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L0080 - A novel low temperature sintering process for PMnN-PZT ceramics
Samples with the composition of 0.07Pb(Mn1/3Nb2/3)O3-0.468PbZrO3-0.462PbTiO3 was prepared in this study. A novel process was adapted to lower the sintering temperature without properties deterioration. The sintering process includes a vacuumed heating stage, a air-venting heating stage, and a final sintering at 1050°C with certain holding time without PbO compensating atmosphere. The influence of holding time at the final sintering stage on the characteristics of the ceramics was studied. The air-venting stage caused a large shrinkage (about 10%) and then slowing down the shrinking rate when the sample was heated up from 800 to 1050°C. The relationships between the crystalline characteristics and physical properties, such as microstructure, the mechanical quality factor (Qm), and electromechanical coupling factor (kp), are discussed in this paper.
C-Y. Chen, Y. Hu, H-L. Lin, Materials Chemistry and Physics 99 (2006) 26-29
L0079 - The effects of the physical states of a simulated fission product on the linear thermal expansion of (U0.924Ce0.076)O2
The linear thermal expansions of an (U0.924Ce0.076)O2 pellet, doped a simulated fission product (Nd2O3 or Ru), were measured from room temperature to 1673K in a flowing argon atmosphere using TMA. Nd2O3 and Ru represent the physical states of a fission product, a dissolved oxide and a metallic precipitate, respectively. Using the measured data, the mean coefficients of a linear thermal expansion was obtained as a function of the temperature, and the effects of the physical states of a simulated fission product on the thermal expansion were investigated. In the case of the Nd2O3 forming a dissolved oxide, the thermal expansion of the sample increased and the increment was proportional to the Nd contents, because the melting point of the Nd2O3 was lower than that of UO2 and although the metallic precipitate hardly affected the crystal structure, the linear thermal expansion also increased with an increasing Ru contents.
D-J. Kim, Y-S. Kim, J-H. Yang, S-H. Kim, Y-W. Lee, H-S. Kim, Journal of Alloys and Compounds 421 (2006) 151-155
L0078 - Development of Mg/Cu nanocomposites using microwave assisted rapid sintering
In the present study, magnesium composites containing different amounts of nano-size Cu particulates were successfully synthesized using powder metallurgy (PM) technique incorporating microwave assisted two-directional sintering. The sintered specimens were hot extruded and characterized in terms of physical, microstructural and mechanical properties. Microstructural characterization revealed minimal porosity and the presence of a continuous network of nano-size Cu particulates and Mg2Cu intermetallic phase decorating the particle boundaries of the metal matrix. Coefficient of thermal expansion (CTE) value of magnesium matrix was improved marginally with the addition of nano-size Cu particulates. Mechanical characterization revealed that the addition of nano-size Cu particulates lead to an increase in hardness, elastic modulus, 0.2% yield strength (YS), ultimate tensile strength (UTS) and work of fracture of the matrix. An attempt is made in the present study to correlate the effect of increasing amount of nano-size Cu reinforcement on the microstructure and properties of monolithic magnesium.
W.L.E. Wong, M. Gupta, Composites Science and Technology 67 (2007) 1541-1552
L0076 - Modelling of the grain growth and the densification of SnO2-based ceramics
This work consisted in the kinetic study of grain growth and densification processes for SnO2 and Sn0.94Zr0.06O2 ceramics between 1100 and 1200°C. From dilatometric experiments, it appeared that zirconia additions inhibited the final densification rate. For pure SnO2, the rate limiting step of the densification mechanism would correspond to the grain boundary or volume diffusion. From normal grain growth kinetics, the corresponding limiting step has been identified, i.e. either the surface diffusion in pores or grain boundary diffusion for ZrO2 free-SnO2 and Sn0.94Zr0.06O2, respectively. All of these results permit establishing the corresponding sintering map. For pure SnO2 ceramic, the experimental data have been well restored by modelling.
