silicon for the chemical and solar industry XIII

1 Background and Selfrag principle

SELFRAG plants are based on high voltage (HV) pulse power technology. Its

principle is based on the introduction of energy via electrical discharges into solids

immersed in water and situated between or near two electrodes. To achieve that,

SELFRAG reduces the voltage pulse rise time to below 500 ns (Figure 1). At such

situations water has a higher breakdown voltage than the solid (1). A discharge enters

the material and interacts with the solid by polarisation and field distortion effects. If

the discharge interconnects to the counter-electrode the track is filled with energy to

produce shock waves with local pressures of 10

[Pa]. Following fragmentation occurs

in a tensile dominated stress regime.

Selfrag principle for silicon crushing

The strength of the discharge and shock wave depends on the generator setup and can

be closely controlled in exact ranges. The energy depends on the available capacitors

and chosen voltage. Therefore the generator can be customized for any application.

To achieve fragmentation the introduced energy per surface must be high enough to

overcome elastic behaviour of the material.

For the crushing of silicon a Marx-generator with the following process setup has

been chosen to perform tests on pilot plant level:

Voltage (kV)

90-200

Pulse energy (J)

150-750

Electrode gap (mm)

10-60

Feed size (mm)

50-500

Processing mode

Batch

Max throughput (kg/h)

600

Figure 1:

Physical principle of the SELFRAG process

Table 1:

Parameter of Marx-generator and pilot plant