Beta Alumina Research Articles

Synthesis of Lanthanum Beta Alumina by the Polymeric Precursor Technique

Lanthanum beta alumina powders were obtained by the polymeric precursor technique using lanthanum nitrate, aluminum nitrate, ethylene glycol and citric acid. The transformations that occur during thermal treatment of the precursor solution were evaluated by thermogravimetric and differential thermal analysis. Fourier Transform Infrared analysis for residual carbon qualitative detection and gas adsorption analysis for evaluating specific surface area, BET method, were carried out in powder specimens heat treated at different temperatures. High calcination temperature leads to the formation of hard agglomerates. The powders calcined at 800°C for 4 h have high specific surface area, ~ 120 m2/g. All processed powders and green pellets sintered at different temperatures were analyzed by X-ray diffraction for structural phase determination. Single phase LaAl11O18 pellets have application as solid electrolytes in disposable electrochemical devices for monitoring dissolved oxygen species in molten steel at very high temperatures, > 1500 °C, during steel production.

Preparation and property of textured beta alumina

Preparation and property of textured beta alumina

443 SOFC-AMTECの複合モジュール化に関する性能解析(燃料電池,電力貯蔵,環境保全型エネルギー技術)

The alkali metal thermal to electric converter (AMTEC) is a device for the direct conversion of heat to electrical power. Operating hot-side temperatures of AMTEC cells are well compatible with those of solid oxide fuel cells (SOFC), so that the stacks of the SOFC can be directly coupled to hot-side of the AMTEC cells. The AMTEC cells would produce electrical power from released heat of the SOFC, as well as control the SOFC operating temperatures by modulating current of the AMTEC cell. A new honeycomb type AMTEC cell is discussed in this paper. The cell uses advanced beta"-alumina solid electrolyte (BASE) configurations to improve the device performance over the conventional tube BASE systems. Expected power densities and efficiencies were calculated. The influence of temperature differences between heat source and anode side electrode is also discussed for vaper-fed type and vaper-vaper-fed type cells.

Investigations on the factors assisting a one-step synthesis cum sintering of sodium beta alumina using microwaves

An understanding of a simultaneous microwave synthesis cum sintering taking place in case of MgO stabilized Na-β″-alumina has been made on the basis of the investigations on the crystal structure of a metastable intermediate called mullite-like-alumina (m-Al 2O 3). The presence of chemically bonded H 2O molecules in the m-Al 2O 3 intermediate was proposed based on the crystal structure derived and the same verified by other independent techniques. Based on this result, the metastable intermediate can be expected as a microwave active material. The product, Na-beta-alumina is already known to be a good absorber of microwaves. The microwave activity of both the intermediate and the product thus renders possible a direct one-step synthesis cum sintering when the intermediate precursor is exposed to microwaves.

Performance of Large Electric Power Equipment and Future View: Large Capacity Battery System-Sodium-Sulfur Battery-

The Ford Motor Company proposed the principle of the sodium-sulfur battery based on a beta-alumina solid electrolyte in 1967. Accordingly, sodium-sulfur battery technology was initially developed primarily for electric vehicle applications. Later, the Tokyo Electric Power Company (TEPCO) selected the sodium-sulfur battery technology as the preferred system for a dispersed utility energy storage system to substitute for the pumped hydro energy storage system. NGK Insulators, Ltd. (NGK) and TEPCO have jointly carried out the development of the sodium-sulfur battery since 1984. In April 2002, TEPCO and NGK made the sodium-sulfur battery for use as an energy storage system commercially available.

Thermodynamic characterization of microwave sintered sodium beta alumina by a potentiometric technique

The characterization of the phase equilibrium in microwave sintered sodium beta alumina was carried out by following up the variation in the sodium oxide activity on changing sodium activity in the ambience. The microwave-processed material was found to respond much faster in adapting to the surrounding atmosphere when compared to the conventionally processed materials. The results of the present investigation helped in assessing the suitability of the microwave sintered sodium beta alumina for technological applications.

