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T0006 - Effect of water on thermally stimulated currents in oxidised low-density polyethylene
The electrical conduction properties of low-density polyethylene (LDPE) oxidised in an ozone atmosphere produced by an electrical discharge in air, particularly the current behaviour in a short-circuited state, have been investigated. An anomalous discharging current and a reverse TSC flowing in the same direction as the charging current were observed. It has been found that the cause of these unique phenomena exists not on the cathode side, but on the anode side and that the water absorbed in the oxidised LDPE plays an important part. It is suggested that these unique properties are due to protons (H+) injected at the anode, possibly associated with an anode oxidation reaction at the oxidised LDPE-electrode interface
M. Onoda, H. Nakayama, K. Amakawa, J. Phys. D. Appl. Phys. 23 (1990) 211-217
T0005 - Amorphous phase separation in polypropylene block copolymers as revealed by thermostimulated depolarization measurements. I.complex spectra study
The thermally stimulated depolarization (TSD) technique was used to observe the amorphous phase separation in polypropylene block copolymers and to attribute its various dielectric relaxations to precise mobile entities. The complex thermostimulated spectra of polypropylene block copolymers were compared to complex spectra of polymers of the same nature as those of its main components, i.e., isotactic polypropylene, high-density polyethylene, and propylene-ethylene rubber. With TSD we then studied a binary blend of polypropylene and high-density polyethylene and another blend of polypropylene and propylene-ethylene rubber and also the various parts of polypropylene block copolymer which were separated by a selective solvent extraction. From peak-position and intensity considerations we suggested the origin of the three relaxations appearing from 90 to 290 K in the TSD complex spectra of polypropylene block copolymer
D .Ronarc'h, P. Audren, J.L. Moura, Journal of Applied Physics 58 (1985) 466-473
T0004 - Thermally stimulated current observed in glass transition temperature
x
T. Hino, Y. Kitamura, Electrical Engineering in Japan 95 (1975) 24-30
T0003 - Open-circuit TSD method and anomalous air gap current in Teflon FEP
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J.A. Giacometti, J.A. Malmonge, J.M.G.Neto, IEEE Transactions on Electrical Insulation EI-21 (1986) 383-387
T0002 - Thermal analysis of amorphous phase in a pharmaceutical drug
Thermally Stimulated Current (TSC) spectroscopy and Differential Scanning Calorimetry (DSC) have been applied to the characterization of the microstructure of a pharmaceutical drug. The dielectric relaxation spectrum shows two modes located in the temperature range of the glass transition. They have been attributed to the molecular mobility in the true amorphous phase and in the rigid amorphous region.
F. Fagegaltier, A. Lamure, C. Lacabanne, A. Caron, H. Mifsud and M. Bauer, Journal of Thermal Analysis and Calorimetry 48 (1997) 459-464
T0001 - Molecular mobility study of amorphous and crystalline phases of a pharmaceutical product by thermally stimulated current spectroscopy
Two crystalline forms and the amorphous state of irbesartan, a pharmaceutical drug chosen as a model, were analyzed by Thermally Stimulated Current (TSC) spectroscopy, a powerful technique currently used in polymer science to investigate the molecular dynamics of heterogeneous and complex materials. Whereas no specific dielectric response was noted for the B crystalline form, the A form of irbesartan exhibited molecular motions localized inside its channel structure. The dynamics involved in the dielectric glass transition of amorphous samples followed a compensation law characteristic of highly cooperative relaxation processes. Concerning the amorphous content in physical mixtures, a calibration curve and a limit of detection (2.5%) were established. The limit of detection could be improved by optimizing the TSC experimental parameters. The amorphous sample recrystallized at a single temperature was interpreted by the "idealized one-state model" defined here to describe systems composed of identical semicrystalline particles in which amorphous and crystalline phases are independent of each other (i.e., no chemical and physical interaction between the two phases). Therefore, the idealized one-state model may be simulated by a twostate model, which is representative of the two-phase model. Other samples recrystallized through a complex annealing stage were explained by the classical one-state model in agreement with the three-phase model used to describe bulk semicrystalline systems. These results demonstrate that, as for polymers, the semicrystalline state of pharmaceutical drugs should not be considered as a single state but as a more complex system that can be described as an idealized one-state model or a one-state model depending on the applied thermal treatment. These results give a new view that should be taken into account in the development of amorphous pharmaceutical drugs and formulations
