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Ceramic electrodes for photoelectrolytic decomposition of water
146
CERAMICS
COMPOUNDS
IN THE NazO-Yz03-Si02
SYSTEM
F. Cervantes Lee, J. Marr and F. P. Glasser Data on the synthesis and characterization of six ternary phases in this system are presented. NaY&i6026 is confirmed as having the apatite structure: 39 indexed powder reflections are given. The synthesis of NajYSizO-i is reported, together with unindexed powder data. Much interest centres about the sodium-ion conductor, NasYSi4012, for which indexed powder data are presented. This phase is shown to be one of a family of compounds which have the general formula Na24_3xYSi12036. In this notation, x = 3 for NarYSi4012. At least three other phases are stable up to liquidus temperatures and characterization data are presented for Na9YSi60L8 (x = 2), NajYSijOP (x = 4) and NaYSizOh (x = 6). .
M. Vardelle and J.L. Besson r-alumina massive samples have been made by arc-plasma spraying. Measurements of the temperature and the velocity of the plasma stream as well as surface temperatures and velocities of the alumina particles have been performed which have identified relations between the microstructure and crystallography of the deposits and the working conditions of the arc-plasma spraying device. After optimization of the process, samples 98% dense and containing less than 2% of (Yphase have been obtained.
CERAMIC ELECTRODES FOR PHOTOELECTROLYTIC DECOMPOSITION OF WATER J. M. Kowalski and H. L. Tuller In the last decade a number of semiconducting
oxides have in the photoassisted electrolytic decomposition of water to produce hydrogen fuel. To date, this attractive process still suffers from relatively low solar energy conversion efficiencies. In this paper we outline the operating principles characterizing photoelectrolytic cells, and discuss those materials properties which appear most relevant to their efficient operation. Recent data obtained for BaTiO, and other photoelectrodes are presented which illustrate the importance of materials preparation.
been identified which serve as essential components
Vol. 11, n 4,198s
stage (400-1200%), secondary mullitization stage (1200-l 400 or 1500%) and recrystallization sintering stage (above 1400 or 1500°C). The sinterability of different grades of bauxites is dependent on the A1203 content. The closer is the composition of calcined bauxite to that of mullite, the more difficult is it to sinter. It is postulated that secondary mullitization and liquid phase action are the two principal factors influencing the sintering of these bauxites. Grade II bauxites characterised by maximum secondary mullite formation and relatively low glass content are found to be most difficult to sinter.
NEPHELINE SYENITE-TALC VITRIFIED BODIES D.M. Ibrahim,
?-ALUMINA OBTAINED BY ARC PLASMA SPRAYING: A STUDY OF THE OPTIMIZATION OF SPRAYING CONDITIONS
INTERNATIONAL.
LOW TEMPERATURE
E.H. Sallam, A.A. Khalil and S. M.H. Naga
Compositions in the system, talc-nepheline syenite-quartzchina clay (Kaolinite) were studied. The content of nepheline syenite was kept constant, 250/o, while talc was added in the range of 5-15% at the expense of quartz. This study extended the range of fusible talclnepheline mixes from 15 to 28%. The content of talc dissolved in the glassy phase is limited to 3-40/o. Addition of talc to the compositions caused the dissolution of mullite and increased the glassy phase. The addition of nepheline syenite counteracts the effect of talc on the thermal expansion coefficient of the bodies.
KINETICS OF THE FORMATION Mg0*2Ti02 AND MgO=TiOz Osamu Yamaguchi, Shimizu
Shigeharu
OF ALKOXY-DERIVED
Yamamoto and Kiyoshi
The compounds of Mg0*2Ti02 and MgO*TiOz were formed directly from mixed powders prepared by the simultaneous hydrolysis of magnesium and titanium alkoxides. Both crystallization isotherms were described by the first-order equation - ln(l - f) = k (t - t,). Activation energies corresponding to nucleation and propagation are 57 kcallmol and 21 kcallmol with Mg0*2Ti02 and 61 kcallmol and 29 kcallmol with MgO*TiOz, respectively.