Microwave processing of sodium beta alumina

The conventional processing of sodium beta alumina (SBA) which includes synthesis and sintering in order to obtain dense bodies for use as a solid electrolyte usually requires high temperatures (∼1873 K) and long holding times. A substantial amount of Na 2O may be lost during such high temperature heat treatment, the consequence of which may be deleterious when SBA is used for device applications. To overcome this problem, the use of microwave as heating source for the processing of SBA was attempted in the present process. Preliminary investigations on commercial Na-β-alumina bearing the composition NaAl 11O 17 were carried out and it was found that Na-β-alumina was a very good absorber of microwaves. Following this, a microwave active precursor of MgO-stabilized Na-β″-alumina was synthesized through a novel solution technique, which on compaction and exposure to microwaves yielded dense (94% theoretical) and phase-pure Na-β″-alumina body. This paper presents the results of a direct single-step synthesis cum sintering of MgO-stabilized Na-β″-alumina.

The influence of the electrode size on the electrical response of a potentiometric gas sensor to the action of oxygen

As a part of our research on new gas sensors, an original potentiometric gas sensor was developed. This gas sensor is made of a solid electrolyte (beta alumina) associated with two different metallic electrodes (gold and platinum) located in the same gas mixture. Tests performed under oxygen pressure show that the potential difference read between the electrodes depends on the experimental conditions, oxygen pressure, and temperature, but also on the electrodes surface area ratio. Then, we studied the electrical responses of devices composed of electrodes of the same nature (gold or platinum) but of different size. These electrode size influences are analyzed in terms of different capacitive effects occurring at the electrode-solid electrolyte interface. If we consider that the adsorption of oxygen species is responsible for the electrostatic potential, the proposed model is able to account for the experimental results. It is then possible to explain and to better understand the importance of the electrodes on the electrical response of such a device.

Thermoelectric power studies on MgO-stabilized β″-alumina

A study of the temperature dependence of thermopower is known to yield auxiliary information about the electronic conductivity of a mixed conductor. In light of the above, thermoelectric power (TEP) measurements were made on MgO-stabilized β″-alumina over the temperature range from 773 to 1223 K under conditions of different sodium activities in the ambient in order to substantiate the existing information on the electronic conductivity of sodium beta alumina (SBA). A mixture of NaxSimO2m+x/2 and SiO2 in an environment of fixed \(P_{{\rm O}_{\rm 2} } \) served as electrodes reversible to Na+. The heat of transport obtained using the thermopower data at higher temperatures (973–1223 K) was in fair agreement with the activation energy of electrical conduction determined by other studies like impedance measurements and molecular dynamics simulation. It could be inferred from these results that there is negligible electronic conductivity in SBA under the conditions of measurement. The average TEP for SBA was determined to be 700–800 µV/K and the partial molar entropy of Na+ in SBA was found to be ~98 J mol–1 K–1.

Experimental evaluation of electrode conversion efficiency of alkali metal thermal to electric converter

AbstractThe alkali metal thermal to electric converter (AMTEC) system which utilizes the sodium ion conductivity of a beta″‐alumina solid electrolyte (BASE) is expected to have high conversion efficiency above 30% including practical heat losses. However, the achieved experimental efficiencies have been around 15%. In this paper, current–voltage characteristics and heat and mass transfer processes on a single cell have been examined experimentally and thermal electrode conversion efficiency has been discussed. Measured electrode conversion efficiency without thermal losses showed that it was about 40% at a power density of 0.3 W/cm2. A theoretical analysis on the thermal losses has also been conducted and these losses are estimated to be 0.3 W/cm2 in a practical tube type cell, so that an actual cell system efficiency of 30% is expected. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 234–244, 2001

Alkali metal thermal-to-electric converter development

Initial impedance measurements of multi-BASE tube AMTEC cells have been accomplished. These measurements were based on theoretical analyses performed by the Jet Propulsion Laboratory. These factors are derived from a plot of the apparent charge transfer resistance, R act, as a function of the electrical potential across the beta alumina solid electrolyte. These include the morphology factor, G, the exchange current J 0 0, and α, the transfer coefficient. The factor G was given a value of 50 as a result of the inability of present equipment to achieve 1.6 V across a single electrolyte element. Average values for the temperature independent charge exchange factor, B, are also reported. These results were taken from cells with as few as 3300 h to as many as 12,000 h of operation. The results show that if the value for G is somewhat close to actual values, then J 0 0 and α are much lower than those reported in previous literature, resulting in an increase in the charge transfer resistance.