N. Boutonnet-Fagegaltier, J. Menegotto, A. Lamure, H. Duplaa, A. Caron, C. Lacabanne, M. Bauer, Journal of Pharmaceutical Sciences 91(2002) 1548-1560
L0116 - MgTiO3 for Cu base metal multilayer ceramic capacitors
The evolution of the cost of palladium justifies studies devoted to the use of cheap base metals as electrodes for multilayer ceramic capacitors. In a precedent [J. Eur. Ceram. Soc.10-11(2001) 1681] work we investigated on Mn acceptor together with W donor additions on the properties of MgTiO3 ceramics sintered at 1350°C under a reducing atmosphere (wet N2-1%H2). As in acceptor/donor [Proceedings K1; 1206 CIMTEF, Florence (1998) 88] codoped BaTiO3 the insulating character of MgTiO3 was conserved. In order to employ these materials in the production of type-I multilayer ceramic capacitors with Copper inner electrodes we investigate now on the possibility of sintering magnesium titanate at low temperature. We have studied the densification behavior of different MgTiO3 compositions with lithium salts additions, considering particularly the effect of the non-stoechiometry expressed as the Mg/Ti ratio. Full densification appears below 1000°C. The obtained ceramics, that have been co-sintered in a multilayer structure with Cu electrodes, are characterised by a resistivity higher than 10^(13) ohm cm together with a NPO dielectric constant ranging from 14 to 16 depending on the exact composition together with losses lower than 0.2%.
J. Bernard, D. Houivet, J. El Fallah, J.M. Haussonne, Journal of the European Ceramic Society 24 (2004) 1877-1881
L0115 - Lowering of BaB'1/3B"2/3O3 complex perovskite sintering temperature by lithium salt additions
Complex perovskite materials with the formula BaB'1/3B"2/3O3 have been broadly studied for their attractive dielectric properties. These materials exhibit a high relative dielectric constant and a very low dissipation factor. For example, the BaMg1/3Ta2/3O3 material has a relative dielectric constant close to 26 with a dissipation factor lower than 10^(-4) at 1 MHz. These properties are very promising for applications such as hyper-frequency resonators or/and capacitors. Unfortunately, a high temperature is necessary to achieve a satisfying densification of this materials family (>1400°C) whereas the lowering of this temperature is more and more crucial from the industrial point of view. In particular, the development of Base Metal Electrodes Multi-Layer Ceramic Capacitors (BME-MLCC) requires the sintering of dielectric materials at low temperatures (<1100°C). The aim of the study is thus to lower the sintering temperature of these materials. For this goal, lithium salts (Li2CO3, LiF, BaLiF3 and LiNO3) have been tested as sintering agents to densify BaZn1/3Ta2/3O3, BaMg1/3Ta2/3O3 and BaZn1/3Nb2/3O3 materials. It is shown, for example, that the BaMg1/3Ta2/3O3 sintering temperature is lowered by 300°C when 15 mol % of lithium nitrate is added without affecting the dielectric properties at 1 MHz. For the best sintering agents investigated and each studied materials, the ceramic is characterised in terms of final density, microstructure and dielectric properties and densification mechanisms are discussed.
F. Roulland, R. Terras, G. Allainmat, M. Pollet, S. Marinel, Journal of the European Ceramic Society 24 (2004) 1019-1023
L0114 - CaZrO3, a Ni-co-sinterable dielectric material for base metal-multilayer ceramic capacitor applications
The aim of this work is to obtain CaZrO3 powders that are co-sinterable with nickel electrodes. Since CaZrO3 is often sintered at temperatures higher than 1550°C to achieve high sample densities, obtaining a powder co-sinterable with Ni would require lower sinteringtemperatures. The co-sintering also requires that the reaction takes place in a reducing atmosphere. After optimizingthe thermal cycle for the phase synthesis, several approaches were investigated to decrease the CaZrO3 sinteringtemperature. First, the grain size effect on the densification was studied to enhance the calcined powder's reactivity before sintering. In addition, the Ca/Zr ratio was investigated, and the effect of doping with lithium salts was examined. Similarly, in order to allow co-sintering with basemetal inner electrodes, the sinterability and the properties of the dielectric were examined in a reducingatmosphere. Finally, a cosintered material was synthesized, resultingin good dielectric properties. The samples were analyzed in terms of structure and microstructure. The electric and dielectric properties were also measured on sintered samples.
