silicon for the chemical and solar industry XIII

SiOx nanoparticles (spherical silica)

One of the manufacturing methods for obtaining spherical silica is using metallurgical

silicon, grinding it to very small particles and then oxidizing these particles to obtain

superfine spherical SiOx particules. There are many applications for this product:

- Additive to increase fluidity and reduce flash in various resins (epoxy resins, etc), such

as semiconductor sealants.

- Toner external additive materials.

- Silicone filler.

- Sintering material and sintering agent.

- Filler for liquid type sealants.

- Abrasive powder.

Optical applications

Meseguer et al. introduced the Silicon Colloids which are almost spherical silicon micro

and nanoparticles with a very smooth surface, able to scatter and also trap light very

efficiently in a large-span frequency range, covering from the visible to the far infrared

regions.

This material has potential application in the fields of biomedicine, cosmetics, infrared

protective paints for cars and buildings, thermal and UV resistant plastics, thermal

insulation clothes and thermal insulating creams for winter sports.

Ceramics

Silicon Nitride

Silicon nitride offers solutions to problems faced in industries that require high-

temperature, high-strength materials and very small allowable tolerances. Direct

nitridation is the most well understood Si3N4 synthesis process. The reaction is as

follows:

3Si + 2N --> Si3N4 + Heat (at ~1400°C)

Direct nitridation results in a theoretical weight gain of 66.67% of the weight of silicon

metal; however, empirical evidence shows the weight gain of a fully nitrided part to be

approximately 60% due to volatilization of silicon during the process. The kinetics of the

direct nitridation reaction can be improved through the use of catalysts but not every

producer uses catalysts to avoid contamination.

There are mainly two qualities, Industrial quality (3-4N material) and PV quality. The

former is used as additive for the manufacture of special ceramics as reaction bonded

silicon nitride or SiAlON. Silicon nitride with PV Quality is used as coating on the quartz

crucibles for multicrystalline silicon technology. The needed quality for this silicon is

quite high because the silicon nitride will be in direct contact with liquid silicon.