A. Maître, D. Beyssen, R. Podor, Ceramics International xxx (2007) xxx-xxx
L0075 - Effects of the sintering atmosphere on Nb-based dielectrics
The effects of a forming atmosphere on the stability, the sintering and the dielectric properties of Ba5Nb4O15, BaNb2O6, ZnNb2O6 and Zn3Nb2O8 ceramics were investigated, because of the primary importance of the sintering atmosphere in relation to copper sintering. These Nbbased materials were sintered in air and in Ar/H210%. Zn-containing samples are very sensitive to the reductive atmosphere. ZnO volatilises at 800-850°C and the resulting compound does not exhibit the expected properties. BaNb2O6 and Ba5Nb4O15 are more stable in term of relative weight loss. Nevertheless, the phase analysis reveals a modification of the BaNb2O6 phase, what induces the degradation of the dielectric property stability versus temperature. The properties of Ba5Nb4O15 are not modified by a sintering in reductive atmosphere. A relative permittivity of 38.8, a permittivity temperature coefficient of -150 ppm°C-1 and an insulating resistivity of 10^10.9 V cm were obtained for this latter.
S. d'Astorg, S. Marinel, Ceramics International xxx (2007) xxx-xxx
L0074 - Preparation and properties of dense Ce0.9Gd0.1O(2-d) ceramics for use as electrolytes in IT-SOFCs
Gd-doped ceria solid solutions have been recognized to be leading electrolytes for use in intermediate-temperature fuel cells. In this communication, it reported on the preparation, solubility and densification of Ce0.9Gd0.1O(2-d) ceramics derived from carbonate coprecipitation. The dissolution of Gd2O3 in CeO2 lattice was identified to complete during coprecipitation process by studying lattice parameter against temperature. The calcining temperature was found to have a significant influence on the densification behavior and final sintered density for the carbonatecoprecipitated powder. The samples prepared from the powder calcined at <700°C had an expansion at ~1250 to 1400°C during sintering, and thus lowered sintered density. 800°C was identified to be an optimal calcining temperature for carbonate-coprecipitated powder. The powder calcined at 800°C for 2 h had a mean crystalline size of ~25 nm with nearly spherical shape and narrow particle-size distribution, which had a maximum densification rate at ~1190°C. This temperature (of maximum densification rate) could further be reduced to ~1080°C for the carbonate-coprecipitated powder by adding 0.5 at.% FeO1.5 (atomic ratio). At 1200°C for 5 h, over 98% relative density with an average grain size of ~1.2µm was obtained for the 0.5 at.% Fe-loaded Ce0.9Gd0.1O(2-d) ceramics. Fe loading was also found to have a positive effect on grain boundary conductivity of Ce0.9Gd0.1O(2-d) ceramics. An increase in the grain boundary conduction by over two times was achieved in the present work for the 0.5 at.% Fe-loaded Ce0.9Gd0.1O(2-d) ceramics.
T.S. Zhang, J. Ma, L.H. Luo, S.H. Chan, Journal of Alloys and Compounds 422 (2006) 46-52
L0073 - Abnormal thermal expansion and thermal stability of Ti3Al(1-x)SixC2 solid solutions
Ti3Al(1-x)SixC2 solid solutions exhibited abnormal high coefficients of thermal expansion at temperatures of >940°C during heating, which was ascribed to the precipitation of Si as Ti5Si3. Ti5Si3 phase usually located at the grain boundaries of the solid solutions.
J.X. Chen, Y.C. Zhou and J. Zhang, Scripta Materialia 55 (2006) 675-678
L0072 - Indentation creep behavior of a Zr-based bulk metallic glass
The deformation behavior of a Zr44Ti11Cu10Ni10Be25 bulk metallic glass (LM-1B) was studied in the supercooled liquid region by indentation creep test. Before indentation the glass transition and the crystallization temperatures were determined by calorimeter as 625 and 725 K, respectively. The phases formed during crystallization were identified by X-ray diffraction. The indentation creep experiments were carried out at different temperatures and loads. It was found that the creep can be regarded as Newtonian flow at strain rates between 5x10^(-5) and 5x10^(-4) s-1. The values of the viscosity and the activation energy of deformation were determined in the temperature range of 667-687 K.
