The isothermal hot corrosion behavior of SiC was examined at temperaturerange from 1023 to 1173K for 1.8 to 36ks: Boron-carbon-sintered-, Al₂O₃-sintered and CVD-SiC were used as testing materials. Measurement of mass change, Xray diffraction, surface observation and EPMA analysis were conducted during and after the corrosion experiment. The effect of flowing oxygen on corrosion was also examined. Above 1173K, sintered SiC dissolved into molten salt rapidly. Though CVD-SiC did not dissolve, the surface of it showed a glassy phase with many small holes after the corrosion experiment. At 1023K, any specimen was not corroded. In flowing oxygen corrosion resistance of Al₂O₃ -sintered-SiC was better than that of boron-carbon-sintered specimen. There was no crystalline corrosin product on the corroded SiC surface. These corrosion behaviors were compared with those of nickel base superalloys.

View full abstract

To reveal the solidification mechanism of 5% and 15% Cr white cast irons containing 1-2% B, the microstructures of solid/liquid interface zone and eutectic compounds formed during unidirectional solidification were examined by using metallographic, X-ray diffraction and EPMA techniques.
In the 5% Cr alloys, two types of γ-M₃ (C, B) eutectics were formed, that is, a rod-like two-dimensional dendritic structure was formed in the low B alloy and a lamellar three-dimensional one in the high B alloy. On the other hand, three kinds of two-phase eutectic with different conpounds were found in the 15% Cr alloy, in which following a γ-M₇ (C, B) ₃ eutectic a degenerate γ-M₃ (C, B) eutectic crystallized in the low B alloy, while a γ-M₂ B eutectic primarily crystallized and a lamellar γ-M₃ (C, B) eutectic followed in the high B alloy.
The M₃ (C, B) has a wide solubility range up to C+B≈ 6% and Cr≤22%, but the microstructures vary remarkably with the solute content, though borocarbides have same lattice. The width of solute/liquid interface zone increases with Cr content in every alloy.

View full abstract

Relating to the production of powder compact materials, uneven packing structure of consolidated powder bed was experimentally investigated under piston press through stress propagation characteristics. Measuring the bottom pressure in a cylinder under various conditions, the vertical pressure distribution was approximately expressed in the axial and lateral directions on the basis of author's equation of solids pressure derived for compressible powders. As a result, it was confirmed that the rate of propagation of the compressive pressure applied onto the powder bed surface decreases with increasing bed thickness, the smaller diameter of the cylinder and the higher overall packing density. The nressure was also found to decrease along the radius.

View full abstract

Among V₂O₅ samles prepared at three different temperatures (400, 450 and 500°C), the formation rate of V4O9 was compared in the reduction process with SO₂ gas at the temperatures of 350 to 400°C. The rate, increasing with the decrease of the preparation temperature, was not dependent upon the mean diameters of the samples but upon the microtextures of the particles. Crystallite of V2O5 seemed to play the role in the reduction, according to SEM observation and the measurements of BET surface area (S) and of X-ray peak breadth at half maximum intensity (βhoo). TEM observation of this process showed the topotaxy between V₂0₅ and V₄O₉ crystals as follows; [001] V₂O₅ // [100] V₄O₉ and the angle between [010] V₂O₅ and [010] V₄O₉ was 48°. Then, it can be concluded that V₄O₉ is introduced by removing every fourth oxide layer of V₂O₅ crystal, followed by shearing relatively in 1/6 [103] V₂O₅ direction.

View full abstract

Effect of additives on the degradation of adhesion strength between thick film conductor and multilayer ceramic substrate is studied with special reference to the microstructure. Degradation of adhesion strength is caused by the solder diffusion which brings about the expansion of Ag conductor and destruction of the interface between Ag conductor and multilayer ceramic substrate during ageing at 150°C.
Addition of precious metal such as Pd or Pt is effctive to prevent the degradation of adhesion strength. In the case of Ag conductor, γ-Ag₃ Sn is easily formed during ageing. Addition of Pd or Pt suppress the formation of γ-Ag₃ Sn. Accicular precipitates such as celsian is most effective in toughening the interfacial strength.

View full abstract

Degradation of capacitance and insulation resistance under DC field has been studied with special reference to the microstructure of BaTiO₃-based dielectric materials for Ni-electrode multilayer ceramic capacitors. The presence of dislocation loops, of which formation is pronounced by the low oxygen partial pressure of the ambient atmosphere during firing, has a deleterious effect on the life of insulation resistance under highly accelerated life testing. Tetragonality and the MnO-content are the decisive factors of the deterioration in capacitance under DC field. Dielectric materials composed of BaTiO₃, MgO, CoO, MnO, and Ba_0.4 Ca_0.6 SiO₃ showed superior stability in capacitance.