M. Pollet, S. Marinel, G. Desgardin, Journal of the European Ceramic Society 24 (2004) 119-127
L0113 - Thermal and mechanical properties of cordierite, mullite and steatite produced by plasma spraying
Cordierite, mullite and steatite are silicate materials widely used in the ceramics industry. There is, however, only sparse information on their application in plasma spraying and properties of sprayed materials. Plasma sprayed deposits of cordierite, mullite and steatite contain amorphous phases as the result of rapid cooling of molten particles. The amorphous phase has a significant influence on physical properties, especially in connection with heat treatment. This article deals with phase changes of cordierite, mullite and steatite, resulting from plasma deposition. Special attention is paid to amorphous phase crystallization in subsequent heat treatment. Plasma sprayed deposits were produced using a water stabilized plasma torch WSP®. The processes taking place in the deposits were examined primarily by differential thermal analysis (DTA), thermal dilatometry (TMA) and X-ray diffraction (XRD). These measurements were complemented by the determination of physical properties (namely, density, Young's modulus and strength) and morphological observations. Important thermal characteristics like crystallization temperature and the coefficient of thermal expansion (CTE) of all materials were determined.
P. Rohan, K. Neufuss, J. Matejicek, J. Dubskya, L. Prchlik, C. Holzgartner, Ceramics International 30 (2004) 597-603
L0112 - Nanosized alumina from boehmite additions in alumina porcelain 1. Effect on reactivity and mullitisation
The influence of nanosized alumina additions and of grain size of alumina filler on the reaction-sintering of alumina porcelain is investigated. Phase and porosity evolution has been studied from room temperature up to 1400°C. When vitrification occurs the presence of alumina nanoparticles leads to a new type of mullitisation which has two major consequences: a volume expansion resulting in a shrinkage inhibition and a decrease of the amount of liquid which causes densification problems at usual firing temperatures. This phenomenon is enhanced if the alumina filler is coarse but it is limited when fine and round alumina is used because in that last case vitrification kinetics is slowed down.
F. Belnou, D. Goeuriot, P. Goeuriot, F. Valdivieso, Ceramics International 30 (2004) 883-892
L0111 - Effect of milling on the damping behavior of nano-structured copper
In the present study, elemental Cu powder was mechanically milled (MMed) for 10 h to reduce the grain (crystalline) size in the nano-range (<100 nm). The mechanically milled powder (10 h-MMed) and elemental powder without mechanical milling (MM) (0 h-MMed) was consolidated by die-cold compaction and were further hot extruded at different temperatures to maintain a crystallite size within the nano-range. Further, the specimen was tested by a novel free-free type suspended beam arrangement, coupled with circle-fit approach to determine damping characteristics. The characterization results help to understand the effect of the nano-size grains on the overall damping capacity of the bulk samples compared to a normal micro-crystalline sample. Results show that the damping capacity of the nano-grained material increases due to the presence of process induced microstructural changes similar to the damping behavior of a micro-grain sized specimen.
N. Srikanth, M.A. Thein, M. Gupta, Materials Science and Engineering A366 (2004) 38-44
L0110 - Iron oxide as an effective sintering aid and a grain boundary scavenger for ceria-based electrolytes
The effect of FeO1.5 addition on the densification behavior and electrical properties of Ce0.8Gd0.2O(2-d) ceramics was examined. The small addition of FeO1.5 (e.g., 0.5 at.%) reduced sintering temperature (by ~200°C) and promoted densification rate. When sintered at 1300°C for 5 h, the 0.5 at.% FeO1.5-doped Ce0.8Gd0.2O(2-d) has ~95% relative density, as compared to ~82% relative density for the undoped one. The measurement of lattice parameter indicated that the FeO1.5 addition also promoted the dissolution of Gd2O3 in CeO2 at lower sintering temperatures. On the other hand, the grain boundary (GB) conductivity could be significantly improved by small addition of FeO1.5. The optimum scavenging effect on SiO2 impurity was achieved by adding 0.5 at.% FeO1.5 to Ce0.8Gd0.2O(2-d) ceramics and sintered at 1400-1500°C.
