1. Main core component
The primary chemical constituent of high purity quartz is silicon dioxide (SiO₂), which exists in crystalline form as α-quartz under normal temperature and pressure.
For glass-grade, photovoltaic and semiconductor high-purity quartz products, the mass fraction of SiO₂ is the core grading standard:
- Ordinary glass high-purity quartz sand: SiO₂ ≥ 99.60%
- Ultra-white / photovoltaic glass quartz: SiO₂ ≥ 99.90%
- Electronic & optical high-purity quartz: SiO₂ ≥ 99.99% (4N grade)
- Ultra-high purity semiconductor quartz: SiO₂ ≥ 99.999% (5N grade)
Pure crystalline quartz theoretically contains only Si and O elements at an atomic ratio of 1:2, with a theoretical chemical mass composition:
Silicon (Si): 46.74%
Oxygen (O): 53.26%
2. Harmful trace impurity elements (minor chemical components)
Natural quartz ore inevitably contains lattice-substituted metal ions and associated mineral impurities. These trace oxides determine quartz purity grade and directly damage glass transmittance, melting performance and finished product quality. The main impurity chemical components include:
Metal oxide impurities (most critical for glass manufacturing)
- Iron oxide (Fe₂O₃)
The most destructive impurity for glass. Even ppm-level Fe₂O₃ will make glass turn yellow-green and reduce light transmittance. High-purity quartz for glass requires Fe₂O₃ ≤ 100 ppm; PV ultra-clear glass demands Fe₂O₃ ≤ 10 ppm. - Aluminum oxide (Al₂O₃)
Comes from associated feldspar, mica and clay minerals. Excess Al₂O₃ raises glass melting temperature, increases viscosity and easily generates stone defects in glass. - Titanium dioxide (TiO₂)
Derived from rutile and ilmenite impurities. TiO₂ causes glass turbidity, weakens light transmission and forms black spots after high-temperature melting. - Other alkali & alkaline earth metal oxides
K₂O, Na₂O, CaO, MgO, Li₂O. These alkali metals reduce quartz softening point, cause glass foaming and reduce high-temperature dimensional stability.
Heavy mineral trace impurities
Small amounts of ZrO₂, Cr₂O₃, MnO, V₂O₅, NiO, CuO, PbO, etc. Even ultra-trace contents will form color spots and air bubbles in optical glass and photovoltaic glass.
3. Classification standard by chemical composition purity
Grade 1: Glass-making high-purity quartz sand
Typical chemical composition range:
SiO₂: 99.60% ~ 99.90%
Fe₂O₃: 30 ~ 100 ppm
Al₂O₃: 0.05% ~ 0.30%
TiO₂: < 50 ppm
Total alkali metals (K₂O+Na₂O+CaO+MgO): < 0.15%
Other heavy metal oxides: total < 100 ppm
Grade 2: Photovoltaic ultra-clear quartz sand (high-end glass)
SiO₂ ≥ 99.90%
Fe₂O₃ ≤ 10 ppm
Al₂O₃ ≤ 0.08%
TiO₂ ≤ 15 ppm
Total alkali metal oxides < 0.05%
Heavy metal impurities total < 30 ppm
Grade 3: 4N electronic high-purity quartz (optical glass, quartz tube)
SiO₂ ≥ 99.99%
Total all metal impurity oxides < 100 ppm
Fe₂O₃ < 1 ppm, Al₂O₃ < 30 ppm
Grade 4: 5N ultra-high purity quartz (semiconductor fused quartz)
SiO₂ ≥ 99.999%
Total trace metal impurities below 10 ppm, ultra-low alkali metal and transition metal content.
4. Brief summary of chemical composition characteristics
- Silicon dioxide (SiO₂) accounts for more than 99.6% of the total mass and is the only effective functional component of high-purity quartz for glass melting.
- All other chemical substances exist as trace impurity oxides; their total content must be strictly controlled at ppm levels to meet glass production standards.
- The purification process (scrubbing, magnetic separation, flotation, acid leaching) targets removing Al, Fe, Ti, K, Na and heavy metal oxide impurities to elevate SiO₂ mass fraction.
