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Temperature dependence of electrical resistivity and dielectric characteristics of poled and BaZrO3 modified BaTiO3 ceramics
154
CERAMICS
[AS] are studied. The formation of Ca2(NH4)2(S04)3r CazPzO, and Ca(PO& is observed between 200% and 300%; at 400% CaSd4 appears. From 500 to 700°C, Ca(PO& reacts with Ca SO4 and with HAP and gives P-CazPzO,. Lastly, from 700% to 1000°C, p-Ca2Pz07 reacts with HAP and with CaS04 and gives p-Ca3(PO& [P-TCP]; from 1000 to 1 loo%, P-TCP and CaS04 react and form a sulfate ion containing calcium phosphosulfate, the structure of which is P-TCP.
COMPLETE RHEOLOGICAL CURVES FOR CLAY DISPERSIONS AND PASTES AND THEIR ASSOCIATED ENERGETICS
INTERNATIONAL,
ELEVATED TEMPERATURE INSTRUMENTED IMPACT OF A SINTERED SILICON CARBIDE H.C. Chandan,
L. Hermansson,
Vol. 11, “. 4. 1985
CHARPY
H. Abe and R.C. Bradt
A commercially available, densely sintered alpha silicon carbide was tested in air from room temperature to 1700% using a modified instrumented pendulum unit and standard Charpy size test specimens. The resistance heated silicon carbide specimens exhibited only elastic behavior, even at 1700%. A compliance analysis of the test revealed a linear elastic decrease of the absorbed impact energy and also a decrease of the fracture stress of the silicon carbide with increasing temperature.
N. N. Krugliski and V. Ya. Kruglitskaya The mechanism of structural formation within ceramic systems is determined by the chemical, physical, crystal chemical mineralogical, surface and adsorption properties of the raw materials. Clay minerals (layer silicates) are most common. In processing and formation the ceramic systems are inherent in coagulation set pattern of space-thixotropic nets of certain strength. Their rheological curves are the scientific base for optimization of constructive peculiarities of production equipment taking account of energetic expenditure, in technology. In this connection the curves of clay suspensions having different structure are obtained, the yield and-viscosity points are calculated and peculiarities of the contact interactions within them are stated basing on realization power of dispersed structures.
TEMPERATUREDEPENDENCEOFELECTRICAL RESISTIVITY AND DIELECTRIC CHARACTERISTICS POLED AND BaZrOl MODIFIED BaTi03 CERAMICS
Samples of pure BaTiOj, pure BaZr03 and intermediates containing from 5 up to 30% BaZrOs were carefully prepared by the usual ceramic procedure followed by X-ray diffraction analysis to ensure the complete reaction. Well sintered and translucent ceramic bodies were obtained. Measurements of dielectric constant (E), dielectric loss (tan 6) and ac. resistivity (e) were undertaken as a function of temperature up to 250% and at various frequencies of lo-50 Kc/s before and after polarization (800 V). The effect of poling field is discussed on the basis of the presence of spontaneous polarization in BaTi03 lattice. Finally, it was established that the introduction of Zr“’ ions in BaTiOJ lattice occurs in three steps: firstly, filling of Ba’+ vacancies, secondly solid solution formation from BaZr03 in BaTi lattice and thirdly, occupying interstitial sites in BaTiO? lattice. PHASE IN THE
P. Reynen, A. Firatli, D. von Mallinckrodt,
H. BoeB
Short communication.
STABLE AND METASTABLE PHASE EQUILIBRIA REACTIONS IN THE Si02-aA1203 SYSTEM
M. Lejeune and J.P. Boilot Pb (Mgr,, Nb2,j)Ox perovskite type compound which can be sintered at low temperatures has a ligh dielectric permittivity and so can be used as multilayer ceramic capacitors. In this study we show that ceramic processes resulting in different mixtures of phases and different microstructures strongly influence the dielectric properties (dielectric permittivity, dissipation factor and resistivity). Only a careful characterization in each step of the process allow the optimization of ceramics.
