The effect of the type of alcoholic solvent on the formation of SiO₂ gels in the sol-gel process has been studied by observing the gelation time in a tightly closed system. A large difference in the rate of gelation was found among fifteen kinds of alcohols used as the solvent. The gelation time decreased with increasing boiling point of the alcohol. The gelation time could be correlated with electrical properties, such as the dielectric constant and the solubility parameter of the solvent. The hydrolysated species of tetraalkoxysilane are solvated by alcohol and the degree of this solvation differs among alcohols. A model of the alcohol solvation process is suggested.

抄録全体を表示

Hot corrosion behavior of an Al₂O₃/YAG eutectic composite in molten V₂O₅ at 800°C and 1500°C has been investigated. This composite showed a more stable behavior than polycrystals due to its peculiar microstructure. The surface reaction product of YVO₄ also prevented the penetration of molten V₂O₅. The higher testing temperature resulted in less corrosion, due to V₂O₅ vaporization.

抄録全体を表示

Pressure filtration rate, packing density and microstructural fluctuation in a consolidated powder cake were studied with 5-50 vol% aqueous suspensions of single crystal alumina particles of 0.5 μm size under a pressure range of 200 to 400 kPa. The decreased height of the suspension during the pressure filtration followed t^m of time, where m was in the range form 0.57 to 0.67 at 10 vol% solids (depending on pH of the suspensions) and approached 0.5 at around 20 vol% solids. The consolidation time was longest for the weakly charged particles near the isoelectric point because of the formation of a uniform distribution of small pore channels in the cake. The positively charged particles were densely agglomerated during pressure filtration but the formation of relatively large pore channels between dense particle clusters shortened the filtration time. The packing density of the formed cake increased in the following order: weakly charged particles near the isoelectric point<negatively charged particles<positively charged particles. Increase in the solid content over 30 vol% in the acidic suspensions enhanced the packing density to 65% of theoretical density and also improved the uniformity of green microstructure. The degree of microstructural uniformity (G) of a consolidated alumina compact was quantitatively defined by G=(dN/dS)/(N/S), where N is the number of particles included in a square of observed area, S, on a scanning electron microscope photograph and expressed by a polynomial approximation of S. N/S represents the average number of particles/unit area. The conditions G>1 and G<1 correspond to dense and porous packing of particles in an arbitrary square area, respectively. The microstructural fluctuation was evaluated with the G value.

抄録全体を表示

Crystalline thin films of lead sulfate, Pb_1+ySO_4+z(y=0 or 1, 0≤z≤1) could be prepared by an electron beam method with using a source of PbSO₄+xPbO (0≤x≤1), under the following conditions: substrate temperature; 300°C, acceleration voltage; 20 kV and emission current; 58 mA. The sulfate films formed were composed of PbSO₄ or Pb₂SO₅, and their compositions of the films changed with changing source composition. Either single phase of PbSO₄ (y=0, z=0), or Pb₂SO₅, (y=1, z=1), or a mixture of these phases was formed with the source composition of x=0, x=1, or approximately x=0.5, respectively. Evaluation of the humidity sensitivity for these films revealed that crystalline thin films of PbSO₄ and Pb₂SO₅ had the hydrophobic and hydrophilic properties, respectively, being one of the most promising humidity sensors because of quick response.

抄録全体を表示

Formation mechanism of spherical mesoporous silica particles prepared using dodecylamine (DDA) as a template was investigated by measuring surface tension, conductivity, pH and concentration of silicic acid in the mixed solutions. Porous structure of spherical mesoporous silica was found for irregular structure by means of X-ray diffraction and scanning electron microscopy. The fomation of DDA micell in DDA-H₂O-C₂H₅OH system was confirmed by the presence of inflection points for tension and conductivity curves at about 0.5 mmol/l of DDA concentration. When tetraethyl orthsilicate was added in the solution, the conductivity raised suddenly, stayed the same for a few minutes, and decreased steadily while the concentration of silicic acid decreased largely. In addition, the value of pH shifted from about 11 to 9.8 at the same time. From these results, the formation mechanism of spherical mesoporous silica is considered to be as follows; 1st step: cationization(DDAH⁺) of DDA; 2nd step: formation of DDA H⁺ micell; 3rd step: hydrolysis of TEOS and polymerization of silicic acid; 4th step: complexation of DDAH⁺ and polysilicic acid; 5th step: nucleation and growth of the mesoporous silica; and 6th step: reconfiguration and growth of the mesoporous silica particles.

