Influence Of Oxygen Activity On The Sintering Of MgCr2O4

The sintering behavior of MgCr2O4 powder compacts was investigated as a function of temperature, time, and oxygen activity. The results show that MgCr2O4 cannot be densified to \u3e70% of theoretical density at temperatures up to 1700°C if the oxygen activity exceeds 10−6 atm. The oxygen activity must be decreased to \u3c10−10 atm before densities exceeding 90% of theoretical can be achieved. Weight loss and X‐ray data indicated that maximum density occurred at an oxygen activity just above that where MgCr2O4 becomes unstable. Copyright © 1974, Wiley Blackwell. All rights reserve

Review Of P-type Doped Perovskite Materials For SOFC And Other Applications

p-type perovskite-type oxides are candidates for use as components of high temperature fuel cells and as oxygen separation membranes. The particular properties that these applications require are reviewed. The characteristics that these oxides have which allow them to satisfy many of these requirements are discussed and a defect model presented. The status of the utilization of these oxides and of the areas which need to be addressed such as thermal expansion and sintering characteristics are reviewed. © 1992

Model For Evaporation Of A Grain‐Boundary Phase

The surface profile which develops in the vicinity of a grain boundary precipitate in the course of evaporation is calculated. It is shown that the presence of the grain boundary precipitate affects the profile significantly if the product of the width of the grain boundary precipitate and the ratio of the evaporation rates of the unperturbed surface and the grain boundary precipitate is larger than one. Copyright © 1981, Wiley Blackwell. All rights reserve

Investigation Of Strontium-doped La(Cr, Mn)O3 For Solid Oxide Fuel Cells

The (La, Sr) (Cr, Mn)O3 system was investigated in an effort to develop an interconnect and cathode materials for solid oxide fuel cells. Sintering studies were done in air at temperatures below 1500°C. Significant improvements in densification were observed with substitution of 50 mol% Mn for chromium and a density of 95% theoretical was achieved with the substitution of 70 mol% Mn for chromium in the La(Cr, Mn)O3 system. Electrical conductivity (d.c.) measurements were made as a function of temperature and oxygen activity. At 1000°C and 1 atm oxygen, the electrical conductivity ranged from 2.2-20 S cm-1 for LaCr0.8Mn0.4O3 and La0.9Sr0.1Cr0.2Mn0.8O3, respectively. All of the compositions showed similar dependence of electrical conductivity on the oxygen activity. Dependence was small at high oxygen activities; as the oxygen activity decreased, a break in electrical conductivity at 10-12 atm and 1000°C was observed, and then the electrical conductivity decreased as PO21/4. Sintering and electrical conductivity studies indicate that La0.9Sr0.1Cr0.2Mn0.7O3 appears to be a candidate for solid oxide fuel cell applications. © 1992 Chapman & Hall

Multilayer ceramic oxide solid electrolyte for fuel cells and electrolysis cells and method for fabrication thereof

An unitary layered ceramic structure is disclosed which comprises co-sintered layers. The co-sintered structure comprises a sintered central layer of yttria stabilized zirconia (YSZ) which is about 8 mole percent yttria and having a density of at least about 95% of theoretical, and sintered outer layers of strontium lanthanum manganite (LSM) having the approximate molecular composition La.sub.0.8 Sr.sub.0.2 MnO.sub.3, having a density from about 50 to about 60% of theoretical, and having interconnected porosity from about 40 to 50% with an interconnected pore diameter from about one micron to about five microns. The sintered central layer is sandwiched by and bonded and sintered to the outer layers and is essentially free of significant amounts of manganese. A process for making the unitary composition-of-matter is also disclosed which involves tape casting a LSM tape and then on top thereof casting a YSZ tape. The process comprises presintering LSM powder at 1250.degree. F., crushing the presintered commercially available LSM powder, forming a slurry with the crushed LSM, a binder and solvent, tape casting the slurry and allowing the slurry to air dry. A mixture of commercially available submicron size particle YSZ powder is milled with a dispersant and solvent to disperse the YSZ particles thereby forming a dispersed YSZ slurry. The YSZ slurry is then tape cast on the dried LSM tape. If desired, a third layer of LSM can be cast on top of the dried YSZ layer. After drying the composite LSM/YSZ and LSM/YSZ/LSM tapes are fired at 1300.degree. C. No migration of manganese into the YSZ layer was observed with scanning electron microscope/edax in the sintered multilayer tape