Effect of radiation shield on pressure losses and power output of AMTEC cell

Pressure loss in a PX-3A alkali metal thermo-electric converter (AMTEC) cell was investigated by varying the heat radiation between the beta alumina solid electrolyte (BASE) and the condenser. Chevron radiation shields were used to change the heat radiation between the BASE and the condenser in different numbers and at different angles. Results show that the pressure losses and also the pressure on the cathode side increase using chevron shields. The cell electrical power output and the cell efficiency decrease as the pressure on the cathode side increases when chevron shields are placed. The power output and efficiency increase as the chevron angle increases up to a certain limit.

High-resolution electron microscope observation of interface microstructure of a cast Al-Mg-Si-Bi-Pb(6262)/Al2O3p composite.

High-resolution electron microscopy was employed to characterize the interface structure of a cast Al-Mg-Si-Bi-Pb aluminium(6262)-based composite reinforced by alpha alumina particles with a trace of beta alumina in order to investigate the behaviour of alloying elements in cast composites. Except for a few primary Mg2Si particles, few reaction products were detected at the interface of Al/alpha-Al2O3 due to the unfavourable reaction kinetics during the squeeze-casting process. The Mg2Si particle has an orientation relationship with alpha-Al2O3 of [011]Mg2Si//[1210]alpha-Al2O3 (111)Mg2Si//(0006)alpha-Al2O3. A significant amount of MgAl2O4 was found on the surface of the beta-Al2O3 particles, which is in contrast to the small degree of reaction found on alpha-Al2O3 particles. MgAl2O4 and beta-Al2O3 particles have the following orientation relationship: [011]MgAl2O4//[1210]beta-Al2O3 (111) MgAl2O4//(0006)beta-Al2O3. The similar crystal structure of beta-Al2O3 to MgAl2O4 favours MgAl2O4 nucleation and growth on the surface of beta-Al2O3. Interfacial energy minimization dominates the atomic structure of the interface with the result that close packed planes and directions in the Al2O3 reinforcement and reaction products are parallel to the interfaces. Bi and Pb were found in the form of metallic nanometre particles between Al2O3 particles, or between the MgAl2O4 and Al2O3 particles, or in the open channels of beta-Al2O3 filled by the Al matrix.

Performance analyses of an Nb–1Zr/C-103 vapor anode multi-tube alkali-metal thermal-to-electric conversion cell

The results of performance analyses of a refractory Nb–1Zr/C-103 vapor anode multi-tube alkali-metal thermal-to-electric conversion (AMTEC) cell are presented and discussed. This cell could be used with a radioisotope heater unit to provide electric power from tens to a few hundreds of watts. In the tens of kilowatts electric range, the AMTEC cells could be used with a parabolic solar concentrator or a nuclear reactor heat source. The present cell measures 41.27 mm in diameter and is 125.3 mm high and has eight sodium beta ′′-alumina solid electrolyte (BASE) tubes, which are connected electrically in series to provide a load voltage in excess of 3 V. The hot structure of the cell, including the hot plate, the BASE tube support plate, the hot plenum wall and conduction stud, the evaporator standoff and porous wick and the side wall facing the BASE tubes, is made of Nb–1Zr. The cell's colder structure, which includes the condenser structure, the interior thermal radiation shield, the casing and wick of the liquid sodium return artery and the side wall above the BASE tubes, is made of C-103. This niobium alloy is stronger and has a lower thermal conductivity than Nb–1Zr, reducing the parasitic heat conduction losses in the cell wall, hence enhancing the cell's performance. The base cell weighs 163.4 g and delivers 7 W e at 17% conversion efficiency and load voltage of 3.3 V (cell specific mass of 23.4 g/W e). These performance parameters were for TiN BASE electrodes characterized by B=75 A K 1/2/m 2 Pa and G=50, assuming a BASE/electrode contact resistance of 0.06 Ω cm 2 and a BASE braze structure leakage resistance of 3 Ω. Also, the inner surfaces of the thermal radiation shield and the cell wall above the BASE tubes were covered with low emissivity rhodium. The temperatures of the BASE brazes and the evaporator were below the recommended design limits (1123 and 1023 K, respectively), and the temperature margin was ⩾+20 K to avoid sodium condensation inside the BASE tube, shorting the cell. When high performance electrodes, characterized by B=120 A K 1/2/m 2 Pa and G=10, were used, the cell's electric power increased to 8.38 W e at 3.5 V, and the efficiency increased to 18.8%, decreasing the specific mass of the cell to 19.7 g/W e without exceeding any of the design temperature limits.

