Mituo Harata

Ionic Conduction of Impurity-Doped β-Alumina Ceramics

Beta alumina (Na2O11 Al2O3) with addition of MgO, NiO, ZnO, CuO and CaO, respectively, together with Na2O are sintered. Ionic conduction of Na+ and X-ray diffraction of these samples are investigated. Additions of above divalent ions, except for Ca2+, increase the amount of Na+ in β-alumina, leading to an increase in the ionic conduction of Na+ in β-alumina. All divalent ions effective to increase the ionic conduction are components of aluminum spinel. The limiting process of the D.C. ionic conduction of these sintered samples may be the grain-boundary conduction.

Microstructure and humidity-sensitive properties of ZnCr2O4-LiZnVO4 ceramic sensors

Abstract A ceramic humidiy sensor, composed on ZnO, Cr2O3, V2O5 and Li2O, has been developed for use in air conditioners. The ceramic body, which is mainly constructed from ZnCr2O4 spinel grains, is porous. A vanadium compound in the galssy phase is present on the spinel grains and water vapour adsorbs or desorbs on this vanadium compound. The humidity characteristics of the sensor fluctuate gradually and slightly in response to changes in the surrounding atmosphere humidity. However, these fluctuations are less than 7% RH at 25°C after storage under extremely high-humidity conditions (40°C, 90% RH) and low-humidity conditions (40°C, 30% RH).

Lattice constants of non-stoichiometric beta-alumina

Abstract Mixtures of beta-alumina powder and sodium carbonate were fired at 1700°C. Beta-alumina, with a hexagonal layer structure, was the only phase obtained in the specimens with formulas, (1.16 + x) Na 2 O · 11Al 2 O 3 (x = 0.19 ∼ 0.59). The lattice constant a 0 of beta-alumina increases monotonically from 5.592 A to 5.597 A with increasing x, while c 0 changes from 22.50 A to 22.52 A via a minimum of 22.46 A at x ≅ 0.4. The peculiar behaviour of the c-axis suggests that the origin of the non-stoichiometry is not simply interpreted as the introduction of Na + ions into the [NaO] − layers which accompanies the formation of Al 3+ vacancies near the [NaO] − layers.

Preferred orientation on beta-alumina ceramics

Abstract A β-alumina tube was formed by hydrostatic pressing of raw powder, lathing and subsequent firing. Preferred orientation of tabular crystallites of β-alumina was determined by X-ray diffraction and polarizing microscope technique. The basal planes of the crystallites had a tendency to be perpendicular to the radial direction of the tube. Ionic conductivity in the axial direction was higher by a factor of 1.5 than that in the radial direction. This was consistent with the result on preferred orientation of the crystallites.

Characteristics of the Na/beta-alumina/Na cell as a sodium vapor pressure sensor

Abstract The EMF and voltage-current characteristics for a galvanic cell with the configuration Na vapor ( P 1 )/sodium beta-alumina/Na vapor ( P 2 ) were studied. It was verified that the EMF followed the Nernst relation over a wide pressure range. For example, when P 1 = 2 × 10 -2 mm Hg and beta-alumina temperature = 340°C, the measured EMF agreed with the calculated value in P 2 range from 10 -5 to 10 -2 mm Hg. At lower pressure range, the measured EMF showed a negative deviation. Coexisting argon gas did not influence the cell EMF characteristic. In an atmosphere containing oxygen, the measured EMF was very high at first. Then it decreased and finally approached a value which agreed with the Nernst equation after several hours. At low beta-alumina temperatures, current saturation was observed in the voltage versus current relation with the anode on the P 2 side. Although the sodium pressure could be determined from saturating current measurement, the measurable pressure range was narrower than that for EMF measurement. At high beta-alumina temperature, current saturation was not clear. Values of 6 × 10 -6 (Ω cm) -1 for the electron conductivity and 6 × 10 -10 (Ω cm) -1 for the hole conductivity at 340° were obtained for beta-alumina from the voltage-current characteristics at low sodium pressure.

Formation and ionic conductivity of nitrogen-doped ß-alumina ceramics

Abstract Nitrogen-doped s-Al2O3, (1.2+y) Na 2 O s ( 11−x 2 ) Al 2 O 3 s x AlN , was obtained by hot-pressing technique using AlN as the nitrogen source, Identification of products in the system Na2OAl2O3AlN, lattice-constant measurements of β- and s″-Al2O3 and ionic conductivity measurements were carried out. Monophase s-Al2O3 appeared in the x = 0-0.7 region. Nitrogen stabilized s″-Al2O3. Mixed β- and s″-Al2O3 appeared in the x=1.1–1.3 region. Ionic conductivity for monophase s-Al2O3 appeared in the x=1.1–1.3 increased from 1.0 × 10−1 Ω−1 cm− to 1.5 × 1.0−1 Ω−1 cm−1. Ionic conductivity for mixed β- and s″-Al2O3 was 2.5 Ω−1 cm−1 at x = 1.3.