Ultrasonic Atomization of Alkoxysilane Solution
The ultrasonic atomization of alkoxysilane solution is a common method for depositing thin silica based coatings or preparing fine powders by sol-gel process.
The following is a detailed breakdown of the process, key considerations, and how to achieve the required droplet size.
Process Overview
Essentially, it is the production of aerosols (fine droplet mist) from precursor solutions. This type of aerosol can be:
1. Deposition on substrate (e.g. for anti reflective coatings, hydrophobic layers).
2. Dry in the airflow to form microspheres of silica or other metal oxides.
3. Used in chemical reaction chambers (e.g. for chemical vapor deposition of liquid precursors, LCVD).
Hydrochloric acid (HCl) is a catalyst for the hydrolysis and condensation reactions of alkoxysilane, initiating the formation of a network of silica (SiO).
Key challenges and considerations
The use of ultrasonic atomizers for this specific chemical solution presents several significant challenges that must be addressed in order to achieve success.
1. Chemical compatibility and corrosiveness
- Problem: Hydrochloric acid (HCl) is highly corrosive. Standard ultrasonic atomizers are typically made of stainless steel, plastic, and other materials that rapidly corrode when exposed to acidic vapors and droplets. This corrosion will:
*Pollute your solution.
*Damaged and ultimately destroyed the atomizer.
*Change droplet size and output performance. - Solution: You must use a spray designed for chemical compatibility. seek:
*Hastelloy, titanium or 316L stainless steel spray body and sensor. Titanium has excellent resistance to HCl.
*PTFE (Teflon) or FEP fluid channels and cups. These materials are highly inert and can resist almost all chemicals, including acids and solvents.
*Fluororubber or PTFE seals instead of standard rubber O-rings.
2. Solvent evaporation and blockage
- Problem: Alcohol solvents (such as ethanol, isopropanol) will rapidly evaporate from newly generated droplets. As the solvent evaporates, the hydrolyzed alkoxysilane will start to polymerize and form gel. This gel will quickly block the holes of the spray or cover the surface of the vibration sensor, greatly reducing the performance and preventing the generation of fog.
- Solution:
*Immediate use: Aerosols must be produced and used immediately. Do not let it sit in the confined space near the spray.
*Carrier gas: use dry inert carrier gas (such as nitrogen, nitrogen) ₂) to immediately sweep the droplets away from the spray head and into the reaction zone. This minimizes the opportunity for the equipment itself to form gel.
*Pulse operation: If possible, run the spray in short pulses rather than continuously to minimize heat accumulation and gel formation at the source.
3. Control of sol gel reaction
- Problem: The amount of acid and water in the solution determines the reaction rate. Excessive acid or water can cause the reaction to proceed too quickly, resulting in blockage (as described above) or the formation of large and irregular particles instead of fine mist.
- Solution: Carefully control the chemical composition of the precursor solution. The molar ratio of [water]/[alkoxysilane] and [acid]/[alkylsilane] is crucial. A typical formula may use a small catalytic amount of acid (such as 0.1 M HCl).
About Cheersonic
Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.
Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.
Chinese Website: Cheersonic Provides Professional Coating Solutions