抄録全体を表示

Alumina ceramics were densified by pulse electric current sintering (PECS) using transition alumina powders at temperature range of 1250-1550°C for holding time of 3 min under uniaxial pressure of 30 MPa. The transition alumina powders used for PECS were prepared from polyhydroxoaluminum(PHA) gels, which were calcined at 800-1000°C and then ground by planetary ball mill. Optimization of calcination temperature of PHA gels and sintering conditions of PECS were investigated. The PHA gels were transformed into transition aluminas consisted of γ- and χ-alumina at 800-950°C and partly into α-alumina at 1000°C. The sintered compact obtained by PECS at 1400°C using the sample powders thus prepared had an advantage of a higher density of more than 99% of theoretical density, as compared with that using commercially available γ-alumina powders. Densification of the sintered compacts depended on the calcination temperature of the powder samples; the sintered compacts were more densified as the calcination temperature increased. The inclusion of fine α-alumina particles, which were derived from wet grinding abrasion powders with wearing in planetary ball milling, had a significant effect on densification due to the seeding effect, decreasing the γ- to α-alumina transformation temperature. The bending strength of sintered compact fired at 1400°C reached a value as high as 740 MPa using the sample powders calcined at 900°C.

抄録全体を表示

This paper describes the influence of molecular structures of polymer on the fluidity of CaCO₃ suspension with inorganic salts. With the addition of K₂CO₃, the fluidity of suspensions dosed with comb-type superplasticizers is significantly decreased, which appears to correspond to a decrease in the amount of polymer adsorption. This reason was due to the decrease of Ca²⁺ sites on the surface of particles, leading to the reduction of adsorption sites of the polymer. The polymer having shorter graft lengths is adsorbed more easily even though the number of adsorption sites is decreased, since the shorter the length of the graft chain, the larger the content of carboxyl groups on the main chain of comb-type polymer. The intervals between graft chains were prolonged, with changing composition of the copolymer where methoxypolyethylene is replaced by styrene or allyl sulfonates. When a larger amount of carboxyl groups were introduced on the main chain or when the distance between graft chains was extended, the influence of the inorganic electrolytes on the fluidity of suspension with polymer was decreased. In addition, the introduction of sulfonate groups increases the affinity between the polymer and the solid. These polymers can be adsorbed on CaCO₃ even though the adsorption sites are decreased upon adding inorganic salts. This may decrease the influence of the inorganic electrolyte on the fluidity of CaCO₃ suspension.

抄録全体を表示

Effect of addition of fine-grained quartz powders on the bending strength of alumina strengthened porcelain bodies was investigated. By lowering the content of feldspar, sub-micron particles of quartz dissolved into feldspatic liquid phase and transformed into cristobalite at 1300°C. Bulk density of porcelain body decreased with the decrease in alumina content, together with an increase in cristobalite content. Bending strength of porcelain increased with lower content of feldspar, and a value, 250 MPa was achieved in the case of the porcelain bodies having 10% of feldspar and 10 to 20% of alumina. Important factors for strengthening porcelain were to reduce the content of coarse particles and to increase the total content of crystalline phases, such as alumina, mullite and cristobalite.

抄録全体を表示

Oxidation behavior of Al₄SiC₄-SiC sintered bodies, which were synthesized by using Al, Si and C powders, was investigated under a constant temperature and changing temperature. A protective layer of Al₄SiC₄-SiC sintered bodies, which formed at the beginning of heating in air, inhibited oxidation. Since this protective layer of SiC sintered body consisted of silica phase that was cristobalite and glass, the layer was not stable owing to the formation and growth of pores upon changing temperature. A protective layer of Al₄SiC₄ sintered body consisted of mullite and corundum, but did not sufficiently inhibit oxiddation by diffusing oxygen along the grain boundary between mullite and corundum. On the other hand, a protective layer of Al₄SiC₄-SiC sintered bodies sufficiently inhibited the diffusion of oxygen under a changing temperature, because this layer consisted of mullite or mullite and silica. Consequently, Al₄SiC₄-SiC sintered bodies indicated a superior oxidation resistance.