D. Fatay, J. Gubicza, J. Lendvai, Journal of Alloys and Compounds 434-435 (2007) 75-78
L0071 - Influence of the synthesis route on sol-gel SiO2-TiO2 (1:1) xerogels and powders
Five different sol-gel routes are used in order to synthesize mixed SiO2-TiO2 materials. Simple mixing of the Ti and Si precursors, prehydrolyzing of TEOS, modification of the Ti alkoxide with acetic acid, isoamyl alcohol and acetylacetone lead to translucent gels with different time of gelation. Different techniques such as TGA, DTA, XRD and IR spectroscopy are used to characterize each material. IR spectroscopy revealed the presence of Si-O-Ti and Si-O-Si bonds for all the xerogels letting suppose a composite microstructure of the gels. Pre-hydrolyzing of TEOS and modification of Ti alkoxide with isoamyl alcohol are the most appropriate routes to retain the anatase phase up to 1100°C.
S. Vives, C. Meunier, Ceramics International xxx (2007) xxx-xxx
L0070 - Proton conduction in ceria-doped Ba2In2O5 nanocrystalline ceramic at low temperature
Sintered pellets of Ce-doped Ba2In2O5 (BIC) were prepared from nanopowders. The electrical conductivities were measured using ac impedance spectroscopy under different atmospheres and temperatures. The electrical conductivity of sintered BIC was found sensitive to environmental humidity when the temperature was below 300°C. However, in the presence of hydrogen, the electrical conductivities were independent of water content in the range of 0-30 vol%. The electrical conductivities of BIC were significantly affected by the presence of hydrogen in a temperature range of 100-300°C. The estimated protonic transference number and the measured open circuit voltage suggested the existence of electronic conduction. The coefficient of thermal expansion of BIC is 11.2x10^(-6) K-1 from 25 to 1250°C.
R. Hui, R. Maric, C. Decès-Petit, E. Styles, W. Qu, X. Zhang, J. Roller, S. Yick, D. Ghosh, K. Sakata, M. Kenji, Journal of Power Sources 161 (2006) 40-46
L0069 - A study on sintering aids for Sm0.2Ce0.8O1.9 electrolyte
In this study, an addition of Co oxide or Cu oxide to Sm0.2Ce0.8O1.9 (SDC) was studied to improve the sinterability of SDC. It has been found that both Co and Cu oxide are very effective as sintering aids, and the SDC sintering temperature can be reduced from 1400°C without aids to below 1000°C with only 1 at.% of either Cu oxide or Co oxide. As compared to the pure SDC, a slight decrease of ionic conductivity was observed in SDC with Cu sintering aid. There is no obvious effect on electrochemical property of SDC with Co sintering aid under 2.5 at.%.
X. Zhang, C. Decès-Petit, S. Yick, M. Robertson, O. Kesler, R. Maric, D. Ghosh, Journal of Power Sources 162 (2006) 480-485
L0068 - Electrical properties of low-density polyethylene/multiwalled carbon nanotube nanocomposites
Low-density polyethylene (LDPE)/multiwalled carbon nanotube (CNT) nanocomposites were prepared via melt compounding. The electrical properties of LDPE/CNT nanocomposites as a function of CNT volume content, frequency and temperature were investigated. The results showed that dielectric constant of LDPE/CNT nanocomposites increases slightly with increasing CNT content up to 1.9 vol.%. Thereafter, the dielectric constant of the nanocomposites increases sharply. The dielectric constant of LDPE/3.6 vol.% CNT nanocomposite is more than two orders of magnitude larger than that of pure LDPE. The frequency dependence of electrical properties of LDPE/3.6 vol.% CNT nanocomposite can be well described by the percolation theory.
