The purity of high-purity materials directly affects their performance in fields such as semiconductors, optics, and new energy. The following are the main methods to ensure the purity of high-purity materials, combined with comprehensive control of physics, chemistry, and process technology:
1、 Physical purification technology
1. Magnetic separation for iron removal
By using a high gradient magnetic separator to remove magnetic impurities, the content of Fe ₂ O3 can be reduced to below 10ppm.
Suitable for non-metallic materials such as high-purity quartz sand and graphite.
2. Flotation separation: Separation of aluminum containing minerals such as feldspar and mica through acid flotation or fluoride free flotation, reducing the content of Al ₂ O3 to below 20ppm.
3. Re selection and purification: Spiral chutes remove impurities with high density and improve material purity.
2、 Chemical purification technology
1. Acid leaching process
The mixed acid can be reacted at 70-90 ℃ for 4-8 hours to remove soluble impurities such as iron and aluminum, with a purity of over 99.99%.
Semiconductor grade quartz sand requires microwave-assisted leaching to shorten reaction time by 30%.
2. High temperature chlorination: Inject Cl ₂/HCl gas at 1200-1500 ℃ to generate volatile chlorides from impurities such as Fe and Ti, suitable for purifying ultra-high purity quartz sand.
3. Microbial leaching: using ferrous sulfide bacteria to metabolize acid and dissolve iron oxides, which is environmentally friendly but has a long cycle.
3、 Process control and testing
1. Refining and melting
Electric arc furnace refining combined with argon gas protection, eliminates gaseous impurities through directional solidification, and produces low hydroxyl quartz lumps.
Fire purification (such as blast furnace melting) is used for high-purity metals (silver, gold) by evaporating impurities at high temperatures.
2. Testing technology
ICP-MS (Inductively Coupled Plasma Mass Spectrometry) detects ppb level impurity elements.
GDMS (Glow Discharge Mass Spectrometry) analysis of all elements except C, H, O, and N.
4、 Application scenarios and purity standards
Semiconductor materials: The purity of silicon and germanium should be ≥ 99.9999%, and the impurity element Fe should be ≤ 10ppm.
Optical material: high-purity quartz sand with SiO ₂ ≥ 99.999%, used for lithography machine lenses.
New energy materials: high-purity graphite with a carbon content of ≥ 99.99%, used for lithium battery negative electrodes.
5、 Precautions
Impurity control: Purification processes need to be selected for different materials, such as quartz sand with a focus on removing iron and aluminum, and metal target materials need to control volatile impurities.
Localization progress: China has broken through the mass production technology of 6N high-purity zinc and 7N high-purity gallium, but semiconductor grade materials still rely on imports.
By integrating physics, chemistry, and process optimization, the purity of high-purity materials can be significantly improved to meet high-end manufacturing needs.
