Yasuaki Ueda

Characteristics of Ultraviolet Absorption in TiO2 Composite Powders.

TiO2 powder has been used from old materials of white paints. Its demand has been recently expanding from its great ability of ultraviolet absorption. It is, however, difficult to estimate the ability of ultraviolet absorption. Therefore, photoacoustic spectroscopy (PAS) was applied to the characterization of the UV absorption ability in TiO2 composite powders.Two types of TiO2 powders, one is so-called “coated powder” with Si02 and ZnO and the other is MgOTiO2 composite powder, were prepared by wet method. It was revealed by XPS analysis to the coated powder that SiO2 was thinly coated with relative uniformity, but smooth and uniform coat was not achieved on the powder coated with ZnO. UV spectra of these coated powders showed the same spectra as the original TiO2 powder without any coating. It indicates that coating did not have any effect on the ability of UV absorption of TiO2.Crystal phases in MgO-TiO2 composite powder depended on the initial molar ratio of MgO to TiO2 and the heat treatment conditions, and each crystal phase showed a characteristics of UV absorption. For instance, an absorption spectrum with sharp peak at 280nm was obtained when the composite powder (MgO/TiO2=5/8) was calcined at 1223K. UV spectra could be controlled by controlling the initial composition and the heat treatment conditions.

Surface analysis of Ag-Pd ultrafine powders.

Ag and Pd sub-micron powders and three different types of Ag-Pd ultrafine powders (MIX, COPPT and ALLOY) were prepared. MIX was named for the mechanical mixing powder of Ag and Pd powders obtained by precipitation from each aqueous solution. COPPT powder was made by co-precipitation in the alloy composition. ALLOY was prepared by heat treatment of COPPT powder in a vacuum. Ag3d5/2 and Pd3d5/2 photoelectron spectra and valence band spectra of those fine powders were measured to characterize the surface of the powders.Since the surface of the Pd fine powder was partly oxidized and not completely covered with a dense oxide layer, it showed sufficient electroconductivity. No significant change of Pd valence band spectra was observed in the Pd powders of which average particle size ranged from 20 nm to 500nm. Intensity ratios of Ag3d5/2 to Pd3d5/2 2 spectra of Ag-Pd fine powders were measured with Ar sputtering. It was suggested that Ag was enriched at the surface of the ALLOY type powder when compared with the other powders such as MIX and COPPT even at the same chemical composition.