High-Purity Silica Particles via Alkoxysilane Hydrolysis
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Solution Overview
Problem
Existing methods for producing silica sol and particles face challenges such as incomplete removal of impurities, aggregated particle formation, low purity, and poor moisture absorption resistance due to residual alkoxyl groups and incorporated alkaline species, which hinder their use in high-purity applications.
Innovation Solution
The method involves hydrolyzing alkoxysilane in the presence of a base followed by hydrothermal treatment to produce silica particles with a mean primary particle size of 3 to 20 nm, adjusting the base amount to 0.002 to 0.20 mole ratio, and subjecting them to a temperature of 150 to 350°C to achieve high-purity, high-density silica particles with excellent moisture absorption resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If water glass is used as raw material and neutralization or ion-exchange is performed, then silica sol can be produced, but impurities such as metals cannot be completely removed
Solution Approach 1:
The patent extracts and removes harmful metal impurities through a specific purification process involving hydrolysis of alkoxysilane followed by hydrothermal treatment. The method separates the silica formation process from the impurity removal process, using controlled conditions to eliminate metals while forming high-purity silica particles.
Solution Approach 2:
The patent changes critical parameters including using alkoxysilane as raw material instead of water glass, controlling pH during hydrolysis, and applying specific hydrothermal treatment conditions (temperature, time, atmosphere). These parameter changes enable complete removal of metal impurities while maintaining high silica content.
2Manufacturing precision
If silicon tetrachloride pyrolysis is used to produce silica micropowder, then silica particles can be formed, but the particles aggregate and cannot form monodispersion silica sol
Solution Approach 1:
The patent performs preliminary hydrolysis of alkoxysilane to form colloidal silica particles with controlled size distribution before the hydrothermal treatment. This preliminary action ensures that particles are formed in a dispersed state with uniform size, preventing aggregation during subsequent processing.
Solution Approach 2:
The patent utilizes phase transition during hydrothermal treatment where colloidal silica particles undergo structural reorganization and densification. The transition from as-prepared colloidal particles to hydrothermally treated dense particles occurs controlled, maintaining monodispersity while improving stability.
3Productivity
If alkoxysilane hydrolysis is performed to form silica particles, then silica particles can be produced, but unhydrolyzed alkoxyl groups remain inside the particles causing poor moisture absorption resistance
Solution Approach 1:
The patent performs preliminary hydrolysis to form silica particles with some alkoxyl groups remaining, then applies hydrothermal treatment as a second step to complete the hydrolysis and remove residual alkoxyl groups. This two-stage approach ensures complete conversion while maintaining particle formation efficiency.
Solution Approach 2:
The patent continues the hydrolysis action through the hydrothermal treatment step, ensuring that all alkoxyl groups are progressively removed. The useful action of hydrolysis is extended beyond the initial stage to complete conversion, eliminating residual groups that would compromise moisture resistance.
4Strength
If thermal treatment is applied to silica particles, then particle densification occurs, but pores remain inside the particles failing to produce excellent moisture absorption resistance
Solution Approach 1:
The patent utilizes controlled phase transition during hydrothermal treatment where silica particles undergo densification through reorganization of silicate structures. The phase transition occurs under controlled conditions (temperature, pressure, time) that enable complete densification without leaving internal pores, achieving both high density and excellent moisture resistance.
Solution Approach 2:
The patent changes critical parameters during hydrothermal treatment including temperature (100-350°C), time, and atmosphere control. These parameter changes enable uniform densification throughout the particle structure, eliminating internal pores while maintaining high density and superior moisture absorption resistance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in silica particles with an alkali metal content of 5 ppm or less, moisture absorption of 0.25 mg/m² or less at 50% relative humidity, and a refractive index of 1.450 to 1.460, suitable for high-purity applications like electronic materials, ensuring improved moisture resistance and dispersibility.
Implementation Method 1
hydrolyzing an alkoxysilane in the co-presence of at least one base selected from the group consisting of ammonia, a primary amine, a secondary amine, and a cyclic tertiary amine
Implementation Method 2
subjecting the aqueous dispersion of silica particles to a hydrothermal treatment at 150 to 350°C
Data Source
Figure 1
AI summary
Silica particles for which an alkoxy silane serves as the raw material, and which fulfill the following conditions (a)-(c). (a) The content of alkali metal elements is at most 5ppm relative to silica solids. (b) The moisture absorption at 50% relative humidity is at most 0.25mg/m2, and the refractive index measured by liquid immersion is 1.450-1.460. (c) The mean primary particle diameter as calculated from the specific surface area measured by nitrogen adsorption is 10-100nm.