G.D. Liang, S.C. Tjong, Materials Chemistry and Physics 100 (2006) 132-137
L0067 - Low temperature sintering of ZnTiO3/TiO2 based dielectric with controlled temperature coefficient
Structure, microstructure and dielectric properties of ZnTiO3 and rutile TiO2 mixtures (ZnTiO3 + xTiO2 with x = 0, 0.02, 0.05, 0.1, 0.15 and 0.2) sintered using ZnO-B2O3 glass phase (5 wt.% added) as sintering aid have been investigated. For all compounds, the sintering temperature achieves 900°C. The X-ray diffraction patterns indicate for x = 0.1 that the material is composed by three phases identified as ZnTiO3 hexagonal, TiO2 rutile and ZnO. The presence of ZnO is explained by the introduction of Ti into Zn site to form the (Zn1-xTix)TiO3+x solid solution in resulting the departure of ZnO from the ZnTiO3 structure. The ZnTiO3 + 0.15TiO2 composition sintered at 900°C with glass addition exhibits attractive dielectrics properties (Er = 23, tan(delta) < 10^(-3) and a temperature coefficient of the dielectric constant near zero (t = 0 ppm/°C)) at 1 MHz. It is also shown that the introduction of TiO2 allows to tune the temperature coefficient of the permittivity. All these properties lead this system compatible to manufacture silver based electrodes multilayer dielectrics devices.
A. Chaouchi, S. Marinel, M. Aliouat, S. d'Astorg, Journal of the European Ceramic Society 27 (2007) 2561-2566
L0066 - Synthesis and sintering of a monazite-brabantite solid solution ceramic for nuclear waste storage
Various geological arguments suggest that monazite can be an interesting waste-form for actinides such as Np, Pu, Cm and Am. We set up a simple procedure for making dense pellets of monazite-brabantite solid-solution ceramics with composition Ca0.092Th0.092 Ce0.089La0.727PO4. It consists of co-milling CaCO3, ThO2, CeO2, La2O3, and NH4H2PO4, 1250°C calcination, milling, cold-pressing, and sintering at 1450°C for 4 h. X-ray investigations showed that the reaction scheme from oxides to monazite is complex and involves various P+La-based intermediate compounds. The final density of the the product is around 95% of the theoretical density. The texture is homogeneous with a typical grain of size 5-20 mm. This process is designed to be adapted to hot cells and telemanipulators.
J-M. Montel, B. Glorieux, A-M. Seydoux-Guillaume, R. Wirth, Journal of Physics and Chemistry of Solids 67 (2006) 2489-2500
L0065 - Effects of solid fission products forming dissolved oxide (Nd) and metallic precipitate (Ru) on the thermal conductivity of uranium base oxide fuel
The effects of solid fission products on the thermal conductivity of uranium base oxide nuclear fuel were experimentally investigated. Neodymium (Nd) and ruthenium (Ru) were added to represent the physical states of solid fission products such as 'dissolved oxide' and 'metallic precipitate', respectively. Thermal conductivity was determined on the basis of the thermal diffusivity, density and specific heat values. The effects of the additives on the thermal conductivity were quantified in the form of the thermal resistivity equation - the reciprocal of the phonon conduction equation - which was determined from the measured data. It is concluded that the thermal conductivity of the irradiated nuclear fuel is affected by both the 'dissolved oxide' and the 'metallic precipitate', however, the effects are in the opposite direction and the 'dissolved oxide' influences the thermal conductivity more significantly than that of the 'metallic precipitate'.
D-J. Kim, J-H. Yang, J-H. Kim, Y-W. Rhee, K-W. Kang, K-S. Kim, K-W. Song, Thermochimica Acta 455 (2007) 123-128
L0064 - Microwave synthesis and characterization of metastable (Al/Ti) and hybrid (Al/Ti + SiC) composites
Two-directional microwave assisted rapid sinteringwas carried out to fabricate Al/Ti metastable composites and Al/(Ti + SiC) hybrid composites. The length scale of Ti was in microns (20µm) and of SiC in nanometers (50 nm). Microstructural characterization revealed uniform distribution of Ti particulates and SiC nanoparticulates in the Al matrix, relatively low amount of porosity and good matrix-reinforcement interfacial integrity. Coefficient of thermal expansion of the Al matrix reduced due to the presence of Ti and Ti + SiC reinforcements. The results revealed that addition of SiC nanoparticulates to Al-Ti formulations assisted in increasing microhardness, macrohardness, Al-Ti interfacial hardness, 0.2% YS and UTS while the ductility was marginally affected. Particular emphasis was placed to study the feasibility of using hybrid reinforcements in the Al matrix synthesized by using microwaves.
