Shigeki Endo

Characterization of plasma-sprayed zirconia coatings by X-ray diffraction and Raman spectroscopy

Three zirconia ceramics, ZrO2−4.5mol.%Y2O3, ZrO2−12mol.%Y2O3 and ZrO2−8mol.%MgO, were investigated using X-ray diffraction before and after plasma spraying. The amounts of monoclinic, tetragonal and cubic phases existing in the three zirconia ceramics were determined from the integrated intensity ratios in the {400} and {111} regions of the X-ray diffraction patterns. The tetragonal-to-monoclinic transformation in the plasma-sprayed coatings caused by indentation, fracture and/or heat treatment with a laser beam was examined using Raman spectroscopy. As a result, this spectroscopic technique is shown to be a powerful tool for the observation of this transformation.

Characterization of plasma-sprayed and whisker-reinforced alumina coatings

We have strengthened plasma-sprayed alumina coatings by incorporating SiC or Si3N4 whiskers. As a result, we found that the whisker-reinforced coatings were greatly improved in properties such as thermal shock resistance and adhesion. Major features of the plasma-sprayed Al2O3−5.0 wt % Si3N4, coating were investigated by means of scanning electron microscopy, secondary ion mass spectroscopy, X-ray diffraction, X-ray fluorescence spectroscopy and thermal radiation measurements.

Characterization of plasma-sprayed titanium aluminates by electron spin resonance spectroscopy

Abstract The structures of plasma-sprayed titanium aluminates containing 13 wt.% and 40 wt.% TiO 2 were investigated using electron spin resonance (ESR) and X-ray diffraction. These sprayed materials were identified as mixtures of α-Al 2 O 3 , γ-Al 2 O 3 , β-Al 2 TiO 5 and rutile phases. An ESR peak observed near g = 1.9 at room temperature and 77 K was assigned to Ti 3+ ions in octahedral environments. The relations between the halfwidths of the α-Al 2 O 3 , γ-Al 2 O 3 and β-Al 2 TiO 5 , the linewidth and the g value of the ESR peak suggest that the Ti 3+ ions are in the β-Al 2 TiO 5 lattice. Further, the degree of asymmetry of the environments of the Ti 3+ ions in the β-Al 2 TiO 5 phase depends on the crystallinity of β-Al 2 TiO 5 .

Characterization of Ar+-ion irradiated spinels

Abstract Characterization of single-crystal and plasma-sprayed spinels before and after Ar+-ion irradiation was performed by XPS and RBS techniques. Two Ols and Mg2p peaks were observed in both spinels, respectively, and the second peaks were observed at the positions of higher energies than those in unirradiated spinel. In the Ar+-ion irradiated plasma-sprayed spinel, Ols peak with higher energy was observed predominantly. Two Al2p peaks were observed in Ar+-ion irradiated single-crystal spinel whereas only one Al2p peak was observed in Ar+-ion irradiated plasma-sprayed spinel. It is indicated from these results that plasma-sprayed spinel is easily amorphized by Ar+-ion irradiation, compared with single-crystal spinel.

LASER TREATMENT OF PLASMA-SPRAYED CERAMIC COATINGS

The aim of this study was to examine the effect of laser treatment for plasma-sprayed ceramic coatings by the use of several microanalytical techniques. We found that the coating layer was densified as a result of laser treatment. We also verified that the crystal phases in the coating layer were controlled by the laser treatment.

s-character of Cd+ centre in γ-irradiated alkali silicate glasses

The s-character of Cd+ centres and its fluctuation in γ-irradiated alkali silicate glasses were investigated using ESR spectroscopy. With increasing alkali content, the s-characters of Cd+ centres in sodium and potassium silicate glasses decrease monotonically whereas the s-character in lithium silicate glasses shows a maximum and then decreases. The temperature effect on compositional dependence of the s-character of a Cd+ centre is rarely observed in lithium silicate glasses. On the other hand, the temperature effect is clearly observed in sodium and it is suggested that local structures around Cd+ centres in sodium and potassium silicate glasses is relaxed by annealing at room temperature.

Thermally Stimulated Exoelectron Emission of Plasma-Sprayed Zirconia Coatings

The thermally stimulated exoelectron emissions from plasma-sprayed and X-ray irradiated zirconia coatings were studied and TSEE glow peaks were detected at 200 and 320°C. It is thought that the TSEE is caused by metastable tetragonal zirconia obtained by plasma spraying.

TSEE from Aluminas and Spinels Subjected to Ar + -Ion Irradiation

TSEE from Ar+-ion and/or X-ray irradiated alumina and spinel was investigated. A TSEE peak at 150°C from X-ray irradiated alumina was suppressed when the alumina was further irradiated by Ar+-ions. A TSEE peak at 300°C was observed for Ar+-ion irradiated alumina and was suppressed by the combined effect of Ar+-ion and X-ray irradiatifons. Only weak TSEE peaks were observed between 250 and 350°C in Ar+-ion irradiated spinels. Generally, sprayed spinel specimens showed weaker TSEE peaks than the specimens of a single-crystal spinel. This is attributable to the fact that a plasma-sprayed spinel becomes amorphous more easily than its single crystals. X-ray irradiated spinel single-crystal showed well-defined TSEE when they were not irradiated with Ar+-ions.