Electrostatics Contact/Impact Charging of a Single Particle

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Our basic or beginning concept in the project was as follows:

For a fundamental discussion on the phenomena of electrostatic charging of powder, it is essential to study the charge generation due to a single impact or contact on a single particle. To realize the concept we proposed and performed, in our previous works, so called “impact charging experiments” in which, however, samples were spherical particles mainly with 3 mm in diameter. The size was too much bigger comparing with normal powder size. The major subject of this project of IFPRI was, therefore, to perform the single particle study in the region of the normal particle size from tens to hun- dreds micro-meter. We proposed two approaches to realize the project:

Approach 1: Improvement of the Original Method:

To apply the former version “impact charging experiments” to the smaller particle size, there were two major subjects: improvement of the sensitivity of the charge measurement, and trajectory control of the accelerated particles.

(i) In the firstyear: the trajectory problem was solved with adopting “aerosol beam generator,” also the sensitivity of the charge measurement was improved successfully. These resulted in that the particles with hundreds micro-meter became available.

(ii) In the second year: Actual “impact charging experiments” were performed successfully with using PMMA particles mainly of 200 pm in diameter. The experimental results showed good agreements with “charge relaxation model” which we have proposed as a scheme deter- mining impact charges.

Approach 2: Development of the Method of Electrostatic Adhesive Force Measurement:

This is the completely new approach to determine the amount of charge transferred onto a par- ticle due to a contact from a measurement of adhesive force curve at approaching and separating particle against a metal target.

(i) In the first year: A concept of the mechanism was studied and clarified, and a strict theory was developed to calculate the force curve of a particle charged partially only on a supposed contact area.

(ii) In the second year: As a preparation to realize an actual equipment, performances of some essential parts were tested.

After the results of the first and second year activities, the project work objects in the third year are:

In approach 1:

(i) Actual and further data accumulation will be continued.

(ii) The model called “charge relaxation model” may be verified its applicability for an actual powder region of the particle size, the hundreds micro-meter particle size.

(iii) A further improvement of the sensitivity of the charge measurement to make possible to apply a smaller particle size, from ten-s under to some micrometer particle. Especially, to realize the measurement of particle size around ten micro-meter may be important because the size is of toner particles in electrophotograpy process.

In approach 2: In the first and second year, the concept of the new experimental apparatus was established, and some performances of essential parts of it were tested. In the third year, a prototype will be established and its performance will be tested.