Effect of Ratio of Surface Area to Volume on Oxygen Self-Diffusion Coefficients Determined for Crushed MgO-Al2O3 Spinels

Oxygen self-diffusion coefficients for single-crystal MgO-Al₂O₃ spinels previously determined for crushed particles were recalculated using the microscopic suface area of the sample, as was done for alumina. The corrected results agree well with those of Reddy and Cooper .     

Effects of Na2SiO3 on anodization of Mg-Al-Zn alloy in 3 M KOH solution

The anodic behavior of Mg-Al-Zn alloy (AZ91D) under low potential electrolysis in 3 M KOH solutions was studied with and without addition of 0.5-5 M Na₂SiO₃. Anodic films incorporating silicon were formed during electrolysis, and the films formed under constant potential electrolysis at 4 V in 3 M KOH solution with Na₂SiO₃ were uniform and thicker than the films formed without Na₂SiO₃. A few at% of silicon was present as Mg₂SiO₄ in the films, although the main compound was Mg(OH)₂. The corrosion resistance of the films formed in solutions with Na₂SiO₃ increased in an anodic polarization test in 0.1 M KCl solution.     

Formation of Alkoxy-Derived lead Niobates in the PbO-Rich Region

The formation of lead niobates in the PbO-rich region is studied using powders prepared by the simultaneous hydrolysis of lead and niobium alkoxides. Cubic 3PbO·2Nb_2PO₅ solid solutions crystallize at low temperatures from amorphous materials having concentrations of 58 to 75 mol% PbO. The lattice parameter a increases linearly from 1.0544 to 1.0708 nm with increasing PbO. At higher temperatures the solid solutions made with 66.67 and 71.43 mol% PbO transform into 2PbO·Nb₂O₅ (monoclinic) and 5PbO·2Nb₂O_s (monoclinic), respectively. Monoclinic 5PbO·2Nb₂O₅ transforms into a new modification at = 3850° to = 3900°C. It has a rhombohedral unit cell with a = 0.7461 nm and c = 4.8092 nm ( a = 1.6599 nm, a = 25.97°). In the presence of excess lead, monoclinic 5PbO·2Nb₂O₅ transforms into tetragonal 3PbO·Nb₂O₅.     

Oxygen Self-Diffusion in Single-Crystal Y2O3

Self-diffusion coefficients of the oxygen ion in single-crystal Y₂O₃ were determined by the gas-solid isotope exchange technique. The results in the range 1100° to 1500°C are described by D=7.3 X 10^-6 exp [-19l(kJ/mol)/RT] cm²/s. Comparison of the results with those for oxides with the fluorite-type structure indicates that the regularly arranged vacant anion sites in the C-type structure do not contribute eflectively to oxygen ion diffusion .     

Optimal initial production control period based on a quality growth model

The initial production phase of new products or the initial installation phase of new manufacturing facilities is often unstable because of inexperienced workers and many defective products. An initial production process control, in which the defects in design, production technologies and products are fully fixed and removed, is switched to a normal process control whenever it is ready for actual mass production. This paper discusses a method of deciding the optimal initial production control period, based on a quality growth model. It is determined by the number of products with the minimum expected total quality control cost. Finally a penalty cost due to unattainable loss to the quality goal is introduced in the quality control cost: the realized stabilization level of the initial production process control is lower than the original quality objective. Numerical illustrations of the optimal policy are also presented. Copyright © 1999 John Wiley & Sons, Ltd.     

Technique for recovering uranium from sludge-like uranium-bearing wastes using hydrochloric acid

Sludge-like uranium-bearing wastes generated from uranium refining and conversion R&D facilities are stored at the Ningyo-toge Environmental Engineering Center of the Japan Atomic Energy Agency. So far, approximately 1500 t of uranium wastes with radioactivity levels exceeding 10,000 Bq/g have been generated. We have proposed an environmentally benign aqueous process for recovering uranium from wastes using hydrochloric acid (HCl). This makes it possible to dispose of the wastes easily, and to reclaim uranium as a resource. In this process, first, the uranium content in the calcium fluoride (CaF₂) sludge along with the entire sludge is dissolved almost completely in aqueous solutions containing HCl and aluminum chloride. The uranium species are then recovered as peroxide from the CaF₂ sludge solution. Their characteristics are similar to those specified for uranium ore concentrate. After recovering the uranium content, the uranium concentration in the solution is reduced to below 0.01 mg/L using an iminodiacetic chelating resin. Also, the uranium concentration of the precipitate generated by the neutralization of the barren solution falls below 1 Bq/g.     

