Particle generation during stainless steel tube welding and the effect of tube inner surface smoothness for purging tube surface were investigated in order to achieve an ultra-high purity gas supplying system for semiconductor manufacturing processes. It was shown that particles with diameter larger than 0.1 μm were generated at a concentration of about 108 m-3 during full penetration welding of stainless steel tubes at the moisture concentration of 0.15 ppm in back-sealed gas for welding, because of melting, evaporation and recondensation of stainless steel components. The measured particles had a bimodal size distributions whose minimum appeared at particle diameter of 0.2 μm. In order to reduce the particle generation during stainless steel tube welding, the moisture concentration in back-sealed gas for welding was decreased to less than 10 ppb. As a result, generation level of about 107 m-3 for particles with diameter of larger than 0.1 μm was achieved during stainless steel tube welding, which is one order of magnitude smaller than that at the moisture concentration of 0.15 ppm. It was also shown that smoothing the inner surface of tubes is very effective in reducing the particle purging time.
Membrane filters are recently used as an in-line filter to eliminate particulate matters from process gases because they have a high collection efficiency compared to HEPA filters and shedding of fibers does not occur. The membrane filters are complicated and versatile in structure, making it difficult to predict their collection efficiencies. In the present work, membrane filters were classified into five groups according to the structure, and the collection performances of the filters in each group were evaluated from both collection efficiency and pressure drop by using filter figure of merit. Further, in predicting collection efficiency of membrane filters with fiber-like structure, the applicability of the conventional filtration theory for fibrous filters was tested.
Typical Kosa aerosol was sampled on April 18-20, 1988 at Yaku Island about 60 km SW from the Kyushu Island and about 900 km from the nearest coast of China. The Kosa aerosol was found mainly in the coarse size fraction and showed a highly uniform chemical composition irrespective of particle size. The mineral compositions were close to those in the surface soil in the arid area in the north China. The water extract of the Kosa aerosol showed alkaline reaction, which was attributed to dissolution of calcite mineral (CaCO3). Kosa episode occurs in the spring and seems to have favorable affects to most vegetations as they accerelate biological activity in that season. The total amount of the cations, which are transported as Kosa aerosol and spread over Japan, can be estimated at 4000 eq./ (km2 ·y). Therefore, the Kosa aerosol can be expected to protect, at least partly, against the damages of soil and vegetation associated with the acid rain/deposition.
Several levitation methods of a single aerosol particle were reviewed, specially stressed on the history, basic principles and practice of a quadrupole cell which is based on an electrodynamic balance. The performance of the current quadrupole cells were also criticized and discussed from the viewpoint of stability for a particle trap.