Determination of alpha and beta alumina in ceramic alumina by X-ray diffraction

Determination of alpha alumina (α-Al 2O 3) content has been one of the oldest X-ray diffraction (XRD) methods of analysis. However, rhombohedral aluminas may have a variety of morphological forms for which there are marked differences in relative intensities of their major XRD reflections (the preferred orientation effect). In addition, a specimen X-ray diffracting power may vary making it difficult or impossible to employ a reference material. Consequently, comparing intensities of selected reflections from a sample with those of a reference material may cause a serious analytical error. A conventional XRD and a Rietveld approach were used to analyze nine commercial ceramic aluminas, three NIST standards and two special grades of alumina for alpha and beta alumina (β-Al 2O 3=Na 2O·11Al 2O 3) content. The samples were also analyzed by scanning electron microscopy (SEM) to assess morphology. Increasing the number of XRD reflections analyzed from two to eight did not improve the reliability of the quantification process. The morphological differences among samples could not have been minimized that way. Conventional XRD (two to eight reflections) indicated alpha alumina values varying from 88 to 106% while the Rietveld analysis (full pattern) attributed 100% for all but two. These two samples were found to contain beta alumina. Initial Rietveld refinements indicate that the beta phase contains only a fraction of the total Na 2O content. The preferred orientation was computed for 14 specimens and assessed using a relative scale. The Rietveld least-square refinements would not only provide relatively quick, but also reliable information on alpha and beta content, as well as unit cell parameters of alpha and beta phases.

Design optimization and integration of nickel/Haynes-25 AMTEC cells into radioisotope power systems

A number of nickel/Haynes-25, vapor anode, multi-tube Alkali Metal Thermal-to-Electric Conversion (AMTEC) cell designs, similar to the Pluto/Express series cells, were developed and optimized for improved performance. Optimization calculations investigated the effects of changing the number and length of the sodium Beta”-Alumina Solid Electrolyte (BASE) tubes, the cell length and the condenser temperature on the cell’s electric power output, conversion efficiency, temperature margin and the temperatures of the BASE brazes and the evaporator. Various options of integrating the high performance nickel/Haynes-25 cells with 238PuO 2 General Purpose Heat Source (GPHS) modules, into the electric power system’s configuration proposed by Advanced Modular Power Systems, were explored for satisfying an End of Mission (EOM) electric power requirement of 130 W e at 28 V dc for 10- to 15-year space missions. The power systems’ integration options explored included changing the number of GPHS modules and the number of AMTEC cells in the generator and using either fresh or aged 238PuO 2 fuel in the GPHS modules.

