We deal with a new type ceramics emitter which is composed of a needle-shaped poly-silicon and a silicon carbide ceramic rod for an ionizer used in a semiconductor manufacturing clean room. The ion density measurement, the particle generation test, and the degradation test were carried out for the ceramics emitter comparing with the conventional tungsten emitter and the titanium emitter. After the discharge tests, the oxygen concentration near the surface were analyzed using an Auger electron spectroscopy. In the ion density tests, significant differences could not be found among these emitters. The ceramics emitter shows the smallest particle generation and degradation. The oxide films were formed on each emitter surface. It is considered that the oxide film plays an important role to generate the particle from the emitters.
The effect of moisture on the chemical formation of air ions produced by corona discharge in clean air, and the formation of large clusters were mainly discussed in this paper. We measured the composition of positive and negative air ions generated by corona discharge in clean air using an atmospheric pressure lonization mass spectrometer (APIMS). The positive ions were composed of H+(H2O)n (n= 1 , 2 , 3 , ……), and the negative ions of CO3-(H2O)n, O2-(H2O)n, NO3-, NO2-(H2O)n, O-, and O3-. The degree of hydration, n, in those hydrate ions increased with a moisture increase. Ultra-fine particles of nanometer size were detected in the ionized clean air with a CNC, and the number of them also increased with the moisture increase. Large hydrate ions which have high degrees of hydration, probably constitute those ultra-fine particles.
Membrane filters with a relatively low porosity have net-like or agglomerate-like structure and the internal flow field in these filters is so complicated that neither the channel model nor the single fiber model are directly applicable to predict its collection efficiency for aerosol filtration. The present work proposes a simple method for predicting collection efficiency of these membrane filters in diffusion-interception control regimes based on channel model , which employs an effective pore diameter calculated by the pressure drop and an adjustable parameter of dimensionless pore length. In order to determine diffusion-interception control regimes for particle collection, collection efficiency of a single pore was calculated in terms of interception parameter and Peclet number. Then, the measurements of collection efficiency of net- and agglomerate-like filters were conducted in the interception and diffusion control regime. The experimental particle penetrations were compared with those predicted by the present model. As a result, the proposed model gave a fairly good prediction for both net- and agglomerate-like filters by assuming a value of dimensionless pore length between 0.5 and 0.8.
Super cleaning of a closed space is performed by a newly developed charging and unit for submicron particles. The unit is mainly consisted of a transmission-type photoelectron emitter (Quartz glass coated by ITO with thickness of 5nm and Au of 5nm) and wire-screen-electrode for weak electric field and trapping of charged particles. The developed unit has several advantages as follows : 1) Cleaning of a closed space can be accomplished with minimum voltage supply. 2) Existence of obstacles in the cleaning space does not affect the removal efficiency. 3) The cleanliness higher than class 1 for particles with diameter larger than 0.1 μm can be achieved without forced air circulation.
Aerosol particles deposit onto a pipe wall in a turbulent flow, but the particles are sometimes recognized to rebound from the wall beyond a certain limit of Reynolds number, particle diameter or other parameters involved in the deposition velocity. However, there are few reports which analyze this phenomenon quantitatively. In this paper, therefore, a rebound starting point and an empirical formula for particle rebound from the pipe wall are derived, and the constants contained in the formula are determined based on the existing experimental data with particle rebound. The relations between the constants for different independent variables such as Reynolds number, particle diameter and relaxation time are also discussed.