This study was concerned with the formation and color development of the spinel solid solution in CoO-ZnO-Al₂O₃-Cr₂O₃-TiO₂ system, and its application to colored glazes.
Specimens were prepared by calcining the oxide and hydroxide mixture at 1450°C for 1 h. The formation of spinel solid solution was examined by X-ray diffraction, the color was discussed by measuring the spectral reflectance, and the stability of the spinel in glazes was tested.
The results were summarized as follows.
1) Except a few systems, formation of a continuous solid solution was confirmed by X-ray analysis.
2) As the amount of Cr³⁺ increased in ZnO-Cr₂O₃-TiO₂ system, the color changed from white through leaf to grayish leaf, and the absorption of Cr³⁺ shifted towards violet region.
3) An increase of Al³⁺ in ZnO-Cr₂O₃-Al₂O₃ system, caused the color to change from grayish leaf through grayish yellow and purplish pink to white, and the absorption of Cr³⁺ shifted towards violet region.
4) The color obtained in ZnO-Al₂O₃-Cr₂O₃-TiO₂ system, ranged from leaf through grayish olive green to grayish yellow.
5) An increase of Cr³⁺ in CoO-ZnO-Cr₂O₃-TiO₂ system, yielded the color ranging from grayish yellow through grayish olive to turquoise, and the absorption of Cr³⁺ and Co²⁺ shifted towards violet region.
6) As the amount of Al³⁺ increased in CoO-ZnO-Cr₂O₃-Al₂O₃ system, the color ranging from turquoise through strong blue green to bright blue developed, and the absorption of Cr³⁺ and Co²⁺ shifted towards violet region.
7) As the amount of Al³⁺ increased in CoO-ZnO-Al₂O₃-TiO₂ system, the color changed from grayish yellow through dark yellow to bright blue, and the absorption of Co²⁺ shifted towards violet region.
8) The colors ranging from grayish olive to grayish olive green developed in CoO-ZnO-Al₂O₃-Cr₂O₃-TiO₂ system.
9) According to the result of the colored glaze test, formation of a new spinel was observed in magnesia-lime glaze, and brilliant hue similar to peacock developed over the wide range of CoO-ZnO-Al₂O₃-Cr₂O₃-TiO₂ system in lime or magnesia-lime glaze. Specimens with the composition of Cr³⁺ rich region were stable as a glaze stain.

View full abstract

It is reported that insulating wall of Al₂O₃ was seriously eroded near cathode region only when the current was let flow in plasma. The same phenomena were also observed in electric fused MgO but less in quantity and near anode region.
MHD plasma is characterized by high temperature (-2800°K), high flow velocity (-1000m/s), high heat flux (-300W/cm²) and active atoms such as K and S. These particles deposite upon an insulating wall surface of Al₂O₃ or MgO in a form of K₂SO₄ and K₂CO₃ and the leakage current through the thin layer of K₂SO₄ and K₂CO₃ will erode the insulating wall.
Some simulation tests were carried out to explain these phenomena and summarized as follows.
1) Arc spot is formed upon the insulating wall near cathode region and potassium compound upon the wall functions as a cathode electrode. The insulating wall is eroded by high temperature spot but it depends upon the melting point of ceramics.
2) Blackening of Al₂O₃ is also one of the causes of the deterioration. This is due to SiO₂ under the reductive atmosphere.
3) α-Al₂O₃ is changed into β-Al₂O₃ under the MHD condition and the rate of change is higher in cathode region than anode.
4) Electric fused MgO is superior to Al₂O₃ but it will be also eroded near anode region when long operation.

View full abstract

The particles of hydrous ZrO₂, which were prepared by hydrolysis of ZrOCl₂ solution (0.1mol/l) at 100°C for 140h, were observed under electron microscope, by means of bright-field, dark-field and electron diffraction techniques. The particles are square-like in shape and about 1000Å in size. The particles are made up of a great number of rod-shaped crystals about 100Å long and 30-50Å wide. The long axes of the crystals coincide with the crystallographic direction of ‹101› or ‹101›. The crystals are oriented in such a way that their long axes coincide in direction with the diagonals of the square-like particles.
The electron diffraction patterns of each particles were composed of (hOl) reflection spots and strikingly resembled to that of the (100) twinned crystals. But the radial streak of each spots showed the slight variation of each rod-shaped crystals in orientation.
Lattice images of (100) and dark-field images of (200) and (002) were observed in the whole area of the square-like particles.

