysis.The results show that during the hydrolytic sol-gel process,the Al3+ ions mostly exist in the interspace of Ti-O-Ti network.As a result,only rutile and corundum are separated from the hydrolytic gel,the Al2TiO5 has to be synthesized at 1350℃.Comparatively,the gel network is formed through the polymerization reaction of Al3+ and Ti4+ ions in nonhydrolytic sol-gel process,these ions occupy the similar position to build the gel network together.Therefore,the armorphous phase is directly crystallized at 750℃ as aluminum titanate.The particle size and specific surface area of Al2TiO5 powders prepared by hydrolytic sol-gel method are 1-2μm and 3.2m2/g.It is dropped to 0.1-0.3μm under nonhydrolytic sol-gel method,while the specific surface area of the powders is 35 times of hydrolytic sol-gel sample.The bending strength of the sintered Al2TiO5 ceramic prepared by nonhydrolytic sol-gel method is 2.3 times of hydrolytic sol-gel sample,which is only 7.2MPa.It indicates that the properties of Al2TiO5 powders prepared by nonhydrolytic sol-gel method are better than that of hydrolytic sol-gel sample.

Statistical method to optimize the medium temperature solid oxide fuel cell electrode materials

The research on intermediate-temperature solid oxide fuel cell materials has been largely focussed on three main areas: optimization of material porosity, introduction of nano-scale starting powders, and the search for new, electrochemically more active materials. However, regardless of the large number of papers published on the matter, only very few examples of statistically correct systematic optimization studies have been published. In this paper, the performance of electrolyte-supported Ni/Ce 0.9Gd 0.1O 2− δ |Ce 0.9Gd 0.1O 2− δ |Ln 0.6Sr 0.4CoO 3− δ , Ln = La, Pr, Gd, symmetric single-cells has been optimized for anode diffusion layer porosity, anode functional layer starting powder specific surface area ( S BET,powder), and cobaltite-based cathode material composition in a single designed experiment according to the so-called response surface methodology (RSM). The optimal cell was found to have either an La 0.6Sr 0.4CoO 3− δ or Pr 0.6Sr 0.4CoO 3− δ cathode, an anode active layer prepared of a starting powder of S BET,powder = 135 m 2/g, and a pore former content of 2 wt%. The combination of electrochemical impedance spectroscopy (EIS), equivalent circuit fitting, and mathematical statistics methods proved to be a powerful tool for interpreting solid oxide fuel cell data.

Quantifying Effects of Particulate Properties on Powder Flow Properties Using a Ring Shear Tester

Effects of particle size, morphology, particle density, and surface silicification, on powder flow properties were investigated using a ring shear tester. Flow properties were quantified by flow function (FF), that is, unconfined yield strength, fc, as a function of major principal stress. A total of 11 powders from three series of microcrystalline cellulose (MCC): Avicel (regular MCC, elongated particles), Prosolv (silicified MCC, elongated particles), and Celphere (spherical MCC), were studied. Particle size distribution in each type of MCC was systematically different. Within each series, smaller particles always led to poorer powder flow properties. The slope of FF line was correlated to degree of powder consolidation by external stress. A key mechanism of the detrimental effect of particle size reduction on flow properties was the larger powder specific surface area. Flow properties of Celphere were significantly better than Avicel of comparable particles size, suggesting spherical morphology promoted better powder flow properties. Flow properties of powders different in densities but similar in particle size, shape, and surface properties were similar. When corrected for density effect, higher particle density corresponded to better flow behavior. Surface silicification significantly improved flow properties of finer MCC, but did not improve those of coarser.

Binary mixtures of ultrafine metal powders. II. Rolling of ultrafine powders into porous sheets

The paper examines the possibility of producing porous sheets by rolling binary mixtures of ultrafine powders of nickel, copper, and cobalt. The effect of the rolling rate on the thickness and porosity of sheets and on the specific surface area of powders after rolling is studied. The best rollability is shown by nickel and copper powders and by powders produced from mechanical mixtures of formates.