T.S. Zhang, J. Ma, L.B. Kong, S.H. Chan, P. Hing, J.A. Kilner, Solid State Ionics 167 (2004) 203-207
L0109 - The synthesis mechanism of Ca3Al2O6 from soft mechanochemically activated precursors studied by time-resolved neutron diffraction up to 1000°C
The reaction pathway for the Ca3Al2O6 formation up to 1300°C, from mechanochemically treated mixtures of amorphous aluminum hydroxide and CaCO3; was studied in situ by differential thermal analysis, constant heating rate dilatometry and timeresolved neutron powder diffraction. The experiment was carried out, in an open system, on a sample with the nominal Ca3Al2O6 stoichiometry. The results obtained by neutron diffractometry and thermal analysis were in good agreement with the data obtained by scanning electron microscopy and X-ray diffraction on heat-treated and-quenched samples. The synthesis path implied the formation of cryptocrystalline Al2O3; crystalline CaO, CaAl2O4 and Ca12Al14O33 as transitory phases. Finally the nucleation and growth of the single phase Ca3Al2O6 took place at 1300°C and exhibited porous structure due to CO2 and H2O release.
J.M. Rivas Mercury, A.H. De Aza, X. Turrillas, and P. Pena, Journal of Solid State Chemistry 177 (2004) 866-874
L0108 - Effect of transition metal oxides on densification and electrical properties of Si-containing Ce0.8Gd0.2O(2-d) ceramics
Ce0.8Gd0.2O(2-d) (CGO20) ceramic has been considered as one of the most promising electrolytes for intermediate temperature (IT) fuel cells. It has been reported that some transition metal oxides (TMO), such as MnO2, Fe2O3 and Co3O4, are effective sintering aids for the densification of ceria-based electrolytes. However, very little information is available regarding the effect of TMO addition on the electrical properties of Si-containing CGO20 ceramics. In this study, 0.5 at.% (atomic percent) TMOs have been loaded into the CGO20 with ~30 ppm (pure) and ~200 ppm (impure) SiO2, respectively, and the sintering behavior and ionic conductivity have been investigated. It has been found that Co3O4 is the most effective sintering aid, and the sintering temperature of CGO20 can be reduced by over 200°C by adding 0.5 at.% CoO4/3. All the TMOs used show a slight effect on the grain-boundary (GB) conductivity of the pure CGO20. However, SiO2 additions, together with MnO2 and Co3O4, have found to be extremely detrimental to the GB conduction of CGO20. As compared to the impure CGO20, the GB resistance has been increased by over six times for the impure one with addition of only 0.5 at.% CoO4/3. On the other hand, in contrast to the Mn or Co doping case, small addition of Fe2O3 has a scavenging effect on SiO2 impurity, and significantly improves the GB conduction of the impure CGO20. Therefore, Fe2O3 could be used as an effective sintering aid, as well as a grain-boundary scavenger for SiO2 contaminated ceria-based electrolytes.
T.S. Zhang, J. Ma, Y.J. Leng, S.H. Chan, P. Hing, J.A. Kilner, Solid State Ionics 168 (2004) 187-195
L0107 - The kinetics of surface area reduction during isothermal sintering of hydroxyapatite adsorbent
The behaviour of non-stoichiometric hydroxyapatite (HA) during the calcination in a solid bedwas investigated. The structural properties are described in terms of the specific surface area. Calcination led to a significant decrease of the specific surface area by particle coalescence and densification. Hydroxyapatite begins to shrink near 780°C and reaches 97% theoretical density at 1100°C. The specific surface area and density variations are caused both by sintering and chemical reaction. Sintering data from these solids were correlated as a function of time and temperature. The rate of sintering is assumed to obey an Arrhenius equation. These results are compared with a number of literature models describing the mechanism of sintering kinetics using the specific surface area, and a good agreement is observed. The kinetic equation used is based on sintering driven by the curvature gradient in the interparticle neck region associated with initial stage sintering. Then, the decline in specific surface area is accurately described by the empirical equation of the form dS/dt = -B(T)k^b. The changing value of b, also known as the "order" of the reaction, suggests that the diffusion mechanism for loss of surface area may be a function of the temperature.