Stimulation of fatty acid synthesis by 4β-phorbol-12-myristate-13-acetate in isolated rat hepatocytes

The tumor-promoting agent 4β-phorbol-12-myristate-13-acetate (TPA) is shown to be a potent stimulator of fatty acid synthesis in isolated rat hepatocytes. The maximal effect of TPA is seen at 10⁻⁶ M, and the concentration for half-maximal effect is ca. 10⁻⁸ M. Stimulation of fatty acid synthesis by TPA is shown not to require the presence of extracellular Ca⁺⁺. TPA produces a significant increase in lactate and pyruvate accumulation. The possible involvement of protein kinase C in short-term regulation of fatty acid synthesis in the liver is discussed.     

Effect of Surface Condition on Oxygen Self-Diffusion Coefficients for Single-Crystal Al2O3

Oxygen self-diffusion coefficients were determined for two Al₂O₃ single crystals by the isotope-exchange technique, using chemically polished and Ar -ion-milled samples. Results represented by D=562 exp[–665(kJ/mol)/RT] cm²/s are lower than those for diamond-paste-finished samples and near Reed and Wuensch's results. The oxygen diffusion coefficient determined using crushed particles and the microscopically measured ratio of surface area to volume agreed with these values     

Cation Interdiffusion in Polycrystalline Cubic C-Type Yttria–Zirconia–Hafnia Solid Solutions

Cation inter diffusion in cubic C-type solid solutions was investigated for the polycrystalline systems Y₂O₃—Zr_xHf₁-_x-1O₂ and Y₂O₃–ZrO₂ in the small-grain, deep-penetration condition at 1615° to 1822°C. Lattice and grain-boundary diffusion parameters were calculated from cation concentration distributions by using Oishi and Ichimura's grain-boundary diffusion equation. The results indicated that Zr–Y and Zr–Hf interdiffusion coefficients decreased with an increase in Y content. The cation diffusivities were lower than anion diffusivities, and the interdiffusion parameters were lower in the C-type cubic than in fluorite-type cubic solid solutions. The results were compared with diffusivities in other C-type cubic oxides.     

Effects of phorbol esters,A23187 and vasopressin on oleate metabolism in isolated rat hepatocytes

Studies were conducted to compare the metabolic effects of vasopressin, 4β-phorbol-12-myristate-13-acetate (PMA) and A23187 on ketogenesis and oleate metabolism in isolated hepatocytes from fed rats. Vasopressin inhibited the formation of acid-soluble products from [1-¹⁴C]oleate (0.25 mM, 0.5 mM and 1 mM), the inhibition being most marked at low (0.25 mM) concentration of oleate. Conversion of [1-¹⁴C]oleate into¹⁴CO₂ and esterified products was stimulated by vasopressin. The stimulatory effect of this hormone on¹⁴CO₂ production was most marked at high (1 mM) concentration of oleate, whereas that on [1-¹⁴C]-oleate esterification was most marked at low (0.25 mM) concentration of oleate. These vasopressin actions were abolished when hepatocytes were incubated in the absence of calcium in the medium. Our results strongly suggest that both increase in esterification and increase in oxidation to CO₂ contribute to the anti-ketogenic action of vasopressin when oleate is added as substrate, although the relative extent of their contribution varies according to the oleate concentration. The anti-ketogenic action of vasopressin was mimicked by PMA but not by A23187. PMA also caused a stimulation of [1-¹⁴C]oleate esterification although the effect was diminished at 1 mM [1-¹⁴C]oleate. A23187 failed to affect [1-¹⁴C]oleate esterification. The metabolic effects of PMA were elicited in the absence of extracellular calcium, too. Conversion of [1-¹⁴C]oleate into¹⁴CO₂ was only slightly increased by both PMA and A23187 when 1 mM [1-¹⁴C]oleate was added as substrate. The marked stimulatory effect of vasopressin on¹⁴CO₂ production from [1-¹⁴C]oleate was not reproduced even by the combination of PMA and A23187. The possible involvement of protein kinase C and calcium mobilization in the regulation of oleate metabolism is discussed.