S.K. Thakur, T.S. Kong, M. Gupta, Materials Science and Engineering A 452-453 (2007) 61-69
L0063 - Rheological behaviour of kaolin/talc/alumina suspensions for manufacturing cordierite foams
This paper deals with the preparation and rheological charaterization of concentrated suspensions (40 vol.% solids) of mixtures of kaolin/talc/alumina to relative weight contents of 40/43.8/16.2, respectively. These concentrated suspensions were thixotropic and viscosus, the rheological properties being largely influenced by a number of processing parameters, the most relevant being the nature and content of deflocculant and the pH value. Best results were obtained for a polyacrylic-based polyelectrolyte and pH 11. Green densities of 59 % of TD were obtained. Dynamic and static sintering studies were performed and the analysis of the resulting phases was made by XRD. From these tests it was concluded that cordierite phase needed a thermal treatment of 1300ºC to be formed. The sintered slip cast materials have a large residual porosity because of the coarse particle size of the raw materals. Macroporous cordierite foams are obtained by impregnation of polyurethane foam into the optimized slip and heating at 1350ºC/1h with a burning out step at 550ºC/30 min.
J.B. Rodrigues Neto, R. Moreno, Applied Clay Science 37 (2007) 157-166
L0062 - Modelling WC-Co sintering shrinkage - Effect of carbide grain size and cobalt content
Phenomenological models based on the constitutive parameters uniaxial viscosity, viscous equivalent of Poisson's ratio and sintering stress are used to describe WC-Co sintering shrinkage. Shrinkage is divided into three subsequent stages. The influences of carbide grain size and cobalt content are accounted for and model parameters numerically adjusted to dilatometer results. The model successfully represents published shrinkage data for different materials and milling procedures.
A. Petersson, J. Ågren, Materials Science and Engineering A 452-453 (2007) 37-45
L0061 - Wetting, densification and phase transformation of La2O3/A2O3/B2O3-based glass-ceramics
A lead-free, non-alkali La2O3-Al2O3-B2O3 (LAB) glass with Al2O3 filler had been investigated for low temperature co-firing ceramic (LTCC) application. The glass forming window and several physical properties of the LAB systems were investigated by ICP, TMA, XRD, DSC, and SEM/EDS. The results show that the densification and crystallization temperatures of LAB/Al2O3 were between 700°C and 950°C and depended greatly on the formulation. Crystalline phase LaBO3 (LB) and LaAl2B3O9 (L2A3B) crystallized starting at 825°C and 925°C, respectively. High degree of densification and crystallization of one glass-Al2O3 composition (L30A) was observed with the microstructure composed of tabular L2A3B grains interlocking with submicron Al2O3 and LB grains.
C-L. Chen, W-C.J. Wei, A. Roosen, Journal of the European Ceramic Society 26 (2006) 59-65
L0060 - Processing and characterization of ultra-thin yttria-stabilized zirconia (YSZ) electrolytic films for SOFC
Sub-micron yttria-stabilized zirconia (YSZ) electrolyte layer was prepared by a liquid state deposition method and with an average thickness of 0.5 Am to improve the performance of the anode-supported solid oxide fuel cell (SOFC). The YSZ precursors, containing yttrium and zirconium species and an additive, poly-vinyl-pyrrolidone (PVP), were spin-coated on a Ni/YSZ anode substrate. Several properties, including crystalline phases, microstructures, and current-voltage (I -V) characteristics, were investigated. The thin film of 4 mol% Y2O3-doped ZrO2 (4YSZ) consisted of cubic, tetragonal, and a trace of monoclinic phases, and showed a crack-free layer after sintering at 1300°C. The anode supported SOFC, which consists of the Ni-YSZ anode, 4YSZ electrolyte, and Pt/Pd cathode, showed power densities of 477 mW/cm2 at 600°C, and 684 mW/cm2 at 800°C. Otherwise, the surface cracks of the other YSZ-coated samples (e.g. 8YSZ) can be repaired by a multi-coating method.
Y-Y. Chen, W-C.J. Wei, Solid State Ionics 177 (2006) 351 - 357
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