PETROGRAPHIC AND X-RAY IDENTIFICATION OF PHASES FORMED BY OXIDATION OF SILICON CARBIDE V.A. Lavrenko, S. Jonas and R. Pampuch
PROPERTIES OF SOME HIGH ALUMINA REFRACTORIES OBTAINED FROM DIFFERENT ALUMINA SOUl?CES lbrahim Nasr, F. M. Abdel-Kader
and H. K. Embabi
Within the same alumina level, refractories made using different sources of alumina vary widely in their densification and refractory properties. Refractories based on the more volume stable synthetic mullite and sillimanite grains are dense and more creep resisting than the continuously bloating easily deformed bauxite ones. The mineralogical composition of the grog grain used and the matrix developed in a fired brick appears to be the most important factor determinings its resistance at high temperatures.
SINTERING BAUXITES
CHARACTERISTICS
Zhong Xiangchong
OF CHINESE
and Li Guangping
The sintering behaviour kaolinite type proceeds
Short communication.
of Chinese bauxites of the diasporein three stages, viz: decomposition
OXIDATION OF SILICON NITRIDE HOT PRESSED WITH CeOz AND SiOz ADDITIONS G.N. Babini, A. Bellosi and P. Vincenzini (CeOz + SiO+doped hot pressed silicon nitride shows parabolic oxidation kinetics in dry flowing air at T = 773 to 1673 K. Possible oxidation mechanisms have been proposed. The apparent activation energy for oxidation (-350 kJmol - ‘) suggests migration of impurity cations through the grain boundary phase to the silicon nitride/oxide reaction interface as the probable rate-limiting step. The very low solubility of cerium in silicate melts appears to be an important factor for oxidation. Cristobalite and ceria were the main crystalline oxidation products, the genesis and morphology of CeOz crystals being strictly related to oxidation temperature and cooling rate. A previously unknown hexagonal high-temperature form of ceria crystallized in samples subjected to very fast quenching.
CERAMICS
COMPOUNDS
IN THE NazO-Yz03-Si02
SYSTEM
F. Cervantes Lee, J. Marr and F. P. Glasser Data on the synthesis and characterization of six ternary phases in this system are presented. NaY&i6026 is confirmed as having the apatite structure: 39 indexed powder reflections are given. The synthesis of NajYSizO-i is reported, together with unindexed powder data. Much interest centres about the sodium-ion conductor, NasYSi4012, for which indexed powder data are presented. This phase is shown to be one of a family of compounds which have the general formula Na24_3xYSi12036. In this notation, x = 3 for NarYSi4012. At least three other phases are stable up to liquidus temperatures and characterization data are presented for Na9YSi60L8 (x = 2), NajYSijOP (x = 4) and NaYSizOh (x = 6). .
M. Vardelle and J.L. Besson r-alumina massive samples have been made by arc-plasma spraying. Measurements of the temperature and the velocity of the plasma stream as well as surface temperatures and velocities of the alumina particles have been performed which have identified relations between the microstructure and crystallography of the deposits and the working conditions of the arc-plasma spraying device. After optimization of the process, samples 98% dense and containing less than 2% of (Yphase have been obtained.
CERAMIC ELECTRODES FOR PHOTOELECTROLYTIC DECOMPOSITION OF WATER J. M. Kowalski and H. L. Tuller In the last decade a number of semiconducting
oxides have in the photoassisted electrolytic decomposition of water to produce hydrogen fuel. To date, this attractive process still suffers from relatively low solar energy conversion efficiencies. In this paper we outline the operating principles characterizing photoelectrolytic cells, and discuss those materials properties which appear most relevant to their efficient operation. Recent data obtained for BaTiO, and other photoelectrodes are presented which illustrate the importance of materials preparation.
been identified which serve as essential components
Vol. 11, n 4,198s
stage (400-1200%), secondary mullitization stage (1200-l 400 or 1500%) and recrystallization sintering stage (above 1400 or 1500°C). The sinterability of different grades of bauxites is dependent on the A1203 content. The closer is the composition of calcined bauxite to that of mullite, the more difficult is it to sinter. It is postulated that secondary mullitization and liquid phase action are the two principal factors influencing the sintering of these bauxites. Grade II bauxites characterised by maximum secondary mullite formation and relatively low glass content are found to be most difficult to sinter.