View full abstract

The binary glasses were prepared in the SiO₂-PO_5/2 system containing 0-64.2 and 95.7-100mol% PO_5/2, and in the GeO₂-PO_5/2 system containing 0-48.8mol/ PO_5/2.
In the binary SiO₂-PO_5/2 glasses the transformation temperature (T_g) and the Vickers microhardness (H_v) decreased sharply up to about 30mol% PO_5/2 because of introducing a nonbridging oxygen (P=O) into the glass by the substitution of PO_5/2 for SiO₂. The sharp increases in T_g, H_v and the intensity of the new infrared absorption band due to SiO₆ group at about 670cm^-1, the shift of the position of Si K_α peak to that of crystalline SiP₂O₇ and crystallizing out of SiP₂O₇, reveal the increase in the ratio of six-coordinated Si⁴⁺ with increasing PO_5/2 content in the composition region from 30 to 67mol/PO_5/2. The changes of the molar refractivity (R)- and molar volume (V)-composition curves show that this coordination number change of Si⁴⁺ begins from 28mol% PO_5/2.
In the binary GeO₂-PO_5/2 glasses crystalline GeP₂O₇ was separated out and the new infrared absorption peak due to GeO₆ group appeared at 670cm^-1 even in the composition region of low PO_5/2 content. The expansion coefficient (α), R and V decreased with increase in PO_5/2 content. These facts reveal that Ge⁴⁺ changes its coordination number from 4 to 6 on introducing PO_5/2 into GeO₂ glass. Up to 20mol% PO_5/2 T_g and H_v were held constant because the effect of the nonbridging oxygens (P=O) counteracted that of six-coordinated Si⁴⁺. Crystallizing out of Ge₂P₂O₉ and the similarity of the infrared spectra of the glasses to that of crystalline Ge₂P₂O₉ in the composition region near 50mol% PO_5/2, reveal the resemblance of the structure of these glasses to that of crystalline Ge₂P₂O₉.

View full abstract

Studies on a formation and phase relations of solid solutions in the system Li₂MgSiO₄-Li₂ZnSiO₄ were carried out by DTA and X-ray powder diffraction on the products which were prepared by solid-state reaction at 1100°C using Li₂CO₃, MgO, ZnO and SiO₂ as starting materials and allowed to quench in water from the desired temperatures.
Phase relations of Li₂MgSiO₄ and Li₂ZnSiO₄ are as follows, respectively:
γ₀-Li₂MgSiO₄ 582°C_??_ γ_II-Li₂MgSiO₄
β_I-Li₂ZnSiO₄ 656°C_??_ β_II-Li₂ZnSiO₄ 895°C_??_ γ_II-Li₂ZnSiO₄
Their transformations are reversible and relatively rapid.
The unit monoclinic cell constants, . a₀, b₀, c₀ and β, from γ_II-Li₂MgSiO₄ to γ_II-Li₂ZnSiO₄, which form a complete series of solid solutions at higher temperature, change linearly from 6.3022, 10.689, 4.9958 (Å) and 90.33° to 6.2823, 10.626, 5.0327 (Å) and 90.49° by isomorphous replacement of Mg by Zn. But, there is a discontinuity of the unit monoclinic cell constants between the γ₀-and β_I-phases at lower temperature. Orthorhombic β_II-phase is obtained ranging x=0.9-1.0 in Li₂ (Mg_1-x, Zn_x) SiO₄ at intermediate temperature.
Their crystal structures are inferred to be analogous to Li₃PO₄.

View full abstract

The electrical conductivities of glasses in the Ag₂O-B₂O₃, Na₂O-B₂O₃ and Ag₂O-Na₂O-B₂O₃ (Ag₂O+Na₂O=27.4mol% in average) systems have been determined over the temperature range from room temperature to about 400°C using both d. c. and a. c. measurements. The temperature dependence of the electrical conductivities of the glasses could be described by the Rasch-Hinrichsen equation:
σ=σ₀exp(-ΔH/RT)
The Ag₂O-B₂O₃ glasses showed higher conductivity and lower activation energy for conduction than the Na₂O-B₂O₃ glasses did. The mixed cation effect was observed in the Ag₂O-Na₂O-B₂O₃ system; a minimum in the electrical conductivity and a maximum in the activation energy were found around the Ag/(Ag+Na) ratio of 1/5 on the property-composition curves. A minimum in the dielectric constant was also found. The magnitude of the mixed cation effect in the silver-containing system was, however, considerably smaller than that found in mixed-alkali glasses involving Li, Na, K or Cs ions.
The electrical conductivity was much greater and the activation energy was smaller for the Ag₂O-Na₂O-B₂O₃ glasses of the composition range of Ag/(Ag+Na)>1/5, in which Ag⁺ ions are dominant current carriers, than for the single cation Ag₂O-B₂O₃ glasses of the same Ag₂O content. This indicates that the mobility of Ag⁺ ions is increased on addition of Na⁺ ions in contrast with that of the alkali ions in mixed-alkali glasses which remains the same or is decreased on addition of alkali ions of the other type. Such behavior of the mobility of Ag⁺ ions was discussed by assuming the formation of Ag⁺ ion clusters which results in the shortening of the jump distances required for the migration of Ag⁺ ions.

View full abstract

[in Japanese]

View full abstract

An accurate but convenient method was developed for the determination of boron and lanthanum in lanthanum boride.
Sample was dissolved in hydrochloric acid with small amounts of nitric acid to bring boron into boric acid with special care to avoid any loss of the resulting boric acid during the dissolution procedure.
Boron was first determined by taking an aliquot of the sample solution, isolating out the lanthanum ion with a cation exchanger, and titrating the resulting separated boric acid with a standard sodium hydroxide solution in the presence of mannitol against a pH meter as an end point detector.
Lanthanum was then determined by taking also an aliquot of the sample solution and titrating it with a standard EDTA solution against xylenol orange as a metallochromic indicator. Separation of excess free acid present in the sample solution before the titration procedure was advisable to obtain results with high accuracy.
The method was applied to the determination of boron and lanthanum in high purity lanthanum boride and they could be determined with satisfactory results.

View full abstract