PRE-EUTECTIC OF
Morsy M. Abou Sekkina, M.K. El-Nimr and E. W. ABD Allah
A HIGH TEMPERATURE TERNARY SYSTEM MgO-A120j-Zr02
INFLUENCE OF CERAMIC PROCESSING ON DIELECTRIC PROPERTIES OF PEROVSKITE TYPE COMPOUND: Pb(Mg,,3 Nbz,J)OJ
AND
DENSIFICATION
IN MgF2-CaF2
S.C. Hu and L.C. De Jonghe Increased densification rates were found as much as 200°C below the eutectic temperature (980%) for MgF2 containing small amounts of CaF2. Constant heating rate and costant temperature sintering data, as well as microstructural developments indicated that solid state grain boundary transport rates had been enhanced by the eutectic forming additive. The effect saturated at about 1 wtl% CaF2. The results suggest that densification of ceramic powders could be favorably affected without a substantial increase in the grain growth rate, by the addition of small amounts of eutectic forming additives, and sintering below the eutectic temperature.
DEVELOPMENT OF PHOSPHATE FOR BONE IMPLANTS
GLASS-CERAMICS
F. Pernot, P. Balder, F. Bonnel, J. Zarzycki and P. Rabischong Porous glass-ceramics were prepared by the controlled crystallization of various phosphate MfoarnBbglasses. The crystalline phases were detected and the following properties of the materials were studied: - textural properties: porosity, interconnection pore size distribution; mechanical properties: fracture bending stress, Young’s modulus. It is shown that these properties depend not only on the composition of the base glasses, but also upon the grain size of the foaming agent.
Joseph A. Pask Procedures in the preparation of specimens in this system are critical due to the difficulty of nucleating aAl when the silicate liquid is not saturated with A1201 even though it may be supersaturated relative to crystalline aA120j, and the ease with which mullite growing from an alumino-silicate melt during cooling accomodates an excess of A1203. Metastable phase compositions and microstructures occur commonly. As a result, misinterpretations of experimental data have occurred in published reports. Stable and metastable phase equilibria diagrams in the aA1203-Si02 system are presented.
MECHANICAL
PROCESSING
OF BENTONITES
Jill Bulandr and Jaroslav Dudek Investigations into dry grinding and pneumatic processing of three bentonite types, aimed at improving their quality, were carried out. Grinding tests indicated that changes in bentonite grain size have little effect on its quality, unless it is complemented with rearrangements in smectite texture. Common nonclay admixtures of bentonite were shown to in-
CERAMICS
[AS] are studied. The formation of Ca2(NH4)2(S04)3r CazPzO, and Ca(PO& is observed between 200% and 300%; at 400% CaSd4 appears. From 500 to 700°C, Ca(PO& reacts with Ca SO4 and with HAP and gives P-CazPzO,. Lastly, from 700% to 1000°C, p-Ca2Pz07 reacts with HAP and with CaS04 and gives p-Ca3(PO& [P-TCP]; from 1000 to 1 loo%, P-TCP and CaS04 react and form a sulfate ion containing calcium phosphosulfate, the structure of which is P-TCP.
COMPLETE RHEOLOGICAL CURVES FOR CLAY DISPERSIONS AND PASTES AND THEIR ASSOCIATED ENERGETICS
INTERNATIONAL,
ELEVATED TEMPERATURE INSTRUMENTED IMPACT OF A SINTERED SILICON CARBIDE H.C. Chandan,
L. Hermansson,
Vol. 11, “. 4. 1985
CHARPY
H. Abe and R.C. Bradt
A commercially available, densely sintered alpha silicon carbide was tested in air from room temperature to 1700% using a modified instrumented pendulum unit and standard Charpy size test specimens. The resistance heated silicon carbide specimens exhibited only elastic behavior, even at 1700%. A compliance analysis of the test revealed a linear elastic decrease of the absorbed impact energy and also a decrease of the fracture stress of the silicon carbide with increasing temperature.
N. N. Krugliski and V. Ya. Kruglitskaya The mechanism of structural formation within ceramic systems is determined by the chemical, physical, crystal chemical mineralogical, surface and adsorption properties of the raw materials. Clay minerals (layer silicates) are most common. In processing and formation the ceramic systems are inherent in coagulation set pattern of space-thixotropic nets of certain strength. Their rheological curves are the scientific base for optimization of constructive peculiarities of production equipment taking account of energetic expenditure, in technology. In this connection the curves of clay suspensions having different structure are obtained, the yield and-viscosity points are calculated and peculiarities of the contact interactions within them are stated basing on realization power of dispersed structures.