S. Bailliez, A. Nzihou, Chemical Engineering Journal 98 (2004) 141-152
L0106 - The mechanical behavior of magnesium alloy AZ91 reinforced with fine copper particulates
In this study, a hybrid composite based on magnesium alloy AZ91A reinforced with copper particulateswas fabricated using the disintegrated melt deposition (DMD) processing technique followed by hot extrusion. Microstructural characterization of the as-extruded composite sample revealed a near uniform distribution of the copper particulates and other intermetallic phases through the magnesium alloy metal matrix, good integrity at the copper-magnesium alloy matrix interfaces and evidence of minimal porosity. Mechanical property quantification revealed that addition of copper particulates resulted in a significant increase in elastic modulus, 0.2% offset yield strength and ultimate tensile strength of the composite material. However, ductility of the composite was marginally affected when compared to the unreinforced monolithic counterpart. The overall mechanical properties of AZ91A/Cu composite were found to be higher than the silicon carbide particulate reinforced AZ91 composite, even for higher volume fractions of the particulate reinforcement. Influence of copper in the matrix of magnesium alloy AZ91A is examined in light of intrinsic microstructural features and mechanical properties of the composite.
K.F. Ho, M. Gupta, T.S. Srivatsan, Materials Science and Engineering A369 (2004) 302-308
L0105 - Experimental and numerical analysis of the deformation of ferrite segments during sintering
The thermo-mechanical behaviour of hard ferrite powder compacts at high temperature is investigated with a view to simulating dimensional changes occurring during sintering of industrial components. Emphasis is laid on the anisotropy in both shrinkage and viscosity, which is induced by the prior pressing operation performed under magnetic field. Anisotropic shrinkage and viscosity are described according to an original approach based on an orthotropic thermo-elastic equation, which assumes an analogy between the thermal and elastic terms of this equation and the viscous and free sintering deformations. Finite element calculations using this constitutive equation are then carried out on two industrial parts. The comparison between the obtained numerical results and experimental measurements proves the relevance of the proposed model.
F. Toussaint, D. Bouvard, Ph. Tenaud, E. Di Marcello, Journal of Materials Processing Technology 147 (2004) 72-78
L0104 - Rare earth phosphate powders RePO4 . nH2O (Re=La, Ce or Y) II. Thermal behavior
The thermal behavior, thermostructural and morphological changes, of rare earth phosphate powders RePO4 . nH2O (Re=La, Ce or Y) was investigated up to 1500°C using high temperature X-ray diffraction, FT-infrared and Raman spectroscopies and thermogravimetry coupled with differential thermal analysis. The hydration water of the compounds was zeolitic (for Re=La or Ce) or coordinated (for Re=Y) and was associated with a divariant or a monovariant equilibrium of dehydration, respectively. The high temperature anhydrous monoclinic phase LaPO4 or CePO4 formed irreversibly at about 750°C after the total dehydration of the hexagonal hydrated structure while the dehydration of the monoclinic YPO4 . 2H2O phase began from about 190°C with its simultaneous decomposition into tetragonal YPO4. A polytrioxophosphate secondary minor phase Re(PO3)3 resulting from adsorbed H3PO4 was formed at 950°C and decomposed at 1350°C. The particle morphology did not change with the temperature but grain coalescence occurred below 1000°C.
S. Lucas, E. Champion, D. Bernache-Assollant, and G. Leroy, Journal of Solid State Chemistry 177 (2004) 1312-1320
L0103 - Ce0.8Gd0.2O(2-d) ceramics derived from commercial submicron-sized CeO2 and Gd2O3 powders for use as electrolytes in solid oxide fuel cells
Twenty percentage of Gd2O3-doped ceria solid solution has been prepared as an electrolyte for solid oxide fuel cells via the conventional mixed-oxide method from high-purity commercial CeO2 and Gd2O3. The solubility of Gd2O3 in CeO2 in the temperature range of 1300-1700°C has been examined based on the measurements of the lattice parameter. It is found that the dissolution of Gd2O3 in CeO2 is completed at 1600°C for 5 h. The addition of Gd2O3 increases sintering temperature, retards densification, and also depresses grain growth as compared with undoped CeO2. The sample sintered at 1550°C for 5 h has the highest grain boundary conductivity, while the highest grain interior conductivity is achieved for the sample sintered at 1600°C for 5 h. It is also observed that below 500°C, the maximum total conductivity is exhibited by the former sample, but above 500°C, for the latter one.
J. Ma, T.S. Zhang, L.B. Kong, P. Hing, S.H. Chan, Journal of Power Sources 132 (2004) 71-76
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