Multilayer ceramic oxide solid electrolyte for fuel cells and electrolysis cells

A unitary layered ceramic structure is disclosed which comprises co-sintered layers. The co-sintered structure comprises a sintered central layer of yttria stabilized zirconia (YSZ) which is about 8 mole percent yttria and having a density of at least about 95% of theoretical, and sintered outer layers of strontium lanthanum manganite (LSM) having the approximate molecular composition La.sub.0.8 Sr.sub.0.2 MnO.sub.3, having a density from about 50 to about 60% of theoretical, and having interconnected porosity from about 40 to 50% with an interconnected pore diameter from about one micron to about five microns. The sintered central layer is sandwiched by and bonded and sintered to the outer layers and is essentially free of significant amounts of manganese. A process for making the unitary composition-of-matter is also disclosed which involves tape casting a LSM tape and then on top thereof casting a YSZ tape. The process comprises presintering LSM powder at 1250.degree. F., crushing the presintered commercially available LSM powder, forming a slurry with the crushed LSM, a binder and solvent, tape casting the slurry and allowing the slurry to air dry. A mixture of commercially available submicron size particle YSZ powder is milled with a dispersant and solvent to disperse the YSZ particles thereby forming a dispersed YSZ slurry. The YSZ slurry is then tape cast on the dried LSM tape. If desired, a third layer of LSM can be cast on top of the dried YSZ layer. After drying the composite LSM/YSZ and LSM/YSZ/LSM tapes are fired at 1300.degree. C. No migration of manganese into the YSZ layer was observed with scanning electron microscope/edax in the sintered multilayer tape

Preparation Of Perovskite Pb(Mg1/3Nb2/3)03 Using Pb3Nb208 And MgO

The synthesis of perovskite Pb(Mg1/3Nb2/3)O3 from an equimolar mixture of Pb3Nb208 and MgO was studied by solid‐state reaction techniques. An addition of 1 wt% excess MgO to the stoichiometric composition enhances the formation of the cubic perovskite phase. The absence of free PbO in the initial starting materials minimizes the volatilization loss during firing, thereby reducing the possibility of any compositional change and resulting in a substantial improvement of the perovskite phase purity over the conventional mixed‐oxide processing. Copyright © 1986, Wiley Blackwell. All rights reserve

Compensation Modes In Counterdoped Rutile

Thermogravimetric measurements were conducted on undoped, Nb5+ or Ta5+ donor-doped, and Al3+ acceptor doped rutile at 1000°C and 105-10-7 Pa oxygen activity. Nb5+ or Ta5+ doped rutile was counter doped by Al3+ in order to identify the role of Al3+ acceptor and its effect on donor doped rutile. Our results show that both dopants enter the lattice substitutionally for Ti4+, that Al3+ is as effective an acceptor as Nb5+ or that Ta5+ is effective as a donor, and the compensation occurs on a one-to-one basis. Earlier reports indicate that Al3+ is at best 50-70% efficient as an acceptor. © 1991

Determination Of Oxygen Chemical Diffusion Coefficients In Single Crystal SrTiO By Capacitance Manometry

The oxidation kinetics of a single crystal of SrTiOs were measured with a tensivolumetric system over the temperature range 700 -975 at 0.03 atm oxygen pressure. The oxidation was found to be oxygen diffusion limited with an activation energy of 14.9 - 1.3 kcal/mole. Combining the kinetic data with relative defect concentration data yielded an activation energy for oxygen self-diffusion of 57 - 16 kcal/mole. The enthalpy of formation of doubly ionized oxygen vacancies was calculated to be 126 - 13 kcal/mol. © 1975, The Electrochemical Society, Inc. All rights reserved