View full abstract

Electromagnetic properties of low temperature sintered NiCuZn ferrite has been studies with reference to the microstructure by means of transmission electron microscope (TEM) and secondary ion mass spectrum (SIMS). The temperature dependence of inductance is strongly affected by the stress which can be observed as the distortion in lattice fringe image. The observed stress at the grain boundaries is generated by precipitated calcium oxide introduced in the producing processes.

View full abstract

In order to recover fine particles of rare-earth minerals from beach sand by the liquid-liquid extraction method, fundamental studies were carried out using several kinds of surfactants such as oleate, alkylsulfate, alkylbenzenesulfonate and alkylammonium salts. Isooctane and water were used as two liquid phases. Monazite, xenotime, zircon and quartz were chosen as test samples. The percent recovery of each of these minerals was determined in terms of pH of aqueous solution, type of surfactant and concentration of surfactant.
Zeta potential variations were measured as a function of pH for each of these minerals to determine its isoelectric point (IEP). In the pH range below the IEP of the mineral where the mineral particles were positively charged, high recoveries were obtained when the anionic surfactant was used at its proper concentrations.
To evaluate an oil-wettability of the mineral surface, contact angles in the monazite/isooctane/water system in the presence of the surfactant were measured. Interfacial tensions between isooctane and surfactant solution were also measured. Work of adhesion was then determined. The recovery variations were closely correlated with the work of adhesion.

View full abstract

Photorefractive BaTio₃ single crystal were successfully prepared by a combination of Top-Seeded Solution Growth technigue and suitable poling processes. The single crystals were grown from the melt which was the mixture of TiO₂/BaCO₃=65/35 in molar ratio. The employed sources of TiO₂ and BaCO₃ were 99.99% and 99.999% purity powders, respectively. The asgrown crystal boules, the dimensions of about 20x 20x 15mm³, were cut into 3-5mm rectangular prisms. Subsequently, the crystals were polished, and domain walls of those were removed by applying uniaxal compressive stress and electrical field.
The obtained crystals, whose phase transitions were clearly observed at about 130°C by DSC measurement, exhibited typical ferroelectricity. And furthermore, self-pumped phase conjugation was observed in the single domain BaTiO₃ crystals by using an argon ion laser operating at 515nm.

View full abstract

This report emphasizes the importance of characteristic analysis on elastic wave propagation. Some applications of the characteristic knowledge reconfirms us the importance for analyses of impact problems, and reflection and transmission analyses of ultrasonic waves. It is possible by the application that we can interpret well the dynamic phenomena, get their simple solutions in approximate analysis, and have the characteristic chart. The chart is very convenient for ultrasonic inspection to know the relation between the null reflection and the characteristic wave mode propagation for example.
The first paragraph describes the requisition for our research to promote the wide and various applications of materials in modern industry. The second, describes the impact problem of an elastic plate as an example of the application to deduce the simple approximate solution. The third, describes the proposition of characteristic chart that is available well for the inspection of an immersed plate. The left paragraph describes the application to the reflection and transmission analysis of complex materials such a fiber reinforced composite material and a fluid-filled poroelastic material.

View full abstract

Layered double hydroxides (LDH's), M (II) _1-x M (III) x (OH) ₂ (CO₃) _x/2·nH₂O (M (II) =Mg, Mn, Co, Ni, Cu, Zn, M (III) =Al, Fe) were prepared by the conventional coprecipitation method. The structures of the samples were analyzed by XRD and FT-IR measurements. Methanation of the sorbed CO^2-₃ ions was carried out using a thermo-balance system in H₂ Gas flow of the atmospheric pressure. Apparent CH₄ evolution was observed in the cases of Ni/Al-, Ni/ Fe-, Co/Al- and Co/Fe-systems. Following features ware found concerning to catalytic effects: (1) Nickel-containing LDH's have high activity for methanation, (2) Cobalt-containing LDH's have relatively low methanation activity, (3) The existence of Fe (III) is effective both on lowering the methanation temperature and on increasing conversion to CH₄. Methane generation from these compounds was interpreted in terms of thermodynamic property of metals composing the brucite layers.

View full abstract

The ceramics are used in various fields, and have specific electric functions. The ceramics manufacturing process consists of various operation such as weighing, mixing, crushing, forming, firing and so on. Here, raw material is feed with the powder material. The properties of electro ceramics are effected on properties of raw materials.
In this paper, the powder bulk density that is one of the properties of powder material is taken notice. And the effects of electric field on initial bulk density distribution are experimentally and thermophysically discussed using Xray radiograph system. As the result, initial bulk density distribution is greatly effected on the electric field.

View full abstract