抄録全体を表示

Amorphous carbon thin films containing sulfur were synthesized from thiophene (C₄H₄S) by the r.f. (13.56 MHz) plasma CVD. The r.f. power was applied intermittently to control the deposition temperature (T_d). While maintaining a constant r.f. power (200 W) and reactive pressure (13.3 Pa), we investigated the effect of T_d on the film chemical structures and properties: specifically microroughness, density, microhardness and internal stress. The deposition rate and microroughness of the films decreased with increasing T_d, while the film density, microhardness and internal stress increased with increasing T_d. X-ray photoelectron spectroscopic (XPS) analysis indicated that S/C ratio of the films remained constant and has no connection with T_d. XPS and Raman spectroscopic analyses showed that the films were composed of two kinds of microdomains with sp³ and sp² bonds similar to the diamond-like carbon (DLC) film. Sulfur incorporation into the film significantly reduced the internal stress.

抄録全体を表示

Powders in the CeO₂-ZrO₂-MO_x system were prepared by coprecipitation method. Influence of adding a third components MO_x of transition metal oxides and rare earth metal oxides on the specific surface area (SA) and oxygen storage capacity (OSC) were investigated. It was found that transition metal oxides decrease drastically both SA and OSC values at 1000°C. On the other hand, rare earth metal oxides slightly decreased OSC values. The OSC values of the 20CeO₂-(80-y)ZrO₂-yMO_x powders with y=0-20 mol% LaO_1.5, showed a maximum at around 6 mol% LaO_1.5. In the CeO₂-ZrO₂-MO_x system, 20CeO₂·74ZrO₂·6LaO_1.5 (mol%) powders exhibited the most efficient performance with a high thermal stability up to 1000°C.

抄録全体を表示

Powder of Y₂O₃:Eu red phosphor was synthesized from metal-EDTA complexes as starting materials. The metal-EDTA complexes were formed by thermal drying of a solution mixture of Y- and Eu-EDTA·2NH₄ using a spray dryer. The EDTA powder obtained in this study was consisted of amorphous and spherical microparticles. The Y₂O₃:Eu powder was synthesized in a short time by thermal decomposition of the mixture of Y- and Eu-EDTA·2NH₄ powder. The morphology, crystallizing behavior, metal composition and luminescence characteristic of the samples were examined. The resulting powder indicated sufficient photoluminescence intensity.

抄録全体を表示

Visible-light excited micro-Raman spectroscopic measurements were performed for sliding materials consisting of graphite, in order to characterize structural changes of the material surface induced by electric sliding test with sparkling. Raman spectra of the sliding materials after the test showed a Raman band around 1360cm^-1 besides the usual spectra of graphite. The Raman band, which indicates degradation and disordering in the graphite structure, grew with increasing sparking voltage, while scarce growth of the band appeared under non-electric sliding. Correlation of the structural change at the surface with wear endurance of the sliding materials was also recognized in an accelerated sliding test. It is expected that the Raman measurement will be a convenient method for evaluating the endurance of the sliding materials.

抄録全体を表示

Serpentine is a hydrated ultra-mafic rock, which is primarily composed of magnesium silicate minerals such as chrysotile and antigorite. Fibrous chrysotile is the most common type of asbestos. Since the rich mines supplied serpentine in Japan, application of natural ore “serpentine” as raw materials for ceramics has one of the potentially lowest cost ceramics production. In this study, long afterglow phosphor, Sr₂MgSi₂O₇, has been successfully synthesized using natural ore serpentinite. Eu²⁺ and Dy³⁺ co-doped compounds show long-lasting phosphorescence. This demonstrates that the “serpentine” could be used in preparing alkaline earth silicate phosphors.

抄録全体を表示