NEPHELINE SYENITE-TALC VITRIFIED BODIES D.M. Ibrahim,
?-ALUMINA OBTAINED BY ARC PLASMA SPRAYING: A STUDY OF THE OPTIMIZATION OF SPRAYING CONDITIONS
INTERNATIONAL.
LOW TEMPERATURE
E.H. Sallam, A.A. Khalil and S. M.H. Naga
Compositions in the system, talc-nepheline syenite-quartzchina clay (Kaolinite) were studied. The content of nepheline syenite was kept constant, 250/o, while talc was added in the range of 5-15% at the expense of quartz. This study extended the range of fusible talclnepheline mixes from 15 to 28%. The content of talc dissolved in the glassy phase is limited to 3-40/o. Addition of talc to the compositions caused the dissolution of mullite and increased the glassy phase. The addition of nepheline syenite counteracts the effect of talc on the thermal expansion coefficient of the bodies.
KINETICS OF THE FORMATION Mg0*2Ti02 AND MgO=TiOz Osamu Yamaguchi, Shimizu
Shigeharu
OF ALKOXY-DERIVED
Yamamoto and Kiyoshi
The compounds of Mg0*2Ti02 and MgO*TiOz were formed directly from mixed powders prepared by the simultaneous hydrolysis of magnesium and titanium alkoxides. Both crystallization isotherms were described by the first-order equation - ln(l - f) = k (t - t,). Activation energies corresponding to nucleation and propagation are 57 kcallmol and 21 kcallmol with Mg0*2Ti02 and 61 kcallmol and 29 kcallmol with MgO*TiOz, respectively.
PETROGRAPHIC AND X-RAY IDENTIFICATION OF PHASES FORMED BY OXIDATION OF SILICON CARBIDE V.A. Lavrenko, S. Jonas and R. Pampuch
PROPERTIES OF SOME HIGH ALUMINA REFRACTORIES OBTAINED FROM DIFFERENT ALUMINA SOUl?CES lbrahim Nasr, F. M. Abdel-Kader
and H. K. Embabi
Within the same alumina level, refractories made using different sources of alumina vary widely in their densification and refractory properties. Refractories based on the more volume stable synthetic mullite and sillimanite grains are dense and more creep resisting than the continuously bloating easily deformed bauxite ones. The mineralogical composition of the grog grain used and the matrix developed in a fired brick appears to be the most important factor determinings its resistance at high temperatures.
SINTERING BAUXITES
CHARACTERISTICS
Zhong Xiangchong
OF CHINESE
and Li Guangping
The sintering behaviour kaolinite type proceeds
Short communication.
of Chinese bauxites of the diasporein three stages, viz: decomposition
OXIDATION OF SILICON NITRIDE HOT PRESSED WITH CeOz AND SiOz ADDITIONS G.N. Babini, A. Bellosi and P. Vincenzini (CeOz + SiO+doped hot pressed silicon nitride shows parabolic oxidation kinetics in dry flowing air at T = 773 to 1673 K. Possible oxidation mechanisms have been proposed. The apparent activation energy for oxidation (-350 kJmol - ‘) suggests migration of impurity cations through the grain boundary phase to the silicon nitride/oxide reaction interface as the probable rate-limiting step. The very low solubility of cerium in silicate melts appears to be an important factor for oxidation. Cristobalite and ceria were the main crystalline oxidation products, the genesis and morphology of CeOz crystals being strictly related to oxidation temperature and cooling rate. A previously unknown hexagonal high-temperature form of ceria crystallized in samples subjected to very fast quenching.