How to improve the acid and alkali resistance of quartz sand? Unveiling the
five core processes
Industry standard: For high-end applications, a weight loss rate of <0.5%
after soaking in 99% H₂SO₄ for 24 hours is required (GB/T 32649-2016)
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1. Deep purification process: Reducing reactivity from the source
1. Intensified acid pickling technology
- Optimization of mixed acid formula: a mixed solution of HF (3%-5%) + HCl
(10%-15%) + H₂SO₄ (5%), treated with dynamic circulation at 60℃ for 4-6
hours
- Gradient concentration control:
- Stage 1 (0-2h): Remove metal impurities with a 5% HF concentration
- Stage 2 (2-4h): Dissolve silicate inclusions with a 3% HF concentration
- Ultrasonic assistance: 40kHz ultrasonic waves break down the impurity
coating, improving purification efficiency by 50%
2. High-temperature chlorination purification
- Process parameters: Introduce Cl₂ gas at 1200℃, reaction formula:
`4Fe₂O₃ + 6Cl₂ → 4FeCl₃↑ + 3O₂`
- Impurity removal efficiency: Iron content reduced to <5ppm, acid
resistance weight loss rate decreased to 0.2%
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II. Surface modification technology: building a protective barrier
1. Coating with silane coupling agent
- Preferred model: KH-550 (aminopropyl triethoxysilane)
- Processing technology:
1. Preheat quartz sand to 110℃ for dehumidification
2. Spray coating with 0.5% silane ethanol solution
3. Cure at 120℃ for 30 minutes
- Effect: The resistance to corrosion by 5% NaOH solution is increased by 3
times
2. Alumina nano-coating
- Sol-gel method:
- Alumina sol concentration: 8%-12%
- Dip coating speed: 2mm/s
- Sintering temperature: 600℃ (to form a γ-Al₂O₃ layer)
- Protection mechanism: 20-50nm coating to seal surface pores
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III. Crystal structure reinforcement: blocking corrosion channels
1. High-temperature calcination transformation
- Process curve:
- Room temperature → 800℃ (temperature rise rate: 5℃/min)
- Maintain at 800℃ for 1 hour (β quartz phase transition)
- 800℃→1450℃ (temperature rise rate 3℃/min)
- Maintain at 1450℃ for 2 hours (for cristobalite transformation)
- Improved corrosion resistance: The alkali resistance of cristobalite phase
is 8 times higher than that of quartz sand
2. Toughening through rapid cooling treatment
- Water quenching process: hot sand at 1450℃ is poured into room temperature
deionized water
- Key parameters: sand-to-water ratio of 1:5, cooling rate > 200℃/s
- Function: Forming a microcrystalline glass structure, enhancing thermal
shock resistance to 800℃
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IV. Impurity morphology control: critical element threshold
| Impurity element | Acid resistance threshold | Alkali resistance threshold
| Control method |
|----------|-------------|-------------|------------------|
| Fe₂O₃ | <50ppm | <30ppm | Magnetic separation + acid washing |
| Al₂O₃ | <1000ppm | <500ppm | Flotation desliming |
| CaO | <200ppm | <100ppm | Oxalic acid leaching |
*Note: The formation of soluble [Al(OH)₄]⁻ by Al³⁺ in alkaline environments
is the main cause of corrosion*
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V. Customized Solutions for Application Scenarios
1. Photovoltaic crucible-grade quartz sand
- Process route: chlorination purification (1200℃) + acid washing
(HF-HCl)
- Index: Resistance to erosion by silicon melt at 1600℃ for >100 hours
2. Chemical packing quartz sand
- Process route: Silane coating + Cristobalite transformation
- Indicator: Resistance to annual corrosion rate of 40% H₂SO₄ solution <
0.1mm
3. Semiconductor container lining
- Process route: Alumina coating + Quenching toughening
- Indicator: Resistance to HF acid vapor (200℃) with a lifespan of >2
years
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VI. A transformation case of an enterprise in Jiangsu
Question: The dissolution rate of quartz sand reaches 8% after being soaked
in a 5% NaOH solution for 72 hours
Solution:
1. Adopt 1450℃ cristobalite transformation treatment
2. Apply an 8% aluminum sol coating on the surface
3. Implement coating with KH-550 coupling agent
achievements:
- The alkali resistance dissolution rate has been reduced to 0.6%
- The unit price of the product has increased by 3,000 yuan/ton
- Certified by semiconductor equipment manufacturers
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conclusion
Enhancing the acid-alkali resistance of quartz sand requires a "three-in-one"
strategy:
1. Deep purification (control of Fe/Al/Ca impurities)
2. Structural strengthening (cristobalite transformation + rapid cooling
toughening)
3. Surface armor (silane/alumina protective layer)
Request customized services for the "Quartz Sand Corrosion Resistance
Improvement Plan" immediately, with a professional team providing process
optimization and cost estimation!