High-Performance Radial AMTEC Cell Design for Ultra-High-Power Solar AMTEC Systems

Solar thermal Alkali-Metal-Thermal-to-Electric-Conversion (AMTEC) power systems potentially have several important advantages over current solar photovoltaic power systems in ultra-high-power spacecraft applications for medium-earth orbit (MEO) and geosynchronous orbit (GEO) missions. This work presents key aspects of radial AMTEC cell design to achieve high cell performance in solar AMTEC systems delivering larger than 50 kW(e) with AMTEC cell conversion efficiency larger than 22 percent. A new design parameter methodology is demonstrated establishing optimum design parameters in radial cell design to satisfy high-power mission requirements. Specific temperature- and pressure-dependent relationships define critical dependencies between key cell design parameters, particularly the impact of parasitic thermal losses on Beta Alumina Solid Electrolyte (BASE) area requirements, voltage, BASE tube number, and system power production for maximum power-per-BASE-area and optimum efficiency conditions. High-level system tradeoffs are demonstrated using the design parameter methodology to establish high-power radial cell design requirements and determine optimum radial AMTEC designs. [S0199-6231(00)00102-7]

Experimental Evaluation on Electrode Conversion Efflciency of Alkali Metal Thermal to Electric Converter.

The alkali metal thermal to electric converter (AMTEC) system which utlizes the sodium ion conductivity of beta"-alumina solid electrolyte (BASE) is expected to have high conversion efficiency above 30% including practical heat loss. However, the achieved experimental efficiency have been around 15%. In this paper, current voltage characteristics and heat and mass transfer processes on a single cell have been examined experimentally and thermal electrode conversion efficiency has been discussed. Measured electrode conversion efficiency without thermal losses showed that it was about 40% at a power density of 0.3 W/cm2. A theoretical analysis on the thermal losses has also been conducted and these losses are estimated 0.3 W/cm2 in a practical tube type cell, so it is obtained that the actual cell system efficiency of 30% will be expected.

Beta-alumina solid electrolyte

A beta-alumina solid electrolyte for use in a sodium-sulfur battery is composed of beta-alumina crystals having a degree of orientation toward the C axis thereof, of 0.2-0.4 and an aspect ratio of 4.0 or less. The beta-alumina solid electrolyte is composed of the beta-alumina crystals having a degree of orientation toward the C axis thereof, of 0.2-0.4 and has such a particle diameter distribution that the average particle diameter is 3 μm or less, the proportion of the particles having a particle diameter of 5 μm or less is 90% or more, and the maximum particle diameter is 300 μm or less. A process for producing a beta-alumina solid electrolyte using an alumina source material, a magnesium source material and a sodium source material, uses a magnesium-aluminum spinel as the magnesium source material and subjects all materials to mixing, granulation, molding and firing to obtain a beta-alumina solid electrolyte without subjecting the materials to calcination. The beta-alumina solid electrolyte has a low electrical resistance and a large strength to internal water pressure and exhibits excellent properties when used as a diaphragm for a sodium-sulfur battery.

Preparation of potassium beta aluminas by gel-to-crystallite conversion and their characterisation

A novel method for the preparation of phase-pure K-beta-alumina is reported by the gel-to-crystallite conversion method. Here, coarse gels of hydrated alumina Al2O3 . yH(2)O (80 < y < 120) were reacted with ethanolic KOH,yielding crystalline K-inserted gibbsite or K-pseudoboehmite. Thermal decomposition of these precursors above 500 K yielded intermediate K-inserted boehmite. Above 1473 K, K-beta-alumina was obtained via a modified K-beta-alumina intermediate. The stability range of K-P-alumina can be extended up to 1 : 17 (K2O :Al2O3) by this method. The extended compositional range of stability of K-beta-alumina is explained on the basis of the polysynthetic lamellae arising from the collapse of the layers adjacent to the K-O plane, as revealed by high resolution electronmicroscopy (HREM). The increased number of AlO6 octahedra, in comparison to AlO4 tetrahedra and the prevalence of distorted AlO6 with two or more types of second nearest neighbour interaction is indicated from the solid state Al-27 MAS NMR studies. To obtain K-beta(n)-alumina, Li+ or Mg2+ had to be incorporated. The mechanistic aspects of the formation of K-beta- and K-beta(n)-alumina are described in detail.