Production of Quartz Glass for Semiconductor Applications

Sand is an unconsolidated sedimentary rock on earth and is distinguished by a particle size measuring between 0.063 and 2.0 mm. Also, the composition of mineral can differ considerably. Many occurrences include quartz respectively silicon dioxide (SiO₂). Sand is primarily utilized in the glass and construction industry because of its physical and chemical properties. The analytical assessment of the chemical composition and the appropriateness for the intended applications make it necessary to perform the comminution of quartz sand.

Instruments for Characterization of Particle Size Distribution

FRITSCH provides an extensive range of mills for this purpose. To classify particle size distribution, the company offers tools for the dynamic image analysis, as well as sieve shakers and instruments for particle sizing through dynamic or static light scattering. With the help of these instruments, the monitoring and optimization of the comminution procedures can be achieved easily.

Composition of Silicon Dioxide

Silicon dioxide (SiO₂) is the primary element of quartz sand. The oxygen atoms combine with the silicon atom in the centre to form a tetrahedral structure. Each oxygen atom belongs to two silicon atoms. In this way, the tetrahedral structures exhibit a high-molecular weight, and owing to this reason, silicon dioxide acquires its unique hardness of 7 on the Mohs scale and the high melting point of 1713°C. These aspects make the element suitable for use in the construction or semiconductor industry.

Figure 1. 20 g sand as base material for a test milling.

Use of Quartz Sand

Quartz sand is a naturally-occurring product and is often utilized in glass production as well as in construction. Through numerous developmental stages, now glass can be manufactured economically. The product is ideal for daily use and is used in almost all areas. Nevertheless, additional characteristics were identified and these can be obtained by subjecting quartz sand to physical or chemical treatment.

In 1899, chemist Robert Küch performed the initial melting tests with pure silicon dioxide and subsequently developed pure quartz glass. In addition, pure crystalline SiO₂ displays a heavy piezoelectric effect, which is used in computer chip production and semiconductor technology. Vibratory quartz is normally used in quartz clocks. However, the use of silica sand in concrete production happens to be the most important application.

Figure 2. 20 g sand ground with the P-2 after 30 min.

Quartz sand is also used in a number of areas, such as abrasive products in metal processing, filter sand in waste water treatment plants, and artificial bone substance.

Comminution of Quartz Sand

Sand is brittle in nature and this makes the comminution process quite easy. However, it must be noted that owing to its composition, its abrasiveness may differ. Therefore, a mill with impact forces is selected in order to reduce this influence. To realize quick and effective processing, the FRITSCH Planetary Mills prove to be an ideal solution. A series of interlaboratory comparisons were performed to improve the grinding further with respect to sample amount, instrument choice, liquid addition, and a variety of other parameters. Such interlaboratory comparisons validate that the FRITSCH Planetary Ball Mills surpasses the FRITSCH Mortar Grinder in terms of sand preparation and with respect to grinding duration and effectiveness. This is attributed to the transmission of energy and power. Optimization of Planetary Ball Mills is carried out with regard to highest energy impact. A special feature of the FRITSCH Planetary Ball Mill premium line is through increased rotational speed, wet grinding can be achieved in the particle size down to a few nanometres.

Figure 3. 100 g quartz sand ground 5 min, P-6, 250 ml agate grinding set, 20 mm balls.

The Task

In the concrete case, extremely pure quartz sand has to be ground to a particle size of less than 100 µm. When prepared in this manner, water glass from the ground material could be melted. The iron content can then be determined photometrically without any major issues. In glass, traces of iron can cause discolouration and this could prove hazardous. For instance, drinking glass or window glass would display unrestrained brown discolouration. Hence, it is important to monitor the iron content of quartz sand in the glass industry.

For this task, a mortar mill was utilized. Using the Mortar Grinder PULVERISETTE 2 with agate bowl, 20 g of quartz sand is ground finely; the time taken is 30 minutes. However, using the Planetary Mono Mill PULVERISETTE 6 classic line equipped with 15 agate balls of 20 mm diameter and a 250 ml agate grinding bowl, 100 g of quartz sand is ground to an equivalent fineness in just 5 minutes.

Measurements of Particle Size Distributions

For measurements of particle size distributions, the Laser Particle Sizer ANALYSETTE 22 NanoTec plus was utilized. With rapid dynamic light scattering, effective particle size distributions ranging from 10 nm to 2 mm can be measured.

Figure 4. Particle size distributions of quartz measured with the Fritsch Laser Particle Sizer ANALYSETTE 22

Conclusion

Planetary ball mills are recommended for quick comminution of solid and brittle materials. Under the aspect of a representative sampling, FRITSCH recommends the grinding bowl with 250 volume of the planetary ball mill. Disturbing elements that occur during grinding can be prevented by using grinding sets made of different materials. Agate grinding sets are recommended for concrete applications.

This information has been sourced, reviewed and adapted from materials provided by FRITSCH GMBH - Milling and Sizing.

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