Yoshimi Kizaki

Phenomenological Studies in Laser Cladding. Part I. Time-Resolved Measurements of the Absorptivity of Metal Powder

Time-resolved measurements were introduced to study the dynamic behavior of the absorptivity of metal powder under CO2 laser irradiation conditions. The absorptivity of metal powder was more than 90% under short-term laser irradiation (6-20 ms), but it was below 30% under relatively long-term laser irradiation (50-1000 ms). The experimental results propose that the dynamic change of the absorptivity is caused by time-dependent aggregation of powder particles induced by laser irradiation.

Quantitative analysis of transient surface reactions on planar catalyst with time-resolved time-of-flight mass spectrometry.

A procedure for the quantitative analysis of transient surface catalytic reactions in millisecond time resolution has been studied constructing a specially designed apparatus employing (1) pulsed-gas valves for the injection of reactant molecules onto catalysts and (2) a time-of-flight mass spectrometer (TOF-MS) to detect every reaction product simultaneously. For a better understanding of the catalytic activity and selectivity for products quantitatively, a procedure for measuring an amount of reactant molecules injected onto catalyst surface and calibrating the intensity of mass signal were proposed and implemented. We tested the applicability of this procedure for the quantitative analysis of products of NO+H(2) reaction on Pt-Al(2)O(3) catalysts (a planar catalyst: Pt-Al(2)O(3)Si substrates inserted into a micro-tube-reactor with SiC balls). Although the surface area of the planar catalyst was very small, the mass signal intensities of the reaction products were found to be sufficient for the above procedure. We measured the fragmentation patterns and the inherent sensitivity factors in the TOF-MS using the mixture of the internal standard gas Ar and the N-containing gases. The relative sensitivity factors for NH(3), N(2), NO, and N(2)O and the relative intensities of fragment peaks to the molecular ion peak of H(2)O and N(2)O were estimated. The procedure constructed here has enabled us to analyze the transient consecutive secondary catalytic reactions as well as primary reactions based on the formation rate of product molecules per millisecond instead of the mass signal intensities of the reaction products.

Phenomenological Studies in Laser Cladding. Part II. Thermometrical Experiments on the Melt Pool

A novel two-color pyrometer composed of a high-speed shutter TV camera and an image intensifier is employed to study the surface temperatures of the cladding layer under CO2 laser radiation. The two dimensional image of the surface temperature of the melt pool was stored in the frame memory in National Television System Committee (NTSC) formula. Also, high-speed photography was used to observe the dynamic behavior of the melt pool. The rapid motion and temperature change of the melt pool were observed and the former was greater than the laser scan (200 Hz). From these two time-resolved measurements, the laser cladding layer was found to be under the control of the dynamic behavior of the melt pool.

Laser-induced polymerization of surface adsorbed molecules

The controllability of the chemical composition of acrylic compounds was investigated in ultrathin polymerized films by using a polymerization process in vacuo with a vacuum UV excimer laser. Four different acrylic compounds were polymerized by this process. The analysis of X-ray photoelectron spectroscopy showed that the chemical compositions of polymer film from ethylacrylate were well-preserved monomer compositions. The insulation characteristics of the ultrathin films obtained from the optimized conditions were found to be sufficient for producing a MIS device on n-type GaAs substrates.