How to Calculate the Silica (SiO₂) Purity of Quartz Materials

To begin, you will need a GDMS (Glow Discharge Mass Spectrometry) report. This can be used to make a preliminary estimate of the theoretical purity of silica (SiO₂). However, the following key limitations and calculation methods must be noted:

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GDMS Report

1. Example Method for Estimating SiO₂ Purity

(1) Direct Calculation Method (Main Component Deduction Method)

Assumption:
The main component of the quartz tube is SiO₂, and all other elements are considered impurities.

Formula:
SiO₂ purity ≈ 100% − Σ (content of all impurity elements)

Calculation Steps:

1. Extract from the report the contents of all impurity elements other than oxygen and silicon (in ppm by weight).
2. Add up the impurity contents to obtain the total impurity content.
3. Subtract the total impurity percentage (ppm ÷ 10,000) from 100%.

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(2) Actual Calculation (Based on Report Data)

Determine the total amount of detected impurities (unit: ppm):

Li (0.16) + B (1.1) + Na (0.29) + Mg (0.05) + Al (11) + Ti (3.4) + K (0.58) + other upper limits (e.g., Fe <0.5, Cr <0.5…)

≈ 0.16 + 1.1 + 0.29 + 0.05 + 11 + 3.4 + 0.58 + 0.5 (Fe) + 0.5 (Cr) + 0.05 (Ni) + 0.1 (Cu) + 1 (Ca)

≈ 18.73 ppm (conservative estimate, calculated using upper limits)

SiO₂ Purity:
100% − (18.73 ÷ 10,000) = 99.8127%

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(3) Correction Factors

• Undetected elements: Elements marked as “–” in the report (such as Au, Hg, etc.) may be below the detection limit of the instrument, but are not counted in the total impurities.
• Oxygen content not quantified: The report only marks oxygen as a “main component,” but in actual SiO₂, oxygen accounts for 53.2% of its composition (stoichiometric ratio correction is required).

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2. Purity Evaluation Conclusion

• Conservative purity: ≥ 99.81% (calculated using the upper limits of GDMS-detected impurities)
• Actual purity may be higher: If some elements are well below their upper limits (e.g., Fe is only 0.1 ppm), the purity could reach 99.9%.

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3. Key Limitations and Considerations

(1) Limitations of the GDMS Method

• Semi-quantitative data: For example, Fe <0.5 ppm might actually be 0.1 ppm or 0.01 ppm, which can significantly affect purity calculation.
• Missing light elements: GDMS has weak detection capability for light elements like C and H, which may lead to underestimating total impurities (e.g., hydroxyl OH⁻ not detected).

(2) Comparison with Industry Standards

Material Grade	Typical SiO₂ Purity Requirement	Purity Estimated from GDMS	Meets Standard
Industrial-grade quartz	≥99.5%	99.81%	✅ Yes
Photovoltaic-grade quartz	≥99.9%	Close, but uncertain	⚠ ICP-MS verification needed
Semiconductor-grade quartz	≥99.99%	Not achieved	❌ No

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4. Application Recommendations for the Material

• Industrial/general use: Purity of 99.8% is sufficient and can be used directly.
• Photovoltaic/semiconductor use:
  • Use ICP-MS to confirm whether critical metallic impurities (Fe, Na, etc.) are truly below 0.1 ppm.
  • Supplement with FTIR testing to determine hydroxyl content (OH⁻ < 5 ppm).

Summary:
This material belongs to high-purity industrial-grade quartz but does not meet semiconductor-grade requirements (4N5 or 5N).

Decision basis:
If the customer’s process is sensitive to Fe/Na contamination (e.g., PERC solar cells), priority should be given to verifying the actual impurity levels.