TEMPERATUREDEPENDENCEOFELECTRICAL RESISTIVITY AND DIELECTRIC CHARACTERISTICS POLED AND BaZrOl MODIFIED BaTi03 CERAMICS
Samples of pure BaTiOj, pure BaZr03 and intermediates containing from 5 up to 30% BaZrOs were carefully prepared by the usual ceramic procedure followed by X-ray diffraction analysis to ensure the complete reaction. Well sintered and translucent ceramic bodies were obtained. Measurements of dielectric constant (E), dielectric loss (tan 6) and ac. resistivity (e) were undertaken as a function of temperature up to 250% and at various frequencies of lo-50 Kc/s before and after polarization (800 V). The effect of poling field is discussed on the basis of the presence of spontaneous polarization in BaTi03 lattice. Finally, it was established that the introduction of Zr“’ ions in BaTiOJ lattice occurs in three steps: firstly, filling of Ba’+ vacancies, secondly solid solution formation from BaZr03 in BaTi lattice and thirdly, occupying interstitial sites in BaTiO? lattice. PHASE IN THE
P. Reynen, A. Firatli, D. von Mallinckrodt,
H. BoeB
Short communication.
STABLE AND METASTABLE PHASE EQUILIBRIA REACTIONS IN THE Si02-aA1203 SYSTEM
M. Lejeune and J.P. Boilot Pb (Mgr,, Nb2,j)Ox perovskite type compound which can be sintered at low temperatures has a ligh dielectric permittivity and so can be used as multilayer ceramic capacitors. In this study we show that ceramic processes resulting in different mixtures of phases and different microstructures strongly influence the dielectric properties (dielectric permittivity, dissipation factor and resistivity). Only a careful characterization in each step of the process allow the optimization of ceramics.
PRE-EUTECTIC OF
Morsy M. Abou Sekkina, M.K. El-Nimr and E. W. ABD Allah
A HIGH TEMPERATURE TERNARY SYSTEM MgO-A120j-Zr02
INFLUENCE OF CERAMIC PROCESSING ON DIELECTRIC PROPERTIES OF PEROVSKITE TYPE COMPOUND: Pb(Mg,,3 Nbz,J)OJ
AND
DENSIFICATION
IN MgF2-CaF2
S.C. Hu and L.C. De Jonghe Increased densification rates were found as much as 200°C below the eutectic temperature (980%) for MgF2 containing small amounts of CaF2. Constant heating rate and costant temperature sintering data, as well as microstructural developments indicated that solid state grain boundary transport rates had been enhanced by the eutectic forming additive. The effect saturated at about 1 wtl% CaF2. The results suggest that densification of ceramic powders could be favorably affected without a substantial increase in the grain growth rate, by the addition of small amounts of eutectic forming additives, and sintering below the eutectic temperature.
DEVELOPMENT OF PHOSPHATE FOR BONE IMPLANTS
GLASS-CERAMICS
F. Pernot, P. Balder, F. Bonnel, J. Zarzycki and P. Rabischong Porous glass-ceramics were prepared by the controlled crystallization of various phosphate MfoarnBbglasses. The crystalline phases were detected and the following properties of the materials were studied: - textural properties: porosity, interconnection pore size distribution; mechanical properties: fracture bending stress, Young’s modulus. It is shown that these properties depend not only on the composition of the base glasses, but also upon the grain size of the foaming agent.
Joseph A. Pask Procedures in the preparation of specimens in this system are critical due to the difficulty of nucleating aAl when the silicate liquid is not saturated with A1201 even though it may be supersaturated relative to crystalline aA120j, and the ease with which mullite growing from an alumino-silicate melt during cooling accomodates an excess of A1203. Metastable phase compositions and microstructures occur commonly. As a result, misinterpretations of experimental data have occurred in published reports. Stable and metastable phase equilibria diagrams in the aA1203-Si02 system are presented.
MECHANICAL
PROCESSING
OF BENTONITES
Jill Bulandr and Jaroslav Dudek Investigations into dry grinding and pneumatic processing of three bentonite types, aimed at improving their quality, were carried out. Grinding tests indicated that changes in bentonite grain size have little effect on its quality, unless it is complemented with rearrangements in smectite texture. Common nonclay admixtures of bentonite were shown to in-